Laser Surface Alloying Process Research Articles

Dissolution-induced oxide synthesis using SiO2 microparticles for oxide dispersion strengthening of Fe-based alloys

This study reports on a single-track laser surface alloying process that utilizes SiO2 powder to disperse both SiO2 particles and oxide inclusions in 316L stainless steel for oxide dispersion strengthening (ODS) purposes. In this process, the SiO2 powders partially dissolve in the melt pool, and the released silicon and oxygen atoms nucleate to form oxide inclusions in-situ within the metal matrix. This dissolution-induced oxide synthesis route demonstrated a high potential for ODS, achieving a high particle number density (6.6 × 104 mm−2) and area fraction (3.3%) comparable to that of bulk 316L samples produced via directed energy deposition. The hardness of the SiO2/316L composites reached a maximum of 232.4 HV compared to that of the 316L substrate (average 170.8 HV). The improvement in hardness was theoretically explained and quantified, significantly originating from the enhanced dislocation density strengthening mechanism resulting from the large difference in the coefficient of thermal expansion between SiO2 and 316L.

Investigation of the Implementation of Laser Surface Alloying of Cu with Cr-WC.

This paper presents research on the microstructure and mechanical properties of an alloyed composite copper (Cu) surface layer, reinforced with a mixture of chromium–tungsten carbide (Cr–WC) powders. Copper alloying was performed using a high-power diode laser (HPDL). In the tests, three mixtures of powders with different percentage contents (75%Cr 25%WC, 50%Cr 50%WC, 25%Cr 75%WC) were injected into the melting pool during the laser surface alloying process. Microstructural evolution and the properties of the surface layer of copper after laser alloying were investigated. Structural investigations were performed using light microscopy, scanning and transmission electron microscopy (SEM, TEM) and X-ray diffraction (XRD). Microhardness and wear resistance of the modified surface layer were examined as well. After laser treatment the applied powders appear as uniformly distributed particles in the alloyed zone as well as nanoscale precipitates in the Cu matrix. Several types of precipitate characteristics, in terms of morphology, structure and chemical composition, were observed. Laser alloying of the surface layer modified the microstructure, which resulted in an increase in the hardness of the surface layers compared to the base material.

Simultaneous Optimization of Laser Energy and Coating Thickness in Surface Alloying of Al with Fe

In the two-step deposition technique of the laser surface alloying process, the alloying elements are introduced onto the bulk material’s surface. In such process, two main parameters determine the alloying quality: the thickness of the coating and the laser energy supplied onto the specimen. In this work, the laser surface alloying of aluminium (Al) with iron (Fe) is carried out by optimizing both parameters. This is accomplished by assessing the improvement in the hardness after laser treatment. In general, the thicker coating desires higher laser energy to cause surface melting and sequentially diffusion of Fe into molten Al to occur. This is indicated by the linear relationship between the thicknesses for the peak hardness value with the laser energy whereby the optimum energy shifted to higher energy for a thicker coating. The increase in laser energy increases Fe particle’s chance to migrate via diffusion into the bulk Al substrate. However, at 140μm the optimized energy reaches a peak value at 455mJ which is the maximum energy to be supplied in this process before the coating is lost due to excessive ablation. For thicker coatings, the laser’s action does not penetrate enough onto the substrate to cause sufficient melting of the Al surface for alloy formation. The maximum hardness obtained was 40.8 HV at the optimum condition for 140μm thickness treated with 455 mJ. The formation of an alloyed compound is further confirmed by x-ray diffraction technique whereby compounds such as AlFe, Al13Fe4, and AlFe6Si are present in the treated specimens.

