Laser deposition of Inconel 738 on directionally solidified (DS) Ni-based superalloy demonstrates a strong susceptibility to cracking. Cracks originate from the liquation of low melting point eutectic on the DS grain boundary. Five boundary liquation and interface cracking styles were identified. Sound Inconel 738 deposition layers were achieved free of cracks.

A composite coating with TiC particles of various shapes and sizes embedded in nickel based alloy has been in situ synthesized by laser melting a precursor mixture of nickel based alloy powder, graphite and titanium powders. The experiment result showed that the coating epitaxially grew from the substrate with excellent bonding between the coating and the carbon steel substrate. The coating is uniform, continuous and free of pores and cracks, and about 0.6 mm thick. The microstructure of the coating is mainly composed of g-Ni dendrite, a small amount of interdendritic (g-Ni+M23C6) eutectic, and dispersed TiC particles. The volume fraction of TiC particles and the microhardness gradually increased from the bottom to the top of the coating layer.

In order to improve resistance to high temperature and wear resistance of pure aluminum, laser-cladding experiments were conducted on a 3 kW continuous wave CO2 laser to produce in situ synthesized molybdenum silicide (MoSi2)/SiC composite coatings on pure aluminum. The laser consolidified microstructure and phase evolution were investigated using scanning electron micrograph and X-ray diffraction (XRD). The in situ formation of MoSi2/SiC was carried out by adding a mixture of Mo, Si and C precursor powder layer followed by melting the layer and substrate under a laser beam. The experimental results showed that these compounds, MoSi2 and SiC, can be formed from three distinct powders of Mo, Si and C on Al alloy, and, provided that supplied energy is sufficient to start the reaction between the initial products, a good metallurgical bond between coating and the substrate can be achieved. The microstructures of the coating were composed of MoSi2, Mo5Si3 and SiC phases. The microhardness of coating was about 12 times that of the aluminum substrate, the maximum value reached HV0.2 1200.

激光直接制造技术（LDM）是基于快速成形和激光熔覆技术而发展起来的直接快速柔性制造先进技术，尤其适用于传统方法难以制造的特种材料或特殊形状金属零件。基于太空望远镜准直器特定的形状和材料要求，运用层叠激光熔覆直接制造方法，研究了W和W/Ni合金的多道熔覆特性、微观组织和激光直接制造过程的稳定性。研究表明，W和W90Ni10多层激光熔覆时后续熔覆层的宽度会越来越窄，最终形成三角形截面；而W60Ni40和W45Ni55合金具有良好的成形效果。采用激光功率2000W，光束直径3mm，扫描速度0.3m/min，送粉速度8g/min的优化工艺参数，直接制造出高度为307mm，直径为191mm，壁厚为3mm，平行度不低于2/1000的圆柱状W60Ni40准直器，未出现裂纹和明显的气孔。结果表明激光直接制造技术可以制造出高质量的传统方法难以制造的特殊材料和形状的金属零件。

Detailed experiments have been conducted to produce a nickel-based alloy composite coating reinforced with TiC particles on medium carbon steel substrate by powder feeding laser cladding using a coaxial nozzle. The chemical compositions, microstructures and surface morphology of the coatings were analyzed using scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). Composite coatings with TiC particles of various shapes and sizes embedded in nickel-based alloy were synthesized in-situ during laser processing. An excellent bonding between the coating and the carbon steel substrate was obtainable. The coatings were uniform, continuous and free from cracks. The microstructure of the coating was mainly composed of g-Ni dendrites, a small amount of CrB, Ni3B, M23C6 and dispersed TiC particles. The maximum microhardness of the coating was about HV0.21200.