Search Results (347)

This study presents a systematic investigation of laser surface hardening of 9CrSi tool steel with the aim of establishing the relationships between processing parameters, microstructural evolution, and resulting mechanical and tribological properties under the applied laser conditions. The influence of laser power, modulation frequency, and scanning speed on the hardened layer depth, microstructure, and surface properties was analyzed. Laser treatment produced a martensitic surface layer with varying fractions of retained austenite, while the transition zone consisted of martensite, granular pearlite, and carbide particles. X-ray diffraction identified the presence of α′-Fe, γ-Fe, and Fe₃C phases, with peak broadening associated with increased lattice microstrain induced by rapid self-quenching. The surface microhardness increased from approximately 220 HV_0.1 in the untreated state to 950–1000 HV_0.1 after laser hardening, with hardened layer thicknesses ranging from about 500 to 750 µm depending on the processing regime. Instrumented indentation showed higher elastic modulus values for all hardened conditions. Tribological tests under dry sliding conditions revealed reduced coefficients of friction and more than an order-of-magnitude decrease in wear rate compared with untreated steel. The results provide a parameter–microstructure–performance map for laser-hardened 9CrSi steel, demonstrating how variations in laser processing conditions affect hardened layer characteristics and functional performance. Full article

Early-age shrinkage in 3D-printed concrete constitutes a critical applied challenge due to the rapid development of deformations and the absence of conventional reinforcement systems. From a scientific standpoint, a clear knowledge gap exists in materials science concerning the reliable quantification of very small, rapidly evolving strains in fresh and early-age cementitious materials produced by additive manufacturing. This study investigates practical and low-cost alternatives to commercial optical systems for monitoring early-age shrinkage in 3D-printed concrete, a key challenge given the rapid deformation of printed elements and their typical lack of reinforcement. The work focuses on identifying both the most precise method for capturing minor, fast-developing strains and affordable tools suitable for laboratories without access to advanced equipment. Three mixtures with different aggregate types were examined to broaden the applicability of the findings and to evaluate how aggregate selection affects fresh properties, hardened performance, and shrinkage behavior. Shrinkage measurements were carried out using a commercial digital image correlation system, which served as the reference method, along with simplified optical setups based on a smartphone camera and a GoPro device. Additional measurements were performed with laser displacement sensors and Linear Variable Differential Transformer LVDT transducers mounted in a dedicated fixture. Results were compared with the standardized linear shrinkage test to assess precision, stability, and the influence of curing conditions. The findings show that early-age shrinkage must be monitored immediately after printing and under controlled environmental conditions. When the results obtained after 12 h of measurement were compared with the values recorded using the commercial reference system, differences of 19%, 13%, 16%, and 14% were observed for the smartphone-based method, the GoPro system, the laser sensors, and the LVDT transducers, respectively. Full article

This study provides a comparative and material-specific assessment of how laser cutting parameters affect the surface integrity of three commonly used engineering alloys, thereby extending the current knowledge beyond single-material analyses. The main objective was to quantify and relate changes in surface roughness, microhardness, and microstructure to variations in laser cutting conditions for S355J2 steel, AISI 304 steel, and AlMg₃ aluminum alloy. Variable cutting parameters were applied, including cutting speed, assist gas type and pressure, as well as laser beam power, and their combined effect on the thickness of the remelted and heat-affected zones was evaluated. The results show clear material-dependent trends: S355J2 steel exhibited the lowest surface roughness but the most pronounced surface hardening, with maximum microhardness values reaching approximately 700 HV 0.1 in a relatively narrow heat-affected zone, whereas AISI 304 showed a distinct edge-hardening effect with more moderate roughness. In contrast, the AlMg₃ alloy developed a clearly visible remelted layer and a refined, fine-grained microstructure, accompanied by much lower hardness levels but a more diffuse heat-affected zone. These findings provide original, comparative guidelines for selecting laser cutting parameters tailored to specific materials, enabling the optimization of edge quality and surface properties in industrial applications. Full article

The adjustable-ring-mode (ARM) scanning laser was used to perform butt welding on 0.5 mm thick TA1 titanium alloy and 304 stainless steel (SS304) thin sheets, with 1.2 mm diameter AZ61S magnesium alloy welding wire as the filling material. Microhardness test results show that the hardness distribution presented a trend of being higher in the base metals on both sides and lower in the middle filling area, with no hardening observed in the weld zone. For all specimens subjected to horizontal and axial weld bending tests, the bending angle reached 108° without any cracks occurring. When the ring power was in the range of 800–1000 W, or the scanning frequency was between 100 and 200 Hz, all the average tensile strengths of the welded joints were more than 80% of that of the AZ61S filling material (approximately 240 MPa); the maximum average tensile strength stood at 281.2 MPa, which is equivalent to 93.7% of the AZ61S. As the ring power or scanning frequency increased further, the tensile strengths of the joints showed a decreasing trend. The remelting effect of the trailing edge of the ARM laser under high energy conditions, or the scouring of the turbulent molten flow induced by the scanning beam, damages the weak links at the newly formed solid–liquid interface and increases the Fe concentration in the molten pool. This leads to a thicker FeAl interface layer during growth, thereby resulting in a decline in the mechanical properties of the welded joints. Full article

