Thermally spraying (TS) deposited thermal barrier coatings (TBCs) usually contain pores, microcracks, which introduce oxygen diffusion and crack propagation during high-temperature service. In this study, circular oscillating laser remelting (CO-LR) was applied to a YSZ/MCrAlY TBC consisting of the high velocity oxygen fuel (HVOF) deposited MCrAlY bondcoat and atmospheric plasma spraying (APS) deposited YSZ topcoat. Five CO-LR configurations with different remelted unit numbers and continuities were investigated to evaluate their effects on isothermal oxidation and thermal shock behavior. Laser treatment produced dense U-shaped remelted zones in the YSZ topcoat, with a depth of approximately 0.45 mm, while the main phase c-ZrO2, t′-ZrO2, and minor m-ZrO2 were observed in CO-LR area. During isothermal oxidation at 1000 °C, all laser modified TBCs showed lower mass gain and slower thermally grown oxide (TGO) growth than the as-sprayed coating. The annular configuration yielded the lowest measured apparent TGO growth constant (0.0278 μm2/h), while the total mass gains of the hexagonal and annular configurations were comparable. Under thermal shock, the triangular configuration exhibited the highest damage tolerance, with an average spallation rate of 0.0551
Remelted NiCrBSi coatings deposited by oxy-fuel (OF) and high-velocity oxy-fuel (HVOF) spraying were systematically investigated to establish quantitative relationships between microstructure, nanoscale deformation behavior, and wear mechanisms. Nanoindentation, nanoscratch testing, and groove geometry analysis were employed to characterize the elastic-plastic response and deformation stability of the coatings. The remelted HVOF coating exhibited higher hardness and elastic modulus, together with elevated H/E and H3/E2 ratios, indicating improved resistance to plastic deformation and crack initiation. These mechanical characteristics promoted stable scratch deformation with reduced pile-up and shallower grooves, whereas the OF coating showed unstable material removal behavior. To quantitatively distinguish scratch-induced wear regimes, a dimensionless parameter, fk, is introduced. The OF coating exhibited a high fk value (0.90), corresponding to a microcutting-dominated regime, while the HVOF coating showed a lower value (0.52), indicative of plowing-dominated deformation. The transition from brittle fracture to a more ductile deformation response was further supported by stick-slip behavior and post-scratch surface morphology. The results demonstrate a direct correlation between nanoscale mechanical metrics and macroscopic wear mechanisms, while the proposed fk parameter provides a promising framework for predicting deformation regimes in thermally sprayed coatings. This work introduces a novel dimensionless parameter, fk, derived from nanoscratch groove geometry to quantitatively distinguish scratch-induced wear mechanisms in thermally sprayed coatings. Unlike conventional approaches based on qualitative observations or critical load analysis, fk directly characterizes material displacement and deformation behavior during scratching. Using remelted OF- and HVOF-sprayed NiCrBSi coatings, the study establishes quantitative correlations among processing route, microstructure, nanoscale mechanical properties, and wear response. The proposed framework provides a physically meaningful method for identifying transitions between plowing- and microcutting-dominated deformation regimes and offers predictive capability for coating performance evaluation.
Controllable laser structuring of porous metallic materials demands a parameter-resolved understanding of morphology formation within complex fibrous geometries. In this work, nickel felts were structured using a 193 fs ultrashort-pulse laser at a wavelength of 1030 nm and a repetition rate of 100 kHz under air, argon, and water. Two dominant morphology regimes were identified, namely interference-driven LIPSS and ablation-dominated irregular nanostructuring, with a clear transition controlled by increasing line energy through higher fluence and lower scan speed. LIPSS were dominant at higher scan speeds and showed periodicities of about 600 to 800 nm, while decreasing scan speed promoted redeposition rich ablation morphologies and, in air, strong oxidation, and local fiber damage at high fluence. Within an optimized parameter window, the local fiber surface area was increased up to ninefold relative to the unprocessed reference area. Raman spectra of the laser-modified surfaces show bands of Ni-O compounds, which exhibit atmosphere- and fluence-dependent interactions. This manuscript demonstrates that ultrashort-pulse laser processing can be used for targeted interfacial design on porous nickel felts, extending laser nanostructuring concepts beyond well-studied planar metals to complex porous networks. The work links scan speed and fluence to the transition from LIPSS to ablation-dominated morphologies, quantifies local fiber surface-area enhancement up to 9× while preserving felt integrity, and correlates morphology with atmosphere-dependent NiOx development by Raman spectroscopy. By combining porous geometry, processing atmosphere (air, argon, water), surface-area metrics, and Raman chemistry, the study provides a state-of-the-art framework for scalable laser functionalization of porous metallic materials.
A primary issue in gas turbines is hot corrosion, resulting from the accumulation of combustion ash on high-temperature stainless steel surfaces. To address this issue, the present study investigates the impact of laser cladding on the hot corrosion resistance of Stellite 6 coatings deposited on 17-4PH stainless steel. The assessment involved exposing the samples to high-temperature corrosion at 900 °C for 50 h in a molten salt mixture of sodium sulfate and vanadium pentoxide (Na2SO4-60wt. Unlike previous studies that primarily focused on wear and cavitation resistance, we demonstrate that optimized laser cladding parameters produce a dense, defect-free coating with low dilution (7.96
To improve the robustness of thermal barrier coating testing, a laser rig thermal cycling facility is the focus of this study. The spatial and temporal stability of the laser heating enables to control both in-plane and through-thickness temperature gradients over the button-shaped specimens, by adjusting, respectively, the substrate air cooling and the laser focalization on the ceramic top surface. To this end, a temperature of 1200 °C at the surface of the ceramic is sought while the rear face is cooled in order to keep the substrate’s temperature close to 1000 °C. Such thermal loadings result in thermal gradients reaching about 70 °C/mm across the thickness of tested specimens and up to 40 °C/mm for in-plane thermal gradients in the case when high in-plane thermal gradients are sought. Besides, three interfacial pre-defects localized at the thermally grown oxide/top coat interface were processed by laser shock before laser thermal cycling, using the so-called LAser Shock Adhesion Test (LASAT) method. For large debonding, buckling is observed at the locus of artificial defects. To monitor thermal loading and damage evolution, nondestructive techniques were applied in situ, combining laser pyrometers, infrared thermography, and laser non-contact profilometers. The evolution of blisters, particularly the evolution of the height of the blister measured in situ for the first time, demonstrates a non-monotonic evolution of buckling in the course of thermal cycling, especially in the case of high in-plane thermal gradients. Furthermore, the steadiness of the laser heating source promotes earlier spallation events compared to previous burner rig tests. This clarifies the impact of heating rates and gradients on damage rates for a standard EB-PVD columnar structure of TBC. This article is the first to investigate a laser rig heating facility for thermal cycling of a typical TBC system in combination with the LAser Shock DAmage Monitoring (LASDAM) technique. LASDAM involves creating artificial interfacial defects with a laser shock and monitoring them in situ with infrared thermography and non-contact profilometers. The laser heating allows for variations of the in-plane temperature gradient with a high level of stability during heating as well as a through-thickness temperature gradient induced by air cooling of the substrate. Experimental results show that the impact of the through-thickness temperature gradient on interfacial damage in a typical electron beam physical vapor deposition (EB-PVD) TBC system is greater than that of the in-plane gradient. The enhancement of in situ analysis under severe thermal gradients could then be beneficial for a wide range of coating processes.
