Method for reducing porosity of solid metallic materials or repairing microcracks in said material using hot isostatic pressing

Abstract

The present invention relates to a method for reducing porosity of a solid metallic material thus increasing the density of, or repairing microcracks in, said metallic material, by subjecting said metallic material to hydrothermal hot isostatic pressing (HHIP) involving hydrothermal water conditions and no usage of inert gas. The HHIP is carried out at a temperature which does not result in grain growth in said metallic material and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

Description

METHOD FOR REDUCING POROSITY OF SOLID METALLIC MATERIALS OR REPAIRING MICROCRACKS IN SAID MATERIAL USING HOT ISOSTATIC PRESSINGTECHNICAL FIELD

[0001] The present invention relates to a hydrothermal hot isostatic pressing (HHIP) approach, involving hydrothermal water conditions and no usage of inert gas, aimed at reducing porosity of a solid metallic material, e.g., a metal alloy, thus increasing the density of, or repairing microcracks in, said metallic material.BACKGROUND ART

[0002] Hydrothermal conditions can be used to expose solid metals to unique high- temperature and pressure conditions. In the industrial manufacturing of materials, a set of methods combining pressure and heat are commonly implemented to improve the product's quality following casting or three-dimensional (3D) printing (Zakay and Aghion, 2019). The pressure / heat combination induces diffusivity and hence the closure of voids and defects in the material; by doing so, the samples’ mechanical properties improve. In metals, such porosities and voids are found in casting, and more pertinently, in additively manufactured metal parts.

[0003] Hot isostatic pressing (HIP) is a well-established method for healing internal pores in cast parts and is widely used to significantly increase fatigue life in critical components. Applying HIP to AM AlSilOMg, e.g., is carried out at temperatures of about 500°C and a pressure of 100 MPa (1000 atm). Such conditions can close / heal internal pores and a lack of fusion defects, thus resulting in an increase in the fatigue strength (Macias et al., 2022) and in improved material ductility; however, this reduces the strength (Ertugrul et al., 2020).

[0004] At the reduced yield stress and the higher diffusion rates associated with high temperatures, the applied pressure may lead to pore collapse via small-scale plastic flow and material transport, which, under ideal conditions, also bonds the pore interface (Atkinson and Davies, 2000). In aluminum, although there are standard for the HIP of aluminum alloy casting (ASTM B998-17, 2017) and for ALSilOMg AM manufactured parts (ASTM F3318- 18, 2018), some researchers do not recommend that the HIP treatment is applied as it may destroy the mechanical properties due to grain growth and other unwanted harmful thermaltreatment effects, as recently concluded, e.g., by Hirata et al., 2020, who investigated the applicability of HIP in eliminating the internal pores in selective laser melted (SLM) AlSilOMg. These authors recommended optimizing the SLM irradiation conditions in the fabrication of SLM aluminum alloys, rather than using HIP.

[0005] The HIP conditions are generally chosen such that the gas pressure is greater than the reduced yield point, up to the point of approaching the partial melting of the material at the HIPing temperature. Plastic flow can then occur on a microscopic scale. Under HIP conditions, considerable particle shear occurs, and creep processes such as diffusion through grain interiors, diffusion around grain boundaries and dislocation creep occur at relatively high rates. These are the processes that are primarily responsible for the densification of the subject parts (Atkinson and Davies, 2000).

[0006] In the commonly applied HIP practice, inert gas, such as argon, is compressed inside a furnace to allow simultaneous heating and pressing of the part.

[0007] The main limitations of the current HIP practice are (1) Limited pressure: the commonly used gas compressed HIP systems work in the pressure range of 100-200 MPa (Atkinson and Davies, 2000), which dictates a high working temperature, e.g., Gussev et al., 2018; and Schneller et al., 2019; (2) High temperatures: under a limited gas pressure environment, the sample’s temperature is increased to allow efficient diffusion. Concurrently, the high temperatures often reduce the metals’ mechanical properties owing to the grain growth effect (see, e.g., Uzan et al., 2017); and (3) Costs: a high operating temperature increases energy costs due to a larger heat loss during HIP holding time (Ahlfors, 2018), followed by the coupling of high pressure and temperature which leads to expensive infrastructure and operation costs.

[0008] Cold isostatic pressing (CIP) is also common practice. In this procedure, a pressed liquid (usually oil) isostatically presses a body to increase its density. However, these methods are usually applied for ceramic green bodies. A hydrostatic CIP treatment was recently addressed by Cuesta et al., 2019 for additively manufactured ANSI 316L metallic components, with contradictory results.

[0009] The use of water at high pressure and temperature for the hydrothermal HIP of mica powders was previously proposed and investigated, e.g., by Hattori et al., 1984; and Hattori et al., 1982. However, to the best of our knowledge, the hydrothermal isostaticpressing treatment of metal parts, and more specifically for additive material metal parts, has not been attempted.SUMMARY OF INVENTION

[0010] Disclosed herein is a method for reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, thus increasing the density of said metallic material, or repairing microcracks in said metallic material, said method comprising subjecting said metallic material, for a selected period of time, e.g., for about 2 hours to about 48 hours, to hot isostatic pressing (HIP) using a liquid pressing medium, wherein said HIP is carried out at a temperature which does not result in grain growth in said metallic material, and is lower than the melting point of said metallic material, e.g., at a temperature that is from about 0.3 to about 0.7, or lower than 0.3, of the homologous temperature of said metallic material, or from about 200°C to about 1000°C, and under pressure higher than the flow stress of said metallic material at said temperature.

[0011] In certain embodiments, the liquid pressing medium used in the method of the present invention is an inorganic liquid, e.g., an aqueous solution such as water, preferably distilled or deionized water, optionally free of an externally added oxidizing agent. Thus, in particular such embodiments, said HIP is carried out under hydrothermal conditions, and referred to herein as hydrothermal HIP (HHIP).

[0012] In other words, disclosed herein is a method for reducing porosity of a solid metallic material as defined above, thus increasing the density of said metallic material or repairing microcracks in said metallic material, by subjecting said metallic material to HIP, wherein the improvement results from the fact that said HIP is carried out using a pressing medium which is a liquid; and at a temperature which does not result in grain growth in said metallic material, and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

[0013] The metallic material treated by the method disclosed herein may be obtained by, e.g., casting, sintering, or additive manufacturing process, i.e., 3D printing process. In certain embodiments, said metallic material is obtained following an additive manufacturing process, and said method does not adversly affect static mechanical properties such as strength and hardness, or dynamic mechanical properties such as fatique resistance, of said metallic material.BRIEF DESCRIPTION OF DRAWINGS

[0014] Fig. 1 illustrates experimental hydrothermal HIPing system.

[0015] Fig. 2 shows A16061 cross-section EDS results after HHIP. The dark and bright are the EDS spectra from surface and bulk material, respectively.

[0016] Fig. 3 shows A12024 cross-section EDS results after HHIP. The dark and bright are the spectra from surface and bulk material, respectively.

[0017] Fig. 4 shows AM AlSilOMg cross-section EDS line-scan results following HHIP.

[0018] Fig. 5 shows XRD diffractions of the AM AlSilOMg alloy. Pretreated material (upper panel). Post-treated material (lower panel).

[0019] Figs. 6A-6C show SEM micrographs of AM AlSilOMg alloy. (6A) As-received structure. Note the pores aligned with the printing direction; (6B) Treated material structure. No pores were noticed at low magnification; (6C) High magnification of (6B) shows submicrons round pores.

[0020] Figs. 7A-7B show SEM image of cellular sub-structure. Each cell is decorated with Si nanoprecipitates. (7A) Pretreated material. (7B) Post-treated material. The cells and Si nanoprecipitates have the same size and shape in both materials.

[0021] Fig. 8 shows high magnification SEM image of the treated material. Tiny Si particles can be noted in the cells, as pointed out by the arrows.

