Microstructure Of Laser Cladding Research Articles

Microstructure evolution and property of high manganese steel coatings by laser shock assisted laser wire cladding

Field-assisted laser cladding (FALC) overcomes the limitations of laser cladding through the inherent advantages brought about by the use of various auxiliary energy fields (AEFs). Laser wire cladding (LWC) is limited by the common problems of laser cladding but has a promising future due to the extremely high material utilization rate. In this study, a laser shock assisted laser wire cladding (LSALWC) manufacturing process was proposed. In situ laser shock was introduced into the LWC to obtain finer grains structure and improve product performance. LSALWC does not change the composition of the coating, does not require the use of pretreatment and post-treatment, and does not reduce the efficiency of production. Using high manganese steel (HMS) as the model alloy, LSALWC was employed to achieve the expectation of reducing the proportion of columnar grains, refine the microstructure of columnar grains, and transform columnar grains into equiaxed grains. Compared with the sample (LC) manufactured by LWC, the performance of the sample (LSA) manufactured by LSALWC has been improved, the hardness increased from 285 ± 5 HV0.5 to 303 ± 6 HV0.5, the volume wear rate decreased from 2.1 × 10−4 mm3/N·m to 1.7 × 10−4 mm3/N·m, the primary dendrite spacing of the coating was reduced by 11.5%, and the heterogeneity of coating was more obvious. The cladding process under laser shock was studied using a high-speed camera, and the influence of laser shock on the coating was explained. The mechanism of the performance improvement of the LSA sample was explained. This study showed the disturbance of the molten pool was enhanced by laser shock, and the dendrites at the bottom were deflected or even broken. The broken dendrites were dispersed with the liquid flow and became new nucleation sites. Laser shock increased the supercooling during solidification by reducing the temperature gradient in the molten pool, and created an environment conducive to grain nucleation and growth. This process mitigates various issues in the casting process of HMS and provides a novel method for regulating the grain and microstructure of laser cladding. This research delves into the coupling between the AEF and the dynamic behavior of the molten pool, culminating in a model depicting the evolution of laser cladding solidification under the influence of the AEF, which will provide a new perspective for the research of FALC.

Microstructural evolution and abrasive resistance of WC7Co ceramic particle-reinforced Ti6Al4V composite coating prepared by pulse laser cladding

WC7Co/Ti6Al4V composite coatings are deposited on the pure Ti substrate by pulse laser cladding (LC). During the laser melting process, the decomposition of WC7Co particles will lead to the evolution of microstructure and phases, which is directly related to the wear resistance and mechanism of composite coating. The microstructural evolution, phase compositions and interface reaction of WC7Co/Ti6Al4V composite coating were examined by scanning electron microscopy, energy-dispersive spectrum and X-ray diffraction (XRD). The hardness of different structures and abrasive resistance of composite coating were measured. The results show that the typical microstructure of LC WC7Co/Ti6Al4V composite coating can be classified into dissolved WC7Co composite structure and un-dissolved WC7Co structure. According to XRD results, there are Ti solid solution, W, TiC, VC, Co3W3C and secondary W2C in composite coating. The eutectic structure formed by the dissolved WC7Co particles consisted of W, W2C, TiC and β-Ti solid solution. The mean hardness of different structures exhibits a significant gradient distribution in composite coating. A reaction layer composed of TiC, W and W2C is also generated onto the interface between un-dissolved WC7Co particles and Ti6Al4V alloy matrix. The abrasive mechanisms of WC7Co/Ti6Al4V composite coating are mainly adhesive wear and oxidation wear during the dry sliding process.

Characteristics of dilution and microstructure in laser cladding Ni-Cr-B-Si coating assisted by electromagnetic compound field

Ni-Cr-B-Si coatings were prepared on the surface of pure iron using an electromagnetic field assisted laser cladding technique. The effect of electromagnetic field on the cross-sectional morphology, the microstructure and the element distribution was investigated. The results showed that the dilution rate of coatings reduced and the grain size of Cr borides was refined under the electromagnetic field. The volume fraction of Cr borides in the coatings increased and the distribution morphology of phases is related to grain boundary wettability. The length of columnar dendrite crystals at the bottom of the coatings decreased with the increase of the electromagnetic force.

Preliminary Experimental Study of Laser Cladding Repair on Directionally Solidified Blades

There is large use of directionally solidified superalloy blades in aerospace, but the repair of these blades is a real problem. The laser cladding technology is able to implement the repair. The experiments in this paper study the microstructure of laser cladding, analyze the formation mechanism and control method, implement the directional growth of microstructure in multilevel laser cladding layer, and provide a theoretical and experimental basis of laser cladding repair on directionally solidified superalloy blades.

