Journal
SURFACE & COATINGS TECHNOLOGY
Volume 258, Issue -, Pages 415-425Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.surfcoat.2014.08.059
Keywords
Co-Cr-Fe alloy; Friction stir processing; Laser clad; Microstructure refinement; Severe plastic deformation
Funding
- National Natural Science Foundation of China [51101126, 51475376]
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Friction stir processing (FSP) was carried out on a laser clad Co-Cr-Fe alloy layer in order to transform the coarse laser clad microstructure into nanostructure and improve the mechanical properties. In the microstructure of the laser clad Co-Cr-Fe alloy, coarse brittle carbides precipitated along the grain boundary and formed networks, along which micro-cracks tended to initiate. After FSP, nanostructured surface layers with 20-100 nm grain sizes and 30-65 mu m thicknesses were obtained. The coarse network carbides were significantly crushed to nanosize particles uniformly distributed in the nanostructured Co matrix. The plastic layer showed a gradient grain size that ranged from tens of nanometers at the top surface to tens of micrometers at the interior. A large number of the deformation nanotwins were found in the plastic zone which revealed the deformation mechanism. Moreover, FSP enabled the closure of micro-cracks in the laser-clad microstructure. The formation of nanostructures increased the hardness up to 819 Hv, compared with the 490 Hv of the laser parent alloy. The friction coefficients of the laser-clad Co alloy decreased from about 0.35 to 0.1-02 after FSP, with enhanced wear performance. (C) 2014 Elsevier B.V. All rights reserved.
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