Deformation Mechanism And Mechanical Property Of Pure Titanium Subjected To Severe Torsional Shear Process

Titanium and titanium alloy are widely used in automotive,aviation,aerospace,biomedical,and manufacturing other lightweight structure due to its low density,excellent comprehensive properties,good biocompatibility,and so on.But the pure titanium and titanium alloy prepared by traditional forming process are of lower strength and ductility,thus it is difficult to achieve good matching of mechanical property.And a technical way to solve the problem is to prepare ultrafine grained and even nano structured titanium and titanium alloy by use of severe plastic deformation(SPD).Torsional shear deformation is considered to be a deformation mode with the highest efficiency in terms of accumulated plastic strain,which involves the key role of pure shear and simple shear in accumulating plastic strain and refining grains.This paper aims at exploring the deformation mechanism of torsional shear SPD and strengthening-toughening technology in pure titanium based on the combination of experimental study,theoretical analysis and simulated calculation.The experimental studies of basic deformation mode consisting of single torsion,positive-negative torsion and tension-torsion in pure titanium are conducted firstly,and then the effects of temperature in pure titanium under torsion deformation are analyzed,and finally the co-extruding deformation technology processed by elliptical cross-section spiral equal-channel extrusion(ECSEE)are studied using pure titanium and pure aluminum.This paper has made some research results:(1)The evolution regularity of microstructure and mechanical properties of pure titanium at room temperature in non-proportional loading paths including single torsion,positive-negative torsion and tension-torsion is obtained;the mechanisms of grain refinement and deformation modification in the process of combined torsional shear technology are analyzed and discussed;the evolution path of dislocation and its effects on SPD modification for pure titanium in the process of multi-mode torsional shear deformation are summarized;(2)The evolution regularity of microstructure in torsion deformation under the effect of thermo-mechanical coupling is obtained,and the regulating effect of torsional shear deformation on the morphology of a phase microstructure is analyzed,and also,it is found that ? phase has certain relationship on orientation with precipitated ? and co phases during deformation.And thus it could provide a reference on stabilization in grain refinement and strengthening-toughening in mechanical property for combined torsional shear deformation;(3)The compound forming technology of Al/Ti in a combined tension-torsion deformation mode called elliptical cross-section spiral equal-channel extrusion(ECSEE)is studied,and the deformation damage,evolution of mechanical property and microstructural evolution process during EC SEE in pure titanium and pure aluminum are analyzed and summarized;the grain refinement mechanism,dislocation evolution path and modified method of strengthening-toughening in pure titanium processed by ECSEE are obtained.