Remarkable Enhanced Mechanical Properties of TiAlCrNbV Medium-Entropy Alloy with Zr Additions

Most medium entropy alloys (MEAs) exhibit excellent mechanical properties, but their applications are limited because of their high density. This study explores a series of lightweight nonequiatomic Ti₆₅(AlCrNbV)_35-xZr_x (x = 3, 5, 7, and 10) MEAs with a low density, high strength, and high ductility. To achieve solid solution strengthening, Zr with a large atomic radius was used. In addition, various thermomechanical treatment parameters were adopted to further improve the MEAs’ mechanical properties. The density of the MEAs was revealed to be approximately 5 g/cm³, indicating that they were lightweight. Through an X-ray diffraction analysis, the MEAs were revealed to have a single body-centered cubic structure not only in the as-cast state but also after thermomechanical treatment. In terms of mechanical properties, all the as-cast MEAs with Zr additions achieved excellent performance (>1000 MPa tensile yield strength and 20% tensile ductility). In addition, hot rolling effectively eliminated the defects of the MEAs; under a given yield strength, hot-rolled MEAs exhibited superior ductility relative to non-hot-rolled MEAs. Overall, the Ti₆₅(AlCrNbV)₂₈Zr₇ MEAs exhibited an optimum combination of mechanical properties (yield strength > 1200 MPa, plastic strain > 15%) after undergoing hot rolling 50%, cold rolling 70%, and rapid annealing for 30 to 50 s (at a temperature of approximately 850 °C) with a heating rate of 15 K/s. With their extremely high specific yield strength (264 MPa·g/cm³) and high ductility (22%), the Ti₆₅(AlCrNbV)₂₈Zr₇ MEAs demonstrate considerable potential for energy and transportation applications.     

Microstructure and Mechanical Properties of Novel Lightweight TaNbVTi-Based Refractory High Entropy Alloys

A series of novel lightweight TaNbVTi-based refractory high entropy alloys (RHEA) were fabricated through ball-milling and spark plasma sintering (SPS). The reinforced phase of TiO precipitates were in-situ formed due to the introduction of Al₂O₃ ceramic particles. The RHEA with 15% Al₂O₃ exhibits a high compressive yield strength (1837 MPa) and a low density (7.75 g/cm³) with an adequate ductility retention. The yield strength and density are 32% higher and 15% lower, respectively, compared to the RHEA without Al₂O₃ addition. The specific yield strength (237 MPa cm³/g) of the RHEAs is much higher than that of other reported RHEAs, and is mainly ascribed to the introduction of high volume fraction of Al₂O₃ additives, resulting in solid solution strengthening and precipitation strengthening. Meanwhile, the ductile matrix is responsible for the good compressive plasticity.     

Structure,Properties, and Corrosion Behavior of Ti-Rich TiZrNbTa Medium-Entropy Alloys with β+α″+α′ for Biomedical Application

Five Ti-rich β+α″+α′ Ti–Zr–Nb–Ta biomedical medium-entropy alloys with excellent mechanical properties and corrosion resistance were developed by considering thermodynamic parameters and using the valence electron concentration formula. The results of this study demonstrated that the traditional valence electron concentration formula for predicting phases is not entirely applicable to medium-entropy alloys. All solution-treated samples with homogeneous compositions were obtained at a low temperature (900 °C) and within a short period (20 min). All solution-treated samples exhibited low elastic moduli ranging from 49 to 57 GPa, which were significantly lower than those of high-entropy alloys with β phase. Solution-treated Ti₆₅–Zr₂₉–Nb₃–Ta₃ exhibited an ultra-high bending strength (1102 MPa), an elastic recovery angle (>30°), and an ultra-low elastic modulus (49 GPa), which are attributed to its α″ volume fraction as high as more than 60%. The pitting potentials of all samples were higher than 1.8 V, and their corrosion current densities were lower than 10^–5 A/cm³ in artificially simulated body fluid at 37 °C. The surface oxide layers on Ti₆₅–Zr₂₉–Nb₃–Ta₃ comprised TiO₂, ZrO₂, Nb₂O₅, and Ta₂O₅ (as discovered through X-ray photoelectron spectroscopy) and provided the alloy with excellent corrosion and pitting resistance.     

