Search

In recent years, more attention to unique and complex structures, such as nature-inspired and porous structures for medical applications, has been strongly developed. Open-cell porous metal-based ones display more benefits than rigid ones since they facilitate the transformation of load between the bone and the implants and avoid the phenomenon of stress shielding and bone resorption. By being biodegradable and non-toxic, as well as having lower density and mechanical properties close to those of natural bone, Mg and its alloys are considered promising materials for porous scaffolds. However, a high corrosion rate is the main drawback of Mg alloys. The porosity of porous structures can also worsen it as it enhances the surface area exposed to the corrosive solution and negatively impacts the performance of porous structures, that these issues have not been addressed in detail so far. Since fabrication methods of Mg-based scaffolds can significantly affect the porosity-related properties (e.g., porosity percentage, type, size, and geometry) and, consequently, scaffolds' mechanical behavior and corrosion resistance, this paper reviews and compares the fabrication methods of porous structures and how they affect the resultant properties. However, among different methods, due to the expansion of additive manufacturing as a novel and exciting manufacturing technique, the paper's central focus is on using additive manufacturing in biomedical applications, discussing its advantages over other techniques. The effect of geometrical parameters on mechanical properties and corrosion rate, which strongly affects bio-application, are also given. Moreover, different strategies are briefly introduced for tailoring the high corrosion rate of Mg and its alloys, such as alloying elements and coatings. However, there is still less information regarding the additive manufacturing of porous Mg scaffolds and the optimum way of controlling the corrosion rate of Mg-based parts. [ABSTRACT FROM AUTHOR]

A cross-scale analysis method for predicting the compressive mechanical properties of tin-based bearing alloy was proposed based on microstructure finite element simulation and molecular dynamics (MD) simulation. The actual metallographic microstructure of tin-based bearing alloy taken by optical microscopy was utilized to construct the representative volume element (RVE) model for the computational modeling. The compression stress–strain curves of β-Sn and Cu6Sn5 obtained by MD simulation were used as the input material property parameters of each constituent phase in RVE model for the microstructure finite element analysis. The compression simulation was carried out for the tin-based bearing alloy with the microstructure containing Sn matrix and Cu6Sn5 phase. The results show that the simulation analysis method can predict the compression strength and elasticity of the studied tin-based bearing alloy well by comparing the simulated results with the experimentally obtained data. It is hoped that this paper can provide a simulation method for realizing the prediction of the mechanical properties based on microstructure and revealing the microscope mechanism of materials, thus providing theoretical guidance for the micro-design of high-performance tin-based bearing alloy. [ABSTRACT FROM AUTHOR]

Ductility dip cracking (DDC) is a solid-state failure occurring during multi-pass solidification processes (e.g., welding, additive manufacturing) for FCC alloys that exhibit a distinct dip in their ductility at intermediate temperatures. While the phenomenon has been studied for over a century, the majority of current research focuses on a subset of DDC-susceptible FCC alloys (Ni–Cr–Fe). The review paper herein presents an analysis of published data to evaluate the current state of understanding regarding the materials mechanisms at work. Recent advances in test methods have permitted highly controlled approaches for testing and quantifying DDC, but the wide range of unique tests often provide conflicting results regarding the fundamental materials behaviors and underlying mechanisms. At present, three mechanisms have been proposed for DDC: grain boundary sliding, precipitate-induced strain, and impurity element segregation. While the majority of published studies support grain boundary sliding as the primary mechanism of DDC, an examination of the aggregate data available across multiple studies suggests combinatorial impact of simultaneous (and competing) mechanisms for DDC. Further, the long-held assumptions regarding the negative impact of key alloying elements become less convincing when comparing results across studies. There are considerable future opportunities for research on DDC behaviors in other alloy systems, and there are a lacunae of data when considering the effect of welding process parameters on DDC and the use of modeling and simulation approaches to understand the DDC behavior in the highly susceptible FCC alloy systems. [ABSTRACT FROM AUTHOR]

The ordered γ′-(Ni, Cu)3Al is a crucial strengthening phase that improves the high-temperature resistance of Cu-based alloys, so it is important to predict the kinetic evolution of the composition and microstructure of the phase for high-temperature applications. Herein, this paper discusses the temporal evolution of the composition and coarsening of the γ′ phase in a model ternary Cu50Ni37.5Al12.5 (at%) alloy during isothermal aging at 600, 700, 800, and 900 °C for 1–36 h. It is found that the γ′ phase composition evolves linearly toward a binary γ′ phase as the aging time increases during the process of aging at 800 and 900 °C, which cannot be predicted by the ternary phase diagrams alone. Meanwhile, through the utilization of the aforementioned linear law, the γ phase composition can be predicted at a given temperature within the alloy by determining the volume fraction of the γ′ phase. Additionally, the activation energy for coarsening decreases, and the coarsening rate of the γ′ phase increases owing to the higher diffusion rate of Cu at high temperatures. The addition of microalloying elements with strong enthalpic interactions is beneficial for reinforcing the structural stability of the γ′ phase. This work provides a simple method for the compositional analysis and performance prediction of Cu–Ni–Al alloys at elevated temperatures and sheds light on the subsequent compositional design and optimization of Cu-based high-temperature alloys. [ABSTRACT FROM AUTHOR]

The alloy composition and sensitization behavior are crucial factors that cannot be overlooked in Al–Mg alloys. The effect of Zn addition on mechanical properties and sensitization behavior of 5083 alloy was investigated by tensile tests, weight loss experiments, and first-principles calculation in this paper. The results show that Zn can significantly improve the strength and sensitization behavior of the alloy. The tensile strength of the cold-rolled alloy increased from 459 to 498 MPa with the addition of 1.5%Zn. Furthermore, by incorporating 2.0% Zn, the mass loss of the cold-rolled alloy after sensitization at 170℃/1 h decreased from 49.3 mg·cm−2 to 19.5 mg·cm−2. First-principles calculations indicate that Mg clusters can only exist stably near grain boundaries, while Mg–Zn clusters can exist stably both within and at grain boundaries. This reduces the number of corrosive media at grain boundaries and weakens their continuity. Moreover, the energy barrier that T-phase precipitation needs to overcome during precipitation is lower than β-phase, which transforms the stabilization schedule of the alloy from 240℃/12 h without Zn to that 210℃/4 h with 2.0% Zn-containing. The synergistic effects of Zn content and sensitization on the properties of the alloy were revealed, which sheds some light for the design of the composition and processing method according to application scenarios. [ABSTRACT FROM AUTHOR]

AA6101 Al alloy is widely used as a high-strength conductive aluminum alloy, and the contents and existence of Mg and Si can influence its electrical conductivity and mechanical properties obviously. In this paper, experiments were conducted to find the optimal Mg, Si additions and Mg/Si ratio and then combined with heat treatment to improve the EC and mechanical properties at the same time. Firstly, considering the proper Mg/Si ratio, two optimal Mg and Si additions were determined: Al–0.7Mg–0.5Si and Al–0.4Mg–0.7Si with EC of 51.5%IACS and 51.4%IACS, and through homogenization treatment, their EC improved to 57.0%IACS and 55.7%IACS, respectively. Then, appropriate Fe was added to further control Si to achieve the balance of EC and mechanical properties. Results showed that for AA6101 Al alloy the ideal Mg/Si mass ratio was 1.4 and high Mg and low Si can obtain good EC and mechanical properties. Besides, it can be found that at low Mg/Si ratio, the alloy conductivity takes longer to reach its peak hardness. So the best performance Al–0.7Mg–0.5Si–0.2Fe alloy was obtained within the range of AA6101 national standard. The EC of Al–0.7Mg–0.5Si–0.2Fe can reach 56.3%IACS, and hardness is 91.3 Hv. Based on the study, a schematic diagram was drawn to analyze the influence mechanisms of Mg, Si and Fe on EC and hardness of AA6101 Al alloy. [ABSTRACT FROM AUTHOR]