Fabrication and wear behavior of TiC reinforced FeCoCrAlCu-based high entropy alloy coatings by laser surface alloying

High entropy alloy (HEA) coatings of FeCoCrAlCu reinforced by TiC were successfully fabricated on Q235 steel by laser surface alloying (LSA). The effect of various TiC content on the constituent phases, microstructure, chemical composition, and grain orientation of the HEA coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscattered diffraction (EBSD), respectively. The microhardness and wear properties of the HEA coatings were investigated using micro-hardness tester and wear tester, respectively. Experimental result confirmed that with the optimized processing parameters, the FeCoCrAlCu-based HEA coatings free of pores and cracks were achieved, in addition to obtaining good metallurgical bonding between coating and substrate. The coatings were made up of a single BCC solid solution and a few TiC phases. EBSD maps of the HEA specimens exhibited anisotropy due to the complex heat flux direction during LSA process. The microhardness and the wear resistance of the FeCoCrAlCu-xTiC (x = 0, 10, 30, 50 wt%) composite coating were improved with the volume of TiC increasing from 0 wt% to 50 wt%. Especially for FeCoCrAlCu-50 wt%TiC composite coating, the microhardness, wear volume and specific wear rate were 10.78 GPa, 5.2 × 105 μm3 and 9.6 × 10−5 mm3/N m, respectively.

Fabrication of TiC-Reinforced Surface Layers on Ductile Cast Iron Substrate by Laser Surface Alloying

This chapter presents a novel method for analysis and optimization of the in-situ formation of TiC-reinforced composite surface layers (TRL) on a ductile cast iron substrate during the laser surface alloying process, combining the experimental approach with the computational thermodynamics. The microstructure of the TRLs has been assessed by light optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The results of thermodynamic calculations with the Scheil-Gulliver model showed a good agreement with the experimental results, indicating that the actual solidification path for the analyzed Fe-C-Si-Ti alloy systems under the investigated range of laser processing conditions is close to the Scheil-Gulliver assumption.

Energy Density Effect of Laser Alloyed TiB2/TiC/Al Composite Coatings on LMZ/HAZ, Mechanical and Corrosion Properties

In the present work, TiC/TiB2/Al composite coatings were synthesized onto a precipitation hardened AlSi1MgMn alloy by laser surface alloying (LSA), using 13.3 J/mm2 and 20 J/mm2 laser energy densities. Microstructure evaluation, microhardness, wear and corrosion performance were investigated and compared with the untreated/substrate Al alloy sample. The results confirmed sound, compact, crackles composite coating of low porosity, with a proper surface/substrate interface. Microstructural analyses revealed the formation of extremely fine nano-precipitates, ranging from of 50–250 nm in the laser melted (LMZ) and large precipitates, accompanied with grain coarsening in the heat-affected zone (HAZ), due to the substrate overheating during the LSA process. Nonetheless, both coatings achieved higher microhardness, with almost 7-times higher wear resistance than the untreated sample as a consequence of high fraction volume of hard, wear resistant TiB2 and TiC phases inside the composite coatings. Further, cyclic polarization results in 0.5 M NaCl aqueous solution confirmed general improvement of corrosion resistance after LSA processed samples, with reduced corrosion current by more than a factor of 9, enhanced passivation/repassivation ability and complete prohibition of crystallographic pitting, which was detected with the untreated Al alloy.

Experimental and numerical study of laser surface alloying of Al<SUB align="right">xCu<SUB align="right">0.5FeNiTi high entropy alloy

High entropy alloy possesses superior properties such as high hardness, wear-resistance, thermally stable, high strength to weight ratio, etc. required in industries. The development of high entropy alloy is critical due to the high segregation possibilities of multi-component systems. Processing of high entropy alloy can be done using laser surface alloying. This work reports 3D simulation and, subsequently, an experimental comparison of laser surface alloying process. Such a comparison is crucial to understand the influence of process parameters on bead geometry formation for better process optimisation. This work deals with the processing of AlxCu0.5FeNiTi high entropy alloy over aluminium alloy (AA1050) substrate. The quality parameters (dilution percent, aspect ratio, and bead angle) obtained from experimental and numerical studies are compared. The calculated melt pool depth and width are in a good agreement with the experimental results. An error of 1.72%, 13.95%, and 6.09% in dilution percent, aspect ratio, and bead angle is reported.

