CN112481567B - Processing method for improving strength and plasticity of copper-containing titanium alloy - Google Patents
Processing method for improving strength and plasticity of copper-containing titanium alloy Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
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- C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
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Abstract
The invention provides a processing method for improving the strength and plasticity of a copper-containing titanium alloy. Firstly, heat treatment is carried out on the copper-containing titanium alloy above the transformation point temperature of the copper element, and then the copper-containing titanium alloy is rapidly cooled to room temperature. Then low-temperature heat treatment is carried out, then cold deformation is carried out, and finally medium-temperature heat treatment is carried out on the copper-containing titanium alloy. By the process, grain refining, strengthening and toughening, dispersion strengthening and precipitation strengthening can be simultaneously realized, the strength of the obtained material is improved by 10-50% compared with the strength of the material obtained by the conventional method, the plasticity is still not less than 10%, and the method can be widely applied to the production of various copper-containing titanium alloy sectional materials. The method organically combines the heat treatment and the deformation process, not only can obviously refine the matrix structure of the titanium alloy to reach the micron or submicron level, but also can obviously refine the precipitated titanium-copper precipitated phase to reach the submicron or nanoscale level. In addition, the alpha-Ti phase precipitated in the phase transformation process can be refined, so that the effects of high strength and high plasticity are achieved.
Description
Technical Field
The invention belongs to the field of manufacturing of copper-containing titanium alloy profiles, and relates to a processing method for remarkably improving the strength and plasticity of a copper-containing titanium alloy.
Background
Titanium alloys, including titanium copper alloys, are widely used in industrial fields, particularly chemical, marine and biological materials, due to their excellent corrosion resistance. However, in the use process, in addition to the good corrosion resistance, the characteristics of high strength and high plasticity are desired.
The copper-containing titanium alloy is a titanium alloy that can be strengthened by dispersion strengthening and second phase strengthening of a copper-containing phase. To increase its strength, heat treatment processes involving solid solution and ageing are often carried out to precipitate a large number of second phases containing copper, such as Ti, in a dispersed manner in the titanium alloy2The Cu phase has a strengthening effect. In the process, the grain size of the fine matrix obtained by the previous processing procedure is obviously increased due to the high treatment temperature of the solution treatment, so that the plasticity and the yield strength of the alloy are reduced. Therefore, the conventional processing technology is adopted to obtain high strength, and meanwhile, the plasticity of the alloy is obviously reduced, so that the titanium alloy with both high strength and high plasticity cannot be obtained.
How to fully develop the potential of the copper-containing titanium alloy becomes a difficult problem in developing titanium alloy with high strength and high plasticity.
Disclosure of Invention
The strengthening ways of the alloy material mainly comprise solid solution strengthening, phase change strengthening, dispersion strengthening, second phase strengthening, fine grain strengthening and the like. According to the rules, the high strength can be obtained by increasing the solid solution content of alloy elements in the titanium alloy in a matrix, or increasing the proportion of a high-strength phase in the alloy in a phase change mode, or forming a large amount of nanoscale dispersed phases in the alloy matrix, or increasing the volume fraction of a high-strength second phase or refining the grain size of the matrix. The plasticity of the alloy generally becomes worse as the alloy is strengthened, but becomes better as the grain size of the alloy is refined. Therefore, obtaining fine grain size while obtaining various reinforcements is an effective way to improve the strength and plasticity of alloy materials including titanium alloys.
For the existing titanium alloy, high strength and high plasticity are generally realized by phase change strengthening and fine grain strengthening, for example, the deformation is increased, the fine grain effect is obtained, and not only high strength but also high plasticity can be obtained. The most typical example is a large deformation or equal channel angular extrusion process, and the phase transformation strengthening effect is achieved by performing heat treatment in a two-phase region to obtain fine alpha-Ti.
