Reactive Melt Infiltration Process Of ZRC-W Composites And Microstructure Evolution

ZrC-W composites have been widely used in the field of ultra-high temperaturematerials due to their excellent properties. Compared with other preparationmethods, the reactive melt infiltration method is cost saving and to decrease thesintering temperature and the cost, and realize shape manufacturing. The presentstudy focuses on the effect of prefabrication, infiltration process and heat treatmentprocess on icrostructure of ZrC-W composites prepared by reactive melt infiltrationmethod, finally the microscopic reaction mechanism was discussed.The results of WC perform fabrication process show that with the increase ofcold forming pressure, the porosity of the preform decreases. While under the samepressure, the perform of WC with smaller grain size shows larger porosity.Freeze-dried preform has an average pore size of1.89μm, and an opening porosityof58.36%. After1300°C/1h infiltration, the composite is uniform and dense due tothe complete reaction. The best burn-in process of0.5μm and1μm WC preforms is1300°C/2h, while1400°C/2h for2μm WC preform.Results of infiltration process show that there is more molten alloy in theperform infiltrated by alloy-up method. The reaction degree between WC and Zr inthe composites prepared by continuous impregnation is more complete than thoseby heat treatment after impregnation.After heat treatment of the composites prepared by1100°C/20minimpregnation, the reaction degree between WC and Zr increases with the increasingtemperature and treatment time. After1300°C/120min and1400°C/60min heattreatment, WC and Zr in the composites have completely reacted. Under the sameconditions, increasing the preform porosity or decreasing WC grain size, thereaction rate and reaction degree increase between WC and Zr₂Cu alloys. Thereaction was complete in the composite prepared by the perform of WC with grainsize of0.5μm and57%porosity after heat treatment at1300°C for2h. Theinitial reaction product is ZrCx （x=0.70） and C diffusion was observed apparently.Under the same conditions, both C content in ZrCx and lattice constant increasewith the increasing heat treatment time in the composite with2μm WC particles.Decreasing WC particle size, improving preform porosity or raising heattreatment temperature will induce the reactions within the composite bydissolution-precipitation mechanism. The critical condition was found in thecomposite with1μm and57%porosity WC preform after heat treatment at1300°C.Beyond1300℃the reaction is dominant through dissolution-precipitation mechanism.