Effect Of Different Doping On The Mechanical And Thermal Properties Of Al₂O₃-based Composite Ceramics Material

Alumina ceramics were used widely in aerospace,cutting tool,engines and other fields due to perfect properties such as high melting point,high hardness and acid and alkali corrosion resistance.However,fracture toughness(3 MPa·m^1/2-4 MPa·m^1/2)and flexural strength?400 MPa-600 MPa?of alumina ceramics are relatively low,which greatly limits the future promotion and application.At present,multiple toughening has been the emphases of research and development direction of improving comprehensive mechanical properties of structural ceramics.In this paper,the comprehensive mechanical properties of ceramic materials are enhanced by the combination of transformation and particle toughening.The microsture,mechanical and thermal properties of composites,prepared by Spark Plasma Sintering?SPS?,were characterized by test instrumentation,such as X ray diffractometer,scanning electron microscope?SEM?,laser thermal conductivity,and test measurement,such as archimedes method,single edge notched beam,three-point bending method,analyzing the influence of dopant on physical properties of composites and discussing the related mechanism.The research indicates that:For zirconia toughened alumina composite ceramics,the relative density,fracture toughness and flexural strength reach the maximum when the content of ZrO₂ was20mol%,97.8%,5.2MPa·m¹/2/2 and 954.3MPa respectively.The main reasons for the improvement of mechanical properties of composite ceramics were dispersion strengthening and transformation toughening of ZrO₂ grains.The SEM image showed that intergranular fracture is the main fracture mode of the composite ceramics.Moreover,with ZrO₂ content increasing from 10mol%to 25mol%,the thermal conductivity gradually decreased from 21.7W/m·k to 16.9W/m·k.Meanwhile,the vickers hardness gradually decreased from 21.5GPa to 19.3GPa.For MgAl₂O₄ reinforced ZTA composite ceramics,the introduction of MgAl₂O₄improved comprehensive properties of composite ceramics.The maximum relative density?99.81%?,fracture toughness(8.55MPa.m^1/2)and flexural strength?1056MPa?are achieved when the MgAl₂O₄ content is 15 v.%.The improvement of fracture toughness of composite ceramics can be attributed to fracture mode transformation.In addition,with the MgAl₂O₄ content increasing from 15 v.%to 30 v.%,the thermal conductivity gradually decreased from 18.0W/m·k to 14.2W/m·k.Meanwhile,the vickers hardness gradually decreased from 19.1GPa to 17.5GPa.For micron-sized titanium carbide hard particles?TiC_m?reinforced ZTA composite ceramics,the fracture toughness increased from 4.63 MPa.m¹/2/2 to 6.41MPa.m¹/2/2 with the increasing of TiC_m content.Meanwhile,flexural strength can reach750MPa.The main reasons for the improvement of fracture toughness of composite ceramics were the interaction between high modulus TiC particles and cracks,including crack bending,deflection and arch bridge effect.However,the fracture toughness and flexural strength of the composite ceramics can reach only 4.11MPa·m¹/2/2 and 400MPa,doping with the same proportion of nano-sized titanium carbide hard particles.SEM images showed that the surface of the composite was agglomerated seriously.In addition,the thermal conductivity of the composite ceramics gradually decreased from 16.85W/m·k to 12.63W/m·k with the TiC_m content increasing from 10 v.%to 25 v.%.For micron-sized zirconium carbide hard particle?ZrC_m?reinforced composite ceramics,the fracture toughness and flexural strength can reach up to 10.61MPa·m^1/2and 875MPa when the contents of ZrC_m reached 25 v.%.However,the fracture toughness and flexural strength of composite ceramics were only 6.71 MPa·m¹/2/2 and723 MPa doping with the same proportion of nano-sized zirconium carbide hard particles.This was due to the nanoparticles size is so small that the hindering effect of martensite phase transition it exerts on is greater than the promotion,resulting that the effect of the phase transition toughening weakened.In addition,the vickers hardness of composite ceramics gradually decreased from 17.3GPa to 16.69GPa with the ZrC_n content increasing from 10 v.%to 25 v.%.