Nb合金化对电弧增材制造NiTi基形状记忆合金的影响

NiTi合金是一种应用广泛的形状记忆合金，其中Ti₄₇Ni₄₄Nb₉成分的合金是一种可靠的航空管接头材料. 采用双丝电弧增材制造(WAAM)的方法制备了Ni₅₂Ti₄₈合金，并以Nb元素进行了原位合金化得到了Ti₄₇Ni₄₄Nb₉合金，研究了其典型组织、压缩性能、相变温度与形状记忆效应，分析了Nb元素的添加对WAAM镍钛合金组织及性能的影响. 结果表明，加入Nb元素后，合金的组织除B2相晶粒外，还在晶界处有细小的β-Nb相析出，使得合金的压缩强度在横向与纵向上分别增加了7.9%与3.1%，形状记忆回复率则下降了4.0%，相变温度滞后从?6.4 ℃提升至40.9 ℃，使得该材料作为记忆合金管接头时更加利于储存与装配.

Effect of Nb alloying on wire arc additive manufacturing NiTi-based shape memory alloys

NiTi alloy is a widely used shape memory alloy, in which Ti₄₇Ni₄₄Nb₉ alloy is a reliable material for aviation pipe coupling. In this research, Ni₅₂Ti₄₈ alloy was fabricated by double wire arc additive manufacturing (WAAM) method and Ti₄₇Ni₄₄Nb₉ alloy was obtained by in situ alloying with Nb element. The typical microstructure, compression properties, phase transformation temperature and shape memory effect of the alloy were studied. The effects of Nb element addition on the microstructure and properties of WAAM nickel-titanium alloy were analyzed. The results show that the microstructure of NiTi alloy fabricated by WAAM is characterized by coarse B2 equivalent axonal grains in the lower part, columnar B2 phase dendrite in the middle part, and relatively fine B2 equivalent axonal grains in the top part. Besides B2 phase grains, fine β-Nb phase precipitates at the grain boundary after the addition of Nb element, which makes the compress strength increased by 7.9% and 3.1% respectively in transverse and longitudinal directions, while the shape memory recovery ratio decreased by 4.0%,which is due to the fact that the plastic deformation of β-Nb particles precipitated between grain does not recover during loading, and the hysteresis of phase transformation temperature increased from ?6.4 ℃ to 40.9 ℃, which makes shape memory alloy more convenient for storage and assembly when used as pipe coupling.