Tailoring Compressive Strength and Absorption Energy of Lightweight Multi-Phase AlCuSiFeX (X = Cr,Mn, Zn,Sn) High-Entropy Alloys Processed via Powder Metallurgy

The development of lightweight HEAs with high strength and low cost is an urgent requirement. In this study, equimolar AlCuSiFeX (X = Cr, Mn, Zn, Sn) lightweight HEAs were fabricated by advanced powder metallurgy. The mechanical alloying was performed for 45 h, and the powder compacts were densified at 650 °C. The final results revealed that AlCuSiFeSn lightweight HEA was composed of a single face-centered cubic (FCC) and Cu₈₁Sn₂₂, whereas AlCuSiFeZn showed a dual FCC and body-centered cubic (BCC) structures. Similarly, AlCuSiFeMn alloy contained a BCC + FCC phase with a µ-phase, whereas a σ-phase was present in AlCuSiFeCr in addition to FCC + BCC phases. We also calculated various thermodynamic parameters to predict the solid-solution phase stability of each of the above lightweight HEAs. It was found that lightweight HEAs with additive elements Sn and Zn tend to predominant FCC phases, whereas those with Cr and Mn result in major BCC with hard µ and σ phases, which further improve their mechanical strength. A maximum fracture strain of 23% was obtained for AlCuSiFeSn followed by 19% for AlCuSiFeZn HEA. The compressive fracture mechanisms of these lightweight HEAs are also discussed and reported here.     

Computer Alloy Design of Ti Modified Al-Si-Mg-Sr Casting Alloys for Achieving Simultaneous Enhancement in Strength and Ductility

In this paper, an efficient design of a Ti-modified Al-Si-Mg-Sr casting alloy with simultaneously enhanced strength and ductility was achieved by integrating computational thermodynamics, machine learning, and key experiments within the Bayesian optimization framework. Firstly, a self-consistent Al-Si-Mg-Sr-Ti quinary thermodynamic database was established by the calculation of phase diagram method and verified by key experiments. Based on the established thermodynamic database, a high-throughput Scheil-Gulliver solidification simulation of the A356-0.005Sr alloy with different Ti contents was carried out to establish the “composition-microstructure” quantitative relationship of the alloy. Then, by combining the computational thermodynamic, machine learning, and experimental data within the Bayesian optimization framework, the relationship “composition/processing-microstructure-properties” of A356-0.005Sr with different Ti contents was constructed and validated by the key experiments. Furthermore, the optimum alloy composition of the Ti-modified A356-0.005Sr casting alloy was designed based on this integration method with the Bayesian optimization framework and verified by the experiments. It is anticipated that the present integration method may serve as a general one for the efficient design of casting alloys, especially in the high-dimensional composition space.     

A Lightweight AlTiVNb High-Entropy Alloy Film with High Strength-Ductility Synergy and Corrosion Resistance

The simultaneous improvement of mechanical and corrosion resistance is of great significance for engineering applications. In this work, a novel lightweight amorphous structure AlTiVNb high-entropy alloy (HEA) film was fabricated by magnetron sputtering. The compression test of the AlTiVNb HEA film nanopillar exhibits a high compressive strength of up to 3.6 GPa and deformability approaching 58%. The high strength is affected by the disordered state, the nanostructure, and the lattice distortion effect, while the high ductility comes from the ductile shear band and the island structure. In addition, the AlTiVNb HEA film shows a current density of 4.90 × 10⁻⁸ A/cm² and a potential of −0.234 V in the 3.5% NaCl solution, comparable to that of the 316L stainless steel. The chemical disorder state, cocktail effect, and homogeneous amorphous structure contribute to excellent corrosion resistance. This finding offers new insights into high-performance HEA films with robust mechanical and anticorrosion performances for microelectronic devices and mechanical metamaterials.     

