CN105483585A - Preparation method for titanium-aluminum alloy with excellent room-temperature ductility - Google Patents

Abstract

The invention discloses a method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity. Firstly, the TiAl-based alloy is subjected to homogenization heat treatment, and the TiAl-based alloy after the homogenization heat treatment is subjected to multi-directional isothermal forging deformation treatment, and the deformation temperature is 700- 1000°C, the deformation rate is 0.1-0.001s ^-1 , the deformation amount in a single step is 5-20%, and the deformation pass is 1-3 passes; after forging, the material is annealed and kept at 1150-1350°C for 3 Air cooling after -60min, so as to realize the control of the grain size and grain boundary structure of the TiAl-based alloy. The present invention uses the above deformation heat treatment steps to repeatedly process the material, which has a better grain boundary structure control effect, and can improve mechanical properties such as fracture strength and room temperature plasticity of the TiAl-based alloy.

Description

A preparation method of titanium-aluminum-based alloy with excellent room temperature plasticity

technical field

The invention relates to a technology in the field of high-temperature alloys, in particular to a method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity.

Background technique

Lightweight TiAl-based alloys with good high-temperature strength, high creep resistance, and good high-temperature oxidation resistance are considered to be important high-temperature structural materials in the future aerospace field. However, TiAl-based alloys are brittle at room temperature (poor plasticity below 700 °C, elongation 2%-3%), and the resulting poor processing ability of thermoplastic deformation has become the main obstacle to its application.

In recent years, in order to improve and enhance the room temperature plasticity of TiAl-based alloys, researchers at home and abroad have carried out a lot of research work and obtained rich results, but the room temperature plasticity index has not yet met the practical requirements. At present, grain refinement is considered to be the only effective means to simultaneously improve the strength and plasticity of TiAl-based alloys. Studies have shown that when the grain size of TiAl-based alloy is 50nm, its plasticity at room temperature reaches 50%, far exceeding the plasticity of conventional grain size, and it has superplasticity at room temperature. Therefore, how to obtain a fine and uniform microstructure in TiAl-based alloy samples is a very meaningful work for improving and enhancing its room temperature plasticity.

The large plastic deformation method is an effective way to refine the alloy grains. At present, the research on the plastic deformation of TiAl-based alloys focuses on the sheath forging and unidirectional isothermal compression processes. Sheath forging is the plastic deformation of TiAl-based alloys using the three-way pressure of stainless steel sheath materials, which reduces the tendency of TiAl-based alloys to crack. For rapid forging, although the sheath material can reduce the heat loss of the alloy during the forging process, it still cannot reach the constant temperature deformation condition, and the deformation rate is fast, and there is a tendency to crack; unidirectional isothermal compression is carried out in one direction under high temperature conditions Compression, under constant temperature or near constant temperature conditions, one direction can deform up to 90%, but after the deformation exceeds 60%, the material becomes cake-shaped, the shape changes greatly, and more deformation cannot be carried out, and it is difficult to process into a certain size. parts, and there are cracks. Therefore, although the sheath forging and unidirectional isothermal compression processes can plastically deform TiAl-based alloys with a certain amount of deformation, they cannot achieve large plastic deformation at constant temperature due to the limitations of deformation temperature, deformation rate, and deformation amount.

However, in fact, due to the intrinsic brittleness of TiAl-based alloys, the room-temperature plasticity of nanocrystalline and ultrafine-grained metal materials obtained simply by grain refinement is very low. Studies have shown that polycrystalline TiAl-based alloys hardly exhibit any plasticity before fracture, and intergranular brittle fracture always occurs. Therefore, starting from the intrinsic reasons, it is an effective way to improve the plasticity of the material under the premise of ensuring high strength by changing the internal microstructure state of the material. This patent uses grain boundary engineering methods to further improve the room temperature plasticity of TiAl-based alloys, control and optimize the distribution of grain boundary characteristics of TiAl-based alloy materials, especially to generate a large number of twins (deformation and annealing twins) inside the material, and obtain high strength. It is an effective way for alloy materials with comprehensive mechanical properties such as toughness, which can further improve the room temperature plasticity of TiAl-based alloys on the basis of grain refinement.

The reported grain refinement method of TiAl-based alloy is unidirectional compression deformation at higher temperature, so that the material undergoes dynamic recrystallization to refine the grain. Static recrystallization has been reported to control the grain size of the material. Most of the reported improvements to the room temperature plasticity of TiAl-based alloys start with alloying and grain refinement. The concept of TiAl-based alloys based on grain boundary engineering has not yet been seen. Multi-directional sub-isothermal forging deformation combined with subsequent annealing heat treatment is used to control and Reports on optimizing the GBCD of TiAl-based alloys, improving their room-temperature plasticity, and the interaction mechanism between fracture cracks and grain boundaries.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity.

