The Effects Of High-energy Electropulsing On The Preparation And Properteis Of Biomedical Titanium Alloy

Crrently, titanium alloy TC4(Ti-6Al-4V) is one of the most widely used and the most promising biomedical titanium alloys, how to improve its workabilityand other physical/chemical properties is the key technical problems to be solved. This paper studies the application of high-energy electrical pulses and related mechanisms in the processing and surface modification of titanium alloy TC4.Firstly, by studying the effect of high-energy electrical pulses on the localrecrystallization process of TC4 titanium alloy, it’s found that the electrical pulse enhanced the average elongation of 113.5% and titanium’s strength was almost not changed at the same time. The anisotropic mechanical properties were greatly reduced while the initial microstructure of the strip along the rolling direction was evolved into equiaxed without obvious orientation.Secondly, by studyingthe effect of high-energyelectrical pulses on the completerecrystallizedevolution and texture evolution, it’s found that the apparenttemperature of lamellartwinningdegradation, non-basal plane orientation of grain growth and recrystallization texture evolution was noticeably lowered. In addition, by establishing the thermodynamicand kineticmodel it’s found that whenthe apparenttemperature is higher thanthe thresholdvalue(366 ℃)non-thermal effectsof electrical impulsesdominatedin thecomplete recrystallizationandretreatedtwinningprocess gradually, which is alsoin good agreementwith the experimental results.Furthermore, by studying the effect of high-energy electrical pulse on thephase transition induced globularization process of thermal processed lamellartitanium alloy TC4, it’s found that high energy electrical pulses can significantly improve the plasticity of titanium material(132.4%), and can promote the phasetransition ofβ-Ti → α-Ti and the formation of fine equiaxed microstructure from the lamellar microstructure.In addition, by studying high-energy electrical impulses in the process of preparation of nano materials in the surface of the titanium oxide layer, it’s found that formation of rutile titanium oxide layer on the surface enhanced materials corrosion resistance, while the microwave type titanium surface roughness and bone-like honeycomb structure nanopores enhanced biocompatibility. Thermal effects and electromagnetic fieldsof electrical pulses both accelerated the oxidation rate(two orders of magnitude higher than the surface oxidation rate of the conventional heat treatment) and reduced the thickness of the oxide layer.Finally, the electropulse assisted preparation of high-performance titanium is explored:high-energy electrical pulses assisted ultrasonic surface treatment(electrical shock) and high-energy electrical pulses assisted rolling(electroplastic rolling) process. The research shows that electrical shockinduced generation of nanocrystalline and beta phasesthrough dynamic recrystallization and phase transitions, thus increasing the plastic flow depth and extent of the impactin the surface layer. Consequently, the surface hardness and wear resistance were further increased. The processing temperature(200 ~ 300 ℃lower than hot processing temperature) and deformation resistance of electroplastic rolling were both noticeably reduced. The finished product quality and mechanical properties were therebyimproved.In this electroplastic rolling processing the basal texture was weakened and the median misorientation angle grain boundaries were accumulated by dynamic recrystallization process.