Online monitoring of thermo-cycles and its correlation with microstructure in laser cladding of nickel based super alloy

Laser cladding, basically a weld deposition technique, is finding applications in many areas including surface coatings, refurbishment of worn out components and generation of functionally graded components owing to its various advantages over conventional methods like TIG, PTA etc. One of the essential requirements to adopt this technique in industrial manufacturing is to fulfil the increasing demand on product quality which could be controlled through online process monitoring and correlating the signals with the mechanical and metallurgical properties. Rapid thermo-cycle i.e. the fast heating and cooling rates involved in this process affect above properties of the deposited layer to a great extent. Therefore, the current study aims to monitor the thermo-cycles online, understand its variation with process parameters and its effect on different quality aspects of the clad layer, like microstructure, elemental segregations and mechanical properties. The effect of process parameters on clad track geometry is also studied which helps in their judicious selection to deposit a predefined thickness of coating. In this study Inconel 718, a nickel based super alloy is used as a clad material and AISI 304 austenitic steel as a substrate material. The thermo-cycles during the cladding process were recorded using a single spot monochromatic pyrometer. The heating and cooling rates were estimated from the recorded thermo-cycles and its effects on microstructures were characterised using SEM and XRD analyses. Slow thermo-cycles resulted in severe elemental segregations favouring Laves phase formation and increased γ matrix size which is found to be detrimental to the mechanical properties. Slow cooling also resulted in termination of epitaxial growth, forming equiaxed grains near the surface, which is not preferred for single crystal growth. Heat treatment is carried out and the effect of slow cooling and the increased γ matrix size on dissolution of segregated elements in metal matrix is studied.

Characterization and analyses on micro-hardness, residual stress and microstructure in laser cladding coating of 316L stainless steel subjected to massive LSP treatment

The effects of massive laser shock peening (LSP) treatment on micro-hardness, residual stress and microstructure in four different zones of laser cladding coating was investigated. Furthermore, micro-hardness curves and residual stress distributions with and without massive LSP treatment were presented and compared, and typical microstructure in different zones of both coatings were characterized by transmission electron microscope (TEM) and cross-sectional optical microscope (OM) observations. Results and analyses showed that massive LSP treatment had an important influence on micro-hardness and residual stress of the cladding coating. Special attempt was made to the effects of massive LSP treatment on microstructure in three zones of the cladding coating. In addition, the underlying mechanism of massive LSP treatment on microstructure and mechanical properties of the cladding coating was revealed clearly.

Anisotropic structure affects thickness measurement of laser cladding coating with surface ultrasonic wave based on cross-correlation function

Thickness evaluation of laser cladding coating with surface ultrasonic wave method was introduced in this research. Two surface ultrasonic wave transducers with 5 MHz frequency, distance between which was constant, were employed as signal emitter and receiver. Based on cross-correlation theory, the difference in time of flight between surface ultrasonic signals corresponding to different coating thickness was calculated. The relationship between the difference in time of flight and coating thickness is obtained. The results show that coating thickness evaluation is affected by microstructure of laser cladding coating, and accuracy of coating thickness evaluation increases as step length increases until it attains one cycle. In addition, influence of waveform distortion caused by microstructure of laser cladding coating on coating thickness evaluation is discussed. At last, verification test is carried out and the error is in the allowance range.

电-磁复合场协同作用对激光熔覆层凝固组织的调控研究

电-磁复合场协同作用对激光熔覆层凝固组织的调控研究

交变磁场对激光熔覆铁基复合涂层宏观形貌的影响及其微观组织演变

A alternative magnetic field generator is prepared by special circuits and active coils and the effects of different magnetic field intensities on the macro morphologies and microstructures of Fe-based composite coatings are studied by laser cladding process.Based on the electromagnetic principle and liquid metal solidification theory,it describes the solidification process of laser cladding coatings and reveals the main mechanism that magnetic field induced columnar dendrites transform into equiaxed crystals.The results show that the skin effect of liquid metal molten pool surface and alternating electromagnetic force allow the solidified cladding layer surface morphology to the wave form.The height of cladding layer and cross-section area decrease with the increase of magnetic field current,but the cladding layer width changes a little.The electromagnetic force in molten pool interior drives the dendrite ablation and mechanical break,and the free broken dendrites become a new nuclei to increase the nucleation rate,by which the top microstructure of cladding layer transforms from dendrite crystals to equiaxed crystals.Furthermore,the equiaxed crystal zone becomes wider with the increase of magnetic field current,but the bottom microstructure has a little change.

Composition and Microstructure of Laser Cladding of 316 Stainless Steel

Laser Metal Deposition Shaping (LMDS) is a Rapid Manufacturing (RM) process that can be classified under the area of layered manufacturing techniques, where parts are built in layers. Parts of any complexity can be built directly from the 3D CAD model without much human intervention and requires minimum post-processing. In fact, LMDS technique can be recognized as multilayer laser cladding. Accordingly, it is necessary to perform the elementary laser cladding experiments with common metal powder so as to better understand the LMDS process. Then the characteristics of microstructure, composition and phase of as-deposited clads were analyzed through SEM and XRD, as well as relative model. The results prove that the microstructure of 316 stainless steel deposits is composed of the slender dendrites growing epitaxially from the substrate, and the composition is uniform without obvious segregation. Besides, it can be deduced from XRD diagram that the microstructure is composed of mono-phase γ.

