Laser Surface Cladding Research Articles

Laser (a pulsed Nd:YAG) cladding of AZ91D magnesium alloy with Al and Al2O3 powders

The laser surface cladding of an AZ91D magnesium alloy with Al and Al2O3 powders was investigated using a pulsed Nd:YAG laser. The optimum ratio of Al to Al2O3 and the suitable range of laser processing parameters were identified. The resulting microstructure in the modified surface layer was examined and the wear resistance property was evaluated. The results show that the wear resistance of the laser treated samples was much superior to that of the untreated samples.

Laser surface cladding of Fe–B–C, Fe–B–Si and Fe–BC–Si–Al–C on plain carbon steel

In the present study, an attempt has been made to explore deposition of Fe-based amorphous/glassy layer on a plain carbon (AISI 1010) steel by laser surface cladding (LSC) to improve resistance of the substrate to wear and corrosion. Three known glass forming powder blends (under rapid solidification condition) with nominal compositions of 94Fe4B2C, 75Fe15B10Si and 78Fe10BC9Si2Al1C (all in wt.%) were deposited by LSC using a continuous wave Nd:YAG laser under optimum processing conditions determined by preliminary trials. Following LSC, the microstructure and mechanical properties (microhardness and wear resistance) were evaluated in details. Despite the rapid quenching accompanying LSC, none of the coatings developed/retained amorphous/glassy cladding possibly due to large-scale solute redistribution in the clad zone and/or between the clad layer and substrate. The clad microstructure is characterized by fine dispersion of nano/microcrystalline intermetallic and interstitial compounds/phases in ferritic matrix. Both microhardness and wear resistance showed a significant improvement, particularly after LSC with 94Fe4B2C. Potentiodynamic polarization studies in 3.56 wt.% NaCl solution showed that corrosion resistance of the substrate was remarkably improved by LSC with 94Fe4B2C, but slightly deteriorated after LSC with the other two coatings. Thus, it appears that LSC with 94Fe4B2C, among the present coatings, significantly enhances hardness and resistance to wear and corrosion of the substrate, though fails to develop/retain amorphous microstructure under the present laser processing condition.

Laser Surface Cladding of Al-Si Alloy

The mixture of Ni based alloy powder and WC particles were used as a feeding material to modify the surface properties of cast Al-Si alloy using a CO2 continuous transverse flow laser beam with maximum power of 10 kW. Microstructures and chemical components of the laser surface cladding (LSC) layers were studied using SEM, XRD, TEM and EDS. It is shown that the LSC layers were composed of γ-（ Ni, Cr, Fe, W）matrix phase and many enhancing phases, such as Ni2Al3, Ni3Al, WC, W2C, Cr2B, etc.. The microstructure of the LSC layers was greatly affected by the scanning rate b V and the powder of feeding rate p m under the same laser power. With the increasing of b V and p m , the dissolution phenomenon of WC particles was improved; the length, the diameter and the amount of the acicular constituent were markedly reduced. Microhardness and wear resistance tests were also performed: the average microhardness of the LSC layers was around 5.1 to 5.9GPa, which was five times higher than that of the Al-Si substrate. The wear resistance of the layer was about 20 times as big as that of cast Al-Si alloy when P=6kW, b V =13.3mm s-1, p m =100mg s-1, L=500N. The results showed that the mechanical properties of LSC layers on cast Al-Si alloy can be markedly enhanced with proper processing parameters. However, due to the sudden change of physical and mechanical properties between laser modified layer and substrate, some defects, especially crack, actually occur in the surface modified layer and the interface zone. And finally Ni/WC surface gradient layer was obtained on cast Al-Si alloy through thrice laser scanning technique. The microhardness of the laser gradient layer gradually changed from surface to substrate, so that it can reduce stress concentration in the whole laser surface layer, especially in the interface zone.

Laser surface treatment of grey cast iron for automotive applications

The surface of pearlitic grey cast iron was treated using a 2 kW Nd:YAG laser beam with the final aim to improve its surface properties, mainly for automotive applications. Two kinds of laser surface treatments were experimentally applied. In the laser surface hardening approach the surface of cast iron was hardened simply by passing a laser beam at travel speeds 1-50 mm/s keeping the surface temperature constant in the irradiated area. Detailed structural analysis of the layer modified by the laser treatment was performed by optical and scanning electron microscopy, EDS and orientation imaging microscopy with the electron back scattered diffraction and microhardness profiles were measured. Conclusions concerning the mechanism and kinetics of pearlite-austenite transformation during the laser surface hardening were drawn. The size of the transformed zone was calculated using a three dimensional model for a Gaussian beam distribution in accordance with direct observations of laser beam energy densities. In the laser surface cladding experiments a thick Co-based alloy coating was created on the cast iron surface using so-called side-cladding set-up when the powder of additional material is locally molten together with a small amount of substrate and then rapidly solidified creating a coating with the metallurgical bond to the substrate. A gradual change of a single processing parameter was used for an appropriate experimental analysis and statistical correlation study between main processing parameters and geometrical characteristics of an individual laser track.

