CN106191493A - A kind of preparation method of powder metallurgy titanium alloy - Google Patents

Abstract

The invention relates to a method for preparing a powder metallurgy titanium alloy, comprising the following steps: using _TiH2 powder, Ti powder and other alloying elements as raw materials, mixing them evenly and pressing them into shape, wherein the amount of TiH2 added accounts for ₁₀ % of the total mass of raw materials 3-25%; heating in a high vacuum environment to decompose TiH ₂ , and sintering in a hydrogen atmosphere; then cooling down to 750-1000°C, vacuuming to remove hydrogen; finally, powder metallurgy titanium alloy products are obtained after cooling. In the invention, element H is added to the powder metallurgy titanium alloy in the form of titanium hydride, and the added amount of H is controlled by controlling the amount of titanium hydride. At the same time, the microstructure of the sintered titanium alloy is adjusted by controlling the hydrogen removal temperature of the titanium alloy sintered in a hydrogen atmosphere to obtain a high-performance titanium alloy. The resulting alloy has increased density and increased tensile strength compared to no addition of titanium hydride.

Description

A kind of preparation method of powder metallurgy titanium alloy

technical field

The invention relates to an alloy preparation method, in particular to a powder metallurgy titanium alloy preparation method.

Background technique

Titanium and titanium alloys have been widely used in the manufacture of military products such as aerospace vehicles, ships and weapons due to their low density, high specific strength, corrosion resistance, high temperature mechanical properties, fatigue resistance and creep properties. , also has great application potential in the automotive, chemical and energy industries. In the biomedical field, titanium is non-toxic, light in weight, high in corrosion resistance and strength, and has excellent biocompatibility. It can be used as an implant for the human body. and surgical instruments, etc.

At present, the preparation methods of titanium and titanium alloys are mainly through common plastic processing methods such as casting, and powder metallurgy methods. Because casting is easy to cause defects such as material composition segregation, porosity, shrinkage cavity, etc., it is difficult to obtain high-performance materials. However, titanium and titanium alloys have low room temperature plasticity, low deformation limit, large deformation resistance, and easy cracking at room temperature. Therefore, most titanium alloys still need to be plastically formed at high temperatures, but this also greatly increases the processing cost of titanium alloys. . Although the powder metallurgy technology of titanium alloy can overcome the shortcomings of the first two methods, it has the advantages of both. However, in the commonly used titanium alloy powder metallurgy method, due to the high sintering temperature and long sintering time, the grains of titanium alloy materials are easy to grow, so it is difficult to obtain titanium alloys with high performance.

Initially, hydrogen was viewed as a harmful impurity element in metals. However, in 1959, Schleicher and Zwiecker, two scholars from the former West Germany, added an appropriate amount of hydrogen to titanium alloy ingots such as titanium alloys Ti ₈ Al, Ti ₁₀ Al and Ti ₁₃ Al, and discovered that titanium alloys The hot workability of the titanium alloy has been significantly improved, which puts forward the idea that hydrogen atoms increase the thermoplasticity of titanium alloys, and verifies this idea through experiments. In 1980, Kerr published the article "Hydrogen as analloying element in titanium", proposing the concept of temporary alloying elements, using hydrogen as a temporary alloying element to change the microstructure and mechanical properties of titanium alloys. After that, the hydrogen treatment technology of titanium alloys began to be widely studied.

Titanium alloy hydrogenation methods mainly include liquid hydrogenation method and solid state hydrogenation method. Liquid hydrogen placement refers to a hydrogen placement method that introduces hydrogen into the titanium alloy melt during the melting process of titanium. This method mainly controls the hydrogen content in the titanium alloy by controlling the hydrogen pressure, and the temperature of the titanium alloy in the molten state Higher, so the hydrogen content in the titanium alloy is very small, and the influence on the properties of the titanium alloy in the molten state is also minimal. The titanium alloy solid-state hydrogenation method refers to the method of placing the titanium alloy sample in a high-temperature hydrogen atmosphere to diffuse hydrogen into the titanium alloy. During the hydrogenation process, the titanium alloy sample is always in a solid state. The main disadvantage of this method is that it is a titanium alloy. It is a solid state, so the hydrogen permeation time is longer for titanium alloy materials with a larger thickness, and it is difficult to make the hydrogen uniform in the interior of the titanium alloy. However, the above two methods use gaseous hydrogen, which is extremely unsafe to operate. The effect of hydrogen on the grain refinement of titanium alloys has been studied by many scholars, but its influence on the grain size and structure of sintered titanium alloys is rarely mentioned.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a powder metallurgy titanium alloy preparation process with simple operation, low cost and effective improvement of the performance of titanium alloy.

