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研究了不同Al含量和Ni/(Ti+ Al)原子比对NiTi-Al基合金显微组织的影响.结果表明:在Ni50 Ti50-xAlx(x=0,5,7和9)合金体系中,当Al≤7 at％时,合金的微观组织并未发生明显的变化,均由NiTi基体相和分布于晶界处的Ti2Ni+ NiTi非规则共晶组织构成,而在Al含量升高至9 at％时,Ni2TiAl相则会作为初生相析出.在Ni50-yTi43+yAl7(y=--2,-1,0和2)合金体系中,随着Ni元素含量的增加,Ti2Ni相的体积分数逐渐降低,但当Ni≥51 at％时,Ti2Ni相的体积分数基本保持一致,同时Ti2Ni+NiTi非规则共晶组织消失,Ti2Ni相以短条状或点状形态分布在晶界处.此外,NiTi-Al基合金在经过1200℃×12 h固溶和850℃×10 h时效的热处理之后,会在基体上均析出了大量的Ni2TiAl相,但随着Ni元素含量的增加,Ni2TiAl相的组织稳定性显著降低,并且晶界处的Ni2TiAl相先于晶内的Ni2TiAl相失去与基体之间的共格关系.综合考虑,Ni50Ti43Al7合金有着较低的Ti2 Ni相体积分数以及优异的Ni2TiAl相高温稳定性,是进一步研究NiTi-Al基合金组织与性能的适宜对象.

The effect of Al content and Ni/(Ti + Al) ratio on microstructure of NiTi-Al alloys was investigated.The results show that there is no obvious change in microstructure when Al content is lower than 7 at％ in Ni50 Ti50-x Alx (x =0,5,7 and 9) alloys,and the microstructure is composed of NiTi matrix phase and NiTi + Ti2Ni anomalous eutectic structure.However,Ni2TiAl phase precipitates as primary phase when Al content achieves 9 at％.With the increasing Ni content,the volume fraction of Ti2Ni phase decreases in Ni50-y Ti43+yAl7(y =-2,-1,0 and 2),but remains unchanged when Ni content is higher than 51 at％ and the morphology of Ti2Ni phase changes from anomalous eutectic to strip and point.After solution heat treatment at 1200 ℃ for 12 h and aging at 850 ℃ for 10 h,Ni2TiAl phase will precipitate in NiTi matrix.The microstructure stability of Ni2TiAl phase decreases dramatically with the increasing Ni content and these coarsened semi-coherent Ni2TiAl precipitates tend to appear first in intercellular regions.Due to lower volume fraction of Ti2Ni phase and good microstructure stability of Ni2TiAl phase,Ni50Ti43Al7 is thought to be the appropriate object for further research about the microstructure and property of NiTi-Al alloy.