Nickel superalloy Inconel 718 (IN718) is widely employed in harsh environments with prolonged cyclic stresses in the aerospace and energy sectors, due to its corrosion/oxidation resistance and mechanical strength obtained by precipitation hardening. This work investigates the mechanical behavior in fatigue of IN718 manufactured by Additive Manufacturing (AM), specifically by Laser Powder Bed Fusion (PBF-LB), and compares its results with the material produced by forging and rolling. Samples from both processes were subjected to heat treatments of solution and double aging to increase their mechanical strength. Then, tensile, microhardness, microstructural characterization, and uniaxial fatigue tests were performed (with loading ratio R = −1). The results showed that, although the IN718 produced by AM had higher microhardness and a higher tensile strength limit than the forged and rolled material, its fatigue performance was lower. The S–N curve (stress vs. number of cycles) for the material obtained by PBF-LB demonstrated shorter fatigue life, especially under low and medium stresses. The analysis of the fracture surfaces revealed differences in the regions where the crack initiated and propagated. The shorter fatigue life of the material obtained by PBF-LB was attributed to typical process defects and microstructural differences, such as the shape of the grains, which act as points of crack nucleation. Full article

This article presents the effect of laser alloying with boron on the surface layer of iron alloys: steel and grey cast iron. The general goal of this review is to specify the main differences that can be expected after this treatment of selected iron-based alloys. Boron as an alloying element is first characterized. The effects of laser alloying are described in comparison to diffusion processing. The next section describes the effect of laser alloying with boron on the microstructure, hardness, and wear resistance of the surface layer of selected iron alloys. As a result of the conducted analysis, the most significant differences in the outcomes of laser alloying with boron, which may occur during the processing of various iron alloys, are as follows: the presence of graphite in the surface layer in the case of grey cast iron treatment and a clearly visible transition zone between the alloyed zone and the hardened zone during the treatment of grey cast iron as opposed to steel; variable depths of the modified surface layer and varied grain size in the alloy zone depending on the thermophysical properties of the material being treated. Full article

Aluminum alloys require improved surface performance to satisfy the demands of today’s aerospace, automotive, marine, and structural applications. This paper compares three key surface hardening methods: diffusion-assisted microalloying, thermomechanical deformation-based treatments, and composite/hybrid reinforcing procedures. Diffusion-assisted Zn/Mg enrichment allows for localized precipitation hardening but is limited by the native Al₂O₃ barrier, slow solute mobility, alloy-dependent solubility, and shallow hardened depths. In contrast, thermomechanical techniques such as shot peening, surface mechanical attrition treatment (SMAT), and laser shock peening produce ultrafine/nanocrystalline layers, high dislocation densities, and deep compressive residual stresses, allowing for predictable increases in hardness, fatigue resistance, and corrosion performance. Composite and hybrid reinforcement systems, such as SiC, B₄C, graphene, and graphite-based aluminum matrix composites (AMCs), use load transfer, Orowan looping, interfacial strengthening, and solid lubrication effects to enhance wear resistance and through-thickness strengthening. Comparative evaluations show that, while diffusion-assisted procedures are still labor-intensive and solute-sensitive, thermomechanical treatments are more industrially established and scalable. Composite and hybrid systems provide the best tribological and load-bearing performance but necessitate more sophisticated processing approaches. Recent corrosion studies show that interfacial chemistry, precipitate distribution, and galvanic coupling all have a significant impact on pitting and stress corrosion cracking (SCC). These findings highlight the importance of treating corrosion as a fundamental design variable in all surface hardening techniques. This work uses unified tables and drawings to provide a thorough examination of strengthening mechanisms, corrosion and fatigue behavior, hardening depth, alloy suitability, and industrial feasibility. Future research focuses on overcoming diffusion barriers, establishing next-generation gradient topologies and hybrid processing approaches, improving strength ductility corrosion trade-offs, and utilizing machine-learning-guided alloy design. This research presents the first comprehensive framework for selecting multifunctional aluminum surfaces in demanding aerospace, automotive, and marine applications by seeing composite reinforcements as supplements rather than strict alternatives to diffusion-assisted and thermomechanical approaches. Full article

