In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twi...In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.展开更多
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;...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。展开更多
基金supported financially by the National Key Research and Development Program of China (No.2017YFA0204400)Shenyang National Laboratory for Materials Science(No. 2015RP04)
文摘In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.
