Special Issue: “Effects of Laser Treatment on Surface Characterization and Mechanical Properties of Alloys”

Laser-based material processing methods have emerged as an innovative approach in advanced manufacturing, enabling significant control over microstructural evolution and surface functionality in metallic systems. Modern industrial sectors, such as the aerospace, automotive, biomedical, energy, and marine sectors, require materials that possess superior bulk properties and exhibit engineered surface characteristics tailored to specific performance criteria, such as wear resistance, corrosion protection, thermal stability, or biocompatibility. This Special Issue brings together a diverse and comprehensive selection of recent advancements that reflect the potential of laser technologies across different classes of alloys, coating strategies, and hybrid processing techniques. A total of fifteen articles featured in this Special Issue collectively showcase the strategic deployment of laser in a variety of contexts: laser cladding, laser welding, laser surface texturing, laser milling, and hybrid treatments incorporating ultrasonic vibrations, magnetic fields, or micro-arc oxidation. A key unifying theme across these contributions is the emphasis on process–structure–property relationships, and how specific processing parameters (e.g., laser power, scan strategy, pulse duration, or beam oscillation) directly influence solidification dynamics, microstructural morphology, and, ultimately, mechanical or tribological behavior.

Laser cladding, in particular, remains a focal point of interest due to its capabilities in repairing high-value components and fabricating wear- and corrosion-resistant coatings. The research contributions demonstrate the microstructure modification and mechanical property enhancement of alloy systems, such as ceramic phase-reinforced high-entropy alloy [1], high-hardness Fe-based alloy coatings [2], and Inconel superalloys [3]. The introduction of hard ceramic phases during cladding has shown considerable promise in improving hardness, toughness, and service life under extreme conditions [1]. Incorporating alloying elements (B, Si, Mo, Nb, V, Mn, Cr) can introduce dislocation strengthening, grain refinement strengthening, and solid solution strengthening in Fe alloys, resulting in enhanced hardness [2]. The addition of ceramic and rare-earth oxide particles, and the in-situ synthesis of ceramic particles, can also enhance hardness and mitigate crack formation. Steady-state magnetic fields applied during laser cladding of Inconel 625 can stabilize the crystal structure and refine the grains [3]. The introduction of a low-intensity magnetic field significantly improves the uniformity, surface hardness, tribological performance, and corrosion resistance of the clad layer. Assistance from several other physical fields, such as ultrasonics and thermals, can control porosity and crack formation within the clad layer [2]. Complementing the experimental works, a simulation-driven study explores the solidification dynamics in 316L stainless steel during laser cladding [4]. The melt pool characteristics were simulated by numerical calculation, and the phase field model predicted dendrite formation. This work elucidates the formation of dendritic morphologies and highlights the dominant influence of convective flow within the melt pool, pointing to the importance of precise control over processing parameters in achieving desirable microstructural outcomes. Numerical simulations revealed that ultrasonic acoustic streaming significantly influences dendritic structure formation during the laser cladding process [5]. This multi-scale simulation highlights how ultrasound-assisted flow fields influence dendrite tilt, solute redistribution, and solidification uniformity, leading to defect suppression and structural refinement.

Several studies examine the interplay between laser parameters, scanning strategies, and alloy compositions in shaping the mechanical response of treated surfaces using selective laser melting (SLM) [6,7] and laser material deposition (LMD) [8]. Different laser scanning strategies for SLM-printed K438 superalloys affect crack suppression and mechanical strength [6]. Experimental results demonstrate that strategic scanning paths and post-heat treatment protocols can markedly improve tensile strength and minimize residual stresses, factors vital for high-temperature aerospace applications. The wear performance and morphology of SLM-printed AlSi10Mg can be significantly influenced by exposure to different flames, such as carburizing, oxidizing, and neutral [7]. A broader perspective of macroscopic and microstructural behavior is explained for laser material deposition for thin-wall structures. It emphasizes how process parameters like z-increment and deposition height affect grain growth directionality, hardness profiles, and residual stress distribution, factors crucial to the stability of additively manufactured metallic structures [8]. A key highlight of the issue is the application of advanced simulation tools to gain mechanistic insights into microstructural evolution during laser–material interaction. A phase-field model is developed to simulate dendrite remelting under thermal loads, which provides fundamental insight into how temperature-induced remelting sequences govern solid–liquid interface dynamics [9]. This study highlights how lateral dendrites remelt ahead of primary arms, and how remelting evolves in multiple stages, particularly under inhomogeneous heating, an important factor in layered manufacturing and laser repair operations.

Laser hybrid processes also feature prominently in this issue. The impact of hybrid laser-arc welding on the microstructure and toughness of TC4 titanium alloy joints is discussed in the context of the integration of mechanical enhancements with structural integrity, noting improved impact resistance due to acicular martensite refinement and grain boundary modifications [10]. Their multi-layer, multi-pass welding approach highlights the trade-offs between porosity control, grain refinement, and crack resistance, key concerns for components exposed to cyclic mechanical and thermal loads. The pattern of laser scanning plays a crucial role in shaping the weld pool dynamics, refining the microstructure, and enhancing the mechanical behavior of AA2060 Al-Li alloy joints during oscillating laser beam welding [11].

Improving surface adhesion and corrosion resistance is also addressed through combined laser texturing and ceramic coating by micro-arc oxidation for aluminum alloy [12]. The hybrid laser surface treatment led to a 58% enhancement in adhesive joint strength and shifted the failure mode to cohesive fracture. Laser ablation, performed in a liquid-phase environment, was found to systematically modify the surface morphology of YG8 cemented carbide, with pit shape and taper evolving consistently with increasing ablation cycles [13]. This study shows that the number of ablation cycles governs the transition from convex to cratered morphologies, offering precise control over texture formation for tribo-functional coatings. Another promising direction shown in this issue is the use of laser-induced surface modification to improve tribological performance. The effect of nanosecond-pulsed laser milling on Al₂O₃ ceramics is explored, revealing a strong dependence of surface roughness and milling depth on laser power and scanning frequency [14]. These findings open avenues for tailoring ceramic surfaces for wear-critical applications. Lastly, an improved Archard wear model is developed, incorporating frictional heating effects [15]. The model achieved improved wear prediction accuracy across multiple metallic systems, including stainless steel, aluminum alloys, and titanium. The model better captured wear dynamics under varying loads and sliding velocities, contributing to a better predictive tool for tribological analysis.

This Special Issue showcases a vibrant landscape of research at the intersection of laser–material interaction, alloy design, and mechanical performance. These studies collectively highlight how precise control of laser parameters, supported by robust modeling and experimental validation, can dramatically enhance the functionality of metallic systems across aerospace, automotive, biomedical, and energy sectors.