A metal injection molding method for reducing interstitial contamination of titanium alloy products

Abstract

The present invention discloses a metal injection molding method for reducing interstitial contamination of titanium alloy products, including powder preparation and manufacturing processes. By constructing a multiple regression model, the relationship between powder particle size, sintering temperature, porosity, and tensile strength is determined. According to the required tensile strength and porosity requirements of the titanium alloy products, the particle size of the powder and the sintering temperature used in the manufacturing process are inversely deduced. Then, the prepared powder is processed into titanium alloy products through the manufacturing process. The multiple regression model shows that as the powder size increases and the sintering temperature decreases, the porosity and pore size increase, resulting in a decrease in tensile strength.

Description

Technical Field

[0001] The present invention relates to the field of titanium alloy product processing, and particularly relates to a metal injection molding method for reducing the interstitial contamination of titanium alloy products. Background Art

[0002] The metal powder injection molding process (MIM) is completed by mixing metal powder and binder, performing injection molding and debinding processes, and then performing a high-density sintering process. The metal powder injection molding process has been widely used in the manufacturing of different industries such as medical, automotive, and aerospace. Titanium alloy, as a key industrial metal material, has the advantages of being non-magnetic, having a gorgeous appearance, excellent chemical resistance, excellent strength-to-weight ratio, and good biocompatibility. The MIM process has been widely commercialized in the fields of portable electronic products, healthcare, ships, etc. Compared with products produced by other processes such as die casting, investment casting, sand casting, and forming routes, MIM products have higher strength, high precision, and complexity. Ti-6Al-4V is a commonly used processed metal powder, but titanium is a highly reactive metal that can react with almost all elements. At high temperatures, it can also react with gas compounds such as CO, CO2, water vapor, NH4, and many volatile organic compounds. During the heating process, the reaction of metal elements with the titanium surface results in surface contamination and changes in chemical composition. Some gas elements can not only form compounds on the titanium surface but also enter the metal lattice to form interstitial solid solutions, affecting the quality of the finished product. Among them, porous Ti-6Al-4V alloy has been widely used in industry as a structural or functional material because of its unique corrosion resistance. Porous titanium alloy can reduce the density of titanium alloy, and the presence of micropores can promote its application in biomedical devices. However, this porous titanium alloy is prone to collapse or deformation under mechanical force, resulting in reduced mechanical strength and weak structural integrity, making it difficult to manufacture. In addition, during the processing, the pores may be contaminated by cutting fluids and debris, leading to material degradation over time. The size and distribution of micropores are also difficult to adjust in practical applications, and it is more challenging to manufacture microporous metal parts with complex geometries and high precision.

[0003] Existing porous titanium alloys are mostly processed by using volatiles such as sugar, salt, and polymers as space scaffolds. The traditional method of producing porous Ti-6Al-4V using a space scaffold by metal injection molding (MIM) has some disadvantages. In order to remove the space scaffold, the salt-based material is usually removed by methods such as dissolution, evaporation, and sublimation. However, the dissolution process may be time-consuming, requiring up to 72 hours, and causing the titanium alloy to expand. On the other hand, methods using a vacuum furnace such as evaporation or sublimation may contaminate the vacuum chamber, causing the space holder material to condense in the vacuum pump, resulting in more serious interstitial contamination of the titanium alloy.

[0004] In summary, for porous Ti-6Al-4V alloys, they have a long demolding time, are prone to intergranular contamination in the sintering furnace, the porosity and pore size cannot be controlled, the mechanical properties are poor, and the process is unstable. Therefore, how to reduce the intergranular contamination of Ti-6Al-4V alloys during MIM processing and improve the mechanical properties of the products is an urgent problem to be solved.

[0005] Contents of the present invention

[0006] In view of the above technical problems, the present invention provides a metal injection molding method for reducing the intergranular contamination of titanium alloy products, including: powder preparation and manufacturing process. By constructing a multiple regression model, the relationship between powder particle size, sintering temperature, porosity and tensile strength is determined. According to the required tensile strength and porosity requirements of the titanium alloy product, the powder particle size and the sintering temperature used in the manufacturing process are deduced inversely. Then, the prepared powder is processed into a titanium alloy product through the manufacturing process. The multiple regression model shows that as the powder size increases and the sintering temperature decreases, the porosity and pore diameter increase, resulting in a decrease in tensile strength.

