| With the rapid development of modern science and technology, traditional material used in extrusion die, just like H13 steel, can not accord with the request of society in the certain situation. So it is essential to develop new types of extrusion die material with high performances. Mo-W alloy has been widely used in some industrial areas such as material processing, weaponry, aerospace, atomic energy and microelectronics information, because it possesses lots of super properties, for example, excellent mechanical performances, physical properties and high-temperature behavior. Therefore, in this study, we started from the improvement of the alloy’s plasticity with the mix of Co based on the high performances of the alloy such as high-temperature behavior, high hardness and strength,and excellent wear-resisting and corrosion-resisting behavior. Then we discussed and optimized the parameters of mechanical alloying and vacuum sintering. More experiments were carried out to find out the effect of the heat treatment on the properties of oxidation resistance and in normal and high- temperature behavior. Finally, we prepared the Mo-W-Co alloy with high performances.The alloy studied in the paper was prepared by powder metallurgy. The effect rule of different ball-milling, vacuum sintering and heat treatment parameters were studied by mechanics performance tests at room and high temperature, tensile tests at room temperature,XRD, OM, SEM, BSE and EDS tests. The comprehensive research results are as follows.(1)The alloy powder with equal Co content mills in different time, a portion of powder with 20 h milling changes from ball shape to slice and sheep shape, while the powder with 10 h milling still remain the ball shape; the particle size and tap density of the powder with 20 h milling are better than that with 10 h milling; when the powder with different Co content mills in equal time, the low Co content powder unites more badly than the high Co content powder.When the powder with equal Co content mills in different speed, the size and tap density of high-speed-milling powder is improved compared with that of low speed, and the union of powder has been eased; the parameter of ball-milling: 300r/min mills in 20 h with ethyl alcohol as medium.(2)The microstructrue of sintering alloy is mainly composed of β and μ phases. β phase is the solution of Mo and W, which is the base of alloy, and μ phase is Co7Mo6 and Co7W6 compound,which is the second phase of alloy. The rule of the second phase strengthening is based on the μ distributes in β base with dot or sheet shape, and the hardness of alloy will be enhanced; μ will grow rapidly with the increase of sintering temperature, the shape of μ phase will grow from grainy to sheet and the existence area grows from crystal gap to inner crystal;the hardness of low Co content alloy is higher than high Co content with either sintering parameter and the low Co content alloy that sinters at 1300℃ and preserves 3.5h owns the best mechanical property; the best vacuum sintering parameter: 1300℃, preserves 3.5h.(3)The coating of alloy is composed of the inside and outside one after siliconing. Al2O3 is the main constituent of coating outside while Mo Si2 and Mo5Si3 are the ingredients of coating inside. The hardness has been improved compared with the alloy in sintering state,while it will be decreased after the oxidation resistance experiment; there will be some melting loss during the oxidation resistance experiment and the oxidation layer is mainly including Si O2,Mo O3 and Al2O3; the best formula for siliconing: 60%Si, 25%Al2O3,10%NHCl4, 5%Ca Cl2(wt%).(4)The main phases of alloy after the solution treatment are β, μ and κ. μ will segregatein base and little κ exist and distribute homogeneously; while the content of κ is increasing and μ is decreasing after the aging treatment, in the meantime, the segregation of μ is improved; the highest hardness of alloy after solution is 45.8 with the parameter of 1100℃preserving 1h and then oil quenching; the hardness of alloy in 500℃ and 600℃ is just equal but it will show great brittleness in 700℃; the microstructure of solution and aging is with the aging parameter of 500℃ preserving 10 h, and the highest hardness in normal temperature is HRC43.7; the hardness in high temperature decreases with the increasing of the environment temperature, and the brittleness has been improved in 700℃; the wear rate is increasing with the increasing of the environment temperature; the best solution treatment parameter: 1100℃preserving 1h,oil quenching; the best aging treatment parameter: 500℃ preserving 10 h.Key words: extrusion die material; Mo-W-Co alloy; microstructure; mechanical alloying;... |
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