Plastic Microforming And Cellular Automaton Model Of Ultrafine Grained Pure Titanium By Combined Refining Process

In this paper,the dynamic recrystallization behavior of UGF-Ti and the Plastic microforming properties of UGF-Ti in different annealing states are studied through static compression,microcompression and micro-extrusion experiments,using cellular automata,BP neural network,SEM and TEM,which provides certain theoretical support and scientific guidance for the industrial application of UGF-Ti.The main research contents and conclusions are as follows:UGF-Ti was obtained by equal channel angular pressing(ECAP)and rotary swaging(RS),and after annealing for 1 hour at 200,300,350 and 400℃,5 kinds of ultrafine crystals with different mechanical properties were obtained Pure titanium.The recrystallization temperature of UGF-Ti is 300~400℃,and Equivalent effect variable and the initial structure will affect the static recrystallization temperature of UGF-materials.The deformation of UGF-Ti was studied on a Gleeble 3800 thermal simulation test machine at a temperature of 200 to 450°C and a strain rate of 0.01 ~1 s-1.It found that the flow stress decreased with the increase of temperature and strain rate,and There is a single peak stress in the curve,indicating the occurrence of dynamic recrystallization.Compared with CPTi titanium,dynamic recrystallization under this experimental condition is a significant feature of UGF-Ti.The deformation activation energy corresponding to the peak stress point is 210.56 k J/mol,the accuracy of the Arrhenius constitutive equation is higher,and the average relative error is 7.638%.The cellular automaton model established can simulate the dynamic recrystallization process dynamically and visually,with the small error.The results show that the recrystallized grains are preferentially generated at the grain boundaries with higher energy.As the nucleation and grain growth are synchronized,the original grains are gradually replaced,Finally,as the strain increases,the grain growth is the main factor.The micro-forming experiment was carried out on a DT-C324 micro-plastic forming machine to study the effects of deformation temperature,strain rate,sample size and grain size on the plastic micro-forming performance of UGF-Ti.In room temperature micro-compression experiments,the flow stress increases with strain rate and sample size,but the effect of grain size on flow stress is not significant.In the hot micro-compression experiments,the flow stress increases as the grain size decreases.As the sample size decreases,the dynamic softening behavior gradually changes from dynamic recrystallization to dynamic recovery,resulting in an increase in flow stress as the sample size decreases.Due to the existence of the friction effect,the friction factor decreases as the sample size decreases.In the hot micro-extrusion experiment,the sample with d=270nm has the least deformation resistance and the surface quality is good,indicating that the UGF-Ti annealed at 350℃ for 1h has good plastic microforming performance.The prediction error of BP neural network to the average stress of hot microextrusion is 6.188%,which has a good application prospect in the field of micro-manufacturing.