Laser Cladding Coatings Research Articles

Al2O3 nanoparticles reinforced Fe-Al laser cladding coatings with enhanced mechanical properties

A novel method is developed to fabricate an Al2O3/Fe-Al composite coating on 1045 steel with excellent mechanical properties and wear resistance. Proper thermal treatment of the ball-milling Fe-Al powder is essential to achieve in-situ assembled Al2O3 nanoparticles, which plays a pivotal role in the mechanical properties of the coating obtained by a subsequent laser cladding process. Systematic studies show that the in-situ grown Al2O3 nanoparticles with a diameter of 50–100 nm assembling on the Fe-Al powder is fabricated by thermal treating the ball-milling Fe-Al powder at 850 °C for 2 h under 0.1 Pa vacuum atmosphere. This kind of metal feedstock is important to achieve a uniform Al2O3 nanoparticles reinforced Fe3Al laser cladding coating, with minimum lattice misfit and high thermodynamic stability characteristics. The in-situ grown Al2O3 nanoparticles with proper sizes in the laser cladding coating refine the solidified microstructure and inhibit the growth of cracks, resulting in not only the enhancement of hardness and toughness, but also a lower specific wear rate of 0.1811 × 10−3 mm3 N−1•m−1 in the dry sliding test.

Corrosion Behavior of Fe-Based Laser Cladding Coating in Hydrochloric Acid Solutions

Corrosion Behavior of Fe-Based Laser Cladding Coating in Hydrochloric Acid Solutions

Progress and Challenges of Ultrasonic Testing for Stress in Remanufacturing Laser Cladding Coating.

Stress in laser cladding coating is an important factor affecting the safe operation of remanufacturing components. Ultrasonic testing has become a popular approach in the nondestructive evaluation of stress, because it has the advantages of safety, nondestructiveness, and online detection. This paper provides a review of ultrasonic testing for stress in remanufacturing laser cladding coating. It summarizes the recent research outcomes on ultrasonic testing for stress, and analyzes the mechanism of ultrasonic testing for stress. Remanufacturing laser cladding coating shows typical anisotropic behaviors. The ultrasonic testing signal in laser cladding coating is influenced by many complex factors, such as microstructure, defect, temperature, and surface roughness, among others. At present, ultrasonic testing for stress in laser cladding coating can only be done roughly. This paper discusses the active mechanism of micro/macro factors in the reliability of stress measurement, as well as the impact of stress measurement on the quality and safety of remanufacturing components. Based on the discussion, this paper proposes strategies to nondestructively, rapidly, and accurately measure stress in remanufacturing laser cladding coating.

Effect of molybdenum on the high-temperature properties of TiC-TiB2 reinforced Fe-based composite laser cladding coatings

Fe-Ti-B-Cr-Mo-C composite coatings with different molybdenum (Mo) content were in-situ fabricated on a 5CrNiMo die steel substrate by laser cladding. Effects of Mo on the microstructure and high -temperature properties of coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), high-temperature oxidation and high-temperature wear resistance test. Results showed that block-like or cuboidal TiB2 and Mo2B, as well as flower-like (Ti,Mo)C reinforced particles have been formed in the coatings. Amounts of martensite in the coating increased with the increasing of Mo. However, cracks are found in the coating while the addition of FeMo70 exceeded 9 wt%. Mo improved the high-temperature oxidation resistance and reduced oxidation rate. Besides, the coatings processed the better high-temperature wear resistance with 9 wt% FeMo70.

Effect of Ultra-fine WC Particles on Microstructural Evolution and Wear Behavior of Ni-Based Nano-CeO2 Coatings Produced by Laser

The wear behavior and microstructure of CO 2 laser cladded Ni-based alloy coatings with 1 wt% nano-CeO 2 and 20 wt% WC addition (CeO 2 /Ni) was compared with Ni-based coatings with 1 wt% nano-CeO 2 addition (WC-CeO 2 /Ni). Both coatings were cladded on 30CrMnSiNi2A steel with good metallurgical bounding to substrate. The influence of ultra-fine carbide WC on the microstructure of WC-CeO 2 /Ni alloy composite coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA). WC addition increased M 23 C 6 content, but decreased the M 7 C 3 . The comparison of comprehensive mechanical properties between coatings with and without fine WC particles was conducted on Vickers hardness and wear-resistance test system. Results indicate that the performance of WC-CeO 2 /Ni is better than that of CeO 2 /Ni metal matrix composition (MMC). Few hot cracks appeared in Ni-based WC-CeO 2 MMC production, which were investigated by SEM and EDS. The crack mechanism can be claimed as Fe dilution and coefficient of thermal expansion for WC-CeO 2 /Ni MMC differed from that of base material 30CrMnSiNi2A steel.

