Research On The Hot Forming Simulation And Processing For Small Diameter TC17 Titanium Alloy Bar

Based on the hot deformation characteristics of TC17 titanium alloy,the key problems of hot forging and hot rolling for alloy bar were studied by means of theoretical analysis,experimental research,numerical simulation and practical production.The key problems of billet heating,hot forging and hot rolling were solved.The manufactured TC17 titanium alloy bars with the small diameter could meet the national military standard criteria.The main conclusions were as follows:In order to study the workability of as-cast TC17 titanium alloy,isothermal hot compression tests were conducted.The flow stress-strain data were then employed to derive the strain compensated hyperbolic sine type,modified Arrhenius-type,Johnson Cook and modified Johnson Cook constitutive models.Meanwhile,a new kind of constitutive model named modified multiple nonlinear regression constitutive model was put forward.The results indicated that the modified multiple nonlinear regression constitutive model proposed by this research had more accuracy than other models.The processing maps based on Murty instability criterion were established.The hot deformation mechanism of as-cast TC17 titanium alloy was discussed by combining processing map and microstructures after deformation.From EBSD images,it could be found that the grain size,mesophase size and texture increased with the increase of strain rate at the certain temperature and strain,and decreased with the increase of deformation temperature at certain strain rate.The heating process and the followed hot drawing out forging of TC17 titanium alloy billet were simulated by FEM software.The three-step heating specification was determined by the analysis of temperature field and thermal stress.The variation of strain,stress,deformation temperature and load was acquired by the simulation results of different reduction pattern,initial forging temperatures and pressing speeds.The reliability was then verified by trial production.Isothermal hot compression tests were conducted for the purpose of obtaining the flow stress data of as-forged TC17 titanium alloy.The influence of the deformation parameters on the high temperature flow stress of as-forged TC17 titanium alloy was analyzed by orthogonal test and variance analysis.The results showed that strain,strain rate and deformation temperature had significant effect on flow stress.The strain compensated hyperbolic sine type,modified Arrhenius-type,Johnson Cook,modified Johnson Cook and modified multiple nonlinear regression constitutive model were conducted,and error analysis indicated that strain compensated hyperbolic sine type and the modified multiple nonlinear regression constitutive model had higher precision.The influence of the deformation parameters on the microstructure was analyzed,and the results showed that the microstructure of as-forged TC17 titanium alloy after deformation exhibited difference at various strain;grain size increased with the increase of deformation temperature resulting in inhomogeneity in microstructure;grain orientation showed more uniform with increasing strain rate.The multiple-step groove rolling process was simulated in order to obtain the changing laws of filling,strain field,stress field and temperature field.The practical hot rolling production for small diameter TC17 titanium alloy bar was carried out based on the rolling groove and the initial rolling temperature acquired from simulation results,and TC17 titanium alloy with (?)9mm diameter was rolled successfully.Microstructure analysis and mechanical performance testing showed that the grain was fine equiaxed grain,and mechanical properties met the requirement of GJB 2218A-2018,which indicate the the simulation results were reliable.