Microstructure And Properties Of Co-based Alloy Laser Cladding Layer Reinforcement By TiC

The valse is often in an environment of high temperature and pressure during use. Coupled with the friction and extrusion of valve and its own contact surface or fluid impurities as well as fluid scouring and corrosion, the valve sealing surface damages, resulting in valve scrapped. Using the laser cladding technology to strengthen the surface of the valve sealing surface, can significantly improve the service life of the valve and bring enormous economic benefits to the society.The experiment selects Stellite 6, Stellite F and Tribaloy 400 three cobalt-based alloys as laser cladding materials, and adds a certain amount of TiC powder as strengthening phase, preparing a series of cobalt-based alloy laser cladding layer in 304 stainless steel surface. Refered to shaping rate and dilution rate of the laser cladding layer surface, the paper finds that the laser cladding layer well shapping with the laser power of 5 kw and the scanning speed of 360 mm/min.Stellite 6 laser cladding layer is mainly composed of face-centered cubic (fcc) structure of the primary solid solution γ-Co phase, and a small amount of Cr7C3, CrFe4, Cr2Ni3, Co3W and other phases. After adding TiC, γ-Co phase, which is the main phase of the cladding layer, remains the same. Cr7C3 phase transforms into two-phases of Cr3C2 and Cr23C6. Stellite F laser cladding is mainly composed of γ-Co, Cr2Ni3 and Ni17W3, as well as a small amount of Co7W6, Cr23C6, Ni3C and other phases. After adding TiC, the cladding layer also generates Cr3C2, Co3Ti, TiC and other phases. Tribaloy 400 laser cladding layer is mainly composed of face-centered cubic (fcc) structure of γ-Co、ε-(Co7Mo6)、 Co2Mo3Si phases. After adding TiC, the cladding layer also generates TiC, Cr23C6, Cr3Ti, Co2Ti and other phases.The structure of the Stellite 6 laser cladding layer is similar to Tribaloy 400, which from bottom to top contains, in order, plane crystals, columnar crystals, dendrites and isometric crystals. From the fusion line to the upper surface, the Stellite F laser cladding layer is composed of, in order, plane crystals, dendrites and isometric crystals. After the addition of TiC powder, with the formation of the above structure, the massive phases in different sizes and shapes occur in the laser cladding layer. When the adding amount reaches 20%, the cladding layer surface is evenly covered with massive phases. That is mainly composed of TiC and newly formed titanium alloys.Among the three cobalt-based alloy laser cladding layers, the hardness of Tribaloy 400 cladding layer is the highest, and the average hardness is 567HV. In the wear test under normal temperature, the normal temperature wear-resisting performance of Stellite F laser cladding layer is better and the major wear form is adhesive wear. The normal temperature wear-resisting performance of Stellite 6 and Tribaloy 400 laser cladding layers are worse. The major wear form is abrasive wear. In the high temperature wear test, the friction coefficient of the 304 stainless steel is the biggest. The friction coefficient of Stellite F laser cladding layer is the smallest, which is about 0.771. The major wear form is adhesive wear. Stellite 6 and Tribaloy 400 have similar friction coefficients as well as similar wear forms, which are mainly abrasive wear with a small amount of adhesive wear. The high temperature wear resistance of the two kinds of cladding layer is better, with the high temperature wear amount only 1/5 of 304 stainless steel. In electrochemical experiments, the corrosion resistance of Stellite 6 and Stellite F laser cladding layers is better. The corrosion resistance of Tribaloy 400 is approximate to 304 stainless steel.While adding a small amount of TiC into the three kinds of cobalt-based alloys (with the adding amount of 10% or less), the hardness of laser cladding layer do not rise but lower,and the wear-resisting performance is worse under normal temperature, do not show the strengthening effect of adding ceramic phase. When TiC content reaches 20%, the hardness of laser cladding layer increases significantly, with the average hardness above 800HV. The wear resistance under normal temperature is significantly improved, which is more than 15 times of the 304 stainless steel, and the second phase strengthening effect is obvious. The wear forms mainly consist adhesive wear and contact fatigue wear. The corrosion resistance is slightly reduced compared with cladding layers not adding TiC.