HIGHLY FUSIBLE Ni-BASED ALLOY CONTAINING P

Abstract

The present invention provides a highly fusible Ni-based alloy which has a low solidus temperature and is capable of easily forming, at a low temperature, a coating film that is excellent in terms of corrosion resistance, crack resistance and high toughness. The highly fusible Ni-based alloy contains, in mass%, 0.1% to 7.0% of P, 5.0% or less of B, 5.0% or less of Si, 2.0% or less of C, 30.0% or less of Cr, one or two of Mo and W in the total amount of Mo + W / 2 of 9.0% or less, 10.0% or less of Cu, one or more of Mn, Fe, and Co each in an amount of 10.0% or less, with the balance being made up of Ni and inevitable impurities. The Ni-based alloy has a hard phase that has a P content of 1% or less, and a structure in which P is solid-solved and / or compounds having a precipitation phase size of 10 μm or less and containing P are dispersed in a γ-Ni matrix. In addition, the Ni-based alloy has a solidus temperature of 800°C to 950°C inclusive.

Description

High melting Ni-based alloy containing P

[0001] The present disclosure relates to a Ni-based self-fluxing alloy containing P, an atomized powder thereof, and a metal coating and a steel part using the alloy, which have excellent corrosion resistance, crack resistance, and high toughness. In particular, the present disclosure relates to a high-melting Ni-based alloy having a low solidus temperature, which allows for low-temperature coating formation and densification treatment, and which has a structure in which P is dissolved in a γNi matrix and / or P-containing compounds are finely dispersed.

[0002] Conventional self-fluxing alloys include Ni-based alloys and Co-based alloys, as specified in Japanese Industrial Standard (JIS) H8303 (self-fluxing alloy thermal spraying). These self-fluxing alloys are primarily used in surface treatments such as thermal spraying and overlay welding, and are used to form coatings with excellent corrosion resistance and wear resistance. The hardness of these coatings is approximately 15 to 60 HRC.

[0003] In thermal spraying using nickel-based and cobalt-based alloys containing flux components such as boron (B) and silicon (Si), a dense coating can be obtained by performing a fusing process after thermal spraying. The composition specified in JIS H8303 includes essential components of approximately 1.0 to 4.5 mass% B and 1.5 to 5.0 mass% Si.

[0004] The fusing temperature is usually around 1000 to 1200°C. At this time, some of the easily oxidized B and Si in the alloy are converted to B. ２ O ３ and SiO ２ This flux dissolves the metal oxides in the thermal spray coating and on the substrate surface, turning it into a type of borosilicate glass that floats to the surface of the thermal spray coating like slag. This flux action results in a thermal spray coating with very few oxides and pores. During this fusing process, the spray particles fuse together within the thermal spray coating, resulting in a homogenous structure. Furthermore, during fusing, interdiffusion occurs between the substrate and the thermal spray coating, forming an alloy layer several tens of micrometers thick at the boundary, metallurgically bonding them together.

[0005] Thus, self-fluxing alloys, which contain primary and eutectic oxides and carbides in their structure, exhibit excellent wear resistance and corrosion resistance in various corrosive environments such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and caustic soda.

[0006] Self-fluxing alloys are primarily used in surface treatments such as thermal spraying and overlay welding, forming coatings with excellent corrosion and wear resistance. Their hardness ranges from approximately 15 to 60 HRC. Regarding the density of the coating, the characteristics of self-fluxing alloys are described below. Specified in JIS H 8303 (self-fluxing alloy thermal spraying), these alloys contain flux components such as B and Si in nickel-based and cobalt-based alloys. A dense coating can be obtained by performing a fusing process after thermal spraying. The JIS-specified compositions include approximately 1.0 to 4.5 mass% B and 1.5 to 5.0 mass% Si as essential components.

[0007] Usually, this fusing process is carried out at about 1000 to 1200°C, during which time some of the easily oxidized B and Si in the alloy are converted to B. ２ O ３ and SiO ２ This flux dissolves the metal oxides in the thermal spray coating and on the substrate surface, forming a type of borosilicate glass that floats to the surface of the thermal spray coating like slag. This flux action makes it easier to obtain a thermal spray coating with fewer oxides and pores. Furthermore, during this fusing process, the spray particles fuse together within the thermal spray coating, making it easier to homogenize the structure. Furthermore, interdiffusion occurs between the substrate and the thermal spray coating during fusing, forming an alloy layer with a thickness of about several tens of micrometers at the boundary, making it easier to metallurgically bond them.