Laser (Nd:YAG) cladding of AZ91D magnesium alloys with Al + Si + Al 2O 3

The laser surface cladding of AZ91D magnesium alloy with Al + Si + Al 2O 3 powders (in the wt.% ratio of 7:1:2) was investigated. Laser processing was carried out with a 5 kW Nd:YAG laser. The microstructure and phase analyses of the surface cladding layer were carried out; furthermore, the morphology of the cladding zone, volume fraction and distribution of the Si and Al 2O 3 particles in the laser surface cladding layer were also investigated. The average microhardness of the surface layer was measured in detail as a function of laser parameters. Microhardness of the surface layer was significantly improved to as high as 210 HV 0.05 as compared to 60–70 HV 0.05 of the AZ91D substrate, and the average microhardness of the cladding layer of the composite surfaced specimen decreases with increasing of laser power. However, the rate of decrease is faster at lower power. Though the average microhardness of the surface cladding layer remains constant, there is a little fluctuation in the reading in some regions possibly, because of the random distribution of hard particles in the cladding layer. Finally, the proper processing parameter ranges for formation of a homogeneous microstructure and enhancement of microhardness for laser surface cladding of AZ91D with Al + Si + Al 2O 3 were established.

Main characteristics of calcium phosphate coatings obtained by laser cladding

Laser surface cladding has become an extensively used technique in metallurgical applications in order to improve surface properties of materials. We have proposed this technique in the field of biomaterials to coat the surface of titanium alloy substrates used in orthopaedical implants with a calcium phosphate (CaP) bioceramic to promote the growth of the bone when the implant is inserted in the body. An exhaustive study on the influence of the processing parameters on finished surface, microstructure and superficial composition was carried out. Also, the geometrical features of the CaP coatings were correlated to the relevant processing parameters. Simple linear relationships between the studied clad features and processing parameters have been found. Different techniques applied to characterise the coated samples revealed the gradual composition of the coatings starting with a biphasic calcium phosphate on the surface and ending with a compound between the calcium phosphate and the metallic substrate in the coating–substrate interface.

Microstructure, Microhardness, and Residual Stress Analysis of Laser Surface Cladding of Low-Carbon Steel

This article describes online measurement of thin and flat specimen changes during laser alloying and of the alloyed specimen after treatment. Laser remelting of SiC, Stellite 6, and Stellundum 481 powder was performed on a specimen of low-carbon steel. Experiments were performed with high-temperature resistance-measuring rosettes. Strain was monitored from the beginning to the end of the cladding process (i.e., to a temperature 50°C at the backside of the specimen). Therefore, during the cladding process, the changes in temperature at the backside of the specimen were measured with two Ni-NiCr thermocouples. Other important properties are the size and distribution of residual stresses in the thin cladded specimen (i.e., machine part), because they strongly affect its operational efficiency. Results obtained are analyzed from the viewpoint of minimum final strain of the specimen with the desired variation of residual stresses.

Calcium phosphate coatings obtained by Nd:YAG laser cladding: physicochemical and biologic properties.

The plasma spray (PS) technique is the most popular method commercially in use to produce calcium phosphate (CaP) coatings to promote fixation and osteointegration of the cementless prosthesis. Nevertheless, PS has some disadvantages, such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, we introduce in this work a new method to apply a CaP coating on a Ti alloy using a well-known technique in the metallurgical field: laser surface cladding. The physicochemical characterization of the coatings has been carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). The biologic properties of the coatings have been assessed in vitro with human osteoblast-like MG-63 cells. The overall results of this study affirm that the Nd:YAG laser cladding technique is a promising method in the biomedical field.

