Search Results (432)

As a new type of alloy system composed of five or more principal components, high-entropy alloys demonstrate outstanding comprehensive performance in the field of friction and wear through the synergistic effects of the high-entropy effect, lattice distortion effect, hysteresis diffusion effect and cocktail effect. This paper systematically reviews the research progress on the friction and wear properties of high-entropy alloys. The mechanisms of metal elements such as Al, Ti, Cu and Nb through solid solution strengthening, second-phase precipitation and oxide film formation were analyzed emphatically. And non-metallic elements such as C, Si, and B form and strengthen the regulation laws of their tribological properties. The influence of working conditions, such as high temperature, ocean, and hydrogen peroxide on the friction and wear behavior of high-entropy alloys by altering the wear mechanism, was discussed. The influence of test conditions such as load, sliding velocity and friction pair matching on its friction coefficient and wear rate was expounded. It is pointed out that high-entropy alloys have significant application potential in key friction components, providing reference and guidance for the further development and application of high-entropy alloys. Full article

Nickel is used in aerospace, military, energy, and chemical sectors. Commercially pure (CP) Ni, and its alloys, including solid-solution strengthened (SSS), precipitation strengthened (PS), and specialty alloys (SA), are widely utilized, typically at elevated temperatures, in corrosive settings and in cryogenic milieu. Ni or Ni-based alloys frequently require welding realized, inter alia, via methods using electric arc and beam power. Tungsten inert gas (TIG) and Electron-beam welding (EBW) have been utilized most often. Friction stir welding (FSW) is the most promising solid-state welding technique for connecting Ni and its alloys. The primary weldability issues related to Ni and its alloys are porosity, as well as hot and warm cracking. CP Ni exhibits superior weldability. It is vulnerable to porosity and cracking during the solidification of the weld metal. Typically, SSS alloys demonstrate superior weldability when compared to PS Ni alloys; however, both types may experience weld metal solidification cracking, liquation cracking in the partially melted and heat-affected zones, as well as ductility-dip cracking (DDC). Furthermore, PS alloys are prone to strain-age cracking (SAC). The weldability of specialty Ni alloys is limited, and brazing might provide a solution. Employing appropriate filler metal, welding settings, and minimal restraint can reduce or avert cracking. Full article

Medium-entropy alloys (MEAs) have attracted significant attention due to their unique structure–property relationships. In this study, we examine the effects of lattice distortion on the mechanical properties of Nb-Ti-V-Zr MEAs, focusing on two alloy series: Nb(Ti_1.5V)_xZr and Nb(TiV)_xZr (x = 1, 2, 3, 4 and 5). Experimental results show that the Nb(TiV)_xZr r alloys exhibit greater atomic size mismatches and increased lattice distortion compared to the Nb(Ti_1.5V)_xZr alloys, leading to higher yield strengths via enhanced solid-solution strengthening. However, excessive lattice distortion does not ensure an optimal strength–ductility balance, as the alloys with the highest distortion demonstrate limited plasticity. Thus, moderate reduction in lattice distortion proves beneficial in achieving an excellent compromise between strength and ductility. These findings offer valuable guidance for leveraging lattice distortion in the design of high-strength, high-ductility, body-centered cubic (BCC) MEAs for extreme environments. Full article

In this study, prospects of designing new Al–Ca–Cu–Mn (Zr) alloys for additive manufacturing (AM) were evaluated for the example of laser remelting of thin-sheet rolled products. The new as-cast alloys have a hypereutectic structure containing Al₂₇Ca₃Cu₇ primary crystals and ultrafine eutectic particles of (Al,Cu)₄Ca and Al₂₇Ca₃Cu₇ phases in equilibrium with the aluminum solid solution. The solid solutions are additionally strengthened by alloying with Mn and micro additions of Zr, which contribute to the formation of coarsening-resistant phases without compromising the manufacturability of the alloys. Laser remelting, which simulates AM-typical solidification conditions, promotes the formation of a pseudoeutectic cellular structure without the occurrence of undesirable primary Al₂₇Ca₃Cu₇. The size of the dendritic cells and eutectic particles is 10 times smaller (for solidification rates of ~200 K/s) than that of the as-cast state. This structure provides for a higher hardness of the laser-remelted alloy (96 HV) as compared to the as-cast alloy (85 HV). Data for the alloy after 350–400 °C long-term annealing for up to 100 h show that the hardness of the Al–Ca–Cu–Mn–Zr alloys declines relatively slowly by ~7.5% as compared to the Zr-free alloy, whose hardness decreases by ~22%. Thus, one can consider these alloys as a promising candidate for AM processes that require high thermal stability. Full article

