Method for producing titanium-based sintered body

Abstract

To provide a method for producing a titanium-based sintered body capable of producing a titanium-based sintered body having a desired shape.SOLUTION: There is provided a method for producing a titanium-based sintered body which comprises: a step of mixing a raw material powder containing titanium and a lubricant; a step of compression molding the raw material powder mixed with the lubricant to prepare a green compact; a step of cutting the green compact; a step of removing the lubricant from the green compact by heat treating the green compact after cutting in an inert atmosphere at 400°C or less; and a step of sintering the green compact after removal of the lubricant in a vacuum atmosphere to prepare a titanium-based sintered compact.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a titanium-based sintered body. [Background technology]

[0002] Titanium alloys containing titanium have excellent mechanical properties, and therefore titanium-based ingots and sintered bodies made of titanium alloys are used in the components of various machines.

[0003] Patent Document 1 discloses a method for producing a titanium-based compact by isostatically pressing a raw material powder to produce a titanium-based compact, and also discloses a method for producing a titanium-based sintered body by sintering the titanium-based compact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2022 / 190601 Summary of the Invention [Problem to be solved by the invention]

[0005] Cutting is used to process titanium alloy members into complex shapes. However, because titanium alloys are very hard, the machining tools are easily damaged. When the machining tools are damaged, the machining accuracy decreases. Therefore, it is difficult to form titanium alloy members into the desired shape.

[0006] An object of the present disclosure is to provide a method for producing a titanium-based sintered body, which is capable of producing a titanium-based sintered body having a desired shape. [Means for solving the problem]

[0007] The method for producing a titanium-based sintered body according to the present disclosure includes the steps of: mixing a raw material powder containing titanium with a lubricant; a step of pressurizing the raw material powder mixed with the lubricant to produce a green compact; A step of cutting the powder compact; a step of heat treating the powder compact after cutting in an inert atmosphere at 400° C. or less to remove the lubricant from the powder compact; and sintering the powder compact from which the lubricant has been removed in a vacuum atmosphere to produce a titanium-based sintered body. Effect of the Invention

[0008] The method for producing a titanium-based sintered body according to the present disclosure can produce a titanium-based sintered body having a desired shape. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart showing steps of a method for producing a titanium-based sintered body according to an embodiment. [Diagram 2] FIG. 2 is a graph showing the test results of Sample No. 21 described in Test Example 2. [Diagram 3] FIG. 3 is a graph showing the test results of Sample No. 22 described in Test Example 2. [Figure 4] FIG. 4 is a cross-sectional photograph of the titanium-based sintered body of Sample No. 31 described in Test Example 3. [Diagram 5] FIG. 5 is a cross-sectional photograph of the titanium-based sintered body of Sample No. 32 described in Test Example 3. [Figure 6] FIG. 6 is a cross-sectional photograph of the titanium-based sintered body of Sample No. 33 described in Test Example 3. [Figure 7] FIG. 7 is a cross-sectional photograph of the titanium-based sintered body of Sample No. 34 described in Test Example 3. [Figure 8] FIG. 8 is a cross-sectional photograph of the titanium-based sintered body of Sample No. 35 described in Test Example 3. [Figure 9] FIG. 9 is a schematic diagram showing a test piece for the tensile test described in Test Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described.

[0011] <1> The method for producing a titanium-based sintered body according to the present disclosure includes the steps of: mixing a raw material powder containing titanium with a lubricant; a step of pressurizing the raw material powder mixed with the lubricant to produce a green compact; A step of cutting the powder compact; a step of heat treating the powder compact after cutting in an inert atmosphere at 400° C. or less to remove the lubricant from the powder compact; and sintering the powder compact from which the lubricant has been removed in a vacuum atmosphere to produce a titanium-based sintered body.

[0012] In the method for producing a titanium-based sintered body disclosed herein, the raw material powder contains a lubricant, and the powder compact obtained by pressing the raw material powder also contains a lubricant. Therefore, when cutting the powder compact, the cutting tool is less likely to be damaged and the processing accuracy is less likely to decrease. Therefore, by sintering the powder compact processed into the desired shape, a sintered body having the desired shape can be easily obtained.

[0013] In the manufacturing method of the titanium-based sintered body disclosed herein, after cutting of the powder compact, the lubricant is removed from the powder compact in an inert atmosphere at 400°C or less. Therefore, the constituent elements of the lubricant are unlikely to remain in the titanium-based sintered body obtained by sintering the powder compact. The constituent elements of the lubricant are, for example, oxygen and carbon. The constituent elements remaining in the titanium-based sintered body may deteriorate the mechanical properties of the titanium-based sintered body. In the manufacturing method of the titanium-based sintered body disclosed herein, since the lubricant is removed from the powder compact before sintering the powder compact, problems caused by the constituent elements of the lubricant are unlikely to occur.