The technical scheme of the present invention is: a kind of preparation method of powder metallurgy titanium alloy, comprises the following steps:

Use TiH ₂ powder, Ti powder and other alloying elements as raw materials, mix them uniformly and press them into shape, where the amount of TiH ₂ added accounts for 3-25% of the total mass of raw materials; heating in a high-vacuum environment makes TiH ₂ decompose and keeps in hydrogen Atmosphere sintering; then lower the temperature to 750-1000°C, vacuumize and remove hydrogen; finally, obtain powder metallurgy titanium alloy products after cooling.

The other alloying elements are metal powders containing β-stabilizing elements of the titanium alloy. For example, the metal powder containing β-stabilizing elements of the titanium alloy is a metal powder having one or more elements of V, Fe, Mo, Nb, Ta, Ni and Mn. In a specific embodiment of the present invention, the prepared target alloy is titanium hexaluminum tetravanadium titanium alloy.

Preferably, the added amount of TiH ₂ accounts for 4.5-22.5% of the total mass of raw materials.

Preferably, the temperature is lowered to 750-900° C., and hydrogen is removed by vacuuming.

Further, the ethanol solution of polyethylene glycol is used as a release agent during compression molding.

The high vacuum environment and vacuuming refer to a vacuum degree lower than 1×10 ^-3 Pa.

As a further improvement, when sintering and loading the furnace, the green body is placed in the boat, and a certain amount of pure titanium powder is placed on both sides of the boat to absorb the residual air. A porous furnace plug is placed on both sides of the boat.

In a preferred embodiment, the sintering process includes: while vacuuming, first raise the temperature to 120-160°C to remove impurities and moisture in the furnace; then heat to 250-350°C and keep for 10-30 minutes; stop vacuuming, Then heat to 600-800°C and keep for 1-2h to balance the decomposition reaction of titanium hydride; then heat to 1000-1250°C for sintering and keep for 1-3h.

Preferably, heating is performed at a rate of 1.5-2.5 °C/min to 600-800 °C, and at a rate of 4-6 °C/min to 1000-1250 °C.

Preferably, the temperature is lowered to 900-750°C at a rate of 5-8°C/min, and then vacuumed and maintained for 2-4 hours; or the temperature is lowered to 1000°C at a rate of 4-6°C/min while being vacuumed.

In the invention, element H is added to the powder metallurgy titanium alloy in the form of titanium hydride, and the added amount of H is controlled by controlling the amount of titanium hydride. At the same time, the microstructure of the sintered titanium alloy is adjusted by controlling the hydrogen removal temperature of the titanium alloy sintered in a hydrogen atmosphere to obtain a high-performance titanium alloy. The resulting alloy has increased density and increased tensile strength compared to no addition of titanium hydride.

Description of drawings

Fig. 1 is the temperature-time craft curve figure of embodiment 1 sintering process;

Fig. 2 is the metallographic photo comparison diagram of the powder metallurgy titanium alloy prepared by removing H at 750 DEG C in embodiment 1;

Fig. 3 is the metallographic photo comparison diagram of the powder metallurgy titanium alloy prepared by removing H at 850 DEG C in embodiment 1;

Fig. 4 is the metallographic photo comparison diagram of the powder metallurgy titanium alloy prepared by removing H at 900 DEG C in embodiment 1;

Fig. 5 is the metallographic photo comparison diagram of the powder metallurgy titanium alloy prepared by removing H at greater than 1000°C in Example 1;

Fig. 6 is a comparison chart of the true stress and true strain curves of the tensile test of the powder metallurgy titanium alloy prepared by removing H at 750°C in Example 1;

Figure 7 is a comparison of the true stress and true strain curves of the tensile test of the powder metallurgy titanium alloy prepared by removing H at greater than 1000°C in Example 1;

Legend: a indicates that the amount of H added is 0%, b indicates that the amount of H added is 0.18%, c indicates that the amount of H added is 0.36%, d indicates that the amount of H added is 0.54%, e indicates that the amount of H added is 0.72%, and f indicates that the amount of H added is 0.72%. The amount of H added was 0.9%.

detailed description

The present invention will be fully and detailedly described below in conjunction with the accompanying drawings and embodiments.

