CN110643851A - A kind of TiAl matrix composite material and its thermomechanical treatment method - Google Patents

Abstract

The invention relates to a TiAl-based composite material reinforced with in-situ self-generated TiB2 whiskers and a thermomechanical treatment method thereof. According to the calculation formula of B element addition control amount, an appropriate amount of B element is added to the TiAl alloy, so that the in-situ self-generated slender secondary eutectic reaction of L→β+TiB2 and L+β→α+TiB2 is formed in the TiAl alloy. While avoiding the generation of coarse granular primary TiB2 phase, a TiB2 whisker reinforced TiAl-based composite material can be prepared by ingot-casting metallurgical method. Then, the TiB2/TiAl composite material can be prepared into fine-grained rods or fine-grained cake blanks by wrapping hot extrusion or wrapping forging, and the slender TiB2 whiskers are broken into short whiskers, which are then treated by a special heat treatment process. , a fine-grained basket-like structure or a fine-grained full-sheet structure can be obtained. This TiB2/TiAl composite has high strength from room temperature to high temperature of 850 °C, and also has excellent room temperature plasticity, so it has a good application prospect in the aerospace field.

Description

A kind of TiAl matrix composite material and its thermomechanical treatment method

technical field

The invention belongs to the field of composite material preparation, relates to a TiAl matrix composite material and a thermomechanical treatment method thereof, in particular to an in-situ self-generated TiB2 whisker reinforced TiAl matrix composite material and a thermal processing and heat treatment method thereof.

Background technique

γ-TiAl-based intermetallic compound alloys have excellent properties such as low density, high specific strength, high specific modulus, high creep resistance, oxidation resistance, and combustion resistance, so they have attracted much attention as a new generation of high-temperature structural materials. Become a key material for a new generation of high thrust-to-weight ratio aero-engines.

The high temperature strength and high temperature durability of TiAl alloy can be improved by adding granular and fibrous reinforcement to TiAl alloy to prepare TiAl matrix composite material. However, since the room temperature plasticity of TiAl alloy is only 1-2%, when adding reinforcement to TiAl alloy, the room temperature plasticity will be further reduced, so it is often difficult to prepare large-sized TiAl matrix composites. The reinforcement and matrix of TiAl-based composites often undergo strong interfacial reactions during the preparation process, resulting in a significant decrease in the performance of the composites. For example, the powder metallurgy method is used to prepare SiC fiber reinforced TiAl matrix composites. Because the linear expansion coefficients of SiC fibers and TiAl alloys are too different, the thermal stress generated during the cooling process leads to cracks along the radial direction of the SiC fibers. Al ₂ O ₃ fiber reinforced TiAl composites were prepared by powder metallurgy method, and it was found that the interface reaction between Al ₂ O ₃ fibers and TiAl matrix was extremely violent. The thermal processing performance of powder metallurgy TiAl composites is very poor. During the hot deformation process, a strong concentration of stress and strain occurs near the reinforcement, resulting in the formation of cracks.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a TiAl-based composite material and a thermomechanical treatment method thereof, so as to solve the problem that the interface reaction between the matrix and the reinforcement of the current TiAl-based composite material or the stress concentration near the interface produces greater brittleness, and it is difficult to prepare high-strength plastic TiAl Technical issues of matrix composites.

In order to solve this technical problem, the technical scheme of the present invention is:

In one aspect, the present invention provides a TiAl-based composite material, the TiAl-based composite material contains by atomic percentage: 0.5%-1.5% B, 42%-45.5% Al, 1%-2% Cr, 3% ~6%Nb, 0.1%~0.5%Ta, 0~0.2%Si, 0%~2%C, the balance is Ti and inevitable impurities, of which oxygen content≤0.2wt%, nitrogen content≤0.03wt%, Hydrogen content≤0.02wt%;

The elastic modulus of the TiAl-based composite material is E≥150GPa;

The reinforcing body of the TiAl-based composite material is a dispersion-distributed TiB ₂ short whisker; the whisker length is less than or equal to 30 μm.

Preferably, the present invention provides a TiAl-based composite material, the TiAl-based composite material contains by atomic percentage: 45.5% Al, 0.5% B, 1.5% Cr, 4% Nb, 0.2% Ta, 0.2% Si , the remainder is Ti and inevitable impurities.

Preferably, the present invention provides another TiAl-based composite material, the TiAl-based composite material contains by atomic percentage: 44% Al, 0.8% B, 1% Cr, 4% Nb, 0.2% Ta, the remainder for Ti and inevitable impurities.

