激光熔覆制备高熵合金涂层研究进展

激光熔覆具有加热和冷却速度快、稀释度低(<5％)、热影响区小以及可以对表面性质进行精准调整等优点,是当今工业应用较为广泛的表面改性技术之一.利用激光熔覆技术制备高熵合金涂层,既能保证涂层具有简单的相结构和优异的性能,又可使涂层与基体之间获得良好的冶金结合.主要对激光熔覆制备高熵合金涂层的设计准则、性能及提高机理、凝固行为以及数值模拟的研究进行阐述.首先从设计理论方面对高熵合金进行概念阐述,由熵和吉布斯自由能可知,通过增加主元(至少5个)和位形熵来设计元素组成,通过吉布斯自由能控制相的稳定性.其次,对涂层的性能提高机理分类总结,其中高熵合金的四大效应与激光熔覆快冷快热的特点相结合是涂层性能提高的主要原因.此外,还阐述了激光熔覆过程中熔池的凝固行为,包括凝固过程中的晶粒生长方式和液相分离现象,以及其他因素引起的凝固行为变化.之后,对粉末流动特性、熔池温度场和熔覆层性能的数值模拟以及这些模型的缺陷进行综述与分析.最后,总结与展望激光熔覆制备高熵合金涂层研究的发展前景与应用方向.

Advances in the Preparation of High Entropy Alloy Coatings by Laser Cladding

Laser cladding is one of the surface modification techniques widely used in today''s industry due to its several advantages such as high velocity of heating and cooling, low dilution, small heat affected zone and allows the precise adaptation of surface properties. When the HEAs is prepared by laser cladding technology, it can not only ensure the coating has simple phase structure and excellent performance, but also obtain good metallurgical bonding between the coating and the substrate. In this paper, the design criterion, performance and improvement mechanism, solidification behavior and numerical simulation of the HEAs prepared by laser cladding are described. Firstly, the concept of high entropy alloy is expounded from the design theory. It can be known from the configuration entropy and gibbs free energy that the composition of elements is designed by increasing the principal element (at least 5) and configuration entropy, and the phase stability is controlled by the gibbs free energy. Secondly, the mechanism of coating performance improvement was classified and summarized, among which the combination of the four effects of high entropy alloy and the characteristics of fast cooling and fast heating of laser cladding was the main reason for the improvement of coating performance. In addition, the solidification behavior of the molten pool during the laser cladding process is described, including the grain growth pattern and liquid phase separation during the solidification process, as well as the solidification behavior changes caused by other factors. Moreover, the numerical simulation of powder flow characteristics, temperature field of molten pool and properties of cladding layer and the defects of these models are summarized and analyzed. In the end, the development prospect and application direction of the HEAs prepared by laser cladding are summarized and prospected.