Research On The Forming And Microstructure Evolution During Cross Wedge Rolling Of TC6 Alloy Blade

The manufacture of aero-engines is an extremely complex system,of which the most important components are blades.Due to the fact that their performance directly affects the performance and safety of the aero-engine.TC6 titanium alloy,a typical ?+? titanium alloy,has been widely used in the manufacturing of areo-engine blades.At present,the typical process for manufacturing blades is free forging,while the free forging forming process has the disadvantages of artificial dependency,poor process stability and low production efficiency.Therefore,in this work,cross wedge rolling,which is a high efficiency and near-net forming process,has been proposed to produce preforms of titanium alloy blades.This thesis focuses on engineering science problems and technical difficulties corresponding to the high-temperature deformation and microstructure evolution,forming precision and mechanical properties during the cross wedge rolling of TC6 alloy.Firstly,the high temperature phase transformation and hot compression tests were carried out.The experiment results showed that the high temperature flow curves of TC6 alloy is of typical characteristics of work hardening and flow softening.The dynamic globuluaization of platelet alpha phase can be attributed to the grain-boundary separation.Due to the local plastic strain,the softer beta phase can penetrate into the stripe alpha phase and large/low angle alpha boundary or sub-boundary can generate.When the thickness of the penetrating beat phase reaches half of the platelet thickness,the platelet is fractured,and the separated regions gradually become equiaxed.Based on the experiment results,a set of unified constitutive model was established with the interaction among the phase transformation,dynamic globularization and dislocation density considered.The model constants were determined using a Genetic Alogrithm-based optimization method.Afterwards,a thermal-mechanical-microstructure multi-field coupled finite element model was built based on the DEFORM-3D software,and the effects of process parameters on the microstructure evolution during the cross wedge rolling of TC6 alloy were investigated based on this developed finite element model.The results showed that with the increasing of initial deformation temperature,the average volume fraction of alpha phase decreases.Increasing the area reduction,the deformation gradually expands to the core to allow more materials to participate in deformation,causing a larger area of plastic temperature rise and leading to the volume fraction of alpha phase decreases but distributes more uniform.Rolling speed exerts a complex influence on the microstructure evolution.Under lower rolling speed,the temperature drop plays dominant role.With the rolling speed increasing,the plastic temperature rise gradually counterbalances the temperature drop and takes a dominat position.The model parameters do not directly affect the heat exchange mechanism,so it has less impact on the microstructure evolution.To obtain the better strength and plascity of TC6 alloy blades,the response surface model were used to optimize the process parameters,and the results showed that the initial deformation temperature was 870?890 ?,and the rolling speed was 7?10 r/min.Based on the optimized parameters,the TC6 blade was succesfulled manufactured by the new sequence of cross wedge-rolling and isothermal forging.The microstructure of the rolled part is of uniform distribution,and the tensile strength and elongation of the entire workpiece were 11.07.03 MPa and 14.3%,respectively.The isothermal forged blade were complete filling and with smooth streamling.The volume fraction of the alpha phase of the entire blade was greater than 0.3.The tensile strength and elongation of the blade at room temperature were 1196 MPa and 15.7%.Meanwhile,the tensile strength at high temperature of 400?was up to 894 MPa,which can meet the needs of aero-engine blade to delivery.In a word,the basic experiemt of metallic materials,numcrical simulation and cross wedge-rolling experiments were conducted to investige the deformation behaviour and microsture evolution.The new sequence of cross wedge-rolling and isothermal forging was applied to manufacture the TC6 alloy areo-engine blades,whose microsture and mechanical properities meet the requirements of the technical standards.This work not only enriches the practical theory and technological basis of the preform of cross wedge rolling of titanium alloy,but also is expected to solve the technical difficulty of preforming the titanium alloy areo-engine blades.Furthermore,it provides a new method and guidance for establishing the shaping and microstructure controlled production chain of titanium alloy blades which can be popularized by inducstrialization.