Search Results (8)

This study examines in situ induction-heating thermal field assistance during laser cladding of Stellite 6 on 17-4PH stainless steel. Single-layer, multi-track coatings (~2.3 mm) were produced at induction powers of 0, 300, 600, and 900 W while keeping laser parameters constant. Surface morphology, phase constituents, and microstructures were characterized by LSCM, OM, XRD, SEM, EDS, and EBSD, and nanoscale features were probed by TEM for the 600 W condition; microhardness and coating-only tensile properties were evaluated. Thermal assistance improved surface finish (minimum Sa = 16.67 μm at 600 W) and suppressed hot cracking. XRD/EBSD revealed a γ-Co matrix with interdendritic carbides and an increased ε-Co fraction under thermal assistance; TEM further showed stacking-fault lamellae and a distinct FCC/HCP interface, supporting a fault-assisted, diffusionless γ → ε transformation. Increasing induction power coarsened the microstructure (larger D_E and SDAS), decreasing hardness from 537.1 to 461.5 HV_0.1 and lowering yield/ultimate strengths from 1046 MPa and 1512 MPa to 849 MPa and 1423 MPa, while elongation increased from 4.37% to 6.27%. Considering crack-free valve hardfacing with acceptable strength loss and improved ductility, 600 W provides the best overall performance. Full article

Cobalt-based alloys such as Stellite 6 are widely applied in demanding conditions because of their good resistance to wear, erosion, and corrosion, but further improvements in erosion resistance are still required. This work analyzes the effect of adding titanium and tungsten on the structure and properties of Stellite 6 coatings produced by laser cladding, aiming to enhance their erosion resistance. Penetrant tests confirmed that the additions did not reduce coating quality, and macroscopic observations showed that appropriate process parameters allowed for defect-free coatings with strong bonding to the substrate. Microstructural studies carried out by SEM/EDS (Scanning Electron Microscopy/ Energy Dispersive Spectroscopy) and XRD (X-ray Diffraction) revealed that the reference Stellite 6 coating consisted of a cobalt-based austenitic matrix with interdendritic chromium carbides, while Ti and W additions led to the in situ formation of primary and eutectic (Ti,W)C carbides. Transmission electron microscopy showed a gradient in tungsten concentration inside the primary carbides, with progressive tungsten dissolution into the TiC lattice. Although different powder compositions had only a moderate effect on hardness, erosion tests demonstrated that the coatings with Ti and W exhibited clearly improved resistance. In particular, the in situ carbides enhanced erosion resistance at 30° impingement angles, while also maintaining high resistance under 90° impact. These findings confirm that modifying Stellite 6 with Ti and W during laser cladding is an effective way to improve its durability in erosive conditions. Full article

Laser cladding is a modern surface treatment process used for the regeneration of damaged components and deposition of coatings for protection against corrosion and wear. Precise process control enables the production of claddings on small surfaces (<1 cm²). However, in some cases (e.g., cladding of turbine blades), there is a limited possibility of heat dissipation into the substrate material, which causes its rapid heating to several hundred degrees Celsius. This work’s objective is to determine the effect of the substrate temperature and laser cladding parameters of a Stellite 6 cobalt-based alloy on the Inconel 718 nickel-based alloy substrate on the geometry of a single cladding track, as well as its microstructure and hardness. Laser cladding with Stellite 6 powder was performed using an Yb:YAG TruDisk 1000 laser. The varied process parameters included the laser beam power density, cladding speed, and powder flow rate. The samples were preheated using a chamber furnace to a temperature ranging from 20 to 800 °C. The geometry of the single tracks produced by laser cladding and the substrate material dilution ratio were determined by measurements conducted on their cross-sections. Further microstructure investigations were performed by means of electron microscopy (SEM). Additionally, hardness measurements (HV0.3) were conducted on the cross-section of each cladded track. It was found that a higher substrate temperature causes melt pool widening and increases the melt depth, while the height of the single cladded track remains only slightly altered. These phenomena lead to the excessive dilution of the substrate material in the cladding (>35%) and result in a decrease in its hardness to the values characteristic of the Inconel 718 substrate (395 HV0.3). Full article

