超声表面滚压纳米化304L不锈钢的冲蚀损伤机理研究

Erosion-corrosion (E-C) Damage is always caused by synergistic effects of erosion and corrosion. The main focus of E-C damage is on bridging the gap between macroscopic erosion damage and microscopic corrosion diffusion and further cognizing the multi-scale E-C synergistic effect. This has an important scientific significance in developing E-C resistant materials and evaluating E-C synergistic damage mechanisms. Consequently, the typical stainless steel 304L (SS 304L) is used in this study. Firstly, the SS 304L will be modified by ultrasonic surface rolling extrusion processing (USRE) to obtain nanocrystallised surface layer. Secondly, the objects of “quantum chemistry information of passive film-damage evolution law of passive film-coupling field between passive film and two phase flow”for the SS 304L after surface nanocrystallization are studied by quantum mechanics, three-dimension cellular automata (CA) method and fluid-structure interaction finite element method, respectively. Thirdly, three-dimension CA is overlapped with quantum mechanics and fluid-structure interaction finite element method, which is like a bridge connected microscopic and macroscopic scales. Combined with results of E-C experiments, we can gradually build a multi-scale model that can describe the E-C Damage behaviors. This study would reveal new laws on the passive film producing, interaction between passive film and corrosive medium, passive film damage evolution, distribution of shearing stress on the passive film and the distribution of principal displacement, stress and strain of passive film under E-C condition for surface nanocrystallised SS 304L. This model can guide designing the E-C resistance materials by exploring the effect of surface nanocrystallization process on E-C resistance properties of SS 304L and predicting the E-C failure of SS 304L. This project has an important theoretical value in depressing the E-C velocity and extending the service life of mechanical components under E-C condition.

冲蚀损伤是冲刷磨损和腐蚀协同作用的结果，构建宏观磨损损伤与微观腐蚀扩散间的联系、明确冲刷腐蚀跨尺度交互作用对耐冲蚀材料的设计及其冲蚀损伤机理研究具有重要的科学意义。因此，项目利用超声表面滚压技术对304L不锈钢表面进行纳米化改性。采用量子力学、三维元胞自动机（CA）和有限元液固耦合方法对表面纳米化不锈钢的“钝化膜量子化学信息-钝化膜损伤演化规律-钝化膜与两相流交互作用场”进行探究，将三维CA方法与量子力学和有限元液固耦合方法“握手”，以三维CA为“桥梁”结合冲蚀试验构建能够描述冲蚀损伤行为的跨尺度模型，逐步揭示表面纳米化不锈钢钝化膜的产生、与腐蚀介质交互作用、损伤演化，冲蚀下钝化膜表面剪切应力分布及主位移、应力、应变分布规律。探究表面纳米化工艺对不锈钢耐冲蚀性能的影响，指导耐冲蚀材料的设计并实现冲蚀失效的预测。该研究对降低冲蚀速率、延长冲蚀条件下机械零部件寿命具有重要的理论价值。

多相流下选矿设备的冲蚀现象普遍存在，它是选矿设备破坏或失效的重要原因之一。每年有巨大数量的钢材被冲蚀、空蚀消耗，造成惊人的经济损失。本项目以选矿工业中常用材料304奥氏体不锈钢（304 SS）为对象，首先利用表面超声滚压（SURP）方法对304 SS进行表面改性，分别对304 SS基体和SURP试样的微观形貌、力学性能、表面电势、钝化膜性质、电化学性质进行了表征。结果表明：超声滚压 5~10遍后，试样表面维氏硬度增加且部分奥氏体转化成马氏体，试样表面出现明显的晶粒细化；同时，SURP试样钝化膜中高价态金属氧化物（CrO3、Ni2O3）和致密性氧化物（Fe2O3、Cr2O3、Ni2O3）的含量增多。因此SURP 304 SS在保留耐蚀性的同时，耐磨性也有所提高。其次，对SURP试样在不同的滚压工艺和冲蚀工艺参数下进行了宏观冲蚀试验。试验表明：浆料浓度、浆料pH值、冲蚀速度、冲击角度、气含量均会影响SURP 304 SS的冲蚀性能，但是SURP能大幅减少304 SS在多相流环境下的冲蚀损伤，且SURP 5~10遍时试样具有最佳的抗冲蚀损伤性能。最后，以宏观试验和微观表征为基础，利用分子动力学模拟和宏观流体力学模拟，对SURP 304 SS界面钝化膜和多相流体之间的相互作用进行了跨尺度模拟研究。分子动力学表明，SURP试样表面钝化膜中高价态金属氧化物和致密性氧化物（Fe2O3和Cr2O3）中O元素和Fe、Cr元素的s轨道电子形成共价键不能自由运动，产生电流的电子为受到较强的原子核束缚力电子和d轨道电子，因此SURP试样具有良好的抗腐蚀性能；宏观流体力学试验表明，冲蚀率是冲蚀速度、冲蚀角度和颗粒粒径的函数，同时模拟揭示了冲蚀条件下钝化膜内剪切应力分布及主位移、应力、应变分布规律，且模拟结果与试验规律吻合较好。该项目对探究表面改性工艺对不锈钢耐冲蚀性能的影响、指导耐冲蚀材料的设计、延长冲蚀条件下机械零部件寿命具有重要的理论价值。