Direct laser metal deposition of a medium carbon low alloy steel was performed on a round bar sample. Taguchi design was used to investigate the effect of three process parameters with three different levels on the microstructure and properties of single- and multitrack clad samples. Microstructural analysis showed that coalesced bainite and lath martensite exist in the clad area. Two different kinds of cracks occurred in multitrack clad samples. When laser power is not sufficient or scanning speed is high, cracks can occur in the laser clad area because of the accumulation of trapped defects inside the molten pool, e.g., inclusions, voids, and low melting point constituents alongside insufficient molten metal back-filling at interdendritic regions. These cracks can be considered as solidification cracks. Another type of cracks can occur in previous tracks of multitrack clads which actually are the heat affected zones (HAZ) of newly deposited clad tracks, because of high tensile stress on HAZ and the presence of oxide and sulfide constituents at interdendritic regions. These cracks can be considered as reheating cracks. According to the result of Taguchi design experiments, using optimum laser parameters like high laser power, medium scanning speed, and sufficient powder feed rate, crackfree clad layers can be obtained via the prevention of formation of unfavorable constituents at interdendritic regions.

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Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber. The results showed that microstructures and mechanical properties were significantly affected by different laser powers. Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids, which brings more elongation to the samples. Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite, and the amount of proeutectoid ferrite increased with increasing laser power. Moreover, microstructures of previous layers were completely altered in high laser power. Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers. Hardness of deposited samples increased from the bottom layer toward the top layer. By using a diode laser with a spot diameter size of 2 mm, the 900-W laser power is suitable for producing crack-and void-free samples. However, post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.

Composite materials are made of multiphase materials composed of two or more materials with different properties. Hard composite materials are often used as alloy materials for tool production due to their high hardness, high strength and good wear resistance. This paper briefly introduces the domestic and foreign research progress and technical status of hard composite materials by laser area melting, summarizes the influence of forming powder and process parameters on the forming performance characteristics of hard composite materials, as well as selective laser melting area of hard composite materials. The quality inspection and molding process simulation of the company, and prospects for the future development, provide a reference for the laser melting “3D printing” of hard composite materials.