The present study investigated the effect of rotational speed on the mechanical and microstructural properties of dissimilar joints between EN24 steel and Al6063 alloy produced using solid-state rotary friction welding (RFW). Four rotational speeds (1000, 1200, 1400, and 1600 rpm) were selected, and other welding parameters (friction pressure, friction time, upset pressure, and upset time) were kept constant. Radiographic inspection confirmed the absence of internal defects in all welded joints. Samples welded at 1400 rpm exhibited the highest tensile strength (193.86 MPa) and hardness (90-95 HV). This finding is associated with effective diffusion and optimal development of the intermetallic compound (IMC) layer. A further increase in rotational speed to 1600 rpm reduced the weld strength to 147.11 MPa, which is attributed to increased heat input and consequent thickening of the IMC layer at the interface. Additionally, axial shortening increased from 5.31 to 9.17 mm with increasing rotational speed, primarily due to deformation and temperature-induced softening on the Al6063 side. The maximum joint efficiency for dissimilar Al6063–EN24 welding reached 77.91
Dynamic recrystallization (DRX) is the key softening mechanism in 7xxx-series aluminum alloys, including discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and geometric dynamic recrystallization (GDRX). Owing to the indistinct morphological boundaries among the three DRX modes, accurate identification of each mechanism remains challenging. To clarify the respective microstructural characteristics, uniaxial hot compression tests were performed to explore the high-temperature deformation responses of 7050 aluminum alloy. A DRX kinetic model was established, and electron backscatter diffraction (EBSD) was used to analyze the microstructural evolution, aiming to reveal its underlying mechanism. The results demonstrate that the Avrami exponent is approximately 2, indicating relatively limited nucleation sites. EBSD analysis identified three distinct forms of CDRX: isolated grains at curved grain boundaries, grains formed by subgrain fragmentation, and grain clusters formed by subgrain rotation near grain boundaries. In addition, GDRX was observed at low strain rates, producing grain sizes 2-5 times larger than those of CDRX grains. In contrast, DDRX only occurred to a small extent at highly bent grain boundaries under high strain conditions. This study provides experimental and theoretical support for distinguishing complex DRX mechanisms.
As TBM tunneling projects advance into deep and complex geological strata, conventional H13 and DC53 cutter ring steels are increasingly prone to abnormal failures during rock breaking, such as edge chipping and fracture. To extend cutter ring service life, this study systematically compared the microstructure, hardness, impact toughness, wear resistance, and rock-breaking performance of H13, DC53, and a newly developed SKL-1 steel. Through compositional optimization and tailored heat treatment, SKL-1 steel exhibited a tempered martensitic matrix containing fine and uniformly distributed carbides. It achieved a stable hardness of 60.1 HRC. The impact toughness of SKL-1 was 31.43 and 327.8
The increasing demand for multi-material components in advanced engineering systems, particularly in thermal management, power generation, and electronic industries, necessitates the development of reliable strategies for joining stainless steel to copper. Wire arc additive manufacturing (WAAM) has emerged as a promising approach for joining dissimilar metals by enabling controlled heat input, compositional grading, and layer-by-layer fabrication. In the present study, a multilayer deposition strategy was employed to join AISI 304 stainless steel to pure copper using WAAM through a cold metal transfer (CMT) mode. Detailed microstructural characterization using optical microscopy, scanning electron microscopy, and electron backscatter diffraction revealed the formation of a defect-free joint facilitated by a diffusion-driven bonding, exhibiting gradual compositional transition from coarse columnar SS304 grains to comparatively fine equiaxed Cu grains across the interface. Significant grain evolution without any preferred crystallographic orientation was observed on the Cu side, with greater diffusion depth of SS304 into Cu. Microhardness mapping indicated that the interfacial properties were governed by the harder SS304 phase. The hardness values across the interface varied between 109 and 187 HV, indicating a gradual transition from the softer Cu region to the stronger SS304 side. The SS304-Cu bimetallic joint exhibited a UTS of 290 MPa and 0.2