The scope of protection of the present invention is not limited to the following selected powder metallurgy titanium six aluminum four vanadium titanium alloy, the present invention is applicable to most powder metallurgy titanium alloys, such as Ti-Al-Fe-Mo, Ti-6Al-6V-2Sn , Ti-Fe-4.5Al, Ti-22V-4Al, Ti-15V-6Cr-4Al and other (α+β) titanium alloys and β titanium alloys. That is, the method of the present invention is suitable for alloys that can change the β-transition temperature of titanium alloys during hydrogenation sintering.

Various raw materials, reagents, instruments and equipment used in the present invention can be purchased through the market, if there are special circumstances, otherwise specified.

Example 1

The steps of preparing powder metallurgy titanium alloy of the present embodiment are as follows:

(1) Using Ti powder with a particle size of -200 mesh, TiH with a particle size of -325 mesh and _Al6V4 master alloy powder with a particle size of -325 mesh as raw materials, the final sintered product is titanium six aluminum four vanadium titanium alloy as the target preparation.

Refer to the national standard GB/3620.1-2007 to weigh the required raw material powder according to the stoichiometric ratio of Ti-6Al-4V titanium alloy, in which HDH titanium powder and Al-V master alloy are mixed at a mass ratio of 9:1, called No. 1 powder ; Titanium hydride powder and Al-V master alloy powder are mixed at a mass ratio of 9.38:1, called II powder; then I and II powders are mixed according to a certain ratio, and finally mixed powders with different hydrogen contents are obtained. Each mixing process is carried out in a DL-SHL-5L high-efficiency double-arm mixer, and the time is 1h.

_The amount of TiH added (accounting for the mass percentage of the total raw material) and the equivalent H element content are shown in Table 1. In order to ensure good pressing performance, the amount of TiH ₂ added should not exceed 25%.

Table 1

(2) The powder mixed in step (1) was formed by unidirectional pressing, the mold size was 17×80 mm, the pressing pressure was 300 MPa, and the holding time was 2 minutes to obtain a powder pressing blank.

Before pressing, ensure that the mold cavity wall is smooth and clean, use polyethylene glycol ethanol solution as a release agent to evenly coat the contact surface between the mold and the powder, and dry the surface of the mold cavity with a hair dryer. The polyethylene glycol covering the surface of the mold cavity can lubricate the pressing, make the blank sample easy to release, and protect the mold from wear.

Due to the different sizes and shapes of the compacted blanks, and the different additions of TiH, the required pressing pressure is also different (for example, the range of ₂₀₀ to 500 MPa). _In the present invention, as the addition of TiH increases, the pressing pressure will increase. .

(3) Sinter the green sample obtained in step (2) according to the sintering process shown in Fig. 1 .

The hydrogen sintering and dehydrogenation of the blank are a continuous process, and they are all carried out in the GSL1600X vacuum tube furnace. The dehydrogenation process uses the GZK-103 high vacuum system connected to the tube furnace, and the vacuum degree can reach ≤10 ^-3 Pa.

The whole process can be divided into three stages:

The first stage, furnace loading. Put the green body in the corundum boat, put a small amount of pure titanium powder on both sides of the boat to absorb the residual air, and reduce the pollution of the residual air to the blank sample during sintering after vacuuming; put the corundum with the sample The boat is put into the vacuum tube sintering furnace, and a porous furnace plug is placed on both sides of the corundum boat for heat preservation and adsorption of impurities in the furnace after the temperature rises; the vacuum system is turned on, and the air in the sintering furnace tube is removed by vacuuming.

