通常认为Fe-Ni-Cr合金在过时效后晶界上析出的η相为裂纹源, 恶化合金性能. 通过对一种Fe-Ni-Cr合金进行过时效后晶界上析出$\eta$相的研究发现,由于晶界η相与合金基体保持共格关系, η相对合金的室温性能影响不大；并且在高温变形条件下η相形成凸起, 阻碍晶界滑动, 减小在晶角处的应力集中, 从而提高合金的高温塑性.断口扫描电镜观察表明, 晶界η相的析出使合金高温断裂方式由原来的沿晶脆性断裂转变为穿晶韧窝状断裂. 通过在合金中添加Nb, 可以在晶界上析出更为弥散的η相, 从而使得合金在高温下获得相当高的塑性.
The microstructures and mechanical properties of an Fe-Ni-Cr austenite alloy undergone different ageing treatments have been examined. Theη phase precipitated on the grain boundary of the over-aged alloy. Contrary to be crack sources and make mechanical properties of alloys deteriorate as it has been always considered, ηphase was found to have little effect on room temperature properties and furthermore, it improved the high temperature ductility of the alloy via blocking the grain boundary slip due to its coherency with the austenite matrix. SEM fractography shows that the 1023 K tensile fracture transforms from intergranular mode to microvoid coalescence mode due to the presentation ofηphase. Addition of Nb causes more dispersed distribution ofη phase along grain boundaries and therefore results in higher high temperature ductility.
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