PHASE INVESTIGATION OF A COBALT-BASE ALLOY CONTAINING CR, NI, W AND C

A cobalt base alloy with composition Co-27.74Cr-19.27Ni-6.11W-1.1C was cast, some pieces of this alloy being cooled in water and liquid nitr ogen after annealing. Metallographic investigations showed that the ca st sample had a dendritic microstructure with eutectic carbides solidi fied in the inter-dendritic regions. In the samples cooled in water an d liquid nitrogen, the carbide phases solidified in the inter-dendriti c regions in the cast sample dispersed in the dendritic grains, as a r esult of this dispersion, the dendritic grains becoming smaller and th e branches of dendrites becoming thinner. In accordance with these met allographic observations, the hardness measurements showed that the ha rdness of the samples cooled in water and liquid nitrogen increased ac cording to the cast sample. It was seen from the X-ray diffraction inv estigations that various carbides such as M7C3, M23C6, M3C2, Co3C, Ni3 C, and sigma phase may exist in these samples. In addition, DSC (Diffe rential Scanning Calorimetry) measurements showed that some recovery p rocesses occur in these samples in the heating regime in the temperatu re region between 238 and 287 degrees C. (C) 1998 Elsevier Science S.A .