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.

Various weight ratios of TiC particulate nickel-based composite coatings were produced on carbon steel substrates by laser cladding. The experimental results showed that the coating was uniform, continuous and free of cracks when a CaF2 flux was used. Excellent bonding between the coating and the medium carbon steel substrate was ensured by the strong metallurgical interface. The microstructures of the coating were mainly composed of g-Ni dendrites, M23C6, a small amount of CrB, and dispersed TiC particles. The morphologies of TiC particles changed from the globular, cluster to flower-like shape. The volume fraction of TiC particles and the microhardness gradually increased from the bottom to the top of the coating, and the volume fraction of TiC particles increased with increasing of volume fraction of Ti and C. The maximum microhardness of the coatings with 10, 15 and 20 wt.% (TiqC) in the preplaced alloy powder was approximately HV0.2750, HV0.2850 and HV0.2920, respectively, which was much larger than that of the steel substrate, HV0.2240.

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。

Laser direct manufacturing (LDM) has been intensively developed in recent years to directly and flexibly manufacture metallic components with full metal density, functions and properties, especially for some specific materials or geometry. This paper presents a projectwork on laser direct manufacturing a novel designed collimation component for an out-space hard X-ray modulation telescope. The research work contained the characteristics of overlap multi-pass laser cladding of tungsten or tungsten nickel alloys, microstructure analyses, technique stability of laser direct manufacturing, and the final direct manufacturing of tungsten nickel collimation component. The results proved that laser direct manufacturing could be well used to manufacture specific material and geometry component of good quality, which are very difficult or even impossible by conventional manufacturing methods.