W/Cu joining is key for the fabrication of high heat load components for fusion reactors, which however suffers from the low W/Cu bonding strength due to the immiscible nature of W-Cu system. In this study, we proposed a method for strengthened W/Cu joining based on femtosecond (fs) laser induced micron-scale W/Cu interface structure. W surfaces were irradiated by fs laser to form micron-scale cubes array, and then joined to Cu by hot pressing at 1000 °C, 80 MPa for 2.5 hours. The tensile strength of the W/Cu joining samples was investigated. The results show that micron-scale cubes array was successfully introduced into W/Cu interface without any cracks or pores. The interface structure helps to increase the W/Cu bonding strength to as high as 59.61 MPa, increased by about 50% as compared to W/Cu joining with a flat interface (bonding strength 40.11 MPa). The W/Cu bonding strength shows positive correlation with the W/Cu interface area, indicating the possibility to control the W/Cu bonding strength by simply adjusting the fs laser ablation parameters for the fabrication of cubes array on W surface. Our research provides a method for strengthened joining between intrinsically immiscible materials, including but not limited to W and Cu.
In many applications such as cylinder body, sleeve and mould side wall, vertical surfaces need to be strengthening together with horizontal surfaces. In this paper, a new powder feeding nozzle for laser vertical surface treating was designed and a whole laser surface modification system with powder feeding for vertical surfaces is developed. By using this system, experimental work on laser remelting, laser alloying with powder feeding, laser cladding with powder feeding was performed on vertical surfaces of gray iron substrates. The microstructure, composition and hardness distribution were analyzed. The results indicate that the properties of the vertical surfaces have been greatly improved after these treatments. The powder feeding nozzle and vertical processing can realize various vertical surface modifications with or without powder feeding, which has a promising prospect in industry applications.
Different weight ratio of titanium, zirconium, WC and Fe-based alloy powders were mixed, and cladded onto a medium carbon steel substrate using a 3kW continuous wave CO2 laser, aiming at producing Ceramic particles- reinforced metal matrix composites (MMCs) layers. The microstructures of the layers are typical hypoeutectic, and the major phases are Ni3Si2, TiSi2, Fe3C, FeNi, MC, Fe7Mo3, Fe3B, γ(residual austenite) and M(martensite). The microstructure morphologies of MMCs layers are dendrites/cells. The MC-type reinforcements are in situ synthesis Carbides which main compositions consist of transition elements Zr, Ti, W. The MC-type particles distributed within dendrite and interdendritic regions with different volume fractions for single and overlapping clad layers. The MMCs layers are dense and free of cracks with a good metallurgical bonding between the layer and substrate. The addition ratio of WC in the mixtures has the remarkable effect on the microhardness of clad layers.
In the research hotspot of particle reinforced metal-matrix composite layer produced by laser cladding, in-situ reinforced particles obtained by adding strong-carbide-formation elements into cladding power have been attracting more attention for their unique advantage. The research has demonstrated that when adding strong-carbide-formation elements-Ti into the cladding powder of the Fe-C-Si-B separately, by optimizing the composition, better cladding coating with the characters of better strength and toughness, higher wear resistance and free of cracks. When the microstructure of cladding coating is hypoeutectic microstructure, its comprehensive performance is best. The research discovered that, compositely adding the strong-carbide-formation elements like Ti+V, Ti+Zr or V+Zr into the cladding coating is able to improve its comprehensive capability. All the cladding coatings obtained are hypoeutectic microstructure. The cladding coatings have a great deal of particulates, and its average microhardness reaches HV0.2700-1400. The research also discovered that the cladding coating obtained is of less cracking after adding the Ti+Zr.
Laser strengthening of U71Mn rail steel was performed under different parameters using a narrow line-shaped CO2 laser beam formed by newly developed binary optics. The microstructure, microhardness and wear resistance of the strengthened layers were investigated. Laser strengthening of PD3 rail steel was performed using a normal circle-shaped beam, and the contact fatigue resistance of samples obtained by optimized laser processing parameters was investigated. The research results showed that a layer with fine martensite was produced on the surface of the rail steels after laser strengthening. The wear resistance to sliding friction was improved over 1.3-2.5 times than that of original steel U71Mn. And the rolling contact fatigue property was improved over 4-5 times than that of steel PD3. The results also indicated that the laser strengthening processing parameters should be selected not to melt and overheat the surface.
This paper presents the research on direct laser deposition of Inconel 738 alloys on directionally solidified (DS) Ni-base supperalloy substrate in order to strengthen or repair the DS gas turbine blades. The results indicate that cracks occur very easily during the deposition process and cracks in laser deposited Inconel 738 on DS Ni-base supperalloy substrate are mostly thermal cracks which may originate on the interface between deposited layers and DS substrate, and develop to multi-deposited layers. The low melting temperature point eutectics between the grain boundaries of DS Ni-base superalloy substrate are the main sources of thermal cracks. Strict control of the heat input of the deposition process can dramatically decrease the cracking tendency. Layers with the DS characteristics are achieved by direct laser deposition on Ni-base superalloy substrate with good shaping and free of cracks by optimizing the deposition technique and laser parameters. Compared with the substrate, the microstructure of the layers is much finer, the average primary spacing of the dendrites is about 5μm. The microhardness of Inconel 738 multi-deposited layers is very uniform, indicating the structure of the layers is homogeneous. The results demonstrate the feasibility and great foreground in repairing and fabricating local parts on DS Ni-base superalloy turbine blades by direct laser fabrication technology.