[0007] The porosity is denoted as Y 1 , the powder size is denoted as X 1 , the sintering temperature is denoted as X 2 , the fitting dependency is:

[0008] Y 1 = -0.0072×X 1 2 -0.0001×X 2 2 +0.0004×X 1 ×X 2 +1.031X 1 +0.185X 2 -50.9(1)

[0009] The formula represents the relationship between the porosity (Y 1 ) and the powder size (X 1 ) and the sintering temperature (X 2 ). Among them, -0.0072×X 1 2 represents the influence of the square of the powder size on the porosity, 0.00041×X 1 ×X 2 represents the influence of the interaction between the powder size and the sintering temperature on the porosity, 1.031X 1 represents the linear influence of the powder size on the porosity, 0.185X 2 represents the linear influence of the sintering temperature on the porosity, and -50.9 represents the intercept of the model;

[0010] The tensile strength is denoted as Y2 , the dependency relationship after fitting is:

[0011]

[0012] Further, the powder material includes irregularly shaped Ti–6Al–4V powder obtained by a hydrogenation-dehydrogenation method and a polyoxymethylene binder. The hydrogenation-dehydrogenation process includes the hydrogenation of sponge titanium, the crushing of the resulting brittle hydride, and the dehydrogenation to obtain the powder.

[0013] Further, the P-value is used to measure the likelihood of observing the data if there is no relationship between the porosity or tensile strength and the variables. A low P-value indicates the sufficiency of a strong correlation with the variables. The P-values of Equation (1) and Equation (2) are both less than 0.001.

[0014] Further, the goodness of fit of the regression model is measured by R-sq. A high R-sq indicates a good fit of the model to the data. The R-sq of Equation (1) is 97.5%, and the R-sq of Equation (2) is 97.79%.

[0015] Furthermore, the manufacturing process includes the mixing and crushing of powder particles, injection molding, debinding, sintering, and post-treatment. The manufacturing process also includes setting the crushed particle size of the powder material and the sintering temperature according to the required tensile strength and porous porosity requirements. Description of the Drawings

[0016] The present invention will be further described below with reference to the accompanying drawings.

[0017] Figure 1 (a) is a graph showing the relationship between powder size, sintering temperature, and porosity;

[0018] Figure 1 (b) is the order of constructing the porosity model;

[0019] Figure 1 (c) is for Y 1 The statistical significance relationship with the X variable;

[0020] Figure 1 (d) is the R-sq accuracy of the model;

[0021] Figure 1 (e)-(g) are graphs showing the relationship between porosity and powder size and sintering temperature respectively;

[0022] Figure 2 (a) Graph showing the relationship between powder size, sintering temperature, and tensile strength;

[0023] Figure 2 (b) is the order of constructing the tensile strength model;

[0024] Figure 2 (c) is Y 2 The statistical significance relationship with the X variable;

[0025] Figure 2 (d) is the R-sq accuracy of the model;

[0026] Figure 2 (e)-(g) are the graphs showing the relationships between the tensile strength and the powder size and the sintering temperature respectively. Detailed implementation manners

[0027] The following further details each aspect of the present invention.

[0028] Unless otherwise defined or stated, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the methods of the present invention.

[0029] The present invention provides a metal injection molding method for reducing the interstitial contamination of titanium alloy products, including powder preparation and manufacturing processes. By constructing a multiple regression model, the relationships between the powder particle size, sintering temperature, porosity, and tensile strength are determined. According to the required tensile strength and porosity requirements of the titanium alloy product, the powder particle size and the sintering temperature used in the manufacturing process are inversely deduced. Then, the prepared powder is processed into a titanium alloy product through the manufacturing process. As shown in Figure 1 (a), it reflects the relationship between the powder size, sintering temperature, and porosity. When the initial powder size (denoted as D50) decreases and the sintering temperature increases, the porosity of the specimen will decrease. When the powder with D50 = 100 μm is sintered at 1000 °C, a high porosity of 74% can be achieved. Figure 1 (b) shows the order of model construction. Compared with the sintering temperature, the powder size has a greater impact on the porosity. The multiple regression model shows that as the powder size increases and the sintering temperature decreases, the porosity and pore diameter increase, resulting in a decrease in the tensile strength. The porosity is denoted as Y 1 , the powder size is denoted as X 1 , the sintering temperature is denoted as X 2 , the P value measures the likelihood of observing the data when there is no relationship between the Y and X variables. A low P value indicates the sufficiency of the strong correlation between the Y 1 and X variables (X 1 and X 2 ). Figure 1 (c) indicates that there is a statistically significant relationship (p < 1 ) between Y