In this paper, perfect interface model of Al/AlCu alloy and defect interface model of Al/AlCu alloy after cracks were introduced at different positions of the interface were established by using cohesive zone modeling method. Classical molecular dynamics simulation was used to study the deformation behavior and microstructure evolution of Al/AlCu alloy interface model at a strain rate of 0.05 Å/ps and the temperature of 300 K. The simulation results show that perfect interface exhibits a uniform plastic deformation stage due to structural relaxation after yielding, while there is no structural relaxation during the deformation of defect interface and the tensile strength is much lower than that of perfect interface as well. In the process of deformation, stacking faults formed in perfect interface and cracks are generated and expanded in Al matrix, while there was no stacking faults forming along with the expansion and cracking at the position of introduced cracks in defect interface. Massive dislocation nucleation leads to the reduction in stress at the perfect and defect interfaces after yielding. The extension of Shockley partial dislocation and the nucleation of Stair-rod dislocation are the main mechanisms of interface deformation. Densities of Shockley partial dislocation and Stair-rod dislocation decrease with increasing strain before crack propagation. This study enriches the analysis of microstructure evolution of Al/AlCu alloy interface and similar interfaces during deformation. [ABSTRACT FROM AUTHOR]

In this paper, the effect of deep cryogenic treatment (DCT) on the microstructure and properties of automotive 6063 aluminum alloy at different times was investigated with automotive 6063 aluminum alloy as the research object. The results show that under the conditions of deep cryogenic treatment, the lattice distortion occurs in the alloy matrix microstructure, and the resulting internal stress promotes the large proliferation of dislocations within the alloy and the increase of dislocation density; meanwhile, after the deep cryogenic treatment, the deformed grains are transformed into recrystallized and sub-crystals structural grains, the grains are refined, and the size of the grains is refined from the original 25.2 μm to 20.3 μm, with fine equiaxed crystals. Among them, the mechanical properties of the DCT36h specimen were the best, and its hardness, tensile strength, yield strength and elongation reached 142.44 HV, 328.32 MPa, 177.42 MPa, and 29.29%, which were 34.17%, 5.62%, 11.10%, and 32.77% higher than the original sample, respectively. We believe that the main mechanism for the increase in toughness is multiple reinforcement such as dislocation strengthening, grain refinement strengthening, precipitated phase strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]

High frequency fatigue behavior of near surface of turbine disk are critical for its application and operation. High frequency indentation fatigue tests of GH4169 alloy under different load amplitudes, frequencies and mean loads at small length scale were conducted, and the dependence of load amplitude, load frequency and mean load on high frequency indentation fatigue property of GH4169 alloy are discussed in this paper. Depth amplitude (ha), mean depth (hm) and depth propagation rate (dh/dN) were employed as evaluation indicators of the indentation behavior. Results show that depth amplitude is only relevant with load amplitude, while mean depth is related to all the adopted influencing factors, ranked in an ascending order as load amplitude, mean load and frequency with a ranking relation of nm1=1.4 < nm2=1.71 < nm3=2.02. Furthermore, a modified Paris law was utilized to reveal the fatigue mechanism, and found the fatigue mechanism is dominated by intrinsic mechanism under the influence of mean load and load amplitude, while for the influence of frequency, the fatigue mechanism is governed by extrinsic mechanisms. Combined with SEM results and three-dimensional morphology analysis, it can be deduced that dislocation movement mode in high frequency indentation fatigue is dislocation slip. [ABSTRACT FROM AUTHOR]

Flexible linear aqueous zinc-ion hybrid supercapacitors are considered as ideal materials for flexible and wearable electronic devices due to their advantages of safety, high flexibility and good wearable ability. Materials based on shape memory can satisfy the needs of fatigue resistance and deformation recovery, and have great advantages in the assembly of flexible wearable devices. In this paper, aqueous zinc-ion hybrid supercapacitor with shape-memory function was assembled by using PANI/NiTi shape-memory alloy wire as the cathode electrode and flexible zinc wire as the anode electrode. The device can be bent into different angles from 0° to 180°, after repeated bending for 200 times and heating to its deformation temperature, the original shape can still be restored, and the capacitance retention rate is up to 90%, with good mechanical resistance. By assembling with flexible zinc wire, the potential window can be expanded to 1.6 V, and the energy density has been greatly improved. Its energy density can reach 55.9 Wh kg−1 at 3 A g−1, which greatly improves its energy density and has great development potential in flexible and portable electronic devices. [ABSTRACT FROM AUTHOR]

Layered double hydroxide (LDH) films have attracted extensive attention in Mg alloy anti-corrosion due to their unique physical barrier function and ion exchange performance. However, most of the LDH films on Mg alloy have problems of harsh preparation conditions, poor anti-corrosion stability, and poor adhesion. In this paper, a typical Li–Al-alanine (Ala) LDH film has been successfully prepared on AZ91D Mg alloy surface under milder conditions using multi-arc ion plating and in-situ dipping for the first time. Then an improved vacuum impregnation further modified the Li–Al-Ala LDH film in an ethanol solution of stearic acid (SA) to improve its protective stability. The potentiodynamic polarization curves and electrochemical impedance spectra (EIS) showed that the Li–Al-Ala LDH/SA film's corrosion resistance is more than three orders of magnitude higher than that of the blank Mg alloy in 3.5 wt% NaCl, showing a highly increased corrosion resistance. The long-term immersion experiments found that the surface structure and corrosion resistance of the Li–Al-Ala LDH/SA film did not change much after immersion in 3.5 wt% NaCl for 432 h. The bonding force between the film and the Mg alloy substrate can reach grade 0 based on the standard from International Standardization Organization (ISO). And the hydrophobicity of the film can remain stable with the water contact angle (WCA) being steady at about 140° after a certain distance of external abrasion, showing excellent mechanical wear resistance. The study provides a new milder approach to fabricating superhydrophobic LDH films with durable anti-corrosion resistance, good adhesion, and mechanical stability on Mg alloy surface. [ABSTRACT FROM AUTHOR]

The CuZr-based bulk metallic glass matrix composites have attracted great attention in recent years owing to their unique mechanical properties compared to bulk glassy samples. The vital effect of B2 CuZr phase on mechanical properties was previously confirmed in CuZr-based alloys with equiatomic concentrations of copper and zirconium. In this paper, the structures and mechanical properties of the Cu45Zr48Al7 alloy, which has hypereutectoid composition with respect to stoichiometric B2 CuZr phase, were studied. This alloy exhibits high glass-forming ability, but low tendency to form the B2 CuZr phase during solidification. However, we demonstrated that depending on the cooling rate during solidification, governed by sample diameter, either bulk metallic glass or bulk metallic glass matrix composite can be produced. In order to allow partial crystallization of the B2 phase during solidification with the volume fraction allowing to observe the strain hardening effect, the minimum cooling rate should be lower than 40 K/s. The composite consisting of a glassy outer layer and a crystalline core composed of the B2 phase exhibits fracture strength of the same level as the bulk glassy sample (above 1800 MPa) obvious work-hardening with a plastic deformation of about 6%. [ABSTRACT FROM AUTHOR]