[0008] Self-fluxing alloys contain primary and eutectic oxides and carbides in their structure, and are therefore generally expected to have excellent wear resistance, as well as corrosion resistance in various corrosive environments such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and caustic soda.

[0009] The applicant of the present application also reported that the composition of the alloy contains P: 0.2 to 6.0%, B: 0.1 to 4.5%, Si: 0.1 to 5.0%, C: 0.00 to 2.00%, Cr: 0.0 to 30.0%, Mo: 0.0 to 9.0%, W: 0.0 to 18.0%, Cu: 0.0 to 10.0%, Mn: 0.0 to 10.0%, Fe: 0.0 to 10.0%, Co: 0.0 to 10.0%, Al: 0.00 A Ni-based self-fluxing alloy consisting of P: 0.00 to 0.20%, Ti: 0.00 to 0.20%, Zr: 0.00 to 0.20%, and Hf: 0.00 to 0.20% and satisfying 2.3≦P%+B%+Si%≦11.0, Mo%+W% / 2≦9.0, and Al%+Ti%+Zr%+Hf%≦0.20 has been proposed (see Patent Document 1 (JP 2023-31420 A)).

[0010] JP 2023-31420 A

[0011] JIS H 8303:2010 "Self-fluxing alloy thermal spraying"

[0012] In recent years, the applications of self-fluxing alloys for surface treatment have expanded, and applications to a wide range of fields, such as aircraft, automobiles, boilers, and agricultural machinery, which require greater durability than previous applications, are being considered. Therefore, the required properties are increasing so that the alloys can be used in different environments in addition to the traditional applications.

[0013] Until now, it has been common to use a base material with a high melting point, typically an Fe-based material such as stainless steel SUS304 (melting point 1398-1427°C) or general structural steel (melting point approximately 1580°C), and then coat it with a Ni-based self-fluxing alloy to improve corrosion resistance, wear resistance, etc. For this reason, the temperature during application such as thermal spraying, or the subsequent remelting process, has had little effect on the melting or deformation of the base material.

[0014] On the other hand, for components that require high thermal conductivity and electrical conductivity, surface treatment of substrates such as Cu (melting point 1084°C), which has a lower melting point than conventional materials, is also required. However, when forming a coating using a Ni-based self-fluxing alloy on such low-melting-point substrates, the temperature of the remelting process, as well as the temperature during application, have a significant impact on the substrate. Remelting with conventional Ni-based self-fluxing alloys requires remelting at around 1000 to 1200°C, but in this case, melting and deformation of the substrate and deterioration of the substrate's properties due to these thermal effects are unavoidable.

[0015] In addition, the higher the temperature during coating application or remelting treatment, the more likely the contained B will diffuse and react with Fe, Cr, etc. in the substrate, causing the crystallization of hard, coarse borides and potentially impairing the adhesion between the substrate and the coating.

[0016] Furthermore, the crystal grains of the stainless steel substrate become coarse, causing a decrease in strength, and the corrosion resistance at the interface with the Ni-based self-fluxing alloy coating may be excessively deteriorated.

[0017] In addition, the higher the temperature during coating and remelting, the more fuel is used and the greater the amount of CO ２ It leads to emissions.

[0018] Furthermore, in conventional materials, B and Si crystallize as hard borides and silicides, which effectively contribute to hardness and wear resistance. On the other hand, in cases where crack resistance and high toughness are more important than hardness and wear resistance, attempts have been made to address this by lowering the Cr content to suppress the crystallization of these hard phases, such as SFNi1 (15-30 HRC), SFNi2 (30-40 HRC), and SFNi3 (40-50 HRC). However, these conventional materials only control the hardness of the hard phase crystallization, making it impossible to achieve both hardness and toughness. Furthermore, the reduction in the hard phase makes it difficult to obtain other properties, such as wear resistance.

[0019] In order to address these problems, there is a need for the development of a high-melting Ni-based alloy that can be processed and densified at temperatures lower than conventional materials and that can be applied to a wider range of fields and applications.

[0020] The Ni-based self-fluxing alloy of Patent Document 1 contains P, so its solidus or liquidus temperature is low, allowing a coating to be formed by treatment at a relatively low temperature, and the main part is less likely to be exposed to high temperatures. However, since the remelting heat treatment temperature remains high as in the past, coarse P compounds tend to form, a fine structure is not obtained, and the substrate is prone to deformation when forming the coating, which is still not satisfactory.