Reliable railway infrastructure depends on the durability of pearlitic steels, which are subjected to severe mechanical stresses under service conditions. This study compares unused and used rail steels of similar chemical composition to understand how exposure affects the microstructure, mechanical properties, and corrosion susceptibility. The CCT analysis showed pearlite formation at lower cooling rates (0.1‐1 °C/s) and bainite/martensite at higher cooling rates (10‐100 °C/s), thus providing a roadmap for producing high-strength rails with a fully pearlitic microstructure, avoiding brittle phases of bainite/martensite. The undamaged lamellar pearlite with a spacing of 130 nm was found in unused samples, whereas used rails exhibited obvious degeneration with a finer spacing of 80 nm and strain accumulation, as dislocation density increased from 1.95 × 1014 to 18.15 × 1014 m−2. The surface hardness was increased by 30 HV due to work hardening, representing an increase of 10
Powder bed fusion (PBF) with a laser beam (PBF-LB) of 17-4 precipitate-hardened (PH) stainless steel (SS) has been widely investigated for process optimization, microstructure, powder recycling, and thermal conditioning. While prior studies have reported the effects of powder reuse and metastructure on mechanical performance, the temperature-dependent, stimulus-responsive (4D) behavior of 17-4 PH SS fabricated via PBF-LB has not yet been systematically explored. In this study, tensile coupons with different metastructures (solid, octet, and Weaire–Phelan (WP) as infill) were fabricated using both primary and secondary recycled 17-4 PH SS powders, thermally conditioned at 450 °C before fabrication, via PBF-LB, and compared with counterparts produced from virgin and non-heat-treated recycled powders. For functional prototypes (under tensile loading) prepared using primary recycled 17-4 PH SS powder (without heat treatment), ultimate tensile strength (UTS) initially declined but was restored to near-virgin levels after heat treatment. In contrast, the strain (in functional prototypes fabricated by PBF-LB) was initially increased for primary recycled powder (without heat treatment) and later restored to virgin levels after thermal conditioning at 450 °C. Further, results revealed that using secondary recycled powder (of 17-4 PH SS in PBF-LB) thermally conditioned at 450 °C results in a 10
We systematically investigate the wetting behavior of GaInSnBiZn high-entropy alloy on micron-scale copper-patterned sapphire substrates. By fabricating copper-patterned arrays with five characteristic dimensions ranging from 250 to 760 μm and employing the sessile drop method assisted by saturated hydrochloric acid vapor, it reveals the significant influence of pattern size on wetting characteristics: densely packed copper arrays (250-350 μm) exhibit rapid wetting features (contact angles of 38-61°) due to triple-line localization effects, whereas nondensely packed arrays (500-760 μm) show contact angle hysteresis (84-124°) caused by pinning effects. Interfacial analysis identifies a layered intermetallic compound structure (zinc-rich regions Cu5Zn8/CuZn2 and gallium-rich regions Cu9Ga4/CuGa2), confirming that the reactivity between gallium and copper is stronger than that between zinc and copper. The established modified Cassie model—which fundamentally distinguishes itself from purely empirical fits by physically correlating the triple-line localization factor (r) with subsurface reactive penetration and the pinning coefficient (β = 2.20) with thermodynamic energy barriers successfully quantifies the relationship between apparent contact angle and pattern size, providing crucial wetting design guidelines for the application of high-entropy alloys in fields such as electronic packaging.