Molybdenum alloys as refractory alloys can provide strength levels at operating temperatures higher than that of Ni-base superalloys, yet their ductility is usually inferior to Ni-base alloys. Currently, commercialized Mo alloys are much fewer than Ni alloys. The motivation of this work is to explore opportunities of discovering useful alloys from the usually less investigated binary Mo-X systems (X = alloying element). With computational thermodynamics (CALPHAD), first-principles calculation, and mechanistic modeling combined, in this work a large number of Mo-X binary systems are investigated in terms of thermodynamic features and mechanical properties (yield strength, ductility, ductile-brittle transition temperature, creep resistance, and stress-strain relationship). The applicability of the alloy systems as solution-strengthened or precipitation-strengthened alloys is investigated. Starting from 92 Mo-X systems, a down-selection process is implemented, the results of which include three candidate systems for precipitation strengthening (Mo-B, Mo-C, Mo-Si) and one system (Mo-Re) for solid-solution strengthened alloy. In a composition optimization of Mo alloys to reach the properties of Ni-base superalloys, improving ductility is of top priority, for which Re plays a unique role. The presented workflow is also applicable to other bcc refractory alloy systems. Full article

In this study, we investigated the electrochemical corrosion behavior and mechanisms of FeCrNi/WC alloys with varying contents of CTC-S (spherical WC) and CTC-A (angular WC) in a 3.5 wt.% NaCl solution, addressing the corrosion resistance requirements for stainless steel composites in marine environments. The electrochemical test results demonstrate that the corrosion resistance of the alloy initially increases with the CTC-A content, followed by a decrease, which is associated with the formation, stability, and rupture of the passivated film. Nyquist and Bode diagrams for electrochemical impedance spectroscopy confirm that the charge transfer resistance of the passivated film is the primary determinant of the composite’s corrosion performance. A modest increase in CTC-A contributes to the formation of a more heterogeneous second phase, providing a physical barrier and enhancing solid solution strengthening, and thus delaying the cracking and corrosion processes of the passivation film. However, excessive CTC-A content leads to significant dissolution of the alloy’s reinforcement phase and promotes decarburization, resulting in the formation of corrosion pits, craters, and cracks that compromise the passivation film and expose fresh alloy surfaces to further corrosion. When the CTC-A content is 10% and the CTC-S content is 30%, this combination results in minimal degradation in the corrosion performance (0.213 μA·cm²) while balancing the hardness and toughness of the alloy. Additionally, electrochemical evaluations reveal that incorporating angular CTC-A particles at 10 vol% effectively delays the breakdown of the passivation film by mitigating the interfacial galvanic coupling through enhancing the mechanical interlocking at the WC/FeCrNi interface. The CTC-A/CTC-S hybrid system exhibits a remarkable 62% reduction in the pitting propagation rate compared to composites reinforced solely with spherical WC, which is attributed to the preferential dissolution of angular WC protrusions that sacrificially suppress crack initiation at the phase boundaries. Full article

This study systematically investigates the effects of heat treatment at 800–1000 °C on the microstructure and mechanical properties of 10 wt.% TiB₂@Ti/AlCoCrFeNi_2.1 eutectic high-entropy alloy matrix composites (EHEAMCs) prepared by vacuum hot-pressing sintering. The results show that the materials consist of FCC, BCC, TiB₂, and Ti phases, with a preferred orientation of the (111) crystal plane of the FCC phase. As the temperature increases, the diffraction peak of the BCC phase separates from the main FCC peak and its intensity increases, while the diffraction peak positions of the FCC and BCC phases shift at small angles. This is attributed to the diffusion of TiB₂@Ti from the grain boundaries into the matrix, where the Ti solid solution increases the lattice constant of the FCC phase. Microstructural observations reveal that the eutectic region transforms from lamellar to island-like structures, and the solid solution zone narrows. With increasing temperature, the Ti concentration in the solid solution zone increases, while the contents of elements such as Ni decrease. Element diffusion is influenced by binary mixing enthalpy, with Ti and B tending to solidify in the FCC and BCC phase regions, respectively. The mechanical properties improve with increasing temperature. At 1000 °C, the average hardness is 579.2 HV, the yield strength is 1294 MPa, the fracture strength is 2385 MPa, and the fracture strain is 19.4%, representing improvements of 35.5% and 24.9% compared to the as-sintered state, respectively, without loss of plasticity. The strengthening mechanisms include enhanced solid solution strengthening due to the diffusion of Ti and TiB₂, improved grain boundary strength due to the diffusion of alloy elements to the grain boundaries, and synergistic optimization of strength and plasticity. Full article