This work investigates the effect of the addition of tungsten carbide (WC) particles as reinforcements to Ni (Inconel 625) versus Co (Stellite 6) alloys during deposition by laser cladding to form wear-resistant metal matrix composite (MMC) coatings. While the related literature often associates the presence of WC with the enhanced wear performance of MMC coatings, this work shows that such an effect is not universal as it may critically depend on the metallic matrix employed. Thus, to demonstrate whether the reinforcement and matrix act synergically in such a scenario or not, MMC coatings formed by Inconel 625 and Stellite 6, both with WC content ranging from 10% to 40%, were deposited under the same laser cladding setup on AISI 304 stainless steel substrates, being WC-free samples produced together for comparison basis. As expected, the hardness levels increased with more WC presence in both matrices, but the wear resistance was specifically evaluated by means of the metal wheel abrasion test (ASTM B611). The results revealed that the use of WC as a reinforcement indeed affects the matrix materials differently; for Stellite 6, the wear resistance increased with up to 20% of WC (in contrast to the hardness indication), whereas for Inconel 625, the wear resistance progressively decreased with more WC content. It was observed via scanning electron microscopy (SEM) that the WC particles within the Inconel 625 alloy tended to intensive cracking, being in this way more prone to detach from the matrix and hence representing a weakening factor for the effectiveness of the coatings produced. Thus, it is concluded that the addition of WC particles, as potential reinforcements for MMC coatings, is not always effective (synergic with the matrix) in providing wear resistance, hence, opposing the prevailing consensus. This outcome and its reasons will certainly help with insights into proper design of MMC coatings, starting with the importance of matrix material selection. Full article

The article presents research results on the possibility of shaping the structure and properties of Co-Cr-W-C-Ti alloys (type Stellite 6) using laser cladding technology. Cobalt-based alloys are used in several industries because they are characterized by high erosion, abrasion, and corrosion resistance, retaining these properties at high temperatures. To further increase erosion resistance, it seems appropriate to reinforce material by in situ synthesis of hard phases. Among the transition metal carbides (TMCs), titanium carbide is one of the hardest and can have a positive effect on the extension of the lifetime of components made from cobalt-based alloys. In this article, concentration of C, W, and Ti due to the possibility of in situ synthesis of titanium carbides was subjected to detailed analysis. The provided research includes macrostructure and microstructure analysis, X-ray diffraction (XRD), microhardness, and penetrant tests. It was found that the optimal concentrations of Ti and C in the Co-Cr-W-C alloy allow the formation of titanium carbides, which significantly improves erosion resistance for low impact angles. Depending on the concentrations of titanium, carbon, and tungsten in the molten metal pool, it is possible to shape the alloy structure by influencing to morphology and size of the reinforcing phase in the form of the complex carbide (Ti,W)C. Full article

Laser cladding (LC) is a versatile additive manufacturing process where strands of metallic material are deposited and melted by a laser. However, there are some limitations associated with this process that may affect the performance of the final manufactured parts. In the present work, the influence of laser shock peening (LSP) on the fatigue life of 304 stainless steel flat specimens with a cobalt-based alloy (Stellite 6) coating applied by LC was investigated. The analysis was carried out both experimentally and numerically. In the LSP simulation, the ABAQUS/Explicit code was used to determine the residual stress distribution of specimens with double central notches with a radius of curvature of 5, 10, 15, and 20 mm. From the numerical results, an improvement was found regarding fatigue life up to 48% in samples with LSP. Experimentally, 14% in fatigue life enhancement was observed. The residual stress, determined by the contour method, showed good agreement with the LSP simulation. The SEM images revealed that the fatigue failure started at the Stellite 6 coating and propagated towards the center of the specimen. LSP has been shown to be a suitable postprocessing alternative for laser-cladded parts that will be subjected to fatigue loading since it led to fatigue improvement through the introduction of compressive residual stresses on clad coatings. Full article

Tram or light rail systems are heavily relied upon for passenger transit; however, low-carbon steel grades commonly used in special trackwork, such as in switches, are prone to wear, rolling contact fatigue (RCF), and deformation under cyclic wheel–rail contact. To address this, laser cladding can be used to apply a metal coating to protect the underlying substrate and rebuild the worn rail profiles. Laser cladding may also be applied to remove cracking by rebuilding the rail head. The tribological characteristics of light rail components after laser cladding with Stellite 6 and a newly developed martensitic stainless steel were investigated, using roller-on-disc wear testing. Analysis of the microstructure, mechanical properties, and wear performance was undertaken to develop a comprehensive understanding of the influence of the laser cladding type on the wear and surface fatigue performance. Both cladding alloys significantly improved the tribological performance. These findings were compared to those for a laser cladded hypereutectoid rail type (reported in our previous study). It was found that laser cladding with a suitable alloy was an effective technique for improving the tribological properties, increasing the wear resistance, and increasing the retardation of cracking on both substrates. These findings suggest laser cladding may be used to repair light rail components, and this technique can be optimized to suit different rail grades. This makes laser cladding a flexible and versatile maintenance strategy, in both coating and repair applications, to prolong the operational lifetime of critical components for the railway industry. Full article

The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS₂, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS₂ and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr₂₃C₆, and CoC_x. Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS₂) were 587.3 HV_0.5, 0.426, and 5.61 × 10⁻⁵ mm³/N·m, respectively. Full article