A carbide-complex concentrated alloy composite powder and method of forming thereof

Abstract

An ultra-hard composite material, comprising a sintered composite powder comprised of agglomerated particles of powder, said agglomerated particles comprising a substantially homogenous mixture of: (a) at least one ceramic phase powder; and (b) a multi-element complex concentrated alloy powder, wherein the multi-element complex concentrated alloy powder consists of 4 to 11 elements, with every principal element occupying a 5 to 35 molar percentage of the multi- element complex concentrated alloy powder, wherein the elements of the multi- element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids.

Description

[0001] A CARBIDE-COMPLEX CONCENTRATED ALLOY COMPOSITE POWDER AND METHOD OF FORMING THEREOF

[0002] PRIORITY CROSS-REFERENCE

[0003]

[0001] The present application claims priority to Australian provisional patent application No. 2023902184 filed on 7 July 2023, the content of which should be understood to be incorporated into this specification by this reference.

[0004] TECHNICAL FIELD

[0005]

[0002] The present invention relates to a carbide-complex concentrated alloy composite powder, a method of forming a carbide-complex concentrated alloy composite powder, and the composite powder produced by that method. The invention is particularly applicable to composite powders that can be used as a powder feedstock for surface coating processes, such as laser material deposition and thermal spray, as well other advanced manufacturing processes such as additive manufacturing. However, it is to be appreciated that the invention is not limited to those applications and could be used in other types of applications that utilise a hard composite material, particularly a hard composite powder material.

[0006] BACKGROUND OF THE INVENTION

[0007]

[0003] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[0008]

[0004] Ultra-hard composite materials have been widely applied in industry due to excellent properties such as high hardness, high wear resistance, and high erosion resistance. A ceramic phase powder with high melting point, high hardness, and high brittleness such as tungsten carbide, titanium carbide, vanadium carbide, niobium carbide, chromium carbide, or tantalum carbide (or combinations of these) are combined with a metallic binder with low hardness and high toughness to form a cemented carbide / hard metal composite. The conventional metal binder used for this hard material has one metal or a combination of two metals as a major part (>50 wt %) doped with other metal elements, for example cobalt, nickel or nickel-molybdenum alloy.

[0009]

[0005] Conventional cemented carbides / hard metals of this type have shown excellent hardness and wear resistance and have been primarily applied in the form of thermal spray coatings to provide protection against extreme engineering environments in various industries. However, their application is limited up to 400 °C and mostly in room temperature wear environments. In addition, the cost of the principal metal binders - Co and Ni - is rapidly rising due to the scarcity of raw materials, resulting in extreme cost inflation of the composite material. Furthermore, Co or Ni binders are magnetic, can deteriorate at high temperatures, and can have corrosive properties for the overall composite system. More importantly, these binders in their elemental form are hazardous to human health with possible carcinogenic effects, leading to controlled production and usage.

[0010]

[0006] Carbide-complex concentrated alloys composites have been proposed as an alternative to conventional cemented carbides / hard metals. Complex concentrated alloys (CCAs) consist of multiple principal elements, which are not only less expensive but exhibit outstanding technical benefits by stabilizing solid solutions over intermetallics. Based on the entropy stabilization, these alloys are termed as medium-entropy alloys (MEAs) or high-entropy alloys (HEAs), depending upon the number of elements and their absolute molar percentages. Their reported physical properties are well-suited as binder materials to form composite hard materials, in combination with ceramic phase type materials.

[0011]

[0007] CCAs have already been used as the metallic binder element for carbides such as WC, NbC or TiC to form a composite hard material. A CCA binder metal shows characteristics such as high-entropy effect, sluggish effect, lattice distortion effect, and cocktail effect, and has thermal resistance and hardness, such that the composite using the binder metal has high hardness, high thermal resistance, and high wear resistance. Additionally, because elements within the binder metal combines with carbon to form carbides, the hardness of the composite is increased. Moreover, the use of more than two elements - far more than conventional binder metal - allows the use of a number of elements that can be selected to enhance the properties of the overall composite material.

[0012]

[0008] Whilst CCAs are known to be suitable metallic binder elements for forming powdered carbide composites, the actual method of forming the powder has not yet been finalised or optimised to the extent that a practical and usable powder has been produced for use as a feedstock for thermal spray coating and / or laser material deposition.

[0013]

[0009] United States patent publication No. 20090074604 teaches one method of forming a carbide-complex concentrated alloy composite material formulated by mixing at least one ceramic phase powder and a multi-element high-entropy alloy powder to form a mixture, green compacting the mixture, and sintering the mixture to form an ultra-hard composite material, wherein the multi-element high- entropy alloy powder consists of five to eleven principal elements with every principal element occupying a 5 to 35 molar percentage of the multi-element high- entropy alloy powder. However, whilst an ultra-hard composite material can be produced using this method, the application of the material has been found to be limited for carbide-complex concentrated alloys composite powder formation due to the non-homogeneity of the composition of the particles formed in the material. In particular, this method may not produce a good bond between the complex concentrated alloy binder and the carbide, and thus produces a heterogenous particle chemical composition throughout the ultra-hard composite material. More importantly, ball milling alone typically results in an intermediate powder with a non-homogenous size and shape, diminishing the flowability of the resultant powder which restricts the achievement of high density and precise dimensions of the subsequent sintered bodies, and more particularly for powder formation. Also, the combined ball milling of ceramic and binder phase lead to inter-reactions between two phases, therefore, losing their individual characteristics within a composite system.

[0014]

[0010] Similarly, Chinese patent publication CN114480938A teaches a method of preparing a high-entropy steel hard alloy with a core-edge structure. The method comprises the steps of: mixing and ball-milling into a single solid solution comprising 50 to 60 wt% of titanium carbide powder, 10 to 20 wt% of tungsten carbide powder, 15 to 20 wt% of iron powder and 10 to 15 wt% of high-entropy alloy powder using a paraffin binder in an absolute ethyl alcohol ball-milling medium; drying and sieving to obtain mixed powder; pressing the mixed powder, and moulding into pellets, and then sintering the pellets, thereby producing a high-entropy steel bond hard alloy with the core-edge structure. Similar to US20090074604, this method is not ideal for optimal carbide-complex concentrated alloys composite powder formation, as mixing and ball milling of the material followed by sintering alone may not produce a good bond between the complex concentrated alloy binder and the carbide, and thus may produce a heterogenous particle chemical composition throughout the high-entropy steel bond hard alloy.

[0015]

[0011] It would therefore be desirable to provide a new or improved carbide- complex concentrated alloy composite powder that preferably has improved material properties compared to previous carbide-complex concentrated alloy composite powders, and / or a new or improved method of forming that carbide- complex concentrated alloy composite powder.

[0016] SUMMARY OF THE INVENTION

[0017]

[0012] The present invention provides an ultra-hard composite powder material that uses an alternate binder material, a method of forming a hard composite material with a ceramic phase material using an alternative binder material to the existing cemented carbide metallic binders, and an ultra-hard composite powder material formed by that method. The present invention uses complex concentrated alloys (CCAs) as the alternate binder material.

[0018]

[0013] A first aspect of the present invention provides an ultra-hard composite material, comprising a sintered composite powder comprised of agglomerated particles of powder, said agglomerated particles comprising a substantially homogenous mixture of:

[0019] (a) at least one ceramic phase powder; and

[0020] (b) a multi-element complex concentrated alloy powder, wherein the multi-element complex concentrated alloy powder consists of 4 to 11 elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder, wherein the elements of the multi-element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids.

[0021]

[0014] It should be appreciated that the ultra-hard composite material may include minor additional elements for example to improve properties such as flowability or other functional characteristics, as well as including additional elements that may result from unavoidable impurities. However, the major constituents that the material essentially consist of are at least one ceramic phase powder and the multi-element complex concentrated alloy powder.

