Modeling of Ni_4Ti_3 precipitation during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys  

双晶体NiTi形状记忆合金在无/有应力作用时效下的Ni_4Ti_3相沉淀行为模拟(英文)

作　　者：柯常波[1,2] 曹姗姗[2] 马骁[2] 张新平[2] 

机构地区：[1]华南理工大学机械与汽车工程学院,广州510640 [2]华南理工大学材料科学与工程学院,广州510640

出　　处：《Transactions of Nonferrous Metals Society of China》2012年第10期2578-2585,共8页中国有色金属学报（英文版）

基　　金：Project (50871039) supported by the National Natural Science Foundation of China;Project (2011ZB0007) supported by the Fundamental Research Funds for Central Universities of China;Project (201104090881) support by China Postdoctoral Science Foundation

摘　　要：The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys （SAMs） with two different initial Ni-contents of 51.5% and 52.5% （mole fraction）, respectively. The simulation results show that, during stress-free aging of the NiTi alloy with a low supersaturation of Ni （i.e., Ti-51.5%Ni）, the Ni4Ti3 precipitates exhibit a heterogeneous distribution with a high number density of particles at the grain boundary, leaving most of the grain interiors free of precipitates; while for the NiTi alloy with a high supersaturation of Ni （i.e., Ti-52.5%Ni）, the Ni4Ti3 precipitates show a homogeneous distribution across the entire simulation system. The stress-assisted aging can give rise to homogeneous distribution of the precipitates, regardless of the initial Ni-content; however, the distribution of variant type within the two grains is heterogeneous.运用相场方法研究双晶体NiTi形状记忆合金分别在无应力和有应力作用下时效过程中Ni4Ti3相的沉淀行为,模拟研究两种不同初始过饱和度(Ni含量分别为51.5%和52.5%,摩尔分数)的NiTi基体并考虑外加应力的影响。模拟结果表明,在无应力作用的体系中,当体系Ni原子初始浓度相对较低(51.5%Ni)时,Ni4Ti3相以非均匀的方式析出,其中晶界上存在大量的Ni4Ti3变体,晶界内大部分区域无变体;当体系Ni原子初始浓度较高(52.5%Ni)时,Ni4Ti3在整个双晶体系中均匀析出。在所研究的两种初始浓度下,一定大小的外加应力将直接导致Ni4Ti3变体在整个模拟体系中均匀析出,而两晶粒中变体的类型分布有所不同。

关 键 词：NiTi shape memory alloy Ni4Ti3 precipitate low-angle grain boundary martensitic transformation phase field simulation 

分 类 号：TG139.6[一般工业技术—材料科学与工程]