Preferably, the present invention provides a third TiAl-based composite material, the TiAl-based composite material contains by atomic percentage: 42% Al, 0.5% B, 1.5% Cr, 5% Nb, 0.2% Ta, the balance for Ti and inevitable impurities.

On the other hand, the present invention provides a kind of preparation method of TiAl composite material, and the steps are as follows:

Step 1: Ingot smelting: After mixing the raw materials uniformly according to the composition ratio, press it into an electrode block on a press; carry out three vacuum consumable smelting; obtain a composite material ingot with a diameter of Φ180mm～Φ300mm;

Step 2: Extrusion deformation: The obtained composite material ingot is subjected to wrapping and extruding deformation, heat insulating material is added between the wrapping and the composite material ingot, and the composite material bar is air-cooled or furnaced after the extrusion deformation. cool to room temperature;

Step 3: Homogenization annealing: heating the material obtained in the previous step to 1050°C to 1200°C, keeping the temperature for 6 to 48 hours, and then cooling to room temperature or directly heating up to the solution temperature;

Step 4: Solution heat treatment: the material after homogenization annealing is subjected to solution heat treatment in a two-phase region or a single-phase region;

Step 5: Aging heat treatment: The material after solution heat treatment is heated to 850°C to 950°C, kept for 2 to 8 hours, and then cooled to room temperature in the furnace.

The parameters in the first step: the smelting vacuum degree is lower than 5Pa, the smelting current is 3kA-6kA, and the smelting voltage is 23-27V.

The parameters of the second step: the sheath material is stainless steel, the extrusion deformation temperature is in the range of 1100°C to 1250°C, and the extrusion ratio is greater than 6:1.

The solid solution heat treatment in the two-phase region is the solid solution heat treatment in the γ+α two-phase region, and the details are as follows:

The heat treatment temperature is 1200℃～T _α -15℃, where T _α is the γ→α phase transition temperature; the temperature is kept for 0.5 to 6 hours, and then air-cooled or furnace cooled to room temperature.

The single-phase region solid solution heat treatment is the α single-phase region solid solution heat treatment, and the details are as follows:

The heat treatment temperature is T _α +5℃～T _α +20℃, where T _α is the γ→α phase transition temperature; keep for 5min～2 hours, and then air cooling, furnace cooling or oil quenching to room temperature

The step of isothermal forging is also included before the third step, specifically:

The composite material bar is heated to 1050℃～1250℃, the forging die is heated to 900℃～1150℃, the forging deformation rate is 0.001s ^-1 ～ 0.05s ^-1 , the forging deformation is ≥40%, and the forging is air-cooled after forging deformation Or oven cool to room temperature.

The beneficial effects of the present invention are:

(1) The reinforcement of TiAl matrix composites (TiB ₂ /TiAl) TiB ₂ whiskers are directly generated in situ from the liquid phase by the eutectic reaction, and there is no interface between the TiB ₂ whisker reinforcement and the TiAl alloy matrix response question.

(2) The in-situ self-generated TiB ₂ whiskers can significantly refine the casting structure, which is beneficial to improve the thermal processing performance of TiB ₂ /TiAl composites.

(3) After the thermal mechanical treatment of TiB ₂ /TiAl composites, the slender TiB ₂ whiskers are broken into short whiskers, and the dispersed short TiB ₂ whiskers can inhibit the grain growth, improve the plasticity, and increase the strength.

In the past, researchers usually added B as a trace element to TiAl alloys, and the addition amount was less than 0.2 at%, because it was worried that a large number of _TiB particles would lead to the reduction of room temperature plasticity. Since the addition amount of B in these TiAl alloys is relatively low, there is not enough TiB ₂ phase, and the strengthening effect is not obvious, so the strength of TiAl alloys cannot be effectively improved. Our research shows that when the B content is above 0.5at%, the grain size of TiAl alloy ingot can be reduced by an order of magnitude, and the upper limit of the B content can be controlled well, which can make TiB2 grow into _whiskers through eutectic reaction, without It grows into coarse granular TiB ₂ , and this slender, whisker-like TiB ₂ phase will be broken into short whiskers after subsequent thermal processing, which can significantly improve the high temperature strength of TiB ₂ /TiAl composites, and also has good properties. Plasticity at room temperature, so it has good engineering application prospects.

Description of drawings

In order to illustrate the technical solutions implemented by the present invention more clearly, the following will briefly explain the accompanying drawings that need to be used in the examples of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for those skilled in the art, other drawings can also be obtained from these drawings without creative effort.

