Creep life prediction of single crystal superalloys

Abstract

There has been a limited attempt to map the creep performance of superalloy single crystals for all possible orientations as it requires a very large number of experi-ments, some of which may run for several years. Convent-ional life prediction techniques would indeed require a large data-base for a reliable estimation of the creep life of a single crystal. Moreover single crystals with a tensile axis having a low symmetry orientation would und-ergo a time dependent rotation well. Therefore life predi-ction in this case is no doubt more complex and it needs an entirely different approach. Creep in single crystals is known to take place through viscous glides on several slip systems such as (111) <101>, [0011<110> and (111) (112> in the case of Ni based superalloys. The paper rev-iews he such information has recently led to the devel-opment of a generalised model of creep deformation in cubic single crystals. Using this approach it is possible tonume-rically simulate the creep test on a crystal of arbitrary orientation based-on the material constants estimated from a limited database on <001> and <111> crystals. Although this approach has been used to explain the creep behaviour of SRR99 a Ni base superalloy it is applicable to any cubic crystal. Such an analysis not only helps to identify the operative slip systems but also predicts both strain-time plots and crystal rotations that are consistent with the experimental observations.