Research On The Quality Of Ta-2.5W Deep Drawing Thin-Wall Revolving Part And The Evolution Of Microstructure

With the development of modern military industry,refractory alloys with excellent high temperature mechanical properties are widely used in more applications.Besides high temperature oxidation resistance,Ta-W alloys show the unique advantages of its relatively good formability to manufacture complex shell parts comparing to the traditional refractory alloys.However,due to the immature process of cold rolling and stamping performance of the Ta-W sheets,the obviously plastic anisotropy of the sheet occurs,which severely deteriorates the plastic forming ability of the plate.Therefore,it is of great significance to explore the correlation between microscopic characteristics and the macroscopic forming properties of tantalum tungsten alloy sheets,and to define the quality of stamping properties from a microscopic view.This paper has systematically studied the macro forming properties and the microscopic characteristics on Ta-2.5W sheets with two values of 1mm and 0.5mm in thickness.The correlation between texture components of Ta-2.5W sheet and deepdrawing forming properties has been revealed.The prediction model for macroscopic plastic strain ratios(r values)and the evolution of micro-textures have been established.The model defined the shaping quality of deep-drawing of thin-wall revolving parts and explained the mechanisms of the anisotropic deep drawing fractures.The deep drawing properties of Ta-2.5W sheets with two thicknesses(1 mm,0.5 mm)were evaluated by tensile tests at room temperature.Compared with 1 mm sheet,0.5 mm sheet shows serious anisotropy of r value,which drastically deteriorated the deep drawing properties.The microstructures and orientation information during the rolling process were analyzed by EBSD technique.With the increase of rolling deformation,the grains gradually turned fibrous,and the grain orientations gradually transforms into rolling texture dominated by α-fiber texture(<110>//RD)and γ-fiber texture({111}//ND).When the sheet is cold rolled to 0.5 mm,the {001}<110> texture of the sheet rises significantly,deteriorating the deep drawing performance of the sheet.According to the orientation space division principle,a theoretical model for calculating r(θ)curves of Ta-2.5W sheet based on polycrystalline texture information.Compared with measured r values by tensile tests,the model shows high accuracy,and verifies the effect of increasing the {001}<110> texture on the r value of the 0.5 mm sheet.During the deep drawing process,the grains at the straight wall of the 1mm thinwall revolving part were elongated to be similar to the cold-rolling elongated fiber grains.The fracture phenomenon of fiber grains occurred in the wall of 0.5mm deep drawing part due to the shear band.When the thickness of drawing part is 1mm,the calculated r(θ)curve based on texture information could predict the fracture part of the straight wall,which proved that the increase of the {001}<110> orientation and the decrease of the γ-fiber texture deteriorated the plastic deformation ability,which was the main cause of the macroscopic fracture phenomenon of thin-wall revolving part.For the part with 0.5mm thickness,the tiny size of grains replaced its orientation information as the more important factor influencing its forming quality.The serious dislocation tangling phenomenon gained the difficulty in continuous deformation.The anisotropy of the deep drawing fracture morphologies on the straight wall in thin-wall revolving part reflects the evolution of its microstructure and grain orientation.When the fracture is parallel to the rolling direction,the fracture formation mechanism is slip separation;when the fracture is perpendicular to the rolling direction,the fracture formation mechanism is shear dimples.