A study on in-situ synthesis of TiCN metal matrix composite coating on Ti–6Al–4V by laser surface alloying process

Laser surface alloying of Ti6Al4V substrate with in-situ synthesized TiCN was carried out by melting preplaced titanium and graphite powders in 3:1 ratio (wt%) in nitrogen atmosphere at different scan speeds in 400–1400 mm/min range, maintaining the laser power and the beam diameter constant at 1200 W and 3 mm respectively. Molten pool thermal history during the alloying process was recorded using an IR pyrometer. With the decrease in scan speed, the cooling rate was found to decrease, while the molten pool lifetime increased which caused densification of TiCN dendritic structure. Though it enhanced the hardness, coatings were found to fail exhibiting brittle fracture during the scratch test, while coatings processed at higher scan speeds (800 mm/min −1400 mm/min) were found to be intact. Further, coatings processed at higher scan speeds also exhibited better wear resistance. Linear polarization electro-chemical corrosion test was performed on the coatings and it was observed that even corrosion properties were better in case of coatings processed at higher scan speeds.

Microstructural Evolution During Laser Surface Alloying of Ductile Cast Iron with Titanium

AbstractDiode laser surface alloying process was used to the in-situ synthesis of TiC-reinforced composite surface layers on the ductile cast iron substrate. The obtained composite surface layers were investigated using optical and scanning electron microscopy, and XRD diffraction.It was found that the morphology and fraction of TiC phase is directly dependent upon both the concentration of titanium in the molten pool and also the solidification rate. With increasing titanium content, the fraction of TiC increases, whereas the fraction of cementite decreases. The TiC phase promotes a heterogeneous nucleation of primary austenite grains, what reduces a tendency of cracking in the alloyed layers.

A Comparison of Numerical Strategies for Modeling the Transport Phenomena in High-Energy Laser Surface Alloying Process

A comparative assessment is done on the effectiveness of some developed and reported macroscopic and mesoscopic models deployed for addressing the three-dimensional thermo-fluidic transport during high power laser surface alloying process. The macroscopic models include the most celebrated k-e turbulence model and the large eddy simulation (LES) model, whereas a kinetic theory based lattice Boltzmann (LB) approach is invoked under the mesoscopic paradigm. The time dependent Navier-Stokes equations are transformed into the k- turbulence model by performing the Reynolds averaging technique, whereas a spatial filtering operation is used to produce the LES model. The models are suitably modified to address the turbulent melt-pool convection by using a modified eddy viscosity expression including a damping factor in the form of square root of the liquid fraction. The LB scheme utilizes three separate distribution functions to monitor the underlying hydrodynamic, thermal and compositional fields. Accordingly, the kinematic viscosity, thermal and mass diffusivities are adjusted independently. A single domain fixed-grid enthalpy-porosity approach is utilized to model the phase change phenomena in conjunction with an appropriate enthalpy updating closure scheme. The performance of these models are recorded by capturing the characteristic nature of the thermo-fluidic transport during the laser material processing. The maximum values of the pertinent parameters in the computational domain obtained from several modeling efforts are compared in order to assess their capabilities. The comparison shows that the prediction from the k-e turbulence model is higher than the LES and LB models. Additionally, the results from all three models are compared with the available experimental results in the form of dimensionless composition of the alloyed layer along the dimensionless depth of the pool. The comparison reveals that the LB and the LES approaches are better than the k-e turbulence approach in reproducing the experimental results.

Diode Laser Surface Alloying of Armor Steel with Tungsten Carbide

AbstractMetal matrix composite (MMC) surface layers reinforced by WC were fabricated on armor steel ARMOX 500T plates via a laser surface alloying process. The microstructure of the layers was assessed by scanning electron microscopy and X-ray diffraction.The surface layers having the WC fraction up to 71 vol% and an average hardness of 1300 HV were produced. The thickness of these layers was up to 650 μm. The addition of a titanium powder in the molten pool increased the wettability of WC particles by the liquid metal in the molten pool increasing the WC fraction. Additionally, the presence of titanium resulted in the precipitation of the (Ti,W)C phase, which significantly reduced the fraction of W-rich complex carbides and improved a structural integrity of the layers.