[0022] Fig. 9 shows EBSD grain map showing that the treatment did not result in a consequential change in the grain size. Pretreated sample in which the measured average grain size is 8.2 μm (left panel). Post-treated material in which the average measured grain size is 9.5 μm (right panel).

[0023] Fig. 10 shows EBSD phase map. Al - dark grey, Si - light grey, Mg2Si - black. Very small Al and Mg2Si are detected in both samples. Pretreated material (left panel). Posttreated material (right panel).

[0024] Figs. 11A-11D show EBSD texture maps of the pretreated material (11A, 11B), and the post-treated material (11C, 11D). A preferred directionality of Al and Si was detected in the pretreated material (11A, 11B, respectively). Following the treatment, the preferred directionality was less significant (11C) Al, (11D) Si.DETAILED DESCRIPTION

[0025] Exemplified herein, as proof of concept (PoC), is a new cost-effective hydrothermal hot isostatic pressing (HHIP) approach, involving hydrothermal water conditions and no usage of inert gas, carried out on 3D-printed aluminum alloy samples, more specifically Al-10%Si-0.3%Mg (%wt) samples (aluminum alloys were selected at this stage because of their low melting temperature). While the “regular” argon HIP treatment for aluminum and its alloys is carried out at 500°C / 100 MPa (Atkinson and Davies, 2000; Hirata et al., 2020), the HHIP treatment exemplified herein was performed at 250- 350°C / 300-350 MPa range. The aluminum-based metal was practically inert at the applied HHIPing conditions of 300-350 MPa and 250-350°C, which enabled the employment of a long (6-24 h) HHIP treatment with hardly any loss of material (the overall loss due to corrosion was mostly <0.5% w / w). Applying the new approach on the above-mentioned samples resulted in an 85.7% reduction in the AM micro-pores, along with a 90.8% reduction in the pores’ surface area at a temperature of 350°C, which is much lower than the 500- 520°C applied in common argon-based aluminum HIPing treatments, while practically maintaining the as-received micro structure. These results show that better mechanical properties can be expected when using the suggested treatment without affecting the material fatigue resistance due to grain growth. The concept disclosed herein can pave the way to applying the new HHIPing approach to other AM metal parts.

[0026] The HHIP treatment exemplified is based on feeding water to the HIP chamber, and then raising it to the required operating pressure and temperature by a high-pressure water pump and an electrical heater. The proposed treatment has the potential to dramatically decrease the process temperature and the retention time of the procedure, owing to the much higher applied pressure. This has the potential to open a new branch of isostatic pressure treatments, with decreased grain growth (which tempers the mechanical properties) due to the lower time and temperature exposure. Furthermore, the water media is safer, cheaper, and more environmentally friendly than the pressed inert gas solution currently applied in state-of-the-art HIP systems.

[0027] In one aspect, the present invention thus provides a method for reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, to thereby increase the density of said metallic material, or repairing, i.e., healing, microcracks in said metallic material, said method comprisingsubjecting said metallic material, for a selected period of time, to HIP using a liquid pressing medium, wherein said HIP is carried out at a temperature which does not cause, i.e., does not result in, grain growth in said metallic material, and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

[0028] The term “porosity” (also known as “void fraction”) as referred to herein with respect to the solid metallic material subjected to the method of the present invention is measured as the void, i.e., empty, spaces in said metallic material, reflects the ratio between the overall volume of said voids and the total volume of said metallic material, and may be represented as either a fraction (between 0 to 1) or as a percentage (between 0% to 100%). The porosity of the solid metallic material may be tested and measured using various technologies such as industrial CT scanning, as well as optical, ultrasonic or density measurement methods. The method disclosed is aimed at reducing the porosity of a solid metallic material as defined above, to thereby increase the density of, or repairing microcracks in, said metallic material. In certain embodiments, the porosity of the metallic material treated by said method is reduced by at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 85%, at least 90%, or at least 95% (expressed by the number of voids, the overall size thereof, or the overall volume thereof) compared to the porosity of said metallic material before treatment.

[0029] The HIP treatment to which the solid metallic material is subjected is carried out at a temperature which is lower than the melting point of said metallic material and does not cause grain growth in said metallic material, i.e., does not result in grain growth higher than 10% in said metallic material. In certain embodiments, said HIP treatment results in grain growth of up to about 9%, up to about 8%, up to about 7%, up to about 6%, up to about 5%, up to about 4%, up to about 3%, up to about 2%, or up to about 1%, only.

[0030] The metallic material treated by the method disclosed herein may be either a metal or an alloy, metal matrix composite, or intermetallic compound thereof.

[0031] In certain embodiments, the metallic material treated by the method disclosed is a metal. Examples of such a metal include, without being limited to, aluminum, manganese, copper, magnesium, zirconium, zinc, iron, titanium, chromium, nickel, lead, cobalt, tantalum, tungsten, niobium, gold, silver, and tin.

[0032] In other embodiments, the metallic material treated by the method disclosed is a metal alloy.

[0033] The term “metal alloy” as used herein refers to a mixture of chemical elements of which at least one is a metal, i.e., a material or substance which combines more than one metal or mixes a metal with other non-metallic elements, and wherein the atoms are joined by metallic bonding rather than by covalent bonds typically found in chemical compounds. Examples of metal alloys include, without limiting, alloys of aluminum, manganese, copper, magnesium, zirconium, zinc, iron, titanium, chromium, nickel, lead, cobalt, tantalum, tungsten, niobium, gold, silver, or tin.

[0034] In certain particular such embodiments, the metallic material treated by the method of the invention is an aluminum alloy, i.e., an alloy in which aluminum is the predominant metal, and the alloying elements are, e.g., at least one of copper, magnesium, manganese, silicon, tin, nickel, zirconium, lithium, scandium, silver, titanium, boron, vanadium, and zinc. More particular such alloys are those wherein aluminum is the predominant metal, and the main alloying elements are: (a) copper, magnesium and manganese; (b) copper, magnesium and titanium; (c) scandium and magnesium; (d) silicon; (e) silicon and magnesium; (f) silicon, manganese and magnesium; (g) silicon, iron and copper; (h) silicon, boron and copper; (i) silicon, magnesium and copper; or (j) magnesium. Specific aluminum alloys include, without being limited to, A12024, A16061, Al-Sc-Mg such as Scalmalloy®, AlSilOMg, AlSi7Mg03, AlCu4MgTi, AlCu4MnMg, AlSilOMnMg, AlSil2, AlSi9Cu3(Fe), AlSi8Cu3, AlSi7Cu3Mg, and AlMg3.

[0035] In other particular such embodiments, the metallic material treated by the method of the invention is a copper alloy, i.e., an alloy in which copper is the predominant metal, and the alloying elements are, e.g., at least one of nickel, aluminum, silicon, tin, silver, lead, chromium, zirconium, tungsten, iron, gold, niobium, phosphor, molybdenum, beryllium, and zinc. More particular such alloys are those wherein copper is the predominant metal, and the main alloying elements are: (a) zinc; (b) tin; (c) chromium; (d) chromium and niobium; or (e) chromium and zirconium. Specific copper alloys include, without limiting, brass (Cu- Zn), bronze (Cu-Sn), GRCop-42 and GRCop-84 (Cu-Cr-Nb), C18150 (copper, chromium, zirconium), and Cl 8200 (copper chromium).

[0036] In still other particular such embodiments, the metallic material treated by the method of the invention is a magnesium alloy, i.e., an alloy in which magnesium is thepredominant metal, and the alloying elements are, e.g., at least one of aluminum, zinc, manganese, copper, calcium, cerium, bismuth, cadmium, iron, thorium, strontium, lithium, tin, lead, silver, chromium, silicon, gadolinium, yttrium, antimony, and zirconium. More particular such alloys are those wherein magnesium is the predominant metal, and the main alloying elements are: (a) aluminum and zinc; (b) aluminum, zinc and calcium; (c) aluminum, zinc and tin; (d) aluminum and silicon; (e) aluminum and manganese; (f) cerium, yttrium, neodymium and zirconium; or (g) cerium, neodymium, zinc, gadolinium and zirconium. Specific magnesium alloys include, without being limited to, AZ91, AZ91+Ca, AZ91+Sn, AM50, WE54, WE43, and Elektron 21.