Strain Measurement during Laser Surface Cladding of Low-Carbon Steel and Analysis of Residual Stresses

The paper will describe the online measurement of thin and flat specimen changing during laser alloying and measurement of alloy specimen after treatment. SiC, Stellite 6 and Stellundum 481 powder were added separately into the parent metal of low-carbon steel during laser remelting and alloying. Experiments were performed with high-temperature strain gage rosettes. Strain was monitored from the beginning to the end of the remelting and alloying process, i.e., to a temperature of 50°C at the back side of the specimen; therefore, during the remelting and alloying process, the changes in temperature at the back side of the specimen were measured with two Ni-NiCr thermocouples. It was found that the magnitude of strain is affected by energy input and the direction by the mode of laser-beam movement. Three modes of movement of the laser beam with the same degree of overlapping and the same size of treated area will be represented. It is important for industrial applications of laser remelting and alloying to have specimens with the lowest strain since this means low cost of final grinding. Other very important properties are the size and distribution of the residual stresses in the thin remelting and alloying specimen, i.e., machine part, because they strongly affect its operational efficiency. The paper will analyze the results obtained from the viewpoint of minimum final strain of the specimen with the desired variation of residual stresses.

Cladding of Ni–Cr–B–Si coatings with a high power diode laser

Laser surface cladding is a well recognised technique to obtain wear and corrosion resistance coatings, or for repairing damaged parts. Recently, the use of high power diode laser (HPDL) has undergone rapid growth for materials processing. The present work describes the process for obtaining two boride-containing nickel-based hardfacing alloy coatings, primarily composed of Ni–Cr–B–Si on carbon steel using a HPDL. After laser treatment the microstructure is composed of a matrix of γ-Ni with different intermetallics depending on the initial composition of the powder. For the alloy with lower concentration of alloying elements, X-ray diffraction indicates the presence of nickel (Ni 3Fe, Ni 3Si,), boron (B 4C, CrB) and chromium (Cr 3Si) intermetallics. On the other hand, for the alloy with higher amount of C, B and Cr, the analysis revealed the presence of Ni 3B together with lesser proportions of Ni 3Fe and Ni 3Si and the presence of chromium carbides Cr 23C 6 and (Fe·Ni) 23C 6.

Laser Surface Cladding: A New Promising Technique to Produce Calcium Phosphate Coatings

Laser Surface Cladding: A New Promising Technique to Produce Calcium Phosphate Coatings

Production of calcium phosphate coatings on Ti6Al4V obtained by Nd:yttrium–aluminum–garnet laser cladding

Among the various techniques that have been investigated to produce Hydroxyapatite (HA) coatings in order to promote fixation and osteointegration of cementless prosthesis, the plasma spray (PS) technique is the most popular method commercially in use. PS presents some disadvantages such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, an approach on how to bind HA to the Ti alloy will be introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding. Different techniques were applied to characterize the coated samples, including x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis.

Fe-based thick amorphous-alloy coating by laser cladding

New thick Fe-based amorphous alloy coatings have been synthesized by laser surface cladding, with the nominal composition of Fe 57Co 8Ni 8Zr 10Si 4B 13 (at.%). The supercooled liquid region, Δ T x, defined by the difference between the glass transition temperature ( T g) and the onset temperature of crystallization ( T x) was as large as 62 K and T g was 821 K. The high thermal stability of the supercooled liquid enabled the synthesis of a coating with maximum thickness of 1.2 mm. The amorphous alloy coating had a high Vickers hardness of 1270 and good corrosion resistance.

Structure of laser cladded tungsten carbide composite coatings

Carbide-metal matrix composite materials are used in applications were high wear resistance is critical. The laser surface cladding technique offers new advantages in depositing composite materials wear resistant coatings. Layers of WC in Co and Ni-based alloys matrix composites have been laser cladded on a low carbon steel substrate. Due to the right selection of the laser processing parameters during laser surface cladding porosity and crack free WC-metal composite coatings have been produced. The results of optical and SEM microstructure observations, X-ray phase, and EDS chemical composition analysis as well as cross-sectional microhardness distribution have been presented. The longer the laser beam–composite material interaction time, the higher level of the dissolution of primary carbide phase in metal matrix is to be expected. The primary WC particles dissolution degree depends also on their mesh size and volume fraction in composite material. The processing conditions should be optimized to keep the primary carbides dissolution at minimum.