Microstructure and Tribological Properties of a Ni-Base Laser Cladding on Aluminum Bronze

In the paper, a Ni-base composite cladding was cladded on the surface of QAl9-4 aluminum bronze by laser cladding technology, as well as its microstructure and tribological properties are studied. The results show that the microstructure of laser cladding is affected by solidification rate, and its wear behavior mainly lies on microstructure and lubrication condition. The microstructure of laser cladding is made up of cellular crystal and dendrite crystal. The microstructure of the surface cladding is cellular crystal, the middle section is crassitude dendrite crystal, and the bottom is coarse dendrite crystal and cellular crystal. Under dry friction condition, wear mechanism is abrasive wear and shedding strengthen phase, which has higher volume’s wear rate. Under lubricate condition, wear mechanism is abrasive wear and adhere wear, which has lower volume’s wear rate than that of dry friction. The average friction coefficient of the cladding under dry and lubricate condition are 0.39 and 0.15, the volume’s wear rate are 7.88×10-8mm3/N.mm and 1.56×10-9mm3/ N.mm, respectively. Therefore, the cladding has favorable wear resistance property under lubricate condition，and can be used as an excellent wearable material.

Abrasive wear performance and microstructure of laser clad WC/Ni layers

WC/Ni clad layers were produced on H13 tool steel substrates with a pulsed Nd:YAG laser and optical fibres using the injected powder technique. The effects of parameters, such as laser beam profile, WC powder shape and substrate pre-heat temperature on the clad layer microstructure and wear properties were investigated. The microhardness of the clad layers was measured using a Vickers microhardness tester. The microstructure of the clad layers was assessed by optical and scanning electron microscopy. The results show that up to 1 mm thick, fully dense and crack-free of WC/Ni clad layers can be formed on H13 substrates. The results further show that the higher is the microhardness of the clad layers, the higher is its wear resistance. Average surface microhardness values of the clad layers were as high as 650 HV. WC particle shape influences the microstructure and wear resistance of clad layer with crushed particles producing more wear resistant surfaces. The clad layers’ abrasive wear resistance was a factor of 5–10 times higher than that of unclad H13 tool steel.

Microstructure of laser clad TiC/NiAl–Ni3(Al,Ti,C) wear-resistant intermetallic matrix composite coatings

TiC-reinforced NiAl–Ni3(Al,Ti,C) intermetallic matrix composite coatings are fabricated by laser cladding with powder blends of Ni–Al–Ti–C on substrate of electrolyzed nickel plate. The microstructure consists of TiC particles, primary NiAl dendrites and the interdendritic Ni3(Al,Ti,C) phase; the composite coatings can be obtained with the features of high-quality metallurgical bonding with the substrate. The volume fraction of Ni3(Al,Ti,C) phase increases with increasing laser scanning speed, but that of dendritic NiAl intermetallic alloy shows a decreasing tendency. Furthermore, the growth morphology of reinforcements changes from octahedron to developed dendrite with laser scanning speed.

Comparison of laser-clad and furnace-melted Ni-based alloy microstructures

Optimization of process variables for laser cladding of Ni-based alloys was performed using the pre-placed powder method. The microstructure of laser clad, under optimal processing conditions, and furnace melted, under near equilibrium conditions, Ni-based alloys has been comparatively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Comparison of the microstructures of the laser-clad and furnace-melted alloys revealed a remarkable difference. The microstructure of the laser cladding is complex, composed of blocky CrB type chromium carbon borides, orthorhombic structured Cr 7C 3 type dendritic carbides, cellular-dendritic ν-Ni solid solution, different interdendritic eutectics and amorphous phases along grain boundaries. The interdendritic eutectics, either ν-Ni+M 23C 6 or ν-Ni+Ni 3B (Ni 2B), can form depending on the local composition. ν-Ni+Ni 3B stable solidification and ν-Ni+Ni 2B metastable solidification exist simultaneously because of the non-equilibrium rapid solidification involved during the laser cladding. In contrast, the microstructure of furnace-melted Ni-based alloy under near equilibrium solidification is composed of hexagonal structured Cr 7C 3 type carbides with hexagonal prism morphologies, near-equiaxed ν-Ni solid solution dispersed with fine Ni 3Si precipitates, ν-Ni+Ni 3B near lamellar eutectic and near-spherical Ni 3B compound. ν-Ni is the main microstructural constituent in both the laser clad and furnace melted alloys. From the grain size, it was evident that the former is one to two orders finer than the latter.