THE LOCATION OF ATOMS IN RE-CONTAINING AND V-CONTAINING MULTICOMPONENT NICKEL-BASE SINGLE-CRYSTAL SUPERALLOYS

The atomic structure of some Ni-base single-crystal superalloys has been investigated using atom-probe field ion microscopy (APFIM) and the results compared with numerical estimations obtained from the alloy design program (ADP) and the cluster variation method (CVM). Re-containing CMSX4 and V-containing RR2000 alloys, together with TMS63 are the subjects of this study. It is found that Ti, Ta and Hf have a strong preference for the gamma' phase, whereas Cr, Co, W, Re and Mo tend to dissolve in the gamma phase. V has a very weak preference for the gamma phase. The results agree very well with both ADP and CVM. The APFIM analyses have also revealed that Re atoms in CMSX4 tend to preferentially occupy the sites normally designated for Al atoms in the gamma' phase. It is demonstrated that the site occupancy of other alloying elements such as Ta, W, Mo and Co can be estimated accurately using CVM, although there are some discrepancies for the distributions of Cr, Ti and Ni. The effect of solute atom distribution on creep properties is discussed briefly.