Effect Of Graphene On Microstructure And Mechanical Properties Of Tial-based Alloy Prepared By Powder Metallurgy

Ti Al-based alloys are considered one of the most promising high temperature structure materials to take the place of nickel-based alloys in the field of automotive components and aerospace for its excellent mechanical properties, such as light weight and high specific strength, resistance to oxidation and creep. However, poor plasticity and low forming property limit their practical application as a structural material. Powder metallurgy is considered to be an important way to prepare Ti Al-based alloys for it can receive refined grain and can fulfill near net shape, what’s more it’s convenient to add alloyed elements. It has been reported that alloying elements and wild phase can reinforce the mechanical properties of Ti Al alloys. Therefore, a new material graphene, which is ultrathin and has high fracture strength, was added to Ti Al-prealloyed powders to prepare alloy through spark plasma sintering.The average size of the prealloyed powders is 171 um. Its shape is almost regular circle shape, with defects such as cracks and stomata occasionally. There are different dendritic structures in the surface and internal of the powder. The powder is consist of α2 phase and γ phase, and most is α2 phase. Graphene powders with atom fraction of 0.2%, 0.4%, 0.6%, 0.8% respectively were added into the Ti Al-prealloyed powders. Different processes have been tried to mix them together. Results showed that 16 hours was the best which 20r/min and 30r/min executing alternately every two hours. Furthermore, the progress was operated in glovebox which was full of argon.The mixed powders was sintered in the condition of 1250℃/20min/50 MPa, then received column of φ60×10mm, whose density were 98%. The microstructure without graphene was heterogeneous, which was formed by tiny γ phase and thick sheet structure. The microstructure was becoming more and more refined, with the increasing of graphene. Finally the Ti2 Al C phase was found.Mechanical properties of the sintered ingot were tested. The researched results showed that, the bending strength becomed higher and higher, which increased from 602 MPa to 999 MPa, and the friction coefficients decreased from 0.6 to 0.4,whose wearability was improved remarkably, with the increasing of graphene. But the compression strength decreased first and then increased, which increased from 2001 MPa to 2347 MPa, when adding 0.8% grapnene.The heat treatment experiments of 1250℃ to 1300℃ showed that, the duplex microstructure could be got in the condition of 1290℃/4h cooling inside the furnace. With the increasing of the amount of graphene, there appeared more and more Ti2 Al C phase which distributed in the boundaries.