The surface of 17-4PH martensitic stainless steel was laser-cladded with Ni60 and Ni60+nano-WC composites and a comprehensive investigation was conducted of the microstructure and wear mechanism. The findings demonstrate that despite the added nano-WC particles being fused and dissolved during laser cladding, they still lead to a reduction in grain size and a decrease in crystallographic orientation strength. Furthermore, the dissolution of nano-WC makes the lamellar M₂₃C₆ carbides transform into a rod or block morphology, and leads to the CrB borides becoming finer and more evenly dispersed. This microstructural evolution resulted in a uniform increase in hardness and wear resistance, effectively preventing crack formation. When the nano-WC addition increased to 20 wt.%, there was a 27.12% increase in microhardness and an 85.19% decrease in volume wear rate compared to that of the pure Ni60 coating. Through analysis of the microstructure and topography of wear traces, it can be inferred that as the nano-WC addition increased from 0 wt.% up to 20 wt.%, there was a gradual transition from two-body abrasive wear to three-body abrasive wear, ultimately resulting in adherent wear.

The excess heat generated during the laser additive manufacturing process is prone to cause coating defects; a water-cooled substrate can effectively remove the excess heat and improve the hardness of the coating. In this study, the effects of water-cooled substrate on the microstructure and hardness of laser additive manufactured nickel-based coatings were investigated by experimental and numerical simulations. The results showed that the water-cooled substrate decreased the size of columnar crystals and increased the number as well as the length of secondary dendrite crystals at the bottom of the nickel-based coatings. There was also a noticeable increase in the size of equiaxed grains and the quantity of the solid solution in the middle of the coatings. The hardness value of the coating increased at the water velocity of 200 mL/s and 500 mL/s and finally decreased at 700 mL/s. A finite element model was established by ABAQUS software to numerically simulate the temperature field of the laser additive manufactured nickel-based coating with the water-cooled substrate. The results revealed significant differences in the temperature distribution of the coatings with different velocities. As the water velocity increased, the peak temperature at the center of the coating’s molten pool gradually decreased. In addition, the cooling rate of the specimens increased with the application of the water cooling, leading to a more concentrated temperature distribution near the laser heat source.

Laser-directed energy deposition (DED) offers significant potential for the additive manufacturing of thin-walled Inconel 718 aerospace components. However, the structural defects readily formed during deposition, along with the extensive precipitation of long-chain Laves phases between coarse dendrites, can severely compromise the mechanical properties of as-fabricated Inconel 718 parts. To address this, an ultrasonic-assisted DED (UDED) method was employed to reduce the deposited structural defects and refine crystalline structures, and the influences of ultrasonic energy fields on the microstructure and mechanical properties of thin-walled Inconel 718 samples were systematically investigated. The results demonstrated that ultrasonic vibration significantly enhances the microstructural quality by reducing porosity and pore size, weakening texture intensity, fragmenting long-chain Laves phases, mitigating severe elemental segregation, and refining matrix grains. Consequently, the UDED thin-walled Inconel 718 sample exhibited an approximately 15% increase in microhardness compared to the conventional DED counterpart, alongside satisfactory strength and ductility. This study highlights the superiority of UDED for microstructure tailoring and its potential for mechanical property regulations in thin-walled Inconel 718 aerospace components.

A FeCrMoNiCuBSiC metallic glass coating was designed and then deposited by the high-velocity oxygen fuel (HVOF) spraying technique. X-ray diffraction, a scanning electron microscope, and a microhardness tester were applied to characterize the phase, microstructure, and mechanical properties of the coating. The amorphous phase was the main phase in the coating, and crystal phases were almost undetectable in the XRD results. The coating had a dense structure (the porosity was 1.47 ± 0.32%) and high Vickers microhardness (848 ± 22 HV_0.3). The wear behavior of the coatings sliding against WC-Co was studied with a pin-on-disc wear test system and was compared with that of 316L stainless steel. The coating improved the wear resistance of the steel by around 7–9 times at different sliding speeds. As the sliding speed was increased, the wear loss rate of the steel obviously increased, yet the loss rate of the coating decreased first and then increased. This happened because the contact flash temperature induced by friction increases with the sliding speed, which results in oxidative behavior and crystallization events in the coating. The dominating wear mechanism of the coating is fatigue wear combined with oxidative wear.

Ultrasonic-assisted laser-directed energy deposition (UA-DED) is a promising combined technology for manufacturing high-value thin-walled Inconel 718 components in aerospace. Nevertheless, the optimal ultrasonic frequency—a key parameter for achieving desirable performance in thin-walled Inconel 718 alloys—remains to be determined. In this study, we systematically investigated the influence of ultrasonic frequency (12–20 kHz) on the microstructure and mechanical properties of thin-walled Inconel 718 fabricated by UA-DED. The results revealed that an ultrasonic frequency of 20 kHz was optimal and can yield significant improvements in the microstructures of the as-deposited sample coordinate planes, manifested by the complete suppression of large pores, three-dimensional refinement of the γ matrix grains, alleviation of Nb and Mo segregation, the reduction of fragmented Laves particles, a decrease in residual macroscopic stresses, and homogeneous distributions of γ′/γ″ phases and γ-grain orientation. Meanwhile, the application of a 20 kHz ultrasonic frequency endows the manufactured thin-walled 718 parts with superior mechanical properties, including a tensile strength of 899 MPa in the laser scanning direction and 877 MPa in the build direction, along with the corresponding elongations of 34.8% and 38.9%. This work demonstrates the potential of modulating ultrasonic frequency to tailor microstructures and produce high-performance thin-walled Inconel 718 aerospace components.

In this work, a Fe-based amorphous coating (Fe₄₄Cr₁₈Mo₇Ni₄Cu₂B₂₀Si₃C₂) was fabricated via high-velocity oxygen fuel (HVOF) spraying, and the effect of annealing temperature on its microstructure, phase composition, and corrosion resistance in 3.5 wt.% NaCl solution was investigated. The as-sprayed (AS) coating exhibits an amorphous content of 85.71% and a porosity of 1.37%. Annealing at 540 °C (H540) reduces porosity to 0.98% without significant crystallization, whereas annealing at 640 °C (H640) and 740 °C (H740) triggers extensive crystallization (amorphous content drops to 24.18% and 19.20%), and porosity increases to 1.82% and 2.17%. Electrochemical tests show that corrosion resistance deteriorates progressively with increasing temperature. i_corr increases from 3.56 μA/cm² (AS) to 50.0 μA/cm² (H740), while R_p decreases from 8472 to 669 Ω·cm². EIS reveals that the AS coating is dominated by the inner barrier layer (R_b >> R_t), whereas annealing causes a drastic collapse of R_b (from 8.374 × 10⁴ to 5.011 Ω·cm²). This degradation is attributed to crystallization-induced grain boundaries and reduced effective Cr content, which impair passive film integrity and accelerate corrosion.