In-situ preparation and properties of ZrB2 ceramics by boron/carbothermal reduction combined with hot pressing sintering
To reduce the cost and improve the performance,ZrB2 ceramics were prepared using ZrO2,B4C,and carbon black as the raw materials,with n(ZrO2)∶n(B4C)∶n(C)ratios of 2∶1∶3,2∶1.1∶3,2∶1.2∶3,2∶1.3∶3,by the boron/carbothermal reduction combined with hot pressing sintering.The probabilities and initial reaction temperatures of various reactions in the ZrO2-B4C-C system in different CO partial pres-sures(10 5,10 2,1,10-2 Pa)were calculated using reaction thermodynamics.The effects of the n(ZrO2)∶n(B4C)∶n(C)ratios and the heat treatment temperatures(1 800,1 850,1 900,and 1 950 ℃)on the proper-ties,phase composition,and microstructure of the specimens were investigated.The results indicate that:(1)low CO partial pressure significantly reduces the initial temperature of each reaction in the ZrO2-B4C-C system;(2)as the B4C addition increases,the content of ZrB2 increases;when n(ZrO2)∶n(B4C)∶n(C)=2∶1.2∶3,the oxygen content in the synthesized ZrB2 powder(in the form of B2O3 and ZrO2)is only 0.333 mass％;(3)with increasing heat treatment temperature,the specimen density and hardness gradual-ly increase,while flexural strength and fracture toughness initially increase and then decrease;when the heat treatment temperature is 1 900 ℃,the specimen exhibits the best comprehensive performance,with the relative density,fracture toughness,flexural strength,and cold hardness of 91.75％,4.87 MPa·m1/2,525 MPa,and 18.6 GPa,respectively.
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