Study On Microstructure Control And Freacture Michanism Of Dissimilar Titanium Alloy Linear Friction Welded Jionts After Welding

The high quality integrated bladed-disks(blisks)of dissimilar titanium alloys formed by linear friction welding can maximize the performance advantages of the two materials and meet the requirements of different service conditions of blade and disk,but the equiaxed grains formed in the weld zone and the microstructure of the thermomechanically affected zone lead to a significant decrease in joint toughness.This article takes TC11/TC17 dissimilar titanium alloy linear friction welded joints as the research object,and the microstructure evolution of the joint was regulated by the bulk heat treatment and electropulsing local treatment conditions.The toughness and strength plasticity changes of the joint structure after regulation were discussed,so as to establish the interdependence between "heat treatment process-microstructure evolution-fracture mechanism" of the joints,and realizes servo control of heat treatment process on solid phase transformation and mechanical properties of the joints.The process optimization criteria for the best matching of joint strength and toughness are formed,providing theoretical basis and technical support for the welding design and preparation of high-performance heterogeneous titanium alloys.Based on the performance control methods of linear friction welded joints with different heat treatments,the microstructure and crystal texture of the joints were characterized by optical microscope(OM),scanning electron microscope(SEM),electron backscatter diffraction(EBSD)and X-ray diffraction(XRD).The results show that after bulk heat treatment,the microstructure difference on the weld zone of the joint decreases.On the TC11 side,fine acicular martensite α’ phase becomes into lamellar α’ phases.On the TC17 side,the equiaxed αgrains are broken and the orthorhombic martensite α" phase transforms into lamellar α+α ’phase;the texture density and dislocation density decrease,whereas the substructured grains increases,and the Schmid factor is uniformly distributed throughout the entire weld zone.After electropulsing treatment,on the TC11 side,the tips of the acicular secondary α’ phase undergoes a local phase transformation,with its tips transformed into the β phase significantly;on the TC17 side original β grains become equiaxed grains,α lamellae becomes thinner,obtaining a complete layer α+β microstructure with refined β grain.In this article,the fracture mechanism of the joint was studied by impact toughness and fracture toughness tests,and the strength and plasticity of the joint were studied by microhardness tests and tensile tests.The mechanical performance test results show that the toughness of the untreated joint after welding is poor,and the fracture morphology is cleavage fracture,exhibiting a brittle fracture mode.The strength and plasticity of the joint are between TC11 and TC17 base metals,and the microhardness values on both sides of the joint fluctuate significantly.After bulk heat treatment or electropulsing treatment,the microhardness on both sides of the joint is more uniform and stable.After double furnace cold annealing,the impact toughness and fracture toughness are increased by 203%and 137%respectively compared with the original joint,after solid solution and high-temperature aging,the impact toughness and fracture toughness are increased by 185%and 129%respectively compared with the original joint,and the fracture surface is a typical ductile fracture mode;After 70s of electropulsing treatment,the impact toughness of the joint significantly increased to 33.5 J/cm2,even equivalent to the TC11 base material.Transgranular fracture and a large number of equiaxed dimples appeared on the fracture surface,and the plasticity of the joint was significantly increased to 14.5%,while the strength remained basically unchanged.By studying the microstructure evolution and fracture mechanism of TC11/TC17 joints under different bulk heat treatment and electropulsing treatment conditions,the interdependent relationship between heat treatment process,joint microstructure texture,and strength and toughness is established,which provides theoretical basis and technical support for the design and manufacture of high-performance aero-engine blisks.