Laser rapid manufacturing based on laser cladding is a novel layer additive manufacturing technology, which can be well used for producing specific material, geometry and properties components normally unavailable or very costly by conventional methods. This paper presents a project research work on laser rapid manufacturing of special pattern Inco 718 nickel based alloy component with special pattern for aeronautical application. The required pattern Inco 718 nickel based alloy component was manufactured directly by laser deposition with optimized parameters: laser power: 800W, laser beam diameter: 0.8 mm, scanning speed: 0.5 m/min, powder feeding rate: 3g/min; The basic microstructure of laser deposited sample is directionally solidified columnar structure, with metallurgical bound to the substrate. Laser deposited component has good metallurgical and compositional and hardness homogeneity. The average hardness is about Hv0.2 440. The tensile strength of the laser deposited Inco 718 sample is respectively 121 and 116 kgf/mm2 at room temperature and at 650°C, which are a little bit less than the data of forged Inco 718 plate 142 and 127 kgf/mm2 due to its directional solidified columnar structure perpendicular to the tensile test force.
Different weight ratio of nickel based alloy, titanium and graphite powders were mixed and then laser cladded onto carbon steel substrate to produce a surface metal matrix composite layer. The experimental results showed that the coating was uniform, continuous and free of cracks. An excellent bonding between the coating and the carbon steel substrate was ensured by the strong metallurgical interface. The microstructures of the coating were mainly composed of γ-Ni dendrite, M23C6, a small amount of CrB, and dispersed TiC particles, and the in-situ generated TiCp/matrix interfaces were clean and free from deleterious surface reaction. The morphologies of TiC particles changed from the global, cluster to flower-like shape, the volume fraction of TiCp and the microhardness gradually increased from the bottom to the top of the coating layer, and the maximum microhardness of the coating was about HV0.2850, 3 times larger than that of steel substrate. The volume fraction of TiC particles increased with increasing of volume fraction of Ti and C too.
Metal matrix composites (MMCs) layers reinforced by in situ carbide particles were formed by laser cladding using preplaced (2.4%Zr+1.2%Ti+15%WC)/FeCSiB alloy powders on a medium carbon steel matrix. The microstructures of cladded layers, composition and distribution of in situ particles in the cladded layers were observed with optical microscopy (NEOPHOT), scanning electron microscopy (OPTION CSM-950, KYKY2000) and metallographic microstructure computer analysis system. HX-200 micro-Vickers was used to examine the cladded layer microhardness. The microstructure characteristics of MMCs layers are typical hypoeutectic which y austenite dendrites distributed on the FeCSiB quaternary eutectic substrate. The energy dispersive spectroscopy (EDS) analysis shows the reinforcements are in situ synthesis carbides which compositions consist of main transition elements Zr, Ti, w and carbon. The compound carbide particles distributed within dendrite and interdendritic regions with 3.6— 5.8% volume fractions. The martensite transformation went with the rapid cooling processes also. The MMCs layers are dense and free of cracks with a good metallurgical bonding between the layer and matrix. The microhardness values across layer cross section vary between HV0.2 8OO—HV0.2 1000.
With Ni/Al cladding powders and coaxial powder-feeding mode, Ni35A12OFe intermetallic coating was successfully prepared by laser cladding. The optimizing principles of processing parameters of laser cladding were proposed. The shaping and microstructure of laser cladding coating were analyzed. The experimental results indicated that lower laser power; slower scanning velocity and larger beam diameter could ensure excellent shaping and metallurgical quality. Under the optimum processing, laser cladding Ni35Al2OFe intermetallic coating was free of porosity and cracks and a fully metallurgical adhesion was achieved between the coating and the substrate. The microstructure was composed of refine ?-NiAl intermetallic phase as the base and a few dispersed ? phase particles precipitated along crystal grain boundaries and within the grains. The formation of ?-NiAl phase dissolved with Fe, precipitation of ductile ? phase and refined crystal grains were favorable of not only higher strength but also enough ductility and toughness of laser cladding coating.
