Preparation And Properties Of TiAl-based Alloys By Directional Solidification And Bicrystals

As an intermetallic compound,TiAl-based alloys have some of the characteristics of metals and ceramics,and they have many advantages such as high temperature resistance,oxidation resistance,and low density.However,TiAl-based alloys have obvious room temperature brittleness,which leads to poor plastic deformation processing ability,which hinders their industrial application.In this paper,directionally grown Ti47Al alloy is prepared by directional solidification technology.The effect of drawing speed on its microstructure and mechanical properties is studied.Bicrystals are cut from the directional solidification structure,and the correlation between its deformation behavior and grain boundary structure is studied.The regulation of grain boundary structure provides some basis for improving its brittleness at room temperature,and its oxidation behavior is studied.The main conclusions are as follows:(1)In the process of directional solidification,with the increase of the drawing speed,the grain size and average lamellar spacing in the stable growth zone gradually decrease.Compression tests on directional solidified samples and original ingots with different drawing speeds found that the yield strength,compressive strength,and ultimate compression rate of directional solidified samples gradually increased with the increase of the drawing speed.There is a relatively large correlation between mechanical properties and lamellar spacing..(2)During compressive deformation of directionally solidified specimens,the lamellae perpendicular to the loading direction exhibit greater compressive capacity than the lamellae parallel to the loading direction.Cracks are more likely to occur in the latter and expand along the interface of the lamellae.Part will pass through the sheet,and there are fewer cracks in the vertical sheet.Cracks are prone to grow at the interface of the lamellar interface and extend along the interface.(3)The study of the deformation behavior of the bicrystal specimens shows that the cracks will initiate at the large-angle grain boundaries and propagate along the lamellae of adjacent grains,and the grain boundaries with small orientation differences will hinder the crack propagation.(4)Both the bicrystal and the original ingot follow the parabolic oxidation rule.Elemental analysis of the surface and section shows that the constant temperature oxidation at 800°C for 6h is only in the initial stage of oxidation,and a complete three-layer oxide scale has not been formed.The uneven oxidation of the bicrystal sample relative to the original ingot is caused by the coarse structure,and the oxidation rate is related to the?₂ phase content.