Influence Of Thermal Cycling On Mechanical Properties And Friction And Wear Behaviors Of Zirconia-Alumina Multiphase Ceramics

ZrO₂-Al₂O₃composite ceramics have good mechanical properties,excellent wear and oxidation resistance.At present,the choose of materials mainly depends on the properties at room temperature.However,in most cases,the material will undergo multiple thermal cycling with high temperatures.Fatigue damage results in performance degradation.However,the previous research found that ZrO₂-Al₂O₃ceramics have special high-temperature performance due to the phase transformation of ZrO₂.In this work,we prepared ZrO₂-Al₂O₃composite ceramics with zirconia content of 20 wt%,40 wt%,60 wt%,80 wt%,respectively,and studied the composite ceramics after multiple thermal cycling treatment at 1200℃,1300℃,and1400℃.Changes in phase composition,mechanical properties and friction and wearl properties are analyzed.XRD phase analysis of the prepared ceramics showed that the zirconia is tetragonal in the composite ceramics with zirconia content of 20 wt%and 40 wt%.Monoclinic phase begins to appear when the zirconia content is 60 wt%,and the monoclinic phase further increases at 80wt%ZrO₂.As the content of zirconia increases,the bending strength and fracture toughness of the composite ceramics gradually increase.When the content of zirconia is 80 wt%,the mechanical properties of the composite ceramics reach the best,and their bending strength and fracture toughness reach 800MPa and 7.32 MPa·m^1/2respectively.The surface morphology shows that the crystals are more uniform distributed in the composite ceramic with 80wt%zirconia content.After 5 cycles thermal treatment at 1200°C,1300°C and 1400°C,the hardness of ZTA ceramics（20 wt%,40 wt%zirconia）increased after thermal cycling,and the bending strength and fracture toughness decreased.At this time,the fracture morphology observation shows the existence of cracks and the appearance of grain pulling-out,and intergranular fracture is the main fracture model;the phase analysis of ADZ ceramics（zirconia content is 60wt%,80wt%）shows that the proportion of zirconia tetragonal phase varies with the thermal cycling temperature.The tetragonal zirconia gradually increased,and the proportion of tetragonal phase with 80 wt%zirconia at 1400℃reached 75.6%.The bending strength increased from800MPa without thermal cycling treatment to 973MPa after thermal cycling.The phase transformation toughening of zirconia is the main reason for the improvement of mechanical properties.Under dry friction conditions,the friction coefficient and wear of samples with zirconia content of 20 wt%,60 wt%,and 80 wt%after 5 cycles of thermal treatment at 1400°C showed a downward tendency.The wear rate when the content of zirconia is 20 wt%reaches the lowest value of 1.12×10^-8mm³/N·m at 1400℃,which is 84%less than the initial sample without thermal cycling.The wear morphology is obviously smooth after thermal cycling.The furrow is shallower,and the volume of the shedding pit is reduced.