Effect of laser power and powder feeding on the microstructure of laser surface alloying hardened H13 steel using SKH51 powder

The surface of H13 steel was hardened with laser surface alloying by using an alloy powder (SKH51) and melting the surface with a Yb-YAG disk laser, at varying powder feeding rates and laser power. A laser speed of 70mm/s and a beam interval of 0.45mm, which were found to be the optimal conditions for productivity maximization in a previous study, were set as fixed conditions for this laser surface alloying process. Under these experimental conditions, a higher laser power caused an increase in the depth of the alloy layer, but a decrease in the surface hardness. On the other hand, a higher powder feeding rate increased the surface hardness, without causing any significant change in depth. The increased hardness is ascribable to the carbides formed from C, W, Cr, Mo, and V contained in the SKH51 powder at the dendrite boundary of the alloy layer along with the formation of 100-nm-sized lath martensite during the fast quenching of the molten portion. The hardness of the laser surface alloyed layer reached values up to 791Hv, which is 190Hv higher compared to the hardness obtainable through a common solid state quenching process. The laser-hardened depth could be maintained at 0.4–0.5mm.

Surface Alloying of Copper Substrate Coated by Fe-Si by Using CO<sub>2</sub> Laser

Advanced industrial applications require materials with special surface properties such as high hardness and high wear resistance. In this study, copper substrate samples where coated by Fe-Si by using thermal evaporation technique under high vacuum, then subjected to surface laser treatment by using 720 watt CO2 laser beam. The purpose was to perform local alloying in the form of surface network of four tracks (each two are parallel and perpendicular to the other two) to produce a good thermal and electrical properties bulk material with reasonable surface hardness properties. The morphological features of the subsurface laser treated layers and their mechanical properties (microhardness) have been studied on oblique sections through the laser fused tracks. The results show that there were an intensive re-evaporation of the coating material, probably because of the high laser power density applied and the use of deep vacuum during the laser surface alloying process. Generally hardness recorded to be increased in the laser-fused tracks locations, but the bottom of the laser fused tracks showed a number of spherical voids causing a drastic decrease in the hardness values. The middle parts of the tracks showed columnar structure and elevated hardness values.

Design and optimization of microstructure for improved corrosion resistance in laser surface alloyed aluminum with molybdenum

The in-situ measurement of dilution during the laser surface alloying process is an enormously difficult task, due to the localized nature of laser energy and very short laser-material interaction time. Therefore, a computational approach (finite-element method and analysis of variance) was effectively employed to evaluate the dilution during the laser surface alloying process. Firstly, a finiteelement model based on COMSOL™ multiphysics was developed to predict the dilution of Mo with Al during non-equilibrium laser surface alloying process. Secondly, the optimization model based on Design-Expert® was developed to find the optimal laser surface alloying parameters (laser power, scanning speed, and fill spacing) to obtain a microstructure suitable for improved corrosion resistance that is primarily attributed to the formation of Al5Mo intermetallic phase (16.7 at% Mo). The present optimization model utilized the prior experimental and computational (finite-element) modeling data for the concentration of Mo (at%). The optimization analyses were carried out for the all the current datasets and the analysis revealed 44 optimal solutions that indicate the highest desirability. The confirmation runs were carried out to validate the optimization model. The experimental observation showed that the sample processed with optimal processing conditions demonstrates good corrosion resistance.

Crack-Growth Behavior of Laser Surface-Alloyed Low-Carbon Steel

Crack-growth behavior of Nd:YAG laser surface-alloyed as-received low-carbon steel Fe360B was evaluated. Thin surface layer was alloyed with silicon carbide SiC. During laser surface alloying process SiC powder dissolved in the melted pool. The surface-alloyed layer had as-solidified structure composed mainly of dendrites of ferrite, fine martensite needles, and retained austenite. The micro-hardness of the laser surface-alloyed layer was about 850 HV0.1. In laser surface-alloyed layer compressive residual stresses of average amount of σ RS = −100 MPa were obtained. In crack-growth tests comparison between specimens of as-received low-carbon steel Fe360B and the same steel with laser-alloyed surface was made. As the crack propagation was perpendicular to the interface between the laser-alloyed layers and the base metal, laser surface-alloyed specimens exhibited higher crack-growth resistance in the low stress intensity factor range ΔK th than as-received steel specimens.