[0021] Therefore, the present invention aims to provide a high-melting Ni-based alloy and atomized powder that (1) contains P, which has a lower solidus temperature than conventional self-fluxing alloys (JIS H 8303), allows for easy film formation at low temperatures, and enables subsequent heat treatment to form a dense film at low temperatures, and (2) has a structure in which P is dissolved in a γNi matrix and / or compounds containing P are finely dispersed. Another object of the present invention is to provide a film using the alloy and atomized powder that has excellent corrosion resistance, crack resistance, and high toughness, and to provide a part equipped with such a film.

[0022] Therefore, the inventors thought that if it were possible to have a eutectic structure at a temperature lower than the conventional Ni-Si-B ternary eutectic temperature, it might be possible to lower the solidus temperature, and focused on P. The eutectic temperature of Ni-P is 870°C, and it was thought that adding P would result in a solidus temperature that is dramatically lower than that of conventional materials (Ni-Si-B system).

[0023] In fact, by substituting P for B and Si, it is possible to obtain Ni-Ni compounds instead of CrP compounds. ３ It was found that the alloy has a P eutectic structure, and the solidus temperature was successfully reduced by more than 100°C compared to conventional alloys.

[0024] This allows for processing at lower temperatures than before, which reduces the following problems: (i) melting and deformation of the substrate during remelting processing, (ii) reduced adhesion between the substrate and the coating due to hard and coarse borides generated by the diffusion of B, (iii) reduced strength and corrosion resistance due to coarsening of the substrate crystal grains, and (iv) CO emissions due to increased fuel use. ２ We were able to solve all of the issues, such as increasing emissions.

[0025] Furthermore, because low-temperature processing is now possible, when applying a coating, for example when spraying atomized powder of the material of the present invention to form a coating, spraying can be done at a lower temperature than before, and we have succeeded in not only the remelting process but also in lowering the temperature during spraying. Also, whereas there was a limit to the spraying distance in the past, it is now possible to spray over longer distances, which has led to improved handling during spraying.

[0026] By adding P, P dissolves in the γNi matrix and / or precipitates containing P with a size of 10 μm or less are dispersed, and these compounds form a mesh-like network structure, which improves the strength of the matrix. ３ The finely dispersed P eutectic compounds with precipitated phases of 10 μm or less maintain uniform strength in the matrix, resulting in a uniform hardness for the coating. This has enabled the company to achieve not only wear resistance but also both hardness and toughness, which was previously difficult to achieve.

[0027] As such, there has been no detailed study of the effects of P and its organizational structure to date.

[0028] The present disclosure provides the following aspects: [Aspect 1] A high melting point Ni-based alloy comprising, by mass%, P: 0.1 to 7.0%, B: 0.0 (inclusive 0%) to 5.0%, Si: 0.0 (inclusive 0%) to 5.0%, C: 0.0 (inclusive 0%) to 2.0%, Cr: 0.0 (inclusive 0%) to 30.0%, one or both of Mo and W: a total of Mo+W / 2 of 0.0 (inclusive 0%) to 9.0%, Cu: 0.0 (inclusive 0%) to 10.0%, one or more of Mn, Fe, and Co: 0.0 (inclusive 0%) to 10.0% for each element, and the balance being Ni and unavoidable impurities, The high melting point Ni-based alloy has a hard phase with a P content of 1% or less and a structure in which P is dissolved in a γNi matrix and / or P-containing precipitated phases with a size of 10 μm or less are dispersed, and the high melting point Ni-based alloy has a solidus temperature of 800°C or more and 950°C or less. [Aspect 2] The high melting point Ni-based alloy according to Aspect 1, wherein the hard phase is a boride or carbide, the equivalent circle diameter of the hard phase is 20 μm or less, and the area ratio of the hard phase is 20% or less. [Aspect 3] The high melting point Ni-based alloy according to Aspect 1 or 2, wherein the high melting point Ni-based alloy has a liquidus temperature of 1000°C or more. [Aspect 4] A high melting point Ni-based alloy coating made of the high melting point Ni-based alloy according to any one of Aspects 1 to 3. [Embodiment 5] The high melting point Ni-based alloy coating is a remelted coating that has been remelted at a temperature of less than 940°C, and the porosity P Ａ and the porosity P of the thermal spray coating before the remelting treatment Ｂ But, P Ａ / P Ｂ ≦0.5, and the remelted coating has a network structure of a γNi matrix containing P. [Aspect 6] Atomized powder for coating formation, comprising the high melting point Ni-based alloy according to any one of Aspects 1 to 3. [Aspect 7] A part having the coating according to Aspect 4 or 5, and having excellent hardness, corrosion resistance, and crack resistance.