The technical solution for realizing the purpose of the present invention is: a method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity, comprising the following steps:

The first step is to perform homogenization heat treatment on the TiAl-based alloy;

In the second step, the homogenized heat-treated TiAl-based alloy is subjected to multi-directional isothermal forging deformation treatment, the deformation temperature is 700-1000°C, the deformation rate is 0.1-0.001s ^-1 , and the deformation amount in a single step is 5-20% , the deformation pass is 1-3 passes;

In the third step, the deformed alloy is finally annealed, and air-cooled after heat preservation.

In the first step, the TiAl-based alloy is kept at 1150±20° C. for 45-50 hours and then cooled with the furnace for homogenization heat treatment.

In the third step, the annealing temperature is 1150-1350° C., and the holding time is 3-90 minutes.

Compared with the prior art, the present invention has the following significant advantages:

(1) A block material with excellent room temperature plasticity can be prepared by the present invention, and isothermal multidirectional forging is a plastic processing technology that heats the mold and the blank to the forging temperature and maintains this temperature to carry out large plastic deformation with low strain rate deformation , there is no cracking tendency, and the precision of forgings with small allowance or almost no allowance can be obtained, especially suitable for those hard-to-deform materials with narrow forging temperature range. Compared with severe plastic deformation methods such as ECAP and HPT, the outstanding advantages of the multi-directional sub-isothermal forging method are that the sample size is not limited, the equipment is simple and the efficiency is high.

(2) The material processed by the present invention is made into a standard metallographic sample, and after grinding, polishing, and electrolytic polishing, the grain boundary characteristic distribution of the material is tested by backscattering diffraction technology, and the ratio of special grain boundaries in the tissue reaches more than 45%. , the grain size was reduced to about 20 μm; comparing the sample after multi-directional isothermal forging and subsequent heat treatment with the homogenized heat treatment material, under the same compression test conditions, the compressive strength of the material increased by about 80%, and the ultimate compression rate increased About 20%, the room temperature plasticity and mechanical properties of TiAl-based alloys are improved.

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is a schematic diagram of the characteristic distribution of the grain boundaries of the γ-TiAl-based alloy of the present invention (a before treatment, b after treatment).

detailed description

The principle of the present invention: based on the principles of fine grain strengthening and grain boundary engineering, through multi-directional sub-isothermal forging combined with subsequent annealing heat treatment, the TiAl-based alloy simultaneously refines the grains and optimizes the grain boundary structure, thereby improving the plasticity of the TiAl-based alloy at room temperature.

The large plastic deformation method adopted in the present invention is a multi-directional isothermal forging combined with annealing heat treatment method, which repeatedly deforms the alloy in different axial directions, and achieves the purpose of large plastic deformation by accumulating each deformation amount, and then performs annealing heat treatment, The effect of refining grains and optimizing the distribution of grain boundary characteristics can be achieved at the same time. The outstanding advantages of this deformation method are that the sample size is not limited, the equipment is simple and efficient, large plastic deformation can be performed at relatively high temperature, and there is no risk of cracking.

The preparation method of the aluminum-based alloy of the present invention comprises the following specific steps:

1. First, homogenize the heat treatment on the γ-TiAl-based alloy. The homogenization heat treatment method is 1150±20°C for 45-50 hours and then cool with the furnace;

2. By adjusting different combinations of deformation parameters such as 700-1000°C forging temperature, 0.1-0.001s ^-1 forging rate, 5-20% single-step deformation and 1-3 deformation passes, etc., the alloy is multi-directional Isothermal forging deformation treatment (each pass deforms 3 faces of alloy forging);

3. Finally, the forged material is placed in a heat treatment furnace, the holding temperature is 1150-1350°C, the holding time is 3-60min, and air-cooled after holding.

In the following examples and comparative examples, the average grain size (μm) is used to represent the refinement effect of the grains inside the material, and the smaller the value, the better the refinement effect. The special grain boundary percentage (%) is used to represent the optimization effect of the material grain boundary structure, and the higher the value, the better the grain boundary optimization effect.

Example 1

Table 1 Test results of different forging temperatures

The isothermal multidirectional forging equipment Gleeble-3500 is used to deform the γ-TiAl-based alloy at different forging temperatures. The forging temperatures are 1000, 900, 850, 800, and 700°C, the forging rate is 0.01s ^-1 , and the deformation is performed in a single pass. The deformation amount of a single step is 20%, and the specific process is shown in Table 1. Subsequently, the γ-TiAl-based alloy after the deformation heat treatment was annealed at 1100° C. for 90 minutes, and air-cooled after the annealing. The average grain size and the proportion of low-energy CSL (coincidence site lattice) special grain boundaries in the sample after deformation heat treatment change with the forging temperature. The specific process parameters and test results are shown in Table 1.

Example 2

Table 2 Test results of different forging deformation rates

The isothermal multidirectional forging equipment Gleeble-3500 is used to deform the γ-TiAl-based alloy at different forging rates. The forging temperature includes 900 and 800 °C, the forging rate is 0.001, 0.01, and 0.1s ^-1 , single-pass deformation, simplex The step deformation is 20%, and then the γ-TiAl-based alloy after the deformation heat treatment is annealed at 1100° C. for 90 minutes, and air-cooled after the annealing. The average grain size and the proportion of low-energy CSL (coincidence site lattice) special grain boundaries in the sample after deformation heat treatment change with the change of forging temperature. The specific process parameters and test results are shown in Table 2.

