Effects of Silicon Content on the Microstructure and Mechanical Properties of Cobalt Based Tribaloy Alloys

Abstract

Cobaltbased Tribaloy alloys are strengthened mainly by a hard, intermetallic Laves phase consisting of Co3Mo2Si or/and CoMoSi; therefore, silicon content plays a large role in the microstructure and performance of these materials. In this research, the microstructures of two cobaltbased Tribaloy alloys that are largely different in Si content are studied using scanning electron microscopy (SEM) with an EDAX energy dispersive Xray (EDX) spectroscopy, and Xray diffraction (XRD), fatigue strength under rotatingbending test, mechanical behavior under nanoindentation, and hardness at room and elevated temperatures using a microindentation tester. It is revealed that with higher silicon content (2.6 wt. %), T400 has a hypereutectic microstructure with Laves phase as primary phase, whereas with lower silicon content (1.2 wt. %), T401 has a hypoeutectic microstructure with solid solution as primary phase. T400, containing lager volume fraction of Laves phase, exhibits better fatigue strength, in particular, at high stresses, while T401, with less volume fraction of Laves phase, has improved ductility, exhibiting better resistance to fatigue at low stresses. The hardness of both alloys decreases with temperature, and T401 shows higher reduction rate. T400 is harder than T401.