Preparation,Strengthening And Toughening Mechanism Of Al₃Ti Intermetallic Compound Composites

With the rapid development of industries such as aerospace,armor protection,and high-speed transportation,the Ti-Al intermetallic compound Al₃Ti has attracted increasing attention due to its lowest density（3.36 g/cm³）,highest elastic modulus（216 GPa）,relatively high melting point（1360℃）,and excellent high-temperature oxidation resistance.However,the stability of the Al₃Ti crystal structure,which is a tetragonal D0₂₂structure,results in almost no slip system at room temperature,and its room temperature brittleness significantly limits its engineering applications.In order to improve the room temperature brittleness of Al₃Ti intermetallic,enhance its room temperature plastic deformation capability while maintaining its strength,and explore its toughening mechanism,this paper proposes a design concept based on metal matrix composites.Firstly,a layer structured toughened Al₃Ti intermetallic composite material,TC4-Al₃Ti,was prepared by using a vacuum hot pressing sintering method.In addition,in order to further improve the strength and toughness of Al₃Ti intermetallic,a novel（Ti₃Al C₂+Al₂O₃）_p/Al₃Ti composite material was prepared by using Ti O₂,Al,and Ti C composite powders to enhance the in-situ reinforcement phase in the Al₃Ti matrix.Based on the layer structure toughening and in-situ particle toughening,detailed research was conducted on the microstructure,formation mechanism,and mechanical performance changes of the two prepared composite materials under external load conditions.The reinforcing mechanisms of the layer structure and in-situ reinforcement phase were studied in detail,and the effects of the two toughening methods were comprehensively evaluated.Finally,a toughening concept for Al₃Ti alloy was proposed,which provides a scientific reference for further promoting the practical engineering applications of Al₃Ti intermetallic.It is extremely difficult to study the deformation behaviors of TC4-Al₃Ti laminated composite material through the direct experimental observations.In this work,GND density was used to study the deformation process of composites under the incremental compression test.The SEM and EBSD techniques were used to investigate the microstructure,phase formation process and deformation process of Ti-Al laminated composites in detail.Results show that:during the deformation process,the GND density of the Al and Ti layers gradually increased,while the Al₃Ti layer decreased first and then increased.And the Al₃Ti layer was a coordinated deformation under the constraint of layered structure and then plastic deformation occurred.GND was uniformly distributed in the Al layer first and then concentrated at the Al/Al₃Ti interface,while it was not uniformly distributed in the Ti layer.In addition,we also investigated the formation process and fracture morphology of the Al₃Ti layer,which can provide beneficial assistance for the further development and application of TC4-Al₃Ti laminated composites.In order to further enhance the strength and toughness of Al₃Ti intermetallic,this study also utilized vacuum hot pressing technique to prepare a novel（Ti₃Al C₂+Al₂O₃）_p/Al₃Ti composite material using Ti C,Ti O₂,and pure Al powders.Its phase formation and microstructure evolution were systematically investigated by X-ray diffraction（XRD）,differential scanning calorimetry（DSC）,transmission electron microscope（TEM）and a scanning electron microscope（SEM）with an energy-dispersive spectrometer system（EDS）.The mechanical properties of the（Ti₃Al C₂+Al₂O₃）_p/Al₃Ti composite were measured using compression test and nanoindentation test.The results show that Ti₃Al C₂is mainly grown from the intact Ti C grains through epitaxial nucleation mechanism,while Al₂O₃is precipitated via dissolution-precipitation mechanism.The measured mechanical properties show that the hardness of the Al₃Ti alloy increases from 6.2 GPa to 8.79 GPa,and the strength of the composite has an increase of～15%while having a higher ductility.The enhancement of mechanical properties is attributed to the load transfer strengthening,which is related to the refinement of Al₃Ti grains,the CTE mismatch between the Al₃Ti matrix and the reinforcements,and dislocation multiplication caused by the precipitated Al₂O₃particles in the Al₃Ti matrix.