Accelerated grain refinement induced by dispersed coarse particles

在真空中以1×10^~(-3)的真实应变速率，在773K~873K的温度范围内，对直径为1~3μm的弥散分布的粗大氧化物颗粒的Ni-30质量分数Fe合金进行了多向锻造。作为对比，还制备了无颗粒的Ni-Fe合金，并进行了MDFED。在873K时，两种合金在MDF过程中都出现了明显的流动软化现象，尤其是弥散分布的合金，而在773K时，两种合金都出现了加工硬化和稳态流动。随着累积应变的增加，平均晶粒度逐渐细化。然而，不同的温度和颗粒的分散度，其演变的微观结构有很大的不同。873K时，在累积应变μ=2.4时，合金中平均约1.3Σεm的等轴细晶均匀演化，而773K时，组织仍然不均匀。上述实验结果表明，粗大颗粒在促进晶粒细化方面起着重要作用。

A Ni-30 mass% Fe alloy with dispersed coarse oxide particles, ranging from 1 to 3 μm in diameter, was multi-directionally forged (MDF) at temperatures between 773 K and 873 K at a true strain rate of 1 × 10^<-3> s^<-1> in vacuum. For comparison, a particle-free Ni-Fe alloy was also prepared and MDFed. At 873 K, an obvious flow softening occurred during MDF especially in the alloy with dispersed particles, while work hardening followed by steady-state flow appeared at 773 K in both alloys. With increasing cumulative strain, the average grain size became gradually finer. However, the evolved microstructure was quite different depending on temperature and dispersion of particles. At 873 K, in the alloy with particles, equi-axed fine grains of about 1.3 μm in average was uniformly evolved at a cumulative strain ofΣε=2.4, while at 773 K the microstructure was still inhomogeneous. The above experimental results suggest important role of coarse particles to stimulate grain refinement.