Effect Of Particle Size Of Al₂O₃ Ceramic Particles On Microstructure And Properties Of Al₂O₃/Mo Composites

In the present research,Al₂O₃/Mo composites were prepared by powder metallurgy method and the preparation technology of the composites was studied.Besides,the microstructure and properties of the prepared composites were analyzed,and the relationship between microstructure and properties were discussed.The main conclusions are as follow:The Mo-Al₂O₃ composite powder still maintains the Mo and Al₂O₃ two-phase state after strong milling and 1800 ? sintering,which demonstrates a high degree of chemical stability between Mo and Al₂O₃.Compared with Mo particles,Al₂O₃ particles are easier to be finely polished by means of ball milling,and the fragmented alumina powder is evenly distributed between the Mo particles and adheres to the larger Mo particles,thus forming the embedded particles resulting from ball milling.The optimum pressing pressure of Mo-Al₂O₃ composite powder die-forming is reduced with the increase of alumina content,which is determined by the deterioration of the forming performance of the composite powder.For the fabricated composite material,the grain size of the substrate decreases sharply as the Al₂O₃ volume content increases from 0 vol.%to 5 vol.%,and when the Al₂O₃ volume content exceeds 5 vol.%,the grain size of the substrate decreases slowly and is close to the limit grain size.The addition of Al₂O₃ particles can not only enable the Mo substrates to form fine grain structure,but also prevent the composite material from grain coarsening and performance degradation due to the long-term use at high temperatures,as the second phase of A1203 particles have the function of stabilizing the substrate grain size.The enhancement mechanism of Al₂O₃ particles on Mo substrate mechanical properties is as follows:the sintering promoting effect of Al₂O₃ enables Al₂O₃ particles to be closely integrated with Mo substrates to form a dense structure;the dispersive distribution of Al₂O₃ particles has a blocking effect on Mo atomic diffusion,resulting in the fine grains and grain refinement strengthening for Mo substrates;when the composites are under stress,the pinning of Al₂O₃ particles in Mo grains suffers dislocation glide,and the pinning grain boundary glide of the alumina particles on the Mo grain boundary occurs;besides,the high strength of Al₂O₃ particles can help the substrate bear more load.Al₂O₃/Mo composites,have better wear resistance than substrate Mo at high temperatures,and the mechanism is as follows:the hardness of Al₂O₃/Mo composites is always higher than that of pure Mo material at both low and high temperatures,and therefore the wear resistance is better than that of the substrate Mo metal;adding Al₂O₃ particles causes the fine grains of Mo substrates,which not only improves the strength and plasticity of substrate Mo,but also improves the overall toughness of the Al₂O₃/Mo composites,thus making the surface crack not easy to occur in the process of friction,and then enhancing the wear resistance of the material.