Abstract
Advanced amorphous coatings consisting of Co-based metallic glasses with ultrahigh strength (6 GPa) and high microhardness (up to 17 GPa) can significantly improve the surface properties of matrix materials. However, the intrinsic brittleness of Co-based metallic glasses can lead to the initiation of microcracks caused by the inevitable generation of thermal stress during the laser cladding process, which severely limits the potential application. In this paper, the methods of increasing substrate temperature and fabricating composite coatings with the addition of toughened Fe powders were adopted to inhibit the generation of microcracks in the Co55Ta10B35 amorphous coatings. Moreover, neutron shielding performances of the cladding coatings with high B content were investigated with a wide range of neutron energy (wavelength: 0.15–0.85 nm). The results indicate that the fully amorphous coating and composite ones can be fabricated successfully. The increase in the substrate temperature and the addition of Fe powders can effectively inhibit the initiation and propagation of microcracks. The fully Co-based amorphous coating with high B content (35 at.%) can exhibit excellent neutron shielding performance. With the addition of Fe powders, the neutron shielding performance is reduced gradually due to the dilution effect of B in the composite cladding coatings, but the microcrack will be completely restrained.
Highlights
Amorphous alloys show special atomic arrangement structure in long-range disorder and short-range order without microstructural characteristics like grain boundary and phase segregation
Jung et al used a heated substrate to eliminate cracks, and the results indicated that the method could be suitable for amorphous alloys with a large glass-forming ability (GFA) [32]
The results indicate that Co55 Ta10 B35 amorphous coating prepared by laser cladding can significantly improve the surface hardness of the matrix
Summary
Amorphous alloys ( called “metallic glasses”) show special atomic arrangement structure in long-range disorder and short-range order without microstructural characteristics like grain boundary and phase segregation. The prepared amorphous coating can inherit the advantages of high strength, high hardness and good wear and corrosion resistance for bulk metallic glasses, and, for the most part, avoid the limitations of glass formation over the critical size. Since Yoshioka et al prepared Ni-Cr-P-B amorphous coatings on the surface of mild steel by laser cladding in 1987 [21], a large amount of works have been done to develop. Demonstrated fabrication of Co-based amorphous coatings with the high thermal stability (the supercooling liquid region is 44 K) by laser cladding [34]. The effects of increase in the substrate temperature and improvement of the mass ratio of ductile Fe powders to the Co-based amorphous ones on the initiation, propagation and suppression of crack in the resulting coatings were investigated
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