冲蚀磨损诱导非晶合金涂层表面纳米化及自增强机理研究

This project is based on the actual needs from the wear-resistant coating of dredging equipments. According to the previous findings about the erosion-induced surface crystallization of amorphous alloy coating, the erosion mechanism of amorphous alloy coatings under the solid-liquid two-phase flow will be researched from a new perspective of surface phase transformation. So this project will firstly study the surface structure evolution of amorphous alloy coating during slurry erosion wear and explore the key compositional and erosive requirements determining the behavior of surface crystallization. Then the dynamic process of erosion-induced nanocrystallization, including precipitation, growing, attrition and a new generation of nanocrystallines will be studied. The relationship between the erosion parameters and the nanocrystalline's type, distribution and quantity will be analyzed. And the mutual influence of surface nanocrystallization and erosion wear will be clarified. The influence of erosion-resistant performance by nanocrystallization will be explored. With the differential thermal analysis, the new amorphous coating composition will be optimised and the selective precipitation of nanocrystallines will be adjusted. The self-reinforcing mechanism of the erosion-induced surface nanocrystallization improving the erosion-resistant properties will be revealed. Implementation of this project will not only be expected to reveal the wear mechanism of amorphous alloy behind the appearance of erosion from a new angle and provide a new idea for the composition design of amorphous alloy coatings but also to play the metastable characteristics of amorphous alloy and to fabricate a wear-resistant coating with self-reinforcing effect, and will also provide a theoretical basis for improving the life of the dredging equipments.

本项目从疏浚机具耐磨涂层的实际需求出发，根据前期研究发现的冲蚀磨损诱导非晶合金涂层表面晶化现象，从表面相变的新视角，研究固液两相流中非晶合金涂层的冲蚀磨损机理。为此，本项目首先研究泥浆冲蚀磨损过程中非晶合金涂层表面结构的演变规律，探寻决定表面晶化行为的关键成分与冲蚀条件；然后，研究涂层中冲蚀诱导纳米晶的形成、长大、磨耗及新的纳米晶再生成的动态过程，分析纳米晶的种类、分布及数量与冲蚀磨损参数的关系，并阐明表面纳米化与冲蚀磨损的关联作用；进而探寻表面纳米化对冲蚀磨损性能的影响；再结合差热分析优化涂层成分，调控纳米晶的选择性析出，揭示冲蚀诱导表面纳米化提高冲蚀磨损性能的自增强机理。本项目的实施，不但从一个新角度揭示隐藏在非晶合金磨损表象背后的磨损机理，为非晶合金涂层的成分设计提供新思路，而且有望发挥非晶合金的亚稳态特性、制备具有自增强效应的耐磨涂层，并为提高疏浚机具的使用寿命提供理论依据。

本项目从水利枢纽启闭机液压缸活塞杆的需求出发，开展非晶合金涂层的制备及其摩擦磨损研究。首先，研究激光熔覆工艺参数对非晶合金涂层成形性及非晶化程度的影响，揭示逐层制备非晶合金涂层的组织结构与性能；并获得一种由非晶合金粉末制得的具有高耐腐蚀磨损的合金涂层。在空气和去离子水中，9层非晶涂层的平均摩擦系数均低于316L不锈钢。而且，它在去离子水中的体积磨损率比316L不锈钢低约6.5倍。其次，研究非晶涂层在模拟海水及模拟体液等多种环境下的腐蚀磨损行为，揭示非晶合金在腐蚀环境下的优异耐磨性。在SBF溶液中9层非晶涂层的平均摩擦系数是316L不锈钢的一半；其体积磨损率比316L不锈钢低5.5倍。最主要的，研究了冲蚀磨损诱导的非晶合金纳米晶化行为及其影响因素，揭示了冲蚀磨损诱导的非晶合金纳米晶化机制。冲蚀磨损诱导非晶合金最上层表面形成厚度为1-2μm的微结构演变层。并且在微结构演变层中存在短程原子排序，其中嵌入在非晶基质中的晶体尺寸为约2-3nm。由于元素的氧化，泥浆冲蚀后合金最上表面为含有氧化物的复合层。阐明了由于较低的活化能和热稳定性，涂层的低凝固冷却速率会促进表面纳米晶化。同时，冲蚀诱导的微观结构演变导致非晶合金的表面硬化和强化。所以，非晶合金的微观组织演变机制受到凝固冷却速率和冲击引起的温升、冲击引起的塑性流动、以及金属元素相互扩散和氧化的综合作用。此外，还研究了非晶合金的冲蚀磨损行为，揭示了非晶合金的耐磨性明显好于不锈钢；30°冲蚀时非晶合金的冲蚀磨损机制主要为微切割和犁削，90°冲蚀时以凿削为主；阐明了冲蚀诱导的晶化对非晶合金的冲蚀磨损行为与性能的影响，它提高了非晶大角度下的冲蚀耐磨性，降低了小角度下的冲蚀耐磨性。上述工作促进了非晶态材料的摩擦学研究，扩大了摩擦诱导相变的研究范围，也为推动非晶合金在我国水利及海洋工程装备中的应用提供理论依据，具有显著的科学意义和应用前景。