The solid solubility of copper element in titanium matrix is changed greatly, for example, the maximum solid solubility in beta-Ti can reach 30%, and the solid solubility at room temperature is very small and less than 1%. Thus, it is possible to precipitate a finely dispersed copper-containing second phase, such as Ti, in a copper-containing titanium alloy by a solution and aging process2And the Cu phase achieves the effects of dispersion strengthening and second phase strengthening, and the strength of the copper-containing titanium alloy is obviously improved. This is different from existing titanium alloys such as pure titanium, Ti-6Al-4V, etc. In order to achieve high strength and antibacterial effect, the copper-containing second phase reinforced titanium alloy must be first supersaturated and dissolved in a titanium alloy matrix, and then artificially aged to precipitate copper as a fine copper-containing phase, thereby achieving the effects of improving strength and imparting antibacterial properties. However, with the conventional solution-aging heat treatment process, although the aging precipitation of the second phase of titanium and copper can significantly improve the strength of the titanium alloy, the grain size of the matrix is significantly increased during the solution treatment, and the plasticity of the alloy is significantly reduced. Thus adopting appropriate additionThe technology ensures that the grain size of the matrix is not increased or is rarely increased while various strengthening measures are ensured, and is a basic idea for improving the strength and the plasticity of the titanium alloy.
The invention aims to provide a processing method capable of simultaneously improving the strength and the plasticity of a copper-containing titanium alloy. The method is divided into four steps.
First, high temperature heat treatment. And (3) preserving the temperature of the copper-containing titanium alloy after the primary processing for a period of time above the phase transition point temperature of the copper element, and then rapidly cooling to room temperature. The copper element in the alloy is completely dissolved in the titanium matrix to form a supersaturated solid solution. The transformation point temperature of the copper element refers to the temperature at which the copper element in the copper-containing titanium alloy is dissolved in the titanium matrix. This temperature varies with the copper content of the alloy, decreasing with increasing copper content when the copper content of the alloy is less than 7 wt.%, and increasing with increasing copper content when the copper content of the alloy is between 7-17.2 wt.%. Generally, the solid solution temperature of a titanium-copper binary alloy system is in the range of 790-1250 ℃. The temperature of the transformation point is different due to different alloy components, so the temperature of the transformation point of the copper element of the titanium alloy needs to be determined according to the copper content of the alloy, and then the temperature of high-temperature heat treatment is selected. The higher the high-temperature heat treatment temperature is, the higher the speed of dissolving the copper element in the titanium matrix is, and the higher the solid solubility of copper in the titanium matrix is. However, the high heat treatment temperature also brings about the remarkable increase of the grain size of the titanium alloy, so that the lower the heat treatment temperature is, the better the heat treatment temperature is on the premise of ensuring the complete solid solution of the copper element. The length of the holding time also depends on the copper content of the alloy, the amount and size of the copper-containing phase and the size of the component. The higher the copper content, the greater the number and size of the copper-containing phases, and the greater the thickness of the component, the longer the time required for complete dissolution of the copper element in the titanium matrix and, consequently, the longer the holding time. After the high-temperature solution heat treatment, the titanium alloy needs to be rapidly cooled to room temperature to ensure that the copper element is completely dissolved in the titanium alloy matrix in a solid solution atom form. The cooling means include water cooling and air cooling.
Specifically, when the copper content in the titanium alloy is not more than 17.2 percent by weight, the temperature of the high-temperature solution heat treatment is controlled at 790-1200 ℃, and the heat preservation time is not more than 24 hours.
Further, when the copper content in the titanium alloy is not more than 7 weight percent, the temperature of the high-temperature heat treatment is controlled at 790-1200 ℃, and the heat preservation time is not more than 16 hours.
And secondly, low-temperature heat treatment. And (3) preserving the heat of the copper-containing titanium alloy subjected to the high-temperature heat treatment at a low temperature for a period of time, and then cooling to room temperature. The rapidly cooled high-temperature heat treatment titanium alloy component has a lot of stress caused by cooling in the component, the stress cannot be released slowly, and a crack source can be formed in the subsequent low-temperature deformation process, so that deformation and cracking are caused. In addition, after high-temperature heat treatment and rapid cooling, the copper element is supersaturated and dissolved in the titanium matrix, and is in an unstable state. The low-temperature heat treatment has a high temperature and a high possibility of precipitating the copper-containing second phase although the stress is eliminated quickly. The presence of the copper-containing second phase prevents subsequent cold deformation of the titanium alloy, and therefore the low temperature heat treatment avoids precipitation of the copper-containing second phase. The duration of the low-temperature heat treatment also depends on the complexity of the alloy component, and the more complex the alloy component is, the greater the stress formed during the rapid cooling process, and the longer the low-temperature heat treatment duration is. Under the condition of ensuring that no copper-containing phase is precipitated, the time of low-temperature heat treatment is properly prolonged, and the residual stress in the component can be eliminated to the maximum extent.