The second stage is hydrogen sintering. Start the vacuum tube sintering furnace, raise the furnace temperature from room temperature to 150°C at 5°C/min, keep it for 10 minutes to remove impurities and moisture in the furnace; then raise the temperature to 300°C at 3°C/min, keep it for 30 minutes to remove the residue on the surface of the blank polyethylene glycol; at this time, titanium hydride will start to decompose, close the high vacuum system, so that the blank sample is in the closed environment of the tubular sintering furnace; control the temperature of the furnace to increase at 2°C/min, so that the titanium hydride is decomposed slowly and uniformly; When the temperature rises to 700°C, keep it warm for 1-2 hours, so that the _H2 produced by the decomposition of titanium hydride fully reacts with the titanium powder in the blank to reach equilibrium; then raise the temperature to the sintering temperature at 5°C/min, and finally select the sintering temperature The temperature is 1250℃, and the sintering time is 1~3h.

The third stage, hydrogen removal. In this study, according to the (Ti-6Al-4V)-xH pseudo-binary phase diagram, the hydrogen removal temperatures were selected to be above 1000 °C, 900 °C, 850 °C and 750 °C. Remove hydrogen above 1000°C, turn on the high vacuum system to remove hydrogen at the end of sintering at 1250°C, and at the same time cool down to 1000°C at 5°C/min, and then cool with the furnace. The process temperature has been above 1000°C, and hydrogen can be easily removed in a relatively short period of time. Hydrogen is removed at 900°C, 850°C and 750°C, and the temperature is lowered to this temperature at 6.5°C/min from the end of sintering at 1250°C, and then the high vacuum system is turned on to remove hydrogen. Since the temperature is relatively low at this time, hydrogen is not easy to remove, and the hydrogen removal time is longer, the time is 3 hours, and then cooled with the furnace to obtain titanium six aluminum four vanadium titanium alloy products.

The hydrogen content of the alloy is lower than 0.0013% as determined by a carbon-sulfur analyzer CS600, which is below the safe value (0.002%).

The titanium alloy product of this example was tested by the drainage method, and the results are shown in Table 2. From the density results of hydrogen sintered Ti-6Al-4V alloy, it can be known that the density of hydrogen sintered alloy is higher than that of non-hydrogen sintered alloy, and the relative density of hydrogen sintered alloy reaches more than 98.5%.

Table 2

Tensile strength test: the tensile strength of titanium alloy products sintered in hydrogen atmosphere (code b-f) can reach up to 1178MP, as a comparison, the tensile strength of titanium alloy products without adding hydrogen atmosphere (code a) is only 943MP. (Note: The tensile test at room temperature is performed on the INSTRON 1346 electronic universal material testing machine for axially loaded static tension, reference standard: GB4338-1995, the tensile speed is 1mm/min, and each group is repeatedly tested for three samples.)

For specific comparison, see Table 3 for the tensile strength of Ti-6Al-4V after sintering at 1250°C×3h and dehydrogenation above 1000°C, and for the tensile strength of Ti-6Al-4V after sintering at 1250°C×3h and dehydrogenation at 750°C Table 4.

table 3

Table 4

The tensile test results show that the tensile strength of the hydrogenated sintered alloy is obviously higher than that of the hydrogenated alloy. Among them, the tensile strength of the alloy increased by about 6% after H removal at 1000 °C, from 943.99 MPa to 1010.91 MPa; after H removal at 750 °C, the tensile strength of the alloy increased by 13% to 25% and increased with the increase of hydrogen addition. increased from 943.99MPa to 1178.57, and finally stabilized.

In order to explore the effect of hydrogen removal temperature on the metallographic structure of the final alloy, hydrogen removal was carried out at 750°C, 850°C, 900°C and above 1000°C for comparison. The metallographic photos of the prepared powder metallurgy titanium alloys are shown in Figures 2-5 . The results show that the microstructure composition and morphology of the alloy can be controlled by controlling the dehydrogenation temperature of the hydrogen sintered Ti-6Al-4V alloy. When the dehydrogenation temperature is higher than the β-transus temperature of Ti-6Al-4V alloy at 1000℃, the microstructure and morphology of the alloy after dehydrogenation are not significantly affected by the amount of hydrogen added. When the hydrogen removal temperature is 900°C and 850°C, when it is lower than the β-transition temperature of Ti-6Al-4V alloy at 1000°C, but higher than the actual β-transition temperature of the alloy in hydrogen atmosphere at about 800°C, with the removal of hydrogen , the microstructure of the Ti-6Al-4V alloy begins to refine, forming a widmansite structure; when the dehydrogenation temperature is reduced to 750°C, which is lower than the actual β-transition temperature of the alloy in a hydrogen atmosphere of about 800°C, the alloy The phenomenon of tissue refinement is more obvious, forming a basket structure composed of fine α phase and β phase. And the degree of refinement is related to the original hydrogen addition. When the original hydrogen addition is high, such as when the hydrogen content is 0.54%, the Ti-6Al-4V alloy structure is finer than that when the original hydrogen addition is lower than 0.54%.

