Search Results (321)

This study systematically investigates the effects of various direct aging (DA) treatments on the residual stress, mechanical properties, and microstructure of laser powder bed fusion (LPBF) fabricated TiB₂/AlSi7Mg composites. The results demonstrate that during aging at 120 °C, the hardness exhibits a typical age-hardening behavior. The residual stress relief rate increased to 45.1% after 336 h, although the stress relief rate significantly diminished over time. Increasing the aging temperature effectively enhanced residual stress removal efficiency, with reductions of approximately 40% and 62% observed after aging at 150 °C for 4 h and 190 °C for 8 h, respectively. Regarding mechanical properties, aging at 150 °C for 4 h resulted in an optimal synergy in yield strength (YS = 358 MPa) and elongation (EL = 9.2%), followed by aging at 190 °C for 8 h with YS of 320 MPa and EL of 7.0%. Microstructural analysis revealed that low temperature aging promotes the formation of nanoscale Si precipitates, which enhance strength through the Orowan mechanism. In contrast, high temperature annealing disrupts the metastable cellular structure, leading to the loss of strengthening effects. This work provides fundamental insights for effective residual stress management and performance optimization of LPBF Al–Si–Mg alloys. Full article

Single-lip deep-hole drilling is a key technology for the precision machining of high-temperature nickel-based alloy pore structures in aero engines. However, the intense thermo-mechanical coupling effects during machining can easily lead to surface integrity deterioration, and the correlation mechanism between microstructure and properties remains unclear. By adjusting the spindle speed and feed rate, a series of orthogonal experiments were carried out to study the integrity characteristics of the machined surface, including surface morphology, roughness, work hardening, and subsurface microstructure. The results reveal gradient structural features along radial depth: a dynamic recrystallized layer (RL) at the surface and a plastically deformed layer (PDL) containing high-density subgrains/distorted grains in the subsurface. With the increase in the spindle speed, the recrystallization phenomenon is intensified, the RL ratio of the machined-affected zone (MAZ) is increased, and the surface roughness is reduced to ~0.5 μm. However, excessive heat input will reduce the nanohardness. Low feed rates (<0.012 mm/rev) effectively suppress pit defects, whereas high feed rates (≥0.014 mm/rev) trigger pit density resurgence through shear instability. Progressive material removal rate (MRR) elevation drives concurrent PDL thickness reduction and RL proportion growth. Optimal medium MRR range (280–380 mm³/min) achieves synergistic RL/PDL optimization, reducing machining-affected zone thickness (MAZ < 35 μm) while maintaining fatigue resistance. These findings establish theoretical foundations for balancing efficiency and precision in aerospace high-temperature component manufacturing. Full article

Welding of maraging steels leads to a microstructural gradient from base material (BM) to weld metal (WM). During post-weld heat treatment (PWHT) the precipitation and reverted austenite (γ_r) reactions will occur defining the mechanical properties. These reactions are affected by the microstructure and local chemical composition of each zone in the “as welded” (AW) condition. This effect has not been clearly described yet nor the evolution of the microstructure. The objective of this work was to analyse the phase transformations at the different zones of the welded joint during the PWHT to explain the microstructure obtained at each zone. Samples of C250 maraging steel were butt-welded by GTAW-P (Gas Tungsten Arc Welding—Pulsed) process without filler material. The AW condition showed an inhomogeneous microhardness profile, associated with a partial precipitation hardening in the subcritical heat affected zone (SC-HAZ) followed by a softening in the intercritical (IC-HAZ) and recrystallized heat affected zone (R-HAZ). A loop-shaped phase was observed between low temperature IC-HAZ and SC-HAZ, associated with γ_r, as well as microsegregation at the weld metal (WM). The microstructural evolution during PWHT (480 °C) was evaluated on samples treated to different times (1–360 min). Microhardness profile along the welded joint was mostly homogeneous after 5 min of PWHT due to precipitation reaction. The microhardness in the WM was lower than in the rest of the joint due to the depletion of Ni, Ti and Mo in the martensite matrix related with the γ_r formation. The isothermal kinetics of precipitation reaction at 480 °C was studied using Differential Scanning Calorimetry (DSC), obtaining a JMAK expression. The average microhardness for each weld zone was proposed for monitoring the precipitation during PWHT, showing a different behaviour for the WM. γ_r in the WM was also quantified and modelled, while in the IC-HAZ tends to increase with PWHT time, affecting the microhardness. Full article

