Cu-Al-Fe三元合金的bcc相分离组织控制及其高温形状记忆特性研究

In the past decades, Cu-Al based high-temperature shape memory alloys (HTSMAs) were widely researched due to its low cost, good conductivity and simple production process, comparing with other many HTSMAs. However, up to date, in the case of polycrystalline Cu-Al based HTSMAs, their poor ductility and thermal stability are the biggest obstacles for its further applications. In the previous investigations of Cu-Al based HTSMAs, the trial-and-error method was mainly adopted to improve their ductility and thermal stability with a large amount of experimental works. Since phase diagram has been recognized as an important tool in the design and applications of metal materials, this method is widely used because it can significantly decrease the amount of experimental works. The purpose of this research is to investigate the influence of microstructural control of bcc structured phase separation on the high-temperature shape memory properties of Cu-Al-Fe alloys. Firstly, based on several bcc-type miscibility gap with different order degree in ternary Cu-Al-Fe system, including A2+A2, A2+B2 and B2+B2, the compositions of two-phase Cu-Al-Fe HTSMAs with different order degree will be designed. Then the volume fracrions of each phase in two-phase alloys can be calculated using CALPHAD(calculation of phase diagrams) method. Furthermore, the influence mechanism of microstructural control of bcc structured phase separation with different order degree on ductility, thermal stability and high-temperature shape memory properties of Cu-Al-Fe HTSMAs will be uncovered.The present results may be useful for developing new low cost Cu-Al-Fe HTSMAs with good properties. It may also provide important information for the improvement of ductility, thermal stability and shape memory properties for some brittle shape memory alloys.

Cu-Al基高温形状记忆合金因其生产成本低，导电导热性能优异和生产工艺简单，因而其应用前景十分诱人。但是，其塑性和热稳定性是制约该合金发展和应用的瓶颈，至今仍无较好的解决办法。本项目采用材料的成分设计、组织控制和性能研究相结合的方法。以Cu-Al-Fe三元系相图为基础，巧妙地利用Cu-Al-Fe三元系中bcc相的有序无序转变及其两相分离现象所形成的不同有序度的bcc两相分离区域（A2+A2、A2+B2和B2+B2），优化设计具有不同有序度的bcc双相Cu-Al-Fe高温形状记忆合金。并拟通过相图的热力学计算，对双相合金中各相的体积分数进行准确预测，从而实现对合金微观组织的控制。在此基础上，详细研究不同有序度的bcc两相组织对合金的塑性、热稳定性和高温形状记忆特性的影响机理。通过本项目的研究，可望获得综合性能优异的低成本新型Cu-Al-Fe高温形状记忆合金。

Cu-Al基形状记忆合金因具有成本低廉和制造工艺简单等优点吸引着大批学者的兴趣，但是Cu-Al基合金的多晶脆性，较差的热稳定性和形状记忆效应阻碍了它的发展。因此在本项目中，我们基于Cu-Al-Fe体系中的BCC相分离现象，详细研究了Cu-Al-Fe基形状记忆合金在不同热处理条件下的微观组织结构演变、可逆马氏体相变行为、力学以及形状记忆性能，较好地完成了本项目的计划研究内容。具体的研究结果如下：.（1）详细研究了Cu84-xAl11+xFe5 (x = 0，1，2, wt.%)高温形状记忆合金的微观组织结构、马氏体相变、力学及形状记忆性能。在该体系中，我们观察到了明显的富Cu相和富Fe相的BCC相分离现象。研究结果表明：适量的Fe的添加（x = 1）可以抑制Cu-Al系在时效过程的γ1(Cu9Al4)相的析出，因而可以显著改善合金形状记忆效应。x = 1合金在时效后的形状回复应变和回复率基本等同于淬火状态，其回复应变随着真实应变的增加而逐渐增加，达到约为1.6%的最大值。.（2）在Cu84Al10Fe6 合金中添加Ta或Nb，都将导致合金析出富Ta和富Nb相。 上述合金在时效后，由于合金中析出大量塑性α(Cu)相，因此合金的塑性得到显著改善，但是此时合金的形状记忆效应基本消失。.（3）本项目基于Cu-Ta体系的相分离现象，在Cu-Al合金中添加适量的Ta，发展了一种新的Cu86Al12Ta2高温形状记忆合金。拉伸结果显示：合金的形状记忆效应随着真实应变的增加逐渐增加，并达到最大值3.2%。合金在预应变小于2.5%时具有100%的形状回复率，其后随着真实应变的增加，合金的形状回复率随之逐渐减少。.（4）本项目发现了一种新颖的Cu-Al-Fe-Mn形状记忆合金，它的应力应变和形状回复行为与传统的形状记忆合金不同。一种“稳定的应力诱发马氏体”现象存在，其次一个巨大的9%的卸载应变可以在加热过程中瞬间完全回复，并伴随着样品的“跳跃”，显示出极度“温度敏感”性。这种Cu-Al-Fe-Mn合金具有发展成为新颖的温度敏感型金属功能材料的巨大潜力。.（5）本项目为了发展更多的高温形状记忆合金，也研究了双相Ni-Mn-Ga/In基高温形状记忆合金。