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning grain boundaries and improving strength. Prolonged aging (750 °C, 5000 h) caused M₂₃C₆ to coarsen into brittle chain-like structures (width up to 1.244 μm) and precipitated M₆C carbides, degrading grain boundaries. Aging at 950 °C accelerated this coarsening via LSW kinetics (rate constant: 6.83 × 10⁻² μm³/s), with Mo segregation promoting M₆C formation. Tensile properties resulted from competing γ′ precipitation strengthening (post-aging strength increased up to 23.3%) and grain boundary degradation (elongation dropped from 70.1% to 43.3%). Fracture shifted from purely intergranular (cracks along M₂₃C₆/γ interfaces at 750 °C) to mixed mode (cracks initiated by M₆C fragmentation at 950 °C). These insights support superalloy microstructure optimization and lifetime prediction. Full article

The CASTRIP process is an innovative method for producing flat rolled low-carbon and low-alloy steel at very thin thicknesses. By casting steel close to its final dimensions, enormous savings in time and energy can be realized. In this paper, an ultra-high-strength low-alloy corrosion-resistant steel was produced through the CASTRIP process. Microstructure and properties were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser confocal microscopy (LSCM), electron backscattered diffraction (EBSD), and tensile testing. The results show that the microstructure is mainly composed of polygonal ferrite, bainite ferrite, and acicular ferrite. The bainite ferrite forms parallel lath bundles nucleating at austenite grain boundaries, propagating perpendicularly into the parent grains. The acicular ferrite exhibits a cross-interlocked morphology preferentially nucleating at oxide/sulfide inclusions. Microstructural characterization confirms that the phase transformation of acicular ferrite and bainite ferrite introduces high-density dislocations, identified as the primary strengthening mechanism. Under the CASTRIP process, corrosion-resistant elements such as Cu, P, Sb, and Nb are completely dissolved in the matrix without grain boundary segregation, thereby contributing to solid solution strengthening. Full article

This article studies the effects of a laser remelting treatment on the microstructure and properties of Al-Cu-Mn alloy surfaces, as well as the effects of a heat treatment process on the microstructure and mechanical properties of the matrix zone and remelting zone. The results showed that the remelting zone structure was mainly composed of equiaxed dendrites and fine columnar dendrites. The α(Al) phase and θ(Al₂Cu) phase were greatly refined after laser remelting. The T(Al₁₂CuMn₂) phase was completely dissolved into the α(Al) matrix. The hardness of the remelting zone increased significantly with an increase in the height of the molten pool, and the strengthening mechanism was mainly fine grain strengthening and second phase strengthening. For identical aging treatments, the solution treatment at 530 °C for 4 h yielded the highest hardness. Relative to samples aged without prior solution treatment, hardness increased by 80% in the matrix zone and 59.1% in the remelting zone. When the solid solution process was the same, the time to reach peak hardness was shortened when the aging temperature increased, and the hardness of both the matrix zone and remelting zone reached its peak at 175 °C for 8 h of aging. After aging, the friction coefficient of the alloy decreased due to the increase in the strength of the alloy. Full article

Enhanced hard coatings with exceptional mechanical and thermal qualities have prompted substantial study into multicomponent nitride systems. TiAl(Si)N coatings have emerged as viable possibilities owing to their remarkable hardness, thermal stability, and oxidation resistance. This work involved the fabrication of thickness-varied TiAl(Si)N gradient coatings using reactive magnetron sputtering, employing a controlled modulation of aluminum and silicon content across the film thickness. Three samples, with thicknesses of ~400 nm, ~600 nm, and ~800 nm, were deposited under uniform Ar/N₂ gas flow ratios, and their microstructural, mechanical, and tribological characteristics were rigorously examined. SEM investigation demonstrated a significant change across thicknesses. XRD results validated the emergence of a predominant cubic TiAl(Si)N phase alongside a secondary hexagonal AlN phase, signifying partial phase segregation. The nanoindentation results indicated that Sample 2 exhibited the maximum hardness (~38 GPa) and Young’s modulus (~550 GPa) due to an optimized equilibrium between solid solution strengthening and nanocomposite production. Tribological testing revealed that Sample 1 displayed the lowest and most consistent friction coefficient, corresponding to its superior H/E and H3/E2 ratios, which signify improved elasticity and resistance to plastic deformation. The findings emphasize that the implementation of a compositional gradient, especially in the distribution of Si and Al, markedly affects the microstructure and performance of TiAl(Si)N coatings. Gradient structures enhance the microstructure, optimize hardness, and increase the friction coefficient. Ongoing refinement of gradient profiles and deposition parameters may further improve the characteristics of TiAl(Si)N coatings, facilitating their wider industrial use. Full article

