There have been many studies on the forming process of CoCrFeNi high-entropy alloy by laser additive manufacturing, but there is a lack of systematic research on the numerical simulation of the forming process. This paper establishes a three-dimensional transient model of laser additive manufacturing high-entropy alloy by combining numerical simulation with experiment. The temperature field distribution of laser additive manufacturing CoCrFeNi high-entropy alloy on 316L substrate is simulated. The temperature distribution cloud diagram is obtained under different laser process parameters and the temperature change curve at the same node. The mechanism of surface spheroidization, pore, and metallurgical defect formation is revealed, and the experimental verification is realized. Finally, the forming process of laser cladding CoCrFeNi high entropy alloy block was explored. The results show that the maximum temperature of the cladding layer can reach more than 5000 °C during the cladding process. When other conditions remain unchanged, when the laser power increases from 1000 W to 1400 W, the temperature at the junction increases from 1588.63 °C to 2238.64 °C. At the same time, due to the insufficient melting of metal powder and the impact of powder on the molten pool, the surface of the additive is powdered and spheroidized. In addition, low laser power and low scanning speed will cause metallurgical defects between the cladding and the substrate.
An approach of laser remelting (LR) during laser melting deposition (LMD) process was applied to improve the forming quality and mechanical properties of the AlCoCuFeNi high entropy alloys (HEAs). In particular, the effect of laser remelting on the surface morphology, phase, microstructure and hardness of the parts were investigated using LSCM, SEM, XRD and Vickers microhardness tester. The results show that both LMD and LMD+LR samples dominantly consisted of a body-centered-cubic (BCC) and face-centered cubic (FCC) solid solution phases. There are many splash particles on the surface of the LMD part, which is attributed to the serious balling effect. The analysis shows that the LR process can improve the surface quality and microhardness of the LMD HEA samples due to the elimination of balling defects (microcracks and porosity).
In situ carbides (TiC/Cr7C3) reinforced CoCrMoNbTiC0.2 high-entropy alloy coatings were prepared on the Ti-6Al- 4V titanium alloy substrate by laser melting deposition technology. Effect of the laser power on the surface morphology, phase consistent, microstructure and microhardness were investigated. The results show that the coatings were composed of a simple BCC solid solution and a small amount of TiC and Cr7C3 carbides. The in-situ MC (TiC/Cr7C3) carbides were evenly distributed in the BCC matrix. The laser power has a significant impact on the forming quality and mechanical properties of the coatings. As the optimal laser power of 1500 W were applied, the coating mostly free of defects exhibited a fine dendritic microstructure. With the increasing laser power, the microhardness of the coatings was first increased and then decreased gradually. The highest microhardness of the coating (1500 W) was up to 650 HV0.5, which was 2 times higher than that of the substrate. The excellent mechanical properties of the coatings were attributed to the synergetic effects of the second phase strengthening, solid solution strengthening and fine microstructure.
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