升温速率对Micro-FAST制备NiTi合金的影响

Effect of heating rate on the preparation of NiTi alloy during Micro-FAST

摘要:

本文采用多物理场活化烧结微成形技术（Micro-FAST），低温（850℃）、短时间内（约8分钟）成功制备了尺寸为Φ4?mm的NiTi微型圆柱，并研究了升温速率对制备NiTi合金的影响。研究结果表明，试样在快速升温阶段发生最大的收缩量，直接影响了试样的烧结质量。在实验范围25℃/s到125℃/s内，随着升温速率的提高，NiTi合金的相对密度降低。升温速率越大，电流越大。大电流促进原子扩散，形成富Ni区，利于NiTi2和Ni3Ti相的形成，并加剧Kirkendall效应，生成更多孔隙；试样在电流作用下产生局部高温，促使局部液相生成，融化周围粉末生成孔隙。

Abstract:

In this paper, a novel method Micro-fields activated sintering technology was applied to the preparation of NiTi alloy. Cylindrical specimens with the diameter of 4mm and a height of 4mm were prepared successfully in a short time (about 8mins). The effect of heating rate on the preparation of NiTi alloy was discussed. The research result shows that the axial reduction in rapid heating stage was the biggest among the four sintering stages of Micro-FAST, which directly influenced the quality of sintering samples. In the experimental range of 25℃/s to 125℃/s, the relative densities of NiTi alloy sintered by Micro-FAST was decreased with the increasing heating rates. The higher the heating rate, the bigger the electric current is. Under electric current, atomic diffusion was promoted. As a result, NiTi2 and Ni3Ti were easier to be formed, and the effect of Kirkendall was aggravated. Meanwhile, local liquid-phase was produced by local high temperature under electric current, which promoted the fusions of particles and pores.