Research On Preparation And Diffusion Reaction Mechanism Of TiAl/Nb Composite Material

TiAl-based alloys are considered to be ideal aerospace materials because of their high strength,low density and good oxidation and high temperature resistance.However,the TiAl-based alloy has extremely high brittleness and poor hot workability,so that it is difficult to plastically process it,which limits its application in the industrial field.While Nb has good high temperature strength and good low temperature plasticity,it is an excellent choice to improve the room temperature ductility of TiAl alloy by adding it to TiAl-based alloy as a binder phase.TiAl alloy and Nb rely on the diffusion reaction in the process of forming composite materials,and the interface microstructure and properties formed play a decisive role in the physical and mechanical properties of composite materials.Therefore,it is very important to accurately grasp the diffusion progress,reaction products and reaction speed.In this paper,two kinds of TiAl/Nb composite materials were prepared respectively by powder metallurgy technology,using high-purity Nb block and Nb powder as raw materials and Ti-47Al-2Cr-2Nb powder prepared by atomization method.Through optical microscope(OM),Scanning electron microscopy(SEM),energy spectrum analysis(EDS)and other test and analysis methods have systematically studied the microstructure and element distribution of samples that have been heat-treated with different parameters in a vacuum high-temperature tube furnace.The thickness of the product produced represents the degree of reaction progress,and a reaction kinetics equation expressing the relationship between the degree of reaction,time and temperature is established.The mechanical properties of the material are analyzed through thermal simulation compression experiment and room temperature tensile experiment,and the strengthening mechanism of Nb phase in the deformation process is explored and discussed.The main contents are as follows:The TiAl-9%Nb composites prepared by powder metallurgy were subjected to vacuum heat treatment in the range of 1160?-1320?,and their thermal diffusion structure was characterized.It is found that the TiAl particles in the original structure have basically no deformation and are dispersed in the continuous area sintered by the Nb powder;increasing the heat treatment temperature and maintaining a longer heat treatment time can promote the diffusion of elements in the structure;in the initial stage of the diffusion reaction,the main diffusion The elements are Al and Nb,When the elemental Nb is not completely diffused,the phase composition of the relatively stable diffusion layer around it is mostly?-Nb2Al+O-Ti2Al Nb+?-TiAl;the diffusion process can be divided into the initial diffusion stage,The reaction diffusion stage and the stable zone generation stage;through diffusion reaction,TiAl elemental zone,TiAl diffusion zone,TiAl reaction stable zone,Nb reaction stable zone,Nb diffusion zone,and Nb elemental zone can finally be formed.By sintering the Nb block and TiAl powder to obtain a clear interface sample,the thermal diffusion experiment was carried out at the temperature of 1120?-1320?,and it was found that when the Nb block and the TiAl powder sintered sample are diffused,the Nb element is more likely to move to Diffusion in the TiAl phase,forming a larger stable diffusion zone on the TiAl structure side.The growth kinetic equation of the total thickness of the TiAl-Nb diffusion reaction product is calculated.The kinetic constant is0.2 and the reaction activation energy is 647.4 k J/mol.Through the thermal simulation compression experiment,it is found that the true stress-strain curve of the material includes three stages:increasing hardening,decreasing softening,and tending to stabilize.Increasing the compression temperature and reducing the strain rate will reduce the stress peak of the material.The minimum stress peak is350.3MPa under the compression parameter of 1000?and 0.001s^-1,and the compression parameter of 800?and 0.01s^-1.There is a maximum stress peak value of 666.11MPa;a large amount of?-TiAl/?₂-Ti₃Al lamellar structure is formed between the original TiAl particles and the Nb phase;the Nb phase in the sample bears a large amount of deformation.An adiabatic shear zone appeared in the center of the sample,the lamellar?/?₂ brittle structure was bent and deformed,and microcracks appeared at the lamellar phase interface,which would become the starting position of material failure.The addition of the Nb phase component improves the deformation ability of the material at room temperature.In the room temperature tensile experiment,the tensile strength of the sample decreases slightly,but the elongation rate of the material reaches 3.4%.