Study On Preparation, Microstucture And Mechanical Properties Of Cr-W-Mo-Al₂O₃Cermets

In this paper, from the requirement for the life of the hot-extrusion die, Cr-W-Mo-Al2O3cermets with high strength, high toughness, high hardness, oxidation resistance and thermal stability were studied. Cr-W-Mo-Al2O3cermets were prepared by hot-pressing, and their microstructure, mechanical properties, fracture mode and the behavior of thermal expansion were investigated. the following conclusions were obtained:(1) W-20vol.%Mo-20vol.%Cr-vol.%Al2O3and W-20vol.%Mo-20vol.%Cr-20vol.%Al2O3cermets were prepared by hot-pressing. Metal and ceramic phases distributes homogeneously. W, Mo, Cr can be dissolved into each other, and Cr can dissolves into A12O3ceramic phase. With the content of A12O3increasing, the hardness increases, but the strength and toughness decreases. The composites exhibit fracture mode of intergranular fracture between metal phases and ceramic phase and cleavage fracture in metal phase.(2) Cr-15vol.%A12O3and Cr-12vol.%Mo-15vol.%Al2O3cermet were prepared by hot-pressing, the addition of Mo makes the hardness of Cr-Al2O3increases, but makes its strength decreases because of the weak bond of Mo/Al2O3interface. The fracture mode of Cr-Al2O3and Cr-Mo-Al2O3cermet is mainly along the interface of metal and ceramic phase. With the adding of Mo, the thermal expansion coefficient of Cr-Al2O3decreases, and becomes stabilized.(3) Cr-10vol.%Al2O3and Cr-20vol.%W-10vol.%Al2O3cermets with different Cr particle size (12μm,60μm)were prepared by hot-pressing. The effect of the Cr particle size and the addtion of W on Cr-Al2O3and Cr-Al2O3were investigated. The results shows the flexural strength of cermets increases with decreasing Cr particle size as well as the addtion of W. The highest strength of932.10MPa was tested on the Cr-20%W-10%Al2O3with small Cr particle. W-rich phase has fine tear ridges, indicative of the ductile fracture. The Cr-W-Al2O3cermet exhibits mixed fracture mode of intergranular fracture and transgranular fracture, brittle fracture and ductile fracture. the small Cr partile size stabilizes the curve of the thermal expansion coefficient of Cr-Al2O3and Cr-W-Al2O3; and the addtion of W remarkbly decreases the thermal expansion coefficient of Cr-Al2O3.