In this study, we studied the dual role of magnesium on the high-temperature deformation mechanisms and microstructural evolution of high-Mg 5383 aluminum alloys. We developed a quantitative framework to characterize high-temperature flow behavior and constructed 3D processing maps to identify processing instabilities. The results indicate that solid solution strengthening induced by Mg atoms leads to a substantial increase in peak flow stress. The thermal activation energy rises significantly from 182 kJ/mol to 209 kJ/mol at a Mg content of 5 wt.%, which highlights the pronounced solute drag effects on dislocations. Moreover, Mg-modified grain boundary dynamics enhance power dissipation efficiency by 34% (from 35% to 47%). With an increasing Mg content, the processing instability domains expand, thereby shifting the optimal processing parameters towards higher-temperature and lower-strain-rate regions (500 °C/0.05 s⁻¹). The results provide a theoretical foundation for optimizing the thermal processing characteristics and mechanical properties of high-Mg aluminum 5xxx series alloys. Full article

316L stainless steel is widely employed in various industrial sectors, including shipbuilding, offshore plants, high-temperature/high-pressure (HTHP) piping systems, and hydrogen infrastructure, due to its excellent mechanical stability, superior corrosion resistance, and robust resistance to hydrogen embrittlement. This study presents 316L stainless steel alloys fabricated via hot isostatic pressing (HIP), conducted at 1300 °C and 100 MPa for 2 h, incorporating Cr₂N powder and an optimized Ni/Mn ratio based on the nickel equivalent (Ni_eq). During HIP, Cr₂N decomposition yielded a uniformly refined, dense austenitic microstructure, with enhanced corrosion resistance and mechanical performance. Corrosion resistance was evaluated by potentiodynamic polarization in 3.5 wt.% NaCl after 1 h of OCP stabilization, using a scan range of −0.25 V to +1.5 V (Ag/AgCl) at 1 mV/s. Optimization of the Ni/Mn ratio effectively improved the pitting corrosion resistance and mechanical strength. It is cost-effective to partially substitute Ni with Mn. Of the various alloys, C13Ni-N exhibited significantly enhanced hardness (~30% increase from 158.3 to 206.2 HV) attributable to nitrogen-induced solid solution strengthening. E11Ni-HM exhibited the highest pitting corrosion resistance given the superior PREN value (31.36). In summary, the incorporation of Cr₂N and adjustment of the Ni/Mn ratio effectively improved the performance of 316L stainless steel alloys. Notably, alloy E11Ni-HM demonstrated a low corrosion current density of 0.131 μA/cm², indicating superior corrosion resistance. These findings offer valuable insights for developing cost-efficient, mechanically robust corrosion-resistant materials for hydrogen-related applications. Further research will evaluate alloy resistance to hydrogen embrittlement and investigate long-term material stability. Full article

This study evaluates the effectiveness of rigid node connection prototypes for joining bamboo, in response to the growing need for sustainable construction solutions. Considering the superior mechanical properties of bamboo, including its flexibility and strength, the research focuses on the design and testing of nine connection prototypes subjected to compression, shear, and tensile tests in a laboratory. The results obtained demonstrate that the prototypes significantly exceed the established minimum strength criteria, with average maximum loads of 62.19 kN in compression tests, 10.16 kN in shear tests, and 25.41 kN in tensile adhesion tests. These findings not only confirm the viability of bamboo as a sustainable construction material but also highlight the need to develop efficient connection methods that integrate bamboo’s flexibility with the strength of other materials. Through these connections, bamboo presents itself as a solid alternative to address housing deficits and promote responsible construction practices. The research suggests continuing additional studies to strengthen knowledge about bamboo’s behavior in different construction contexts, thereby contributing to a more sustainable future in building. Full article

This study investigates the effects of B₄C content (2.5, 5, 7.5, and 10 wt.%) on the microstructure and wear resistance of laser cladding 316 stainless steel coatings on a 2Cr12MoV steel substrate. The coating was prepared by laser cladding technology. The phase composition, microstructure evolution, microhardness, and tribological properties of the coating were analyzed. The results show that the decomposition of B₄C particles is complete, and the phase composition of the coating includes Austenite, Fe₂₃ (B₃C₃), Cr₂₃ (B_1.5C_4.5), and a Fe-Ni solid solution. The increase in B₄C content significantly increased the microhardness of the material from 206 HV_0.2 (substrate) to 829 HV_0.2 (10 wt.% B₄C) by 4.02 times. Wear resistance also improved, with the 10 wt.% coating exhibiting the lowest wear rate (10 × 10⁻⁸ mm³/N·m) due to fine-grained and dispersion strengthening mechanisms. However, excessive B₄C (10 wt.%) induced cracks from increased brittleness, resulting in higher friction coefficients. The wear mechanism consists of fatigue wear, adhesive wear, and oxidative wear, and the degree of wear decreases with the increase in B₄C content. This work demonstrates that the addition of B₄C effectively improves the hardness and wear resistance of 316 stainless steel coatings, providing practical insights into surface engineering in high wear applications. Full article