| With the development of industrial,the application of seamless steel pipe has become increasingly widespread,and the demands and production quantity requirements have been raised rapidly.The outside mold sleeve is an essential part in the seamless steel pipe production process.Traditional outside mold sleeve is prepared from H13 tool steel which has good overall performance.Though H13 steel has better combination property,the outside mold sleeve is easily damaged by the strong impact and the effect of friction and wear during the production process.The shorter service life leads to the rise in the cost of production and significantly limits the mass-production and the use of the seamless steel tubes.Therefore,the aim of this paper is to fabricate Al2O3/W-Cr metal matrix composites as a new outside mold sleeve material instead of H13 tool steel.An appropriate preparation method is performed and the enhanced particle formation mechanism is proposed.The influences of refinement of reinforcing particles,the strengthening phase Al2O3 content,the pressing pressure and the sintering process are studied during the experiment.The hardness and density of composite material are tested by the use of rockwell hardness tester and Archimedes drainage method,respectively.The friction and wear properties of composites at room temperature are researched by HT-1000 friction and wear testing machine.The microstructures of Al2O3/W-Cr composite are observed and the composition and worn surface morphology are analyzed.In addition,SEM and EDS are used to discuss the connecting method between metal matrixes and reinforce particles,as well as the friction and wear mechanism of composite at room temperature.The main research works and conclusions are as follows:(1)By comparison with two methods(ordinary powder metallurgy method and sol-gel and raw powder metallurgy method),the antigenic alumina reinforcement particles are distributed uniformly in Al2O3/W-Cr composite prepared by sol-gel and raw powder metallurgy method and combine with tungsten-chromium matrix well.In addition,the aggregation phenomenon of reinforcing particles is obviously improved and the problem of associativity caused by large density difference and poor wettability between alumina and tungsten-chromium is overcome.The results indicated that the proposed method is appropriate for fabrication of Al2O3/W-Cr composite.(2)The alumina reinforcing particles in Al2O3/W-Cr composite prepared by sol-gel and raw powder metallurgy method are obtained by heating dehydration decomposition of Al(OH)3 that is generated by sol-gel.The α-Al2O3 which has the best enhancement properties can be obtained when Al(OH)3 is heated at 1200℃ for one hour.According to the particles reinforcing mechanism,the strengthening effect can be enhanced when reinforced particles are refined.Therefore,two different refining methods for alumina reinforcing particles are adopted and validated,i.e.,organic solvent displacement method(alcohol washing method)and polyethylene glycol dispersant inhibition method.(3)The relations among density,hardness of the composite and pressing pressure,sintering processing and content of Al2O3 are determined by this study.The optimal processing for preparing Al2O3/W-Cr composite is that the pressing pressure is defined at 500MPa,the sintering temperature is 1600℃ and the volume fraction of alumina reinforced phase is 10%.In this processing,the composite’s rockwell hardness can be up to 59.3,and the density can be up to 95.63%.(4)The matrix of Al2O3/W-Cr composite is composed of tungsten,chromium and tungsten-chromium solid solution,the reinforced phase is composed of alumina,and there are chromium-aluminum compounds in the composite.Moreover,the combination between alumina reinforcing particles and tungsten-chromium matrix is close.The chromium plays a role of connecting transition in Al2O3/W-Cr composite.And the interface adhesion way between alumina particles and tungsten-chromium matrix is metallurgical bonding instead of mechanical package.(5)With the increase of Al2O3 volume fraction,the friction coefficient and wear rate of Al2O3/W-Cr composite will be significant decreased.On the other hand,with the increase of test load,the friction coefficient will be first increased and then decreased,while the wear rate will be increased.When the volume fraction of Al2O3 or test load is lower,the wear of Al2O3/W-Cr composite is dominated by abrasive wear.But when the volume fraction of Al2O3 or test load is higher,the wear is dominated by adhesion wear,and accompanying abrasive wear. |
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