Investigation Of The Microstructure And Properties Of Co-based Alloy Coatings Prepared By Laser Cladding

The amorphous alloys find wide applications in the machinery, automobile, aerospace and many other areas, due to their high strength, hardness, wear resistance and corrosion resistance resulting from the special structural and compositional characteristics. However, the vigorous preparation process has limited their applications since only amorphous alloys of ribbons as thin as tens of millimeters, filaments or powder are available. Laser cladding is an integrated physical and metallurgical process of the rapid heating and then rapid cooling far away from the equilibrium state, which can meet the conditions for the amorphous alloy formation. Amorphous alloys coatings with special properties can be prepared on the surface of cheap metal products by laser cladding, promising to enlarge the applications of amorphous alloys.In this study, Co61.2B26.2Si7.8Ta4.8alloy coatings were prepared by laser cladding on45steel. The microstructure and properties of the coatings obtained at different laser power were investigated by X-ray diffraction, scanning electron microscopy, electron probe micro-analyzer, Vickers hardness tester and frication wear testing machine. The results showed that the microstructure of the clad layer was featured with Co2B equiaxed dendrite on the amorphous matrix. Changes of micro-area liquid composition and solidification parameters at the edge completely crystallized the amorphous clad layer into binary structure constituted of Co2B and Co3B phases. As the depth of the clad layer increased, the fine dendrite Co2B phases grew into coarse columnar structure, while the interface bonding zone consisted of a’-(CoFe) phase precipitated from a-(CoFe) matrix. With increasing laser power, average hardness value of the coating decreased due to increasing amorphous phase content and decreasing Co2B intergranular precipitation at the edge zone, while wear resistance and anti-attrition property increased gradually.Besides, a higher glass-forming ability was obtained by the partly substitution of Ni for Co on the basis of Co61.2B26.2Si7.8Ta4.8alloy composition. In the present work, the alloy coatings with different Ni content were prepared by laser cladding. The results revealed that Co-based amorphous alloy coatings with changing Ni content were mainly of the amorphous phase precipitated with CO2B, Ni4B3Ni2B intermetallic phases but the glass forming abilities and microstructure of the coating changes along the Ni content. Near the surface of the cladding coating were basically composed of dendrites with0.1Ni and when Ni content in the range of0.2-0.4, the microstructure was mainly of the amorphous phase, with the quantity of amorphous alloys decreased against Ni content. The average hardness of the clad layer was lowered with increasing Ni content. The wear resistance of coating also declined as increasing Ni content within the range0.2-0.4, while the worst wear resistance occurred with0.1Ni.