The Pilot Study On Synthesizing Metal/Metal Silicide Multiphase Alloys By Hot-pressing In-situ Reaction Sintering

Transition metal silicides have been considered as promising candidate structural materials to be used at high temperatures due to their high melting points, high strength retention at high temperatures, reasonable densities and oxidation-resistant. However, its brittleness is the drawback hindering its industrial applications. The brittle behaviour can be reduced effectively by two different means: by alloying, or by microstructure control including in-situ composites. It is compared the microstructures and properties of silicides made hot-pressing(HP) method with those materials made by cast and reactive hot pressing without pre-alloyed mixture powder that the former has a density and homogeneous structure without segregation and crack.With the thought of in-situ compositing, Cu-Mo-Si composite silicide (with metal solid solution/metal silicid structure), Co-Mo-Si and Ni-Mo-Si composite silicides (with metal solid solution/Laves phase structures) were prepared by MA+HP method using the raw materials of Cu, Co, Ni, Mo and Si powder. Then the composite silicides were characterized through XRD, OM, SEM and EPMA etc. The Cu-Mo-Si, Co-Mo-Si and Ni-Mo-Si ternary metal silicide alloys have a dense and uniform microstructure consisting of the metal silicids (Mo₅Si₃,Co₃Mo₂Si,Ni₃Mo₂Si) and the metal (Cu, Co, Ni) solid solution. With the increasing of the metal (Cu, Co, Ni) content, volume fraction of the metal silicids (Mo₅Si₃, Co₃Mo₂Si,Ni₃Mo₂Si) and the average hardness of the Me-Mo-Si (Me=Cu, Co, Ni) alloys decrease, nevertheless the bending strength of the alloys increase, 435.7⁷84.8MPa, 335.7⁷56.2Mpa, 375.7-1323.1MPa, respectively. Compared with the single-phase ternary metal silicides, the metal solid solution toughened metal silicide alloys have an excellent balance of strength and ductility, which was attributed to the effective toughening of ductile metal (Cu, Co, Ni) solid solution.Furthermore the sintering process of the Me-Mo-Si (Me=Cu, Co, Ni) metal silicde alloys was disgussed, the model of the sintering/metal silicide formation was builded.