Creep of CMSX-4 single crystals of different orientations in tension and compression

Abstract

Creep tests of γ′ strengthened superalloy CMSX-4 single crystals of different orientations were performed at 950 °C, in both tension and compression at constant load (initial stress 250 MPa) as well as at constant stress (250 MPa). It was found that the creep resistance depends strongly on the crystal orientation. For creep in tension it decreases in the sequence 〈111〉, 〈001〉, 〈011〉 and for creep in compression it decreases in the sequence 〈001〉, 〈111〉, 〈011〉. Constant stress tests in tension generally reveal a higher creep resistance than the constant load tests in tension. In compression the differences in the mode of testing lead only to small and unsystematic differences in creep behavior. Comparison of constant stress tests in tension and compression shows that the creep curves practically coincide at the early stages of the test. In tension there is later tertiary creep terminating in fracture. In compression no tertiary creep occurred within the test run up to a strain of about 2%. In all the tests a massive rafting, i.e. directional coarsening of γ′ particles, was observed.