Figure 1 shows the TEM morphology of TiB ₂ whiskers in TiB ₂ /TiAl composites;

Figure 2 shows the effect of B content on the grain size of TiAl alloy;

Figure 3 shows the TiB ₂ short whiskers in the composite material after hot extrusion deformation in Example 1.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The features of various aspects of the embodiments of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. The following description of the embodiments is only for a better understanding of the present invention by illustrating examples of the invention. The present invention is not limited to any specific arrangements and methods provided below, but covers all product structures, any improvements, substitutions, and the like of methods covered without departing from the spirit of the present invention.

In the various drawings and the following description, well-known structures and techniques have not been shown in order to avoid unnecessarily obscuring the present invention.

Example 1:

In the present invention, an appropriate amount of B element is added to the TiAl alloy, and slender TiB ₂ whiskers are generated in-situ on the TiAl alloy matrix by ingot smelting, and the TiB ₂ /TiAl composite material is prepared by subsequent thermomechanical treatment. . The TiB ₂ phase in the composite is composed of elongated secondary TiB ₂ whiskers grown in situ coupled with the matrix by L→β+TiB ₂ and L+β→α+TiB ₂ eutectic reactions during solidification of liquid metal (see Fig. 1), the whiskers have a width of about 0.5 μm and a length of several tens of microns.

The TiB ₂ /TiAl composite material of the present invention can be produced in the following manner:

The TiB ₂ /TiAl composite material of this Example 1 was prepared by the following steps:

The raw materials of TiB ₂ /TiAl composite material are zero-grade sponge titanium, A00-grade high-purity aluminum, metal Cr, Al-Nb master alloy, Al-Ta master alloy, Al-Si master alloy and Al-Ti-B master alloy. According to atomic percentage, it contains: 45.5% Al, 0.5% B, 1.5% Cr, 4% Nb, 0.2% Ta, 0.2% Si, and the rest is Ti.

After the raw materials are mixed uniformly, they are pressed into electrode blocks on a press. After the electrode block is welded, three times of melting are carried out in the vacuum consumable melting furnace. The melting vacuum degree is lower than 5Pa. ingot.

The TiB ₂ /TiAl composite material ingot is extruded and deformed by wrapping, the wrapping material is made of stainless steel, and heat insulating material is added between the wrapping and the TiB ₂ /TiAl composite material ingot, and the extrusion temperature range is 1200℃～1250℃. The extrusion ratio is 10:1, and the bar is air-cooled to room temperature after extrusion deformation. After hot extrusion deformation, the TiB ₂ phase in the TiB ₂ /TiAl composite material was broken into fine and dispersed short whiskers with an average length of 15 μm, which were arranged along the extrusion deformation direction, as shown in Figure 3.

The extruded bar is blanked and then subjected to isothermal die forging, the billet is heated to 1150 °C, the forging die is heated to 1000 °C, the forging deformation rate is controlled within the range of 0.001s ^-1 ~ 0.01s ^-1 , the forging deformation is 50%, and the forging After deformation, the forgings are air-cooled to room temperature.

The TiB ₂ /TiAl composite extruded bars or isothermal forgings are subjected to homogenization annealing treatment at 1150°C/16 hours/air cooling; then solution treatment at 1300°C/0.5 hours/air cooling; and finally a furnace at 900°C/6 hours Cold aging heat treatment.

Table 1 and Table 2 are the room temperature and 850°C tensile properties of Example 1, respectively. The room temperature plasticity of TiB ₂ /TiAl composites after thermomechanical treatment can reach more than 2%, the room temperature yield strength is more than 600MPa, and the yield strength at 850℃ remains above 400MPa.

Table 1 Room temperature tensile properties of Example 1

Table 2 Tensile properties at 850°C of Example 1

Example 2:

The TiB ₂ /TiAl composite material of Example 2 was prepared by the following steps:

The raw materials of the TiB ₂ /TiAl composite material in Example 2 are zero-grade sponge titanium, A00-grade high-purity aluminum, metal Cr, Al-Nb master alloy and TiB ₂ powder. By atomic percentage, it contains: 44% Al, 0.8% B, 1% Cr, 4% Nb, 0.2% Ta, and the rest is Ti.

After the raw materials are mixed uniformly, they are pressed into electrode blocks on a press. After the electrode block is welded, three times of melting are carried out in the vacuum consumable melting furnace. The melting vacuum degree is lower than 5Pa. ingot.