It is essential to develop the optimal hot-working process of the (CoCrNi)₉₄Al₃Ti₃ alloy, a recently developed precipitation-hardened medium-entropy alloy with promising mechanical properties, for its industrial application. In this study, the hot workability of the as-forged (CoCrNi)₉₄Al₃Ti₃ alloy was investigated over a temperature range of 1000 °C to 1150 °C and a strain rate ranging from 0.001 to 1 s⁻¹ using a Gleeble-1500D thermal simulation machine of Dynamic Systems Inc., USA. As a result, the constitutive relationship was established, and the hot deformation activation energy was calculated as 433.2 kJ/mol, suggesting its well-defined plastic flow behavior under low-energy-input conditions. Hot-processing maps were constructed to identify the stable hot-working regions. Microstructure analysis revealed that the hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy exhibited continuous dynamic recrystallization (CDRX) behavior under optimal hot-working conditions. Considering the hot-processing maps and DRX characteristics, the optimal hot-working window of hot-forged (CoCrNi)₉₄Al₃Ti₃ alloy was identified as 1100 °C with a strain rate of 0.1 s⁻¹. This work offers valuable guidance for developing high-efficiency forming processes for (CoCrNi)₉₄Al₃Ti₃ medium-entropy alloy. Full article

Cementing operations are among the most critical steps in oil-well construction. When performed improperly, the integrity and useful life of the well can be significantly compromised. Light cement pastes are used to cement formations with a low fracture gradient to ensure zonal isolation and maintain the integrity of the casing. Extenders are additives used to reduce the density of cement pastes, ensuring that the paste has desirable properties before and after setting. This work aimed to evaluate the application of palygorskite clay as an additive in lightweight cement pastes for oil wells, highlighting how its fibrous morphology influences the microstructure and enhances the macroscopic properties of the hardened cement matrix. For this, the clay sample was initially characterized regarding its physicochemical properties using X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetry (TG), textural analysis (BET/N₂), and scanning electron microscopy (SEM). Lightweight pastes (1.56 g/cm³) were then formulated, varying the clay concentration by 1%, 3%, and 6% of the total mass. Cement pastes using bentonite were also formulated for comparison. Technological tests of atmospheric consistency, rheological behavior, free water, and stability were applied. It can be noted that the pastes formulated with palygorskite had lower viscosity, reflected in the reduced plastic viscosity and yield stress values, indicating easier flow behavior when compared with bentonite-based pastes. The pastes formulated with 6% palygorskite and 3% bentonite showed satisfactory stability and drawdown results. Therefore, applying palygorskite satisfies the minimum requirements for acting as an extending agent for lightweight cement pastes and is an option for application in oil-well cementing operations. Full article

This study developed a vinyl acetate-ethylene rapid repair mortar (VAE-RRM) by using a binary blended cementitious system (ordinary Portland cement and sulfoaluminate cement) and vinyl acetate-ethylene (VAE) redispersible polymer powder. The effects of the polymer-to-cement ratio (P/C: 0~2.0%) on setting time, mechanical properties, interfacial bonding, and microstructure were systematically investigated. The results reveal that VAE delayed cement hydration via physical encapsulation and chemical chelation, extending the initial setting time to 182 min at P/C = 2.0%. At the optimal P/C = 0.9%, a synergistic organic–inorganic network enhanced flexural strength (14.62 MPa at 28 d, 34.0% increase) and interfacial bonding (2.74 MPa after interface treatment), though compressive strength decreased to 65.7 MPa due to hydration inhibition. Excessive VAE (P/C ≥ 1.5%) suppressed AFt/C-S-H growth, increasing harmful pores (>1 μm) and degrading performance. Microstructural analysis via scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) demonstrates that VAE films bridged hydration products, filled interfacial transition zones (ITZ), and refined pore structures, reducing the most probable pore size from 62.8 nm (reference) to 23.5 nm. VAE-RRM 3 (P/C = 0.9%) exhibited rapid hardening (initial setting time: 75 min), high substrate recovery (83.3%), and low porosity (<10%), offering an efficient solution for urban infrastructure repair. This work elucidates the dual mechanisms of pore refinement and interface reinforcement driven by VAE, providing theoretical guidance for designing high-performance repair materials. Full article

