低温HVOF微粒撞击稀土镁合金表面纳米化的组织特征

Microstructure Characteristics of Rare-Earth Magnesium Alloy of Surface Nanocrystallization by Low-Temperature HVOF Particles Bombarding

摘要:

材料失效多发生于表面，采用超音速火焰喷涂设备获得了低温HVOF微粒，对稀土镁合金表面进行纳米化处理，并利用金相显微镜和透射电镜对处理后的试样进行微观组织表征分析，沿试样厚度方向进行显微硬度测试。结果表明：镁合金表层晶粒细化明显，形成了晶粒尺寸小于20 nm的随机取向的纳米晶，纳米晶层深约80 μm，随着深度的增加晶粒尺寸增加。表面纳米化是通过位错和孪晶的协调变形，导致大晶粒被分割细化而成。表层硬度显著提高，是基体硬度的2倍。

Abstract:

Material failure usually occurs on the surface. A nanocrystallization surface layer on the rare-earth magnesium alloy was fabricated by low-temperature HVOF particles obtained from novel HVOF equipment. The microstructure of the surface layer was characterized by OM and TEM. The micro-hardness was also tested along the sample thickness direction. The results show that the surface grain refinement of rare earth magnesium alloy is obvious and the grain size is less than 20 nm; grain orientation is random and the depth of the nanocrystallization layer is about 80 μm. The grain size increases with increasing of the distance from the surface. The formation mechanism of nanocrystallization is as follows: the coordinated deformation of twins and dislocation lead to segmentation and refinement of large grains. The surface hardness is increased significantly, which is about twice as high as the hardness of the matrix.