[0014] Titanium easily reacts with nitrogen at an atmospheric temperature above 400°C, and titanium nitride is generated by the reaction between titanium and nitrogen. Titanium nitride is brittle, so when titanium nitride is contained in a titanium-based sintered body, the mechanical properties of the titanium-based sintered body are reduced. Titanium nitride also inhibits sintering, so the mechanical properties of the titanium-based sintered body are reduced. In the manufacturing method of the titanium-based sintered body disclosed herein, the lubricant is removed in an inert atmosphere at 400°C or less, so titanium nitride is unlikely to be generated when the lubricant is removed. Here, sintering is performed in a vacuum atmosphere, so titanium nitride is unlikely to be generated during sintering.

[0015] <2> the above <1> In the method for producing a titanium-based sintered body described in The amount of the lubricant mixed with the raw material powder may be 0.05% by mass or more and 0.5% by mass or less, when the raw material powder is taken as 100% by mass (percent).

[0016] If the amount of lubricant mixed relative to 100% by mass of the raw material powder is 0.05% by mass or more, the green compact can be easily machined. If the amount of lubricant mixed relative to 100% by mass of the raw material powder is 0.5% by mass or less, the green compact can easily have a high density.

[0017] <3> the above <1> or <2> In the method for producing a titanium-based sintered body described in The lubricant may be stearic acid.

[0018] Stearic acid is almost completely removed from the powder compact at temperatures below 400°C. This prevents oxygen and carbon, which are constituent elements of stearic acid, from remaining in the titanium-based sintered body when the powder compact is sintered. Oxygen and carbon may reduce the strength of the titanium-based sintered body.

[0019] <4> the above <3> In the method for producing a titanium-based sintered body described in The temperature of the inert atmosphere may be 270°C or higher and 380°C or lower.

[0020] If the temperature of the inert atmosphere is within the above range, the generation of titanium nitride can be effectively suppressed. Stearic acid vaporizes at 270°C or higher. Therefore, by heating the powder compact in an inert atmosphere of 270°C or higher and 380°C or lower, most of the stearic acid is removed from the powder compact.

[0021] <5> the above <1> from <4> 2. The method for producing a titanium-based sintered body according to claim 1, The raw material powder may include a powder made of titanium and a powder made of a compound of aluminum and vanadium.

[0022] the above <5> According to the method for producing a titanium-based sintered body described in the above, a titanium-based sintered body made of a titanium alloy containing titanium (Ti), aluminum (Al) and vanadium (V) can be produced. The titanium alloy is, for example, Ti-6Al-4V, or so-called 64 titanium. 64 titanium has extremely excellent strength.

[0023] <6> the above <1> from <5> 2. The method for producing a titanium-based sintered body according to claim 1, The raw material powder may further include a ceramic powder.

[0024] By including ceramic powder in the raw powder, it is possible to obtain a titanium-based sintered body made of, for example, a metal matrix composite (MMC) in which ceramics are precipitated in a titanium alloy matrix. MMCs are lightweight and have excellent wear resistance and heat resistance.

[0025] <7> the above <1> from <6> 2. The method for producing a titanium-based sintered body according to claim 1, In the step of producing the powder compact, the raw material powder may be pressure-molded by cold isostatic pressing.

[0026] Because the cold isostatic press mold is not made of metal, the titanium contained in the raw powder does not stick to the mold, making it easier to increase the pressure and increase the density of the green compact.

[0027] <8> the above <1> from <7> 2. The method for producing a titanium-based sintered body according to claim 1, The method may further include a step of compressing the titanium-based sintered body by hot isostatic pressing.

[0028] Hot isostatic pressing further increases the density of the titanium-based sintered body, improving the strength of the titanium-based sintered body.

[0029] [Details of the embodiment of the present disclosure] Hereinafter, specific examples of the manufacturing method of the titanium-based sintered body of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. The size of the members shown in each drawing is expressed for the purpose of clarifying the description, and does not necessarily represent the actual size. Note that the present invention is not limited to these examples, but is indicated by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

[0030] <Embodiment 1> As shown in the flow chart of FIG. 1, the method for producing a titanium-based sintered body according to the embodiment includes the following steps. -Preparing raw powder A process of mixing raw powder and lubricant The process of compressing and molding the raw powder - A process for cutting powder compacts Lubricant removal process - Sintering the powder compact - A process of compressing titanium-based sintered bodies using hot isostatic presses. Finishing process Each step will be described in detail below.

