退火温度对ECAP挤压两道次Fe基形状记忆合金微观组织的影响

Effect of Annealing Temperature on the Microstructure of Fe-based Shape Memory Alloy After Two Passages ECA Pressing

对不同退火温度时ECAP两道次Fe17.80Mn4.73Si7.80Cr4.12Ni合金的微观组织进行分析,研究变形后组织对形状恢复率的影响机理.研究结果显示,ECAP挤压后300 ℃退火,合金恢复率只有33%,提高退火温度,形状恢复率迅速升高,最佳退火温区600～650 ℃,此时恢复率高于固溶态试样.TEM分析显示挤压后晶粒明显细化,但是较低温度时,退火晶粒中包含大量的位错和亚结构,不利于肖克莱不全位错的滑移,导致恢复率很低.500 ℃退火时变形组织已经部分回复,晶内位错仍然存在,但是数量已大大减少,开始出现一些低位错密度的区域.600～650 ℃之间退火时,变形带来的位错等回复完成,层错组织仍存在,恢复率达到最大值.700 ℃退火30 min后晶粒再结晶完成,新生成晶粒在0.3～2.5 μm左右,固溶态试样晶粒100 μm,相比晶粒明显细化.

Structure of Fe17.80Mn4.73Si7.80Cr4.12Ni alloy annealed at different temperature after two passages ECA pressing was studied. The effect of deformed structure on the shape memory effect（SME） was analyzed. When annealed at 300℃ for 30 minutes after pressing, SME is 33%, while SME increases rapidly with the increase of the annealing temperature. The optimal annealing temperature lies in 600～650℃ with best SME which is superior to solution ones. The SAED patterns by transmission electron microscope（TEM） suggest that the grains are obviously refined after pressing. The vast scale of dislocations, stack defaults and substructure are included in grains annealed at low temperature. These dislocations are harm to SME because they impede sliding of Sheckley imperfect dislecations. With annealing temperature increasing to 500℃, substructure are partially reversed with decreasing of dislocations and appearing some fields with less dislocations. Annealing at 600～650℃ removes dislocation while preserves stack defaults so that SME is optimal. Morphologies showed that recrystallization are completed at 700℃ with fine grains about 0.3 μm introduced by ECAP plus annealing processing.