This paper focuses on finding an optimum composition for the TiTaHfNbZr quinary high entropy alloy (HEA) system with an elastic modulus close to that of bone in order to attain a better biomechanical compatibility between the bone and the implant in orthopedic applications. To obtain the composition providing the desired structural match, machine learning (ML) tools were implemented in the current work instead of conventional trial-and-error methods. The ML algorithms utilized in this study were trained using experimental data available in the literature and then utilized to predict the optimum HEA compositions with the lowest elastic moduli. Consequently, the Ti23Ta10Hf27Nb12Zr28 and Ti28Ta10Hf30Nb14Zr18 compositions were predicted as the optimum HEA compositions with elastic moduli of 83.5 ± 2.9 and 87.4 ± 2.2 GPa, respectively. The materials were manufactured, and the elastic moduli were validated with nanoindentation experiments. The samples were also exposed to static immersion experiments in simulated body fluid (SBF) for 28 days to gain insight and information regarding the ion release and ensure that the new HEAs are biocompatible. The findings of the work reported herein demonstrate that the proposed ML model can successfully predict HEA compositions for an optimized biomechanical compatibility for orthopedic applications and warrant further biomedical research on the two new HEAs prior to their utility as orthopedic implant materials. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to design an Al–Cu–Ag–C material system to address the deterioration of mechanical properties caused by intermetallic compounds generated during Al–Cu sintering. The in situ pyrolytic C layer was encapsulated on the surface of the raw material particles, which prevented Al–Cu diffusion and reduced the generation of intermetallic compounds. The microstructure of the Al–Cu–Ag–C composites illustrates that several alloy phases of Al2Cu, Al4Cu9, and Ag2Al are formed. The addition of Ag significantly improved the mechanical properties of the composite due to the formation of the Ag2Al phase and Cu–Ag solution. The tensile strength and compressive strength of Al–52Cu–3Ag–C are increased by 123.9% and 64.9% over Al–52Cu–C, and the strain is also considerably improved. The strength enhancement derived from the Orowan strengthening contributed by Ag2Al, and the solid solution strengthening contributed by Ag–Cu solid solution, respectively. The presence of Ag2Al also enhances the hardness of the composite. [ABSTRACT FROM AUTHOR]

TiAl alloy becomes a promising high-temperature structural material due to excellent mechanical properties at elevated temperature. However, the inherent brittleness makes it difficult to be processed by traditional technologies. Therefore, an innovative twin-wire plasma arc additive manufacturing (TW-PAAM) process is developed to fabricate TiAl alloy. Substrate heating is indispensable during additively manufactured TiAl alloy, which can alleviate its crack tendency. In this paper, crack-free TiAl alloy samples are fabricated using TW-PAAM, and the effect of substrate temperature (560, 620 and 680 °C) on as-deposited TiAl alloy is investigated in detail. With the increase in substrate temperature, microstructural lamellar spacing and colony size exhibit the tendency of increase. Also, α2 phase content, recrystallization degree and high Schmid factor frequency present the decrease tendency. These variations of microstructure characteristics further lead to the decrease in both microhardness and tensile properties of the deposit. These findings provide a valuable reference for optimizing microstructures and mechanical properties of additively manufactured TiAl alloys. [ABSTRACT FROM AUTHOR]

Aluminum–lithium alloys are widely used in aerospace due to their excellent comprehensive mechanical properties. The key to accelerate the composition design of aluminum–lithium alloys is to generate accurate precipitate structure models at the atomistic scale and quantify the effects of the secondary phase on the properties of the alloy. In this article, the development process of high-strength composition design of aluminum–lithium alloys is reviewed. The T1 phase is considered to provide the highest strength in Al-Cu-Li alloys, and we further discuss the characteristics of the crystal structure, orientation relationship and morphology of the main strengthening phase. Additionally, this paper highlights the atomic structure model, microstructure parameters of T1 phase and the precipitate–dislocation interaction relationships. Practically, the widely accepted atomic model of T1 phase characterized with a corrugated Al-Li layer at the interface remains controversial. Moreover, the strengthening mechanism of Al-Li alloy is discussed. Based on the shearing and bypassing interaction mechanism between the T1 precipitates and the matrix dislocations, some quantitative contribution models to the strength of Al-Cu-Li alloys are concluded. These models can effectively predict the variation of yield strength of Al-Cu-Li alloy, but the transition of T1 phase from shearing mechanism to bypassing mechanism is not considered. However, the T1 diameter threshold that activated this transition has not been completely determined, which need to be further studied by obtaining a wider range of T1 microstructures. [ABSTRACT FROM AUTHOR]

This paper reports atomistic simulation studies of tensile and compressive behavior of nanowires of a model quinary high entropy face-centered cubic (FCC) alloy. The simulations employ empirical interatomic potentials and use massively parallel molecular dynamics techniques at the atomistic level to study the deformation mechanisms. The studies consider pristine cylindrical nanowires oriented along various crystallographic directions. The focus is the role that local composition fluctuations in the random alloy plays in the deformation response. The deformation behavior observed for the complex random alloy is compared with a corresponding "average atom" material that has the same average properties but no local compositional fluctuations. In all cases, deformation is governed by dislocations emitted from the free surface. Twinning was also found, depending on the crystallographic orientation and loading mode. We show that for all orientations, the high entropy alloy (HEA) wires show the onset of plasticity at lower stress levels than the average atom material. However, after the onset of plasticity, the HEA presents a higher strength, mostly driven by the fact that the dislocations emitted from the surface do not glide as easily in the random alloy as they do in the average atom material. [ABSTRACT FROM AUTHOR]

NiTi alloy is considered to have great application potential in the fabrication of metal implant materials. However, the NiTi alloy still suffers from some disadvantages, such as poor corrosion resistance and health hazards caused by the release of nickel ions. In order to improve the corrosion resistance of NiTi alloy, a healing composite coating was prepared on NiTi alloys by micro-arc oxidation doped with ZnO nanoparticles and sol–gel sealing with polyacrylamide. The surface morphology, composition, roughness, thickness, and electrochemical performance of the prepared coating were investigated by SEM, EDS, Eddy current thickness gauge, electrochemical workstation, and so on. The adhesion of the prepared coating was also tested using the pull-off method. The results show that compared with NiTi alloy substrate, composite coating of MAO–ZnO@PAM has a dense microstructure, a flatter surface, the largest inner and interfacial charge transfer resistances, outstanding corrosion resistance, and possesses the self-healing ability under the humid condition. [ABSTRACT FROM AUTHOR]

The present study conducted a detailed investigation to determine the effects of adding Sc and applying low-frequency electromagnetic casting (LFEC) on the bendability and ductility of hot-rolled 7A36 alloy using optical microscopy, electron backscatter diffraction, and scanning electron microscopy by two different solid solution heating rate treatments. Results showed that the rapidly solid-solution-heated rates specimen (R specimen) exhibited several micro-cracks, while the slow solid-solution-heated rates specimen (S specimen) displayed visible cracks and even fractures. Additionally, increasing the solid solution heating rate resulted in a decreased diameter of the second phase but larger average grain size. The coarse second-phase grains of the alloys most likely lead to the formation of microcracks; however, the coarse recrystallized grains prevent the further propagation of bending cracks. The strap-like and finer recrystallized grains of the R specimen lead to an improved bendability of the 7A36 alloy by coordinating plastic deformation and accommodating more dislocations. Further, adding Sc improves the bendability and tensile properties by refining grain size and improves the texture strength, while applying LFEC slightly increases the average grain size and the recrystallizing degree, which result in a high Schmid factor value and lower texture strength, and dislocation density benefits the bendability and ductility of the 7A36 alloy with a little strength reduction. [ABSTRACT FROM AUTHOR]