Achieving Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nb Alloys with High Strength and Moderate Ductility through Selective Laser Melting

Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nb (TA32) titanium alloy is a kind of near α high temperature titanium alloy with great application prospects in aero-engine afterburners and cruise missiles. However, there are still few studies on the microstructure and mechanical properties of TA32 specimens produced by selective laser melting (SLM) technology. In this study, TA32 specimens with high strength (tensile strength of 1267 MPa) and moderate ductility (elongation after fracture of 8%) were obtained by selective laser melting. The effect of laser power on the microstructure and mechanical behavior was studied and the results demonstrated that the average grain size increases with increasing laser power from 200 W to 400 W. Micro-zone composition analysis was carried out by energy dispersion spectrum (EDS), showing that the Al concentration inner grains is higher than that near grain boundaries. Fracture analysis results demonstrated that the fracture mode of SLM TA32 specimens was cleavage fracture. The tensile strength of the specimens built with a laser power of 250 W at 500 °C, 550 °C and 600 °C was measured as 869 MPa, 819 MPa and 712 MPa, respectively.     

Fabrication,Structure, and Thermal Properties of Mg–Cu Alloys as High Temperature PCM for Thermal Energy Storage

This work studied the thermophysical properties of Mg-24%Cu, Mg-31%Cu, and Mg-45%Cu (wt.%) alloys to comprehensively consider the possibility of using them as thermal energy storage (TES) phase change materials (PCMs) used at high temperatures. The microstructure, phase composition, phase change temperatures, and enthalpy of these alloys were investigated by an electron probe micro analyzer (EPMA), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The XRD and EPMA results indicated that the binary eutectic phase composed of α-Mg and Mg₂Cu exists in the microstructure of the prepared Mg–Cu series alloys. The microstructure of Mg-24%Cu and Mg-31%Cu is composed of α-Mg matrix and binary eutectic phases, and Mg-45%Cu is composed of primary Mg₂Cu and binary eutectic phases. The number of eutectic phases is largest in Mg-31%Cu alloy. The DSC curves indicated that the onset melting temperature of Mg-24%Cu, Mg-31%Cu, and Mg-45%Cu alloys were 485, 486, and 485 °C, and the melting enthalpies were 152, 215, and 91 J/g. Thermal expansion and thermal conductivity were also determined, revealing that the Mg–Cu alloys had a low linear thermal expansion coefficient and high thermal conductivity with respect to increasing temperatures. In conclusion, the thermal properties demonstrated that the Mg–Cu alloys can be considered as a potential PCM for TES.     

Development of Precipitation-Strengthened Al0.8NbTiVM (M = Co,Ni) Light-Weight Refractory High-Entropy Alloys

Single-phase solid-solution refractory high-entropy alloys (RHEAs) have been receiving significant attention due to their excellent mechanical properties and phase stability at elevated temperatures. Recently, many studies have been reported regarding the precipitation-enhanced alloy design strategy to further improve the mechanical properties of RHEAs at elevated temperatures. In this study, we attempted to develop precipitation-hardened light-weight RHEAs via addition of Ni or Co into Al_0.8NbTiV HEA. The added elements were selected due to their smaller atomic radius and larger mixing enthalpy, which is known to stimulate the formation of precipitates. The addition of the Ni or Co leads to the formation of the sigma precipitates with homogeneous distribution. The formation and homogeneous distribution of sigma particles plays a critical role in improvement of yield strength. Furthermore, the Al_0.8NbTiVM_0.2 (M = Co, Ni) HEAs show excellent specific yield strength compared to single-phase AlNbTiV and NbTiVZr RHEA alloys and conventional Ni-based superalloy (Inconel 718) at elevated temperatures.     

