AbstractThe microstructure and hardness of Tribaloy 700 (T 700) of nominal composition (wt-%) 50Ni–32Mo–3Si–15Cr and two alloys of similar Ni, Mo, and Cr contents, but having no or 6%Si have been determined. The microstructure of the three alloys consisted of a primary Laves phase in a eutectic matrix, but the volume fraction and crystal structure of the primary Laves phase and the morphology of the eutectic matrix were different. The presence of Si increased the proportion of primary phase, stabilised the hexagonal form of the Laves phase, and produced an ill defined eutectic. The hardnesses of the as cast alloys were similar, but T 700 was the most stable at elevated temperatures.MST/881