Hot corrosion is one of the crucial failure modes of Ni-based superalloy components operating at high temperatures, which inevitably affects the subsequent mechanical properties of the alloys. In this research, damaged Inconel 718 alloy components with a pre-made trapezoid groove are repaired using laser additive manufacturing technique, and the change mechanisms of the microstructure and tensile properties of the repaired Inconel 718 alloy due to the hot corrosion in the salt mixture of 87.5 wt.% Na₂SO₄ + 5 wt.% NaCl + 7.5 wt.% NaNO₃ at 650 °C for different durations are investigated. The results show that oxidation and Cr-depletion occur on the repaired components due to the hot corrosion, and the corrosion products are mainly composed of Cr₂O₃, Fe₃O₄, and Ni₃S₂. The tensile strength and elongation of the as-repaired specimens are 736.6 MPa and 12.5%, respectively. After being hot corroded for 50 h, the tensile strength increases to 1022.9 MPa and elongation decreases to 1.7%. However, after being hot corroded for 150 h, both tensile strength and elongation of the repaired specimens drop to 955.8 MPa and 1.2%, respectively. The mechanical performance alteration is highly related to thermal effects instead of the molten salt attack.

The process parameters of laser remanufacturing technology have significant effects on the geometric characteristics of the single clad layer in the laser remanufacturing process. In this study, the effects of laser power, laser scanning velocity, and powder feeding rate on the geometry characteristics of a clad layer are investigated by depositing Inconel 718 powder on Inconel 718 alloy via coaxial laser cladding. Based on the experimental results, the mathematical models of geometry characteristics are created using the response surface methodology and checked by the analysis of variance. The verification results indicate that the predicted values coincide with the measured ones, which confirms the reliability effectiveness of the models derived from the regression analysis. Finally, the relationship between the main process parameters and geometric characteristics is studied. The modeling results show that laser power has a positive effect on all the geometry characteristics, while the powder feeding rate has a positive effect on the clad height and a negative impact on the width, depth, W/H (the ratio of clad width to height), and dilution rate of the clad layer. The scanning velocity has a positive effect on the W/H and dilution rate of the clad layer and a negative effect on the width, depth, and height of the clad layer.

Porous TiO2 ceramic coatings with high contents of Si and P were fabricated on a Ti6Al4V alloy using hybrid processing of laser surface melting (LSM) and microarc oxidation (MAO). The effect of LSM pretreatment on the growth behavior and mechanical properties of the MAO coating was studied. The results showed that the MAO coating on LSM pretreatment Ti6Al4V (LSM-MAO) had quite different surface morphologies, thickness, and compositions compared to the MAO coating on as-received titanium alloy. Grain refinement and dislocation in the LSM-treated Ti6Al4V alloy provided extra energy and more numbers of discharge channels during the MAO process. LSM–MAO coating exhibited a more uniform pore distribution, relatively small pores, and larger thickness compared to the MAO coating. The LSM-MAO coating had higher hardness and better wear resistance than the MAO coating. LSM is deduced to be an appropriate and efficient pretreatment method for achieving a high-quality MAO coating on titanium alloy.

As a widely used approach for surface modification, laser cladding plays a significant role in surface hardening and repairing of metallic parts. However, the defects existing in laser cladding parts, such as cracks, tensile residual stress, and pores, significantly affect the performance and the application of the cladding parts. In this study, an SS316L layer was fabricated on a 45 steel substrate using a laser cladding process assisted by three-dimensional vibration. The microstructures and the properties of the coating and the bonding interface with various vibration parameters were analyzed and compared. The microstructures of the cladding layer and the matrix were analyzed by an optical microscope and a scanning electron microscope. The results show that the three-dimensional vibration is able to refine the columnar dendrites in the cladding layer. The oscillation accelerates both the liquid flow and the thermal transfer of the molten pool, which not only reduces the temperature gradient but also increases the solidification growth rate. Meanwhile, the porosity and the maximum pore size in the cladding layer were significantly reduced by the vibration. The average microhardness of the cladding layer significantly increased assisted by the three-dimensional vibration. Experimental results demonstrate that the effects of the three-dimensional vibration are more significant than the single vertical vibration. The proposed approach provides a potential way to improve laser additive manufacturing and remanufacturing.

The supersonic laser deposition (SLD) of diamond/Cu composite powder is studied over a range of laser power. The deposition efficiency, coating microstructure, cohesive/adhesive bonding, phase composition, micro-hardness, and tribological property of the diamond/Cu composite coating are investigated. The results indicate that, as laser power is increased, deposition efficiency initially increases and then declines. The diamond particles distribute uniformly in the composite coating. Due to the increase of velocity ratio and total energy by laser irradiation, the cohesive/adhesive bonding of the composite coating is improved. The composite coating can preserve the phase composition of the origin powders due to the relatively low heat input during the SLD process. Slight oxidation of the Cu powder can be detected in the coatings prepared with high laser power, which has adverse effects on material deposition. The SLD-diamond/Cu composite coating has superior wear-resistance because of low friction coefficient, high micro-hardness, and uniformly distributed diamond particles.

Laser cladding is a promising surface modification technology to fabricate high-performance parts. However, defects such as porosity, cracks and residual tensile stress are easily produced in laser cladding, leading to significant property reduction and poor reliability. In this study, laser cladding with multidimensional high-frequency vibration was investigated. The effects of multidimensional high-frequency vibration on the improvement of microstructure and mechanical properties were analyzed and discussed based on the vibration-assisted laser cladding experiments. In addition, a numerical model was conducted to help understand the significance of the vibration on flow field and temperature field. Results show that 3D vibration led to the primary dendrite spacing reduction from 11.1 to 6.8 μm, microhardness increase from 199 to 221 HV_0.2, and a nearly 110% improvement in the elongations. The findings of this study confirmed the significant benefits of multidimensional high-frequency vibration applied in laser cladding and provided a basis to uncover the underlying mechanisms of multidimensional vibration on the rapid melting and solidification.