[0037] In yet other particular such embodiments, the metallic material treated by the method of the invention is a zirconium alloy, i.e., an alloy in which zirconium is the predominant metal, and the alloying elements are, e.g., at least one of tin, niobium, iron, chromium, and nickel.

[0038] In further particular such embodiments, the metallic material treated by the method of the invention is a zinc alloy, i.e., an alloy in which zinc is the predominant metal, and the alloying elements are, e.g., at least one of aluminum and copper.

[0039] In still further particular such embodiments, the metallic material treated by the method of the invention is a ferrous alloy, i.e., an alloy in which iron is the predominant metal, and the alloying elements are, e.g., at least one of chromium, carbon, silicon, manganese, tungsten, molybdenum, titanium, cobalt, copper, sulfur, phosphor, niobium, vanadium, aluminum, and nickel. More particular such alloys are those wherein iron is the predominant metal, and the main alloying elements are: (a) chromium; (b) chromium, copper and nickel; (c) chromium, copper, nickel, manganese, silicon, and niobium; (d) chromium, silicon and manganese; (e) chromium, silicon, manganese, and nickel with regular and low carbon content; (f) chromium, vanadium, molybdenum, and silicon; (g) chromium and molybdenum; (h) cobalt and silicon; (i) silicon; (j) nickel; or (k) nickel and molybdenum. Specific ferroalloys include, without limiting, 15-5 PH, 17-4 PH, SS316, SS316L, SS304, SS304L, SS420, H13, AISI4130, FeCoSi, FeSi, FeNi, FeCr, and FeNiMo.

[0040] In yet further particular such embodiments, the metallic material treated by the method of the invention is a titanium alloy, i.e., an alloy in which titanium is the predominant metal, and the alloying elements are, e.g., at least one of aluminum, manganese, zirconium, chromium, molybdenum, vanadium, niobium, tantalum, zirconium, iron, nickel, copper,aluminum, tin, palladium, ruthenium, silicon, and cobalt. More particular such alloys are those wherein titanium is the predominant metal, and the main alloying elements are: (a) aluminum and vanadium; (b) iron; or (c) chromium. Specific titanium alloys include, without being limited to, Ti-6A1-4V, Ti-6A1-4VELI, and CP Ti.

[0041] In still other particular such embodiments, the metallic material treated by the method of the invention is a chromium alloy, i.e., an alloy in which chromium is the predominant metal, and the alloying element is, e.g., cobalt.

[0042] In yet other particular such embodiments, the metallic material treated by the method of the invention is a nickel alloy, i.e., an alloy in which nickel is the predominant metal, and the alloying elements are, e.g., at least one of chromium, copper, iron, titanium, niobium, tantalum, manganese, tungsten, vanadium, zirconium, carbon, cobalt, aluminum, boron, rhenium, hafnium, silicon, lanthanum, yttrium, ruthenium, and molybdenum. More particular such alloys are those wherein nickel is the predominant metal, and the main alloying elements are: (a) chromium, cobalt, molybdenum, titanium, aluminum, and tantalum; (b) chromium, iron, molybdenum, niobium, tantalum, and cobalt; or (c) chromium, iron, manganese, cobalt, silicon, and tungsten. Specific nickel alloys include, without limiting, Inconel 718, Inconel 625, and HX.

[0043] In still further particular such embodiments, the metallic material treated by the method of the invention is a lead alloy, i.e., an alloy in which lead is the predominant metal, and the alloying elements are, e.g., at least one of antimony, arsenic, calcium, copper, tin, tellurium, and silver.

[0044] In yet further particular such embodiments, the metallic material treated by the method of the invention is a cobalt alloy, i.e., an alloy in which cobalt is the predominant metal, and the alloying elements are, e.g., at least one of iron, carbon, chromium, nickel, molybdenum, silicon, manganese, titanium and tungsten. More particular such alloys are those wherein cobalt is the predominant metal, and the main alloying elements are: (a) chromium; (b) chromium and molybdenum; or (c) chromium, molybdenum and tungsten. Specific cobalt alloys include, without being limited to, CoCr, CoCrMo (F75), and CoCrWMo.

[0045] In yet other particular such embodiments, the metallic material treated by the method of the invention is a tin alloy, i.e., an alloy in which tin is the predominant metal, and the alloying elements are, e.g., at least one of copper, lead, zinc, and antimony.

[0046] In still other particular such embodiments, the metallic material treated by the method of the invention is a complex composite alloy comprising quite equal atomic percentages of metals selected from Al, Co, Cr, Cu, Fe, Mo, Nb, Ni, Ta, Ti, V, W, and Zr. Particular such complex composite alloys include, without limiting, CoCrCuFe, NiAlx, AlCrMoNi, TaNbHfZrTi, TaNbMoW, and TaNbVMoW.

[0047] In yet other embodiments, the metallic material treated by the method disclosed is a metal matrix composite.

[0048] The term “composite material” as used herein generally refers to a material made of two or more constituent materials (“individual elements”) having different chemical or physical properties, wherein said constituent materials are merged within the finished structure to create a material with properties different from those of each one of the individual elements, but yet remain separate and distinct.

[0049] The term “metal matrix composite” (MMC) as used herein refers to a composite material consisting of a metal matrix, into which fibers or particles of a secondary phase (also referred to as “reinforcing material”) are dispersed or embedded. The secondary’ phase is typically ceramic, e.g., alumina or silicon carbide, or another metal such as steel. Unlike two or more materials sandwiched together, the matrix in metal matrix composites is a monolithic material into which the reinforcement i s embedded, and i s completely continuous such that there is a path through the matrix to any point in the material.

[0050] In certain particular such embodiments, the metallic material treated by the method of the invention is a metal matrix composite comprising a metallic matrix comprising one or more of copper, aluminum, cobalt, magnesium, titanium, silicon, carbon, boron, tungsten, and iron, which is optionally reinforced by an oxide or carbide component. Specific examples of metal matrix composites include, without being limited to, Co-WC, Al-SiC, Al- A12O3, Mg-SiC, Mg-A12O3, Mg-TiC, Ti-TiB2, Ti-TiC, and copper matrix reinforced with ultra-fine alumina particles such as GlidCop®.

[0051] In further embodiments, the metallic material treated by the method di sclosed is an intermetallic compound.

[0052] The term “intermetallic compound” also known as “intermetallic alloy”, as used herein, refers to a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements, or in other words, to a substance composed of a definite proportion of two or more metallic elements, having a defined crystal structure with specificsites assigned for the atoms of each constituent element, and properties that are often markedly different from those of its constituents.

[0053] In certain particular such embodiments, the metallic material treated by the method of the invention is an intermetallic compound comprising aluminum and titanium, e.g., TiAl or Ti3AI; aluminum and nickel, e.g., NiAl; aluminum, nickel and cobalt, e.g., AlNiCo; aluminum and iron, e.g., FeAl; or nickel and titanium, e.g., Nitinol (a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages).

[0054] According to the method of the present invention, the solid metallic material treated is subjected, for a selected period of time, to HIP using a liquid pressing medium, carried out at a temperature which does not result in grain growth in said metallic material, and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

[0055] The selected period of time during which the solid metallic material is subjected to said HIP can be any time period, depending on the physical properties of said metallic material as well as the temperature and pressure utilized. In certain embodiments, said period of time, regardless of the specific solid metallic material treated and according to any one of the embodiments above, is from about 2 hours to about 48 hours, e.g., from about 4 hours to about 42 hours, from about 6 hours to about 36 hours, from about 8 hours to about 30 hours, from about 10 hours to about 24 hours, or from about 12 hours to about 18 hours. In other embodiments, regardless of the specific solid metallic material treated, said time period is up to 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, or 48 hours.

