| TC16 Titanium(Russian designation BT16)which nominal composition is Ti-3Al-5Mo-4.5V is a martensitic typed a+P two-phase high-strength titanium alloy.It can be cold headed to form in the annealed condition,and can achieve the strength requirements by work hardening caused by cold deformation,and can be used directly without subsequent solution plus aging heat treatment,so it is a kind of ideal material for fasteners.Aiming at the process of TC16 alloy wire upsetting,the following research work has been carried out:(1)Upsetting deformation behavior and microstructure evolution in different temperatures,different strain rates,different heating holding time and different starting height of samples;(2)Using the finite element to simulate upsetting deformation process of room tempertureand and 500?,to calculate the equivalent Cauchy stress field and equivalent plastic strain field and shear Cauchy stress field.Studies have shown that,the flow stress is sensitive to temperature at the strain rate of 10s-1,the higher the temperature is,the lower the flow stress is.At room tempertureand and 500 ?,flow stress to strain rate response is not strong,there is no obvious regularity of flow stress changes at different strain rates,.Holding a short period of time has little effect on the flow stress at 500?.Flow stress variation is similar before reaching the maximum deformation resistance for different starting height samples,but the sample with larger starting height occurs flow instability after the maximum deformation resistance.The rising of temperature from the plastic deformation work is smaller when deforming temperature is higher,Large plastic deformation work is generated at lower temperatures,only less plastic deformation work can be generated at high temperature,and thermal conversion coefficient ?is smaller at high temperatures.At room tempertureand,the average activation energy is 190.64kJ/mol,at 500? the average activation energy is153.35kJ/mol.With increasing deformation temperature,? phase increases and a phase reduces.?phase ratio was higher than a phase in the sample central region.At room tempertureand,the degree of deformation of a phase and ? phase increase with increasing strain rate.At 500 ?,when the strain rate is 0.001s-1,? phases distribute as blocks in the sample central area,and a phases disperse inside beta phases.When the strain rate is10s-1,a phase and ? phase exhibit as strips in the sample central area.With increasing strain rate,the block-shaped ? phases in the sample central region gradually transformed into strip-shaped ? phases.At 500?,microstructures do not change obviously with duration in a short holding period.The higher of starting sample height is,the more serious distortion of a phase and ? phase is,and the higher proportion of ? phases are.Finite element simulation results show that a good hexagon head type can be got when the starting size of of the sample is ?6.0× 12.0mm and the reduction is 8.15mm.When the friction factors are equal,the size and distribution of the equivalent plastic strain at 500 ? and room tempertureand are similar,and the distribution of equivalent Cauchy stress and shear Cauchy stress are similar.When the deformation temperature is equal,the size and distribution of the equivalent plastic strain,equivalent Cauchy stress and shear Cauchy stress have a greater difference with the change of friction factor.There is a big difference of two-side metals flowing velcity at where metal flowing line is changed seriously.The deformation is heavier where flowing lines are more concentrated.Sample deformation process should ensure symmetrical force distributing,which is advantageous for the formation of a symmetric flow line and advantageous for ductility deformation.The choice of first heading die has an important influence on the distribution state of hexagon bolt head flowing line.The first heading die with chamfers can reduce the severe degree of curvature of the flowing lines,which is favourible for the forming of the following fine heading. |
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