Ti-V-Al基轻质记忆合金的马氏体相变与力学行为

发布时间：2018-08-31 11:14

【摘要】：Ti-V-Al合金密度低、冷热加工性能优异,是一种极具潜力的轻质记忆合金。但该合金马氏体相变热循环稳定性差,形状记忆效应有待提高。目前关于Ti-V-Al合金结构、相变和性能与合金成分及处理工艺之间的内在联系尚不清楚。论文优选合金成分并采用热机械处理提高形状记忆效应和马氏体相变的热循环稳定性,采用X射线衍射分析、透射电子显微分析、示差扫描量热分析及室温拉伸试验等方法系统研究了Al和Fe含量以及热机械处理对合金的组织结构、马氏体相变、力学行为和形状记忆效应的影响规律及机制。研究发现,固溶态Ti-13V合金室温组织由体心立方β相以及弥散分布的六方淬火ω相组成。Al添加抑制了淬火ω相的形成。当Al含量超过3at.%时,室温组织为单相α"马氏体,无ω相。冷轧退火后,Ti-13V-3Al合金室温组织由α"马氏体与少量六方α相组成。退火温度升高,α相减少,尺寸增大,分布均匀性变差。Al含量和热机械处理对Ti-V-Al合金的马氏体相变、力学行为和形状记忆效应有显著影响。马氏体逆转变温度随Al含量增加而降低。退火温度升高,冷轧Ti-13V-3Al合金的马氏体逆转变温度先降低后升高。Al增加和热机械处理提高了马氏体相变热循环稳定性。Al含量增加,固溶态Ti-V-Al合金的平台应力下降,抗拉强度、延伸率和可恢复应变先升高后降低,当Al含量为3at.%时均达最大值。随冷轧后退火温度升高,平台应力下降,延伸率增大,700°C退火时应力-应变曲线上出现了较明显的对应于马氏体变体再取向的应力平台,延伸率为17%。热机械处理显著改善了形状记忆效应,冷轧Ti-13V-3Al合金经700°C退火后,完全可恢复应变达7.5%。少量Fe添加大幅降低了Ti-V-Al合金的马氏体相变温度,提高了延伸率,改善了形状记忆效应。1at.%Fe添加使马氏体逆转变温度下降约250°C。当Fe含量为0.5at.%时,室温组织由α"马氏体与少量β相组成,Fe含量增加,α"马氏体数量减少,β相数量增多。当Fe含量为1.5at.%时,室温组织为单相β相,无α"马氏体。随着Fe含量增加,Ti-V-Al-Fe合金的平台应力升高,延伸率增大,可恢复应变先增大后减小。热机械处理显著提高了形状记忆效应,Ti-13V-3Al-1Fe合金冷轧后经750°C退火,预变形8%时,可恢复应变达7.3%;同时具有大延伸率,达35%。基于组织结构演化分析,揭示了适当Al和Fe添加及热机械处理改善形状记忆效应、提高马氏体相变热循环稳定性的微观机制。热机械处理细化了晶粒,引入了适当的位错,形成细小均匀的α相,以及Al和Fe的固溶强化,提高了母相强度,抑制了变体再取向过程中的塑性变形。同时,α相分割马氏体变体,使其尺寸变小,界面可动性增加。上述因素的共同作用有效改善了形状记忆效应。Al和Fe的增加及热机械处理抑制了ω相在热循环过程中的析出,提高了马氏体相变热循环稳定性。
[Abstract]:Ti-V-Al alloy is a kind of light memory alloy with low density and excellent cold and hot processing properties. However, the thermal cycling stability of martensite transformation is poor, and the shape memory effect needs to be improved. At present, the relationship between the structure, phase transformation and properties of Ti-V-Al alloy and the alloy composition and treatment process is not clear. In this paper, the composition of alloy is selected and thermo-mechanical treatment is used to improve the thermal cycling stability of shape memory effect and martensite transformation. X-ray diffraction analysis and transmission electron microscopy analysis are used. Differential scanning calorimetry (DSC) and tensile test at room temperature were used to study the effects of Al and Fe contents and thermo-mechanical treatment on the microstructure, martensite transformation, mechanical behavior and shape memory effect of the alloy. It is found that the microstructure of solid solution Ti-13V alloy at room temperature consists of bulk centered cubic 尾 phase and hexagonal quenched 蠅 phase with dispersion distribution. The addition of Al inhibits the formation of quenched 蠅 phase. When the content of Al exceeds 3 at.%, the microstructure is single phase 伪 "martensite without 蠅 phase at room temperature. The room temperature microstructure of Ti-13V-3Al alloy after cold rolling annealing consists of 伪 "martensite and a small amount of hexagonal 伪 phase." The increase of annealing temperature, the decrease of 伪 phase, the increase of size, the distribution uniformity, the content of Al and the thermo-mechanical treatment have significant effects on the martensite transformation, mechanical behavior and shape memory effect of Ti-V-Al alloy. The reverse temperature of martensite decreases with the increase of Al content. With the increase of annealing temperature, the reverse temperature of martensite of cold-rolled Ti-13V-3Al alloy decreases first and then increases. Al and the thermal mechanical treatment increase the thermal cycle stability of martensite transformation. The content of Al increases, and the plateau stress decreases and the tensile strength of Ti-V-Al alloy in solution state decreases. The elongation and recoverable strain increased first and then decreased, and reached the maximum when the content of Al was 3 at.%. With the increase of annealing temperature after cold rolling, the stress of platform decreases, and the elongation increases by 700 掳C. The stress-strain curve is obviously corresponding to the reorientation of martensite variants, and the elongation is 17.7%. The shape memory effect was significantly improved by thermo-mechanical treatment. After annealing at 700 掳C, the fully recoverable strain of the cold-rolled Ti-13V-3Al alloy was up to 7.5. The martensite transformation temperature of Ti-V-Al alloy was decreased by adding a small amount of Fe, the elongation was increased, and the shape memory effect was improved by 0.1 at.The addition of Fe reduced the temperature of martensite reversal by about 250 掳C. When the content of Fe is 0.5 at.%, the content of 伪 "martensite and a small amount of 尾 phase in room temperature structure increases, the amount of 伪" martensite decreases and the number of 尾 phase increases. When the content of Fe is 1.5at.%, the microstructure is single phase 尾 phase at room temperature, and there is no 伪 "martensite." With the increase of Fe content, the plateau stress of Ti-V-Al-Fe alloy increases, the elongation increases, and the recoverable strain increases first and then decreases. The shape memory effect of Ti-13V-3Al-1Fe alloy annealed at 750 掳C after cold rolling was significantly improved by thermo-mechanical treatment. When pre-deformed at 8 鈩，

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