[0056] According to the method of the present invention, the HIP is carried out at a temperature which does not cause, or does not result in, grain growth in said metallic material, and which is lower than the melting point of said metallic material. The term “grain growth” as used herein refers to the increase in size of grains (crystallites) in a solid metallic material as referred to herein, treated at high temperature, due to an alteration of the internal energy of the molecular structure of said metallic material, and may result in increased probability for crevice, intergranular and grain boundary corrosion.

[0057] In certain embodiments, the temperature at which said HIP is carried out, according to any one of the embodiments above, is from about 0.3 to about 0.7 of the homologous temperature of said metallic material, or lower than 0.3 of the homologous temperature ofsaid metallic material. The term “homologous temperature” as used herein with respect to a metallic material denotes the ratio of the absolute temperature of said metallic material to its melting point, i.e., expresses the temperature of said material as a fraction of its melting point temperature using the Kelvin scale.

[0058] In other embodiments, the temperature at which said HIP is carried out, according to any one of the embodiments above, is up to about 1200°C, 1300°C, 1400°C, or 1500°C, e.g., from about 200°C to about 1000°C, from about 250°C to about 950°C, from about 300°C to about 900°C, from about 350°C to about 850°C, from about 400°C to about 800°C, from about 450°C to about 750°C, from about 500°C to about 700°C, or from about 550°C to about 650°C.

[0059] According to the method of the present invention, the HIP is carried out at a temperature as defined above, and under pressure which is higher than the flow stress of said metallic material at said temperature. The term “flow stress” as used herein with respect to a solid metallic material as defined herein refers to the instantaneous value of stress required to continue plastically deforming said metallic material, i.e., keep it flowing, and it depends inter alia on the temperature to which said metallic material is exposed. The flow stress of a metal is the stress at which the material yields, or deforms plastically, and it can be determined most easily with a tensile test.

[0060] In certain embodiments, the pressure under which said HIP is carried out, according to any one of the embodiments above, is up to about 1100, 1200, 1300, 1400, or 1500 megapascal (MPa), e.g., from about 200 MPa to about 1000, 1250 or 1500 MPa, from about 250 MPa to about 950 MPa, from about 300 MPa to about 900 MPa, from about 350 MPa to about 850 MPa, from about 400 MPa to about 800 MPa, from about 450 MPa to about 750 MPa, from about 500 MPa to about 700 MPa, or from about 550 MPa to about 650 MPa.

[0061] In certain embodiments, the liquid pressing medium utilized in the HIP, according to any one of the embodiments above, is an inorganic liquid, organic liquid, or a mixture thereof. In particular such embodiments, said liquid pressing medium is free of an externally added oxidizing agent. The term “oxidizing agent” as used herein refers to an electron recipient or electron acceptor, i.e., a substance in a redox chemical reaction that "acceptsV'receives" an electron from a reducing agent. Non-limiting examples of externally added oxidizing agents include a halogen such as fluorine, chlorine and bromine; oxygen;an oxyanion such as permanganate ion (MnO4-) nitrate ion (NO3-) persulfate ion (SO52-, S2O82-), and dichromate ion (Cr2O72-) ; and an oxyacid such as sulfuric acid and nitric acid.

[0062] In certain particular such embodiments, the liquid pressing medium utilized in the HIP is an inorganic liquid, more specifically an aqueous solution such as water including fresh water, tap water, distilled water, and deionized water. In certain preferred such embodiments, said liquid pressing medium is distilled water or deionized water. In certain embodiments, the liquid pressing medium utilized is an aqueous solution as defined herein, e.g., water such as distilled or deionized water, and the HIP is carried out under hydrothermal conditions, i.e., at a temperature higher than the boiling point of the water, and high pressure.

[0063] In other particular such embodiments, the liquid pressing medium utilized in the HIP is an organic liquid (solvent) which may be either polar or non-polar organic liquid. Examples of polar organic liquids include, without being limited to, acetic acid, acetone, acetonitrile, methanol, ethanol, propanol, isopropanol butanol, Z-butyl alcohol, chloroform, ethylene glycol, diethylene glycol, ethyl acetate, methylene chloride, chlorobenzene, 1,2- dichloroethane, and mixtures thereof; and examples of non-polar organic liquids include, without limiting, (CvCsJalkancs such as pentane, hexane, heptane, and octane, cyclohexane, diethyl ether, benzene, and mixtures thereof.

[0064] The solid metallic material treated by the method of the present invention may be any solid material selected from a metal and an alloy, metal matrix composite, or intermetallic compound thereof, each as defined in any one of the embodiments above, and may be obtained by any process, or utilizing any technology, known in the art.

[0065] In certain embodiments, said solid metallic material is (or has been) obtained following a casting; sintering; or additive manufacturing process, i.e., 3D printing process. In particular such embodiments, said metallic material is obtained following an additive manufacturing process, and said method does not adversly affect static mechanical properties such as strength and hardness, or dynamic mechanical properties such as fatique resistance, of said metallic material.

[0066] In certain embodiments, the method disclosed herein is aimed at reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, thus increasing the density of said metallic material, or repairing, i.e., healing, microcracks in said metallic material, said method comprising subjecting said metallic material, for a time period of from about 2 hours to about 48 hours, e.g., from about4 hours to about 42 hours, from about 6 hours to about 36 hours, from about 8 hours to about 30 hours, from about 10 hours to about 24 hours, from about 12 hours to about 18 hours, or from about 6 hours to about 24 hours, to HIP using water free of an externally added oxidizing agent, preferably distilled or deionized water, as the liquid pressing medium, wherein said HIP is carried out under hydrothermal conditions (i.e., subjecting said metallic material, for a time period of from about 2 hours to about 48 hours, to HHIP treatment, using water free of an externally added oxidizing agent, preferably distilled or deionized water, as the liquid pressing medium). According to the invention, said HHIP treatment may be carried out at a temperature from about 0.3 to about 0.7 of the homologous temperature of said metallic material, or lower than 0.3 of the homologous temperature of said metallic material (e.g., at a temperature up to about 1200°C, 1300°C, 1400°C, or 1500°C, such as from about 200°C to about 1000°C, from about 250°C to about 950°C, from about 300°C to about 900°C, from about 350°C to about 850°C, from about 400°C to about 800°C, from about 450°C to about 750°C, from about 500°C to about 700°C, or from about 550°C to about 650°C); and / or under pressure that is from about 200 MPa to about 1000, 1250 or 1500 MPa, from about 250 MPa to about 950 MPa, from about 300 MPa to about 900 MPa, from about 350 MPa to about 850 MPa, from about 400 MPa to about 800 MPa, from about 450 MPa to about 750 MPa, from about 500 MPa to about 700 MPa, or from about 550 MPa to about 650 MPa.

[0067] In particular such embodiments, the solid metallic material treated is a metal alloy, metal matrix composite, or intermetallic compound, each as defined in any one of the embodiments above. In more particular such embodiments, said metallic material is a metal alloy, e.g., (i) an aluminum alloy such as such as A12024, A16061, Al-Sc-Mg such as Scalmalloy®, AlSilOMg, AlSi7Mg03, AlCu4MgTi, AlCu4MnMg, AlSilOMnMg, AlSil2, AlSi9Cu3(Fe), AlSi8Cu3, AlSi7Cu3Mg, and AlMg3, e.g., wherein said HIP is carried out at a temperature from about 220°C to about 38O°C, e.g., from about 250°C to about 350°C, and under pressure from about 280 MPa to about 380 MPa; (ii) a titanium alloy such as Ti- 6A1-4V and Ti-6A1-4VELI; and said hot isostatic pressing is carried out at a temperature from about 400°C to about 800°C, e.g., at about 500°C, and under pressure from about 300 MPa to about 1500 MPa, e.g., at about 600 MPa; (iii) a ferroalloy such as 15-5 PH, 17-4 PH, SS316, SS316L, SS304, SS304L, SS420, H13, AISI4130, FeCoSi, FeSi, FeNi, FeCr, and FeNiMo; and said hot isostatic pressing is carried out at a temperature from about 400°C toabout 1000°C, e.g., at about 550°C, and under pressure from about 700 MPa to about 1500 MPa, e.g., at about 800 MPa; or (iv) a nickel alloy such as Inconel 718, Inconel 625, and HX; and said hot isostatic pressing is carried out at a temperature from about 600°C to about 900°C, e.g., at about 800°C, and under pressure from about 300 MPa to about 1500 MPa, e.g., at about 1100 MPa.

