Wenxing Wu

IN738LC is a γ′-strengthened superalloy for hot-section components up to 900 °C, but its high Al + Ti content makes it susceptible to cracking during laser-directed energy deposition (LDED). Adding IN718 suppresses cracking but degrades the intrinsic γ′ fraction and the calculated high-temperature strength. A multi-constraint screening framework bounded the admissible composition, and experiments identified the lowest effective addition among the tested compositions: the γ′-solvus criterion allowed up to about 12 wt%, whereas the Fe ≤ 0.5 wt% criterion limited standard-compliant additions to about 2 wt%. Because the IN738LC + 2% deposit still cracked, IN738LC + 3% was selected (nominal Fe 0.65 wt%) together with 5 wt%. Cracks in the as-built IN738LC are associated with γ/γ′ eutectic liquid films; none were detected in the inspected regions of the IN738LC + 3% and IN738LC + 5% deposits. IN738LC + 3% showed the highest room-temperature ultimate tensile strength (UTS; 1467 MPa) with 13.8% elongation, versus 1240 MPa and 3.9% for the cracked IN738LC, and the best 900 °C properties (632 MPa, 8.0%); the room-temperature gain contains an inseparable crack-elimination contribution, isolated by comparing the two deposits in which no macroscopic cracks were detected. The framework provides quantitative bounds and trend indicators for crack-susceptible alloy design in the IN738LC–IN718–LDED system.

The corrosion problem of Mg alloy limits its application in many engineering fields. Plasma electrolytic oxidation (PEO) is an economical and eco-friendly technology that can create a dense oxide layer on Mg alloy, offering a solution to the corrosion issue. This research summarizes the use of PEO technology in developing corrosion-resistant coatings for Mg alloys and examines the growth mode and corrosion process of PEO coatings. It is concluded that current efforts to enhance the corrosion resistance of PEO coatings on Mg alloys can be categorized into two approaches: improving the internal structure of the coating and enhancing the phase composition. This includes optimizing coating thickness, roughness, and density; repairing micropores and cracks; and introducing corrosion-resistant compounds by doping. Micropores and cracks are identified as vulnerable points for corrosion, and sealing is an effective strategy to address this. By modifying the phase composition of the coating, corrosion occurrence can be minimized, significantly boosting the corrosion resistance of Mg alloys. Finally, future challenges and potential advancements in corrosion-resistant PEO coatings for Mg alloys are discussed.

Titanium alloys are considered lightweight alloys and are widely applied across various industries. However, their low hardness, poor wear resistance, and limited oxidation resistance restrict their prospects for wider application. In this paper, nitride coatings were prepared using three preparation processes, namely laser surface nitriding (LSN), physical vapor deposition (PVD), and plasma ion implantation (PII). Their microstructure, microhardness, tribological behavior, and high-temperature oxidation characteristics were compared. The experimental results revealed that nitrided coatings were successfully prepared using the three methods. However, a comparison of these data shows that the LSN coating exhibited superior comprehensive performance. It achieved the maximum thickness within the shortest preparation time: the thickness was about 280 μm and the deposition rate of the LSN method was 2250 and 90,000 times higher than those of the PVD and PII methods. Nitrides have high hardness, but the carrying capacity could be attributed to the thickness of the coatings: the PVD coating could withstand a force of 500 g, while the PII coating only withstood a force of less than 25 g. In addition, as hardness is the most important factor for excellent wear resistance, the average volumetric wear rate of the LSN and PVD coatings was about 9 × 10⁻⁶ mm³/m·N, and their relative wear resistance was 49.2 times that of Ti6Al4V. Meanwhile, the excellent bond between the LSN coating and the substrate was evidenced by a high-temperature oxidation test during a rapid heating–cooling cycle.

In order to minimize the gaps between the direct laser deposition channels and improve the quality and performance of the formed parts, the process of direct laser deposition is utilized in laser additive manufacturing to create sequential, single- and double-channel deposition layers on 304 stainless steel plates. Under the premise of keeping the layer rate and defocusing amount unchanged, this study investigates the effects of laser power, scanning speed, and powder feeding rate on the morphology and inclusions of single- and double-channel deposited layers. The aim is to determine the optimal process parameter values for direct laser deposition of single-layer, single-channel Inconel 738. The effects of the three process parameters on the response values were investigated using a multi-factor, multi-level experimental design. The evaluation indexes for the analysis included the deposited layer wetting angle and aspect ratio. The analysis involved one-way extreme analysis and ANOVA analysis. The optimal process parameters are a laser power of 550~750 W, a scanning speed of 7~13 mm/s, and the powder feeding rate was 2.1~4.33 g/min. At the same time, the relationship between surface tension and gravity was integrated with the spherical coronal model and Young’s equation to develop a mathematical model of the direct laser deposition process at a theoretical level. The mathematical model of the direct laser deposition process was utilized to analyze the correlation between the geometric parameters of the cross-section of the deposited layer. This analysis provides a valuable data reference for future Inconel 738 direct laser deposition.

IN 625 is one of the most widely used nickel-based high-temperature alloys. However, the unstable high-temperature mechanical properties of IN625 and the difficulty of processing complex parts have limited its wider application. This work fabricated IN625 coatings with Co/TiAl (1.25, 1.55, and 1.85) on 304SS using laser melting deposition technology, with excellent high-temperature mechanical properties. The effects of Co/TiAl on the microstructure and properties of the laser-cladded resulting coatings have been carefully investigated. Compared to the IN625 coating, the addition of Co, Ti, and Al to the IN625 laser cladding coating significantly enhances its hardness and strength at room temperature, while reducing the elongation rate sharply. After heat treatment (900 °C × 10 h + 850 °C × 2 h), the hardness of the IN625 coating decreases, while the hardness of the IN625 laser cladding coating with added Co, Ti, and Al significantly increases. At a temperature of 850 °C, the yield strength and elongation rate of the IN625 laser cladding coating with Co, Ti, and Al additives exhibit an increasing-then-decreasing trend as the Co/TiAl ratio rises. The results exhibited that the coating had excellent high-temperature mechanical properties when the Co/TiAl is 1.55, and its hardness, tensile strength, yield strength, and elongation rate are 48.62 HRC, 735 Map, 665 MPa, and 11.3%, respectively.

The effects of laser parameters on the microstructure and properties of plasma-sprayed yttrium oxide coating on the graphite matrix were investigated. Tensile strength, porosity, roughness, and scratch meter tests were carried out to evaluate the critical load and mechanical properties of the coating after spraying and laser micro-melting. When the porosity and surface roughness of the coating are minimum, the critical load of the coating is 7.85 N higher than that of the spraying surface. After laser micromelting, the crystal phase of Y₂O₃ coating surface does not change, the crystallinity is improved, and fine grain strengthening occurs. When the laser power density is 75 W/mm², the scanning speed is 30 mm/s, and the defocusing distance is 40 mm, the film base bonding performance and wear resistance of the material reach the maximum value. The failure of Y₂O₃ coating is mainly due to the degradation of mechanical properties such as film base bonding strength, surface porosity, and surface roughness, which leads to the local collapse of the material. The coating after laser micro-melting only presents particle disintegration at the end of the scratch area.