粉体预氧化对NiAl激光熔覆涂层组织和性能的影响

目的 激光熔覆是集节能、环保、减排于一身的低碳技术,能够解决涂层存在的粗大枝晶、较大开裂敏感性及纳米增强颗粒昂贵等难题。方法 借助Al颗粒的易氧化特性,提出一种预氧化气固反应手段,原位制备铝粉表面附着氧化铝的复合型粉体,采用激光熔覆技术将复合粉末制备成冶金涂层,并考察预氧化方法对NiAl涂层组织和性能的改性规律。结果 通过预氧化方法获得了铝粉表面附着氧化铝的复合型粉体,且制备的涂层成形良好、无缺陷;预氧化涂层的枝晶更细小,XRD测试表明预氧化涂层中出现了Al₂O₃。由于预氧化方法带来的细晶强化和第二相强化作用,使得预氧化涂层的硬度在NiAl涂层的基础上提升了约20%,预氧化方法引入的氧促使摩擦界面形成了一层氧化物润滑膜,使得预氧化处理后涂层的摩擦因数降低了约23%,同时耐磨性得到显著提升。结论 采用预氧化方法以低成本原位合成了复合型粉体,通过预氧化方法使涂层实现了从组织结构到性能的良性转变,为推动绿色低碳技术发展,高性能新型粉体的研发,以及NiAl涂层的应用提供一些思路与方法。

Effect of Powder Pre-oxidation on Microstructure and Properties of NiAl Laser Cladding Coating

Laser cladding is a technology with advantages of low carbon, energy saving, environmental protection and emission reduction and so on. It can obtain surface coating with excellent wear resistance, corrosion resistance and heat resistance, and its performance is better than that of the matrix material. However, it is found that the laser cladding coating often forms thick dendrites and has great cracking sensitivity. In addition, ceramic powder is very expensive as the strengthening material. According to the above technical problem, in this study, the NiAl with the great potential application was applied as the cladding material. A kind of pre-oxidation gas-solid reaction method was put forward based on effective refinement effect of the ceramic phase to the cladding ceramic coating organization with the aid of easy oxidation properties of Al material, and Al particles in oxidation atmosphere were put into furnace to make its surface evenly in situ synthesis of alumina oxide. In this way, the composite powder with alumina on the surface of aluminum powder was synthesized. Al2O3 in situ synthesized by pre-oxidation means had the minimal lattice mismatch with NiAl, which was very suitable as the enhancement phase of NiAl material, so as to refine the coarse dendrites in the coating structure and improve the performance of cladding coating. Composite powder was prepared to metallurgical coatings by laser cladding method. SEM, XRD, EDS, hardness, friction and wear tests were used to investigate the modification law of microstructure and properties of NiAl coatings by pre-oxidation. There was a very obvious "oxygen coating layer" around the pre-oxidized Al powder. The composite powder with alumina attached on the surface of aluminum powder was successfully prepared by pre-oxidation, and the pre-oxidized NiAl coating prepared by laser cladding technology formed well and had no defects. Compared with NiAl coating, the dendrites of the pre-oxidized coating were smaller, and the XRD test showed that Al2O3 existed in the pre-oxidized coating. The hardness of the pre-oxidation coating was improved by about 20% on the basis of NiAl coating. The oxygen was introduced by the pre-oxidation method which made the friction interface form a layer of oxide lubrication film, so that the friction coefficient of the coating after the pre-oxidation treatment was reduced by about 23%, at the same time, the wear resistance of the coating was also significantly improved due to the improvement of the hardness. Comprehensive analysis showed that the performance improvement was due to the synergistic strengthening mechanism of the fine grain strengthening and second phase strengthening which was brought about by the pre-oxidation method. The Al/Al2O3 composite powder in situ synthesized by pre-oxidation method owns the advantages of simple equipment and convenient operation. The complicated manufacturing process of micro and nano-particles is eliminated by simple synthesis steps. The composite powder is synthesized in situ at low cost and has significant positive benefits, and the coating can achieve a benign transformation from microstructure to properties by means of pre-oxidation. This article can provide some ideas and methods to promote the development of green low-carbon technology, high-performance new powder research and the application of NiAl coatings.