[0031] <Process for preparing raw powder> The raw powder includes titanium. The raw powder may be composed of a powder made of pure titanium, or may be composed of a powder made of a titanium alloy. The raw powder may be composed of a powder made of pure titanium and a powder containing a first element that can be alloyed with titanium. Alternatively, the raw powder may be composed of a powder made of a titanium alloy and a powder containing the first element. The elements other than titanium in the titanium alloy and the first element are, for example, aluminum (Al), vanadium (V), tin (Sn), chromium (Cr), molybdenum (Mo), or zirconium (Zr). The elements other than titanium in the titanium alloy and the first element are appropriately selected depending on the composition of the titanium-based sintered body to be produced. An example of a specific raw powder includes Ti powder made of pure titanium and Al-V powder made of a compound of aluminum and vanadium. A titanium-based sintered body made of Ti-6Al-4V alloy is obtained by using a raw powder containing Ti powder and Al-V powder.

[0032] The raw material powder may further contain a ceramic powder. The ceramic powder is, for example, titanium diboride (TiB2). By carrying out the method for producing a titanium-based sintered body of the present embodiment using a raw material powder containing a ceramic powder, a titanium-based sintered body made of an MMC is produced. The MMC comprises a matrix containing titanium and a plurality of ceramic precipitates dispersed in the matrix. The MMC may be lighter in weight and have better mechanical properties than a titanium-based sintered body made of only pure titanium or a titanium alloy.

[0033] The grain size of the raw material powder is, for example, 0.1 μm or more and 100 μm or less. When fine raw material powder is pressure-molded, air is likely to be trapped in the gaps between the particles constituting the powder compact, and the oxygen concentration of the powder compact is likely to be high. The oxygen contained in the powder compact may deteriorate the mechanical properties of the titanium-based sintered body obtained by sintering the powder compact. If the grain size of the raw material powder is 0.1 μm or more, aggregation during mixing can be suppressed. If the grain size of the raw material powder is 100 μm or less, the density of the powder compact and the titanium-based sintered body is likely to be high. The grain size of the raw material powder may be, for example, 0.5 μm or more and 90 μm or less.

[0034] <Step of mixing raw material powder and lubricant> The mixing method for mixing the raw material powder and the lubricant is not particularly limited. For example, the raw material powder and the lubricant may be mixed by a ball mill, an attritor, or a jet mill. The mixing method using a ball mill, an attritor, or a jet mill is a mixing method that imparts high energy to the raw material powder. Alternatively, the raw material powder and the lubricant may be mixed by a V-type mixer. In the mixing method using a V-type mixer, the energy imparted to the raw material powder is relatively low.

[0035] When the raw powder is composed of multiple types of powder, the multiple types of powder may be mixed stepwise. For example, when the raw powder is composed of a first powder, a second powder, and a ceramic powder, the first powder and the ceramic powder are mixed to prepare a mixed powder, and then the mixed powder, the second powder, and a lubricant are mixed. The first powder or the second powder is a powder composed of titanium or a titanium alloy.

[0036] The first mixing step of mixing the first powder and the ceramic powder can be carried out, for example, by a ball mill, an attritor, or a jet mill. By mixing two or more types of powder including the ceramic powder by a mixing method capable of imparting high energy to the powder, the ceramic powder can be easily finely dispersed. The second mixing step of mixing the mixed powder and the second powder can be carried out, for example, by a V-type mixer.

[0037] The lubricant is, for example, stearic acid, zinc stearate, stearic acid amide, or ethylene bis stearic acid amide. Stearic acid in particular vaporizes at 270° C. or higher, and is therefore suitable for the method of producing a titanium-based sintered body of this embodiment.

[0038] The amount of lubricant mixed with respect to the raw material powder is, for example, 0.05% by mass or more and 0.5% by mass or less when the raw material powder is 100% by mass. If the amount of lubricant mixed with respect to 100% by mass of the raw material powder is 0.05% by mass or more, the powder compact can be easily cut in the step of cutting the powder compact described below. If the amount of lubricant mixed with respect to 100% by mass of the raw material powder is 0.5% by mass or less, the amount of lubricant relative to the raw material powder is not too large, and the density of the powder compact can be easily increased. The amount of lubricant mixed may be 0.2% by mass or more and 0.5% by mass or less, or 0.3% by mass or more and 0.4% by mass or less.