[0022]

[0015] For the present invention, the multi-element complex concentrated alloy powder serves as a binder metal combined with ceramic phase powder (such as WC, TiC, TaCx, NbC, O3C2 or the like, or combinations thereof) to improve the material properties of the ultra-hard composite compared to conventional cemented carbide powders and coatings, thereby extending operating lifespan of that material in various applications. Complex concentrated alloys (CCAs) have advantageous properties when used as binders for ceramic phase material due to their solid solution stability characteristics, high-temperature stability and capability, wear and corrosion resistance. In addition, the equiatomic or non- equiatomic distribution of elements that form a CCA can lower the cost of the material considerably compared to conventional individual binder materials, such as Co and Ni. The use of carbide-complex concentrated alloys enhances the overall properties of the composite system and also considers economic and environmental aspects.

[0023]

[0016] It should be understood that “complex concentrated alloys (CCAs)” is a known and accepted term of art in the alloy field for a new family of metallic materials based on the multi-component and high proportion element concepts, similar to the previous high entropy alloys and multi-principal element alloys definitions. However the advantage of CCA’s permit the presence of a lower number of elements, lower concentrations, and intermetallic compounds. Complex concentrated alloys (CCAs) are materials comprising three or more elements in similar proportions and possessing structural but no chemical long- range order. In this sense, CCAs consist of multiple principal elements, which are not only less expensive but exhibit outstanding technical benefits by stabilizing solid solutions rather than intermetallics. Based on the entropy stabilization, these alloys are termed as medium-entropy alloys (MEAs) or high-entropy alloys (HEAs), depending upon the number of elements. Their reported physical properties are well-suited as binder materials to form composite hard materials, in combination with ceramic phase type materials.

[0024]

[0017] The composite material of the present invention has enhanced bonding between the ceramic and CCA with the retention of their individual characteristics / properties compared to prior art ceramic-CCA powders. In this respect, the individual ceramic and CCA powders are bonded together in particles that comprise an agglomerated and sintered substantially homogenous mixture of the two powder phases. The enhanced bonding leading to this agglomerated structure, and the retention of the individual powder properties is advantageous for the overall composite material.

[0025]

[0018] The constituent ceramic phase powder and multi-element complex concentrated alloy powder form a substantially homogenous mixture within the agglomerated particles of the composite powder. In some particle morphologies, the agglomerated particles comprise the ceramic phase powder enveloped around the CCA powder phase. Here the soft and ductile CCA powder phase is enveloped by the hard ceramic phase, producing enhanced bonding between these phases.

[0026]

[0019] The multi-element complex concentrated alloy powder may comprise a high-entropy alloy or a medium-entropy alloy. A variety of high-entropy alloy powder, or a medium-entropy alloy powders can be used in the process of the present invention. In embodiments, the multi-element complex concentrated alloy powder consists of 4 to 11 principal elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder. The term ‘principal element’ refers to the major alloying element with the highest molar contribution within the multi-element complex concentrated alloy as opposed minor elements. It should be appreciated that this type of multielement complex concentrated alloy powder can comprise a multi-element high- entropy alloy powder, or a multi-element medium-entropy alloy powder depending on the number of principal elements comprising within the multielement complex concentrated alloy powder. In embodiments, the multi-element complex concentrated alloy powder comprises at least 4 elements in equiatomic ratios, preferably at least 5 elements in equiatomic ratios. However, it should be appreciated that the complex concentrated alloy powder may comprise at least 4 elements in non-equiatomic ratios, typically a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder.

[0027]

[0020] Various metallic elements can be used in the multi-element complex concentrated alloy powder. The elements of the multi-element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids. In otherwords, the elements comprising the complex concentrated alloy powder may be selected from: transition group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) and the boron and carbon groups. In embodiments, the elements comprising the complex concentrated alloy powder may be selected from: a scandium group, a titanium group, a vanadium group, a chromium group, or a manganese group, an iron group, a cobalt group, a nickel group, a copper group, a zinc group, a boron group or a carbon group, where ‘group’ is defined according to periodic table nomenclature. In embodiments, the elements comprising the complex concentrated alloy powder may be selected from: a carbon group, an aluminium group, a chromium group, a cobalt group, a copper group, an iron group, a nickel group, a vanadium group, a titanium group, a silicon group, or a manganese group, where ‘group’ is defined according to periodic table nomenclature. For example, the elements comprising the complex concentrated alloy powder may be selected from: Al, Cr, Co, Cu, Fe, Ni, V, Ti, Si or Mn.

[0028]

[0021] One exemplary powder formed by the present invention comprises a CoCrFeNi CCA powder. However, it should be appreciated that the process of the present invention is applicable to a wider range of multi-element high-entropy alloy powders than that particular example. As noted above, the CCA powder can be composed of more than four elements in equiatomic or non-equiatomic ratios. Examples of particular CCA powders include (but are not limited to) CoCrFeNi, AICoCrFeNi, Alo.sCoCrFeNi, and Alo.sCrFeNiTio.s. Again, it should still be appreciated other CCA powders could equally be used.

[0029]

[0022] The multi-element complex concentrated alloy powder can have a variety of particle sizes depending on the desired powder properties and applications. In embodiments, the particle size of the multi-element complex concentrated alloy powder for composite hard material formation can be between 1 to 20 pm, preferably 1 to 10 pm, and more preferably 2 to 6 pm. In embodiments, the particle size of the multi-element complex concentrated alloy powder for composite hard material formation is between 2 to 15 pm. The particle size can be selected to suit the desired powder composition, properties and powder application; for example, large particle sizes, up to 80 pm would be preferred for additive manufacturing methods. In these embodiments, the particle size of the multi-element complex concentrated alloy powder for composite hard material formation can be between 1 to 80 pm, preferably 10 to 75 pm, and more preferably 20 to 70 pm.

[0030]

[0023] The ceramic phase powder provides a hard phase to the carbide-CCA composite. In numerous embodiments, the ceramic phase powder comprises a carbide based ceramic phase powder, i.e. the ceramic phase powder comprises at least one carbide. A variety of carbides can be used for this hard phase. In embodiments, the carbide comprises at least one of: tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), niobium carbide (NbC), chromium carbide (CrsC2), or tantalum carbide (TaCx). In exemplary embodiments, the carbide composition comprises WC. The particle size of the ceramic phase powder is selected to provide the desired properties to the ceramic-CCA powder composite. In some embodiments, the carbide powder has a 1.0 to 1.5 pm particle size, preferably 1.1 to 1.4 pm. However, it should be appreciated that other particle sizes could be used depending on the application and desired ceramic-CCA powder composite properties.

[0024] Finally, the ceramic phase powder and the multi-element complex concentrated alloy powder can be present in any desired weight ratio. In embodiments, the described ceramic phase powder and the multi-element complex concentrated alloy powder have a weight ratio of 90:10 to 60:40, respectfully.

[0031]

[0025] The agglomerated particles are preferably a substantially homogenous particle shape, and preferably a shape that is suited to thermal spray or laser material deposition, cold spray coating, additive manufacturing processes or the like. In embodiments, the agglomerated particles are substantially spherical (or near-spherical) in shape. This spherical shape is advantageous for the overall composite material, and assists in advanced flowability of the material, and more uniform melting behaviour. Powders that are generally spherical or substantially spherical in shape are easier to feed in a thermal spray gun, a laser deposition source, or when used in other advanced manufacturing processes such as additive manufacturing.

[0032]

[0026] The agglomerated particles preferably have a substantially homogenous particle size, more preferably a particle size within a strict size range or limit. In embodiments, the agglomerated particles have a particle size of less than 100 pm, preferably less than 63 pm. However, it should be appreciated that any suitable particle size range could be specified to suit a particular manufacturing process or application.

[0033]

[0027] In embodiments, the ceramic phase powder comprises a carbide based ceramic phase powder, i.e. the ceramic phase powder at least one carbide, preferably at least one metal carbide. Examples of suitable carbides include at least one of tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), niobium carbide (NbC), chromium carbide (CrsC2), or tantalum carbide (TaCx), preferably tungsten carbide or titanium carbide.

[0034]

[0028] In embodiments, the elements are selected from a carbon group, an aluminium group, a chromium group, a cobalt group, a copper group, an iron group, a nickel group, a vanadium group, a silicon group, or a manganese group.

[0029] The described ceramic phase powder and the multi-element complex concentrated alloy powder have a weight ratio of 90:10 to 60:40.