The true stress and true strain curves of the tensile test of the powder metallurgy titanium alloy prepared by removing H at 750 °C and 1000 °C are shown in Figures 6 and 7. It can be seen from the figure that the tensile strength of the alloy increases evenly with the increase of hydrogen addition, but the tensile strength of the alloy with the addition of H at 750 °C increases even more. With the increase of hydrogen addition, the yield plateau of the tensile curve gradually shortened; the strain also decreased with the increase of hydrogen addition.

Claims (10)

1. the preparation method of a powder metallurgy titanium alloy, it is characterised in that include following step:

With TiH₂Powder, Ti powder and other alloying elements are raw material, and mix homogeneously is the most compressing, wherein TiH₂Addition account for former The 3～25% of material gross mass；

Under high vacuum environment, heating makes TiH₂Decompose, be maintained at hydrogen atmosphere sintering；

Then 750～1000 DEG C are cooled to, evacuation dehydrogenation；

Finally, powder metallurgy titanium alloy product is obtained after cooling.

The preparation method of powder metallurgy titanium alloy the most according to claim 1, it is characterised in that other alloying elements described For comprising the metal dust of titanium alloy beta stable element.

The preparation method of powder metallurgy titanium alloy the most according to claim 2, it is characterised in that described in comprise titanium alloy beta steady The metal dust determining element is to have the metal dust of one or more elements in V, Fe, Mo, Nb, Ta, Ni and Mn.

The preparation method of powder metallurgy titanium alloy the most according to claim 3, it is characterised in that the subject alloy of preparation is Titanium six aluminum four V-Ti.

The preparation method of powder metallurgy titanium alloy the most according to claim 1, it is characterised in that TiH₂Addition account for raw material The 4.5～22.5% of gross mass.

6. according to the preparation method of the powder metallurgy titanium alloy described in claim 1,4 or 5, it is characterised in that cool to 750～ 900 DEG C, evacuation dehydrogenation.

The preparation method of powder metallurgy titanium alloy the most according to claim 1, it is characterised in that use poly-time compressing The ethanol solution of ethylene glycol is as releasing agent；High vacuum environment and evacuation refer to that vacuum is less than 1 × 10^-3Pa；Sintering shove charge Time, green compact are placed in boat, put a certain amount of pure titanium valve in boat both sides, and for adsorbing the air of residual, the boat that will be equipped with sample is put Enter in sintering furnace, and respectively place a porous stove plug in boat both sides.

8. according to Claims 1 to 5 and the preparation method of one of 7 described powder metallurgy titanium alloys, it is characterised in that agglomerant Skill includes: while evacuation, first rises to 120～160 DEG C, removes impurity and aqueous vapor in stove；It is heated to 250～350 DEG C afterwards, Keep 10～30min；Stop evacuation, be then heated to 600～800 DEG C, keep 1～2h, make titantium hydride decomposition reaction put down Weighing apparatus；It is heated to 1000～1250 DEG C of sintering followed by, keeps 1～3h.

The preparation method of powder metallurgy titanium alloy the most according to claim 8, it is characterised in that with 1.5～2.5 DEG C/min Speed be heated to 600～800 DEG C, be heated to 1000～1250 DEG C with the speed of 4～6 DEG C/min.

10. according to the preparation method of the powder metallurgy titanium alloy one of Claims 1 to 5,7 and 9 Suo Shu, it is characterised in that with 5 ～the speed of 8 DEG C/min cools to 900～750 DEG C, then evacuation keep 2～4h；Or evacuation simultaneously with 4～6 DEG C/ Min is cooled to 1000 DEG C.