Modification of creep and low cycle fatigue behavior induced by welding

• We evaluate the effect of a TIG process on the mechanical strength of a Ni superalloy.
• Low-cycle fatigue and creep tests are carried out on flat specimen.
• Applied strain range are similar to working condition (Δε = 0.4–0.9%).
• The hysteresis cycles are often fully elastic due to the low applied strain range.

In this work, the mechanical properties of Waspaloy superalloy have been evaluated in case of welded repaired material and compared to base material. Test program considered flat specimens on base and TIG welded material subjected to static, low-cycle fatigue and creep test at different temperatures.Results of uniaxial tensile tests showed that the presence of welded material in the gage length specimen does not have a relevant influence on yield strength and UTS. However, elongation at failure of TIG material was reduced with respect to the base material.Moreover, low-cycle fatigue properties have been determined carrying out tests at different temperature (room temperature RT, 538 °C and 760 °C) in both base and TIG welded material. Welded material showed an increase of the data scatter. Fatigue strength was reduced, with respect to the base material. During test, all the hysteresis cycles were recorded in order to evaluate the trend of elastic modulus and hysteresis area against the number of cycles. A clear correlation between hysteresis and fatigue life was found.Finally, creep test carried out on a limited number of specimens allowed establishing some changes about the creep rate and time to failure of base and welded material. TIG welded specimen showed a lower time to reach a fixed strain or failure when a low stress level is applied. In all cases, creep behavior of welded material is characterized by the absence of the tertiary creep.