[0035]

[0030] The ultra-hard composite material can have a variety of applications, but is particularly useful as a powder feedstock for thermal spray coating, laser material deposition process, cold spray coating, or an advanced manufacturing process such as additive manufacturing (an additive manufacturing process). In this regard, the developed agglomerated and sintered carbide-CCA composite powder is intended to be used as feedstock to develop thermal spray coatings, which can be used in engineering applications requiring high wear and corrosion resistance with high-temperature stability such as required for aerospace, power generation or mining industrial equipment. The ultra-hard composite material can also be a powder feedstock for other advanced manufacturing processes such as additive manufacturing.

[0036]

[0031] A second aspect of the present invention provides a method of forming novel carbide-complex concentrated alloys composites that have an agglomerated and sintered powdered form that can, in exemplary embodiments, be used as a feedstock powder material, for example for laser material deposition or thermal spray coating processes, as well other advanced manufacturing processes such as additive manufacturing. This second aspect of the present invention provides a method of forming a carbide-complex concentrated alloy composite powder comprising: mixing at least one ceramic phase powder, a multi-element complex concentrated alloy powder, a liquid phase, at least one polymer binder, and at least one dispersant to form a slurry, wherein the multi-element complex concentrated alloy powder consists of 4 to 11 elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder, and the elements of the multi-element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids; subjecting the slurry to a slurry mechanical alloying process to produce a milled slurry; spray drying the milled slurry to form a spray dried powder mixture; and sintering the spray dried powder mixture, thereby forming an agglomerated and sintered carbide-complex concentrated alloy (CCA) composite powder.

[0037]

[0032] Whilst not wishing to be limited to any one theory, the Inventors have surprisingly found that the combination of spray drying (which functions as an agglomeration step) and a sintering process provides greater bonding between the carbide and CCA binder phase, which is beneficial in introducing homogeneity within the composition and structure of the particles of the final formed powder. The method of the present invention typically produces carbide-CCA-composite powders that exhibits similar morphological characteristics as conventional carbide-Co / Ni material. The inventive composite powder is expected to achieve superior properties when used as a powder feedstock for advanced manufacturing processes.

[0038]

[0033] Again, for this aspect of the present invention, a multi-element complex concentrated alloy powder serves as a binder metal combined with ceramic phase powder (such as WC, TiC, TaCx, NbC, CT3C2 or the like) to improve the material properties of the ultra-hard composite compared to conventional cemented carbide powders and coatings, thereby extending operating lifespan of that material in various applications. Complex concentrated alloys (CCAs) have advantageous properties when used as binders for ceramic phase material due to their solid solution stability characteristics, high-temperature, wear and corrosion resistance. In addition, the equiatomic or non-equiatomic distribution of elements that form a CCA can lower the cost of the material considerably compared to conventional individual binder materials, such as Co and Ni. The use of carbide-complex concentrated alloys enhances the overall properties of the composite system and also considers economic and environmental aspects.

[0039]

[0034] The multi-element complex concentrated alloy powder may comprise a high-entropy alloy or a medium-entropy alloy. A variety of high-entropy alloy powder, or a medium-entropy alloy powders can be used in the process of the present invention. In embodiments, the multi-element complex concentrated alloy powder consists of 4 to 11 principal elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder. By principal element, it is meant major alloying element with highest contribution within the multi-element complex concentrated alloy as opposed minor elements. It should be appreciated that this type of multi-element complex concentrated alloy powder can comprise a multi-element high-entropy alloy powder, or a multi-element medium-entropy alloy powder depending on the number of principal elements comprising within the multi-element complex concentrated alloy powder. In embodiments, the multi-element complex concentrated alloy powder comprises at least 4 elements in equiatomic ratios, preferably at least 5 elements in equiatomic ratios. However, it should be appreciated that the complex concentrated alloy powder may comprise at least 4 elements non-equiatomic ratios, typically a 5 to 35 molar percentage of the multielement complex concentrated alloy powder.

[0040]

[0035] Various metallic elements can be used in forming the multi-element complex concentrated alloy powder. The elements of the multi-element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids. In otherwords, the elements comprising the complex concentrated alloy powder may be selected from: transition group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) and the boron and carbon groups. In embodiments, the elements comprising the complex concentrated alloy powder may be selected from: a scandium group, a titanium group, a vanadium group, a chromium group, or a manganese group, an iron group, a cobalt group, a nickel group, a copper group, a zinc group, a boron group or a carbon group, where ‘group’ is defined according to periodic table nomenclature. In embodiments, the elements comprising the complex concentrated alloy powder may be selected from: a carbon group, an aluminium group, a chromium group, a cobalt group, a copper group, an iron group, a nickel group, a vanadium group, a titanium group, a silicon group, or a manganese group, where ‘group’ is defined according to periodic table nomenclature. For example, the elements comprising the complex concentrated alloy powder may be selected from: Al, Cr, Co, Cu, Fe, Ni, V, Ti, Si or Mn.

[0036] One exemplary powder formed by the present invention comprises a CoCrFeNi CCA powder. However, it should be appreciated that the process of the present invention is applicable to a wider range of multi-element high-entropy alloy powders than that particular example. As noted above, the CCA powder can compose of more than four elements in equiatomic or non-equiatomic ratios. Examples of particular CCA powders include (but are not limited to) CoCrFeNi, AICoCrFeNi, Alo.sCoCrFeNi, and Alo.sCrFeNiTio.s. Again, it should still be appreciated other CCA powders could equally be used.

[0041]

[0037] The multi-element complex concentrated alloy powder can have a variety of particle sizes depending on the desired powder properties and applications. In embodiments, the particle size of the multi-element complex concentrated alloy powder for composite hard material formation can be between 1 to 20 pm, preferably 1 to 10 pm, and more preferably 2 to 6 pm. In embodiments, the particle size of the multi-element complex concentrated alloy powder for composite hard material formation is between 2 to 15 pm. The particle size can be adjusted to suit the advanced manufacturing process; for example, large particle sizes, up to 80 pm would be preferred for additive manufacturing methods. In these embodiments, the particle size of the multi-element complex concentrated alloy powder for composite hard material formation can be between 1 to 80 pm, preferably 10 to 75 pm, and more preferably 20 to 70 pm.

[0042]

[0038] The ceramic phase powder provides a hard phase to the carbide-CCA composite. In numerous embodiments, the ceramic phase powder comprises a carbide based ceramic phase powder, i.e. the ceramic phase powder comprises at least one carbide. A variety of carbides can be used for this hard phase. In embodiments, the carbide comprises at least one of: tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), niobium carbide (NbC), chromium carbide (CrsC2), or tantalum carbide (TaCx). In exemplary embodiments, the carbide composition comprises WC. The particle size of the ceramic phase powder is selected to provide the desired properties to the ceramic-CCA powder composite. In some embodiments, the carbide powder has a 1.0 to 1.5 pm particle size, preferably 1.1 to 1.4 pm. However, it should be appreciated that other particle sizes could be used depending on the application and desired ceramic-CCA powder composite properties.

[0043]

[0039] Finally, the ceramic phase powder and the multi-element complex concentrated alloy powder can be mixed in any desired weight ratio. In embodiments, the ceramic phase powder and the multi-element complex concentrated alloy powder are mixed to have a weight ratio of 90:10 to 60:40.

[0044]

[0040] The advantageous properties of the produced composite material substantially stems from the combination of spray drying (agglomeration) followed by the sintering process. Whilst not wishing to be limited by any one theory, the Inventors consider that these two processes provide greater bonding between the carbide and CCA binder phase, which is beneficial in forming a homogenous coating, for example using thermal spray coating or laser material deposition, or homogeneous free form for additive manufacturing, with enhanced overall material properties. In addition, the inclusion of a spray drying step for composite powder manufacturing is advantageous to tailor the desired powder properties such as size, shape, morphology and flowability, all critical for coating and advanced manufacturing processes. Spray dried powders are generally spherical in shape, which are easier to feed in a thermal spray gun or a laser deposition source or additive manufacturing machine.

