Effect Of Processing And Heat Treatment On The Microstructure Evolution Of TA18 Titanium Alloy

TA18 titanium alloy is a low-alloy near α titanium alloy developed in the United States in the late 1960 s.Because of its excellent mechanical properties,corrosion resistance and excellent welding properties and cold forming properties,the alloy is applied to the aircraft pipeline system and the preparation process is becoming increasingly mature.TA18 titanium alloy usually using the traditional thermal processing technology to prepare the tube blank into tube,in the whole process,because the different positions of tube blank and tube have the characteristics of microstructure difference,texture difference and uneven mechanical properties,it will seriously affect the tube service performance,so it is necessary to establish the correlation between the microstructure of the alloy and texture and the corresponding mechanical properties.In order to obtain the tube billet with fine and uniform microstructure for producing high strength TA18 titanium alloy tube,the microstructure,texture and mechanical properties of TA18 titanium alloy bars with a diameter of 40 mm after radial precision forging and hot rolling were investigated by metallographic microscopy and electron backscatter diffraction(EBSD)technique.The bars were subsequently annealed for 1.5 hours at 700℃ and 800℃,respectively.The influence of subsequent heat treatment on the α phase microstructure and mechanical properties were analyzed.The compression experiments with compression deformation of 10%,20%,30%,50%and 70% carried out for the nearly α type TA18 titanium alloy bars after radial precision forging and hot rolling.The bars were subsequently annealed for 2 hours at510℃.Combined with the microstructures and mechanical properties of rod billet,tube blank and the tube,studying the influence of different processing processes and heat treatment systems on the tissue evolution and mechanical properties of TA18 titanium alloy.The research results can provide a reference for the study and regulation of TA18 titanium alloy microtissue characteristics,and can also provide a theoretical basis for the preparation and production of TA18 titanium alloy tubes.After the analysis of the microstructure and mechanical properties of the TA18 titanium alloy caused by different processing processes and heat treatment,a strong tissue heritability was found inside the alloy.It is found that TA18 alloy can achieve uniform microstructures after both radial precision forging and hot rolling,and the edge and center regions of the bar have the same texture type,where the α grains exhibited strong preferred orientation and presented <10-10> fiber texture.The mechanical properties of the alloy after radial precision forging and hot rolling were basically consistent.The grain size and distribution of the alloy were still relatively uniform after annealing,and the texture type of each part was basically unchanged,but the texture intensity was weakened.According to the tissue uniformity and mechanical properties of the rod after heat treatment,the fine forging process and 800℃/1.5h annealing heat treatment process are recommended.In the next step,the pipe preparation and combining the microtissue morphology and crystal orientation characterization results are needed to study the influence of different processing processes and heat treatment systems on the microstructure and mechanical properties of TA18 titanium alloy.