Research On Texture And Corrosion Properties Of ECAP Deformed SLM Printing Pure Titanium

Pure titanium is widely used as biomedical materials because of its excellent corrosion resistance and biocompatibility.However,the low hardness and strength of pure titanium limit its application.In this paper,equal channel angular pressing(ECAP)technology and selective laser melting(SLM)technology are combined to successfully prepare pure titanium with excellent mechanical properties and corrosion resistance.In this paper,the microstructure of SLM pure Ti and SLM+ECAP pure Ti was systematically studied by Electron backscattered diffraction(EBSD),optical microscope(OM),transmission electron microscope(TEM),X-ray diffraction(XRD).The effect of ECAP on the microstructure evolution of SLM printing pure Ti was revealed;At the same time,the room temperature tensile and hardness test of SLM pure Ti and SLM+ECAP pure Ti,as well as electrochemical experiments in the environment of simulating body fluid and oral saliva,the effects of ECAP deformation on the mechanical properties and corrosion resistance of SLM pure Ti were studied.The main findings are as follows:After SLM pure Ti undergoes ECAP single-pass extrusion deformation,the structure is obviously refined,the grain size is reduced by about 46%,Increased dislocation density within the grain,and the structure presents a lath shape with uneven boundaries and a large number of dislocation tangle zones and dislocation cells.In the EBSD photographs,it is observed that the proportion of small-angle grain boundaries has increased and is accompanied by continuous dynamic recrystallization.Combined with the TEM photographs,it was found that {10(?)1}((?)012)compression twins and{10(?)2}((?)011)tensile twins appeared after ECAP deformation.The texture has evolved from a typical C1 cylinder texture to a B texture after a single pass of ECAP.The P1 basal texture always exists;at the same time,the extreme density values of the pole figure and the inverse pole figure have increased.Comparing the stress-strain curves and hardness cloud diagrams of SLM pure Ti and SLM+ECAP pure Ti,the results show that:after a single pass of ECAP deformation,the yield strength and tensile strength of the sample increase by 18%and 20.4%,respectively,while the elongation is slightly reduced;the microhardness also rises from the original 257HV to 290HV,with an increase of 13%.This is related to the strengthening of fine grains,the strengthening of twin crystals and the increase of dislocation density after deformation.Comparing the corrosion resistance of SLM pure Ti and SLM+ECAP pure Ti in a simulated body fluid and oral saliva environment,it is found that after soaking for 1 hour,the open circuit potential of SLM+ECAP specimens is higher than that of SLM specimens and tends to be stable earlier than SLM specimens.The self-corrosion current density(Icorr)is small and the polarization resistance(Rp)is large.Using Zsimpwin software,the electrochemical impedance spectroscopy experimental results of the two pure titanium samples were fitted and analyzed.It was found that the fitting points and the experimental measurement data points basically coincided with each other,and the results were in good agreement.The results show that SLM+ECAP pure Ti is more resistant to corrosion in simulated body fluids and oral saliva than SLM pure Ti.This is related to the thickening of the passivation film and the increase of electrical resistance of the pure titanium sample after ECAP deformation.