[0030] 0.001) and the X variable. The fitted dependency relationship is:

[0031] Y 1 = -0.0072×X 1 2 - 0.0001×X 2 2 + 0.0004×X 1 ×X 2 + 1.031X 1 + 0.185X 2 - 50.9(1)

[0032] The formula represents the relationship between the porosity (Y 1 ) and the powder size (X 1 ) and the sintering temperature (X 2 ). Among them, -0.0072×1 2 represents the influence of the square of the powder size on the porosity, 0.00041×X 1 ×X 2 represents the influence of the interaction between the powder size and the sintering temperature on the porosity, 1.031X 1 represents the linear influence of the powder size on the porosity, 0.185X 2 represents the linear influence of the sintering temperature on the porosity, -50.9 represents the intercept of the model;

[0033] Figure 1 (d) shows that this model can achieve an R-sq of 97.5%, demonstrating the accuracy of the model. As a function of the two X variables, the powder size and the sintering temperature, the predicted change in porosity is plotted in Figure 1 (e)-(g). It can be seen that the porosity has a positive / negative correlation with the powder size and the sintering temperature respectively. This can be understood as that as the temperature increases, the sintering neck size increases, which may reduce the porosity. On the contrary, a larger powder size with an irregular shape results in poor connection between particles and a smaller specific surface area, requiring more energy to form a sintering neck, resulting in an increase in porosity.

[0034] As Figure 2 (a) shows, a higher sintering temperature and a smaller powder size promote the formation and growth of intergranular sintering necks, enhance the intergranular bonding, reduce the porosity of the material, and ultimately result in a higher tensile strength. Under the conditions of a powder size of D50 = 32 μm and a sintering temperature of 1200 °C, the highest tensile strength of 457 MPa was achieved. Figure 2 (b) shows the order of model construction, demonstrating the order of variable addition. Compared with the sintering temperature, the powder size has a greater influence on the tensile strength.

[0035] The tensile strength is expressed as Y 2 , and the fitted dependency is:

[0036]

[0037] Figure 2 Y is shown in (c). 2 The significance of the statistical relationship between Y and the X (X 1 and X 2 ) variables, with a P-value less than 0.001. As Figure 2 shown in (d), an R-sq of up to 97.79% was achieved in this regression model, indicating that the regression model is very accurate and almost all of the Y 2 variation can be explained by the variation in the X variables. The predicted dependence of the tensile strength on the powder size and sintering temperature is given according to Equation (2), as Figure 2 shown in (e)-(g). It can be clearly seen from the data that there is a negative correlation between the powder size and the tensile strength, which means that a larger powder size leads to a lower tensile strength. This is because larger powder particles result in larger pores after sintering, reducing the effective cross-sectional area of the material under tensile loading and creating stress concentration points that can initiate and propagate cracks, leading to premature failure. In contrast, the sintering temperature is positively correlated with the tensile strength, which means that as the sintering temperature increases, the tensile strength also increases. This is because a higher sintering temperature leads to better densification and bonding of the powder particles, increasing the effective cross-sectional area of the material under tensile loading, reducing the size and number of pores, reducing the stress concentration points that can initiate and propagate cracks, and improving the material properties. To maintain the tensile strength of the Ti-6Al-4V MIM samples, the porosity must be minimized and any remaining pores must be small and sealed. This model can be used to predict the optimal values of the powder size and sintering temperature to achieve the desired porosity and tensile strength, or to evaluate the effect of these variables on the material properties. Equations (1) and (2) provide an empirical model of the correlation between two key properties (porosity, tensile strength) and two controllable variables (powder size and sintering temperature), which can facilitate the internal customized design of industrial porous Ti-6Al-4V materials. This model can be used to predict the optimal powder size and sintering temperature values for the desired porosity and tensile strength, or to evaluate the effect of changes in these variables on the material properties.