The microstructure, compressive properties and in vitro degradation behavior of as-cast Mg alloys with high Zn or Ca content were investigated. The results showed that the addition of Ca (1 wt%) to Mg–5Zn or Zn (1 wt%) to Mg–5Ca changed the shape, distribution, volume fraction and the type of second phase. When 1 wt% Ca was added to Mg–5Zn alloy, the second phase changed from Mg7Zn3 to Ca2Mg6Zn3 phase and it was distributed from granular formation to a continuous network structure. While the second phase was changed from Mg2Ca in Mg–5Ca alloy to the coexistence of Mg2Ca(Zn) and slight Ca2Mg6Zn3 phase in Mg–5Ca–1Zn alloy. The second phase exhibited a continuous network distribution in both of Mg–5Ca and Mg–5Ca–1Zn alloys, but the width of Mg2Ca(Zn) phase was reduced obviously after adding 1 wt% Zn to Mg–5Ca alloy. The compressive test revealed that Zn element was contributed to the promotion of ultimate compressive strength and fracture elongation, while Ca element was beneficial for improving the yield strength of Mg alloys. The immersion test proved that the weight loss of Mg–5Zn–1Ca was the highest, followed by Mg–5Zn, Mg–5Ca and Mg–5Ca–1Zn alloy. The Mg–5Zn-based alloys suffered severe pitting, while Mg–5Ca-based alloy exhibited a relatively uniform corrosion. The Ca addition accelerated the corrosion of Mg–5Zn alloy due to the expansion of potential difference between second phase and Mg matrix, while Zn addition reduced the micro-galvanic corrosion of Mg–5Ca alloy due to the lowest potential difference between Mg2Ca(Zn) phase and Mg matrix. [ABSTRACT FROM AUTHOR]

To conquer the trade-off between strength and ductility, a new strategy for preparing heterostructured (HS) 2024Al alloys with various heterogeneity levels through introducing submicro-Al3Ti particles and adjusting partial remelting duration of powder thixoforming was proposed. The results indicate that the difference in volume fraction between soft and hard domains of the resultant HS alloys gradually decreases from 0.27 to 0.02, while that of microhardness also decreases from 1.58 to 1.17 GPa, i.e., the heterogeneity level gradually decreases with prolonging the remelting time. The excellent strength–ductility synergy is simultaneously achieved by a moderate heterogeneity level (the differences in microhardness of 1.23 GPa and volume fraction of 0.02) in the HS alloy thixoformed at the partial remelting time of 80 min. This is primarily ascribed to the largest strain gradient caused by the accumulation of the highest density dislocations at the boundary during deformation, which produces the highest heterodeformation-induced (HDI) strengthening and hardening. In addition, the dislocations emitted from the submicro-Al3Tip during the later deformation stage also improve the strain strengthening and hardening, further leading to the improvement in strength–ductility synergy. [ABSTRACT FROM AUTHOR]

Introducing of thermodynamically stable strengthening phases is an important means enhancing the properties of magnesium alloys. To introduce a stable Al2Nd strengthening phase, the Mg-Al-Nd alloys were prepared with a fixed atomic ratio of 2:1 for Al and Nd. The total content of Al and Nd was varied at 1%, 3%, 5%, and 7%, respectively. The effects of Al2Nd phase on the microstructure and mechanical properties of the Mg-Al-Nd alloys were systematically studied in this work. The experimental results indicated that the as-cast alloy primarily consisted of the acicular Al11Nd3 phase as a secondary phase. After undergoing a homogenization treatment at 500 °C for 12 h, the secondary phase underwent a transformation, resulting in the formation of short rod shape Al2Nd structures. Simultaneously, layered Al2Nd precipitated within the α-Mg matrix. The formation of twinning was inhibited, while the Al2Nd phase promoted recrystallization and refined the microstructure through the mechanism of particles stimulated nucleation (PSN), as the Al and Nd contents increased during thermal deformation. At the same time, the increases of Al2Nd phase can enhance the strength and the plasticity of the alloy. The mechanical properties of extruded Mg-1.36Al-3.64Nd (AE5) alloy were excellent with yield strength of 175 MPa, ultimate tensile strength of 249 MPa, and the elongation of 15.4%. The enhanced performance can be primarily attributed to the refined microstructure and the presence of Al2Nd precipitates with small size, which contributed to effective fine grain strengthening and secondary phase strengthening. [ABSTRACT FROM AUTHOR]

Data-driven methodology has become a key tool in computationally predicting material properties. Currently, these techniques are priced high due to computational requirements for generating sufficient training data for high-precision machine learning models. In this study, we present a support vector regression (SVR)-based machine learning model to predict the stability of silicon (Si)–alkaline metal alloys, with a strong emphasis on the transferability of the model to new silicon alloys with different electronic configurations and structures. We elaborate on the role of the structural descriptor in imparting transferability to the model that is trained on limited data (~ 750 Si alloys) derived from the Material Project database. Three popular descriptors, namely X-ray diffraction (XRD), sine coulomb matrix (SCM), and orbital field matrix (OFM), are evaluated for representing Si alloys. The material structures are represented by descriptors in the SVR model, coupled with hyperparameter tuning techniques like Grid Search CV and Bayesian optimization, to find the best performing model for predicting total energy, formation energy and packing fraction of the Si alloy systems. The models are trained on Si alloys with lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and aluminum (Al) metals, where Si–Na and Si–Al systems are used as test structures. Our results show that XRD, an experimentally derived characterization of structures, performs most reliably as a descriptor for total energy prediction of new Si alloys. The study demonstrates that by qualitatively selection of training data, using hyperparameter tuning methods, and employing appropriate structural descriptors, the data requirements for robust and accurate ML models can be reduced. [ABSTRACT FROM AUTHOR]

The effect of grain size and second-phase distribution on the corrosion performance of metal inert gas-welded Al–MgSi–Mn–Cr alloy in different regions was investigated. Due to the welding heat, the transformation of the strengthening phase β″ (Mg5Si6) to B′ phase (Al3Mg9Si7) in heat-affected zone I leads to the reduction in strengthening ability of the joint. In comparison with the equiaxed grain of weld zone, base metal exhibits high grain boundary density of the fibrous grain and a large amount of second phases on the grain boundary, which increases the anodic dissolution site, leading to the highest pitting corrosion susceptibility. Additionally, the continuous distribution of β (Mg2Si) precipitate and Al(MnFe)Si dispersoid at grain boundary forms a corrosion channel, which promotes the corrosion propagation along grain boundary. [ABSTRACT FROM AUTHOR]

Hafnium (Hf) was added as an alloying element to enhance the strength in the NiCoCrAlYMoHf alloys, and the effects of Hf content on constituent phases, microstructural characteristics, and mechanical properties of the as-cast alloy were investigated. The experimental results showed that microstructure of the alloy with 1.0 wt.% Hf was composed of β phase and γ′ phase. The experimental results showed that microstructure of the alloy with 1.0 wt.% Hf was composed of β phase and γ′ phase. With increase in Hf content, the β phase content increased, while the γ′ phase content decreased, and σ phase gradually appeared and precipitated at grain boundary, which resulted in an increase in the hardness of alloys from 429 to 586 HV. The indentation hardness, Young's modulus, and compressive strength of NiCoCrAlYMoHf alloy with 4.0 wt.% Hf could reach 7.12 GPa, 185.52 GPa, and 2659 MPa, respectively, which means that more addition of Hf is beneficial for improving performances of NiCoCrAlYMoHf alloys. The microhardness value is 1.95 times higher than that of the Hf-free alloy. Furthermore, the nanoindentation hardness and Young's modulus are 1.05 and 1.75 times higher, respectively, than those of the Hf-free alloy. [ABSTRACT FROM AUTHOR]