Modulation of Multiple Precipitates for High Strength and Ductility in Al-Cu-Mn Alloy

The category and morphology of precipitates are essential factors in determining the mechanical behaviors of aluminum alloys. It is a great challenge to synthetically modulate multiple precipitates to simultaneously improve strength and ductility. In the present work, by optimizing the precipitations of the GP zone, θ’-approximant and θ’ phase for an Al-Cu-Mn alloy, a high tensile strength of 585 MPa with large elongation of 12.35% was achieved through pre-deformation and aging. The microstructure evolution pattern was revealed by detailed characterizations of scanning electron microscopy and transmission electron microscopy. It was found that such high tensile strength of the samples was due to a combination of strengthening by the high density of dispersive fine precipitates and dislocations, and the high elongation to failure was primarily attributed to the multimodal precipitates and elimination of precipitation-free zones along the grain boundaries. The strategy proposed here is a promising way of preparing ultra-strong Al-Cu-Mn alloys.     

Recent Progress on Regulating Strategies for the Strengthening and Toughening of High-Strength Aluminum Alloys

Due to their high strength, high toughness, and corrosion resistance, high-strength aluminum alloys have attracted great scientific and technological attention in the fields of aerospace, navigation, high-speed railways, and automobiles. However, the fracture toughness and impact toughness of high-strength aluminum alloys decrease when their strength increases. In order to solve the above contradiction, there are currently three main control strategies: adjusting the alloying elements, developing new heat treatment processes, and using different deformation methods. This paper first analyzes the existing problems in the preparation of high-strength aluminum alloys, summarizes the strengthening and toughening mechanisms in high-strength aluminum alloys, and analyzes the feasibility of matching high-strength aluminum alloys in strength and toughness. Then, this paper summarizes the research progress towards adjusting the technology of high-strength aluminum alloys based on theoretical analysis and experimental verification, including the adjustment of process parameters and the resulting mechanical properties, as well as new ideas for research on high-strength aluminum alloys. Finally, the main unsolved problems, challenges, and future research directions for the strengthening and toughening of high-strength aluminum alloys are systematically emphasized. It is expected that this work could provide feasible new ideas for the development of high-strength and high-toughness aluminum alloys with high reliability and long service life.     

Development and Characterization of Lightweight Geopolymer Composite Reinforced with Hybrid Carbon and Steel Fibers

The aim of this paper is to analyze the influence of hybrid fiber reinforcement on the properties of a lightweight fly ash-based geopolymer. The matrix includes the ratio of fly ash and microspheres at 1:1. Carbon and steel fibers have been chosen due to their high mechanical properties as reinforcement. Short steel fibers (SFs) and/or carbon fibers (CFs) were used as reinforcement in the following proportions: 2.0% wt. CFs, 1.5% wt. CFs and 0.5% wt. SFs, 1.0% wt. CFs and 1.0% wt. SFs, 0.5% wt. CFs and 1.5% wt. SFs and 2.0% wt. SFs. Hybrid reinforcement of geopolymer composites was used to obtain optimal strength properties, i.e., compressive strength due to steel fiber and bending strength due to carbon fibers. Additionally, reference samples consisting of the geopolymer matrix material itself. After the production of geopolymer composites, their density was examined, and the structure (using scanning electron microscopy) and mechanical properties (i.e., bending and compressive strength) in relation to the type and amount of reinforcement. In addition, to determine the thermal insulation properties of the geopolymer matrix, its thermal conductivity coefficient was determined. The results show that the addition of fiber improved compressive and bending strength. The best compressive strength is obtained for a steel fiber-reinforced composite (2.0% wt.). The best bending strength is obtained for the hybrid reinforced composite: 1.5% wt. CFs and 0.5% wt. SFs. The geopolymer composite is characterized by low thermal conductivity (0.18–0.22 W/m ∙ K) at low density (0.89–0.93 g/cm³).     