In manufacturing processes, both material processing methods and the resulting microstructure play a fundamental role in determining material behavior during component fabrication and subsequent service conditions. Materials produced by additive manufacturing exhibit a unique microstructure due to the rapid heating and solidification cycles inherent to the process, distinguishing them from conventionally cast counterparts and leading to differences in mechanical and functional properties. This article presents problems related to the longitudinal turning of Ti6Al4V titanium alloy elements produced by the casting and powder laser sintering (DMLS) methods. The authors made an attempt to establish a procedure for determining the optimal parameters of finishing cutting while minimizing the specific cutting force, taking into account the criterion of machined surface quality. In the course of the experiments, the influence of the cutting data on the cutting force values, surface roughness parameters, and chip shape was examined. The material hardening state during machining and the variability of the specific cutting force as a function of the cross-sectional shape of the cutting layer were also tested. The authors presented a practical application of the proposed optimization algorithm. It was found that by changing the shape of the cross-section of the cutting layer, it was possible to carry out the turning process with significantly reduced specific cutting force (from 2300 N/mm² to 1950 N/mm²) without deteriorating the surface roughness. Full article

Laser additive manufacturing shows great promise for repairing high-value carburized gears, but the underlying relationships among thermal history, microstructure, and properties remain insufficiently quantified. This study uniquely integrates finite-element modeling with microstructural mapping to decipher thermo-mechanical coupling during gear repair. A thermal simulation model that combines a double-ellipsoidal heat source with phase-transformation kinetics achieves 91.1% accuracy in predicting melt pool depth and hardened-layer depth. The cladding process induces a substantial increase in subsurface hardness, primarily due to phase-transformation-induced refinement and regeneration of martensite during rapid thermal cycling. This results in a peak hardness of 64 HRC and a tensile strength of 2856 MPa in the secondary-hardened layer, both exceeding those of the original carburized substrate. The presence of beneficial compressive residual stresses further improves fatigue resistance. Spatial gradients in elastic modulus, strength, and hardness, measured by flat indentation and microhardness testing, are quantitatively correlated with simulated peak temperatures and predicted phase distributions. These correlations establish a causal link from the thermal history to phase transformations, microstructural evolution, and the resulting local hardness and strength. These findings provide a mechanistic foundation for precision repair and service-life prediction of high-carbon gear steels using laser additive manufacturing. Full article

Maraging steels encounter tremendous aerospace applications, such as in landing gears, rocket motor casing, pressure vessels, satellite launch vehicles, etc. Laser welding is considered one of the most effective manufacturing processes due to its minimal instances of wider heat-affected zones (HAZs), precipitate accumulation, and other benefits. However, it should also be noted that their severe effect is still evident in terms of the tensile strength and fatigue strength of laser-welded maraging steel. This paper provides a critical review of the evolution of microstructural features and mechanical properties of laser-welded maraging steel, including corresponding factors in terms of microstructures and the formation of reverted austenite, as well as precipitation hardening from various studies on maraging steels. We examined the influence of precipitation, reverted austenite, welding, and post-weld heat treatment on mechanical properties like hardness, tensile strength, yield strength, elongation, and fatigue strength of laser-welded maraging steel. It is worth mentioning that the laser welding process is generally insufficient for welding sheets with a thickness over 10 mm or those requiring multi-pass welding. The reheating process becomes unfavorable for maraging steel in the multi-pass welding process since it may induce localized heat treatment. Although hybrid welding may resolve an arising thickness issue, the reversion of austenite and complexity are still difficult to overcome due to the dual nature of welding processes, resulting from the use of both arc and laser. Furthermore, maraging steel produced via additive manufacturing tends to avoid austenite reversion with effective heat treatment prior to any welding process. Post-weld heat treatment and cryogenic treatment have been found to be favorable for desired reverted austenite formation. Finally, the proposed constructive framework specifically applies to the welding process of maraging steel, particularly for aerospace applications. Full article

Alloy gradient-grained structures (represented by copper as a typical single-phase face-centered cubic (FCC) metal), known for their superior mechanical properties such as enhanced strength, ductility, and fatigue resistance, have become increasingly important in aerospace and automotive industries. These alloys are often fabricated using advanced processing techniques such as laser welding, electron beam melting, and controlled cooling, which induce spatial gradients in grain size and optimize material properties by overcoming the traditional strength–ductility trade-off. In this study, a deep learning-based inversion framework combining Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) networks is proposed to efficiently predict key constitutive parameters, such as the initial critical resolved shear stress and hardening modulus, in alloy gradient-grained structures. The model integrates spatial features extracted from strain-field sequences and grain morphology images with temporal features from loading sequences, providing a comprehensive solution for path-dependent mechanical behavior modeling. Trained on high-fidelity Crystal Plasticity Finite Element Method (CPFEM) simulation data, the proposed framework demonstrates high prediction accuracy for the constitutive parameters. The model achieves an error margin of less than 5%. This work highlights the potential of deep learning techniques for the efficient and physically consistent identification of constitutive parameters in alloy gradient-grained structures, offering valuable insights for alloy design and optimization. Full article