[0039] <Process of compressing raw powder> The pressure molding is performed, for example, by cold isostatic pressing. The molding temperature is from 0°C to 50°C. The mold for cold isostatic pressing is made of a nonmetallic elastic material, such as urethane rubber, acrylic resin, acrylic resin containing elastomer, or polylactic acid (PLA) resin. Since the mold for cold isostatic pressing is not metal, titanium does not seize onto the mold. The shape of the green compact obtained by cold isostatic pressing is relatively simple. For example, the shape of the green compact is columnar or cylindrical.

[0040] The molding pressure is appropriately selected depending on the material of the raw material powder and the density of the green compact. For example, the molding pressure is 200 MPa or more. The molding pressure may be 350 MPa or more, or 500 MPa or more. The upper limit of the molding pressure depends on the capacity of the equipment. For example, the upper limit of the molding pressure is 800 MPa. The higher the molding pressure, the higher the density of the green compact tends to be.

[0041] <Step of cutting the powder compact> The cutting process is performed, for example, by a lathe or a machining center. The cutting process may be continuous cutting using a cutting tool or intermittent cutting using a rotary tool. Since the powder compact of this example contains a lubricant, the cutting tool is less likely to be damaged during the cutting process. Since the cutting tool is less likely to be damaged, the increase in the cost of cutting process associated with the replacement of the cutting tool can be suppressed. In addition, the cutting accuracy is less likely to decrease, and the surface quality of the cut powder compact is improved.

[0042] The greater the content of the lubricant in the powder compact, the less likely the cutting tool is to be damaged and the easier it is to improve the surface properties of the powder compact. The content of the lubricant relative to the raw material powder in the powder compact may be considered to be the same as the amount of lubricant mixed with the raw material powder when the raw material powder and the lubricant are mixed.

[0043] <Process for removing lubricant> In the step of removing the lubricant, the powder compact is heat-treated in an inert atmosphere at 400°C or less. The inert atmosphere is, for example, a nitrogen atmosphere or an argon atmosphere. In an inert atmosphere at 400°C or less, titanium contained in the powder compact is difficult to nitride. Since titanium nitride is brittle, if titanium nitride is generated in the powder compact, the mechanical properties of the titanium-based sintered body obtained by sintering the powder compact may be deteriorated. In addition, titanium nitride may inhibit the sintering of the powder compact and deteriorate the mechanical properties of the titanium-based sintered body. Here, even if the powder compact is heat-treated in an argon atmosphere, titanium nitride may be generated in an argon atmosphere above 400°C because the powder compact may contain air.

[0044] Stearic acid vaporizes at 270°C or higher. Therefore, a powder compact containing stearic acid as a lubricant is heat treated, for example, in an inert atmosphere at 270°C or higher and 380°C or lower. If the temperature range of the inert atmosphere is 270°C or higher and 380°C or lower, most of the stearic acid is removed from the powder compact. Furthermore, within the above temperature range, the generation of titanium nitride in the powder compact can be effectively suppressed.

[0045] The time for which the powder compact is maintained within the above temperature range, i.e., the heat treatment time, is, for example, 10 minutes or more and 8 hours or less. If the heat treatment time is 10 minutes or more, the temperature at the center of the powder compact becomes sufficiently high, and the lubricant is easily removed from the entire powder compact. If the heat treatment time is 8 hours or less, the production time of the titanium-based sintered body is not too long. The heat treatment time may be 3 hours or more and 6 hours or less. After the heat treatment, the powder compact is cooled to room temperature in a furnace.

[0046] <Step of sintering the powder compact> In the process of sintering the powder compact, the powder compact from which the lubricant has been removed is sintered in a vacuum atmosphere. The atmospheric pressure is, for example, 0.1 Pa or less. The atmospheric temperature is appropriately selected depending on the material of the raw material powder. For example, the atmospheric temperature is 1100°C or more and 1400°C or less.

[0047] The sintering time is, for example, 1 hour or more and 25 hours or less. If the sintering time is 1 hour or more, the entire powder compact is likely to be sintered sufficiently. If the sintering time is 25 hours or less, the production time of the titanium-based sintered body is not too long. The sintering time may be 8 hours or more and 18 hours or less. The titanium-based sintered body is cooled to room temperature in the furnace.

[0048] Even in a vacuum atmosphere, there is a small amount of air. Therefore, there is a risk that the nitrogen in the air will react with the titanium contained in the powder compact when it is sintered. The amount of titanium nitride in the titanium-based sintered body can be reduced by embedding the powder compact in zirconia balls and further placing a getter made of titanium pieces on top of the zirconia balls.

