Behavior of stress–relaxation and the estimation of creep in Zr–1.1Nb–0.05Cu alloy

Creep of Zr–1.1Nb–0.05Cu alloy was predicted from a stress–relaxation test. There are several approaches to predict the creep using a stress–relaxation test. However, most experiments were performed using polymers or soft materials. In the case of metals, we found that the strain levels and strain rates are not solely determined using a conventional method, but have to apply both the graphical and analytical methods together. Stress–relaxation behavior was investigated under compressive stresses of 70–350 MPa at 380 °C. Reduction in the applied stress was detected for at least 6 h after holding the applied compressive load. The stress-reduction rate during the relaxation was greater than 0.1 MPa/s at the onset of the test, and decreased to below 0.001 MPa/s at the end of the test. The stress–relaxation was interpreted to predict the creep behavior of the studied alloy. The saturated primary creep strain (ϵsat)(ϵsat) was obtained with the incipient stress releasing behavior by applying a graphical conversion procedure. Also, the steady-state creep rate (ϵ˙ss) was calculated from the curvature of stress–relaxation with time analytically. The determined values were ϵsat=0.014-0.022,ϵ˙ss=2.8-4.1×10-8s-1 for the creep of Zr–1.1Nb–0.05Cu under 80–120 MPa at 380 °C. The predicted creep behavior matched well with the experimental creep data.

► Experimental data from a stress–relaxation test were analyzed to estimate the creep. ► The saturated primary creep strain was obtained after a graphical conversion process. ► The steady-state creep rate was determined through an analytical conversion process. ► Both conversion processes were required to predict the accurate creep of metals. ► The approach enabled to estimate the creep with a relatively short time.