Modern energetic materials (EMs) have many different civil applications. One of their most promising applications in civil engineering is explosive hardening, which facilitates the fast and cost-effective improvement of mechanical properties in the treated material. In this work, we present the results of our investigation on the explosive hardening of S235JR Steel with PBX formulations containing silicone binders and 1,3,5-trinitro-1,3,5-triazinane (RDX). In terms of safety, the impact (5–15 J) and friction (240–360 N) sensitivity of the tested plastic-bonded explosives (PBXs) was verified, simultaneously with DSC tests, energy of activation calculations, and critical diameter measurement. The developed material, prepared with techniques similar to the anticipated working conditions, is characterized by a high detonation velocity (up to 7300 m/s), low sensitivity for mechanical factors (10 J, 288 N), and a small critical diameter (3.3 mm). The developed PBX based on a silicone binder demonstrated grain fragmentation, recrystallization, and an increase in the surface hardness of S235JR steel, which was confirmed with SEM, EBSD, microstructure analysis, and microhardness studies. Full article

In this work, the effects of the Cu/Li ratio on the mechanical properties and corrosion behavior of Sc-containing Al-Cu-Li alloys were systematically investigated by utilizing age-hardening behavior, tensile property, corrosion behavior, and electrochemical behavior, complemented by microstructural characterization through EBSD and TEM. The results show that the peak aging strength of the alloys remained relatively consistent but slightly decreased with the decrease in Cu/Li ratio, and the yield strengths were 585 MPa, 578 MPa, and 573 MPa, respectively. The changes in the Cu/Li ratio caused different matching patterns of precipitates in the peak aging alloys. The cumulative precipitation strengthening by T₁, θ′, δ′, and S′ phases are equal within the alloys with different Cu/Li ratios. However, the strength contribution of the T₁ phase decreases from 81% to 66% with the decrease in the Cu/Li ratio. Concurrently, the precipitates of LAGBs gradually increase in number and are continuously distributed, and the precipitates of HAGBs become larger in size with lower Cu content as the Cu/Li ratio decreases, all of which leads to a weakening of the intergranular corrosion (IGC) resistance within the low Cu/Li ratio alloy. Full article

In this paper, a new TaMoNbTiZr multielement alloy has been designed, using chemical elements that exhibit extremely low bio-toxicity for the human body. The alloy was obtained by melting in vacuum arc remelting (VAR) equipment MRF ABJ 900 from high-purity chemical elements (99.5%) as mini-ingots having about 40 g weight each. The biocompatible alloys underwent changes in hardness after performing the annealing at 900 °C for 2 h, followed by cooling in water. The new alloy had an average hardness in the cast state of 545 HV0.5, and after heat treatment, it hardened to a value of 984 HV0.5, over 40% higher than that in the casting state, which ensures a longer working period. To use them as materials for medical instruments, their biocompatibility was highlighted through specific laboratory tests. For this, mesenchymal stem cells isolated from bone tissue and a human fibroblast cell line were cultured in vitro on the TaMoNbTiZr alloy’s surface. The biocompatibility of the alloy with the biological environment was evaluated by analyzing cell viability, adhesion, and proliferation, and in parallel, the cytolysis effects manifested by the increase in lactate dehydrogenase activity in the culture media were analyzed. Full article