[0038] At different powder sizes, the sintered density and relative density are negatively correlated with porosity. Therefore, for all powder sizes, as the sintering temperature increases, the sintered density and relative density increase, indicating that the pore size decreases, and sintering at higher temperatures helps improve the densification of the material. The sintered density and relative density also increase with the decrease in powder size, meaning that smaller particles have higher surface energy and shorter diffusion distances, thus accelerating the densification process. Similar to the tensile strength, the 10% compressive strength is also affected by the powder size and sintering temperature of the porous Ti-6Al-4V material. Generally, higher density results in higher strength. Smaller particles tend to form finer grains and more uniformly distributed pores, thus enhancing the strength. The sample with the highest compressive strength is the one with a powder size of 32 μm and a sintering temperature of 1200 °C, which has the highest density. The contents of interstitial elements such as carbon, nitrogen, and especially oxygen after sintering are also affected by the particle size and sintering temperature. Smaller particles have a larger specific surface area and more adsorbed interstitial elements. Higher temperatures also contribute to the diffusion of interstitial elements into the metal matrix. The best conditions for reducing the content of interstitial elements are to use larger powder sizes and lower sintering temperatures.

[0039] Therefore, by using the processing method in the present invention to predict and reverse-infer each property during processing, porous Ti-6Al-4V titanium alloy products with suitable porosity can be processed without the need for a space support, and can be used in the field of medical implants.

[0040] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A metal injection molding method for reducing gap contamination of titanium alloy products, characterized in that: Including powder configuration and manufacturing process, by constructing a multivariate regression model to determine the relationship between powder particle size, sintering temperature, porosity and tensile strength, according to the required tensile strength and porosity requirements of the titanium alloy product, the powder particle size and the sintering temperature used in the manufacturing process are inferred, and then the configured powder is processed into a titanium alloy product through the manufacturing process. The multivariate regression model shows that the increase in powder size and the decrease in sintering temperature increase the porosity and pore size, resulting in a decrease in tensile strength; The porosity is represented by Y1, the powder size is represented by X1, and the sintering temperature is represented by X2. The dependence after fitting is: The formula represents the relationship between porosity (Y1) and powder size (X1) and sintering temperature (X2), where represents the effect of the square of the powder size on the porosity, represents the effect of the interaction between powder size and sintering temperature on porosity, 1.031X1 represents the linear effect of powder size on porosity, 0.185X2 represents the linear effect of sintering temperature on porosity, and -50.9 represents the intercept of the model; The tensile strength is expressed as Y2, and the dependence after fitting is: The powder material includes irregularly shaped Ti-6Al-4V powder obtained by a hydrogenation-dehydrogenation method and a polyoxymethylene binder, wherein the hydrogenation-dehydrogenation process includes hydrogenation of titanium sponge, crushing of generated brittle hydride, and dehydrogenation to obtain the powder; The P value is used to measure the possibility of observing the data if there is no relationship between porosity or tensile strength and variables. A low P value indicates the sufficiency of the strong correlation between the variables. The P values ​​of the fitting equation (1) and the fitting equation (2) are both less than 0.

001. The R-sq is used to measure the degree of fit of the regression model. A high R-sq indicates that the model fits the data well. The R-sq of the fitting equation (1) is 97.5%, and the R-sq of the fitting equation (2) is 97.79%.

2. A metal injection molding method for reducing gap contamination of titanium alloy products as claimed in claim 1, characterized in that: The manufacturing process includes powder particle mixing and crushing, injection molding, degreasing, sintering and post-processing.

3. A metal injection molding method for reducing gap contamination of titanium alloy products as claimed in claim 2, characterized in that: The manufacturing process also includes setting the crushing particle size of the powder and the sintering temperature of the sintering according to the required tensile strength and porous porosity requirements.

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