In addition, the low-temperature heat treatment can also adjust the distribution of copper in the alloy in the matrix, so that the copper is enriched at certain special parts, but a copper-containing second phase is not precipitated, the good low-temperature deformation performance of the alloy is ensured, the low-temperature deformation process is facilitated, meanwhile, the local deformation is accelerated, the refining effect is increased, and the fine grain size is obtained.
Generally, the low temperature heat treatment temperature does not exceed 400 ℃ and the treatment time does not exceed 72 hours.
In some cases, when the test piece is small and the cooling speed is low, the stress of the test piece does not influence the subsequent cold deformation; or when the copper content is higher, the local enrichment of the copper element already occurs in the high-temperature heat treatment and cooling processes, and at the moment, the low-temperature heat treatment process step can be omitted, so that the implementation of the patent cannot be influenced.
And thirdly, low-temperature deformation treatment. And (3) carrying out low-temperature deformation on the copper-containing titanium alloy subjected to high-temperature solution treatment and low-temperature heat treatment, and fully refining the matrix structure to form micron, submicron or nanometer grain sizes. The larger the amount of deformation, the lower the deformation temperature, and the finer the grain size formed. However, some titanium alloys have poor low-temperature deformability, and the cold deformation temperature can be appropriately increased to reduce the deformation amount each time. The low-temperature deformation can meet the requirement of deformation amount by adopting one-time large deformation and can also meet the requirement of deformation amount by multi-pass deformation.
Generally, the temperature of cold deformation does not exceed 400 ℃ and the deformation is not less than 10%.
Furthermore, the cold deformation temperature is not more than 200 ℃, and the deformation is not less than 30 percent
Further, the cold deformation temperature does not exceed room temperature.
Further, the amount of deformation is preferably 30 to 90%.
Fourthly, medium temperature heat treatment. In the process, the copper-containing second phase is rapidly precipitated from the matrix as a nano phase, so that the dispersion strengthening effect is achieved, and meanwhile, the matrix keeps the characteristic of fine grains. The mesophilic heat treatment temperature and time affect the rate of precipitation and subsequent growth of the copper-containing phase. The higher the heat treatment temperature is, the faster the copper-containing phase is precipitated, the greater the tendency of precipitated phase growth is, even the growth of crystal grain size and the coarsening of precipitated phase can be caused, and the dispersion strengthening effect is weakened; the grain size grows and the plasticity of the alloy is reduced. The longer the heat treatment, the greater the amount of copper-containing phase precipitated, the better the strengthening effect, but the higher the temperature and the longer the time, the coarsening of the grain size may also be caused, reducing the strength and plasticity.
Generally, the medium temperature heat treatment temperature is not more than 700 ℃, and the holding time is not more than 48 hours.
Furthermore, the temperature of the medium-temperature heat treatment is not more than 500 ℃, and the heat preservation time is not more than 24 hours.
After the above treatment, the copper-containing titanium alloy not only has micron, submicron or nanometer size crystal grain size (the submicron crystal grain size of the fine-grained titanium alloy of example 3 is shown in fig. 1), but also has high-density, dispersed and distributed nanometer-level copper-containing precipitated phase (the nanometer copper-containing precipitated phase in the copper-containing titanium alloy of example 3 is shown in fig. 2). The micron, submicron or nanometer-scale matrix grain size not only ensures high strength and high plasticity of the titanium alloy, but also the micron and nanometer-scale copper-containing precipitated phase can remarkably strengthen the titanium alloy, thereby obtaining the copper-containing titanium alloy with high strength and high plasticity.
The process is suitable for all copper-containing titanium alloys, including but not limited to copper-containing binary titanium alloys, copper-containing ternary titanium alloys, copper-containing quaternary titanium alloys, and copper-containing quinary titanium alloys.
The copper content in the copper-containing titanium alloy is not more than 40 percent by weight.
Further, the copper content in the copper-containing titanium alloy is not more than 17.2% by weight.
Still further, the optimum copper content is not more than 7% by weight.
The invention has the beneficial effects that:
the invention adds low temperature heat treatment and low temperature deformation treatment process in the conventional solid solution aging heat treatment system, so that the copper-containing titanium alloy has the dispersion strengthening effect generated by micron, submicron or nanometer copper-containing phase and has good plasticity of the matrix ensured by the grain size of micron, submicron or nanometer matrix, therefore, the fine crystal strengthening and dispersion strengthening are combined together, so that the strength of the titanium alloy is obviously improved while the plasticity is not reduced.
