| The atoms of amorphous alloys only keep short-range order in three-dimensional space, this unique structure determines it has some excellent performances which crystalline metals never have, such as high microhardness, strength and excellent resistance to wear and corrosion. In this paper, laser processing technology was used to prepare Zr55Al10Ni5Cu30amorphous composite coating on the carbon steel in order to improve the mechanical properties and corrosion resistance of the surface as well as to expand the applications of amorphous alloys.First, the laser cladding process parameters were determined according to the bulk amorphous glass-forming ability and the wetting behavior of the coating and the substrate metal in laser processing conditions. Then a Zr-based amorphous composite coating was successfully fabricated by laser multi-layer cladding and laser rapid remelting technology. The microstructure, phases, hardness, thermal stability and corrosion resistance of the composite coating were systematically studied by using optical microscopy, scanning electron microscopy, X-ray diffraction detector, microhardness tester, differential scanning calorimetry and electrochemical workstations. A pit crucible resistance furnace was carried out to heat the coating specimens to different crystallization temperature with aims to investigate the influences on microstructure and properties of the coating after crystallization.Experimental results showed that, the interface between the coating and substrate had no defects. The thickness of the coating was about660μm. The coating can be divided into two regions, one was rich in amorphous phase named the remelted layer the other was rich in crystals named the cladded layer. The remelted layer owing a large area of unorganized feature region had a thickness of about200μm, its corrosion potential, polarization resistance and corrosion current density was-0.261V,0.573μA·cm-2and236.201Ω·cm-2, respectively, which were significantly superior to the middle and bottom organization of the coating.The main phases of the original amorphous composite coatings were zirconium intermetallic compounds Al5Ni3Zr2, Ni10Zr7, NiZr and Cu10Zr7etc, as well as some oxides of Cu, Zr and Al. The relative content of amorphous phase in upper part of the coating was up to about75vol%, the relative content of amorphous phase in the middle of the coating which has a distance about350μm from the fusion line while the bottom one was150μm were about16vol%and24vol%, respectively.The whole original coating had a high hardness, which increased in the beginning and then decreased, the maximum value was about1061Hv0.1. After the heat treatment, the hardness of the coating gradually reduced, and the changes tended to be slow. The highest hardness value after second crystallization heat treatment was879.3Hvo.i. The phases, organizational structures and corrosion resistance had significantly changed. After the first treatment, there was still a certain amount of amorphous phase, but after another crystal heat treatment with higher temperature the coating was completely crystalline and the remelted layer had been observed having no non-organizing feature area. Crystal phases remained Cu10Zr7, Ni10Zr7, NiZr and Al3Zr5such Zr intermetallic compounds. Further, during the heat treatment, corrosion resistance of the remelted layer was significantly reduced, but its final corrosion potential-0.440V still higher than the original cladding layer which was-0.453V and-0.583V, corrosion current density were1.126μA·cm-2and7.675μA·cm-2smaller than the middle and bottom part of the original, respectively. These data showed that the remelted layer after crystal heat treatment still had good corrosion resistance. |
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