[0029] The present invention, by adding P, allows processing at a lower temperature than conventional methods, and therefore, prevents (i) melting and deformation of the substrate during remelting processing, (ii) deterioration of adhesion between the substrate and the coating due to hard and coarse borides generated by the diffusion of B, (iii) reduction in strength and corrosion resistance due to coarsening of the crystal grains of the substrate, and (iv) CO2 emissions due to an increase in the amount of fuel used. ２ This solves the problems of increased carbon dioxide emissions and increased carbon dioxide emissions. Furthermore, because low-temperature processing is now possible, when applying a coating, for example, when spraying atomized powder of the material of the present invention to form a coating, spraying can be done at a lower temperature than before, and the effects of low temperatures can be obtained not only for the remelting process but also during spraying. Furthermore, whereas there was a limit to the spraying distance in the past, it is now possible to spray over longer distances, which also leads to improved handling during spraying.

[0030] Furthermore, by adding P, P dissolves in the γNi matrix and / or compounds containing P precipitates with a size of 10 μm or less are dispersed, and these compounds form a mesh-like network structure, which can improve the strength of the matrix. ３ The finely dispersed P eutectic compounds with precipitated phases of 10 μm or less maintain uniform strength in the matrix, resulting in a uniform hardness for the coating. This not only improves wear resistance, but also achieves both hardness and toughness, which was previously difficult to achieve.

[0031] Fig. 1 is an optical microscope image showing a cross-sectional micrograph of a coating as sprayed on a substrate using a Ni-based alloy having the composition of the present invention. Fig. 2 is an optical microscope image of an example of the present invention showing a cross-sectional micrograph of the coating shown in Fig. 1 after remelting treatment at less than 940°C. Fig. 3 is an optical microscope image of a comparative example showing a cross-sectional micrograph of the coating shown in Fig. 1 after remelting treatment at 940°C or higher.

[0032] Before describing the embodiments of the present invention, the reasons for specifying the alloy components of the present disclosure will be explained. Note that % in the following compositions refers to % by mass.

[0033] P: 0.1 to 7.0% In the alloys disclosed herein, P is an essential element for lowering the solidus temperature. However, if added in excessive amounts, coarse phosphides crystallize, resulting in excessively high hardness, embrittling the coating and making machining difficult. Addition of less than 0.1% does not sufficiently lower the solidus temperature, while addition of more than 7.0% excessively raises the liquidus temperature. Preferably, P is more than 0.2% and less than 6.0%, and more preferably more than 0.5% and less than 5.0%.

[0034] In particular, the effect of P makes it possible to obtain an unprecedentedly low solidus temperature that could not be obtained by adding only B or Si, making it possible to perform remelting treatment at temperatures below 1000°C, or even below 950°C, and even at temperatures as low as the 800°C range.

[0035] This low solidus temperature makes it possible to spray at lower temperatures than conventional methods, which means that coating can be achieved not only by remelting but also when the thermal energy required for coating application is reduced by 10 to 20 percent.

[0036] Furthermore, when the coating is produced under conventional application conditions, it is possible to extend the distance during coating application (spraying distance) to 1.5 times the normal distance.

[0037] Here, it is presumed that the significant effect of adding P in lowering the solidus temperature is due to the fact that the solidus temperature in the binary phase diagram with Ni is approximately 1093°C for B and approximately 1143°C for Si, while that of P is approximately 870°C, which is significantly lower.

[0038] Furthermore, the addition of P suppresses deterioration of corrosion resistance at the interface between the substrate and the coating. When this alloy was thermally sprayed onto a stainless steel SUS304 base material, remelted, and subjected to a salt spray test, rusting at the interface was suppressed compared to a conventional P-free Ni self-fluxing alloy. Microstructure observation of the interface with the base material revealed that in the conventional P-free Ni self-fluxing alloy, the B contained in the Ni self-fluxing alloy diffused excessively to the grain boundaries of the SUS304 base material, reacting with Cr in the SUS304 to form Cr-based borides. As a result, the Cr concentration in the surrounding SUS304 matrix decreased, a phenomenon similar to the so-called sensitization of stainless steel was observed, and corrosion resistance was deteriorated. In contrast, in the P-containing alloy disclosed herein, the grain boundary diffusion of B was suppressed, and it is presumed that the P, which diffuses to grain boundaries in the same way as B, suppressed the diffusion of B. The grain boundary diffusion of B in a P-free Ni self-fluxing alloy generates Cr and Mo-based borides in, for example, a stainless steel SUS316 base material, which deteriorates the corrosion resistance of the surrounding base material, and in the case of a mild steel base material, the generated Fe borides themselves have lower corrosion resistance than the surrounding base material.

