Microstructure and mechanical properties at TiC//p/Ni-alloy interfaces in laser-synthesized coatings

关键词 Titanium carbide;Nickel alloys;Phase interfaces;Microstructure;Composite materials;Laser beam effects;Cladding (coating);Synthesis (chemical);Plastic deformation;Precipitation (chemical);Epitaxial growth;Elastic moduli;Crack initiation摘　　要Titanium carbide particle (TiC//p) reinforced Ni alloy composite coatings were synthesized by laser cladding using a cw 3 kW CO//2 laser. Two kinds of coatings were present in terms of TiC//p origins, i.e. undissolved and in situ reacted TiC//p respectively.The former came from the TiC//p pre-coated on the sample, whereas the latter from in situ reaction between titanium and graphite in the molten pool during laser irradiation.Conventional and high-resolution transmission electron microscope observations showed the epitaxial growth of TiC, the precipitation of CrB, and the chemical reaction between Ti and B elements around phase interfaces of undissolved TiC//p.The hardness, H, and elastic modulus, E, were measured by nanoindentation of the matrix near the TiC//p interface.For undissolved TiC//p, the loading curve revealed pop-in phenomena caused by the plastic deformation of the crack formation or debounding of TiC//p from the matrix.As for in situ generated TiC//p no pop-in mark appears.On the other hand, in situ reacted TiC//p led to much higher hardness and modulus than that in the case of undissolved TiC//p.The coating reinforced by in situ generated TiC//p displayed the highest impact wear resistance at both low and high impact conditions, as compared with coatings with undissolved TiC//p and without TiC//p.The impact wear resistance of the coating reinforced by undissolved TiC//p increases at a low impact work but decreases at a high impact work, as compared with the single Ni alloy coating.The degree of wear for the composite coating depends primarily on the debonding removal of TiC//p. copy 2001 Elsevier Science B.V. All rights reserved.

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