Abstract
Considering the high thermal stability of TaC carbide and Ni3Al (γ′) intermetallic compound, TaC was in situ synthesized in laser clad Ni-Al-Cr coating to produce the composite coating with an excellent performance in high-temperature wear resistance. The composite coating contains γ-Ni, spheroidal-shaped γ′, primary TaC particles and script-like TaC eutectics, rather than thermally-unstable Cr7C3 carbide. Except at 300 ℃, the composite coating showed greater wear resistance than the original Ni-Al-Cr coating at room temperature, 550 ℃ and 700 ℃, which makes it advantageous over commercial NiCrBSi coating when the temperature reaches above 550 ℃. However, the original coating shows similarity in wear resistance to the composite one at 300 ℃ due to a continuous compact oxide layer which tends to spall off at 550 ℃ when the rapid growth of oxides causes the oxide layer to loosen. Since Ta promotes the sintering of a protective oxide layer by suppressing the growth of Al2O3 oxide, a continuous compact oxide layer develops on the worn surface of the composite coating at high temperatures. The lubricant phases (NiO, NiCr2O4, and NiAl2O4) begin to develop in the oxide layer of the composite coating at 300 ℃, and NiCr2O4 disappears at 700 ℃.
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