Aluminum alloy hot stamping technology has quickly become a research hotspot for many scholars due to its ability to solve key challenges such as poor formability, large rebound, and low dimensional accuracy of aluminum alloy sheets at room temperature. This work systematically reviews the progress of Hot-Forming-Quenching (HFQ^®) technology and its optimization processes. The effects of key forming parameters are summarized, including temperature, forming rate, friction, and crimping force on the forming properties of aluminum alloys. Additionally, an ontological model of thermal deformation behavior and damage evolution during hot forming is analyzed. A multifactorial strength prediction model, integrating grain size and reinforcement mechanisms, is highlighted for its ability to accurately predict post-forming yield strength. To address the limitations of HFQ^®, optimization methods for solid solution and aging heat-treatment stages are categorized and evaluated, along with their advantages and disadvantages. Furthermore, the latest advancements in two innovative hot stamping processes (Low-Temperature Hot Form and Quench (LT-HFQ^®) and pre-hardened hot forming (PHF)) are reviewed. LT-HFQ^® improves formability by pre-cooling the sheet while maintaining solution treatment, while PHF utilizes pre-hardened aluminum alloys, enabling brief heating, forming, and quenching to significantly reduce cycle time while ensuring component strength. Finally, by summarizing current technological progress and challenges, future directions for aluminum alloy hot stamping are outlined, including advancements in forming processes, material modeling, and optimization through multidisciplinary collaboration and artificial intelligence to drive further innovation. Full article

In this study, friction stir welding was first applied to the 1.4 mm thick TRIP590 steel sheets at a constant transverse speed of 100 mm/min and different rotation speeds from 200 to 500 rpm. Then, the obtained joints received deep cryogenic treatment in liquid nitrogen for 24 and 48 h, respectively. It was revealed that the content of retained austenite in the stir zone of the welded joints decreased from 3.3% to 0.2% when the rotation speed increased from 200 rpm to 500 rpm. The stability of retained austenite increased due to grain refinement and work hardening at low rotation speeds. After deep cryogenic treatment of the welded joints, the retained austenite in the stir zone partially transformed into martensite, which led to the precipitation of nano-sized carbide in the ferrite matrix and the release of local stress. As a result, both the strength and plasticity of the stir zone after 48 h of deep cryogenic treatment increased from 798 MPa, 15% to 927 MPa, 17% for the 200 rpm joint, and from 914 MPa, 14% to 1086 MPa, 16% for the 300 rpm joint during the tensile tests. Full article

Magnesium phosphate cements (MPCs) are a class of inorganic cements that have gained significant attention in recent years due to their exceptional properties and diverse applications in the construction and engineering sectors, particularly in the confinement of radioactive waste. These cements set and harden through an acid–base reaction between a magnesium source (usually dead-burnt magnesia) and a phosphate source (e.g., KH₂PO₄). The dead-burnt MgO (DBM) used is typically obtained by calcining pure MgCO₃ at temperatures between 1600 and 2000 °C. The present work explores the possibility of using low-grade magnesia (≈58% MgO), a secondary waste product generated during the calcination of magnesite for sintered MgO production. Low-grade magnesia is a by-product from the calcination process of natural magnesite. In this manner, the cost of the products could be substantially diminished, and the cementitious system obtained would be a competitive alternative while enhancing sustainability criteria and recyclability. This paper also evaluates the effect of the M/P ratio and curing conditions (especially relative humidity) on the mechanical, microstructural, and mineralogical development of these cements over a period of up to one year. Results indicate that low-grade MgO is suitable for the preparation of magnesium potassium phosphate cements (MKPCs). The presence of minor phases in the low-grade MgO does not affect the precipitation of K-struvite (KMgPO₄·6H₂O). Moreover, the development of these cements is highly dependent on both the M/P molar ratio and the RH. Systems prepared with an M/P ratio of 3 demonstrated good compressive strengths, low total porosity, and stable mineralogy, which are essential parameters for any cementitious matrix that aims to be considered as a potential confiner of radioactive waste. Full article

