EFFECTS OF AGING TEMPERATURE AND ALLOY COMPOSITION ON LONG-RANGE ORDERING IN NI-CR-FE ALLOYS DURING ISOTHERMAL AGING

摘要

Long-range ordering (LRO) in Ni-Cr-Fe model alloys during isothermal aging treatment at 360 °C, 400 °C and 500 °C was investigated by microhardness and transmission electron microscopy (TEM) measurements. Increasing the aging temperature shortened the ordering incubation period and increased the ordering transformation rate. The Ni:Cr atomic ratio of approximately 2:1 promoted LRO of the binary Ni-Cr alloys. In the ternary Ni-Cr-Fe alloys, 1 at.% iron content decreased the ordering transformation rate and insignificantly affected the ordering incubation period, furthermore, 3 at.% iron content prolonged the ordering incubation period. Tensile tests in air at room temperature and high temperature water at 290 °C with a strain rate of 10~(-4) s~(-1) were conduct to investigate the effects of LRO on the mechanical properties of Ni-Cr-Fe alloys. High degree of LRO in the Ni-Cr-Fe alloy increased the yield strength and ultimate tensile strength by about two times. LRO in the Ni-Cr-Fe alloys also transformed the fracture pattern from ductile fracture to brittle fracture. The elongation and reduction in area were slightly reduced with the precipitation of LRO in the Ni-Cr-Fe alloys.