Effects Of Shock Treatment On Mechanical Properties And Microstructure Of Titanium Alloy

Titanium and titanium alloys are widely used in various fields because of their excellent performance,such as specific strength.In some applications titanium alloys are often subject to dynamic loads.In this thesis,TA2(? phase)and TC4(?-? two-phase)alloys were impacted by explosively propelled flyer;then the mechanical behavior of the impacted materials was studied.The hardness,quasi-static and dynamic properties of TA2 plate,TA2 bar and TC4 bar were measured and the corresponding microstructures were observed using metallographic microscopy and scanning electron microscopy.Consequently,the effect of shock loading on the mechanical properties and microstructure of TA2 and TC4 alloys was analyzed.The tensile plasticity of TA2 plate along rolling direction(RD)is compared to the one along transverse direction(TD);both the fractures show obvious ductile fracture.But the strength along TD is higher than the one along RD.TA2 is a strain rate sensitive material,the yield strength of which under compression increases as the strain rate is rising.Although the yield strength in TD is higher than the one in RD,the strain hardening in RD is greater than in TD.The TA2 and TC4 bars show strain rate effect under axial dynamic compression,both of which present shear failure with high strain rate.The failure mode of TA2 is biconial failure and the TC4 is shear failure with 45 o to the axis of compression.The shock treatment of material was conducted using planner and tubular flyer driven by detonation of explosive.The grain refining was observed for the TA2 plates after shock loading,but was not observed for the TA2 bars.The grain of TA2 bar was elongated along the direction vertical to shock loading.The shock loading didn't change the fracture mode of the studied materials.The orientation of TA2 plates and the strain rate effect of TA2 and TC4 in a large strain rate range were sustained.However,the shock treatment has some effect on the dynamic and static mechanical properties of the materials.For TA2 plate,the shock treatment reduces its tensile strength and increases its tensile plasticity.But under the dynamic compression,the treated TA2 has higher yield strength,lower compressive strength and lower hardening modulus within a certain strain rate range.For TA2 and TC4 bar,explosive treatment improves its hardness and compressive strength,but reduces its plasticity at lower strain rate and strain rateenhancement effect in the higher strain rate range.