SEM-EDX Analysis of Laser Surface Alloying on Aluminum

Microstructure and chemical composition changes on the alloyed aluminum surface were investigated using SEM-EDX analysis. A Q-switched Nd:YAg laser was focused to induce breakdown and plasma formation. The high plasma temperature and the shock wave pressure were responsible for speeding up the laser surface alloying process. The rapid heat and cooling process introduced a non-equilibrium condition causing changes in the microstructure as well as the chemical composition of the alloyed aluminum surface. The remelted layer and molten pools were realized after the aluminum received a power density greater than 5 x 10 8 Wcm -2 . The chemical composition change confirms that the convection process had taken place during the alloying process.

Dilution of molybdenum on aluminum during laser surface alloying

A multiphysics based computational model was developed to predict the dilution of molybdenum (Mo) on an aluminum (Al) substrate during the laser surface alloying process. The influence of laser surface alloying processing parameters such as input energy, scanning speed, and overlapping ratio on dilution of Mo in Al was explored via computational model. The computational model, closely predicts the melt pool geometry (width and depth) that subsequently helps in estimating dilution. It was observed that the dilution increases with the increase in laser power, while it decreases with the increase in scanning speed. The phase and microstructural analyses revealed the existence of Al5Mo intermetallic for most of the laser surface alloying processing conditions. However, at higher (3.18×107J/m2) and lower (1.91×107J/m2) laser energy densities, the Al8Mo3 intermetallic was also evolved. These experimental observations validate the model’s predictions and points to its reliability in predicting the expected intermetallics in Al–Mo system for various laser surfacing alloying processing conditions.

Computational modelling of transport phenomena in high energy materials processing application: large eddy simulation and parallelisation

A comprehensive three-dimensional numerical model is presented in order to address the coupled turbulent momentum, heat and species transport during molten metal-pool convection in association with continuous evolution of solid-liquid interface typically encountered in high energy materials processing applications. The turbulent aspect is handled by a large eddy simulation (LES) model and the phase changing phenomena is taken care of by a modified enthalpy-porosity technique. The proposed finite volume based LES model is subsequently parallelised for effective computational economy. To demonstrate the effectiveness of the present model, a systematic analysis is subsequently carried out to simulate a typical high power laser surface alloying process, where the effects of turbulent transport can actually be realised.

Entropy generation analysis for the free surface turbulent flow during laser material processing

PurposeThe purpose of this paper is to carry out a systematic energy analysis for predicting the first and second law efficiencies and the entropy generation during a laser surface alloying (LSA) process.Design/methodology/approachA three‐dimensional transient macroscopic numerical model is developed to describe the turbulent transport phenomena during a typical LSA process and subsequently, the energy analysis is carried out to predict the entropy generation as well as the first and second law efficiencies. A modified k–ε model is used to address turbulent molten metal‐pool convection. The phase change aspects are addressed using a modified enthalpy‐porosity technique. A kinetic theory approach is adopted for modelling evaporation from the top surface of the molten pool.FindingsIt is found that the heat transfer due to the strong temperature gradient is mainly responsible for the irreversible degradation of energy in the form of entropy production and the flow and mass transfer effects are less important for this type of phase change problem. The first and second law efficiencies are found to increase with effective heat input and remain independent of the powder feed rate. With the scanning speed, the first law efficiency increases whereas the second law efficiency decreases.Research limitations/implicationsThe top surface undulations are not taken care of in this model which is a reasonable approximation.Practical implicationsThe results obtained will eventually lead to an optimized estimation of laser parameters (such as laser power, scanning speed, etc.), which in turn improves the process control and reduces the cost substantially.Originality/valueThis paper provides essential information for modelling solid–liquid phase transition as well as a systematic analysis for entropy generation prediction.

Process monitoring of powder pre-paste laser surface alloying

Instead of the continuous powder delivery method using a powder feeder for thick layer laser cladding, pre-pasting of the alloying powder on the substrate is a widely used method to supply the coating powders into the melt pool for LSA. A method to monitor the process of laser surface alloying based on the infrared emission from the melt pool using infrared photodiodes was developed. The technique is solely aimed at the process of laser surface alloying using pre-paste metal powder on the substrate surface prior to laser melting. This monitoring technique is able to distinguish the existence or the absence of the pre-paste powder and the consistency of the laser surface alloying process. The technique is of low cost and is simple to implement into the process.