[0068] In sharp contrast to the typical HIP, which involves the use of external inert gas such as argon as the pressing medium, i.e., so as to apply a pressure of up to 100-150 MPa, the method disclosed herein comprises HIP under pressure that is much higher, simply by applying a liquid such as water, which is much less costly and easy to compress, as the pressing medium. The very high pressure applied during the process helps in closing the pores, i.e., reducing the porosity of the metallic material treated and / or repairing microcracks in said metallic material, at significantly lower temperature.

[0069] Thus, in another aspect, in a method for reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, thus increasing the density of said metallic material, or repairing microcracks in said metallic material, by subjecting said metallic material to HIP, the improvement wherein said HIP is carried out using a pressing medium which is a liquid [rather than an inert gas], said HIP being carried out at a temperature which does not cause, i.e., does not result in, grain growth in said metallic material, and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

[0070] The liquid pressing medium utilized in the HIP, according to the method disclosed herein, is either an inorganic liquid or organic liquid, each as defined above, or a mixture thereof. Said liquid pressing medium may be free of an externally added oxidizing agent.

[0071] In certain embodiments, the liquid pressing medium utilized is an inorganic liquid, more specifically an aqueous solution such as water including fresh water, tap water, distilled water, and deionized water. In particular such embodiments, the liquid pressing medium utilized is an aqueous solution such as water, e.g., distilled or deionized water, and the HIP is carried out under hydrothermal conditions.

[0072] Unless otherwise indicated, all numbers expressing, e.g., temperatures or pressures, used in this specification, are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth inthis specification are approximations that may vary by up to plus or minus 10% depending upon the desired properties to be obtained by the present invention.

[0073] The invention will now be illustrated by the following non-limiting Examples.EXAMPLESStudy 1. Hydrothermal hot isostatic pressing (HHIP) - experimental proof of conceptMaterials and Methods

[0074] Materials. Three aluminum alloys were selected for the PoC experiments. Two commercial aluminum alloys (A16061 / 2024) were used for the screening corrosion experiment under hydrothermal conditions, and AlSilOMg was selected for the AM HIP experiments. The AM samples were stress relieved at 300°C for 120 min prior to removal from the SLM base plate. The composition of the selected alloys is shown in Table 1. Deionized water (DIW) at EC=0.5-l pS / cm was used in all the experiments. The A16061 / 2024 samples were made of 1 mm thick plate strip cuts. The AlSilOMg AM sample was a 3 mm ID / ca. 20 mm cylinder, produced by the EOS M290 3D printer (EOS GmbH, Krailling Germany) using 20-75 μm raw material particles, after common practice stress relief.Table 1: Metal samples' composition (%wt)(1)United Aluminum. Aluminum Alloy 6061 Data Sheet. 2023.(2)United Aluminum. Aluminum Alloy 2024 Data Sheet. 2023.(3)EOS Metal Solutions. EOS Aluminum AlSilOMg Material Data Sheet. 2022.

[0075] Experimental system. The experimental system is shown schematically in Fig. 1. The required pressure was created using a manual high-pressure screw piston, manufactured by Sitec High-Pressure Technology AG (Zurich, Switzerland). All piping and fittings were supplied by the same manufacturer. Heating was applied using a horizontal Carbolite 2" furnace (Carbolite Gero, Hope Valley, UK), with a heating capacity of up to 1500±l°C. The HIPing reactor was a 9 / 16” 200 mm SS316Ti spool rated for 400 MPa with an internal diameter of 4.8 mm. Water samples were extracted via valve V-3.

[0076] Hydrothermal experiments. A set of ten PoC hydrothermal experiments were divided into preliminary aluminum compatibility corrosion tests, which aimed to verify the low reactivity of the aluminum alloys, and hydrothermal HIP experiments for the AM AlSilOMg samples. The possible working conditions were limited by the design pressure of the test reactor (400 MPa). Hence, the working conditions varied between temperatures of 250, 300 and 350°C, and pressures of 300 and 350 MPa. The treatment duration was either 6-8 h or 24 h. The complete experimental setup is shown in Table 2, with the relevant water analysis results. During the heating step and the corresponding water expansion, the system was regulated to attain the required pressure by adjusting the manual high-pressure screw pump.

[0077] Analysis. The inorganic species composition of the water samples was determined using a Thermo Fisher Scientific ICP-OES (Thermo Fisher Scientific, Cambridge, UK). This was performed for the various aluminum alloys constituents, as well as for the HIP reactor and piping SS316Ti alloying species. The concentrations of dissolved Al, Cr, Cu, Fe, Mo, Ma, Ni, P, Si, Ti, S, Mg were quantified in the prewash solution, the solution inside the reactor and the final wash solution that followed each of the experiments.

[0078] To evaluate the corrosion of the non- AM samples (A12024 and A16061) and the AM AlSilOMg samples before and after the hydrothermal treatment, the samples were embedded in conductive Bakelite, ground using 220 MESH SiC paper, polished using the diamond suspension, and etched with colloidal silica. Their cross-sections were evaluated by Energy-Dispersive X-ray Spectroscopy (EDS) analysis, performed using the FEI Inspect S50 microscope (FEI, Moravia, Czech Republic). The system’s EDS detector was INCA Penta FETx3 (Oxford Instruments, Belfast, UK).Table 2: Experimental conditions, sample weight, and ICP results in the surrounding water samplesTable 2: Continuation

[0079] Measuring the pore sizes and distribution in the AM AlSilOMg samples was performed using EasyTOM XL, a flexible X-ray micro and ultra tomography system (RX Solutions, Chavanod, France). The results were evaluated using Xact and VGStudio max 3.50 tools. A voxel size of 3.5 μm, 2625 slices, 1 1OkV, and 80μA were the main analysis setup parameters.

[0080] The hardness of the samples was measured using Future-Tech Microhardness Tester, FM-110 (Future-Tech Corp., Kanagawa, Japan).

[0081] Phase analysis was performed using a Rigaku SmartLab X-ray diffractometer, which operated in a continuous scanning mode with CuKa radiation. The microstructure, local phase identification, distribution, and local composition were studied using a Zeiss Ultra-Plus FEG-SEM equipped with an Oxford EDS detector and Bruker EBSD (electronbackscatter diffraction) detector. The micro structure was captured using a high -definition back-scattered electrons detector.Results and DiscussionCorrosion

[0082] Experimental conditions and the resulting species in the water samples. Table 2 lists the experimental conditions and the ICP results of the main dissolved species encountered in the water samples in the various tests. The reactor volume was 3.62 mL. The weight change calculation in each sample is based on the samples' weight, thereby including the added weight of the oxide corrosion layer. The weight loss calculation is based on the aqueous concentration of the Mg2+(which is absent in the reactor and piping metal), considering its alloying composition in the tested models.

[0083] The results shown in Table 2 indicate, based on samples weights and aqueous metal concentrations, that the overall corrosion of the part samples was in most cases less than 0.5% w / w during the HIP treatment timeframe. Furthermore, in all the aqueous samples, titanium ions, which may stem from the corrosion of the reactor wall, were not detected at all.

