Study On TiC_0.7N_0.3-VC Ceramic Tool Material And Its Thermal Shork Resistance

The aim of this study is to improve the comprehensive mechanical properties of TiC_0.7N_0.3 ceramic tool materials,especially flexural strength.According to the designing principles and the aim of this study,TiC_0.7N_0.3 was chosen to be the based material,VC as second phase,Ni-Mo as metallic additive.And the wettability between Ni and TiC_0.7N_0.3 was studied.And the physicochemical compatibility between raw materials was also studied.Furthermore,the preparation technology,preparation process,sintering process and methods of properties test were introduced in detail,which further proved the feasibility of this study.First,the effects of VC content on microstructure and mechanical properties of TiC_0.7N_0.3 ceramic tool materials have been studied.The results shows that when sintering temperature was 1550?,the content of Ni-Mo was8wt.%,with the content of VC increased from 5wt.%to 20wt.%,the Vickers hardness of TiC_0.7N_0.3-VC ceramic tool material increased gradually,flexural strength and fracture toughness increased first and then decreased.When the content of VC was 10wt.%,TiC_0.7N_0.3-VC ceramic tool materials obtained excellent comprehensive mechanical properties,its Vickers hardness was22.89GPa,flexural strength was 926.77MPa and fracture toughness was7.09MPa·m^1/2.To further improve the mechanical properties of TiC_0.7N_0.3-VC ceramic tool materials,this study optimized the preparation process by orthogonal experiments.The results showed that the optimal system was that of1500?sintering temperature,10wt.%VC content and 8wt.%Ni-Mo content,which was not exists in the previous orthogonal experiments.So,the optimal system needs to be verified by experiment.TiC_0.7N_0.3-VC ceramic tool materials have been prepared with the optimal system.The results showed that the microstructure of TiC_0.7N_0.3-VC ceramic tool materials was distributed homogeneously,and obtained the best mechanical properties,its Vickers hardness was 23.86GPa,flexural strength was1164.62MPa and fracture toughness was 6.03MPa·m^1/2.The Vickers hardness and fracture toughness of TiC_0.7N_0.3-VC ceramic tool materials prepared under the optimal system scheme were not decreased obviously,however its flexural strength increased sharply.The mechanical properties of TiC_0.7N_0.3-VC ceramic tool materials prepared under the optimal system scheme were agreed with the theoretical results,and its toughening mechanism was crack deflection.This article studied the thermal shock resistance of TiC_0.7N_0.3-VC ceramic tool materials prepared under the optimal system scheme.According to the C1525-04,the residual flexural strength and the fracture morphologies have been studied.The results showed that when the thermal shock temperature was lower than 1000?,the oxide layer of TiC_0.7N_0.3-VC ceramics cooling in air was thinner that in boiling water,which was mainly because the internal stress was small when the material cooling in air,and dense oxide layer could protect the inner material of TiC_0.7N_0.3-VC ceramics.When the thermal shock temperature was 1000?,the thickness of oxide later was increased sharply,which was mainly because microcracks were generated on the surface and inner of TiC_0.7N_0.3-VC ceramics.The generated microcracks lead the oxygen permeated into the under surface of TiC_0.7N_0.3-VC ceramics,which made the oxide layer thicken.According to the C1525-04 standard,the Critical thermal shock temperature of TiC_0.7N_0.3-VC was 870?cooling in air and 810?cooling in boiling water.