CREEP AND FRACTURE OF NICKEL-ALUMINIUM ALLOY

Document Type : Original Article

Author

Associate Professor., Mechanical Engineering Department, AL-Azhar University, Nasr City, Cairo, Egypt.

Abstract

Creep and fracture behaviour of Nickel-Aluminium alloy with Aluminium concentration of 7.13% was investigated at 1073 K over a range of stresses from 40 to 115 MPa. The alloy consists of solid solution matrix strengthened by Ý (Ni3 AL) particles. High precision constant stress creep curves have been obtained and analysed in terms of creep rate and fracture life. Over most of the transient and steady creep curve, the strain at any instant can be described accurately as :
Ɛ=Ɛ0+Ɛp (1-e-mt) + Ɛst.
where Ɛo is the instantaneous strain on loading, Ɛp the total transient strain, Ɛs the steady-creep rate, and m a constant relating to the rate of exhausion of transient creep. Analysis of the tertiary creep curves in terms of particle coarsening has been made and compared with the experimental results and also with different equations based on strain dependent damage. The results of the analysis combined with the scanning electron microscope observations of the fractured surfaces have shown that damage in the form of intergranular cavitation and cracking is the most probable mechanism responsible for creep fracture in this case.