Some aspects of laser surface cladding in the turbine industry

Water droplet erosion of leading edge of the blade in a steam turbine could impair its efficiency and lifetime. To overcome this problem, laser cladding of the leading edge with Co-based stellite powder is commonly used. This paper discusses microscopically the effect of power density and beam interaction time in such a cladding process. It is realized that the beam interaction time has a significant effect on solidification and microstructure development process. The results indicate that the dendrite structure shall be fine for short interaction time compared to the coarse structure for long interaction time. Macro- and micro- cross-section electron probe microanalysis (EPMA) and microhardness profile has been employed to characterize the cladding. The results are correlated with the clad quality. Microstructure, hardness and dilution are discussed as a function of the processing parameters. A few of the actual results of the laser cladding of stellite 6L on 12Cr–Ni turbine blades are presented. Since the dilution of the base material into the cladding is significantly low at short interaction times, the clad could retain significant strength after long-term exposure, a unique feature for the turbine industries. Such possible applications are illustrated as well.

Vacuum laser cladding and effect of Hf on the cracking susceptibility and the microstructure of Fe–Cr–Ni laser-clad layer

An investigation is reported of the laser surface cladding of self-fluxing Fe–Cr–Ni alloys on a medium carbon steel substrate using the preplaced powders method with gas shielding or vacuum protection. The cracking susceptibility and microstructure of the laser-clad layer have been studied in terms of Hf additions. Hf can change the microstructure of the Fe–Cr–Ni alloy clad layer from eutectic to hypoeutectic. The lowest cracking susceptibility occurs when the Hf content in the laser-clad layer is approximately 0.9% wt. But to achieve this effect there must be 3.0% wt. Hf in the alloy powders when shielding with gas. The effect of the protecting condition on cracking susceptibility of the laser-cladding layer is also reported

Cracking susceptibility of a laser-clad layer as related to the melting properties of the cladding alloy

Abstract An investigation is reported of the laser surface cladding of self-fluxing Fe–Cr–Ni–B––Si alloys on a medium carbon steel substrate using the preplaced powder method. The cracking susceptibility of the laser-clad layer has been studied in terms of the melting properties of the cladded alloy. The smaller the fusion temperature zone and fusion-end temperature of the cladded alloy, the lower the cracking susceptibility of the laser-clad layer. The effect of the latent heat of fusion of the cladded alloy on cracking susceptibility is not apparent.

Evaluation of alloy element redistribution within laser-melted layer

Abstract When laser surface alloying and laser surface cladding, a redistribution of alloying elements occurs owing to the mixture between the added material and the substrate as well as the oxidation reaction. This results in a variation in the concentration of alloying elements from point to point within the solidified pool. In order to evaluate the redistribution of alloying elements, a scheme is proposed using a sub-unit model. The model may give two important parameters for a local sub-unit, i.e. D j the mixture ratio between the substrate material and the added material, and μ i the transport coefficient of the i th element from the added material and the substrate into the solidified pool. For each local sub-unit, the only input data is the concentration of each alloying element in the investigated system. By resolving a non-linear equation group, D j and μ i may be calculated for each sub-unit. Laser surface alloying experiments putting Ni base alloy powder onto a cast iron substrate were taken as an example to show the application of this evaluation method.

Microstructural characterisation of laser clad coating of nickel based alloy with dissolved SiCp

A laser surface cladding technique was used to form an Ni–Cr–B–Si–C alloy coating doped with 30 vol.-%SiCp on an AISI 1045 steel substrate. The SiC particles completely dissolved during the melting stage of cladding. The bonding zone has a microstructure of a γ-Fe band resulting from epitaxial planar growth followed by a cellular dendritic eutectic of γ-Ni + M23 (C,B)6 on solidification, characterised by directional solidification. The microstructure of the cladding layer is composed of very closely spaced net-like M23 (C,B)6 primary dendrites and a small amount of interdendritic γ-Ni + M3 (B,Si) lamellar eutectic, and has primary small spherical graphite particles in the upper part of the cladding layer. The rapid solidification involved in the laser cladding resulted in substantial extension of solid solubility of Si in the γ-Ni terminal solid solution. The M23 (C,B)6 primary dendrites contain a high density of stacking faults. The eutectic M3 (B,Si) phase exhibits a periodic structure.

Calculation of process parameters for laser alloying and cladding

This article presents a simplified theoretical model for estimating the operating parameters of laser surface alloying and cladding by the direct injection of powder into the molten bath. It is shown that use of the Mie theory takes into account the influence of the injected particles on laser beam energy transfer to the treated surface. Due to the reasonably good agreement between the calculated and the experimental data, this analytical model is applicable to the development of laser surface alloying and cladding by direct powder injection.