[0084] Inspection of the surface corrosion of Al 6061 / 2024 samples. Figs. 2 and 3 show the cross-section EDS results of the A16061 (Experiment 3) and A12024 (Experiment 5) respectively, following the hydrothermal treatment. The figures consist of SEM pictures, indicating the bulk (yellow circle) and surface (red circle) spot locations of the EDS analysis. The elemental analysis results (in wt.%) are shown in Fig. 2; these clearly indicate the surface oxygen and the relevant silicon, magnesium, and aluminum peaks. Similar analyses of the A12024 pretreated sample (not presented) showed a 2.5 μm Al / O layer, whereas no oxide layer was visible in the A16061 pretreated sample. As indicated in the results shown in Figs. 2 and 3, a very thin corrosion layer was visible in the Al 6061 post- treatment sample. Pointing the EDS exactly on the sample surface resulted in a minor oxygen peak.

[0085] That said, a certain corrosion layer was found during the EDS surface layer evaluation of the A12024 (Experiment 5) after the hydrothermal treatment, as shown in Fig. 3. Silicon and copper accumulation were detected within the corrosion layer, together with alumina (Al / O ratio close to AI2O3).

[0086] Fig. 4 shows a 3-3.5 μm Al / O layer. The results indicate that the surface oxide layer was increased by about 1 μm during the 24 h hydrothermal HIP treatment. However, the corrosion indications on the surfaces of the non-AM A16061, A12024 and AM AlSilOMg post-treated samples are totally different from the fast dissolution of the aluminum in the 25 MPa / 300-400°C experiments previously reported. The aluminum samples in the current research, which were exposed to hydrothermal conditions of 300-350 MPa / 250-350°C, showed minimal corrosion effects, which were consistent with the PhreeQC simulation.

[0087] Tomography tests (MicroCT) . To examine the effectiveness of the hydrothermal HIP treatment for the closure of internal micropores, three AM AlSilOMg treated samples (Experiments 8-10) were scanned against an untreated AM sample. Table 3 shows the four microCT sample results.Table 3: Results of microCT tests on the AM AlSilOMg samples

[0088] The results of the microCT tests indicate that the hydrothermal HIPing can reduce the volume of the pore by 85% at a temperature of 350°C, which is much lower than the temperature applied in common aluminum HIPing. The cross-section of the pores (or “defects”) was reduced by more than 90%, which should manifest itself in better mechanical properties. A study of the high-temperature mechanical properties of the AM AlSilOMg after HIPing at various conditions is pending. However, the high -temperature mechanical properties of the unHIPed AM AlSilOMg was previously studied by Uzan et al. (2018). According to this work, AM AlSilOMg, an aluminum matrix reinforced by submicron Si particles, exhibited, e.g., a creep parameter with a stress exponent of 25+2, which is five times higher than the value of a pure aluminum alloy. This fact may explain the rather low value of pore closure at 250°C, even at an applied pressure that was more than twice thevalue of the yield stress (YS) of this AM material. Furthermore, according to Uzan el al., 2018, the YS of AlSilOMg at 350°C is 30 MPa, i.e., much lower than 132 MPa at 250°C, which may explain the high closure of pores in the current study (85.7%). Nevertheless, a much higher pressure (300MPa, 10 times the YS) was required.

[0089] A preliminary hardness analysis of the small AM AlSilOMg post-treated samples did not show any conclusive hardness change, as shown in Table 4. Further mechanical property analyses should be performed in future experiments.

[0090] Grain size and the microstructure of the AM AlSilOMg samples. The bulk X-ray diffraction (XRD) measurements of the pretreated and post-treated (Experiment 10) samples show that both samples consisted of Al and Si. The differences in the Al peak ratios between the pretreated sample and the post-treated sample may suggest differences in orientation due to the treatment. No similar differences were detected in the case of Si. No additional phase was detected, as shown in Fig. 5.Table 4: AM AlSilOMg sample hardness

[0091] The micro structure of the pretreated material, shown in Fig. 6, reveals elongated and aligned pores (indicated by the white arrows) along the printing direction. However, pores are not visible at the same magnification in the post-treated material micro structure (Fig. 6). Upon closer inspection of the post-treated material micro structure, sub-micron round pores (indicated by the white arrows) can be observed in Figs. 6b-6c. Fig. 7 displays the microstructures of both samples, which comprise small grains and exhibit a fine cellular structure that is decorated with nanoparticles (indicated by the white arrows). The size of the cells is approximately 1 pm, while the particle size ranges from 200 to 400 nm. Examination with a higher magnification uncovered even smaller particles within these cells (indicated by the white arrows), as illustrated in Fig. 8 for the pretreated material. The compositional measurements indicate that the nanoparticles decorating the cellular structure are Si. No eutectic structure was observed in either case.

[0092] Fig. 9 shows the EBSD grain maps of both materials. Only a slight difference in the grain size after the treatment was detected: 8.2 μm in the pretreated material vs. 9.5 pm in the post-treated sample.

[0093] The EBSD phase mapping demonstrates the presence of very small Si and Mg2Si dispersions in both cases, as shown in Fig. 10. No significant difference was observed between both samples, suggesting that the proposed HHIP did not impact or impair the material’s microstructure.

[0094] The EBSD texture analysis indicated a preferred directionality of Al and Si in the pretreated material (Figs. 11A-11B). Less significant directionality was observed in the posttreated material (Figs. 11C-11D).

[0095] The Al-Si phase diagram is a well-known eutectic diagram showing the minimal solubility of Silicon (Si) in Aluminum (Al). Adding a small amount of magnesium (Mg) further reduces the solubility of Si in Al. The Mg addition results in the formation of Mg2Si, but the formation of the Al-Si eutectic structure can still be expected.

[0096] Due to the high cooling rate characteristic of AM, a network eutectic structure is formed, which is composed of small aluminum grains, 8-9 μm in size (Fiocchi et al., 2021). These grains are made up of a network of silicon nanoparticles, each of which is approximately 100 nm in size, and the cells of this network are about 1 pm. Additionally, Mg2Si nanoparticles were detected between the Si nanoparticles. Within these cells, smaller Si particles were also found, measuring roughly 10 nm in size, as measured by SEM (Fig. 8). It is worth noting that the Mg2Si phase was not detected by XRD due to its relatively small content (around 1 wt.%), but the EBSD identified it. Upon conducting a comprehensive examination of the two studies, it was revealed that the alloy undergoes a eutectic cellular solidification process in the presence of silicon at the cell boundaries. The printing procedure involves multiple cycles of heating and cooling, which results in the annealing and fracturing of the silicon network, ultimately resulting in the creation of silicon particles at the nano-scale level.

[0097] Following the printing (and stress relief) processes, the material was subject to a HHIP treatment, leading to self-diffusion and plastic flow. Nevertheless, the energy level was insufficient for recrystallization and long-range diffusion, and did not affect the eutectic network structure. The pretreated structure's aluminum and silicon grains exhibited a preferred orientation, which was slightly mitigated after the HHIP treatment.Conclusions

