自由锻Ti-Ni形状记忆合金的显微组织和超弹性

来源期刊:中国有色金属学报(英文版)2018年第3期

论文作者:Abdollah BAHADOR Esah HAMZAH Katsuyoshi KONDOH Tuty ASMA ABUBAKAR Farazila YUSOF Junko UMEDA Safaa N. SAUD Mustafa K. IBRAHIM

文章页码:502 - 514

关键词:形状记忆合金;超弹性;放电等离子烧结;自由锻

Key words:shape-memory alloy; superelasticity; spark-plasma sintering; free forging

摘    要:采用放电等离子烧结(SPS)法将元素钛粉和镍粉制备成Ti-51%Ni 形状记忆合金(SMAs)。研究目的是采用自由锻二次加工以提高SPS合金的性能。对自由锻前后合金的显微组织、相变温度和超弹性进行比较。结果表明,自由锻可以显著提高Ti-Ni 形状记忆合金的拉伸强度和形状记忆性能,自由锻后合金的韧性从6.8% 提高到了9.2%,超弹性的应变范围从5%增加到7.5%,应变恢复速率从72%提高到92%。Ti-51%Ni合金显微组织中含有立方奥氏体相(B2)基体、单斜马氏体相 (B19′)、第二相(Ti3Ni4,Ti2Ni 和TiNi3) 和氧化物相(Ti4Ni2O,Ti3O5)。自由锻后再经500 °C时效处理的最终样品的马氏体相变温度向高温方向偏移,这是由于Ti3Ni4相(透射电镜下可以观察到)的析出而导致基体中Ni含量的减少。总之,自由锻可以提高Ti-51%Ni形状记忆合金的超弹性和力学性能。

Abstract: Elemental titanium (Ti) and nickel (Ni) powders were consolidated by spark plasma sintering (SPS) to fabricate Ti-51%Ni (mole fraction) shape-memory alloys (SMAs). The objective of this study is to enhance the superelasticity of SPS produced Ti-Ni alloy using free forging as a secondary process. Products from two processes (with and without free forging) were compared in terms of microstructure, transformation temperature and superelasticity. The results showed that, free forging effectively improved the tensile and shape-memory properties. Ductility increased from 6.8% to 9.2% after forging. The maximum strain during superelasticity increased from 5% to 7.5% and the strain recovery rate increased from 72% to 92%. The microstructure of produced Ti-51%Ni SMA consists of the cubic austenite (B2) matrix, monoclinic martensite (B19′), secondary phases (Ti3Ni4, Ti2Ni and TiNi3) and oxides (Ti4Ni2O and Ti3O5). There was a shift towards higher temperatures in the martensitic transformation of free forged specimen (aged at 500 °C) due to the decrease in Ni content of B2 matrix. This is related to the presence of Ti3Ni4 precipitates, which were observed using transmission electron microscope (TEM). In conclusion, free forging could improve superelasticity and mechanical properties of Ti-51%Ni SMA.

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