In this study, the gradient microstructure of Mg-Y-Nd-Zr alloy processed by an ultrasonic surface rolling process (USRP) is characterized by electron backscatter diffraction analysis and transmission electron microscopy. The mechanism of microstructure evolution and its effect on mechanical properties of the alloy are discussed in detail. The grain size and orientation of Mg-Y-Nd-Zr alloy after USRP treatment changed gradually along the processing depth. The grain refinement mechanism was elucidated as follows: First, the coarse-grained matrix was subdivided by dislocation slip and twins and further refined into sub-structures by multiple techniques, such as mutual intersection and fragmentation between twins, the interaction between twins and dislocations, and the entanglement of dislocations. Finally, equiaxed nanocrystals with high-angle grain boundaries were formed by sub-grain rotation and recrystallization. The strength improvement of the alloy was mainly attributed to the contributions of grain refinement and dislocation strengthening. The synergistic deformation between the gradient structures is the main reason for the excellent strength and plasticity matching of the alloy. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are conducted to study the self-diffusion process along a < 100 > Σ5(210) symmetric tilt grain boundary in a model equiatomic FeNiCrCoCu high-entropy alloy (HEA), for the directions both perpendicular and parallel to the tilt axis. For comparison, the grain boundary diffusion process is also quantified for each of the pure components of the HEA. Most importantly, the results are compared with the diffusion along the same grain boundary using the corresponding "average atom" potential that has similar average bulk properties but no compositional randomness as in the HEA. These comparisons show that the self-diffusion in the HEA grain boundary is slower than in the average atom material as well as the average of pure components, suggesting that a "sluggish" diffusion effect exists for this special grain boundary in the HEA. This effect is significant at low temperatures but diminishes at higher temperatures, indicating that the grain boundary sluggish diffusion is likely temperature dependent. Interestingly, the grain boundary sluggish diffusion behavior is different from the bulk diffusion that was studied previously using the same methods and interatomic potentials, in which no significant sluggish diffusion effect was observed. Our further analysis suggests that the combination of the "trapping effect" by compositional complexity in the HEA and the confined 2-D diffusion paths at this special grain boundary is responsible for the observed grain boundary sluggish diffusion. [ABSTRACT FROM AUTHOR]

The effects of pre-twinning on the microstructure and dynamic compression properties of non-aged and artificially aged Mg–Y–Nd–Gd–Zr alloys were investigated in this study. Previous studies have shown that in the pre-deformed T3 alloy, precompression along the extrusion direction (ED) generates high-density < a > and < c + a > dislocations and deformation twins, such as the 10 1 ¯ 2 < 10 1 ¯ 1 ¯ > extension, the 10 1 ¯ 1 - 10 1 ¯ 2 double, and 10 1 ¯ 1 < 10 1 ¯ 2 ¯ > compression twins at 86°, 38°, and 56°, respectively. In the pre-deformed T8 alloy artificially aged at 200 °C for 12 h, the dislocation density was found to decrease, with β″ (Mg3Y0.85Nd0.15) and β′ (Mg12NdY) precipitates appearing at both ends of the twin boundary. Subsequently, the precipitates extended toward [0001]Mg and [0001]T in the matrix region and the twin, respectively. The orientation relationships (ORs) between the β″ and β′ precipitates and the matrix/twin were determined to be 01 1 ¯ 0 β ″ / / 0001 Mg / T , 2 1 ¯ 1 ¯ 0 β ″ / / 2 1 ¯ 1 ¯ 0 Mg / T and (001)β′//(0001)Mg/T, 2 1 ¯ 1 ¯ 0 β ′ / / 2 1 ¯ 1 ¯ 0 Mg / T , respectively, in contrast to the counterpart ORs between the β″ and β′ precipitates and the matrix/twin in the non-deformed T61 alloy. Evaluation of the dynamic compression properties showed that compared with the compressive yield strength (CYS) of the T61 alloy, that of the T8 alloy considerably increased from 220 to 339 MPa. However, their ultimate compressive strengths (UCSs) of 363 and 360 MPa, respectively, were similar owing to the synergistic effect between the dislocations, the twin boundaries, and the precipitates. These results suggest that the pre-twinning approach should be adopted to improve the strengths of magnesium alloys. [ABSTRACT FROM AUTHOR]

This study presents the results of an investigation into the magnetocaloric effect (MCE) in the Ni47Mn40Sn13 alloy under the influence of alternating magnetic fields. The study examines the dependence of the MCE on temperature (ranging from 80 to 350 K), magnetic field (up to 8 T), and frequency (1–20 Hz). The maximum values of the MCE observed near the phase transformation temperatures have different signs depending on the type of phase transition, with approximately equal values |ΔTad|≈3.2 K in a field of 8 T. The field dependence of the MCE in the vicinity of the magnetic phase transition is described by an expression of the form ΔTad ~ α⋅Tn, where n = 1 at T < TC, n = 2 at T > TC, and n = 2/3 at T = TC, which is consistent with theoretical predictions. The study also finds that the field dependences of the MCE in the region of the martensitic phase transition show the irreversibility of the phase transition in fields up to 8 T due to the wide temperature hysteresis. Additionally, a sharp, more than twofold decrease in the magnitude of the MCE near TC is found with an increase in the cyclic frequency of the magnetic field from 1 to 30 Hz. This behavior is explained by the influence of magnetic and microstructural inhomogeneities, as well as by the lagging of the magnetization behind the magnetic field in alternating magnetic fields (magnetic viscosity). Finally, the specific cooling power for the Ni47Mn40Sn13 alloy is found to increase as the magnetic field frequency increases, with a value of 0.32 W/g at f = 1 Hz and 4.53 W/g at f = 30 Hz. [ABSTRACT FROM AUTHOR]

The enhancing effect of low melting trace additions (Sn, Cd, In) on the precipitation hardening in the Al–Cu based alloys accounts for the great practical importance of this phenomenon. However, to date, the influence of Sn micro-addition, either separately or jointly with other ones, on the precipitation structure and hardening of the wrought 2219-type alloys based on the Al–Cu–Mn system remains unexplored. In this study, the effect of 0.1 wt% (0.02 at.%) Sn trace addition on the structure and mechanical properties of the new Al–4Cu–1.5Mn (wt%) alloy has been studied using computational (thermodynamic calculations) and experimental techniques. Analysis of microhardness has revealed that the peak hardness at aging of the wrought model Sn-containing alloy reaches ~ 120 HV which is about 43% higher than for the Sn-free alloy. Transmission electron microscopy analysis of the peak-aged hot-rolled sheet alloys has revealed that trace addition dramatically changes the precipitation structure leading to the formation of much finer precipitates (with an average length of 55–60 nm) with a higher number density. Uniaxial tensile tests of the wrought and peak-aged samples have revealed that the mechanical properties of the model Al4Cu1.5Mn0.1Sn alloy (UTS ~ 402 MPa, YS ~ 323 MPa and elongation ~ 9.7%) are very close to those of the industrial 2219-type alloy. However, the new alloy contains a much lower concentration of copper and a superior fraction of Al20Cu2Mn3 phase dispersoids the influence of which on the mechanical properties should be further studied in detail. [ABSTRACT FROM AUTHOR]