Example 3

Table 3 Test results of different forging deformation passes

The isothermal multi-directional forging equipment Gleeble-3500 is used to deform the γ-TiAl based alloy in different deformation passes. The forging temperature includes 900 and 800 ℃, the forging rate is 0.001, 0.01, 0.1s ^-1 , and the deformation passes include one pass. and three passes, the single-step deformation amount is 20%, and then the γ-TiAl-based alloy after the deformation heat treatment is annealed at 1100° C. for 90 minutes, and air-cooled after the annealing treatment. The average grain size and the proportion of low-energy CSL (coincidence site lattice) special grain boundaries in the samples after deformation heat treatment vary with the forging temperature. The specific process parameters and test results are shown in Table 3.

Example 4

Table 4 Test results of different forging deformation steps and deformation amounts

The isothermal multi-directional forging equipment Gleeble-3500 is used to deform the γ-TiAl-based alloy in different deformation steps. There are five different deformation processes, of which there are three first pre-deformation heat treatment processes, namely no pretreatment and 1200 °C /0.001s ^-1 single step 20% single pass deformation without annealing heat treatment and 800°C/0.01s ^-1 single step 20% single pass deformation + 1300°C -5min annealing heat treatment. After the pre-deformation heat treatment, a single-pass multi-directional forging compression extrusion or unidirectional compression deformation treatment is performed, and then the γ-TiAl-based alloy after the deformation heat treatment is annealed at 1300 ° C for 5 minutes, and air-cooled after the annealing treatment. The average grain size and the proportion of low-energy CSL (coincidence site lattice) special grain boundaries in the samples after deformation heat treatment vary with the forging temperature. The specific process parameters and test results are shown in Table 4.

Example 5

Table 5 Test results of different subsequent annealing heat treatment processes

Using the isothermal multi-directional forging equipment Gleeble-3500, the γ-TiAl-based alloy is firstly subjected to 800°C 0.01s ^-1 single-step 20% single-pass deformation + 1300°C-5min annealing heat treatment pretreatment, and one-way isothermal treatment after pre-deformation heat treatment Compression deformation treatment, followed by annealing heat treatment of different annealing heat treatment processes on the γ-TiAl base alloy after deformation heat treatment, and air cooling after annealing treatment. The average grain size and the proportion of low-energy CSL (coincidence site lattice) special grain boundaries in the samples after deformation heat treatment vary with the forging temperature. The specific process parameters and test results are shown in Table 5.

comparative example

Table 6 Test results of treated material and base metal

In order to compare the differences in microstructure and properties between the processed material and the original material, the raw material was subjected to 1150°C-48h homogenization annealing heat treatment, and the material subjected to deformation heat treatment was tested for room temperature compression performance. 0.001s ^-1 , the fracture strength is taken as the compressive strength, and the compressibility at fracture is the ultimate compressibility, which are respectively the strength index and room temperature plasticity index of the material. The test results are shown in Table 6.

The material processed by the present invention is made into a standard metallographic sample, and the grain boundary structure of the material is tested by backscattered electron diffraction technology after grinding, polishing, and electrolytic corrosion. The proportion of special grain boundaries in the structure can be as high as 45%, and the average grain When the particle size is reduced to below about 20 μm, it can be found that under the same compression test conditions, the room temperature strength and room temperature plasticity of the thermomechanical treated material are significantly improved.

Figure 1(a) shows the distribution of grain boundary characteristics in the raw material structure, in which the proportion of special grain boundaries (Σ≤29) is 36.3%, and Figure 1(b) shows the grain boundary in the material structure treated by the above method Characteristic distribution, in which the proportion of special grain boundaries is 41.4%. The black lines in the figure represent high-energy free grain boundaries, and the gray lines represent low-energy ΣCSL grain boundaries.

Claims (3)

1. A method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity, characterized in that, comprising the following steps: The first step is to perform homogenization heat treatment on the TiAl-based alloy; In the second step, the homogenized heat-treated TiAl-based alloy is subjected to multi-directional isothermal forging deformation treatment, the deformation temperature is 700-1000°C, the deformation rate is 0.1-0.001s ^-1 , and the deformation amount in a single step is 5-20% , the deformation pass is 1-3 passes; In the third step, the deformed alloy is finally annealed, and air-cooled after heat preservation. 2. The method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity as claimed in claim 1, wherein in the first step, the TiAl-based alloy is kept at 1150±20° C. for 45-50 hours and then homogenized with furnace cooling heat treatment. 3. The method for preparing a titanium-aluminum-based alloy with excellent room temperature plasticity as claimed in claim 1, wherein in the third step, the annealing temperature is 1150-1350° C., and the holding time is 3-90 minutes.