The Effect of Hf Addition on the Boronizing and Siliciding Behavior of CoCrFeNi High Entropy Alloys

The effect of a boronizing and siliciding process on CoCrFeNiHf_0.1–0.42 high entropy alloys was examined in this study. When increasing the amount of added Hf in CoCrFeNiHf_x, the structure of the alloys gradually transformed from single-phase FCC to firstly Ni₇Hf₂ + FCC, and finally to C15 Laves and FCC phases. The boronizing/siliciding process resulted in the formation of a silicon-rich layer and a boride layer (BL). Increasing the amount of Hf in the alloys resulted in a decrease in the combined layer thickness, which was measured for CoCrFeNi, CoCrFeNiHf_0.1, CoCrFeNiHf_0.2, and CoCrFeNiHf_0.42 to be 70 µm, 63 µm, 20 µm, and 15 µm, respectively. In contrast, the thickness of the transition zone/diffusion zone increased with more Hf in the alloys. While silicon atoms were gathered close to the BL, they were not transferred into the CoCrFeNi substrate. In contrast to the observation for CoCrFeNi, Si atoms penetrated through the Ni-rich phase (Ni₇Hf₂) in the CoCrFeNiHf_x alloys. Furthermore, the Cr-B rich area (Cr₅B₃) in the coating limited the transport of Si into the CoCrFeNiHf_x substrates. XRD analysis showed that the BL contained Ni₂Si, FeB, Fe₂B, Co₂B, and Cr₅B₃ phases.     

Preparation and Physico-Chemical Performance Optimization of Sintering-Free Lightweight Aggregates with High Proportions of Red Mud

Sintering-free lightweight aggregates were prepared with high proportions of red mud and a binder material derived from whole solid wastes through rolling granulation at room temperature. The preparation process was optimized by changing the material matching and size parameters of the SFLAs. The physico-chemical performance, including the density, mechanical strength, water absorption, hydration products, heavy metal leaching, and microstructure were evaluated by jointly employing X-ray Fluorescence, X-ray Diffraction, and Inductively Coupled Plasma Optical Emission Spectrometry, Shadow Electron Microscope, etc. The results indicated that the red mud and waste-based binders were highly compatible in the granulation process, with up to 80% red mud being successfully added. The sintering-free lightweight aggregates products at the binder content of 30% and the size coverage of 10–16 mm exhibited a bulk density of 900–1000 kg·m⁻³, a 28 d cylinder compressive strength of 9.2–11.3 MPa, and water absorption of less than 10%. Owing to the formation of important hydration products, ettringite, the heavy metal leaching of the sintering-free lightweight aggregates was also proven to be environmentally acceptable. This work provides a promising pathway to prepare low-cost, high-strength, and green lightweight aggregates through the large-scale utilization of solid waste red mud.     

Concurrence of High Corrosion Resistance and Strength with Excellent Ductility in Ultrafine-Grained Mg-3Y Alloy

In the field of magnesium-based degradable implantable devices, the Mg-Y-RE-Zr alloying system (WE-type) has gained popularity due to its satisfying degradation rate together with mechanical strength. However, utilization of RE and Zr in the WE-type alloys was originally driven to improve Mg-based alloys for high-temperature applications in the industry, while for medical purposes, there is a question of whether the amount of alloying elements may be further optimized. For this reason, our paper presents the Mg-3Y (W3) magnesium alloy as an alternative to the WE43 alloy. This study shows that the omission of RE and Zr elements did not compromise the corrosion resistance and the degradation rate of the W3 alloy when compared with the WE43 alloy; appropriate biocompatibility was preserved as well. It was shown that the decrease in the mechanical strength caused by the omission of RE and Zr from the WE43 alloy could be compensated for by severe plastic deformation, as achieved in this study, by equal channel angular pressing. Ultrafine-grained W3 alloy exhibited compression yield strength of 362 ± 6 MPa and plastic deformation at maximum stress of 18 ± 1%. Overall, the early results of this study put forward the motion of avoiding RE elements and Zr in magnesium alloy as a suitable material for biodegradable applications and showed that solo alloying of yttrium is sufficient for maintaining desirable properties of the material at once.     

