Mechanical properties of an aged Ni-Cr-Mo alloy and effect of long-range order phase on deformation behavior

Mechanical properties of a Ni-Cr-Mo alloy subjected to an aging treatment at 600 °C and effect of long-range order (LRO) phase on deformation behavior of the alloy are systematically investigated. Results show that peak-aging conditions are reached after 600 h of aging at 600 °C. Meanwhile, the aging treatment at 600 °C in the aging time range of 100–700 h can lead to the precipitation of the coherent Pt₂Mo-type LRO phase in the C2000 alloy. Fine scale Pt₂Mo-type LRO phase exists in the sample aged for 100 h and provides an enhanced yield strength. Because the solution treated sample and the sample aged for 100 h show the almost identical strain hardening behaviors, it can be suggested that the ordered structure of the fine scale LRO phase is destroyed during the quite small plastic deformation. Besides, the ordered structure of the relatively large LRO phase is destroyed after the large deformation. Mechanical twinning occurs in the tensile-failed sample which is aged for 500 h. And, mechanical twinning is responsible for the high ductility of the alloy aged for more than 100 h and the change in the shape of the strain hardening rate vs true strain curve.