The TiB ₂ /TiAl composite material ingot is extruded and deformed by wrapping, the wrapping material is made of stainless steel, and heat insulating material is added between the wrapping and the TiB ₂ /TiAl composite material ingot, and the extrusion temperature range is 1200℃～1250℃. The extrusion ratio is 10:1, and the bar is air-cooled to room temperature after extrusion deformation.

The TiB ₂ /TiAl composite extruded bar was subjected to homogenization annealing treatment at 1150°C/16 hours/air cooling; then solution treatment at 1280°C/0.5 hours/air cooling; and finally furnace cooling at 900°C/6 hours aging heat treatment.

Tables 3 and 4 are the room temperature and 850°C tensile properties of Example 2, respectively. The room temperature plasticity of TiB ₂ /TiAl composites after thermomechanical treatment can reach 2%, the room temperature yield strength is above 550MPa, and the yield strength at 850℃ remains above 400MPa.

Table 3 Room temperature tensile properties of Example 2

Table 4 Tensile properties at 850°C of Example 2

Example 3:

The TiB ₂ /TiAl composite material of Example 3 was prepared by the following steps:

The raw materials of the TiB ₂ /TiAl composite material in Example 3 are zero-grade titanium sponge, A00-grade high-purity aluminum, metal Cr, Al-Nb master alloy and TiB ₂ powder. According to atomic percentage, it contains: 42% Al, 0.5% B, 1.5% Cr, 5% Nb, 0.2% Ta, and the rest is Ti.

After the raw materials are mixed uniformly, they are pressed into electrode blocks on a press. After the electrode block is welded, three times of melting are carried out in the vacuum consumable melting furnace. The melting vacuum degree is lower than 5Pa. The melting current is controlled within the range of 3kA~6kA according to the size of the ingot, and the melting voltage is 23~25V. ingot.

The TiB ₂ /TiAl composite ingot is extruded and deformed by wrapping. The wrapping material is made of stainless steel. Insulation material is added between the wrapping and the TiB ₂ /TiAl composite ingot. The extrusion temperature ranges from 1150°C to 1200°C. The extrusion ratio is 10:1, and the bar is air-cooled to room temperature after extrusion deformation.

The TiB ₂ /TiAl composite extruded rod was subjected to homogenization annealing treatment at 1100°C/16 hours/air cooling; then solution treatment at 1210°C/0.5 hours/air cooling; and finally, furnace cooling at 900°C/6 hours for aging heat treatment.

Table 5 and Table 6 are the room temperature and 850°C tensile properties of Example 2, respectively. The room temperature plasticity of TiB ₂ /TiAl composites after thermomechanical treatment can reach 2%, the room temperature yield strength is above 800MPa, and the yield strength at 850℃ is still above 500MPa.

Table 5 Room temperature tensile properties of Example 3

Table 6 Tensile properties at 850°C of Example 3

The present invention adopts the method of ingot metallurgy to prepare the in-situ self-generated TiAl-based composite material and has the following advantages:

(1) The reinforcement of TiAl matrix composites (TiB ₂ /TiAl) TiB ₂ whiskers are directly generated in situ from the liquid phase by the eutectic reaction, and there is no interface between the TiB ₂ whisker reinforcement and the TiAl alloy matrix response question. As shown in Fig. ₁ , the TEM image shows that the TiB whiskers are well bonded to the TiAl alloy matrix interface, and no interfacial reaction occurs.

(2) The in-situ self-generated TiB ₂ whiskers can significantly refine the casting structure, which is beneficial to improve the thermal processing performance of TiB ₂ /TiAl composites. As shown in Fig. 2, when the B content reaches 0.5 at%, the grain size of the TiB ₂ /TiAl composite decreases by an order of magnitude compared with that of the TiAl alloy without B addition.

(3) After the thermal mechanical treatment of TiB ₂ /TiAl composites, the slender TiB ₂ whiskers are broken into short whiskers, and the dispersed short TiB ₂ whiskers can inhibit the grain growth, improve the plasticity, and increase the strength.

The composite material has excellent high temperature strength and high temperature durability, as well as good room temperature plasticity. The working temperature of TiB ₂ /TiAl composite material can reach 850 ℃, which can be used to manufacture parts such as aero-engine blades, casings, diffusers, and heat-resistant parts of hypersonic aircraft

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited to this. Various equivalent modifications or substitutions should be included within the protection scope of the present invention.

