CREEP OF CMSX-4 SINGLE-CRYSTALS OF DIFFERENT ORIENTATIONS IN TENSION AND COMPRESSION

Creep tests of gamma' strengthened superalloy CMSX-4 single crystals o f different orientations were performed at 950 degrees C, in both tens ion and compression at constant load (initial stress 250 MPa) as well as at constant stress (250 MPa). It was found that the creep resistanc e depends strongly on the crystal orientation. For creep in tension it decreases in the sequence [111], [001], [011] and for creep in compre ssion it decreases in the sequence [001], [111], [011]. Constant stres s 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 cr eep behavior. Comparison of constant stress tests in tension and compr ession shows that the creep curves practically coincide at the early s tages of the test. In tension there is later tertiary creep terminatin g in fracture. In compression no tertiary creep occurred within the te st run up to a strain of about 2%. In all the tests a massive rafting, i.e. directional coarsening of gamma' particles, was observed.