This study presents and discusses experimental results on the durability of W(WC) coating exposed to a high-velocity flow of liquid Pb-Bi eutectic at 210 °C for effective operating time of 7252 h. The inner surface of a tube segment made of 316L steel was coated with a 100 µm thick W(WC) layer by chemical vapor deposition to protect the steel surface from potentially severe erosion by high-velocity flow of Pb-Bi eutectic reached locally 6 m/s. The concentration of oxygen dissolved in liquid metal was controlled at 2 × 10−7 mass
Due to the poor surface quality of the WC/Ni cladding layer, which does not satisfy the required surface roughness criteria for structural applications, post-processing via milling is employed. First, a multi-pass cladding layer with a 40
The current study investigates the development and solid particle erosion behavior of NiCr + 50
This work investigates the synergistic effects of a novel hybridization technique employing a covered carbon lamina, co-curing, and multiwalled carbon nanotubes (MWCNTs)-modified adhesives on the shear and flexural properties of flax fiber-reinforced composite joints. The hybridization technique, in flax fiber-reinforced co-cured composite joints, enhanced joint performance by 169
Magnesium-based materials are promising candidates for solid-state hydrogen storage, but their practical application is limited by sluggish hydrogen sorption kinetics and high operating temperatures. This study investigates the catalytic effect of niobium (Nb) on the hydrogen storage performance of AZ31 magnesium alloy. The addition of Nb results in the formation of NbO0.76 and AlNb2 phases and reduces the average particle size from 25.5 to 19.57 µm. Although the maximum hydrogen storage capacity decreases from 6.41 wt.
This study systematically investigates the thermophysical, oxidation, and elevated-temperature tribological behavior of selective laser melted (SLM) Ti-6Al-4V alloy. The alloy was characterized using XRD, SEM/EDS, DSC, TGA, and transient plane source (TPS) techniques to evaluate its microstructure, thermal transport properties, and oxidation behavior. Dry sliding wear tests were conducted between 350 and 600 °C using a pin-on-disk tribometer. XRD and SEM analyses revealed a predominantly α-Ti matrix with retained β phase and a refined acicular microstructure containing distinct melt-pool boundaries. Thermal conductivity increased from 3.64 to 6.92 W m⁻1 K⁻1 with temperature, while thermal diffusivity decreased from 5.13 to 2.54 mm2 s⁻1, indicating greater heat retention at elevated temperatures. DSC and TGA confirmed good thermal stability up to approximately 500 °C, followed by accelerated TiO2 scale formation. Tribological performance was strongly temperature dependent, with the highest wear at 350 °C due to adhesive and abrasive wear, whereas optimum wear resistance occurred at 550 °C because of the formation of a dense, protective TiO2-rich tribolayer. These results demonstrate that elevated-temperature wear behavior is governed by the combined effects of microstructural stability, thermal transport, and oxidation kinetics, providing guidance for high-temperature applications of SLM Ti-6Al-4V.
This article is based on the geological conditions of the surrounding rock of the opposite heading driving roadway in Mabao Coal Mine as the engineering background. The width range of coal pillar with driving facing mining gob-side entry is calculated to be 6.48 m by the limit equilibrium theory, and according to the theory of internal and external stress field, the maximum width of coal pillar is 8.97 m, so the reasonable width range of coal pillar is 6.48-8.97 m. FLAC3D numerical simulation software is used to simulate the stress distribution, plastic zone distribution, and surrounding rock deformation of coal pillars in the process of 15202 transportation crossheading excavating when the coal pillar width is 5, 6, 7, 8 and 9 m. The simulation results show that with the increase in coal pillar width, the peak stress of coal pillar and the range of plastic zone continue to decrease, after the coal pillar width is 7 m, the peak stress reduction trend and the change of plastic zone are not obvious, and the surrounding rock deformation gradually tends to be stable. Combining with the results of theoretical calculation, the coal pillar width is finally determined to be 7 m. Based on the above research, by simulating the stress changes in different positions of coal pillar during the mining and driving process, it is determined that the influence range of mining stress superposition is 30 − 30 m. Combined with the deformation of the surrounding rock at different positions of the 15202 transportation crossheading, the design scheme of dynamic segmented support was put forward. According to the monitoring, the roof and floor closing amount decreased by 9.6 mm, and the two sides closing amount decreased by 21.1 mm in the solid coal stage; during the mining and driving influence stage, the roof and floor movement amount decreased by 89.9 mm, and the two sides movement amount decreased by 212.6 mm; the roof and floor movement amount decreased by 20.3 mm, the two sides movement amount decreased by 24.2 mm in the gob-side entry stage, and the field application effect was good.
