低的强度极大限制了工业纯钛的应用.采用超声表面深滚压(Ultrasonic severe surface rolling,USSR)制备了高强度、耐腐蚀、光洁表面的高性能纯钛板材.单次USSR加工在纯钛表面获得了厚度约1.3 mm的梯度硬化层和良好镜面效果的光洁表面;USSR试样具有梯度纳米结构表面层,即晶粒尺寸、位错和孪晶密度随深度梯度变化,最表面层晶粒细化至52.2 nm;USSR试样屈服强度和抗拉强度相比未加工试样分别提高了 33.8％和10.9％,表面硬度提高了 50.9％,同时保持了 20.8％的断裂延伸率;USSR试样在Hank's溶液中的钝化电流密度降低,极化电阻增大,钝化膜稳定性和钝化能力提高.USSR试样的高强度主要来源于晶界强化、位错强化、孪晶强化和异质变形诱导强化;高密度非平衡晶界和光洁表面有利于稳定钝化膜的形成,提高了纯钛钝化能力.研究结果为工业纯钛力学性能和腐蚀阻力的改善提供了新的思路.
Preparation,Microstructure and Properties of High-performance Gradient Nanostructured Pure Ti Plate by USSR
Low strength greatly limits the application of industrial pure titanium.High-performance pure titanium plates with high strength,corrosion resistance,and smooth surface are prepared through ultrasonic severe surface rolling(USSR).The results indicate that a gradient hardening layer with a thickness of 1.3 mm and a smooth surface with a good mirror effect is obtained by the single-pass USSR process.The USSR sample has a gradient nanostructured surface layer,that is,the grain size,dislocation,and twin density change with the depth,and the grain size of the topmost surface layer is 52.2 nm.Compared with the unprocessed sample,the yield strength and tensile strength of the USSR sample increase by 33.8％and 10.9％,respectively,and the surface hardness increases by 50.9％.Meanwhile,the elongation to fracture of the USSR sample still maintains at 20.8％.Moreover,the passivation current density of pure titanium in Hank's solution decreases and polarization resistance increases after USSR,giving rise to the improved stability of passivation film and passivation ability.The high strength of USSR sample is mainly derived from grain boundary strengthening,dislocation strengthening,twin strengthening,and hetero-deformation induced strengthening.The high-density non-equilibrium grain boundaries and smooth surface caused by the surface nanocrystalline are beneficial to the formation of stable passivation film,thus improving the passivation ability of pure titanium.The results provide a new idea for improving the mechanical properties and corrosion resistance of industrial pure titanium.
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