[0049] The relative density of the titanium-based sintered body is, for example, 95% by volume or more. In this example, the relative density is the volume ratio of the solid portion to the volume of the object to be measured. Here, even if the relative density of the powder compact before sintering is the same, if the method of manufacturing the powder compact is different, the relative density of the titanium-based sintered body will change. For example, when a powder compact made of a raw material powder made of a prealloy powder is sintered, the relative density of the titanium-based sintered body is unlikely to be high. The prealloy powder is a powder having the same composition as the titanium alloy that makes up the titanium-based sintered body. On the other hand, when a powder compact made of a raw material powder in which a plurality of types of powders are mixed is sintered, the relative density of the titanium-based sintered body is likely to be high.

[0050] The titanium alloy constituting the titanium-based sintered body is, for example, Ti-5Al-2.5Sn, Ti-6Al-4V, Ti-3Al-2.5V, Ti-6Al-4V-2Sn, Ti-15V-3Cr-3Sn-3A, Ti-13V-11Cr-3Al, or Ti-3Al-8V-6Cr-4Mo-4Zr. When the titanium-based sintered body is an MMC including a matrix and a plurality of precipitates, the matrix is, for example, the titanium alloy described above. The precipitates are, for example, TiB.

[0051] <Step of compressing titanium-based sintered body by hot isostatic pressing> Hot isostatic pressing further increases the relative density of titanium-based sintered bodies. The relative density of titanium-based sintered bodies subjected to hot isostatic pressing is 95% or more. It is difficult to increase the density of titanium-based sintered bodies with a relative density of less than 95% by hot isostatic pressing.

[0052] The temperature of the hot isostatic press is appropriately selected depending on the composition of the titanium-based sintered body. For example, the temperature of the hot isostatic press is 800°C or higher and 1100°C or lower. The processing time is, for example, 30 minutes or longer and 6 hours or shorter. If the processing time is 30 minutes or longer, the relative density of the titanium-based sintered body is sufficiently high. If the processing time is 6 hours or shorter, the manufacturing time of the titanium-based sintered body is not too long. The processing time may be 1 hour or longer and 4 hours or shorter. The titanium-based sintered body is cooled to room temperature in the hot isostatic press device. The pressure is, for example, 150 MPa or higher.

[0053] <Finishing process> In the finish processing step, for example, the surface of the titanium-based sintered body is ground. Grinding allows the titanium-based sintered body to have the desired dimensions and makes the surface of the titanium-based sintered body smooth. In addition, impurities concentrated on the surface of the titanium-based sintered body are removed from the surface of the titanium-based sintered body by grinding. Examples of impurities include titanium oxide, titanium carbide, and titanium nitride. Removing impurities from the surface of the titanium-based sintered body improves the mechanical properties of the titanium-based sintered body.

[0054] <Test Example> <Test Example 1> In Test Example 1, the influence of the presence or absence of a lubricant and the amount of the lubricant on the machinability of the powder compact was examined. The samples prepared in Test Example 1 were as follows.

[0055] [Sample No. 1] A first powder made of an Al-V alloy was prepared. The particle size of the first powder was 20 μm or more and 90 μm or less. The first powder was obtained by classifying a commercially available Al-V alloy powder.

[0056] A second powder made of pure titanium was prepared. The particle size of the second powder was 20 μm or more and 45 μm or less. The second powder was obtained by classifying a commercially available titanium powder.

[0057] Ceramic powder made of titanium diboride (TiB2) was prepared. The particle size of the ceramic powder was 0.7 μm or more and 10 μm or less.

[0058] 1221 g of the first powder and 77.9 g of the ceramic powder were mixed in a ball mill to produce a mixed powder consisting of the first powder and the ceramic powder. The container of the ball mill was made of tungsten carbide. The grinding balls put into the container of the ball mill were also made of tungsten carbide. The diameter of the grinding balls was 10 mm, and the number of grinding balls was 50. The mixing conditions were 300 rpm for 1 hour. "rpm" refers to the number of rotations per minute.

[0059] 154 g of the mixed powder and 846 g of the second powder were mixed in a V-type mixer to produce raw powder. This raw powder was pressurized by a cold isostatic press to produce a cylindrical green compact. The pressing pressure was 390 MPa, and the holding time was 30 seconds. The green compact had an outer diameter of 40 mm, an inner diameter of 20 mm, and a height of 30 mm. The green compact did not contain any lubricant.

[0060] [Sample No. 2 to Sample No. 5] The powder compacts of Sample No. 2 to Sample No. 5 contain a lubricant. The only difference between Sample No. 2 to Sample No. 5 and Sample No. 1 is the presence or absence of a lubricant. The lubricant was stearic acid. The lubricant was fed into the V-type mixer together with the mixed powder and the second powder. The amount of lubricant mixed in Sample No. 2 was 0.05 mass% when the raw material powder was taken as 100 mass%. The amount of lubricant mixed in Sample No. 3 was 0.1 mass%, the amount of lubricant mixed in Sample No. 4 was 0.3 mass%, and the amount of lubricant mixed in Sample No. 5 was 0.5 mass%.

