Study On Microstructure And Properties Of Co-Cr-W Alloy Prepared By Powder Metallurgy

In the present research, Co-Cr-W were fabricated by v acuum casting, vacuum suction casting and powder metallurgy, and make sure the best preparation is powder metallurgy method by compared. The effect of different ball-milling time and different ball-milling speed on the qulity of Co-Cr-W alloy powders were quantitatively investigated using the test of comparative, and the effect of different sintering time and sintering temperature on microstructure and properties of Co-Cr-W alloy were investigated.(1) Co-Cr-W were fabricated by va cuum casting, vacuum suction casting and powder metallurgy. The effect of different preparation process on forming able. The result shows that, in contrast to casting, powder metallurgy promotes fine formability, promote product rate, homogeneous microstructure, finer grains. In addition, the more rate of pore in Co-Cr-W were fabricated by powder metallurgy due to the lower bending strength.(2) The composite powders of Co-Cr-W were fabricated by ball milling. The effects of ball milling time on the alloy powder performance of Co-Cr-W were studied. Grain size, micro strain and micro morphology of the milled powders were characterized using XRD and SEM, respectively. And density,hardness and bending strength of bulks by vacuum sintering with milled powders as starting materials were tested. The results indicate that under the condition of a milling speed of 300 r/min and a ball-to-powder mass ratio of 10:1, the particle size of powders decrease quickly and the powder is in the shape of flake at the initial stage of ball milling, with milling time increasing. The powder size increases first and then decreases, while the average grain size of the alloy powder decreases. And the change became gentle after ball-milling for 20 h. With ball milling time increasing, the micro strain and hardness increase obviously.(3) The powder metallurgy method were used to sintering Co-Cr-W cemented carbide in the vacuum conditions. In order to research the effects of sintering temperature on the mechanical properties of the alloys, experiments with the temperature in range of 1250 to 1550℃, and the holding time of 60 min were conducted. The shrinkage, density, hardness,bending strength and microstructure of the samples were systematically measured to analysis the densification behavior. The result shows that, when sintered at the temperature in range of 1250-1450℃, the pore of the alloys reduce and ball, the density, hardness and bending strength are improved with increasing sintering temperature and reach the maximum values of 8.75g/cm3, 63.1HRC and 680 MPa at1450℃. When sintering temperature is more than 1450 ℃ the properties of the alloy begin to decline because of the burning phenomenon. when the sintering temperature is 1550℃ the shape of the samples distorts seriously.