Research On The Microstructure And Mechanical Property Of Metallic Silicide In Mo-Si System

Being one of the most promising high-temperature structural materials used above 1200°C, the intermetallics in Mo-Si system have been investigated widely in recent years. By far most of the research, however, is still at the level of laboratory. The main barriers prevented them from practical use are the deficiency of room-temperature fracture toughness and high-temperature strength and poor high-temperature oxidation resistance. Arc-melting and directionally solidifying were used to prepare alloys and their single crystals in Mo-Si system. The microstructures the alloys were controlled by high-temperature annealing. A series of equipments such as X-ray diffractometer(XRD),scanning electronic microscope(SEM),optical microscope(OM) and transmission electronic microscope(TEM) were used to observed and investigate the microstructures. Mechanical properties were valued by high-temperature compress test, three point bending test and Vicker hardness test.In this article, the intermtallics in Mo-Si system were studied first to obtain the whole understanding of their microstructures and mechanical properties. For some alloy systems, elements as B and Nb were added to in order to change the microstructure and improve the mechanical properties. The alloy system with good properties was chose for a further study. The alloy systems involved in this article are Mo-10Si alloy, Mo3Si-Mo5Si3 eutectic alloy,Mo5Si3-MoSi2 eutectic, hypoeutectic and hypereutectic alloys and(Mo1-x,Nbx)Si2 alloys. The study was focused on(Mo1-x,Nbx)Si2 alloys.Arc-melted Mo-10 alloy which is composed of Mo and Mo3Si phases shows obvious plastic deformation ability and good strength resistance at high temperature, although its high-temperature strength is not very high. Its highest strength is 250MPa at 1300°C with a strain rate of 1×10-4s-1.And its fracture toughness at room temperature is 7.3 Mpam1/2.Mo3Si phase precipitates from Mo matrix phase after annealing at high temperature, and the size of Mo3Si phase precipitated dependents...