Abstract
In this paper, a nickel-based amorphous composite coating was obtained on the carbon steel surface by the laser cladding process. The thermal field and stress distribution were simulated by using ANSYS finite element software where the moving heat source and powder feeding were modelled by the “Element birth and death” method. The simulation results were verified by comparing the cross-sectional profile of fusion lines and X-ray stress measurements, respectively. The results on thermal field showed that the cooling rate of the coating could reach up to 10389.15 K/s and it gradually decreased from the outside surface to the interior, which promoted the formation of amorphous phase. The simulated stress field showed that the coating was in the state of tensile stress after cladding and the longitudinal stress was larger than the transverse stress. The coating was experienced with tensile plastic deformation along the laser scanning direction, which resulted in longitudinal residual stress. A higher stress concentration was occurred between the coating layer and substrate, which increased the susceptibility of crack formation. The test results on transverse residual stress were generally consistent with the simulation. On the contrary, the measured longitudinal stress was nearly close to zero, which was not in agreement with the model due to the formation of cracks.
Highlights
Amorphous alloy, which is known as metallic glass, is a type of metallic material that is disordered in long-range, but ordered in short-range at the atomic level
The particularity of its atomic arrangement differs the performance of amorphous alloy from the traditional crystalline alloyed materials
Amorphous coating can be obtained by applying a high power laser beam, with or without additional feeding material, on the surface of crystalline substrate at a very fast scanning speed, so that a thin layer of material is melted and cooled down at a very high rate
Summary
Amorphous alloy, which is known as metallic glass, is a type of metallic material that is disordered in long-range, but ordered in short-range at the atomic level. Due to the uneven heating and cooling, the amorphous coating that was prepared by laser surface processing technology has a high residual stress peak with gradient distribution characteristic. The element birth and death method was introduced to simulate the powder feeding for the laser cladding process, in which the elements for the clad were “killed” before cladding by multiplying their stiffness by a severe reduction factor, and equivalently deactivating their load, mass, and specific heat. Those elements were reactivated with the scanning speed afterwards. The temperature and the stress fields were verified by comparing cross-sectional profile and X-ray stress measurement, respectively
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