[0039] Furthermore, P promotes densification even in as-sprayed coatings that have not been remelted. While the detailed reasons for this phenomenon are unclear, it is presumed that, in addition to simply having a low solidus temperature, oxides containing P with relatively low sublimation temperatures are gasified slightly while the alloy particles are flying at high temperatures during thermal spraying, reducing the amount of oxide in the coating. In other words, in the thermal spraying method, slight oxidation of the particles is unavoidable while the particles are flying at high temperatures, but it is presumed that the effect of these oxides, which inhibits densification of the coating, is neutralized or reduced by gasification.

[0040] In addition, P disperses in the γNi matrix compounds in which P is dissolved and / or precipitates containing P with a size of 10 μm or less, and these compounds form a mesh-like network structure, which can improve the strength of the matrix. The areas that appear in slightly dark gray in the coatings in Figures 2 and 3 correspond to the areas in which P is dissolved and / or compounds in which P is dissolved and precipitates with a size of 10 μm or less are dispersed. Not only that, Ni-Ni ３The fine dispersion of P eutectic compounds with precipitate phases of 10 μm or less allows the matrix to maintain uniform strength, resulting in a uniform hardness for the coating. This not only improves wear resistance, but also helps achieve both hardness and toughness, which was previously difficult to achieve. A structure with a uniform hardness and finely divided P compounds can be obtained in a coating, for example, by adding P and further setting the remelting temperature to a temperature lower than 940°C.

[0041] B: 0.0 to 5.0% In the alloy of the present disclosure, B may be added as needed to lower the solidus temperature and reduce oxides in the film. ２ O ３ and SiO ２ It dissolves metal oxides in the thermal spray coating and on the substrate surface, forming a type of borosilicate glass that floats to the surface of the thermal spray coating like slag, acting as a flux, effectively reducing oxides and pores in the thermal spray coating and densifying it. However, excessive addition raises the liquidus temperature due to the crystallization of coarse borides. Furthermore, the formation of borides hardens the coating. Since P plays a role in lowering the solidus temperature, no addition is necessary. However, adding more than 5.0% of P excessively raises the liquidus temperature, so the content is preferably less than 4.0%, and more preferably less than 2.0%.

[0042] Si: 0.0 to 5.0% In the alloy of the present disclosure, Si may be added as needed to lower the solidus temperature and reduce oxides in the coating. ２ O ３ and SiO ２ It dissolves metal oxides in the thermal spray coating and on the substrate surface, forming a type of borosilicate glass that floats to the surface of the thermal spray coating like slag, acting as a flux, effectively reducing oxides and pores in the thermal spray coating and increasing its density. However, adding too much P makes the coating excessively hard, embrittling it and making it difficult to machine. Since P plays a role in lowering the solidus temperature, it may not be necessary to add any P. Adding more than 5.0% results in excessively high hardness, so the content is preferably less than 4.0%, more preferably less than 3.0%.

[0043] C: 0.0-2.0% In the alloys disclosed herein, C has the effect of increasing hardness and may be added as needed. However, if too much C is added, the coating becomes excessively hard and embrittled, making machining difficult. Addition of more than 2.0% results in excessively high hardness. Preferably, the content is less than 1.8%, more preferably less than 1.6%.

[0044] Cr: 0.0 to 30.0% In the alloys disclosed herein, Cr has the effect of improving corrosion resistance and may be added as needed. However, if added in excess of 30.0%, the liquidus temperature will rise excessively. Preferably, Cr is less than 20.0%, more preferably less than 18.0%.

[0045] Mo+W / 2: 0.0-9.0% In the alloys disclosed herein, Mo and W have the effect of improving corrosion resistance, and one or both of Mo and W may be added as needed. Note that W has half the effect of Mo in terms of mass %. However, excessive addition raises the liquidus temperature and generates coarse phosphides containing high concentrations of Mo and / or W, resulting in excessively high hardness, embrittling the coating, and making machining difficult. Adding Mo+W / 2 in excess of 9.0% raises the liquidus temperature excessively. It is preferably less than 5.0%, more preferably less than 4.0%.

