MICROSTRUCTURE AND TENSILE CREEP BEHAVIOR OF MULTIPHASE NiAl EUTECTIC ALLOYS MODIFIED WITH ZR OR HF

摘要

The microstructures and tensile creep behaviors of HIPed NiAl-33.5Cr-0.5Zr and DS NiAl-28Cr-5.8Mo-0.2Hf alloys have been investigated. The microstructure of HIPed NiAl-Cr(Zr) alloy consists of NiAl matrix, Cr phase and non-continuous white Zr-rich phase, which distributed on the NiAl/Cr phase boundary. As to the DS NiAl-Cr(Mo,Hf) alloy, it is composed of a combination of dendritic and eutectic microstructures. The dendritic arms are of NiAl phase, the interdendritic region is the NiAl and Cr(Mo) phase eutectic region, and there also existed a Hf-rich phase in the NiAl and Cr(Mo) interface. The creep results indicated that the creep curves of both alloys have similar shapes, which are composed of primary creep stage, steady-state creep stage, longer accelerated creep stage, and about 25-45% creep strain. The apparent stress exponents are in the range of 4.8-7.5 and the apparent activation energies of 520-584kJ/mol were also analyzed. The creep deformations were controlled by the sub-grain boundary formation for the HIP NiAl-Cr(Zr) and dislocation climb for the DS NiAl-Cr(Mo,Hf). The creep rupture data of both alloys obey the Monkman-Grant relationship.