[0098] An innovative hydrothermal HIPing (HHIP) approach was hypothesized and tested. The aluminum-based metal, which, according to thermodynamics, at supercritical water conditions of 25 MPa and 300-400°C should have been totally dissolved, was practically inert at the proposed HHIPing conditions of 300-350 MPa and 250-350°C, applied in this work; this enabled the full HHIP treatment of 6-24 h at these conditions, possibly owing to development of a resistant Al / O native oxides layer. Applying the proposed treatment to AM AlSilOMg samples, which may be regarded as an aluminum structure that is not easily deformed, resulted in 85.7% reduction in AM pores and a reduction of 90.8% in the pore surface area at a temperature of 350°C, which is much lower than the common 500-520°C applied in argon-based HIPing treatments. The AM AlSilOMg maintained its original micro structure after 24 h, the longest HHIPing period applied in this work. The treatment, therefore, has the potential to yield better mechanical properties without the deleterious effect of grain growth or Si phase dissolution. The well-known aluminum micro-composite structure was also preserved after 24h of treatment at 350°C. This proof of concept may pave the way for further work on different treatment conditions, mechanical properties, surface treatments and modelling the behavior of aluminum alloys, as well as other AM metal parts.REFERENCESAhlfors, M. Cost effective hot isostatic pressing. A cost calculation study for AM parts. 2018. Quintus Technologies, https: / / www.researchgate.net / publication / 327561578ASTM B998-17; Standard guide for hot isostatic pressing (HIP) of aluminum alloy castings 1. ASTM International: West Conshohocken, PA, USA, 2017, 1-4ASTM F3318-18; Standard for additive manufacturing-finished part properties- specification for AlSilOMg with powder bed fusion-laser beam 1. ASTM International: West Conshohocken, PA, USA, 2018, 1-8Atkinson, H.V.; Davies, S. Fundamental aspects of hot isostatic pressing: An overview. Metall. Mater. Trans. A 2000, 31A, 2981-3000Cuesta, 1.1.; Martfnez-Paneda, E.; Diaz, A.; Alegre, J.M. Cold isostatic pressing to improve the mechanical performance of additively manufactured metallic components. Materials 2019, 12, 2495Ertugrul, O.; Oter, Z.C.; Yilmaz, M.S.; , Sahin, E.; Co, skun, M.; Tarakci, G.; Koc, E. Effect of HIP process and subsequent heat treatment on micro structure and mechanical properties of direct metal laser sintered AlSilOMg alloy. Rapid Prototyp. J. 2020, 26, 1421- 1434Fiocchi, J.; Tuissi, A.; Biffi, C.A. Heat treatment of aluminum alloys produced by laser powder bed fusion: A review. Mater. Des. 2021, 204, 109651Gussev, M.N.; Sridharan, N.; Thompson, Z.; Terrani, K.A.; Babu, S.S. Influence of hot isostatic pressing on the performance of aluminum alloy fabricated by ultrasonic additive manufacturing. Scr. Mater. 2018, 145, 33-36Hattori, T.; Shigemori, A.; Mohri, J.I.; Yoshimura, M.; Somiya, S. Fabrication of nonadditive mica ceramics by hot isostatic processing. Commun. Am. Ceram. Soc. 1982, 65, C142Hattori, T.; Yahata, A.; Mohri, J.; Yoshimura, I.; Somiya, S. Fabrication of phosphate-bonded mica ceramics by hot isostatic processing. J. Mater. Sci. Lett. 1984, 3, 57- 59Hirata, T.; Kimura, T.; Nakamoto, T. Effects of hot isostatic pressing and internal porosity on the performance of selective laser melted AlSilOMg alloys. Mater. Sci. Eng. A 2020, 772, 138713Macias, J.G.S.; Zhao, L.; Tingaud, D.; Bacroix, B.; Pyka, G.; van der Rest, C.;Ryelandt, L.; Simar, A. Hot isostatic pressing of laser powder bed fusion AlSilOMg: Parameter identification and mechanical properties. J. Mater. Sci. 2022, 57, 9726-9740Schneller, W.; Leitner, M.; Springer, S.; Grun, F.; Taschauer, M. Effect of hip treatment on micro structure and fatigue strength of selectively laser melted AlSilOMg. J. Manuf. Mater. Process. 2019, 3, 16Uzan, N.E.; Shneck, R.; Yeheskel, O.; Frage, N. Fatigue of AlSilOMg specimens fabricated by additive manufacturing selective laser melting (AM-SLM). Mater. Sci. Eng. A 2017, 704, 229-237Uzan, N.E.; Shneck, R.; Yeheskel, O.; Frage, N. High-temperature mechanical properties of AlSilOMg specimens fabricated by additive manufacturing using selective laser melting technologies (AM-SLM). Addit. Manuf. 2018, 24, 257-263Zakay, A.; Aghion, E. Effect of post-heat treatment on the corrosion behavior of AlSilOMg alloy produced by additive manufacturing. JOM 2019, 71, 1150-1157

Claims

CLAIMS1. A method for reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, thus increasing the density of said metallic material, or repairing microcracks in said metallic material, said method comprising subjecting said metallic material, for a selected period of time, to hot isostatic pressing (HIP) using a liquid pressing medium, wherein said hot isostatic pressing is carried out at a temperature which does not result in grain growth in said metallic material, and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

2. The method of claim 1, wherein said metallic material is a metal selected from aluminum, manganese, copper, magnesium, zirconium, zinc, iron, titanium, chromium, nickel, lead, cobalt, tantalum, tungsten, niobium, gold, silver, and tin, or a metal alloy, metal matrix composite, or intermetallic compound thereof.

3. The method of claim 2, wherein said metallic material is a metal.

4. The method of claim 2, wherein said metallic material is a metal alloy selected from an aluminum alloy, manganese alloy, copper alloy, magnesium alloy, zirconium alloy, zinc alloy, ferroalloy, titanium alloy, chromium alloy, nickel alloy, lead alloy, cobalt alloy, tantalum alloy, tungsten alloy, niobium alloy, gold alloy, silver alloy, and tin alloy.

5. The method of claim 4, wherein said metal alloy is:(i) an aluminum alloy wherein aluminum is the predominant metal, and the main alloying elements are: (a) copper, magnesium and manganese; (b) copper, magnesium and titanium; (c) scandium and magnesium; (d) silicon; (e) silicon and magnesium; (f) silicon, manganese and magnesium; (g) silicon, iron and copper; (h) silicon, boron and copper; (i) silicon, magnesium and copper; or (j) magnesium;(ii) copper alloy wherein copper is the predominant metal, and the main alloying elements are: (a) zinc; (b) tin; (c) chromium; (d) chromium and niobium; or (e) chromium and zirconium;(iii) magnesium alloy wherein magnesium is the predominant metal, and the main alloying elements are: (a) aluminum and zinc; (b) aluminum, zinc and calcium;(c) aluminum, zinc and tin; (d) aluminum and silicon; (e) aluminum and manganese; (f) cerium, yttrium, neodymium and zirconium; or (g) cerium, neodymium, zinc, gadolinium and zirconium;(iv) ferrous alloy wherein iron is the predominant metal, and the main alloying elements are: (a) chromium; (b) chromium, copper and nickel; (c) chromium, copper, nickel, manganese, silicon, and niobium; (d) chromium, silicon and manganese; (e) chromium, silicon, manganese, and nickel with regular and low carbon content; (f) chromium, vanadium, molybdenum, and silicon; (g) chromium and molybdenum; (h) cobalt and silicon; (i) silicon; (j) nickel; or (k) nickel and molybdenum;(v) titanium alloy wherein titanium is the predominant metal, and the main alloying elements are: (a) aluminum and vanadium; (b) iron; or (c) chromium;(vi) nickel alloy wherein nickel is the predominant metal, and the main alloying elements are: (a) chromium, cobalt, molybdenum, titanium, aluminum, and tantalum; (b) chromium, iron, molybdenum, niobium, tantalum, and cobalt; or (c) chromium, iron, manganese, cobalt, silicon, and tungsten; or(vii) cobalt alloy wherein cobalt is the predominant metal, and the main alloying elements are: (a) chromium; (b) chromium and molybdenum; or (c) chromium, molybdenum and tungsten.

6. The method of claim 5, wherein said aluminum alloy is A12024, A16061, Scalmalloy (Al-Sc-Mg), AlSilOMg, AlSi7MgO3, AlCu4MgTi, AlCu4MnMg, AlSilOMnMg, AlSil2, AlSi9Cu3(Fe), AlSi8Cu3, AlSi7Cu3Mg, or AlMg3; said copper alloy is brass (Cu-Zn), bronze (Cu-Sn), GRCop-42 and GRCop-84 (Cu-Cr-Nb), C18150 (copper, chromium, zirconium), or Cl 8200 (copper chromium); said magnesium alloy is AZ91, AZ91+Ca, AZ91+Sn, AM50, , WE54, WE43, or Elektron 21; said ferroalloy is 15-5 PH, 17-4 PH, SS316, SS316L, SS304, SS304L, SS420, H13, AISI4130, FeCoSi, FeSi, FeNi, FeCr, or FeNiMo; said titanium alloy is Ti-6A1-4V, Ti-6A1-4VELI, or CP Ti; said nickel alloy is Inconel 718, Inconel 625, or HX; and said cobalt alloy is CoCr, CoCrMo (F75), or CoCrWMo.