[0046] Cu: 0.0 to 10.0% In the alloy of the present disclosure, Cu has the effect of improving corrosion resistance and may be added as needed. However, excessive addition of Cu reduces corrosion resistance. Addition of more than 10.0% reduces corrosion resistance. Preferably, Cu is less than 5.0%, more preferably less than 4.0%.

[0047] Mn, Fe, and Co: 0.0 to 10.0% each In the alloy of the present disclosure, Mn, Fe, and Co are elements that do not significantly affect the properties, and one or more of Mn, Fe, and Co may be added up to an upper limit of 10% for each element.

[0048] (Structural Characteristics) The alloy of the present disclosure has a hard phase with a P content of 1% or less, and a structure in which P is dissolved in solid solution and / or P-containing precipitated phases with a size of 10 μm or less are dispersed in a γNi matrix. In other words, P is only contained in small amounts in the hard phase, and is mainly present in the γNi matrix. The dispersed P is dissolved in solid solution and / or P-containing precipitated phases with a size of 10 μm or less (the dark gray areas in the coatings of Figures 2 and 3), and the resulting structure forms a mesh-like network, which can improve the strength of the matrix. In addition, the Ni-Ni ３ Since the P eutectic contains finely dispersed compounds with precipitate phases of 10 μm or less in size, the matrix can maintain uniform strength, and the coating also has uniform hardness. This not only improves wear resistance, but also makes it possible to achieve both hardness and toughness, which was previously difficult. In this specification, the term "precipitate phase size" refers to the longitudinal length of the precipitate phase (i.e., the major axis).

[0049] The alloys disclosed herein have a solidus temperature of 800°C or higher and 950°C or lower. The addition of P lowers the solidus temperature, but the liquidus temperature varies depending on the content of Cr, B, Si, etc. If the solidus temperature exceeds 950°C, the thermal impact on the substrate during remelting processing increases.

[0050] The alloys of the present disclosure preferably have a liquidus temperature of 1000° C. or higher. If the liquidus temperature is less than 1000° C. and the temperature range between the solidus and liquidus is very narrow, the remelting process conditions become difficult.

[0051] In a preferred embodiment of the present disclosure, the hard phase is a boride or carbide, and the equivalent circle diameter of the hard phase is 20 μm or less, and the area ratio of the hard phase is 20% or less. If 20% or more of coarse hard phases exceeding 20 μm (the size is calculated based on the equivalent circle diameter) are present, the material becomes excessively hard, causing embrittlement and making machining difficult. Furthermore, since corrosion also occurs at the grain boundaries of the hard phase, if the size of the hard phase is less than 20 μm and the area ratio exceeds 20%, corrosion is likely to progress. On the other hand, if the size of the hard phase exceeds 20 μm and the area ratio is 20% or less, cracks may originate from the coarse hard phase, affecting machinability. Therefore, it is preferable that the equivalent circle diameter is 20 μm or less, and the area ratio is 20% or less.

[0052] In a preferred embodiment of the present disclosure, the alloy coating of the present disclosure may be a remelted coating that has been remelted at a temperature of less than 940° C. In this case, the porosity P Ａ and the porosity P of the thermal spray coating before the remelting treatment Ｂ But, P Ａ / P Ｂ It is preferable that the remelted coating has a network structure of a γNi matrix containing P. In this regard, even if the solidus temperature is lowered, if the remelting treatment is carried out at 940°C or higher, for example, at about 1000°C as in the past, the coating will naturally become dense (i.e., P Ａ / P Ｂ For example, in Patent Document 1, only remelting treatment at 940°C is performed, and in this case, the material naturally becomes dense (i.e., P Ａ / P Ｂ ≦0.5). However, if the temperature is too high, the material melts, it is unable to maintain its shape, and sagging occurs. On the other hand, in the present invention, both the above-mentioned structure and densification can be achieved by processing at a lower temperature of less than 940°C.

[0053] In this specification, "porosity" refers to a ratio of the total area of ​​residual pores and residual oxides to the area of ​​a 500 μm square field of view observed with an optical microscope in the thickness direction. The image is then binarized and calculated as the ratio of the total area of ​​residual pores and residual oxides to the area of ​​the field of view. Here, the calculation of porosity takes into account not only residual pores but also residual oxides. This is because, when the observed image is binarized, the residual pores and residual oxides appear the same black color and are indistinguishable, making it necessary to measure their total area. However, because residual oxides are trace components that remain in the coating after processes such as fusing, the residual pores can be considered to account for the majority of the total area of ​​the residual pores and residual oxides. Therefore, the porosity calculated based on the total area of ​​the residual pores and residual oxides can be said to be a value that fully reflects the ratio of residual pores to the field of view.