Corrosion behavior of laser-clad coatings fabricated on Ti6Al4V with different contents of TaC addition

The coatings were produced on Ti6Al4V by laser-cladding the mixture of Ni-based alloy and different contents of TaC (0 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%). The microstructure and corrosion behavior of the coatings were investigated in detail. The coating without TaC is composed of TiNi/Ti2Ni (matrix) and TiC/TiB/TiB2 (reinforcement). Moreover, TaC is precipitated again and TiC/TiB/TiB2 solid solutions containing Ta are formed in the coatings. Corrosion potential of the coatings (− 0.639, − 0.636, − 0.547, − 0.534, − 0.471 and − 0.348 V) increases, and passive current density (1 × 10−5.4, 1 × 10−5.6, 1 × 10−6.4, 1 × 10−6.8, 1 × 10−6.7 and 1 × 10−6.9 A·cm−2) decreases. The passive films are more difficult to break down (breakdown potential of 0.003, 0.080, 0.204 and 0.605 V). When the content of TaC exceeds 20 wt%, no breakdown phenomenon is observed. The passive film on the surface of coating without TaC is mainly composed of TiO2, Al2O3, Cr2O3, CrO3, NiO, Ni2O3 and SiO2. After the addition of TaC, Ta2O5 is formed in the passive films. The content of Ta2O5 presents an increasing trend with the increase in the content of TaC. The addition of TaC has a positive effect on corrosion resistance of the coatings.

An assessment of microstructure and properties of laser clad coatings of ultrafine eutectic β Ti-Fe-Nb-Sn composite for implants

High mechanical strength (1800–2500MPa), elastic modulus (50–110GPa) close to that of human bone and good corrosion resistance are some characteristics of ultrafine eutectic Ti-based nanocomposite alloys. This is explained due to a combination of soft β-Ti (bcc) matrix and hard/refined TiFe and/or Ti3Sn intermetallic particles. The present study focuses on the production and characterization of Ti-Fe-Nb-Sn eutectic alloys using biocompatible β-stabilizer elements, such as Nb, Fe and Sn. Different fabrication techniques based on rapid solidification may be highlighted considering the application of these alloys as implant materials. In the present investigation, the processing routes comprise single tracks and coatings (overlapped tracks) by laser melting of pre-alloyed powders of the Ti66Fe20Nb8Sn6 alloy deposited into a Ti substrate. To select this composition (i.e., the Ti66Fe20Nb8Sn6 alloy), three Ti-Fe-Nb based chemistries (Ti63Fe23Nb8Sn6, Ti60Fe23Nb8Sn9 and Ti66Fe20Nb8Sn6) were originally generated under bulk conditions by using a suction casting apparatus. These alloys were further evaluated. All samples were analyzed by metallography, X-ray diffraction (XRD), scanning electron microscopy (SEM-EBSD and SEM-EDS), microhardness, nanohardness and elastic modulus. The results showed that the proportions of the formed TiFe and Ti3Sn intermetallic particles dispersed within the soft β-Ti matrix play a fundamental role on the final properties. Lower elastic modulus (E ~72GPa) is associated with the Ti66Fe20Nb8Sn6 bulk alloy. The laser clad coatings showed a broad range of nanohardness (4.8–8.0GPa) and elastic modulus (98–150GPa) depending on the related laser power and scanning speeds.

Effect of Isothermal Temperature on Growth Behavior of Nanostructured Bainite in Laser Cladded Coatings.

The growth and propagation behavior of austenite-to-bainite isothermal transformation in laser-cladded, Si-rich, and Fe-based coatings is investigated. The crystallographic features, orientation relationship at different isothermal temperatures, and the morphology of the nanostructured bainite are determined. The Nishiyama-Wassermann type orientation relationship is observed at a high temperature and at a low temperature, and mixed Nishiyama-Wassermann and Kurdjumov-Sach mechanisms are seen. The growth direction is investigated by the partial dislocation theory and an extrapolated model based on the repeated formation of lenticular-shaped subunits and pile-up along the close-packed directions of the close-packed planes. The variants of the bainite growth directions would be more selective at the high transformation temperature.