[0045]

[0041] The spray drying step follows a conventional spray drying process where the milled slurry, comprising solid powder material and solvents, is atomized using an atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size, and those droplets are then rapidly dried with a hot gas, preferably an inert gas, to attain the dried powder particles. In some embodiments, the step of spray drying the milled slurry, uses an inert gas, preferably nitrogen, as drying gas to form a spray dried powder mixture. The slurry used for spray drying preferably consists of ethanol instead of conventionally used water, which enables quick drying of the powder particles at a lower drying temperature and producing the desirable powder particle size for coating processes.

[0042] The spray dried powder mixture preferably undergoes at least one particle sizing / separation step prior to sintering. In embodiments, the separation step includes at least one sieving process to attain a particle size of less than 100 pm, preferably less than 63 pm. The oversized particles from the separation step are typically recycled in the process back for spray drying. The spray dried powder mixture may also undergo at least one fines separation process, preferably a floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation, preferably flotation in water. The fines particles fraction are also typically recycled in the process back for spray drying. The remainder of the separated powder undergoes the sintering process.

[0046]

[0043] The spray dried powder mixture is subjected to a sintering process in which the powder mixture is heated at a temperature below the point in which the powder would be melted to the point of liquefaction. The aim of sintering is to better bond the ceramic phase powder and a multi-element complex concentrated alloy powder, ideally fusing the material / particles of these phases together.

[0047]

[0044] The sintering process of the ceramic phase powder / complex concentrated alloy powder ultra-hard composite material of the invention can be undertaken in a similar process as sintering process undertaken for conventional WC / Co ultra- hard composite material, such as debinding, degassing, sintering or liquid-phase sintering, and cooling for completion. For enhancing sintering density, the sintering process may further include press sintering or hot isostatic pressing after sintering. Steps such as debinding, degassing, and sintering can be processed in a vacuum chamber, or under an inert gas such as argon or the like. The sintering temperature can be adjusted, depending upon the binder metal component.

[0048]

[0045] The sintering process step of the present invention typically comprises at least one sintering step where the spray dried powder mixture is heated to at least 1000 °C, preferably at least 1200 °C. The sintering step is preferably in an inert atmosphere, more preferably Ar. In some embodiments, the sintering step preferably comprises a two-step sintering process comprising the steps (1) heating the spray dried powder mixture to at least 400 °C to remove the polymer binder content; and (2) heating the spray dried powder mixture to at least 1000 °C, preferably in an inert atmosphere, more preferably Ar. In some embodiments, the first sintering step comprises heating the spray dried powder mixture at least 500 °C, preferably for at least 30 mins, more preferably for at least 60 minutes. In some embodiments, the second sintering step comprises heating the spray dried powder mixture at least 1200 °C, for preferably at least 2 hours, more preferably for at least 5 hours. In one exemplary example, the sintering step comprises a two-step sintering process that comprises the steps of: (1) heating at 500 °C for 1 hour to burn off the polymer binder and (2) heating at 1230 °C for 5 hours in a graphite crucible under 99.999 % Ar.

[0049]

[0046] Similar to the spray drying step, the sintered powder mixture preferably undergoes at least one particle sizing / separation step. The separation step(s) preferably include at least one sieving process, to attain a particle size of less than 100 pm, preferably less than 63 pm. The sintered powder mixture may also undergo at least one fines separation process, preferably a floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation, preferably flotation in water. Any oversized particles can be comminuted to fall within the desired particle size range.

[0050]

[0047] The slurry fed into the spray drying step can be formed using any suitable method. In certain embodiments, the slurry is formed by forming a dry powder mixture first, and then adding the liquid phase thereafter. In these embodiments, the slurry may be formed by: mixing at least one ceramic phase powder and a multi-element complex concentrated alloy powder to form a powder mixture; and adding a liquid phase, at least one polymer binder and at least one dispersant to the powder mixture to form a slurry.

[0051]

[0048] A variety of liquid phases, polymer binders and dispersants can be used within the slurry:

[0049] In embodiments, the liquid phase added to form the slurry comprises at least one solvent, preferably at least one of alcohol, polyols, cyclic ether, ketone, or water, more preferably at least one of: methanol, ethanol, isopropanol, ethylene glycol, glycerol, tetrahydrofuran, dioxane, acetone, methyl isobutyl ketone, and yet more preferably ethanol.

[0052]

[0050] In embodiments, the polymer binder added in the slurry comprises at least one of: carboxy-methyl-cellulose, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyethylene glycol (PEG), styrene-acrylic ester copolymer, and yet more preferably polyvinyl butyral (PVB).

[0053]

[0051] In embodiments, the dispersant added in the slurry comprises at least one of poly acrylic acid (PAA), ammonium polyacrylate (PAA-NH4), polyethyleneimine (PEI), and yet more preferably poly acrylic acid (PAA).

[0054]

[0052] In the present invention, mechanical alloying is used to form the carbide- CCA complex and in some embodiments (see below) the multi-element high- entropy alloy powder perse. It should be understood that mechanical alloying is a solid-state and powder processing technique involving repeated cold welding, fracturing, and re-welding of blended powder particles in a high-energy impact mill, typically a ball mill, to produce a homogeneous material. Mechanical alloying is a powder solid-state alloying technology in a non-equilibrium state. During mechanical alloying, for example inside a high-energy ball mill or other suitable impact type mixer or mill, the metal or alloy powder particles are forced to interact due to impact surfaces, such as grinding balls, and the surface of the mill and undergo repeated deformation, cold welding, crushing, and refinement, resulting in the formation of highly deformed particle layers containing mixtures of the various original elements and constantly exposing fresh surfaces. Thus, atomic interdiffusion or solid-state reactions occur in the powder particles to achieve atomic-level inter-element alloying. Here, the individual powders are mixed, cold welded, cracked, and re-cold welded by high energy ball grinding or impacting to complete the alloying and combining mixture process.

[0053] Due to mechanical alloying, the mixed powders of the invention, such as element powders with carbide ceramic phase powders, alloy powders with carbide ceramic phase powders, or element powders, alloy powders and carbide ceramic phase powders together, have the following several properties: (1) alloyed element powders; (2) fine carbide ceramic phase powders; and (3) fine sized alloy powders and a binder metal evenly wrapping the carbide ceramic phase powder surface. For the present invention, the ceramic phase powder and the multi-element high-entropy alloy powder have a weight ratio of 90: 10 to 60:40.

[0055]

[0054] The slurry mechanical alloying process produces a milled slurry with enhanced homogeneity between the two phases, i.e. the ceramic phase powder and the multi-element complex concentrated alloy powder. A variety of mechanical alloying processes can be used for the slurry mechanical alloying process step. In exemplary embodiments, the slurry mechanical alloying process comprises ball milling the slurry. It should be appreciated that a ball mill is a conventional milling apparatus that is used to grind or blend materials through the principle of impact and attrition: mixing, alloying and size reduction is done by impact from a plurality of impact balls that are moved and dropped onto the material withing a rotating container, typically one or more hollow cylindrical shells rotating about its axis. The grinding media are the balls, which may be made of steel, stainless steel, ceramic, rubber, plastic or other suitable material. Ball milling can be undertaken for various durations depending on the operating parameters of the ball mill, apparatus configuration and the like. In some embodiments, the slurry is subjected to ball milling for at least 5 hours, preferably at least 10 h. In some embodiments, ball milling is conducted at 320 rpm. However, it should be appreciated that the particular milling conditions depends on the material and ball milling equipment.

[0056]

[0055] The complex concentrated alloy powder used in the method of the present invention can be provided from various supply means. In some embodiments, the complex concentrated alloy powder is supplied from a commercial source. In other embodiments, the complex concentrated alloy powder is produced using a gas atomisation process. In some embodiments, the complex concentrated alloy powder can be formed by melting and casting, forging, or powder metallurgy. In preferred embodiments, the complex concentrated alloy powder is formed by mechanical alloying. Here preparation of the multi-element complex concentrated alloy powder is formed by a mechanical alloying route by adding individual elemental powders in substantially equiatomic ratios, or non- equiatomic ratios.