[0054] Comparing Figure 1, which shows the sample before remelting at low temperature, with Figure 2, which shows the sample after remelting at low temperature, it can be seen that the number of voids has decreased in Figure 2. Furthermore, if the remelting temperature is too high, a coarse structure will be formed, as shown in Figure 3.

[0055] (1) Powder Preparation Method Raw materials weighed to the compositions shown in Nos. 1 to 20 in Table 1 were melted in a vacuum melting furnace and atomized with high-pressure nitrogen gas to obtain gas atomized powders. These powders were classified by sieving to obtain powders with a particle size range of 45 μm to 125 μm, and used as test powders.

[0056]

[0057] (2) Evaluation of the solidus temperature of the powder The solidus temperature of the test powder was evaluated using a thermal analyzer (DTA). Approximately 30 g of powder was used for the measurement. After evacuation, Ar gas was flowed at 200 ml / min. The powder was heated from room temperature to 1500°C at a temperature increase rate of 20°C / min and held at 1500°C for 5 minutes. After holding, the powder was cooled to room temperature at a rate of -20°C / min. The lowest temperature at which the exothermic peaks appearing in the DTA signal during cooling ended was evaluated as the solidus temperature.

[0058] (3) Method of Fabricating the Thermal Spray Coating: A 50 mm x 50 mm x 9 mm SUS304 plate was used as the substrate. After blasting the 50 mm x 50 mm surface, the test powder was atmospherically plasma sprayed to obtain a coating. The substrate was cooled with air during the thermal spraying process. The substrate with the thermal spray coating was then placed in an electric furnace and heated in an Ar flow atmosphere to a temperature above the solidus temperature and below 940°C for Invention Examples 1 to 12, as shown in Table 2. The temperature was then held for 20 minutes, and the furnace was cooled to obtain a fused coating. The coating thickness was approximately 300 μm. The remelting temperatures for the comparative examples were as shown in Table 2, and comparisons were also made at temperatures above 940°C.

[0059] (4) Evaluation of Residual Pores and Residual Oxides in Thermal Spray Coatings For each of the thermal spray coating before remelting treatment and the remelted coating (in the present invention, the coating was remelted at a temperature above the solidus temperature but below 940°C), test specimens for cross-sectional observation were cut out and polished, and the vicinity of the center of the coating in the thickness direction was photographed using an optical microscope at 100x magnification, and the total area of ​​residual pores and residual oxides with a diameter of 20 μm or more in a 500 μm square field of view was measured. Note that when the shape of the photographed residual pores or residual oxides was elliptical rather than circular, the area of ​​those with a major axis of 20 μm or more was included in the calculation. For each of the thermal spray coating and the remelted coating, the porosity P of the thermal spray coating was determined as the ratio of the total area of ​​the residual pores and residual oxides to the area of ​​the field of view. Ｂ and the porosity P of the remelted coating Ａ The porosity of the remelted coating P Ａ ) / (porosity of thermal spray coating P Ｂ The densification was evaluated by calculating the value of

[0060] (5) Evaluation of corrosion resistance of remelted coatings A corrosion resistance test was carried out on samples that had been cut out and polished from cross sections of the remelted coatings (in the present invention, the coatings were remelted at a temperature equal to or higher than the solidus temperature but lower than 940°C). A salt spray test (5% NaCl, 35°C, 96 hours) was carried out, and samples that showed only partial rusting on the coating and / or at the interface between the coating and the base metal were rated as A, and samples that showed rusting throughout were rated as B.

[0061] (6) Evaluation of Hardness of Remelted Coatings For the remelted coatings (in the present invention, the coatings were remelted at a temperature equal to or higher than the solidus temperature but lower than 940°C), cross sections were cut out and polished to evaluate the Vickers hardness. The test force was 2.94 N, and the average value of five measurements was used to evaluate the hardness.

[0062] (7) Evaluation of deformation of substrate after remelting treatment When a remelted coating (in the present invention, a coating remelted at a temperature equal to or higher than the solidus temperature but lower than 940°C) was placed on a flat base together with the substrate, those that were not in contact with the base were judged to be deformed. Those that were in contact with the base were rated A, and those that the substrate placed on the base was not in contact with the base and was unstable and wobbly were rated B.