A study on the influence of laser power on microstructural evolution and tribological functionality of metallic coatings deposited on Ti-6Al-4V alloy

Metallic Ti–Co binary coatings were fabricated on titanium alloy (Ti–6Al–4V) substrate by laser surface cladding technique using a continuous wave RofinSinar 4 kW Nd: YAG laser. The influence of laser power on microstructure, hardness and tribological performance of Ti–Co laser clad coatings on titanium alloy (Ti–6Al–4V) was examined. Laser powers of 750 and 900 W were varied with constant scan speed of 1.2 m/min. A beam size of 3 mm and argon shield gas flow rate of 1.2 L/min were set as the operating laser parameters. Phase identification and morphological studies of the coatings were carried out using X-ray diffractometry (XRD) and scanning electron microscopy (SEM), respectively. Based on the results of laser process optimisation, it was observed that both laser powers produced clad coatings with good metallurgical bond with no cracks or pores in the coatings. With respect to the substrate (Ti–6Al–4V), the microstructure, hardness and friction/wear behaviour of Ti–Co coatings on Ti–6Al–4V substrate were enhanced obviously.

Microstructure and wear resistance of laser cladding particulate reinforced Fe-based composite coating on railway steel

It has been proved that the laser cladding particulate reinforced metal-based composite coating is of great benefit to industrial applications, owing to its superior properties such as wear resistance, corrosion resistance, and metallurgical bond with a base metal. It is also well-known that the railway switch can easily get damaged due to the abominable conditions of high speed and heavy haul in the rail-wheel mechanical system, and it can cause quite huge loss every year. So, it is of great significance to increase the wear resistance of railway switch steel. In this study, particulate reinforced Fe-based composite coatings were produced on the high carbon manganese rail steel (U71Mn) by laser cladding. The coatings' properties, such as microstructure, microhardness, and wear resistance, were investigated. The wear scar appearance was also detected using a white light interferometer. The results reveal that the composite coatings with good formation and a typical in situ particulate reinforced microstructure can be obtained in proper processing ways. The microhardness of laser cladding coatings reaches HV 750 to HV 800, while the average microhardness of railway steel without laser treatment is HV 390. Furthermore, the properties of wear resistance of the laser cladding coatings have increased by nearly eight times when compared to the untreated railway steel specimen. The adhesion strength of the coatings to the substrate reaches 88% of the shearing strength of the railway steel.

Porosity elimination and heat treatment of diode laser-clad homogeneous coating on cast aluminum-copper alloy

Laser cladding of homogeneous coating onto ZL205A substrate by using a high-power diode laser was investigated in order to repair casting defects of ZL205A aluminum alloy. Single and multi-layer laser cladding was carried out to optimize laser process parameters. Pores on the cross-sections of the laser-clad coatings were chain-like and distributing along the bottom of the molten pool. Lower powder feed rate and relatively higher laser power were helpful in eliminating porosity defects, and pores larger than 100μm in diameter were successfully eliminated by optimizing laser and material parameters. The microstructure of the laser-clad coating was columnar and columnar dendrite structures with reticular Al2Cu phase precipitating in the grain boundary. The microhardness of the laser-clad coating (about 75HV) was significantly lower than that of the substrate (about 152HV), and could be improved to about 134HV after suitable solution treatment afterward artificial aging treatment, which was helpful to the restoration of coatings' mechanical properties.

Tribological and Oxidative Behavior of Thermally Sprayed NiCrBSi Coatings

The behavior of NiCrBSi coatings deposited by three different spraying techniques was studied: flame spray with a subsequent flame treatment (FS + Flame), flame spray with post-laser treatment (FS + Laser) and laser cladding (LC). The coating responses under wear and oxidation conditions were analyzed. Although the microstructure of the coatings deposited by the three different techniques showed similar phases and precipitates, some changes in the size and distribution of these constituents were observed. The pin on disk configuration was used to determine the friction coefficients and wear rates. LC coatings showed the highest wear resistance, with plastic deformation being the main wear mechanism identified for all of the coatings analyzed. Tests under aggressive environments were also performed to determine the oxidation kinetics.

