Effect of heat treatment on microstructure and corrosion resistance of TiC/IN625 coating by extreme-high-speed laser cladding
The TiC/IN625 coatings were prepared on 45 steel substrates by using extreme-high-speed laser cladding(EHLA) technology.The effect of different heat treatment temperatures(800,1000 ℃ and 1200 ℃) on the microstructure,surface morphology,residual stress and corrosion resistance of TiC/IN625 coatings was analyzed.The results show that the coating segregation phenomenon is alleviated with the increase of heat treatment temperature.The distribution of Ti elements in the HT1000 coating is more uniform than that in the HT0 and HT800 coatings.The part Laves phase in the HT0 coatings starts to dissolve in the HT1000 coatings,releasing Nb elements that recombine with C and Ti elements to generate MC (M=Nb,Ti) carbides.The large-sized carbides in the microstructure of HT1200 coatings surface dissolve.The other elements,such as Ti and Ni,more homogeneously distribute and diffuse into the inter-dendritic region.The residual stress on the HT0 coatings surface is mostly expressed as residual tensile stress,with a maximum value of 362 MPa.The electrochemical corrosion tests indicate that the open-circuit potential is increased from-0.139 V for the HT0 coatings to-0.132 V for the HT1200 coatings.The charge transfer resistance (Rct) of HT800,HT1000 and HT1200 coatings is also larger than that of the HT0 coatings,with an increase of 46.2％,31.2％ and 64.3％ compared to the HT0 coating's 4.785×105 Ω∙cm2,respectively.
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