The Preparation And Mechanical Properties Of Ti₃AlC₂ And Ti₃AlC₂/Ti-Al Composites

With the development of aeronautics and space in our country,high temperature structural materials will meet new challenges.Ti-Al intermetallic compounds combined the characteristics of Ti and Al,such as low density,good high temperature resistant,high specific strength,high modulus,low coefficient of thermal expansion and other excellent properties.These properties made a very broad space for its development in the filed of light high temperature resistant material.They have a very potential application,especially in the engines,which can be used as turbine blade,aircraft shell,and automobile engine and so on.But there still exist problems to Ti-Al intermetallic compounds,such as the poor plasticity at room temperature,bad high temperature oxidation resistance above 900? not easy to produce and so on.And those will limit their application.Using composite technology to design Ti-Al based composites is a very effective way to develop Ti-Al intermetallic compounds.MAX phases have the advantages of both ceramic and metal,which has been considered as the ideal reinforcements for the Ti-Al based composites.The Ti-Al based composites reinforced by MAX phases have been designed and studied in this research.The conclusions are as follows:High purity Ti₃AlC₂ are successfully prepared by high temperature hot pressing method at 1350? from Ti-Al-TiC system.And TiC/Ti₃AlC₂ composites can be obtained at 1100?and 1200 ?.It is found that TiAl3 phase formed first in the reaction,then TiAl3,TiC and Ti reacted to form Ti₂AIC phase,finally Ti₂AlC reacted with TiC to form Ti₃AlC₂ phase.The density,vickers hardness,bending strength and fracture toughness of the high purity Ti₃AlC₂ are 4.40 g/cm3,6.74 GPa,340 MPa and 5.92 MPa m1/2 respectively.The comprehensive performance of the TiC/Ti₃AlC₂ composites is better than that of the high purity Ti₃AlC₂,and the density,vickers hardness,bending strength and fracture toughness of the TiC/Ti₃AlC₂ compsites sintered at 1100 ? are 4.35 g/cm3,4.72 GPa,566 MPa and 6.18 MPa·m1/2 respectively.Ti₃AlC₂-Ti₂AlC/TiAl composites are successfully prepared by hot-pressing method from Ti-Al-Ti₃AlC₂ system at 900 ?.With the increasing content of Ti₃AlC₂ in raw materials,the content of Ti₂AlC phase increases in the composite.The microstructure of the composites is more and more loose,and there exists large numbers of transgranular fracture and lamellar tearing in the composite.The density,Vickers hardness and bending strength of the composite reduced.As the content of Ti₃AlC₂ is 5 wt.%,the density,vickers hardness,bending strength and fracture toughness reach to 3.54g/cm3,2.69GPa,310.68MPa and 7.07MPa·m1/2,respectively.Ti₂AlC/TiAl composites are successfully prepared by hot-pressing method from TixAly-Ti₃AlC₂ system at 1150 ?.As the content of Ti₃AlC₂ is 5 wt.%in raw materials,the composite presents the best performances,and its density,Vickers hardness,bending strength and fracture toughness can be reached to 3.86g/cm3,2.57GPa,921.79MPa and 7.18MPa m1/2,respectively.The existence of Ti₂AlC can refine the grains of the composites.And when the composite breaks,there exists large numbers of transgranular fracture,crack deflection,crack branching and bridging,those phenomena are all helped to improve the performance of the material.Ti₂AlC/TiAl composites are successfully prepared by sintering Ti-Al-TiC-CNTs system at 1250 ?.As the content of Ti₃AlC₂ is 30 wt.%in raw materials,the composite presents the best performances,its density,vickers hardness,flexural strength and fracture toughness can reach to 3.80g/cm3,3.92GPa,408.42MPa and 5.41 MPa m1/2,respectively.The structure of the Ti₂AlC/TiAl composites is dense,and the enhancement phases are net-like distributed in matrix.The lamellar tearing,pulling out of particles,crack branching,crack deflection,intergranular fracture,transgranular fracture and bridging prevent in the product,which can extend the cracks effectively,and finally improve the performance of the materials.