Study On The Microstructure And Properties Of CNTS/TiAl And Mo_f/TiAl Composites Prepared By Powder Metallurgy

Compared with traditional aerospace and aerospace metal materials,TiAl-based alloys have attracted widespread attention since the 1970s because of their light weight,high strength,stiffness,and excellent oxidation resistance and creep resistance.It has become a highly competitive material for aero-engine and automotive heat-resistant structural components and is currently used in high-temperature components such as engine blades,turbines and exhaust valves.However,the low temperature performance of the TiAl alloy and the low room temperature toughness limit the further application of TiAl,so it is necessary to improve the room temperature toughness and high temperature strength of TiAl.At present,the casting is still the main molding method of TiAl alloy,but the alloy prepared by casting is prone to casting defects such as shrinkage,shrinkage and segregation.And as hard to add reinforcement,it is not suitable for preparing TiAl-based composite materials.In this paper,by adding two kinds of fiber reinforcements of carbon nanotubes and molybdenum fibers,the purpose of strengthening and toughening TiAl-based alloys is achieved.Ni-CNTS/TiAl and Mo_f/TiAl TiAl-based composites were successfully prepared by hot isostatic pressing and hot pressing.The feasibility of two preparations of TiAl composites was investigated.The effect of micro-reinforcing bodies on the microstructure and mechanical properties（hardness,compression and bending）of the composites,and explains the strengthening and toughening mechanism of the composites.It was found that CNTS/Ti48Al2Cr2Nb composites were successfully prepared by hot isostatic pressing at 1150°C,150 MPa,4h.On the basis of TiAl/CNTS composites,by dispersing nickel on the surface of multi-walled carbon nanotubes,the dispersibility of CNTS in the matrix alloy is significantly improved.The CNTS in the composite material is mainly pinned around the matrix alloy grains,and reacts with the matrix alloy at the interface to form Ti₂AlC and TiC phases.Nickel plating cannot completely prevent the TiAl matrix from reacting with the CNTS,but can improve the dispersibility and chemical compatibility of CNTS in the matrix alloy.The addition of CNTS has a significant refinement effect on the grain of the base alloy.The unnickeled CNTS is in the form of a massive carbon-rich phase in the alloy,while the nickel-plated CNTS is a uniform network and refines the grains more obviously.Compared with CNTS/TiAl composites,Ni-CNTS/TiAl has fewer voids,higher density,higher density,hardness and compressive strength.The Mo_f/Ti48Al composite was successfully prepared by foil-fiber-foil method and hot press sintering.After two-step low-temperature reaction annealing at 635°C/3MPa,10 h+680°C/3 MPa,4 h,the Al in the foil is completely reacted,and the TiAl foil laminate forms a dense Ti/TiAl₃ plate.The alloy is dense and there is no Kerkendall hole.After annealing at 1200°C for 36 h,Ti and TiAl₃ continue to react at high temperature to formγ-TiAl andα-Ti₃Al phases.After the high temperature heat treatment,the molybdenum fiber reacts with the matrix alloy to form a diffusion region.The main phase composition in this region is TiMo and AlMo₃.The molybdenum fiber and the matrix alloy are tightly bonded by diffusion,and there is no hole and crack formed by stress in interface.Compared with the alloy without molybdenum fiber,the bending resistance of the composite with 10vt%molybdenum fiber is obviously improved,and the molybdenum fiber plays a strong and toughening effect in the collective and gold.