Microstructure evolution and mechanical improvement by rapid solidification of polycrystalline Co 35 Ni 32 Al 32 Dy alloy

The Co35Ni32Al32Dy bulk alloys were prepared via suction casting technique and the microstructures obtained after furnace cooling and rapid solidification (RS) were investigated, respectively. The results showed that the microstructure of the alloy that contained the β and γ phases and the intermetallic compound Co5Dy transformed into martensite and γ dual-phase, when the cooling rate (RC) under furnace cooling was increased to 4000 Ks1. Moreover, the dendritic type γ phase fragmented into smaller pieces and distributed with in the grain, and the solid solubility of the alloying element Dy in the matrix was significantly improved by RS. The mechanical properties were substantially enhanced by the RS technique and the maximum tensile strength of 3395 MPa, with the elongation of 35.8% was obtained for the alloy with the cooling rate of 4000 Ks1. Finally, the fracture surface of the sample after furnace cooling and RS demonstrated typical characteristic of ductile fracture. With the increase in RC value, the dimples on fracture surface became more uniform in size with homogeneous distribution.