The Relationship Between The Mechanical Property And The Microscopic Structure Of The Titanium Alloy

This dessertation investigates the fatigue property of the TA15 titanium alloy.This fatigue experiment shows that ,for the same TA15 titanium alloy, the fatigue properties of the base material are very different from the material of electronic beam weldin in high circle fatigue .The difference between the base material and material of electronic beam welding is studied in this dissertation .The basic relationship between the macroscopic mechanical property and the microscopic metallographical structure is the emphered in this dissertation .In this dissertation, the macrocrographic mechanical properties of the TA15 titanium alloy beam-welding joints which is used widespreadly in national defence industry are studied by means of the fatigue experiment , ultrasonic and the extention test for TA15 titanium alloy beam-welding joints .The quantitative metallography analysis is carried out to study the microstructural evaluation of the beam-welding area.This research is carried out by follow three steps:①Study the difference of the mechanical property between the base material and the welding joints through the farigue test and the interface extension test;②Measure the elastic constant of the beam-welding joints based on acoustic microscope technology;③Build the basic relationship between the macrographic mechanical property and the micrographic metallographical structure by quantitative metallography analysis.The important outcomes are as follows:①The high cycle fatigue limit of TA15 alloy base-material is 66.7MPa .It is obvious higher than that of the welding-joint.②The interface broken test shows that mechanical property of the welding-joint is changed by electron beam-welding, The mechanical property of base material is obvious better than that of welded seam.There is a transfer region between them.③Elastic constant of the welding-joint was measured in this dissertation . The Young′s modulus of the base material is obvious higher than that of the welded seam. The area between base material and the welded seam is defined as abnormality area of the Young′s modulus. The average width of the area is 4.16mm. The interval estimation is 3.86mm～4.51mm at confidence level 95%.④The result of the microhardness test, grain size measurement and volume fraction measurement certificates that there is a transitional region between the base material and the welded seam. This area is defined as the abnormality area of paraxialαphase volume fraction,the average width is 1.5 mm.⑤Numerical statement of the fracture position of the high cycle fatigue test sample shows that two in the three samples broke in the Young′s modulus abnormality area .The breakpoint is almost the same as the interval estimation of the Young′s modulus abnormality area at confidence level 95%. The accuracy and reliability of this conclussion are still to be verified though large number of tests.