A composite coating was produced by powder feeding laser cladding. The detailed laser cladding experiments were conducted on a 3kW continuous wave CO2 laser. The diameter of the beam was 3mm, the scanning velocity was 3-10mm/s, and the powder feeding rate was 3.26g/min. The chemical compositions, microstructures and surface morphology of the cladded layer were analyzed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). The experimental results showed that a composites coating with TiC particles of various shapes and sizes embedded in nickel based alloy could be in-situ synthesized from the mixture of nickel based alloy powder, graphite enwrapped with nickel and titanium powders by powder feeding laser cladding. An excellent bonding between the coating and the carbon steel substrate was ensured by the strong metallurgical interface. The coating is uniform, continuous and free from cracks, however there existed some pores in coatings. The microstructure of the coating was mainly composed of ?-Ni dendrite, a small amount of CrB, TiB2, M23C6 and dispersed TiC particles. The maximum microhardness of the coating was about HV021 100 after laser surface remelting .4.5 times larger than that of the steel substrate.
Laser alloying of CSiB+NiMoCo by a 45kW CO2 laser was investigated to achieve sound large functional layer with smooth surface, little oxidation and free of cracks on cheap and broadly used common carbon steel XC38. The protection gas has obvious influence on the alloying results. Compared with Ar and N2, He results in the best surface smooth, finest microstructure (second dendrite arm Ar:N2:He equals 1:1:0.6), highest cooling rate (Ar:N2:He equals 1:1.1:4),highest average hardness HV0.2(Ar:N2:He equals 1:1.14:1.15), most resolvability of alloying elements (about Ar:N2:He equals 1:1.1:1.5). These results can be properly explained by mainly the difference in physical properties of these three gases.
This paper presents the experimental research and analyses on cracking behavior during high power laser cladding of Stellite alloy and NiCrSiB alloy. The experiments demonstrate that Stellite alloy is not sensitive to cracking. Large area stellite laser clad (length 200 mm, width 56 mm, depth 1.9 mm) was achieved by 18 multi-pass overlap. NiCrSiB alloy is very sensitive to cracking and many transverse macro cracks appear on the clad pass. Most cracks originate from the interface between the clad layer and the substrate and then develop up into the surface, which belongs to the cold crack domain. During multi-pass overlap, the as appeared cracks will develop into previous passes or later passes. The cracking phenomenon and behavior is mainly affected by the dynamic interaction between the stress (strain) induced and the thermal plasticity change of the clad material during the solidification, which is related to physical properties of the cladding material, the microstructure and the solidifaction characteristics of the process. The strength and toughness of the as-cladded layer sometimes is more critical to the crack formation than the residue tensile stress induced during the cladding process.
Precision Nd:YAG laser cladding was investigated to achieve laser clads with specific pattern and roughness on very thin metal sheets (0.1 - 0.15 mm) to meet industrial requirements. Characterization of pulsed laser cladding on thin sheet substrate, side nozzle, coaxial nozzle and development, high speed video visualization of powder flow for both nozzles, microstructure evolution, vacuum clamping, chiller cooling were presented. Sound laser clad pattern with height/width ration 0.88 or 0.50 and identical quality was obtained. The present work demonstrates that precision laser cladding and/or direct laser manufacturing on thin sheet is another attracting field on laser cladding.
Bright layers covering 80 percent of the melt area have been achieved by laser glazing on Fe-C-Si-B eutectic matrix prealloyed by laser on nodular iron substrates, which are verified to be metallic glasses by TEM electron diffraction. It is demonstrated in the paper that epitaxial growth from the crystalline substrate in melt bottom is the universal phenomenon and critical factor during laser glazing. The principal condition for glass forming is the abrupt stop of the epitaxial growth during solidification, which is comprehensively dependent upon the eutectic composition, composition homogeneity, microstructure fineness, laser glazing power density and scanning velocity.
This paper reported the research results on 3 kw cw CO2 laser melting-alloying combined strengthening of the camshaft of air-cooled diesel engine used in the desert oil field. The 45 steel camshaft was pretreated with the conventional quenching and high temperature tempering. A focused laser beam with power density 1.5 - 1.7 X 104 w/cm2 was used to alloy the cam lobe area, while the other area of the cam was treated by laser melting using a focused 12 X 1.5 mm rectangular beam (power density 1.1 X 104 w/cm2) produced by a newly developed binary optics. The microstructure of the laser alloyed region is fine Fe-Cr-Si-B multi-element hypereutectic structure with hardness HRC 63 - 64. The melted layer consists of fine needle-shaped martensite and residual austenite structure with hardness HRC 58 - 61. The strengthened layer is 1.0 - 1.3 mm in thickness with pore-free and crack-free and good surface quality. Under the same condition, the Ring-block (SiN ceramic) wear test proves that the wear of the laser alloyed 45 steel ring is only 29 percent of that of induction quenching 45 steel ring. And a 500 hours test engine experiment demonstrates that the average wear of the laser alloyed cam is only 20 percent of that of induction quenched one.
In this paper, laser cladding of CuSnP alloy on HT2040 cast iron was investigated. By adding a proper ratio of Si or H3BO3 to improve the self-melting property of the CuSnP alloy and optimizing the processing parameters, a large area, homogeneous CuSnP clad was achieved. The metallographic structure of the laser clad is (alpha) -Cu + (beta) -Cu5Sn with hardness of Hv150.
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