【摘要】：Ti-V-Al合金密度低、冷熱加工性能優(yōu)異,是一種極具潛力的輕質(zhì)記憶合金。但該合金馬氏體相變熱循環(huán)穩(wěn)定性差,形狀記憶效應(yīng)有待提高。目前關(guān)于Ti-V-Al合金結(jié)構(gòu)、相變和性能與合金成分及處理工藝之間的內(nèi)在聯(lián)系尚不清楚。論文優(yōu)選合金成分并采用熱機(jī)械處理提高形狀記憶效應(yīng)和馬氏體相變的熱循環(huán)穩(wěn)定性,采用X射線衍射分析、透射電子顯微分析、示差掃描量熱分析及室溫拉伸試驗(yàn)等方法系統(tǒng)研究了Al和Fe含量以及熱機(jī)械處理對(duì)合金的組織結(jié)構(gòu)、馬氏體相變、力學(xué)行為和形狀記憶效應(yīng)的影響規(guī)律及機(jī)制。研究發(fā)現(xiàn),固溶態(tài)Ti-13V合金室溫組織由體心立方β相以及彌散分布的六方淬火ω相組成。Al添加抑制了淬火ω相的形成。當(dāng)Al含量超過3at.%時(shí),室溫組織為單相α"馬氏體,無ω相。冷軋退火后,Ti-13V-3Al合金室溫組織由α"馬氏體與少量六方α相組成。退火溫度升高,α相減少,尺寸增大,分布均勻性變差。Al含量和熱機(jī)械處理對(duì)Ti-V-Al合金的馬氏體相變、力學(xué)行為和形狀記憶效應(yīng)有顯著影響。馬氏體逆轉(zhuǎn)變溫度隨Al含量增加而降低。退火溫度升高,冷軋Ti-13V-3Al合金的馬氏體逆轉(zhuǎn)變溫度先降低后升高。Al增加和熱機(jī)械處理提高了馬氏體相變熱循環(huán)穩(wěn)定性。Al含量增加,固溶態(tài)Ti-V-Al合金的平臺(tái)應(yīng)力下降,抗拉強(qiáng)度、延伸率和可恢復(fù)應(yīng)變先升高后降低,當(dāng)Al含量為3at.%時(shí)均達(dá)最大值。隨冷軋后退火溫度升高,平臺(tái)應(yīng)力下降,延伸率增大,700°C退火時(shí)應(yīng)力-應(yīng)變曲線上出現(xiàn)了較明顯的對(duì)應(yīng)于馬氏體變體再取向的應(yīng)力平臺(tái),延伸率為17%。熱機(jī)械處理顯著改善了形狀記憶效應(yīng),冷軋Ti-13V-3Al合金經(jīng)700°C退火后,完全可恢復(fù)應(yīng)變達(dá)7.5%。少量Fe添加大幅降低了Ti-V-Al合金的馬氏體相變溫度,提高了延伸率,改善了形狀記憶效應(yīng)。1at.%Fe添加使馬氏體逆轉(zhuǎn)變溫度下降約250°C。當(dāng)Fe含量為0.5at.%時(shí),室溫組織由α"馬氏體與少量β相組成,Fe含量增加,α"馬氏體數(shù)量減少,β相數(shù)量增多。當(dāng)Fe含量為1.5at.%時(shí),室溫組織為單相β相,無α"馬氏體。隨著Fe含量增加,Ti-V-Al-Fe合金的平臺(tái)應(yīng)力升高,延伸率增大,可恢復(fù)應(yīng)變先增大后減小。熱機(jī)械處理顯著提高了形狀記憶效應(yīng),Ti-13V-3Al-1Fe合金冷軋后經(jīng)750°C退火,預(yù)變形8%時(shí),可恢復(fù)應(yīng)變達(dá)7.3%;同時(shí)具有大延伸率,達(dá)35%。基于組織結(jié)構(gòu)演化分析,揭示了適當(dāng)Al和Fe添加及熱機(jī)械處理改善形狀記憶效應(yīng)、提高馬氏體相變熱循環(huán)穩(wěn)定性的微觀機(jī)制。熱機(jī)械處理細(xì)化了晶粒,引入了適當(dāng)?shù)奈诲e(cuò),形成細(xì)小均勻的α相,以及Al和Fe的固溶強(qiáng)化,提高了母相強(qiáng)度,抑制了變體再取向過程中的塑性變形。同時(shí),α相分割馬氏體變體,使其尺寸變小,界面可動(dòng)性增加。上述因素的共同作用有效改善了形狀記憶效應(yīng)。Al和Fe的增加及熱機(jī)械處理抑制了ω相在熱循環(huán)過程中的析出,提高了馬氏體相變熱循環(huán)穩(wěn)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 偽 "martensite without 蠅 phase at room temperature. The room temperature microstructure of Ti-13V-3Al alloy after cold rolling annealing consists of 偽 "martensite and a small amount of hexagonal 偽 phase." The increase of annealing temperature, the decrease of 偽 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 擄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 擄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 擄C. When the content of Fe is 0.5 at.%, the content of 偽 "martensite and a small amount of 尾 phase in room temperature structure increases, the amount of 偽" 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 偽 "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 擄C after cold rolling was significantly improved by thermo-mechanical treatment. When pre-deformed at 8 鈩，

本文編號(hào)：2214809