7. The method of claim 2, whereas said metallic material is a complex composite alloy comprising quite equal atomic percentages of metals selected from Al, Co, Cr, Cu, Fe, Mo,Nb, Ni, Ta, Ti, V, W, and Zr, such as CoCrCuFe, NiAlx, AlCrMoNi, TaNbHfZrTi, TaNbMoW, and TaNbVMoW.

8. The method of claim 2, wherein said metallic material is a metal matrix composite comprising a metallic matrix comprising one or more of copper, aluminum, cobalt, magnesium, titanium, silicon, carbon, boron, tungsten, and iron.

9. The method of claim 8, wherein said metal matrix composite is selected from Co- WC, Al-SiC, A1-A12O3, Mg-SiC, Mg-A12O3, Mg-TiC, Ti-TiB2, Ti-TiC, and GlidCop (copper and alumina).

10. The method of claim 2, wherein said metallic material is an intermetallic compound comprising aluminum and titanium; aluminum and nickel; aluminum, nickel and cobalt; aluminum and iron; or nickel and titanium.

11. The method of claim 10, wherein said intermetallic compound comprising aluminum and titanium is TiAl or Ti3Al; said intermetallic compound comprising aluminum and nickel is NiAl; said intermetallic compound comprising aluminum, nickel and cobalt is AlNiCo; said intermetallic compound comprising aluminum and iron is FeAl; or said intermetallic compound comprising nickel and titanium is Nitinol.

12. The method of any one of claims 1-11, wherein said period of time is from about 2 hours to about 48 hours, e.g., from about 4 hours to about 42 hours, from about 6 hours to about 36 hours, from about 8 hours to about 30 hours, from about 10 hours to about 24 hours, or from about 12 hours to about 18 hours.

13. The method of any one of claims 1-11, wherein said temperature is from about 0.3 to about 0.7 of the homologous temperature of said metallic material, or lower than 0.3 of the homologous temperature of said metallic material.

14. The method of any one of claims 1-11, wherein said temperature is from about 200°C to about 1000°C, e.g., from about 250°C to about 950°C, from about 300°C to about 900°C, from about 350°C to about 850°C, from about 400°C to about 800°C, from about 450°C to about 750°C, from about 500°C to about 700°C, or from about 550°C to about 650°C; and / or said pressure is from about 200 megapascal (MPa) to about 1000, 1250 or 1500 MPa, fromabout 250 MPa to about 950 MPa, from about 300 MPa to about 900 MPa, from about 350 MPa to about 850 MPa, from about 400 MPa to about 800 MPa, from about 450 MPa to about 750 MPa, from about 500 MPa to about 700 MPa, or from about 550 MPa to about 650 MPa.

15. The method of claim 1, wherein said liquid pressing medium is an inorganic liquid, organic liquid, or a mixture thereof, optionally free of an externally added oxidizing agent.

16. The method of claim 15, wherein said oxidizing agent is selected from a halogen such as fluorine, chlorine and bromine; oxygen; an oxyanion such as permanganate ion (MnOT), nitrate ion (NO3-) persulfate ion (SO52-, S2O82-), and dichromate ion (Cr2O72-) ; and an oxyacid such as sulfuric acid and nitric acid.

17. The method of claim 15 or 16, wherein said inorganic liquid is an aqueous solution.

18. The method of claim 17, wherein said aqueous solution is water.

19. The method of claim 17 or 18, wherein said hot isostatic pressing is carried out under hydrothermal conditions.

20. The method of claim 15 or 16, wherein said organic liquid is a polar or non-polar organic liquid.

21. The method of claim 20, wherein said polar organic liquid is selected from acetic acid, acetone, acetonitrile, methanol, ethanol, propanol, isopropanol butanol, t-butyl alcohol, chloroform, ethylene glycol, diethylene glycol, ethyl acetate, methylene chloride, chlorobenzene, 1,2-dichloroethane, and a mixture thereof; and said non-polar organic liquid is selected from (C5-C8)alkanes such as heptane and hexane, cyclohexane, diethyl ether, benzene, and a mixture thereof.

22. The method of any one of claims 1-21, wherein said metallic material has been obtained following a casting, sintering, or additive manufacturing process.

23. The method of claim 22, wherein said method does not adversly affect static mechanical properties such as strength and hardness, or dynamic mechanical properties such as fatique resistance, of said metallic material.

24. The method of claim 1, for reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, thus increasing the density of said metallic material, or repairing microcracks in said metallic material, said method comprising subjecting said metallic material, for a time period of from about 2 hours to about 48 hours, to hot isostatic pressing (HIP) using water free of an externally added oxidizing agent as the liquid pressing medium, wherein said hot isostatic pressing is carried out under hydrothermal conditions.

25. The method of claim 24, wherein said hot isostatic pressing is carried out at a temperature from about 0.3 to about 0.7 of the homologous temperature of said metallic material, or lower than 0.3 of the homologous temperature of said metallic material; and / or under pressure from about 200 MPa to about 1000, 1250 or 1500 MPa, from about 250 MPa to about 950 MPa, from about 300 MPa to about 900 MPa, from about 350 MPa to about 850 MPa, from about 400 MPa to about 800 MPa, from about 450 MPa to about 750 MPa, from about 500 MPa to about 700 MPa, or from about 550 MPa to about 650 MPa.

26. The method of claim 24 or 25, wherein said metallic material is a metal alloy.

27. The method of claim 26, wherein said metal alloy is an aluminum alloy such as A12024, A16061, and AlSilOMg; and said hot isostatic pressing is carried out at a temperature from about 220°C to about 38O°C, e.g., from about 250°C to about 350°C, and under pressure from about 280 MPa to about 380 MPa.

28. The method of claim 26, wherein said metal alloy is a titanium alloy such as Ti-6A1- 4V and Ti-6A1-4VELI; and said hot isostatic pressing is carried out at a temperature from about 400°C to about 800°C, e.g., at about 500°C, and under pressure from about 300 MPa to about 1500 MPa, e.g., at about 600 MPa.

29. The method of claim 26, wherein said metal alloy is a ferroalloy such as 15-5 PH, 17-4 PH, SS316, SS316L, SS304, SS304L, SS420, H13, AISI4130, FeCoSi, FeSi, FeNi, FeCr, and FeNiMo; and said hot isostatic pressing is carried out at a temperature from about 400°C to about 1000°C, e.g., at about 550°C, and under pressure from about 700 MPa to about 1500 MPa, e.g., at about 800 MPa.

30. The method of claim 26, wherein said metal alloy is a nickel alloy such as Inconel 718, Inconel 625, and HX; and said hot isostatic pressing is carried out at a temperature from about 600°C to about 900°C, e.g., at about 800°C, and under pressure from about 300 MPa to about 1500 MPa, e.g., at about 1100 MPa.

31. In a method for reducing porosity of a solid metallic material selected from a metal, metal alloy, metal matrix composite, and intermetallic compound, thus increasing the density of said metallic material, or repairing microcracks in said metallic material, by subjecting said metallic material to hot isostatic pressing, the improvement wherein said hot isostatic pressing is carried out using a pressing medium which is a liquid, said hot isostatic pressing being carried out at a temperature which does not result in grain growth in said metallic material, and is lower than the melting point of said metallic material, and under pressure higher than the flow stress of said metallic material at said temperature.

32. In a method according to claim 31, wherein said liquid pressing medium is water, e.g., distilled or deionized water, and said hot isostatic pressing is carried out under hydrothermal conditions.

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