NiCrBSi coating reinforced with WC was prepared on the steel substrate surface of 42CrMo alloy structure based on coaxial powder-feeding laser cladding technology by using the YLS-6000 fiber laser. Phase composition, microstructure, microhardness and wear resistance of specimens were discussed by the X-ray diffractometer (XRD), scanning electron microscope (SEM), microhardness meter and ring-block friction wear testing machine. Results demonstrated that the composite coating is mainly composed of γ-Ni solid solution and WC, accompanied with phases like FeNi3, B2Co3, CoCx, FeCr0.29Ni0.16C0.06, W3C and Co3W3C6. The top, middle and bottom of the cladding layer are occupied by tiny dendrites, coarse columnar dendrites and cellular crystals perpendicular to the interface. Moreover, good metallurgical bonding is formed between the coating and base. Hardness and wear resistance of the composite coating are far higher than those of the 42CrMo base. According to west test, the base presents typical adhesive wearing characteristics, while the composite coating mainly shows abrasive wearing performances.
In order to reduce the thermal stress at clad layer and further reduce the crack generation in the laser cladding process, a method of controlling the cracks at clad layer by changing the laser energy density was proposed. The comparative thermal-mechanical coupling nite element analysis was conducted for the uniform rectangular spot and convex shape beam spot cladding processes on plasma-sprayed MCrAlY coating through the numerical simulation method based on the ANSYS software. The results show that the rapid heating and cooling characteristics, which are typical in laser processing, are manifested in the cladding process using the uniform rectangular spot, and the convex shape spot can exert the preheating and slow cooling effects to a certain extent, so as to reduce the temperature gradient of the cladding zone and non-cladding zone. In addition, on the precondition of equivalent cladding effect, the thermal stress at the clad layer is also low, so the cracking tendency of the clad layer can be effectively mitigated. Relative to the laser beam shaped diffractive optical element special for design and manufacturing, superposing two uniform rectangular spots with different sizes and energy densities is a simpler and more effective method of acquiring the convex shape spot.
GH5188 high-temperature alloy specimens were fabricated by selective laser melting (SLM) and influencing laws of laser power, laser velocity and laser energy density on density of specimens were researched. The results shows that along with the laser energy density increases from 73.02 J/mm3 to 88.18 J/mm3, porosity in specimens decrease and relative density increases from 98.86% to 99.75%. However, as the laser energy density increase further, the density begins to decrease continuously. The main causes that effects relatively density including: the powder is not fused at low energy density, as well as the powder splash and gasification at higher energy density. Neither inadequate nor excessive laser energy density is conducive to improvement of density of specimens. As the increase of laser velocity and laser power, density of specimens increases firstly and then decreases. The variation trend of relative density is similar with that of laser energy density and there are reasonable ranges of laser velocity and laser power. However, influencing laws of laser velocity and laser power on density of specimens are different.
In order to reduce the thermal stress at clad layer and further reduce the crack generation in the laser cladding process, a method of controlling the cracks at clad layer by changing the laser energy density was proposed. The comparative thermal-mechanical coupling finite element analysis was conducted for the uniform rectangular spot and convex shape beam spot cladding processes on plasma-sprayed MCrAlY coating through the numerical simulation method based on the ANSYS software. The results show that the rapid heating and cooling characteristics, which are typical in laser processing, are manifested in the cladding process using the uniform rectangular spot, and the convex shape spot can exert the preheating and slow cooling effects to a certain extent, so as to reduce the temperature gradient of the cladding zone and non-cladding zone. In addition, on the precondition of equivalent cladding effect, the thermal stress at the clad layer is also low, so the cracking tendency of the clad layer can be effectively mitigated. Relative to the laser beam shaped diffractive optical element special for design and manufacturing, superposing two uniform rectangular spots with different sizes and energy densities is a simpler and more effective method of acquiring the convex shape spot.
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