[0061] [Sample No. 100] Sample No. 100 is a sintered material obtained by heat treating a powder compact produced by the same method as sample No. 3 in a nitrogen atmosphere at 380°C for 4 hours and then sintering in a vacuum atmosphere at 1300°C for 12 hours.

[0062] [Cutting test] The surfaces of the sintered material of sample No. 100 and the green compacts of sample No. 1 to No. 5 were machined using a lathe. The cutting was dry machining. The peripheral speed S was 180 m / min, the feed F was 0.2 mm / rev, and the cutting depth D was 0.5 mm / rev. The wear of the cutting tools after the cutting test was measured using a measuring device attached to a microscope. As a result, the wear of the cutting tools used in cutting sample No. 2 to No. 5 was smaller than that of sample No. 1 and sample No. 100. In addition, the wear of the cutting tools decreased as the amount of lubricant mixed increased. However, there was almost no difference in the wear between sample No. 4, which contained 0.3 mass% of lubricant, and sample No. 5, which contained 0.5 mass% of lubricant.

[0063] <Test Example 2> In Test Example 2, the effect of the mixing method of the raw material powders on the relative density of the titanium-based sintered body was examined. The samples prepared in Test Example 2 are as follows:

[0064] [Sample No. 21] First, a powder compact of sample No. 21 was produced using the same materials and manufacturing method as sample No. 3. Therefore, the powder compact of sample No. 21 contains a powder of pure titanium, a powder of an Al-V alloy, a ceramic powder of TiB2, and a lubricant.

[0065] The green compact was placed in an inert oven and the stearic acid was removed from the green compact by heat treatment. The atmosphere in the inert oven was a nitrogen atmosphere, the heat treatment temperature was 380°C, and the heat treatment time was 4 hours. The temperature rise rate of the inert oven was 5°C / min.

[0066] The lubricant-removed green compact was placed in a sintering furnace, and titanium-based sintered compacts were produced by sintering. The sintering furnace atmosphere was a vacuum atmosphere of 0.1 Pa or less, the sintering temperature was 1300°C, and the sintering time was 12 hours. The heating rate of the sintering furnace was 6.7°C / min up to 1290°C, and 1°C / min from 1290°C to 1300°C. The titanium-based sintered compact was an MMC with a matrix containing titanium and multiple precipitates dispersed in the matrix. The composition of the matrix was Ti-6Al-4V alloy, a so-called 64 titanium alloy. The composition of the precipitates derived from TiB2 was titanium boride (TiB).

[0067] In Test Example 2, the relative density of the powder compact was measured before sintering the powder compact, and the relative density of the titanium-based sintered body was also measured. The relative density is the volume ratio of the solid part to the volume of the measurement object. The unit of relative density is volume %. The relative density was measured by Archimedes' method.

[0068] The relationship between the relative density of powder compacts and the relative density of titanium-based sintered bodies is shown in the graph of Figure 2. The plot of white circles indicates the relative density of powder compacts, and the plot of black circles indicates the relative density of titanium-based sintered bodies. The horizontal axis of Figure 2 is compacting pressure, and the vertical axis is relative density. The unit of compacting pressure is MPa (megapascals). Figure 2 also shows the relative densities of powder compacts with compacting pressures of 100 MPa, 200 MPa, 300 MPa, and 390 MPa, as well as the relative densities of titanium-based sintered bodies.

[0069] As shown in FIG. 2, it was found that the higher the molding pressure, the higher the relative density of the powder compact. In addition, the relative density of the titanium-based sintered body was increased by 15% or more by volume compared to the relative density of the powder compact before sintering. The relative density of all titanium-based sintered bodies shown in FIG. 2 was 95% or more by volume. From these findings, it was found that even if the relative density of the powder compact is low, a titanium-based sintered body having a relative density of 95% or more by sintering can be produced. On the other hand, when cutting the powder compact, if the relative density of the powder compact is low, the powder compact may chip or crack. From the viewpoint of suppressing cracking or chipping of the powder compact, it is desirable that the relative density of the powder compact is 75% or more by volume. The molding pressure for obtaining a thick powder compact having a relative density of 75% or more by volume is, for example, 300 MPa or more.

