Preparation And Microarc Oxidation Surface Modification Of The Microwave Sintered Titanium Matrix Composites

The titanium matrix composites have been widely used in several industrial field including aerospace,aviation and civil industies due to its excellent mechanical properties under room temperature and high temperature.To further study the influences of different reinforced phases on the microstructure and properties of titanium matrix composites and further improve their surface properties,the TiC/Ti6Al4 V and graphene/Ti6Al4 V composites were prepared by microwave sintering powder metallurgy in this thesis.The effects of microwave sintering temperatures and TiC contents on the microstructure,mechanical properties,wear resistance and oxidation resistance of TiC/Ti6Al4 Vcomposites.Meanwhile,micro-arc oxidation surface treatment technique is adopted to further improve wear resistance and oxidation resistance of TiC/Ti6Al4 V composite,the effects of electrolyte composition and TiC contents on microstructure and properties of MAO coatings were analyzed.At last,the effect of the graphene as a new reinforced phase on the microstructure and properties of the composites was also studied as well as the existence of the questions.The results show that microwave sintered TiC/Ti6Al4 V composites are composed of α-Ti+β-Ti and TiC phases.The matrix(α-Ti+β-Ti)phases exhibit equiaxed organization and TiC phase is in the C-deficient state.The density,microhardness and compressive strength at room temperature of TiC/Ti6Al4 V composites all increase with increasing the sintering temperatures or TiC contents.The density,microhardness and compressive strength of the TiC/Ti6Al4 V composites reach 98.01%,661HV0.1,and 1789 MPa respectively under the optimal sintering conditions at sintering temperature of 1200℃ and TiC contents of 15 wt.%.In GCr15 or ZrO2 friction pairs,the volume wear rate of the composites decreases compared with that of Ti6Al4 V alloy.With increasing the oxidation temperatures,the curve of the oxidation rule is changed from parabolic to linear.With increasing the TiC contents,oxidation activation energy increases,the particle size of oxide decreases and the oxidation resistance of TiC/Ti6Al4 V composites improves.Under NaH2PO2+Na2SiO3 electrolyte,a micro-arc oxidation coating composed ofanatase TiO2 phase can be produced on the surface of TiC/Ti6Al4 V composites.The corrosion current density of the coated composites is two orders of magnitude lower than that of the matrix.At the same time,the coated composites have well wear resistance.The micro-arc oxidation coatings on the surface of TiC/Ti6Al4 V composites further improve the oxidation resistance at high temperature.However,with the increase of TiC contents,the coating spalls off fast.When the graphene as the reinforced phase,the graphene tends to react to Ti interface and produce tiny TiC particles with the increase of sintering temperature.The density and microhardness of the graphene/Ti6Al4 V composites are both enhanced.When the graphene is coated by copper,TiC contents at the interface increase on the contrary.In association with introduction of Ti2 Cu phase,a small amount of copper can decrease the sintering temperature and improve mechanical properties of graphene/Ti6Al4 V composites.