Drawings
FIG. 1 shows the fine grained titanium alloy submicron grain size of example 3;
fig. 2 shows a precipitated phase of nano-copper in the copper-containing titanium alloy of example 3.
Detailed Description
Example 1
The copper-containing titanium alloy is smelted according to the requirement of component design, and can be smelted by methods such as a consumable arc furnace, induction smelting or a consumable electrode and the like to prepare an ingot. In order to achieve uniform alloy components, multiple times of smelting can be adopted, and the macroscopic uniformity of the alloy components is ensured. And then, deforming the experimental titanium alloy ingot into a bar or a plate by adopting a hot rolling deformation process. In this embodiment, a plate material deformed to a certain thickness is selected as the original base material.
Then, the original base material was processed differently according to the process parameters described in table 1 to form an experimental material. The tensile mechanical property is tested on a calibrated drawing machine according to the national standard GB/T228.1-2010 metal material tensile test method, and the drawing speed is 1 mm/min. The tensile yield strength, tensile strength and elongation at break were then calculated according to the standard. The amount of deformation in the test is defined as the percentage of the reduction in thickness of the sheet material to the original thickness. If the processing technology is abbreviated as follows: treating at the high temperature of 900 ℃ for 1h, rapidly cooling by water, treating at the low temperature of 200 ℃ for 10h, then performing low-temperature deformation at the room temperature, wherein the deformation is 20%, and finally performing medium-temperature heat treatment at the temperature of 500 ℃ for 24h, which is abbreviated as: 900 ℃/1h + water cooling +200 ℃/10h + room temperature deformation 20% +500 ℃/24 h.
The mechanical properties of several titanium alloy materials under conventional processing techniques are given in table 1.
TABLE 1 processing and tensile mechanical Properties of Cu-containing titanium alloys
Claims (8)
1. A processing method for improving the strength and the plasticity of a copper-containing titanium alloy is characterized by comprising the following steps:
firstly, high-temperature heat treatment;
heating the copper-containing titanium alloy to a temperature above the phase transformation point, preserving heat to realize complete solid solution of a copper phase in a matrix, and then rapidly cooling to room temperature; the copper content in the copper-containing titanium alloy is not more than 40% by weight; the heat preservation temperature is 790-1200 ℃, and the heat preservation time is not more than 48 h;
secondly, low-temperature heat treatment;
carrying out heat treatment on the copper-containing titanium alloy subjected to the first-step high-temperature heat treatment at a low temperature, eliminating stress formed in the rapid cooling process of the high-temperature heat treatment, and simultaneously adjusting the distribution of copper elements in the alloy; wherein the low-temperature heat treatment temperature is not more than 400 ℃, and the treatment time is not more than 72 h;
thirdly, low-temperature deformation treatment;
refining the matrix by adopting a low-temperature deformation method; the deformation temperature is not more than 400 ℃, and the deformation is not less than 10%;
fourthly, medium temperature heat treatment;
the copper-containing second phase is rapidly precipitated from the matrix in a submicron or nanometer phase, so that the dispersion strengthening effect is achieved, and meanwhile, a fine crystalline structure is kept, so that the alloy has good plasticity and strength; the treatment temperature is not more than 700 ℃, and the heat preservation time is not more than 48 h.
2. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy according to claim 1, wherein the copper content of the copper-containing titanium alloy is not more than 17.2 percent by weight.
3. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy according to claim 1, wherein the copper content of the copper-containing titanium alloy is not more than 7 percent by weight.
4. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy as recited in claim 2, wherein the temperature of the high-temperature heat treatment is controlled to be 790-1200 ℃, and the holding time is not more than 24 h.
5. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy as recited in claim 3, wherein the temperature of the high-temperature heat treatment is controlled to 790-1200 ℃, and the holding time is not more than 16 h.
6. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy according to claim 1, wherein the low-temperature deformation is carried out at a deformation temperature of not more than 200 ℃ and a deformation amount of not less than 50%.
7. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy according to claim 1, wherein the low-temperature deformation is carried out, the cold deformation temperature is not higher than room temperature, and the deformation amount is 30-90%.
8. The processing method for improving the strength and the plasticity of the copper-containing titanium alloy according to claim 1, wherein the temperature of the medium-temperature heat treatment is not more than 500 ℃, and the holding time is not more than 24 hours.
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