Effect of Ir addition on the high-temperature creep strength of B2-type NiAl intermetallic compounds

In order to study the mechanisms of the improvement in high temperature strength of B2-type NiAl intermetallic compound by Ir addition, compressive creep tests and stress-relaxation tests of (Ni, Ir) Al alloys have been conducted in the temperature range from 1273 to 1473 K. The 5 mol%Ir addition increases the creep resistance of NiAl by a factor of approximately 3 at 1273 K. Ir addition significantly enhances the internal stress of the flow stress, and led to a significant improvement in the high-temperature creep strength of NiAl. An effective stress component comprising a flow stress of the (Ni, Ir)Al alloy is caused by the dragging resistance to the jogged screw dislocations. To understand the strengthening mechanisms of the high-temperature strength of NiAl by Ir addition, it is necessary to consider a decrease in self-diffusion coefficient and a significant increase in shear modulus in NiAl by Ir addition. Such variations in the self-diffusion coefficient and the shear modulus, caused by a decrease in vacancy concentration of NiAl, suppress the recovery process and promote the work-hardening, resulting in an enhancement in the high-temperature creep strength of NiAl.