Song Guoqing, Wei Wentian, Shuai Bincai, Liu Botao, Chen Yong
College of Mechanical Engineering, University of South China, Hengyang 421101, China.
Materials (Basel). 2023 Nov 20;16(22):7234. doi: 10.3390/ma16227234.
Micron-sized coatings prepared using physical vapor deposition (PVD) technology can peel off in extreme environments because of their low adhesion. Laser micro-melting (LMM) technology can improve the properties of the fabricated integrated material due to its metallurgical combinations. However, the microstructural changes induced by the high-energy laser beam during the LMM process have not been investigated. In this study, we used the PVD-LMM technique to prepare NiCr coatings with a controlled thickness. The microstructural changes in the NiCr alloy coatings during melting and cooling crystallization were analyzed using molecular dynamics simulations. The simulation results demonstrated that the transition range of the atoms in the LMM process fluctuated synchronously with the temperature, and the hexagonal close-packed (HCP) structure increased. After the cooling crystallization, the perfect dislocations of the face-centered cubic (FCC) structure decreased significantly. The dislocation lines were mainly 1/6 <112> imperfect dislocations, and the dislocation density increased by 107.7%. The dislocations in the twinning region were affected by the twin boundaries and slip surfaces. They were plugged in their vicinity, resulting in a considerably higher dislocation density than in the other regions, and the material hardness increased significantly. This new technique may be important for the technological improvement of protective coatings on Zr alloy surfaces.
采用物理气相沉积（PVD）技术制备的微米级涂层，由于其附着力低，在极端环境下会剥落。激光微熔（LMM）技术因其冶金结合作用，可以改善所制备的复合材料的性能。然而，在LMM过程中高能激光束引起的微观结构变化尚未得到研究。在本研究中，我们使用PVD-LMM技术制备了具有可控厚度的NiCr涂层。利用分子动力学模拟分析了NiCr合金涂层在熔化和冷却结晶过程中的微观结构变化。模拟结果表明，LMM过程中原子的转变范围随温度同步波动，六方密排（HCP）结构增加。冷却结晶后，面心立方（FCC）结构的完美位错显著减少。位错线主要是1/6<112>不完全位错，位错密度增加了107.7%。孪晶区域的位错受孪晶界和滑移面的影响。它们在其附近被堵塞，导致位错密度比其他区域高得多，材料硬度显著增加。这项新技术可能对Zr合金表面防护涂层的技术改进具有重要意义。