Catheter-associated infections remain a major clinical challenge due to bacterial biofilm formation on catheter surfaces. This study investigates laser-induced surface texturing as an additive-free approach to enhance the hydrophobicity and anti-fouling performance of latex rubber. A nanosecond Nd3+:YAG laser (1064 nm, fluence up to 29.3 J/cm2) and a femtosecond laser (1035 nm, 20 µJ per pulse) were employed to fabricate distinct microstructures using two scanning patterns—unidirectional (pattern A) and bidirectional (pattern B)—at varying beam overlaps and repetition rates. Nanosecond texturing at 230 mJ with 90
In the past decade, significant studies were reported on process parameters of powder bed fusion–laser beam (PBF-LB) (such as laser power (LP), layer thickness (LT), scan speed (SSP), and hatch distance (HD), etc.). In addition, several studies have investigated post-processing (via heat treatment) to fabricate functional prototypes of 17-4 precipitate-hardened (PH) stainless steel (SS). Also, the combined effects of metastructure design, powder recycling, and heat treatment on tensile properties were systematically explored. But hitherto, little has been reported on the correlations among thermal behavior, phase evolution, melt pool characteristics, porosity, grain size distributions, and flexural properties. In the present study, flexural specimens of 17-4 PH SS were fabricated using three different metastructures (octet, Weaire–Phelan (WP), and solid), using primary and secondary recycled 17-4 PH SS powders, followed by heat treatment. Analysis was performed by correlating thermal behavior, phase evolution, and melt pool characteristics (using Thermo-Calc simulations), porosity and grain size distributions (using image analysis), and flexural properties. The results indicate that metastructures are highly sensitive to powder reuse, with secondary recycled 17-4 PH SS powder promoting peak temperatures exceeding the evaporation threshold, leading to intense vaporization, vapor recoil pressure, and keyhole melting behavior (with an aspect ratio (δc) up to 1.502 for WP). This results in higher porosity (up to 27.2
This study investigates the mechanisms governing crack initiation and propagation in brittle materials, focusing on single-crystal silicon subjected to Laser Shock Peening (LSP) using a 1064 nm Nd:YAG laser without ablative coatings. A combined experimental and numerical framework was developed to elucidate the role of laser-induced shock wave interactions on crack evolution. The results reveal that reduced laser spacing (0.5 mm) leads to significant overlap of transient stress fields, generating multi-directional tensile zones that promote crack branching instability. In contrast, larger spacing (0.7-1 mm) minimizes stress field interference, resulting in improved crack directionality and reduced branching. Furthermore, pre-defined surface grooves effectively guide crack propagation under dynamic shock loading conditions, demonstrating a robust crack steering strategy for brittle substrates. The experimentally observed crack propagation behavior and crack lengths show good agreement with the extended finite element method (XFEM) simulations, with the maximum relative error in crack length remaining below 7
As a typical elastic-porous damping material, the performance degradation patterns and fatigue failure characteristics of hollow cylindrical metal rubber (HCMR) under dynamic conditions are critical to the reliability evaluation under service conditions. In this study, the fatigue failure criteria of HCMR associated with dynamic characterization parameters, including dynamic strain, dynamic average stiffness, energy dissipation and loss factor, were proposed and determined. Based on the statistical analysis of dynamic fatigue test results, the S-N curves and an empirical model were obtained to describe the dynamic fatigue failure of HCMR as functions of density and operational axial load. Failure analysis results show that the fatigue failure patterns of HCMR under dynamic loading were mainly manifested at the microscopic level, where the internal metal wires experienced sliding, surface scratching, local fretting and fretting-fatigue fracture. Moreover, the macroscopic properties of HCMR, including energy dissipation and dynamic strain in the axial (height) direction, exhibited a continuous degradation pattern. The dynamic fretting-fatigue failure mechanisms of HCMR were found to result primarily from different sliding and extrusion modes of the internal interlocking structure, together with fretting between the metal wires, ultimately leading to fretting-fatigue fracture.