[0057]

[0056] Thus, some embodiments of this second aspect of the present invention further includes the step of: forming a multi-element complex concentrated alloy powder from the constituent elemental powders using a mechanical alloying process prior to mixing at least one ceramic phase powder therein. As for the slurry mechanical alloying process, this mechanical alloying process can be conducted using various impact or shear milling methods. One preferred mechanical alloying process comprises at least one ball milling process. Ball milling can be undertaken for various durations depending on the operating parameters of the ball mill, apparatus configuration and the like. In some embodiments, the mechanical alloying process comprises ball milling the elemental powders for at least 5 hours, preferably at least 10 h, to form the multielement complex concentrated alloy powder. In some embodiments, ball milling is conducted at 350 rpm. However, it should be appreciated that the particular milling conditions depends on the material and ball milling equipment. It should be appreciated that the mechanical alloying process is preferably conducted within an inert gas, preferably argon.

[0058]

[0057] The second aspect of this process preferably forms an ultra-hard composite material, preferably a powder feedstock for at least one of a: thermal spray coating, laser material deposition, cold spray coating, or an advanced manufacturing process such as additive manufacturing (an additive manufacturing process).

[0059]

[0058] A third aspect of the present invention provides an ultra-hard composite material formed from the method according to the second aspect of the present invention. The ultra-hard composite material preferably comprises a powder, more preferably a powder feedstock for thermal spray coating, laser material deposition process, cold spray coating, or an advanced manufacturing process such as additive manufacturing (an additive manufacturing process). In this regard, the developed agglomerated and sintered carbide-CCA composite powder is intended to be used as feedstock to develop thermal spray coatings, which can be used in engineering applications requiring high wear and corrosion resistance with high-temperature stability such as required for aerospace, power generation or mining industrial equipment. The ultra-hard composite material can also be a powder feedstock for other advanced manufacturing processes such as additive manufacturing.

[0060] BRIEF DESCRIPTION OF THE DRAWINGS

[0061]

[0059] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[0062]

[0060] Figure 1 provides a process flow diagram showing the process steps in forming a CCA carbide composite powder according to one embodiment of the present invention.

[0063]

[0061] Figure 2 provides an experimental flow chart depicting the procedure to produce carbide-CCA composite powder using spray drying and sintering according to embodiments of the present invention.

[0064]

[0062] Figure 3 shows an XRD pattern of ball-milled CoCrFeNi CCA powder indicating the formation of FCC based CCA powder.

[0065]

[0063] Figure 4 provides a SEM micrograph of ball-milled CoCrFeNi CCA powder.

[0066]

[0064] Figure 5 provides a SEM micrograph of spray-dried and sintered WC- CoCrFeNi powder particle with corresponding EDS elemental colour maps.

[0067]

[0065] Figure 6 provides a XRD pattern of WC-CoCrFeNi composite powder.

[0068] DETAILED DESCRIPTION

[0069]

[0066] The present invention provides a ceramic-complex concentrated alloy composite powder, and an improved method or process for forming a ceramic- complex concentrated alloy composite that is suitable as a powder feedstock for thermal spray coating, laser material deposition processes, as well as other advanced manufacturing processes such as additive manufacturing. The inventive hard material - a ceramic-complex concentrated alloy composite - comprises a two phase composite comprising a bonded mixture of a ceramic phase powder, typically a metallic carbide, with a complex concentrated alloys (CCAs) metallic binder.

[0070]

[0067] The general process flow diagram of the process of the present invention is shown Figure 1. In this process 100, an agglomerated and sintered carbide- complex concentrated alloy (CCA) composite powder is formed using the following general process steps:

[0071] Step 1 : Slurry Formation Step (120) - At least one ceramic phase powder 115, at least one multi-element complex concentrated alloy powder 112, at least one liquid phase 116, at least one polymer binder 118, and at least one dispersant 119 are mixed together to form a slurry 122.

[0072] Step 2: Slurry Mechanical Alloying Process (130) - the slurry 122 is then subjecting a mechanical alloying process, preferably impact mixing in a ball mill, to produce a milled slurry 132.

[0073] Step 3: Spray Drying Process (140) - the milled slurry 132 is processed through a spray drying process apparatus to form a spray dried powder mixture 142.

[0074] Step 4: Sintering (150) - the spray dried powder mixture 142 is subjected to at least one sintering heat treatment process to sintering the spray dried powder mixture, thereby forming an agglomerated and sintered carbide-complex concentrated alloy (CCA) composite powder 152.

[0075]

[0068] The process may also optionally include a process 110 for forming the multi-element complex concentrated alloy powder 112 from the constituent principal elemental powders 108 as shown in the hatched box in Figure 1. This will be described in more detail below.

[0069] Details of the components of each of these steps is as follows:

[0076] Step 1 - Slurry Formation Step (120)

[0077]

[0070] The slurry 122 fed into the spray drying step 130 can be formed using any suitable method. In one embodiment, the slurry 122 is formed by forming a dry powder mixture between the multi-element complex concentrated alloy powder 112 and the carbide phase 115, and then adding the liquid phase 116, at least one polymer binder 118, and at least one dispersant 119 to the dry powder mixture to form the slurry 122. The ceramic phase powder 115 and the multielement complex concentrated alloy powder 112 can be mixed in any desired weight ratio, for example it can be mixed to have a weight ratio of 90:10 to 60:40.

[0078]

[0071] As discussed above, a variety of liquid phases, polymer binders and dispersants can be used within the slurry. The liquid phase typically comprises at least one solvent, for example at least one of alcohol, polyols, cyclic ether, ketone, or water. Examples include methanol, ethanol, isopropanol, ethylene glycol, glycerol, tetrahydrofuran, dioxane, acetone, or methyl isobutyl ketone. The polymer binder added in the slurry comprises at least one of: carboxy-methyl- cellulose, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyethylene glycol (PEG), styrene-acrylic ester copolymer, and yet more preferably polyvinyl butyral (PVB). The dispersant added in the slurry comprises at least one of poly acrylic acid (PAA), ammonium polyacrylate (PAA-NF ), polyethylenimine (PEI), and yet more preferably poly acrylic acid (PAA).

[0079]

[0072] The multi-element complex concentrated alloy powder comprises a multielement high-entropy alloy powder, or a multi-element medium-entropy alloy powder and typically consists of 4 to 11 principal elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder. In embodiments, the multi-element complex concentrated alloy powder comprises at least 4 elements in equiatomic ratios or non-equiatomic ratios. The elements comprising the complex concentrated alloy powder are selected from: transition metals in groups 3 to 12 or metal / metalloids in groups 13 or 14. For example, the elements comprising the complex concentrated alloy powder may in embodiment be selected from: Al, Cr, Co, Cu, Fe, Ni, V, Ti, Si, or Mn. Examples of particular CCA powders include (but are not limited to) CoCrFeNi, AICoCrFeNi, Alo.sCoCrFeNi, and Alo.sCrFeNiTio.s. However, it should be appreciated other CCA powders could equally be used.

[0080]

[0073] The ceramic phase powder provides a hard phase to the CCA composite. In numerous embodiments, the ceramic phase powder comprises a carbide based ceramic phase powder, i.e. the ceramic phase powder at least one carbide, for example at least one of: tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), niobium carbide (NbC), chromium carbide (CrsC2), or tantalum carbide (TaCx).

[0081] Step 2: Slurry Mechanical Alloying Process (130)

[0082]

[0074] A mechanical alloying process 130 is used to form a milled slurry 130 comprising the initial form of the carbide-CCA complex. Here, a high-energy ball mill or other impact type mixer or mill, is used to impact mix and mill the constituents of the slurry 122 to uniformly mix and distribute the components within the mixed material. The preferred mechanical alloying process 130 is ball milling the slurry. As previously described, a ball mill (not illustrated) is a standard milling apparatus that includes ball shaped grinding media, which may be made of steel, stainless steel, ceramic, rubber, plastic or other suitable material, which rotate within a rotating container, typically one or more hollow cylindrical shells rotating about its axis. Ball milling can be undertaken for various durations depending on the operating parameters of the ball mill, apparatus configuration and the like.

