Microstructure And Properties Of Ti₂ALC Particulate Reinforced Aluminium Matrix Composites Prepared By Squeeze Casting

Aluminium matrix composites reinforced with particulates have high specificstrength, high specific stiffness, low thermal expansion coefficient and excellentthermal conductivity. Besides, the preparation process of these composites isrelatively simple and they are easy to machine. All the properties above makeparticulate reinforced aluminium matrix composites the focus of metal matrixcomposites research, they have shown extensive applications in aerospace, aviation,electronics, automotive industries and advanced weapon systems.However, the friction properties and conductivity of many particulatereinforced aluminium matrix composites can not meet engineering needs. Morover,the machining of some composites are very difficult due to high hardness of theparticulates used as reinforcement, which also leads to poor reliability and damagetolerance. Therefore, it is very important to find a type of particulate reinforcementwith excellent friction and electrical properties which can also maintain theexcellent mechanical properties of traditional aluminium matrix composites.Due toits high strength and stiffness, excellent electrical conductivity, plasticity andmachinability, Ti₂AlC ternary compound has drawn great attention recently and hasenormous advantages and potential as a particulate reinforcement.Two different volume fraction particulate reinforced aluminium matrixcomposites（i.e.20%and40%Ti₂AlC/Al） were fabricated by squeeze casting in thepresent study. Microstructure observation and phase identification were conductedvia X-ray diffractometer and scanning electron microscope. Vickers microhardnesstester and universal testing machine were used to evaluate hardness, tensile strength,compressive strength and fracture toughness of the composites and pure aluminiumat room temperature; the reinforcement mechanism of the Ti₂AlC particulate wasdiscussed. In addition，frication and wear properties at room temperature andelectrical conductivity were also investigated.Phase identification results revealed that20vol.%Ti₂AlC/Al composite wascomposed of Al, Ti₂AlC and small quantities of TiC, while40vol.%Ti₂AlC/Alcomposite was composed of Al, Ti₂AlC and small quantities of TiC and TiAl3. Thephase composition difference between the two composites was explained from theprospective of thermodynamics and phase diagram. Densities of the compositeswere determined by Archimedes’ principle; then relevant densities of the compositeswere calculated, results showed that the relevant density was0.98for20vol.%Ti₂AlC/Al composite and1.00for40vol.%Ti₂AlC/Al composite. Scanning electronmicroscopic observation revealed that Ti₂AlC particulate distributed uniformly in Al matrix; there were small quantities of pores in the20vol.%Ti₂AlC/Al compositebut no pore was observed in40vol.%Ti₂AlC/Al composite.Test results of the composites’ hardness, tensile strength, compressive strengthand fracture toughness test at room temperature indicated that Ti₂AlC particulateincreased the mechanical properties of the composites significantly; and themechanical properties above increased with the increase of Ti₂AlC particulatecontent. Meanwhile, the reinforcement mechanisms of Ti₂AlC particulate wereproposed by studying the hardness indentations and fracture morphology; thedefects in the20vol.%Ti₂AlC/Al composite led to a lower fracture toughness than40vol.%Ti₂AlC/Al composite.Dry sliding friction and wear properties were investigated at room temperature,and it was found that the friction process consisted of three stages: initial stage,fluctuation stage and stable stage; friction coefficients and wear rates decreased withthe increase of the content of Ti₂AlC particulate. The wear processes and effects ofTi₂AlC particulate on wear resistance were discussed, it was found that abrasivewear was the predominant mechanism at the initial stage and fluctuation stage;while at stable stage, abrasive wear and debris wear took place simultaneously.Both composites showed metallic conductivity properties, condiuctivitydecreased with increasing temperature. Conductivity of40vol.%Ti₂AlC/Alcomposite at room temperature was7.10MS/m, which was0.60MS/m for20vol.%Ti₂AlC/Al composite due to the interface effect caused by pores existed in thecomposite.