Study On Ti/Al₂O₃Composite Preparing Processes Based On Hot Press Sintering

Both Ti and Al₂O₃have high strengh and good corrosion resistance with light mass, andthey have similar coefficients of thermal expansion and good chemical compatibility. HotPress （HP） sintering technoledge is wildely used in fabricating cermets with lower sinteringtemperature and shorter holding time. In this article, HP sintering technoledge is adopted tofabricate Ti/Al₂O₃composite for promoting the application of this composite.XRD, SEM, EDS were used to analysis the reaction characteristics of HP-sinteredTi-Al₂O₃interface. Results showed that Al₂O₃dissociate Al and O atoms which diffused intotitanium. Ti3Al and TiAl were detectived nearby the layer of Ti and that of Al₂O₃respectively,which resulted from the reaction between Al and Ti. O atoms solid soluted into Ti. Littlenanocmeter nickel doped could react with Al and Al-Ni intermetallic producted, which slowdown the interface reaction, reduce the distance of Al diffused to Ti and restrained the productof Ti3Al.Ti/Al₂O₃composite was fabricated by HP sintering technoledge. Mechanical propertiesof composite were tested and the thermodynamic parameters of interface reaction3Ti+Al=Ti3Al were calculated. Results showed that relative density of composite increased,while bending strength, fracture toughness, micro hardness increased firstly then decreasedwith the rising of temperature. Acticity coefficient of Ti and Al increased and the Gibbs freeenergy of interface reaction decreased with the rising of temperature, which lead to Ti3Alproduced easily. The increase of Ti3Al degraded composite’s properties.Nano-nickel and niobium were selected as interface reaction control agent to control theTi-Al₂O₃reaction. Results showed that doping of nickel and niobium could slow down theTi-Al₂O₃reaction, prevent the production of Ti3Al and improve mechanical properties ofcomposite.The technological parameters optimized experiments showed that the relative density,bending strength, fracture toughness and micro-hardness could reach98.91%,384.27±13.11MPa,8.02±1.23MPa·m^1/2and16.16±1.43GPa respectively when the Ni contentwas3vol%, sintering temperature was1400℃, holding time was60min and heating rate was20℃/min, while them were98.38%,374.55±42.04MPa,7.62±0.60MPa·m^1/2and 16.56±2.37GPa respectively at the condition of Nb content of1.5vol%, sintering temperatureof1420℃, holding time60min and heating rate of20℃/min.Study on the mechanism of improving properties of Ti/Al₂O₃composite indicated thatdoped metal could take effect the properties of Ti/Al₂O₃composite positively by refininggrains，decreasing porosity of materials, inhibit interface reactions and changing the fracturemode of intercrystalline into the blending fracture mode of intercrystalline andtranscrystalline. The deflection and bridging of crack propagation enhanced the fracturetoughness of composite.