[0083] Step 3: Spray Drying Process (140)

[0084]

[0075] The spray drying step 140 follows a conventional spray drying process where the milled slurry 132 is atomized using an atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size, and those droplets are then rapidly dried with a hot gas, preferably an inert gas such as nitrogen. The slurry used for spray drying consists of ethanol instead of conventionally used water, which enables quick drying of the powder particles at a lower drying temperature and producing the desirable powder particle size for coating processes.

[0085]

[0076] Whilst not illustrated, the spray dried powder mixture can undergo at least one sieving process to attain a particle size of less than 100 pm, preferably less than 63 pm, and at least one fines separation process, for example a floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation, preferably flotation in water. The fines and oversized particles from the separation step can be recycled in the process for spray drying. The remainder of the separated spray dried powder mixture 142 undergoes the sintering process step 150.

[0086] Step 4: Sintering (150)

[0087]

[0077] The spray dried powder mixture 142 is subjected to a sintering process to better bond the ceramic phase powder and a multi-element complex concentrated alloy powder, ideally fusing the particles of these phases together. In most embodiments, the sintering process involves at least one sintering step where the spray dried powder mixture is heated to at least 1000 °C, preferably at least 1200 °C, typically conducted in an inert atmosphere such as Ar. In some embodiments, the sintering step comprises a two-step sintering process comprising the steps (1) heating the spray dried powder mixture 142 to at least 400 °C, preferably at least 500 °C, for at least 30 mins to remove the polymer binder content 118; and then (2) heating the spray dried powder mixture 142 to at least 1000 °C, preferably at least 1200 °C typically within an inert atmosphere, more preferably Ar for at least 2 hours, more preferably for at least 5 hours.

[0088]

[0078] Similar to the spray drying step, the sintered powder mixture can undergo at least one sieving process to attain a particle size of less than 100 pm, preferably less than 63 pm, and at least one fines separation process, for example a floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation, preferably flotation in water. Any oversized particles can be comminuted to fall within the desired particle size range. Optional Step: Formation of CCA powder

[0089]

[0079] The complex concentrated alloy powder 112 used in the method of the present invention can be supplied from a commercial source, or in some embodiments formed in a preliminary powder formation step to the process 100.

[0090]

[0080] As shown in the hatched box 109 in Figure 1 , the process 100 can further include the step of: forming a multi-element high-entropy alloy powder using a mechanical alloying process 110 from the principal elemental powders 108. This mechanical alloying process 110 can be conducted using various impact or shear milling methods, and more typically at least one ball milling process. Ball milling can be undertaken for various durations depending on the operating parameters of the ball mill, apparatus configuration and the like.

[0091]

[0081] An example of a specific process flow diagram 200 for an experimental process for forming a CoCrFeNi CCA - WC composite is illustrated in Figure 2. As shown in Figure 2, the carbide-CCAs composite powder is prepared by the following steps:

[0092] (1) CCA Powder Formation (211) - Preparation of the binder CoCrFeNi CCAs powder by mechanical alloying route, using a ball milling process 210, by adding individual elemental powders 208 in equiatomic ratios into the ball mill 210. Ball milling 210 of the elemental powders 208 is undertaken for 10 h at 350 rpm to form the final CCA powder 216. The composition of the CCA powder can be verified using XRD analysis. The final particle size obtained was between 2 to 15 pm.

[0093] (2) Composite Powder Slurry Formation (220) - A carbide powder, for example WC (particle size 1-1 .5 pm) is mixed with the ball mill produced CCA powder 216 in desirable weight ratios to form a dry powder mixture 221. This dry powder mixture is then mixed with a solvent, for example ethanol 216, a polymer binder, for example polyvinyl butyral (PVB) 218, a dispersant, for example poly acrylic acid (PAA) 219, to form a slurry 222. (3) Mechanical mixing / alloying of the Slurry (230) - The slurry 222 is then fed into a ball mill, and processed in the ball milled at 320 rpm for 10-14 hours to produce a milled slurry 232.

[0094] (4) Spray Drying Process (240) - The milled slurry 232 is then spray dried using nitrogen as drying gas to form a spray dried carbide-CCA powder mixture 242.

[0095] (5) Separation Process (245) - The spray dried powder mixture 242 undergoes a sieving process to attain a particle size of less than 63 pm, and a fines floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation in water. The fines and oversized particles 243 from the separation step can be recycled 244 in the process back for spray drying. The remainder of the separated spray dried powder mixture 242 undergoes the sintering process step 250.

[0096] (6) Sintering (150) - The separated spray dried powder mixture 242 is (i) sintered at 500 °C for 1 hour to burn off the polymer compounds; and then (ii) sintered at 1230 °C for 5 hours in a graphite crucible under 99.999 % Ar to achieve an agglomerated and sintered carbide-CCA composite powder 252. Whilst not illustrated, the final composite powder 252 can be sieved to attain a particle size of less than 63 pm, and also subjected to a fines floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation in water.

[0097]

[0082] It should be appreciated that the newly developed Carbide-CCAs composite powder exhibited similar morphological characteristics as conventional carbide-Co / Ni material and is expected to achieve superior properties in the form of surface coatings.

[0098] EXAMPLES

[0099]

[0083] The proof of the fundamental concept of achieving the agglomerated and sintered carbide-CCA powder with enhanced bonding has been achieved with the development of composite powder through the spray drying route. The initial analysis based on phase composition and microstructural aspects has been completed, verifying the enhanced binding between particles. The following examples provide the experimental procedure and results supporting the method of formation of this agglomerated and sintered carbide-CCA powder.

[0100] Example 1 - Forming CCA powder by mechanical alloying

[0101] 1. Ball Milling (Mechanical Alloying)

[0102]

[0084] Mechanical alloying of the individual powders forming the CCA powder and the CCA powder - carbide mixture is achieved using ball milling. For the present experimental procedure, a planetary ball mill, Retsch PM400 was used using stainless steel milling balls having a 10 mm diameter.

[0103] 1. Equipment Cleaning

[0104]

[0085] Before any ball milling takes place, all equipment were thoroughly cleaned to avoid contamination of the milled powder. This was conducted using a combination of vacuum, dry wiping and cleaning using an ethanol solution. The vials in the ball milling machine are also cleaned iteratively by filling the ball mill vials with ethanol and running for a set period (10 minutes or so) at 200 rpm.

[0105] 2. Powder Preparation

[0106]

[0086] An equiatomic CoCrFeNi CCA is prepared using two 70 gram batches of CCA powders (70 grams per vial). The ratio of ball mass to powder mass (determined empirically) is 10:1. Therefore, to produce 70 grams of powder in a vial, 700 grams of balls are used. The quantity of powders of each element to make 70 grams is calculated based on the atomic weight of each element as shown in Table 1.

[0107]

[0087] Table 1: Mass of each element

[0088] Stearic acid is also added at 1 .4 grams per vial (2% of total vial mass) as a process control agent, to prevent cold welding during milling. 2% was found to be the optimum amount for this particular process.

[0108]

[0089] The vials are filled following the mass amounts in table 1 , and are then placed into the ball milling machine. The vials are then filed with an inert gas, preferably argon. The ball milling machine is operated for a desired time. In this case, powders were milled for 10 hrs. Once the powders are milled for the desired time (10 hrs in this case), the vials are allowed to cool down (usually) for 10-14 hours and the powders are extracted from the vials. The argon-rich environment is maintained inside the vials during the entire milling process and the contents are slowly expose to the atmosphere (air) by placing the vials inside a glove bag with a Ziplock to maintain the argon-rich environment. The samples are then gradually exposed the atmosphere (air). Powder is recovered from the ball mill using ethanol wash and filter methodology. Powder is then recovered after sufficient drying to remove ethanol. Once the ethanol has evaporated, the powder is weighed (Table 2) and stored in a plastic container. Table 2 indicates the amount of powder than can be recovered by this method:

[0109] Table 2: Powder recovered and taken out for XRD analysis.

