The influence of processing methods on creep of wrought and additively manufactured CrCoNi multi-principal element alloys

The influence of vacuum arc melting and mechanical processing (wrought) versus additive manufacturing (AM) on the creep behavior of multi-principal element alloys (MPEA) is investigated in this study. Annealed wrought and hot isostatically pressed (HIP) AM CrCoNi were creep tested under constant tensile stress of 40 to 200 MPa at temperatures of 1023 to 1173 K. Stress exponents of 4.5 +/- 0.2 and 5.9 +/- 0.1 and activation energies ranging from 240 to 259 and 320 to 331 kJ/mol were found for wrought and AM CrCoNi, respectively. The results indicate that the AM material exhibits superior creep resistance and inferior creep ductility compared to the wrought alloy. This difference is attributed to the AM material having a higher percentage of Cr-rich oxides, a smaller total low angle grain boundary (LAGB) length on a percentage basis, and a greater total twin boundary (TB) length on a percentage basis. The AM and wrought materials have similar grain sizes; however, the smaller LAGB length and greater TB length in the AM material reduce slip transmission on the other side of the boundaries and contribute to strength. The dislocation structures of the AM and wrought materials consist of individual curved dislocations with dislocation multijunctions and jogs, which is similar to the arrangements previously observed in CrMnFeCoNi.