The Preparation And Properties Of Al₂O₃/TiAl Composite Materials

TiAl-based intermetallic compounds are used as alternative candidates for nickel-based heat-resistant alloys because of the low density,high strength,and good performance at high temperatures;Their comprehensive utilization methods are severely limited due to their low-temperature brittleness and economical preparation.It is difficult to greatly improve the performance of TiAl alloys solely by means of alloying.To achieve a breakthrough in performance,the development of intermetallic compound-based composite materials is one of the effective methods,and it is aimed at the ball milling of composite materials currently prepared by powder metallurgy Insufficient process research,in this paper,the in-situ synthesis of second-phase Al₂O₃ particles is used to improve the comprehensive properties of TiAl alloy.Element powder or pre-alloyed powder were used as raw materials,alloying was achieved by high-energy ball milling,and sintering and curing were completed by spark plasma sintering(SPS)sintering or hot-pressing sintering to prepare Al₂O₃/TiAl composites.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM),X-ray diffraction analysis(XRD),thermal analysis(DSC)and other methods equipped with energy spectroscopy were used to systematically study the morphology average size,distribution uniformity of the powder during the high energy ball milling process,and the mechanical properties and microstructure of the as-sintered alloy.When Al₂O₃/TiAl composite was manufactured from elemental powder Al powder,Ti powder,and TiO₂ powder,Nb₂O₅ powder,it was found that the milled mixtures experices a continuous cycle of crushing and fracture-cold welding-re-crushing with the alloying phenomenon during the ball milling process.Al₂O₃ and TiAl phases were detected in the XRD of the as-milled powders.The ball-to-material ratio has an effect on the morphology of the powder,but it has little effect on the degree of alloying of the powder.The structure of composite mainly includes TiAl,Ti₃Al,Al₃Nb and Al₂O₃ phases,and the in-situ synthesized Al₂O₃reinforcing phase is distributed on the matrix TiAl grain boundaries in a network manner.By studying the milling time on the preparation of Al₂O₃/TiAl composite,it was found that the alloying was happend during the ball milling process.The as-SPSed compacts were mainly composed of?-TiAl phases,?2-Ti₃Al phases and Al₂O₃ particles that tended to disperse both on the grain boundaries and inside the lamellar microstructure of the matrix.With increasing the milling time of mechanical alloying,Al₂O₃ nucleation at the grain boundary edges and the lamellar colonyof the matrix is facilitated,so that there are more Al₂O₃ particles strengthening phases in the collective.The ultimate compressive strength of the composite material reached a maximum value of 1848 MPa when the mixed powders milled for 15 h,and its hardness value increased with increasing ball milling time.The maximum hardness reached 6.2 GPa at 20 h of ball milling.By studying the the effect of different Al₂O₃ content on Al₂O₃/TiAl composites found that the matrix structure can be refined by the Al₂O₃ particles.The fractions of?₂ phase and?₂/?lamellar colonies increase with the content of Al₂O₃ increasing.The fracture types of Al₂O₃/TiAl composites are mainly composed of transgranular,translamellar and delamination fracture.When the Al₂O₃ content is increased to 0.5wt.%,The composite has the best comprehensive mechanical properties,the yield stress is 1032±13MPa,and the breaking strength is 2668±15MPa.Its friction coefficient is lower than other TiAl composites with Al₂O₃ content.The wear mechanism of TiAl composites is abrasive wear and furrows.The results of electrochemical corrosion experiments show that with the addition of Al₂O₃particles,the chemical corrosion properties of the composites are significantly improved.