[0063]

[0064] In the Ni-based alloys of invention examples 1 to 12, the remelting heat treatment temperatures for all of the coatings were low, at 850 to 920°C, the precipitated phase size of P compounds in the coating was 10 μm or less, the circle-equivalent diameter of the hard phase containing almost no P was 20 μm or less, the porosity of the coating was 0.5 or less in all cases, and a structure in which P was finely dispersed was obtained, resulting in coatings of grade A with good corrosion resistance and substrate deformation evaluation. Furthermore, the P content of the hard phase in the invention examples was approximately 0.04 to 0.09%, and the P content of the hard phase was 1% or less, as analyzed by SEM / EDS. Therefore, uniform strength of the matrix, uniform hardness of the coating, and a balance of hardness and toughness were obtained.

[0065] In Comparative Example No. 13, no P was added to the Ni-based alloy, and the solidus temperature was high, so the remelting heat treatment temperature was also high, and deformation of the substrate was observed. In Comparative Example No. 14, the P content was excessive, so coarse P compounds were crystallized, and the remelting heat treatment temperature was high, so deformation of the substrate was also observed. In Comparative Example No. 15, the P and Cu content was excessive, so corrosion resistance was poor. Deformation of the substrate was also observed. In Comparative Example No. 16, the B, Si, and C content was excessive, so the coating was too hard, coarse P compounds were observed, and corrosion resistance was poor and deformation of the substrate was observed. In Comparative Example No. 17, the Cr content was excessive, so the liquidus temperature was high, so coarse P compounds were observed, and corrosion resistance was poor and deformation of the substrate was observed. In Comparative Example No. 18, P was not added to the Ni-based alloy, and the solidus temperature was high, so the remelting heat treatment temperature was also high, and deformation of the substrate was observed. In addition, the total amount of Mo and W and the total amount of Mn, Fe, and Co were all excessive, so the liquidus temperature was excessively high, the coating was too hard, and the corrosion resistance was poor. In Comparative Example Nos. 19 and 20, the remelting heat treatment temperature was high at 940°C, so coarse P compounds were observed and deformation of the substrate was also observed.

[0066] The present invention can lower the remelting heat treatment temperature of a thermal sprayed coating, and therefore can be widely applied to fields such as aircraft, automobiles, boilers, and agricultural machinery, in addition to situations where thermal sprayed coatings of Ni-based self-fluxing alloys have traditionally been used.

Claims

1. A high melting point Ni-based alloy consisting, by mass, of P: 0.1 to 7.0%, B: 0.0 (inclusive 0%) to 5.0%, Si: 0.0 (inclusive 0%) to 5.0%, C: 0.0 (inclusive 0%) to 2.0%, Cr: 0.0 (inclusive 0%) to 30.0%, one or both of Mo and W: a total of Mo+W / 2 of 0.0 (inclusive 0%) to 9.0%, Cu: 0.0 (inclusive 0%) to 10.0%, one or more of Mn, Fe and Co: 0.0 (inclusive 0%) to 10.0% for each element, and the balance being Ni and unavoidable impurities, The high melting point Ni-based alloy has a hard phase with a P content of 1% or less and a structure in which P is dissolved in a γNi matrix and / or a precipitated phase containing P and having a size of 10 μm or less is dispersed, and the high melting point Ni-based alloy has a solidus temperature of 800°C or higher and 950°C or lower.

2. The high melting property Ni-based alloy according to claim 1, wherein the hard phase is a boride or a carbide, the circle equivalent diameter size of the hard phase is 20 μm or less, and the area ratio of the hard phase is 20% or less.

3. The high melting point Ni-based alloy according to claim 1 or 2, wherein the high melting point Ni-based alloy has a liquidus temperature of 1000°C or higher.

4. A high melting property Ni-based alloy coating comprising the high melting property Ni-based alloy according to claim 1 or 2.

5. A high melting property Ni-based alloy coating made of the high melting property Ni-based alloy according to claim 3.

6. The high melting property Ni-based alloy coating is a remelted coating that has been remelted at a temperature of less than 940 ° C., and the porosity P of the remelted coating Ａ and the porosity P of the thermal spray coating before the remelting treatment Ｂ But, P Ａ / P Ｂ 6. The high melting point Ni-based alloy coating according to claim 5, wherein the remelted coating satisfies the relationship of .gamma.Ni matrix containing P and having a network structure.

7. Atomized powder for forming a coating, comprising the high melting point Ni-based alloy according to claim 1 or 2.

8. A part having the coating according to claim 5 and having excellent hardness, corrosion resistance and crack resistance.

9. A part having excellent hardness, corrosion resistance and crack resistance, which has the coating according to claim 6.

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