Claims (10)

1. A TiAl-based composite material, characterized in that: the TiAl-based composite material comprises the following components in percentage by atom: 0.5 to 1.5 percent of B, 42 to 45.5 percent of Al, 1 to 2 percent of Cr, 3 to 6 percent of Nb, 0.1 to 0.5 percent of Ta, 0 to 0.2 percent of Si, 0 to 2 percent of C, and the balance of Ti and inevitable impurities, wherein the oxygen content is less than or equal to 0.2 percent by weight, the nitrogen content is less than or equal to 0.03 percent by weight, and the hydrogen content is less than or equal to 0.02 percent by weight;

the elastic modulus E of the TiAl-based composite material is more than or equal to 150 GPa;

the TiAl-based composite material has the reinforcing body of TiAl-based composite material which is TiB distributed in a dispersed way₂Short whiskers, wherein the length of the whiskers is less than or equal to 30 microns.

2. The TiAl-based composite material according to claim 1, characterized in that: the TiAl-based composite material comprises the following components in percentage by atom: 45.5% of Al, 0.5% of B, 1.5% of Cr, 4% of Nb, 0.2% of Ta, 0.2% of Si, and the balance of Ti and inevitable impurities.

3. The TiAl-based composite material according to claim 1, characterized in that: the TiAl-based composite material comprises the following components in percentage by atom: 44% of Al, 0.8% of B, 1% of Cr, 4% of Nb, 0.2% of Ta, and the balance of Ti and inevitable impurities.

4. The TiAl-based composite material according to claim 1, characterized in that: the TiAl-based composite material comprises the following components in percentage by atom: 42% of Al, 0.5% of B, 1.5% of Cr, 5% of Nb, 0.2% of Ta, and the balance of Ti and inevitable impurities.

5. A thermal mechanical treatment method of a TiAl-based composite material is characterized in that: the method of thermomechanical treatment using the TiAl-based composite material according to claim 1, comprising the steps of:

the method comprises the following steps: smelting of cast ingots: uniformly mixing the raw materials according to the component ratio, and pressing the mixture into an electrode block on a press machine; carrying out three times of vacuum consumable melting; obtaining a composite material ingot with the diameter of phi 180 mm-phi 300 mm;

step two: extrusion deformation: performing sheath extrusion deformation on the obtained composite material cast ingot, adding a heat insulating material between the sheath and the composite material cast ingot, and performing air cooling or furnace cooling on the composite material bar to room temperature after the extrusion deformation;

step three: homogenizing and annealing: heating the material obtained in the last step to 1050-1200 ℃, preserving heat for 6-48 hours, and then cooling to room temperature or directly heating to a solid solution temperature;

step four: solution heat treatment: carrying out solution heat treatment on the homogenized and annealed material in a two-phase region or a single-phase region;

step five: aging heat treatment: and heating the material subjected to the solution heat treatment to 850-950 ℃, preserving the heat for 2-8 hours, and then cooling the material to room temperature.

6. The method for thermomechanical treatment of TiAl-based composite materials according to claim 5, characterized in that: parameters in the first step are set as follows:

the smelting vacuum degree is lower than 5Pa, the smelting current is 3 kA-6 kA, and the smelting voltage is 23-27V.

7. The method for thermomechanical treatment of TiAl-based composite materials according to claim 5, characterized in that: and in the second step, the jacket material is stainless steel, the extrusion deformation temperature range is 1100-1250 ℃, and the extrusion ratio is more than 6: 1.

8. The method for thermomechanical treatment of TiAl-based composite materials according to claim 5, characterized in that: the two-phase region solution heat treatment in the fourth step is a gamma + alpha two-phase region solution heat treatment, which comprises the following specific steps:

the heat treatment temperature is 1200-T_α-15 ℃ of which T_αIs gamma → alpha phase transition temperature; keeping the temperature for 0.5 to 6 hours, andand then air cooling or furnace cooling is carried out to the room temperature.

9. The method for thermomechanical treatment of TiAl-based composite materials according to claim 5, characterized in that: in the fourth step, the single-phase zone solution heat treatment is alpha single-phase zone solution heat treatment, which comprises the following specific steps:

heat treatment temperature T_α+5℃～T_α+20 ℃ where T is_αIs gamma → alpha phase transition temperature; preserving the temperature for 5min to 2 hours, and then air cooling, furnace cooling or oil quenching to room temperature.

10. The method for thermomechanical treatment of TiAl-based composite materials according to claim 5, characterized in that: before the third step, isothermal forging is also included, specifically:

heating the composite material bar to 1050-1250 ℃, heating the forging die to 900-1150 ℃, and forging the deformation rate of 0.001s^-1～0.05s^-1And the forging deformation is more than or equal to 40 percent, and the forging is cooled in air or furnace to room temperature after the forging deformation.

Images