[0070] [Sample No. 22] The green compact of sample No. 22 was obtained by pressing a mixture of prealloy powder, ceramic powder, and stearic acid. The prealloy powder was a powder made of Ti-6Al-4V alloy. The pressing pressure was the same as that of sample No. 21. The lubricant was removed from the green compact by heat treatment, and a titanium-based sintered compact was produced by sintering. The heat treatment and sintering conditions were the same as those of sample No. 21. The titanium-based sintered compact of sample No. 22 was also an MMC with multiple precipitates dispersed in the matrix.

[0071] The relationship between the relative density of the powder compact and the relative density of the titanium-based sintered body is shown in the graph of Figure 3. The graph of Figure 3 can be read in the same way as the graph of Figure 2. As shown in Figure 3, it was found that the higher the compacting pressure, the higher the relative density of the powder compact. However, the relative density of the titanium-based sintered body was only about 5% higher by volume than the relative density of the powder compact before sintering. The relative density of all of the titanium-based sintered bodies shown in Figure 3 was 85% by volume or less.

[0072] [summary] The results of Test Example 2 show that in order to produce an MMC with a relative density of 95% by volume or more, it is effective to produce a green compact from raw material powders made up of multiple types of powder.

[0073] <Test Example 3> In Test Example 3, the effect of the raw material powder mixing method on the structure of titanium-based sintered bodies was investigated. In Test Example 3, samples No. 31 to No. 35 were produced using different raw material powder mixing methods. In producing samples No. 31 to No. 34, the raw material powder was mixed in two batches. In producing sample No. 35, the raw material powder was mixed all at once. The mixing conditions for each sample using the ball mill were 300 rpm x 1 hour, and the mixing time using the V-type mixer was 1 hour.

[0074] [Sample No. 31] In the first mixing, Al-V alloy powder and TiB2 ceramic powder were mixed in a ball mill to produce a mixed powder. In the second mixing, the mixed powder, pure titanium powder, and stearic acid were mixed in a V-type mixer to produce a raw powder. The amount of stearic acid mixed was 0.3 mass%.

[0075] [Sample No.32] In the first mixing, pure titanium powder and TiB2 ceramic powder were mixed in a ball mill to produce a mixed powder. In the second mixing, the mixed powder, Al-V alloy powder, and stearic acid were mixed in a V-type mixer to produce a raw powder.

[0076] [Sample No. 33] In the first mixing, Al-V alloy powder and pure titanium powder were mixed in a ball mill to produce a mixed powder. In the second mixing, the mixed powder, ceramic powder made of TiB2, and stearic acid were mixed in a V-type mixer to produce a raw powder.

[0077] [Sample No. 34] In the first mixing, Al-V alloy powder and pure titanium powder were mixed in a ball mill to produce a mixed powder. In the second mixing, the mixed powder, ceramic powder made of TiB2, and stearic acid were mixed in a ball mill to produce a raw powder.

[0078] [Sample No. 35] The raw powder was prepared by mixing Al-V alloy powder, pure titanium powder, and TiB2 ceramic powder in a V-type mixer. Sample No. 35 does not contain stearic acid.

[0079] Titanium-based sintered bodies were produced from the raw powders of samples No. 31 to No. 35. The cold isostatic pressing pressure, the heat treatment conditions to remove the lubricant, and the sintering conditions for each sample were the same. The molding pressure was 390 MPa, the heat treatment conditions were 380°C x 4 hours in a nitrogen atmosphere, and the sintering conditions were 1300°C x 12 hours in a vacuum atmosphere.

[0080] The cross section of each sample was observed, and the area ratio of precipitates consisting of TiB was measured. Cross-sectional photographs of the titanium-based sintered compacts of sample No. 31 to sample No. 35 are shown in Figures 4 to 8, respectively. The gray parts in the cross-sectional photographs are a matrix consisting of 64 titanium, and the black parts are precipitates consisting of TiB. Comparing Figures 4 to 8, it was found that TiB precipitates were uniformly dispersed in sample No. 31 and sample No. 32. On the other hand, in sample No. 33 to sample No. 35, numerous spotted areas with few black precipitates were observed, indicating that the precipitates were dispersed non-uniformly.

[0081] Next, the dispersion state of TiB was quantitatively evaluated. The observation field of 13.2 mm × 9.5 mm was divided into 64, and the matrix and TiB in each divided field were distinguished by binarization processing. Then, the area ratio of TiB was calculated using image analysis software when the total area of ​​the matrix and precipitates in each divided field was taken as 100%. The area ratio of TiB is the abundance ratio of TiB, and is expressed in %,. The average value R0, maximum value R1, and minimum value R2 of the abundance ratios obtained from each divided field were calculated. The average value R0, maximum value R1, and minimum value R2 for each sample are shown in Table 1. Samples that satisfy R1≦R0+4.5 and R2≧R0-4.5 were evaluated as ``A'', and samples that do not satisfy these were evaluated as ``B''. Samples that satisfy R1≦R0+4.5 and R2≧R0-4.5 were judged to be samples in which TiB precipitates are uniformly dispersed in the matrix.

