On the short time creep rupture

Abstract

Short time tensile creep rupture tests were made on 7 mil lamp filament wire and on 7 mil undoped tungsten wire in the temperature range 2500 to 3100 K. Steady-state creep rate was described by an expression having the form: ε =ADσ/E)^m whereA is a constant,D is the self-diffusion coefficient, σ is the creep stress,E is the elastic modulus, andm is 5 for undoped tungsten and 25 for lamp grade wire. Activation energy for time to failure of lamp wire was found to vary from 150 to 185 kcal in the range 2500 to 3100 K. Failure mode in this range was slip at high stresses and intergranular brittle fracture at low stresses. The very high creep-strength observed for lamp wire was attributed to a combination of resistance to diffusional creep at low stresses and resistance to dislocation creep at high stresses. The dispersoid structure of lamp wire was suggested as the origin of strength in both cases.