[0110] Example 2 - Forming carbide-CCA composite powder (CoCrFeNi -WC composite)

[0111]

[0090] The powders set out in Table 3 were used in this experimental procedure:

[0091] Table 3: Summary of individual powders for composite powder processing

[0092] The carbide and HEA powders were weighed out into the appropriate amounts to process in batches of 350 to 400g / batch for spray drying. The required quantity of ethanol to achieve the desired solids:ethanol ratio (to control the slurry viscosity) was heated to 50 °C to aid the dissolution of the required polymer binder (polyvinyl butyral) PVB and dispersant (poly acrylic acid)) PAA into the ethanol. The ethanol solution was added to a 1 litre cylindrical bottle, followed by the mixed powder and 500 g of stainless-steel balls. The slurry was left to mix at 320 RPM for 10-14 hours in preparation for spray drying. The slurry formulations used in the WC+CoCrFeNi experiment are as follows:

[0112] • WC: 333.3g

[0113] • CoCrFeNi: 83.3g

[0114] • PVB: 1.1g

[0115] • PAA: 1.0g

[0116] • Ethanol: 208.3g

[0117]

[0093] Spray drying was performed using a Buchi B290 Spray Dryer with a Buchi B295 Inert Loop mode, using nitrogen as the drying gas. The following variables were adjusted to optimise the output powder: Drying gas flowrate, drying gas inlet temperature, aspirator flow, pump speed of slurry and nozzle cleaning frequency. The large variation in density of the carbide powders (WC 15.63 g / cm3) and CCA powder caused diverse spray drying behaviour for each batch of slurries. As a result, the parameters were required to be optimised and adjusted 4 to 6 times across the different batches. Parameter optimisation was a balance between recovery yield and the particle size distribution.

[0118]

[0094] After spray drying the powders were sieved to a particle size of <63 pm. This material was then processed in a water solution to remove the finer material that causes the flowability problems. The powder was vigorously mixed in a large volume of water (>2 litres). The heavier (i.e. larger) particle settle first, while the smaller / lighter particles remain in suspension. Once the solids had settled, the top liquid was extracted using a vacuum pump. The top layer of fine material (approx, the top 30 % of the settled material) was also extracted, collected and dried. This “undersize” fraction and “the >65 pm fraction” were then redispersed in ethanol and reprocessed by spray drying. NOTE: No additional polymer binder or dispersant were added to this reprocessed material since it was expected that the binder was evenly distributed across all of the powder particles. The optimised spray drying parameters are included in the Table 4:

[0119]

[0095] Table 4 - Spray Drying parameters for WC+CoCrFeNi

[0120] N2 Drying gas flowrate (FMR) 60

[0121] Inlet temperature (°C) 120

[0122] Outlet temperature (°C) 73

[0123] Aspirator flow (%) 100

[0124] Pump speed (%) 70

[0125] Nozzle Clean frequency 6

[0126] Chiller temperature (°C) -20

[0127]

[0096] All of the powders were sintered at 500 °C for 1 hour to burn off the polymer compounds and then at 1230 °C for 5 hours in a graphite crucible under 99.999% argon. The furnace tube was first flushed with argon, and then a vacuum pulled on it, before flushing again. This process was repeated three times before the furnace cycle was started to remove ambient oxygen.

[0128]

[0097] After sintering the powder as again sieved through <63 pm. Oversize powder was lightly ground to reduce it in size. The fine material was again separated by the water settlement method and then dried.

[0129] Example 3 - Powder Characterisation

[0130]

[0098] Powder characterization of the formed CoCrFeNi CCA powder and carbide-CCA powder (CoCrFeNi -WC composite) formed according to the method described in Example 2 was carried out using a field emission scanning electron microscope (SEM) (Zeiss SUPRA™ 40VP FESEM system) with a working voltage of 20 kV and a working distance of 12-15 mm. The powder chemical concentrations were analysed using an attached energy dispersive X- ray spectrometer, EDS, (Oxford Instruments, INCAxcat detector). The phase analysis was conducted using Bruker’s D8 Discover Powder X-ray diffraction (XRD) system. Both powder and coating samples were scanned under Cu Ka radiation over a scanning 20 range of 20° to 90° at 40 mA and 40 kV with a 0.05 °20 step size.

[0099] The characterization results of the CCA powder and carbide-CCA powders are shown in Figures 3 to 6 and in Table 5.

[0131]

[0100] Figure 3 shows an XRD pattern of ball-milled CoCrFeNi CCA powder indicating the formation of FCC based CCA powder. The XRD analysis shows that after 10 hours of ball milling, only FCC peaks were observed without evidence of any undissolved elemental peaks, attributing that alloying is complete. The FCC based CoCrFeNi CCA is applied as a soft and ductile binder material for the development of hard carbide-CCA composite material.

[0132]

[0101] Figure 4 provides a SEM micrograph of ball-milled CoCrFeNi CCA powder. The ball milled powder has particle size varying from 2 to 15 pm. The powder is composed of both small and agglomerated particles with evidence of distinctive ball milling characteristics such as fracture and cracks. The difference in size and shape of particles validates the non-homogenous morphological characteristics of the ball milling process.

[0133]

[0102] Table 5: Elemental compositions of ball-milled CoCrFeNi CCA powder evaluated using energy dispersive spectroscopy (EDS) (average and standard deviation of 10 measurements).

[0134]

[0103] The chemical composition of the ball milled CoCrFeNi CCA powder is in close agreement with nominal composition of CoCrFeNi CCA in equi-atomic ratio. The lower value of the standard deviation of different elements in CoCrFeNi CCA demonstrates a homogenously distributed chemical composition.

[0135]

[0104] Figure 5 provides a SEM micrograph of spray-dried and sintered WC- CoCrFeNi powder particle with corresponding EDS elemental colour maps. The SEM image suggests that hard and brittle WC ceramic is enveloped around soft and ductile CoCrFeNi CCA phase with enhanced bonding post-sintering process. The particles are of a near-spherical shape and dense in nature, which improves the flowability of the spray dried and sintered composite powder. The EDS map demonstrates the retention of individual phase characteristics.

[0136]

[0105] Finally, Figure 6 provides an XRD pattern of WC-CoCrFeNi composite powder obtained after the spray drying and sintering process. This XRD pattern indicates the presence of peaks related to the carbide (W) phase and FCC phase from WC and CoCrFeNi CCA, respectively. The XRD pattern validates that the individuality of both the WC and CCA phases was retained in the final powder. This XRD pattern also suggests that there is no interphase dissolution occurred between two powders and no compositional loss was detected due to the powder manufacturing process.

[0137]

[0106] It can be concluded that spray drying followed by the sintering step develops ceramic-CCA composite powder with a near-spherical shape with desired particle size range. The process results in a chemical and microstructural homogenous powder, which can be used as feedstock material for various surface coating processes such as thermal spray or laser material deposition as well other advanced manufacturing processes such as additive manufacturing. The developed powder with enhanced characteristics is intended to develop superior ceramic-CCA composite coatings, an ideal alternative to conventional ceramic-metal composite coatings.

[0138]

[0107] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications that fall within the spirit and scope of the present invention.

[0139]

[0108] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.

Claims

CLAIMS1. An ultra-hard composite material, comprising a sintered composite powder comprised of agglomerated particles of powder, said agglomerated particles comprising a substantially homogenous mixture of:(a) at least one ceramic phase powder; and(b) a multi-element complex concentrated alloy powder, wherein the multi-element complex concentrated alloy powder consists of 4 to 11 elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder wherein the elements of the multi-element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids.

2. The ultra-hard composite material according to claim 1 , wherein the agglomerated particles are substantially-spherical in shape.

3. The ultra-hard composite material according to claim 1 or 2, wherein the agglomerated particles have a particle size of less than 100 pm, preferably less than 63 pm.

4. The ultra-hard composite material according to claim 1 , 2 or 3, wherein the ceramic phase powder comprises at least one carbide, preferably at least one metal carbide.

5. The ultra-hard composite material according to claim 4, wherein the carbide comprises at least one of tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), niobium carbide (NbC), chromium carbide (CrsC2), or tantalum carbide (TaCx), preferably tungsten carbide or titanium carbide.

