Jianhua Yao

Effect of Laser Power on the Cladding Temperature Field and the Heat Affected Zone

H13 powder is cladded on steel P20 (base) by continuous CO2 laser, and the influence of technological parameters such as the laser power is analyzed. The 3-D model of synchronous powder feeding is built under Gauss heat source. The simulative results in the heat affected zone are compared with the experimental ones, and the average errors of width and depth are 15%and 4. 5%, respectively. It is found that the simulative results provide basic data for investigating of laser cladding further.

Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters

Stellite 6 powders were deposited on low carbon steel using SLD (supersonic laser deposition) under optimized parameters. The structure, line scan of elements and porosity of coating were examined and analyzed using SEM (scanning electron microscope), OM (optical microscope) and XRD (X-ray diffraction). The adhesion strength between coating and substrate was tested by PAT-ADHESION/TENSILE and E900STM adhesive. The results showed the deposition characteristics of optimized coating with N2 at apressure of 3.0 MPa, a temperature of 450 °C and a laser power of 1.5 kW were compared with those of Stellite 6 coating deposited by the HVOF (high velocity oxygen fuel).

Simulation Analysis of Stellite 6® Particle Impact on Steel Substrate in Supersonic Laser Deposition Process

The particle impact behavior of Stellite 6 on steel substrate in the supersonic laser deposition (SLD) process is studied using numerical simulation, compared with experimental data. The impact characteristics of Stellite 6 are analyzed with respect to particle size and deposition temperature. The simulation results show that laser deposition temperature of 1000xa0°C for the substrate is the optimal in terms of the interface bonding between the particles and substrate. The particle size of 40xa0μm exhibits the best deposition interface. The simulation results agree well with the experimental measurements. The depths of impact indentation with different particle sizes and at different temperatures are investigated to obtain the relationships between process parameters such as particle diameter, indentation depth, and deposition temperature. To further understand the effects of collisional behavior of multi-particles on the stress-strain distributions and the micro-zone in the particle and substrate system, different micro-zones of the impact particle are analyzed; the variations of the stress and strain with time for the substrate and particle are obtained from the simulation results. The impact characteristics of Stellite 6 deposited on steel substrate are discussed.

Microstructures and Hardness/Wear Performance of High-Carbon Stellite Alloys Containing Molybdenum

Conventional high-carbon Stellite alloys contain a certain amount of tungsten which mainly serves to provide strengthening to the solid solution matrix. These alloys are designed for combating severe wear. High-carbon molybdenum-containing Stellite alloys are newly developed 700 series of Stellite family, with molybdenum replacing tungsten, which are particularly employed in severe wear condition with corrosion also involved. Three high-carbon Stellite alloys, designated as Stellite 706, Stellite 712, and Stellite 720, with different carbon and molybdenum contents, are studied experimentally in this research, focusing on microstructure and phases, hardness, and wear resistance, using SEM/EDX/XRD techniques, a Rockwell hardness tester, and a pin-on-disk tribometer. It is found that both carbon and molybdenum contents influence the microstructures of these alloys significantly. The former determines the volume fraction of carbides in the alloys, and the latter governs the amount of molybdenum-rich carbides precipitated in the alloys. The hardness and wear resistance of these alloys are increased with the carbide volume fraction. However, with the same or similar carbon content, high-carbon CoCrMo Stellite alloys exhibit worse wear resistance than high-carbon CoCrW Stellite alloys.

Beneficial Effects of Synchronous Laser Irradiation on the Characteristics of Cold-Sprayed Copper Coatings

Cold spray (CS) is an emerging materials deposition technique in which metallic particles are accelerated to a high velocity in a supersonic gas flow and then impinged onto a substrate to form a coating at a temperature well below the melting point of sprayed materials. The coating microstructure and properties are greatly influenced by particle preheating and substrate softening. This article presents a study of CS process of copper powder, with assistance of synchronous laser irradiation. The influence of synchronous laser irradiation on the Cu coating characteristics was investigated. The results show that the coating surface with laser irradiation is smoother than that without laser irradiation. The peak coating thickness is increased by about 70% as synchronous laser irradiation is employed, indicating an improvement in deposition efficiency. It is also found that with synchronous laser irradiation the coating is denser and the coating-substrate interfacial bonding is better as compared with that without laser irradiation. Moreover, the EDS and XRD analyses find Cu oxidation occurrence in the SLD coating, but the oxide is trivial. The aforementioned improvements on the coating largely arise from particle preheating and substrate softening by synchronous laser irradiation in the CS process.