We report on the effect of hot isostatic pressing combined with solution and ageing treatment in different sequences on the mechanical properties of Inconel 718 specimens, which in turn have been fabricated by a hybrid additive manufacturing approach. The latter combines conventional laser powder bed fusion and in-situ high speed milling, yielding superior surface quality as being quantified by $R_{\mathrm{a}}$ about 1 μm. In a comparative study between hybrid additively manufactured parts and those built without milling, we find that, in general, any combination of heat treatment leads to a higher ultimate tensile strength and an improved endurance limit, while, however, hot isostatic pressing affects these figures of merit most. In addition, metallographic analysis reveals increased density and hardness for hot isostatic pressed parts due to precipitation hardening. These improvements of the mechanical properties are found to be even more pronounced when the printed parts are manufactured by the hybrid additive approach, i.e., for parts with improved surface conditions. Full article

The aim of this work is to investigate the effect of annealing (at temperatures ranging from 260 °C to 530 °C) of thin-walled Al-Mn-Mg-Ti-Zr samples manufactured by selective laser melting (SLM) on their tensile mechanical properties, hardness, and surface roughness. The results of this study may contribute to the development of post-processing modes for thin-walled products made of corrosion-resistant aluminum alloys with increased strength, manufactured using SLM technology. Hierarchical clustering methods allowed us to identify three groups of thin-walled samples with different strain-hardening mechanisms depending on the annealing temperature. The greatest hardening is achieved in the first group of samples annealed at 530 °C. Metallographic analysis showed that at this heat treatment temperature, there are practically no micropores (macrodefects) and microcracks. X-ray phase analysis showed the precipitation of Ti and Zr, as well as the formation of an intermetallic phase with a composition of Mg8Al16. At lower heat treatment temperatures, from 260 °C to 500 °C, the observed hardening is statistically significantly lower than at 530 °C. This phenomenon, combined with the formation of intermetallic phases and the precipitation of titanium/zirconium, contributes to the hardening of thin-walled Al-Mn-Mg-Ti-Zr alloy samples manufactured by SLM. The main results of this study show that the optimal strain hardening of thin-walled Al-Mn-Mg-Ti-Zr alloy samples manufactured by SLM is achieved by heat treatment at 530 °C for 1 h. The strengthening mechanism has two characteristics: (1) dispersion strengthening due to the formation of precipitates and (2) reduction in macrodefects at high temperatures. Full article

The objective of this study was to investigate electron beam hardening (EBH) technology and compare its performance with laser beam hardening (LBH) in the context of manufacturing components such as gears, which increasingly employ submicron bainitic steels. Given the stringent demands for durability and fatigue resistance of gear teeth, identifying an optimal surface hardening method is essential for extending service life. Comprehensive analyses, including light and electron microscopy, hardness testing, tribocorrosion testing, and X-ray diffraction for phase composition, were conducted. The EBH-treated layer exhibited a slightly higher hardness (by 26 HV) compared to the LBH-treated layer (average 654 HV), while the base material measured 393 HV. The EBH process produced a uniform hardness distribution with a subsurface zone of reduced hardness. In contrast, LBH resulted in a surface oxide layer absent in EBH due to its vacuum environment. Both techniques reduced the residual austenite content in the surface layer from 22.5% to approximately 1.3%–1.4%. Notably, EBH achieved comparable hardening effects with nearly half the energy input of LBH, demonstrating superior energy efficiency and industrial feasibility. Application of the developed EBH process to an actual gear component confirmed its practical potential for modern gear manufacturing. Full article

Multiaxial low-cycle fatigue (MLCF) behavior of laser powder bed fused (L-PBF) Ti-6Al-4V was systematically investigated with four building direction (BD) in this paper. Proportional and non-proportional strain-controlled MLCF tests characterized cyclic softening and fracture mechanisms. L-PBF Ti-6Al-4V exhibits three-stage cyclic softening with occasional initial hardening, while non-proportional softening predominates, contrasting with conventional titanium alloys. Macro-micro characterization reveals that defect density and cleavage morphology strongly influence fatigue performance across BD. Fatigue life was predicted using analytical models (FS and KBMP) and a hybrid physics- and data-driven VAE-ANN model. While the KBMP model improves predictions over FS, both fail to fully account for BD effects. Incorporating macro-micro features, the VAE-ANN model achieves highly accurate MLCF life predictions within 10% error. These results highlight the critical roles of BD and microstructural characteristics in governing the MLCF behavior of L-PBF Ti-6Al-4V. Full article