Influence of large particle size – up to 1.2 mm – and morphology on wear resistance in NiCrBSi/WC laser cladded composite coatings

This paper aims at studying the influence of the reinforcement particle size and morphology on the wear resistance properties of NiCrBSi-based composites. Numerous papers have already been written on this subject but almost all of them studied the “conventional” particle size for laser cladding (i.e. between 20 and 200μm). The objective of this study is to see the influence of coarser reinforcement particles, up to 1.2mm, and the influence of the morphology (spherical and random shaped) on the coatings erosive and sliding wear resistance. Laser clad coatings were deposited on low carbon steel substrate S235JR with various amounts of WC/W2C particles up to 50vol.%. The coatings were processed by using a 3.8kW High Power Diode Laser (HPDL). Spherical tungsten carbide particles from 40μm up to 1200μm were used in this study as well as random shaped particles from 40μm to 400μm. To assess the influence of the reinforcement particle properties on wear properties, wheel tests and pin-on-disk tests were performed on each composition. From this study, it can be concluded that there is an obvious advantage in using larger particles (750–1200μm) in harsh conditions while smaller particles (40–160μm) improve the resistance in sliding conditions. The effect of morphology has not been proved significant.

Comparative Studies of Electrochemical and Mechanical Properties of Nickel Electrodeposited and Laser Fabricated Coatings on Steel

Choosing the right surface coating/modification technique is a challenging aspect of material design in recent years with respect to emerging and developing surface engineering technologies. Ni coatings were fabricated on mild steel (MS) samples using electrodeposition and laser cladding techniques respectively. Optical microscopy (OM), X-ray diffractometer (XRD), and scanning electron microscopy equipped with electron dispersive spectroscopy (SEM/EDS) were used to study the morphology, elemental composition, and phase evolution of coatings. Corrosion resistance and wear behaviour were investigated using electro Potentiostat and sliding ball wear tester, respectively. Laser clad Ni coating exhibited high wear resistance with high coefficient of friction, plastic deformation, and cracks on the surface, while Ni electrodeposited coatings had low wear resistance, low coefficient of friction, and eroded materials on the surface. Protective intermetallic oxide phases evolved on both the electrodeposited and the laser cladded coatings. Greater corrosion resistance in 3.65% NaCl solution was achieved through electrodeposition than through laser cladding of Ni on mild steel.

Effects of La2O3 on the microstructure and property of laser cladding Ni-based ceramic coating

Nickel based composite coatings with La2O3 addition were fabricated on medium carbon steel by laser cladding processing. The microstructure, phase composition, microhardness and corrosion resistance of the laser cladding coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness tester and electrochemical workstation. The results show that the herringbone cracks generated in the deposited Ni-based ceramic coatings and the fracture mechanism exhibits quasi-cleavage fracture, while many tearing ridges and micro plastic deformations are present. A crack-free Ni-based composite ceramic coating is prepared with 0.6wt% La2O3 addition, and refined dendritic microstructures are formed with higher microhardness (659HV0.2). However, the introduction of La2O3 addition has little effect on the phase composition of the Ni-based ceramic coating, composed of γ-(Fe, Ni) solid solution, CrB, Cr23C6, Cr7C3 and WC. In addition, the Ecorr values of two kinds of laser cladding Ni-based coatings are all more positive than that of the as-received medium carbon steel, while the Ecorr value of Ni-based cladding ceramic coating with 0.6wt% La2O3 addition is more positive than that of Ni-based coating. Compared with Ni-based cladding coating, addition of 0.6wt% La2O3 leads to lower corrosion current density, which indicates the improved corrosion resistance.

Microstructure and sliding wear properties of HVOF sprayed, laser remelted and laser clad Stellite 6 coatings

The microstructure and sliding wear properties of Co-Cr-W alloy (Stellite 6) coatings were studied in the dependence on the deposition technology. The HVOF as-sprayed, laser remelted HVOF sprayed and laser clad coatings were evaluated by SEM, XRD and ASTM G-133 reciprocating sliding wear test. In dependence on used deposition technology, the microstructure of coating varied namely in terms of grain size and phase composition. The XRD analyses in the wear track revealed that the strain-induced fcc-to-hcp transformation is taking part during wear of laser remelted HVOF sprayed coatings. The difference of the phase composition, grain size and strain-induced fcc-to-hcp transformation was shown to be responsible for differences in the sliding wear behaviour.

