Study On The Preparation Of Mo/Al₂O₃ Composites And Its Wear And Corrosion Resistance

Molybdenum which has many characteristics such as high melting point,good corrosion resistance,electric and heat conduction and small expansion coefficient is a kind of rare metal with strategic significance,but its low wear resistance and high temperature antioxidation limit the extensive use.While metal-ceramic composites formed by adding alumina to molybdenum synthesize the high hardness and wear resistance of the alumina ceramic,the plasticity and toughness of the molybdenum and their common corrosion resistance,so it can be used in the field which askes for high wear and corrosion resistance.Although it has important theoretical and economic significance,there are few reports for the research of its wear and corrosion resistance so far.In this paper,Mo/Al₂O₃ composites samples with different powder size and component ratio were prepared by pressureless sintering,the phase,composition and microstructure of the sintering samples were analyzed by XRD,EPMA and SEM,and samples sintering characteristic was also tested.Conclusions are as follows:The phase with less percentage composition distributes uniform dispersion in the other matrix phase when the volume content of Mo is lower or higher,When the volume content of Mo is 40%,the continuous distribution of Mo and Al₂O₃ is weakened,and the phase structure under this condition affectes the properties of the materials.The linear contraction rate,relative density and hardness of the Mo/Al₂O₃ composites increase with the rising of temperature.The relative density is higher at 1750℃,and the highest relative density is 96.9%.Except samples with vol.40%Mo,the Mo/Al₂O₃ composites have a similar relative density under this temperature,the linear contraction rate and hardness of the Mo/Al₂O₃ composites decrease gradually with the increasing of the volume content of Mo.The linear contraction rate,relative density and hardness of the Mo/Al₂O₃ composites enhance with the decreasing of powder size. When testing the flexural strength of the Mo/Al₂O₃ composites with the small powder size,it is found that the flexural strength increases with the rising of the volume content of Mo.It is intergranular fracture when the volume content of Mo is lower, while intergranular fracture and transgranular fracture appear when the volume content of Mo is higher.The wear behavior and wear mechanism of Mo/Al₂O₃ composites were studied and worn surfaces were observed by the SEM.Results indicate that the friction coefficient decreases with the increasing of the load and the powder size,and rises with the increasing of the volume content of Mo.The wear rate of the Mo/Al₂O₃ composites increases with the rising of the load and the powder size and shows the rising trend with the increasing of the volume content of Mo,and there is a peak value when this percentage reaches 40.The wear mechanisms are brittleness break off and abrasive wear when the volume content of Mo is low,and it shows abrasive wear when the volume content of Mo is higher.The Mo/Al₂O₃ composites were corroded uniformly in three common acids under normal temperature,its corrosion behaviour and corrosion mechanism were studied and corrosion pattern were observed by the SEM and metalloscope.It is found that the corrosion rate in the nitric acid is greater than that in the sulfuric acid and hydrochloric acid.The Mo/Al₂O₃ composites have good corrosion resistance in the sulfuric acid and hydrochloric acid.The corrosion rate decreases and goes to stabilization with the time prolonging,it also declines with the powder size reducing. The corrosion rate of the Mo/Al₂O₃ composites in the nitric acid shows the rising trend with the increasing of the volume content of Mo,and there is a peak value when this percentage reaches 60,but it is reverse in the sulfuric acid and hydrochloric acid, the corrosion rate declines with the increasing of the volume content of Mo,and there is a peak value when this percentage reaches 40.The corrosion mechanisms are chemical reaction corrosion,pitting corrosion and intercrystalline corrosion.The Mo/Al₂O₃ composites have good wear and corrosion resistance when the powder size is small.