[0082] [Table 1]

[0083] As shown in Table 1, TiB was uniformly dispersed in the matrix in Sample No. 31 and Sample No. 32. These samples were prepared by mixing the ceramic powders in a ball mill in the first mixing step.

[0084] There was variation in the dispersion state of TiB in the matrix in Samples No. 33 and No. 34. These samples were prepared by mixing the ceramic powder with a V-type mixer in the second mixing step.

[0085] There was variation in the dispersion state of TiB in the matrix in sample No. 35. This sample was made by mixing all the raw materials constituting the titanium-based sintered body at once using a ball mill.

[0086] From these results, it was found that in order to uniformly disperse precipitates in the matrix, it is important to mix the raw materials constituting the titanium-based sintered body in several batches, and that it is also important that the ceramic powder is mixed in the first mixing step using a mixing method that applies high stress to the ceramic powder.

[0087] <Test Example 4> The mechanical properties of the MMC were examined in Test Example 4. The samples prepared in Test Example 4 were as follows:

[0088] [Sample No. 40] Sample No. 40 is a cast body made of titanium alloy 64.

[0089] [Sample No. 41 to Sample No. 44] Sample No. 41, Sample No. 42, Sample No. 43, Sample No. 44, and Sample No. 45 are titanium-based sintered bodies having the same configuration as Sample No. 31, Sample No. 32, Sample No. 33, Sample No. 34, and Sample No. 35 of Test Example 3, respectively.

[0090] [Tensile test] A test piece was prepared from each sample, and a tensile test was performed. FIG. 9 is a schematic diagram showing the shape of the test piece 5. The test piece 5 includes a first grip portion 51, a second grip portion 52, and an intermediate portion 50. The diameter of the intermediate portion 50 is 6.35 mm (millimeters), and the gauge length d between the first gauge point 50A and the second gauge point 50B set in the intermediate portion 50 is 25.4 mm. The temperature of the tensile test was room temperature, the strain rate until the 0.2% yield strength was 1.2 mm / min, and the strain rate after the 0.2% yield strength was 12.8 mm / min. The unit of tensile strength was MPa. The test results are shown in Table 2.

[0091] [Table 2]

[0092] As shown in Table 2, the tensile strength of the titanium-based sintered compacts of Samples No. 41 to 45 was equal to or greater than that of the ingot made of titanium 64. From these results, it was found that the titanium-based sintered compacts of this example are useful as materials for components of machines such as automobiles. [Explanation of symbols]

[0093] 1 Titanium-based sintered body 2. Matrix 3 Precipitate 5. Test Pieces 50 Middle 50A First gauge 50B Second gauge point 51 First grip part 52 Second grip part d Gauge length

Claims

1. mixing a raw material powder containing titanium with a lubricant; a step of pressurizing the raw material powder mixed with the lubricant to produce a green compact; A step of cutting the powder compact; a step of heat treating the powder compact after cutting in an inert atmosphere at 400° C. or less to remove the lubricant from the powder compact; and sintering the powder compact from which the lubricant has been removed in a vacuum atmosphere to produce a titanium-based sintered body. A method for producing a titanium-based sintered body.

2. 2. The method for producing a titanium-based sintered body according to claim 1, wherein the amount of the lubricant mixed with the raw material powder is 0.05% by mass or more and 0.5% by mass or less when the raw material powder is taken as 100% by mass.

3. The method for producing a titanium-based sintered body according to claim 1 or 2, wherein the lubricant is stearic acid.

4. 4. The method for producing a titanium-based sintered body according to claim 3, wherein the temperature of the inert atmosphere is 270° C. or higher and 380° C. or lower.

5. 3. The method for producing a titanium-based sintered body according to claim 1, wherein the raw material powder contains a powder made of titanium and a powder made of a compound of aluminum and vanadium.

6. The method for producing a titanium-based sintered body according to claim 5 , wherein the raw material powder further contains a ceramic powder.

7. 3. The method for producing a titanium-based sintered body according to claim 1, wherein in the step of producing the powder compact, the raw material powder is pressure-molded by cold isostatic pressing.

8. 3. The method for producing a titanium-based sintered body according to claim 1, further comprising a step of compressing the titanium-based sintered body by hot isostatic pressing.

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