Abstract Mechanical surface treatments based on repeated impacts are known to create a graded strengthening in-depth by the means of severe plastic deformation. However microstructural evolution mechanisms leading local progressive grain refinement and the resulting surface mechanical hardening are not yet fully understood. It is shown in this paper that micro-percussion testing represents an interesting case scenario to emulate conventional treatments such as shot peening and better characterize microstructural changes at local and global scales. For this technique, every impact is made at the same position by a rigid conical indenter, controlling the number, angle and velocity of each impact. The main issue of this work is as follows: (i) to describe the transformed microstructures by the means of SEM microscopy and EBSD mapping; (ii) to quantify the mechanical gradient in-depth using the micro-pillar compression testing; and (iii) to converge both descriptions to understand the mechanisms involved on the strengthening of refined structures. This coupled experimental analysis would reveal the influence of different strengthening effects as the Hall-Petch effect or the dislocation hardening. This investigation is carried out in pure α-iron.

中文翻译：

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纯铁反复冲击引起的表面强化机制的显微组织和微观力学研究

摘要 众所周知，基于重复冲击的机械表面处理通过严重的塑性变形产生深度梯度强化。然而，导致局部渐进晶粒细化和由此产生的表面机械硬化的微观结构演变机制尚未完全了解。本文表明，微冲击测试代表了一个有趣的案例场景，可以模拟传统的处理方法，例如喷丸处理，并更好地表征局部和全球范围内的微观结构变化。对于这种技术，每次冲击都由刚性锥形压头在同一位置进行，控制每次冲击的次数、角度和速度。这项工作的主要问题如下： (i) 通过 SEM 显微镜和 EBSD 映射描述转变的微观结构；(ii) 使用微柱压缩测试深入量化机械梯度；(iii) 融合两种描述以了解强化精细结构所涉及的机制。这种耦合实验分析将揭示不同强化效应的影响，如霍尔-佩奇效应或位错硬化。该研究是在纯α-铁中进行的。