The thermal history of a part deposited via wire arc additive manufacturing (WAAM) and hence its as-built properties can vary significantly depending on the thermal management applied, especially for metallurgically complex materials. Thus, this work aimed to assess the feasibility of processing thin-walled Scalmalloy^® (Al-Mg-Sc-Zr) structures by WAAM while examining the effects of arc energy and heat dissipation on their response to direct age-hardening heat treatment (without solution annealing). As a complement, the geometry, porosity, and processing time of such parts were also analyzed. The walls were built via the cold metal transfer (CMT) deposition process with different arc energy levels in combination with near-immersion active cooling (NIAC) settings (as thermal management solution), as well as with natural cooling (NC), resulting overall in both low surface waviness and porosity levels. Based on hardness testing, the resultant Scalmalloy^® direct-aging response (relative increase in hardness after direct age-hardening from WAAM as-built state) depended more on the arc energy per unit length of deposit applied. In contrast, the other thermal management approaches (NIAC or NC) helped in maintaining Sc in a supersaturated solid solution during deposition. Thus, Scalmalloy^® strengthening was demonstrated as feasibly triggered by means of a post-WAAM direct age-hardening heat treatment solely. Additionally, in comparison with a thermally equivalent (same interpass temperature) condition based on NC, the NIAC technique allowed the achievement of such a positive result on direct-aging response with much shorter WAAM processing times, therefore improving productivity. Full article

In this study, the microstructure, mechanical properties, wear resistance, and wear-hardening mechanism of Fe-28Mn-8.5Al-1.0C lightweight wear-resistant steel after heat treatment at different aging temperatures were examined. The results show that the nano-scale κ-carbides precipitated in the grains after aging treatment increased the strength and hardness of the material through the strengthening effect of the second phase. The yield strength of the material is 697 MPa, the tensile strength is 905 MPa, and the hardness is up to 294 HB after aging at 500 °C for 5 h. However, the large-sized κ-carbides precipitating continuously at the grain boundary are unfavorable to the plasticity and toughness of the material. Compared with the aging treatment at 300 °C for 5 h, the elongation and low-temperature impact energy decreased by 12.0% and 47.1%, respectively. Except for the dominant wear mechanism being plastic deformation after heat treatment at 500 °C for 5 h with a 4J impact energy, the predominant wear mechanisms for different impact energies under all other heat treatment conditions are micro-cutting. The increase in aging temperature increases the number and volume of κ-carbide precipitation, which leads to enhanced second-phase strengthening and dislocation strengthening, and the wear resistance of the material is improved. The hardening mechanism of the material after wear at different impact energy levels under aging treatment conditions is a cross-distributed dislocation wall and high-density dislocation entanglement. The increase in aging temperature reduces the spacing of the dislocation wall, increases the area and density of dislocation entanglement, and enhances the work-hardening effect. Full article

In this work, the Mg-8Li-3Al-0.3Si (LAS830) alloy was prepared by the vacuum melting method. The as-cast alloy was subjected to backward extrusion at 250 °C and then spun at 250 °C. The microstructure and mechanical properties of the alloy during deformation were studied. The results showed that the LAS830 alloy primarily consisted of α-Mg and β-Li phases, and the AlLi, MgLi₂Al, and Mg₂Si phases were dispersed. After backward extrusion, the grains and AlLi phase were refined, the β-Li phase recrystallized, and the fine MgLi₂Al phase precipitated. The spinning of the extruded alloy tubes resulted in the lamellar distribution of an α/β duplex microstructure, with even finer grains and more dispersed precipitates. The combined deformation significantly enhanced the alloy’s strength and ductility, with the ultimate tensile strength reaching 235.4 MPa and an elongation of 15.74%. In addition, the average hardness of the α/β phase increases after backward extrusion, but the average hardness of the β-Li phase increases further after spinning. The as-cast LAS830 alloy exhibited a high work hardening rate but a low softening rate. With reverse extrusion, the work hardening rate decreased and the softening degree increased. Compared with backward extrusion, the work hardening rate and softening degree of the LAS830 alloy was reduced after spinning due to the combined effect of the lamellar distributed duplex microstructure and the dispersed second phases in the alloy, while its softening rate increased. Full article