Papers by Keyword: Co-Based Alloy

Abstract: 316 stainless steel was surface cladded with Co-based alloy using a high power semiconductor laser system. Microstructure, chemical composition, constituent phases and microhardness of the clad coating were investigated with SEM, EDS, XRD and Vickers hardness tester, respectively. The experimental results show that the microstructure of the layer is dense, no voids, cracks or other defects appearing and metallurgical bond between coating and substrate is perfect, The clad layer was mainly consisted of a fine dendritic structure, the constituent phases of the clad layer are mainly composed of γ-Co, (Cr,Mo)₂₃C₆ and Cr₇C₃, the microhardness of clad layer reaches about 720HV, which is about 3 times larger than that of the 316 stainless steel substrate.

Abstract: Site occupancy of Y in the γ′-Co₃(Al,W) was predicted theoretically by first-principles calculations based on density functional theory. By computing total energy as a function of applied strain, the elastic constants of quaternary Co₃(Al,W) were also predicted. The results suggest that Y preferentially occupies the W sites in Co₃(Al,W). The calculation of heat of formation shows that the occupancy of Y on the W sites decreases the phase stability of Co₃(Al,W). The theoretical calculation also shows that the L1₂ Co₂₄Al₄W₃Y compound is ductile in nature.

Abstract: In the present paper the influence of the addition of MoSi₂ particles on the microstructure and pitting corrosion behaviour of laser cladding Co based alloy coatings deposited on 304 stainless steel substrate has been reported. The coating microstructure was investigated by SEM, OM, XRD and EPMA etc.. And the pitting corrosion resistance of coating was evaluated in the 3.5% NaCl solution. The results showed that: (1) The microstructure is fined by increasing MoSi₂ percentage. And the coating microstructure evolved from dendrites and interdendritic eutectics to various faceted dendrites with the bamboo leaf, flower, or butterfly morphology, when the MoSi₂ content is from 0~20% to 30~40%; (2) the (E_pit-E_prot) of Co based alloy/MoSi₂ composite coating was lower than that of Co based alloy, and which presented higher self-repairing capability. The pitting potential E_pit of Co +(0~20wt.%) MoSi₂ cladding coatings is higher than that of stainless steel, the pitting corrosion resistance is enhanced; When more MoSi₂ (30wt.%) was added, the pitting corrosion resistance decreases due to microstructure inhomogeneity and exiting of inclusion.

Abstract: In order to analyze temperature field and stress field of Co-based alloys laser cladding, the model of Co-based alloys laser cladding with preset-powder method has been made on low carbon steel substrate. The temperature field and stress field of laser cladding process was analyzed by SYSWELD software, and Experimental verification is done. The results showed that temperature field is appear to a trailing tail of comet, favorable metallurgy bonding with 12.3% dilution was obtained by scanning velocity was 4 mm/s. and instantaneous cooling rate of molten pool with 4 mm/s and 5 mm/s are increased to 1.47 times and 2.02 times of 3 mm/s. The transverse residual stress different nodes on the surface of coatings are always tensile stress, and it is almost steady, the maximum deformation is 0.34 mm at the edge of work-piece, these are consistent with experimental results. These results provide reference and guide to obtain high quality coatings.

Abstract: The Co-base alloy laser cladding layer was coated on the 2738 mold steel surface by using the TJ-HL-5000 transverse-flow CO2 continuous laser. The morphology and hardness were investigated by metallography microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness tester. The metallography microscope and SEM investigations show that from interface to surface along the cross section direction, the cladding layers consist of plane crystal layer, columnar crystal layer, dendrites layer and surface cellular crystal layer, respectively. XRD results indicate that the cladding layer is made of γ-Co, Cr23C6, MoC, FeCr and Co3Mo2Si phases. The micro-hardness of the laser cladding coating was about 900-1100HV1, 3 times or more of the steel substrate. And the mechanisms of microstructure formation and strengthening are investigated.

Abstract: Kinetics and products of oxidation behavior of binary Co-10Al, Co-10Si and Co-10Cr alloys at 0.1Mpa oxygen at 973 and 1073K were analyzed and compared. The investigations show that CoO doesn't provide protective properties at high temperatures. Among the three alloy components, Co-10Cr has better oxidation resistance at 973K, while Co-10Al has at 1073K, and the causes are given. In addition, the schematic model of scale growth process is presented.

Abstract: In order to analyze temperature field of Co-based alloys laser cladding, the model of Co-based alloys laser cladding with preset-powder method has been made by finite element method. The temperature field of coatings was analyzed by SYSWELD software, and Experimental verification is done. The results showed that temperature field changed from non-steady-state to steady-state in the laser cladding process. Favorable metallurgy bonding with 8.26% dilution was obtained by scanning velocity was 5 mm/s, the temperature gradient of surface coatings is obviously decreased to 1/20 of bonding interface, the solidification rate of surface is nearly 70 times of bonding interface. Right power with 1.6 kW and 1.87 kW was found when scanning velocity was 3 mm/s and 4 mm/s by SYSWELD software. Based on solidification theory, shape factor of crystallization are analyzed, these are consistent with experimental results. These results provide reference and guide for parametric optimization and control dilution rate of laser cladding. Key words: Laser cladding, Co-based alloy, SYSWELD, Simulation

Abstract: An approach for fabricating functionally graded specimens of Co-based alloy and molybdenum disilicide (MoSi₂) compositions via Selective Laser Cladding (SLD) is presented. The focus aimed at using the functionally graded material (FGM) concept to gradually grade powdered compositions of MoSi₂ within a base material of Co-based alloy. A high power CO₂ laser was used to process the material compositions to a high density with gradual but discrete changes between layered compositions. The graded specimens initially consisted of 100% Co-based alloy with subsequent layers containing increased volume compositions of MoSi₂ (0-80wt.%). Specimens were examined for porosity, phase composition and microstructure. It was found that crack sensitivity of layer can be reduced by adding Co-based alloy into the pure MoSi₂ powder.

Abstract: With the help of applying the welding method of DC transverse magnetic field plasma arc surfacing, the powder of Co-based alloy is built up welding on surface of low carbon steel, the refinement effect of primary and secondary crystal structure inflicted by the magnetic field is confirmed through hardness test, wear resistance test, metallographic test and XRD analysis. And study systematically the law of DC transverse magnetic field influencing the surfacing layer metal hardness and wear resistance. The results show that the mechanical properties of surfacing layer achieve the best value when appropriate overlaying welding current match with magnetic current. "Magnetic blow" can be improved with the addition of transverse magnetic field, improving the stability of overlaying welding arc process.

Abstract: The StelliteNo6 alloy was surfaced on low carbon steel by plasma arc surfacing with LMF or TMF. The magnetic field current could been changed during surfacing. After plasma arc surfacing with magnetic field, the OM, XRD, wear loss test, micro-hardness test were used to analyze the effect of magnetic field style on microstructure and properties of overlay deposit. The acting mechanisms of magnetic field style and parameters on properties and microstructure of overlay deposit were researched. The results indicate that LMF and TMF all can improve the properties of overlay deposit. The active effect of TMF is better than LMF because of TMF can make the matrix metal γ-Co finer, second phase (CoCx、Cr₇C₃、Cr23C and FeNi) dispersion.