High temperature low cycle fatigue and thermo-mechanical fatigue of a 6061 A1 reinforced with SiC_W

The high temperature isothermal low cycle fatigue (IF) and thermo-mechanical fatigue (TMF) of a 6061 A1 alloy reinforced with 28 vol.% silicon carbide whiskers were studied. IF experiments were conducted at a temperature of 300°C, and two types of TMF tests, i.e. in-phase (IP) and out-of-phase (OP), were performed with temperature cycling between 150 and 300°C. All experiments were carried out under mechanical strain range control. Experimental results of mechanical behavior and mean stresses for TMF and IF loadings are provided. It can be seen that both IP and OP TMF show continuous cyclic softening until failure, while IF loading initially shows several cycles of cyclic hardening followed by cyclic softening until final fracture. A comparison of TMF and IF lives has been made and various damage mechanisms operative under different strain ranges and loading conditions have been explained. SEM micrographs show that damage processes under both IF and TMF conditions consist of initiation, growth and coalescence of voids in the matrix around whiskers. Due to the complexity of the relationship between IF and TMF damage, IF data cannot be used to evaluate TMF life. (C) 2000 Elsevier Science S.A. All rights reserved.