Exploring the chemical micro- and nanostructure of metal alloys is essential to understand their physical properties, such as magnetism or hardness. Additively manufactured (AM) materials, e.g. via laser powder bed fusion (LPBF) followed by various heat treatments, can raise further questions concerning the printed material. For the in-situ alloyed, spinodal Fe54Cr31Co15 system, the macroscopic magnetic behaviour is greatly influenced by subsequent homogenisation and heat treatment steps. Here we show that the decomposition takes place on the nanometre scale, resulting in ferromagnetic FeCo-rich particles embedded in a Cr-rich matrix. By studying phenomena like chemical homogeneity, grain structure, and texture of the in-situ alloyed material at different scales, we reveal correlations between the heat treatment and the resulting nanostructure and its ferromagnetic properties. We found that the isothermal heating conditions determine the degree of phase segregation and that a homogenization step can be omitted for additively manufactured, in-situ alloyed FeCrCo alloys. The approach thereby offers insight and a path for also tailoring specific manufacturing parameters to provide the right quality printed materials with desired functionalities. For example, magnetic FeCrCo alloys are often used in electric motors or magnetic sensors, and the flexibility of the presented approach can lead to optimal use of the material. [ABSTRACT FROM AUTHOR]

Recently, the HfNbZrTi high-entropy alloy (HEA) has received extensive attention due to its exceptional mechanical properties, which is ascribed to the significant lattice distortion and complex structural evolution induced by inherent chemical short-range order (CSRO). In this study, we employ molecular dynamics (MD) technique to study nanoscale CSRO phenomenon and its influence on the mechanical response of Σ5(210) and Σ5(310) grain boundaries (GBs) in HEA under shear loadings. Results reveal an apparent CSRO manifested by clustering of Hf-Nb and Zr-Ti pairs consistent with experimental observations. Further analyses on some representative Σ5 GB models unveil that the presence of CSRO can induce transformation of GB structure, which not only causes a transition in deformation behavior from migration-dominated to sliding but also raises the yield strengths. Moreover, after probing into the stress–strain curves and the relative sliding energy curves of massive GB models, we discover that the transition in GB behavior is ascribed to the CSRO impeded dislocation motion. The findings of this work promote atomistic understanding on the CSRO modulated shear response of GBs in HfNbZrTi HEA. [ABSTRACT FROM AUTHOR]

Various electrochemical techniques were used to study the corrosion behaviour of the CNT-reinforced NiAl alloys under NaCl and Na2SO4 environments. The potentiodynamic polarization curves revealed activation Tafel behaviour when the NiAl alloy specimens were immersed in NaCl solution while passivation followed by slight development of transpassivation resulted under Na2SO4 environment. The reinforcement of pure NiAl alloy with up to 1.0 wt.% CNT increased the corrosion rate from 0.10 to 0.63 mm/yr under NaCl environment, while under Na2SO4 environment, the corrosion rate increased from 0.04 to 0.12 mm/yr. The observed increase in corrosion rate with an increase in CNT reinforcement (under both NaCl and Na2SO4 environments) suggested that the reinforcement of NiAl alloys with CNT reduced the corrosion resistance of NiAl. The X-ray diffraction analysis revealed that the corrosion products consisted of oxides including Al2O3 under NaCl environment, while scanning electron microscope analysis showed a porous passive layer on the surface of the alloy specimens immersed in Na2SO4 solution. [ABSTRACT FROM AUTHOR]

The half-metallic and pressure-induced elastic properties of PdVSi, PdVGe, PdVSn, and PdVSb were investigated. First, FM phases were obtained energetically as the most stable. The semiconducting characters seemed in spin-down states. The band gaps were calculated as 0.807 eV, 0.676 eV, 0.481 eV and 0.370 for PdVSi, PdVGe, PdVSn, and PdVSb, respectively. Since the spin polarization value of PdVSb alloy is less than 100% in GGA method, it is nearly half-metallic ferromagnetic, while other alloys are true half-metallic ferromagnetic. However, in HSE method, the forbidden and half-metallic band gaps were also calculated for PdVSb alloy as 0.375 eV and 0.134 eV, respectively. HSE method has a direct effect on the band gap values. PdVSi, PdVGe, and PdVSn, alloys have 1.00 μB/f.u. total magnetic moments, while PdVSb alloy has 2.00 μB/f.u. total magnetic moment. According to elastic results, all alloys are elastically stable and ductile materials. Debye temperatures were obtained as 371.53 K, 317.71 K, 311.78 K, and 263.13 K at 0 GPa pressure. PdVSi, PdVGe, PdVSn, and PdVSb alloys have been obtained as very remarkable materials with their structural, electronic, magnetic and pressure-induced elastic properties. [ABSTRACT FROM AUTHOR]

The present work focuses on the development of Al/SiC materials manufactured by laser powder bed fusion (L-PBF). More specifically, our goal is to address the issue of the SiC dissolution kinetics, with the objective of preventing or at least limiting SiC decomposition into Al4C3 in melted aluminum. To do so, Al/SiC powder composites with SiC particles of various sizes, namely from circa 35 nm to 4.5 µm, using a standard AlSi7Mg0.6 alloy as host material are first successfully prepared, and these composite powders are printed in a standard L-PBF equipment. The resulting parts are then thoroughly characterized. An important result is that only the largest 4.5 µm particles can be partially preserved. These findings are consistent with the results of a diffusion-based numerical model, which allows in addition to study the kinetics of powder dissolution as a function of thermophysical and process parameters. A general finding of the present work is that a thermodynamically unstable nanoparticle cannot survive the L-PBF process. [ABSTRACT FROM AUTHOR]

Historically, titanium alloys have been developed disregarding the addition of eutectoid β-stabilisers as they generally lead to the formation of brittle intermetallic phases upon solidification of the alloy. However, such phenomenon can be prevented using powder metallurgy. Thus, this study considered the concurrent addition of cheap strong eutectoid β-stabilisers, namely Mn and Fe, for the development of new ternary Ti–Mn–Fe alloys, reducing the intrinsic cost of Ti alloys. It is found that the progressive addition of Mn and Fe in equal concentration enhances the densification of Ti during sintering, leading to lower amount of residual porosity, the transformation of the microstructure from purely lamellar to metastable, and the associated refinement of the microstructural features (grains and lamellae), as well as the stabilisation of a greater amount of β phase, and the formation of the metastable α″ phase. Such microstructural changes result in the strengthening (higher yield and ultimate tensile strength and hardness) and embrittlement of the alloy by changing the fundamental strain hardening mechanism of the ternary Ti–Mn–Fe alloys. [ABSTRACT FROM AUTHOR]

Cold angular rolling process (CARP) has emerged as a potential continuous severe plastic deformation technique enabling the processing of bulk metal sheets with improved mechanical properties. The CARP technique involves a combination of cold rolling of a sheet by a single rotation roller followed by equal-channel angular pressing of the sheet passing through a bent channel. The present work uses finite element method (FEM) to model CARP by considering processing conditions, including different friction values and processing velocities for different copper and stainless steel alloys. The simulations reveal the influence of these processing parameters on distributions of strain, strain rate, stress (in both the metal sheet and the CARP tool), temperature, and torque requirements through one pass of CARP on the metal sheets. The modeling results are validated by the experimental characterization of the hardness distribution and microstructure after CARP on a copper sheet. The results from FEM are used to estimate the energy incorporated into different metal alloys at various processing conditions. Finally, this study discusses the feasibility of scaling up the CARP technique. [ABSTRACT FROM AUTHOR]

The present study aims to collect data, compare results and assess techniques used for improving corrosion resistance and mechanical properties of biodegradable Mg alloys for fixation elements and orthopedic applications. A general description of biomaterials used for orthopedic implants is performed, including non-bioabsorbable materials. Different methods for reducing the corrosion rate in Mg alloys are researched, and the efficiencies are assessed. After evaluating different techniques, surface modification is found to be the most promising technique to reduce the corrosion rate with an efficiency of 85%. Regarding the Mg alloying agents, Zn is considered as the best candidate to improve the corrosion response and biocompatibility of the Mg. [ABSTRACT FROM AUTHOR]

