等通道转角挤压FeMnSiCrNiC形状记忆合金时效过程中碳化物析出的研究

Carbide Precipitation of FeMnSiCrNiC Shape Memory Alloys during Aging by Equal Channel Angular Pressing

研究了等通道转角挤压后时效处理对FeMnSiCrNiC合金碳化物的析出和形状记忆效应的影响。结果发现,挤压态合金经973K时效处理150min后,平均晶粒尺寸约10μm,同时晶内和晶界处析出大量碳化物。碳化物析出在回复完成前即开始,挤压产生的大量缺陷降低了碳化物析出的激活能,促进了碳化物析出。细晶强化和碳化物析出强化的共同作用显著提高了合金的基体强度,抑制预变形中的塑性变形,使更多的变形由应力诱发马氏体承担。因此,合金形状回复率达到89.4%(预变形4.33%时),比固溶态高120%,比直接时效高40%。

Effects of equal channel angular pressing （ECAP） and subsequent aging on the carbides precipitation and shape memory effect of an FeMnSiCrNiC alloy have been studied. The results show that the average size of grains is only about 10 μm after ECAP and subsequent ageing at 973 K for 150 min. In addition, many carbides start to precipitate inside the grains and on the grain boundary at low temperature before the recovery is completed due to a great amount of defects introduced by ECAP, which can remarkably decrease the activation energy for the nucleation of precipitates As a result, the strengthening by grain refinement and the second-phase hardening both effectively improve the strength of matrix, suppressing the plastic deformation during pre-strain. Consequently, the shape memory ratio of aged specimens after ECAP is up to 89.4% for a pre-strain of 4.33%, 120% higher than that of the as-quenched specimens and 40% higher than aged specimens without ECAP.