Relations of Chemical Composition to Solidification Behavior and Associated Microstructure of Stellite Alloys

Stellite alloys are a family of superalloys, which can be categorized as CoCrW and CoCrMo systems. Ten selected Stellite alloys from these systems, with low carbon or high carbon content, are studied with respect to solidification and microstructure using differential scanning calorimetry (DSC), scanning electron microscopy with an energy dispersive x-ray spectroscopy, and x-ray diffraction. The objective of this work is to investigate the effects of carton content and other alloying elements on the solidification behavior and associated microstructure of Stellite alloys, to provide the materials industry with technical guidance in design, manufacturing, processing, and heat treatment of these alloys. The phase transformation temperatures of these alloys during heating and cooling are determined under the DSC test. The solidified microstructures and the phases present are analyzed and discussed with emphasis on the relation to chemical composition.

Deposition Behavior at Different Substrate Temperatures by Using Supersonic Laser Deposition

The supersonic laser deposition (SLD) is a new fabrication process which combines the supersonic powder stream found in cold spray with laser heating of the deposition zone. Because of the instantaneity of particles impact, the deformation behaviors and the adhesion behaviors of particles impacted on the substrate by SLD cannot be well investigated through experiments. Therefore, a finite element model was developed to solve the problems above. Meanwhile, the heat effect of the substrate heated by laser was discussed. The effective plastic strain and the effective stress between the particle and substrate at different laser preheat temperatures were studied. The results show that laser depositing temperatures of 1000 and 1100 °C on substrate would be the optimized for the bonding of particles and substrate. In addition, the simulation results conformed to experimental results.

Laser remanufacturing to improve the erosion and corrosion resistance of metal components

Abstract: This chapter looks at laser remanufacturing processes and their application to typical failed components. The failure of four typical components is analyzed and then laser solutions are described, including special material design, technique optimization, field testing and application. The results show that laser remanufacturing is an effective method for hardening and repairing failed components which can be reused with high corrosion and erosion resistance.

MICROSTRUCTURE AND WEAR RESISTANCE OF LASER-TREATED Ni–P–Al2O3 ELECTROLESS DEPOSITION COMPOSITE COATING

A uniform Ni–P–Al2O3 electroless plating layer was produced on medium carbon steel and then scanned by high-power continuous wave CO2 laser beam. The entire coating is divided into three regions: laser-strengthened region, transition zone, and heat-affected zone. The strengthened coating shows good performance characterized by uniform components and refined microstructures. The main phase is comprised of Ni3P with some non-equilibrium phases. The reinforced particles, Al2O3, are homogeneously dispersed in the coating. Its abrasive resistance also increases because of the Al2O3 particles.

Study of microstructure and properties of laser cladding TiC-H13 composite coating

As one kind of excellent hot-working die steel, H13 has been widely used. But the surface failure was usually found which can decrease the service life. In this paper, TiC ceramic powders were introduced to strengthen H13 steel by continuous wave CO2 laser cladding. The macro surface quality and microstructures was investigated by optical microscopy (OM) and scanning electronic microscopy (SEM). Thermal stability and anti-wear performance were measured. TiC was uniformly dispersed in the coating. But the morphologies of TiC in the cladding coating were different for temperature gradient during laser cladding. Near the surface of cladding coating, TiC have been partially molten shown as dendritic structure while in the cladding coating was irregular shape such as subrounded or rhombic. The abrasion resistance of laser cladding TiC-H13 was increased about 3 times than the H13 substrate. The thermal stability of composite coating was a little higher than that of substrate after experiments at 873K.