In order to obtain compact epoxy-based organic coatings with superior corrosion resistance and self-healing performance, a novel Ti3C2Tx/LDH-epoxy hybrid coating was prepared on AZ31 magnesium alloy in this work. The layered double hydroxide (LDH) adopted here is MgAl-LDH intercalated by the cysteine acid (Cys), an environmentally friendly organic acid anions, as corrosion inhibitors, and the MXene (Ti3C2Tx)/MgAl-LDH (TML) heterostructure nanosheets were grown by a facile in situ assembled method. The morphology, composition, structure and the corrosion protection of the Ti3C2Tx/MgAl-LDH-epoxy (EP-TML) composite coatings were systematically investigated and compared with the other three epoxy-based coatings: bare waterborne epoxy resin (EP), Ti3C2Tx pigmented in EP (EP-T), MgAl-LDH in EP (EP-ML). It is found that the TML heterostructure has good dispersion and compatibility with the epoxy resin. The corrosion current density and the impedance value at low frequency (|Z|0.01 Hz) of the EP-TML composite coating are 1.4 × 10–9 A/cm2 and 1.66 × 107 Ω cm2, which is 4 orders of magnitude lower than that of the uncoated Mg substrate and 1–2 orders of magnitude higher than that of EP (8.7 × 105 Ω cm2), respectively, indicating its excellent corrosion resistance. And the self-healing efficiency of EP-TML composite coating is found to be higher as 56.17% after 6 days immersion in a corrosive environment. The significant improvement of the anti-corrosion and self-healing performance of the EP-TML composite coating are mainly ascribed to the synergistic effect of "barrier effect" of TML and the corrosion inhibition effect of the cysteine acid encapsulated in MgAl-LDH. This work provides some valuable insights to widen the functional application of Ti3C2Tx and the design of highly corrosion-resistant and self-healing organic coatings for Mg alloys. [ABSTRACT FROM AUTHOR]

Cold rolling the CC AA 5754 aluminum alloy to different reductions was followed by an hour of annealing at 537 °C under varied pressures. The changes in microstructure and texture were studied. According to the findings, high-pressure heat treatment restricts recrystallization, and the restriction effect is stronger as pressure rises. The refining impact of high-pressure heat treatment can refine recrystallized grains, and it becomes stronger as the rolling reduction gets higher. The variation of recrystallization texture is significantly affected by high-pressure heat treatment. The sheet with a 19.6% reduction is found to have a weak cube texture at atmospheric pressure and 2 GPa, but the sheet that has been annealed at 4 GPa and 6 GPa has a strong cube texture and a weak β fiber rolling texture. High-pressure heat treatment improves the intensities of the cube and R textures in the fully recrystallized sheets with the same reduction. The strengthening impact of R texture from high-pressure heat treatment improves with increasing rolling reduction. [ABSTRACT FROM AUTHOR]

The Ti–15Mo alloy has become a widely recognized biomedical Ti alloy due to its excellent properties, including a low Young's modulus that is close to that of a human bone. Selective laser melting (SLM) additive manufacturing (AM) offers both advanced manufacturing capabilities to the processing of the alloy and the potential to make customized implants. The feedstock cost of pre-alloyed Ti–15Mo powder, however, is high, like that of many other Ti alloys, and can be a major obstacle to the wider application of the AM technique. This study focused on mitigating this problem by using an in situ laser alloying approach, wherein a low-cost hydride-dehydrate (HDH) Ti powder was mechanically mixed with elemental Mo powder to form a composite powder feedstock (i.e., Ti + Mo). The Ti–15Mo alloy could be printed with a high relative density (~ 99.76%). A finite element simulation was performed to study the melt pool during the SLM process with subsequent detailed discussions to understand the in situ alloying mechanism. Mechanical property indicates the as-printed Ti–15Mo has high strength (~ 1170 MPa) but low ductility, while the latter has been much improved by introducing a merely 0.2 wt% of yttrium (Y). Based on the optimized Ti–15Mo–0.2Y alloy with a strength of ~ 1300 MPa and a modulus of ~ 85 GPa, different amounts of elemental Ag powder were further alloyed in situ to acquire antibacterial properties. Compared with the antibacterial activity of the control group, that of the final material, i.e., in situ laser alloyed Ti–15Mo–0.2Y–2.5Ag, reached 92–95%; the addition of Ag had a minimal effect on the cell viability. In vivo experiments demonstrated the Ag-containing alloys to exhibit good biocompatibility. [ABSTRACT FROM AUTHOR]

Thermoelastic martensitic transformation plays an important role in shape memory effects and superelasticity. The thermoelastic martensite reduces the elastic strain energy during transformation via a combination of multiple variants (i.e., self-accommodation). We investigated the microstructural characteristics and self-accommodation of the martensite in equiatomic ZrPd and near-equiatomic NiZr alloys by X-ray diffraction analysis, scanning electron microscopy–electron backscatter diffraction analysis, and transmission electron microscopy (TEM) observation. The space group of the equiatomic ZrPd and near-equiatomic NiZr alloys at room temperature was determined to be Cm. In the equiatomic ZrPd alloy, two habit plane variants (HPVs) were bounded by a {021}Cm compound twin. The minimum self-accommodation unit necessary to relax the strain energy due to the B2-to-Cmcm martensitic transformation is a pair of HPVs with plate- and polygonal-like morphologies. In addition, the strain energy resulting from the martensitic transformation from the Cmcm to the Cm phase is released by the formation of a {001}Cm compound twin as a lattice invariant shear (LIS). The near-equiatomic NiZr alloy had coarse variants with a grain size of several hundred micrometers and thin variants with a width of a few tens of nanometers; the interface of these variants was a {021}Cm deformation twin. TEM in situ heating observations revealed that the near-equiatomic NiZr alloy transformed from the Cm to the Cmcm structure around 573 K and that the {001}Cm compound twins induced as an LIS disappeared. Clarifying the thermoelastic martensitic transformation in such Zr-based alloys is useful for the development of high-temperature shape memory alloys. a Inverse pole figure map of the Cm martensite. b Lattice correspondence variants map. c and d Pole figures taken by {021}Cm, and {111}Cm planes, respectively. [ABSTRACT FROM AUTHOR]

The morphology and microstructures of Ti-6.5Al-2Zr-1Mo-1V (TA15) samples at different stages of martensite decomposition fabricated by selective laser melting are characterized during the in situ tensile test, and the deformation and crack mechanisms are discussed. The results show that the as-deposited samples with full martensite structure, former being recognized as a state of poor plasticity, possess excellent ductility (with a maximum displacement of 0.74 mm) due to the cooperative deformation behavior of hierarchical martensites. The full-annealed sample, consisting of lamella (α + β) laths, also shows good ductility (0.65 mm) with the enhanced collaborative deformation behaviors between α and β laths. However, for samples with partially decomposed martensite structure, abrupt fracture after yielding was observed with deteriorated ductility (0.54 mm), as the slipping of dislocations is hampered by the dispersive nano-β precipitations. [ABSTRACT FROM AUTHOR]

A novel precipitation strengthening Cu–Fe–Zr alloy was designed and prepared based on the results of calculation of the phase diagram. After solid solutionizing, rolling and aging at 450 °C for 1 h, the alloy had a tensile strength of 515 MPa and an electrical conductivity of 72% IACS. There were two kinds of precipitates in the alloy after aging at 450 °C for 1 h. Fe precipitates with an average diameter of 4.3 nm were present in the deformed grains. Fe2Zr precipitates with an average diameter of 29.1 nm were present in the recrystallized grains. Both the Fe and Fe2Zr precipitates had coherent interfaces with the Cu matrix. The precipitation kinetics and effects on the properties of the alloy were discussed. It is found that the cold rolling enhanced the driving energy of precipitation. The precipitation of Fe and Fe2Zr had a dominant effect on the increase in electrical and mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]