6. The ultra-hard composite material according to any one of claims 1 to 5, wherein the multi-element complex concentrated alloy powder comprises a high- entropy alloy or a medium-entropy alloy.

7. The ultra-hard composite material according to any one of claims 1 to 6, wherein the multi-element complex concentrated alloy powder comprises at least 4 elements in equiatomic ratios, preferably at least 5 elements in equiatomic ratios.

8. The ultra-hard composite material according to any one of claims 1 to 7, wherein the ceramic phase powder and the multi-element complex concentrated alloy powder have a weight ratio of 90:10 to 60:40.

9. The ultra-hard composite material according to any one of claims 1 to 8, wherein the elements comprising the complex concentrated alloy powder may be selected from: Al, Cr, Co, Cu, Fe, Ni, V, Ti, Si or Mn.

10. The ultra-hard composite material according to any one of claims 1 to 9, wherein the multi-element complex concentrated alloy powder comprises one of: CoCrFeNi, AICoCrFeNi, Alo.sCoCrFeNi, Alo.sCrFeNiTio.s.11 . The ultra-hard composite material according to any one of claims 1 to 10, wherein the ultra-hard composite material comprises a powder feedstock for thermal spray coating, laser material deposition, cold spray coating process, or an additive manufacturing process.

12. A method of forming a carbide-complex concentrated alloy composite powder comprising: mixing at least one ceramic phase powder, a multi-element complex concentrated alloy powder, a liquid phase, at least one polymer binder, and at least one dispersant to form a slurry, wherein the multi-element complex concentrated alloy powder consists of 4 to 11 elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element complex concentrated alloy powder, and the elements of the multi-element complex concentrated alloy powder are selected from group 3 to 12 transition metals, or group 13 or 14 metals or metalloids; subjecting the slurry to a slurry mechanical alloying process to produce a milled slurry; spray drying the milled slurry to form a spray dried powder mixture; andsintering the spray dried powder mixture, thereby forming an agglomerated and sintered carbide-complex concentrated alloy (CCA) composite powder.

13. The method of claim 12, wherein the multi-element complex concentrated alloy powder comprises a high-entropy alloy or a medium-entropy alloy.

14. The method according to claim 11or 12, wherein the multi-element complex concentrated alloy powder comprises at least 4 elements in equiatomic ratios, preferably at least 5 elements in equiatomic ratios.

15. The method according to any one of claims 12 to 14, wherein the elements comprising the complex concentrated alloy powder may be selected from: Al, Cr, Co, Cu, Fe, Ni, V, Ti, Si or Mn.

16. The method according to any one of claims 12 to 15, wherein the multielement complex concentrated alloy powder comprises one of: CoCrFeNi, AICoCrFeNi, Alo.sCoCrFeNi, Alo.sCrFeNiTio.s.

17. The method according to any one of claims 12 to 16, wherein the ceramic phase powder and the multi-element complex concentrated alloy powder have a weight ratio of 90: 10 to 60:40.

18. The method according to any one of claims 12 to 17, wherein the ceramic phase powder comprises at least one carbide.

19. The method according to claim 18, wherein the carbide comprises at least one of: tungsten carbide (WC), titanium carbide (TiC), vanadium carbide (VC), niobium carbide (NbC), chromium carbide (CrsC2), or tantalum carbide (TaCx).

20. The method according to any one of claims 12 to 19, wherein the step of spray drying the ball milled slurry, uses an inert gas, preferably nitrogen, as drying gas to form a spray dried powder mixture.

21. The method according to any one of claims 12 to 20, wherein the spray dried powder mixture undergoes at least one separation step, preferably at least one sieving process to attain a particle size of less than 100 pm, preferably less than 63 pm.

22. The method according to claim 21 , wherein the oversized particles from the separation step are recycled for spray drying.

23. The method according to any one of claims 12 to 22, wherein the spray dried powder mixture undergoes at least one fines separation process, preferably a floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation, preferably flotation in water.

24. The method according to claim 23, wherein the fines particles fraction are recycled for spray drying.

25. The method according to any one of claims 12 to 24, wherein sintering the spray dried powder mixture comprises at least one sintering step where the spray dried powder mixture is heated to at least 1000 °C, preferably at least 1200 °C, and preferably within an inert atmosphere, and more preferably Ar.

26. The method according to any one of claims 12 to 25, wherein the sintering step comprises a two-step sintering process that comprises the steps (1) heating the spray dried powder mixture to at least 400 °C to remove the polymer binder content; and (2) heating the spray dried powder mixture to at least 1000 °C, preferably within an inert atmosphere, more preferably argon.

27. The method according to claim 26, wherein the first sintering step comprises heating the spray dried powder mixture at least 500 °C, preferably for at least 30 mins, more preferably for at least 60 minutes.

28. The method according to claim 26 or 27, wherein the second sintering step comprises heating the spray dried powder mixture at least 1200 °C, for preferably at least 2 hours, more preferably for at least 5 hours.

29. The method according to any one of claims 12 to 28, wherein the sintered powder mixture undergoes at least one separation step, preferably at least one sieving process, to attain a particle size of less than 100 pm, preferably less than 63 pm.

30. The method according to any one of claims 12 to 29, wherein the sintered powder mixture undergoes at least one fines separation process, preferably a floatation separation step, in which a fines particles fraction is separated from a denser particle fraction by floatation, preferably flotation in water.31 . The method according to any one of claims 12 to 30, wherein the slurry is formed by: mixing at least one ceramic phase powder and a multi-element complex concentrated alloy powder to form a powder mixture; and adding a liquid phase, at least one polymer binder and at least one dispersant to the powder mixture to form a slurry.

32. The method according to any one of claims 12 to 31 , wherein the liquid phase added to form the slurry comprises at least one solvent, preferably at least one of alcohol, polyols, cyclic ether, ketone, or water, more preferably at least one of: methanol, ethanol, isopropanol, ethylene glycol, glycerol, tetrahydrofuran, dioxane, acetone, methyl isobutyl ketone, and yet more preferably ethanol.

33. The method according to any one of claims 12 to 32, wherein the polymer binder added in the slurry comprises at least one of: carboxy-methyl-cellulose, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyethylene glycol (PEG), styrene-acrylic ester copolymer, and yet more preferably polyvinyl butyral (PVB).

34. The method according to any one of claims 12 to 33, wherein the dispersant added in the slurry comprises at least one of poly acrylic acid (PAA), ammonium polyacrylate (PAA-NH4), polyethylenimine (PEI), and yet more preferably poly acrylic acid (PAA).

35. The method according to any one of claims 12 to 34, wherein the slurry mechanical alloying process comprises ball milling the slurry.

36. The method according to claim 35, wherein the slurry is subjected to ball milling for at least 5 hours, preferably at least 10 h.

37. The method according to any one of claims 12 to 36, further including the step of forming a multi-element complex concentrated alloy powder from the comprising elemental powders using a mechanical alloying process prior to mixing at least one ceramic phase powder therein.

38. The method according to claim 37, wherein the mechanical alloying process comprises at least one ball milling process.

39. The method according to claim 37 or 38, wherein the mechanical alloying process comprises ball milling the elemental powders for at least 5 hours, preferably at least 10 h, to form the multi-element complex concentrated alloy powder.

40. The method according to claim 37, 38 or 39, wherein the mechanical alloying process is conducted within an inert gas, preferably argon.41 . The method according to any one of claims 11 to 40, wherein the particle size of the multi-element complex concentrated alloy powder is between 1 to 20 pm, preferably 1 to 10 pm, more preferably 2 to 6 pm, or is between 1 and 80 pm, preferably between 2 and 75 pm.

42. The method according to any one of claims 12 to 41 , wherein the carbide- complex concentrated alloy composite powder comprises feedstock powder for at least one of a: thermal spray coating; laser material deposition, cold spray coating process, or an additive manufacturing process.

43. An ultra-hard composite material formed from the method according to any one of claims 12 to 42.

44. The ultra-hard composite material according to claim 43, wherein the ultra- hard composite material comprises a powder, preferably a powder feedstock for thermal spray coating, laser material deposition, cold spray coating process, or an additive manufacturing process.

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