Effect of process parameters on the microstructure evolution and wear property of the laser cladding coatings on Ti-6Al-4V alloy

In this paper, Co-based composite coatings were fabricated by laser cladding Co42 + B4C mixed powders on Ti-6Al-4V titanium alloy. The comprehensive effects of laser power and scanning velocity on the microstructure evolution and wear property of the laser cladding coatings were studied. Results indicated that the coatings were mainly comprised of γ-Co/Ni, TiC, TiB2, TiB, NiTi, CoTi, CoTi2, and Cr7C3. With the decreasing of laser specific energy (from 12.7 kJ cm−2 to 4.9 kJ cm−2), the TiC dendrites and TiB particles were refined. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced obviously. Lower laser specific energy led to higher microhardness and better wear resistance owing to more TiB2 bulks distributed in the cladding coating.

Laser cladding: The alternative for field thermite welds life extension

Thermite field welds are the link of rails; however, they experience plastic deformation (batter) along the area above the heat affected zone (HAZ). Here we present the benefits of using laser cladding to minimize the plastic deformation on the HAZ. Our test consisted of a laboratory and a full scale approach under the most extreme revenue service conditions known in North America. The laser cladding coatings were used in the past for rails but its life was terminated in their infancy (after approximately 3–4MGT) due to the presence of un-tempered martensite that negatively affected the rail toughness. The new tested laser cladding design is capable of producing a sound coating with tunable hardness (from 360–430HBN). This is possible through a new heat treatment procedure carried using a propane torch or induction heating at temperatures between 400 and 500°C and cooling rates below 3°C/s. The microstructure shows that the rail after laser cladding is fully pearlitic. The laser cladded welds sustained up to 42milliongrosstons in heavy haul traffic that is between 1000 and 1400% improvement when compared to other previous works.

Microstructure and corrosion resistance of laser cladding and friction stir processing hybrid modification Al-Si coatings on AZ31B

Al-Si coatings were prepared on AZ31B magnesium alloy by laser cladding (LC), friction stir processing (FSP) and hybrid technology (LC-FSP). The coating microstructure, composition and corrosion resistance were investigated using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical measurement. The results indicated that compact, uniform, crack and porous free coatings, which metallurgically bonded to the AZ31B magnesium alloy substrate, were achieved compared with LC coatings. The coatings mainly consisted of Mg2Si, Al12Mg17 and AlMg phases. The coatings contained multiplicate Mg intermetallic compounds exhibited better corrosion resistance as compared with the untreated AZ31B. The formation of compact and uniform Mg intermetallic compounds in the coatings remarkably improved corrosion resistance as compared with LC coatings.

Hot corrosion behavior of Al2O3 laser clad plasma sprayed YSZ thermal barrier coatings

In the present study, the laser cladding of Al2O3 on the top surface of air plasma sprayed (APSed) yttria stabilized zirconia (YSZ) coatings was carried out to improve the hot corrosion resistance of the thermal barrier coatings (TBCs) in the presence of molten salts. The coatings with and without laser cladding were subjected to a hot corrosion test at 1000°C for 30h in which a mixture of 55wt% V2O5 and 45wt% Na2SO4 was used as the corrosive salt. SEM micrographs and EDS analysis confirmed the formation of YVO4 rod-shaped crystals dispersed on the surface of the APSed YSZ coatings after hot corrosion test, while these crystals were hardly detected in the laser clad coatings. The SEM micrograph of the cross section of the APSed YSZ coatings revealed cracks and a thermally grown oxide (TGO) layer in the bond coat/top coat interface, which led to the complete delamination of the coatings. Supporting the SEM micrographs, XRD patterns indicated the transformation of metastable tetragonal zirconia (t′-ZrO2) to monoclinic zirconia (m-ZrO2) after hot corrosion test. This structural transformation was due to the reaction of the molten salts with Y2O3 (zirconia stabilizer) which destabilized the t′-ZrO2. To compare the hot corrosion resistance of the APSed YSZ and the laser clad coating, the volume percentage of the undesirable m-ZrO2 was then calculated after the hot corrosion test. This calculation revealed a higher amount of m-ZrO2 in YSZ (about 70vol%) compared to that of the laser clad coating (about 13vol%).