Effect of Heat Treatments on the Corrosion Resistance of a High Strength Mg-Gd-Y-Zn-Zr Alloy

Magnesium-rare earth (Mg-Re) alloys are very promising structural materials in lightweight industries, while the poor corrosion resistance limits their widespread application. In this work, to provide insights into the functions of precipitate characteristics on the corrosion behaviors of Mg-Re alloys, the influence of heat treatments on the corrosion behavior of Mg-11.46Gd-4.08Y-2.09Zn-0.56Zr alloy was investigated via an immersion test, electrochemical experiment and scanning electron microscope (SEM). The results showed that the corrosion rate of Mg-11.46Gd-4.08Y-2.09Zn-0.56Zr alloy specimens decreased by 17.58% and 20.44% after T5 and T6 heat treatment, respectively. In the heat-treated specimens, the corrosion did not extend further into the matrix but formed fine corrosion grooves along the extrusion direction. The improved homogeneity reduced the residual stress and the β’ precipitate introduced as a corrosion barrier after T5 and T6 heat treatment reduced the corrosion rate of the studied Mg alloy. In addition, the volume fraction of the long-period stacking-ordered (LPSO) phase decreased after heat treatment, which effectively reduced galvanic corrosion and enhanced the protective effect on the Mg matrix.     

Influence of High Temperature Curing and Surface Humidity on the Tensile Strength of UHPC

The objective of this study is an investigation of the different parameters that influence the tensile strength of ultra-high performance concrete (UHPC). Apart from the shrinkage and stiffness, the tensile strength is an important parameter for the design of crack-free concrete elements, e.g., in machine tool construction. One focus of our work is the influence of concrete curing and the great impact of the mechanical and physical characteristics of hydrated UHPC. For this reason, different curing regimes were investigated. The results show that even after heat treatment or autoclaving, the centric tensile strength of UHPC specimens is strongly influenced by the surrounding ambient humidity. Test specimens that were stored under water after a heat treatment or autoclaving and were still wet during the test had the highest tensile strengths. Storage at 20 °C and 65% relative humidity (rH), however, results in a 25% reduction in tensile strength. Alternating storage between water storage at 20 °C water and storage at 65% rH can also reduce the tensile strength dramatically by up to 70%. In particular, samples that were stored at 65% rH right before testing had very low tensile strengths. Surprisingly, the initially low tensile strength of previously dry stored UHPC can be restored by subsequent water storage. In the absence of any microstructural defects, e.g., microcracks, a possible explanation for this phenomenon can be the stress differences due to a humidity gradient between the core and surfaces and shrinkage combined with a continued reaction of the unhydrated binders of the UHPC.     

Formation of Nanoscale Al2O3 Protective Layer by Preheating Treatment for Improving Corrosion Resistance of Dilute Fe-Al Alloys

In this work, an attempt was made to improve the corrosion resistance of dilute Fe-Al alloys (1.0 mass% Al) by preheating treatment at 1073 K in H₂ atmosphere. In comparison with pure Fe and unpreheated Fe-Al alloys, the resistance to oxidation at 673 K in pure O₂ and to electrochemical corrosion in 5 wt.% NaCl solution is significantly improved for preheated Fe-Al alloys. This improvement is attributed to the formation of a 20 nm thin, but dense Al₂O₃ protective layer on the surface of preheated Fe-Al alloys.     

Effects of Aging Process on the Damping Performance of ZK60 Magnesium Alloys Prepared by Large Strain Rolling

In this study, the effects of an aging treatment (T5) and a solution + aging treatment (T6) on the microstructure and damping properties of a ZK60 magnesium alloy prepared by large strain rolling (LSR) were studied by an optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and dynamic thermomechanical analysis (DMA). The results showed that both the T5 and T6 processes had a great impact on the microstructure and damping properties of the ZK60 magnesium alloy. With the increase in aging time, the grain size was basically unchanged, and the amount of the second phase increased, resulting in a gradual decrease in the damping performance. However, compared with the damping performance of the un-aged ZK60 magnesium alloy, the damping performance of the 4 h-aged ZK60 magnesium alloy was enhanced. At the same aging time, the increase in the aging temperature promoted the precipitation of the second phase, thereby reducing the damping performance of the ZK60 magnesium alloy. It was found that the T6-treated ZK60 magnesium alloy had a larger grain size, which led to a better damping performance; in addition, the T6-treated ZK60 magnesium alloy exhibited a damping plateau, which was determined by the distribution and amount of the second phase.