Laser Powder Bed Fusion (PBF-LB/M) additive manufacturing (AM) induces high magnitude residual stress (RS) in structures due to the extremely heterogeneous cooling and heating rates. As the RS can be deleterious to the fatigue resistance of engineering components, great efforts are focused on understanding their generation and evolution after post-process heat treatments. In this study, one of the few of its kind, the RS relaxation induced in an as-built PBF-LB/M AlSi10Mg material by a low-temperature heat treatment (265 °C for 1 h) is studied by means of X-ray and neutron diffraction. Since the specimens are manufactured using a baseplate heated up to 200 °C, low RS are found in the as-built condition. After heat treatment a redistribution of the RS is observed, while their magnitude remains constant. It is proposed that the redistribution is induced by a repartition of stresses between the α-aluminium matrix and the silicon phase, as the morphology of the silicon phase is affected by the heat treatment. A considerable scatter is observed in the neutron diffraction RS profiles, which is principally correlated to the presence (or absence) of pockets of porosity developed at the borders of the chessboard pattern. [ABSTRACT FROM AUTHOR]

This work investigated the tensile creep behaviors of hot-extruded Mg–0.9Mn (0Ce) alloy and Mg–0.9Mn–0.5Ce (wt%) (0.5Ce) alloy. Tensile creep tests were conducted at 423 K under the applied stresses of 20 MPa, 30 MPa and 40 MPa along the extrusion direction (ED) and transverse direction (TD). Regardless of alloy composition, it was shown that creep behavior exhibited obvious dependence on the loading direction. The intensive basal slip and 10 1 ¯ 2 twinning caused the poorer creep resistance along the TD than that along the ED. More importantly, experimental results showed that 0.5Ce alloy had more excellent creep resistance than that of 0Ce alloy when crept along the same direction, and the corresponding mechanism on the enhancement of creep resistance by dilute Ce addition was uncovered. When crept along the ED, the dynamically co-precipitated α-Mn and Mg12Ce phases effectively increased the creep resistance by impeding the dislocation movements even basal slip was catalyzed in 0.5Ce alloy. When crept along the TD, addition of Ce enriched the creep mechanism and impaired the adverse effects of basal slip to creep. Besides, the dynamically co-precipitated α-Mn and Mg12Ce phases also improved the creep resistance of 0.5Ce alloy. Unexpectedly, it was discovered that Ce atoms tended to segregate toward grain boundaries during creep, which strongly contributed to the excellent creep resistance of 0.5Ce alloy by decreasing the mobility of grain boundaries. The finding of Ce segregation at the grain boundaries provides important thought for designing high heat-resistant Mg–Mn–Ce-based alloys by grain boundary engineering. [ABSTRACT FROM AUTHOR]

The explosive cladding process of Monel alloy/Cu bimetallic bonded rod was numerical simulated with nonlinear explicit dynamics software of ANSYS/AUTODYN. The unique phenomenon of explosive cladding (e.g., jetting, wavy interface) and the distribution and evolution law of dynamic cladding parameters (e.g., pressure, velocity, stress, effective plastic strain/train rate, temperature) were accurately reproduced with 2D numerical simulation. The entire explosive cladding process, the flight speed of the cladding tube and the pressure variation during the cladding process were obtained by 3D numerical simulation. The metallurgical bonding mechanism of Monel alloy/Cu explosive cladded rod was discussed and compared with experimental observations. The simulation results were in high accordance with theoretical calculations and experimental observations. This work deepens the understanding of explosive cladding and provides theoretical guidance for the optimal selection of process parameters to fabricate high-performance bimetallic explosive cladded rods. [ABSTRACT FROM AUTHOR]

The Hall–Petch relationship and deformation process in Ti3Al nano-polycrystalline alloys are investigated using molecular dynamics simulations in this research. The impact of different grain sizes and temperatures on mechanical characteristics was considered. Different Hall–Petch relations were detected for samples with the grain sizes ranging from 2 to 20 nm, inverse Hall–Petch relations in big grain sizes ranges, and positive Hall–Petch relations in the medium grain size region, respectively. A transition zone formed at the interception of positive and inverse Hall–Petch relations, which will vanish as the temperature rises. The critical grain size of the positive Hall–Petch relation decreases as the temperature rises from 10 to 600 K. With the grain size increases in the smaller grain size range, the yield stress increases, which is made by the grain boundary motion and rotation. Besides, temperatures affect mechanical characteristics. The rising temperatures lead to the decreasing dislocation density and a high grain boundary fraction. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are a new class of advanced metallic alloys that have received significant attention in recent years due to their stable microstructures and promising properties. However, exploration of the functional properties of these alloys as thermal-sprayed coatings has not been undertaken so far. In the present study, novel equiatomic AlCoCrFeMo, AlCoCrFeMoW, and AlCoCrFeMoV HEA coatings were fabricated using flame spraying to understand the impact of tungsten (W) and vanadium (V) additions in AlCoCrFeMo HEA coatings on microstructure evolutions, phase formations, microhardness, and electrical resistivity. The microstructure revealed the occurrence of mixed oxides and BCC phases, with an apparent porosity range between 2 and 4%. Despite the lower fraction of oxide phases, higher hardness was achieved for AlCoCrFeMoV HEA coatings (714 ± 64 HV), followed by AlCoCrFeMoW (609 ± 61 HV) and AlCoCrFeMo (592 ± 58 HV) HEA coatings. The higher hardness might be attributed to combined interactions of hard oxide phases, solid solution strengthening, and BCC phases. The electrical resistivity values showed a noticeable difference between HEA coatings and control Ni–20Cr coatings, whereby higher electrical resistivity values were achieved for AlCoCrFeMo HEA coatings due to topological lattice distortion and higher oxide fractions. Joule heating testing showed a higher rate of increase in surface temperature for all the HEA coatings than that of Ni–20Cr flame-sprayed coatings for a given electrical power input. The results suggest that the improved electrical properties and heating performance capabilities of flame-sprayed HEA coatings make them an excellent choice for use in high load resistive heating applications. [ABSTRACT FROM AUTHOR]

The impact of the surface corrosion product layers on the pitting corrosion behavior of three Al–Cr–Mn–Co–Zr alloys has been studied using a combination of electron microscopy, X-ray and electrochemical techniques. These alloys contain an FCC Al matrix, different volume fractions of icosahedral quasicrystalline (I-phase) dispersoids and minority grain boundary phases. The I-phase dispersoids act as cathodic sites, and alloys with higher I-phase volume fractions have lower open circuit potentials and higher corrosion current densities before salt fog exposure. Upon ASTM salt fog exposure for 6 weeks, these trends reverse due to the development of a corrosion product bilayer. The bilayer consists of a dense outer layer with angular crystallites of bayerite, and an inner boehmite layer with a fibrillar morphology and a gradient structure with the highest density at the interface with the alloy. This bilayer was more well developed at higher I-phase volume fractions and after upset forging. The layer was found to improve the resistance of the alloys to pitting corrosion, with the pitting potentials increasing dramatically to values as high as 1432 mV (with respect to saturated calomel electrode) after the salt fog exposure. These values were significantly higher than those for the conventional high-strength Al alloys Al 6061 (− 126 mV) and Al 7075 (− 706 mV) tested under identical conditions. [ABSTRACT FROM AUTHOR]