Properties Of Alloys Research Articles

Empirical tight-binding method for large-supercell simulations of disordered semiconductor alloys

We analyze and present applications of a recently proposed empirical tight-binding scheme for investigating the effects of alloy disorder on various electronic and optical properties of semiconductor alloys, such as the band gap variation, the localization of charge carriers, and the optical transitions. The results for a typical antimony-containing III-V alloy, GaAsSb, show that the new scheme greatly improves the accuracy in reproducing the experimental alloy band gaps compared to other widely used schemes. The atomistic nature of the empirical tight-binding approach paired with a reliable parameterization enables more detailed physical insights into the effects of disorder in alloyed materials.

Bimodal grain structure and balanced mechanical properties of cryo-rolled Mg-Zn-Y alloy via twinning-induced recrystallization

The microstructure and mechanical properties of the hot-rolled and cryo-rolled Mg-2Zn-0.85Y (wt.%) alloys before and after annealing were studied comparatively. The results show that the cryo-rolled alloy after annealing exhibits a strength and plasticity product of up to 6885 MPa·%, which is the highest among these alloys. The good combination of strength and ductility is mainly attributed to the bimodal grain structure with a weakened texture. Recrystallization primarily occurs in grains with <112¯0>/30.1° twinning, but not in the grains without <112¯0>/30.1° twinning, resulting in the formation of the bimodal structure. The cryo-rolling process could become a promising method for regulating the microstructure and properties of magnesium alloys.

Additive manufacturing Ti-22Al-25 Nb alloy with excellent high temperature tensile properties by electron beam powder bed fusion

Additive manufacturing of TiAl alloys remains challenging due to their poor high-temperature tensile properties. In this work, electron beam powder bed fusion (PBF-EB) was applied to fabricate Ti-22Al-25 Nb alloy with a high pre-heating temperature (830℃), achieving a breakthrough in improving the tensile properties of TiAl alloys by additive manufacturing. The microstructure and tensile properties of Ti-22Al-25 Nb fabricated by laser beam powder bed fusion (PBF-LB) and PBF-EB were investigated. Excellent tensile strength (803 MPa) at 650℃ was obtained by PBF-EB, which was attributable to the precipitation and growth of the O phase at a suitable pre-heating temperature. An in-depth microstructure analysis of the deformation and fracture mechanisms of the as-printed samples was performed via Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The area fraction of the O phase in the PBF-EB sample was approximately 6 times higher than that of the PBF-LB sample. The PBF-EB sample exhibited transgranular fracture at 650 °C, in contrast to the PBF-LB samples. The shape and quantity of the O phase and β phase played an important role in improving the tensile properties of the Ti-22Al-25 Nb alloys at high temperature.

Biodegradable PMMA coated Zn–Mg alloy with bimodal grain structure for orthopedic applications - A promising alternative

The study examines the impact of microstructure and polymethyl methacrylate (PMMA) grafting on the degradability of Zn–Mg alloys. The mechanical properties of a Zn alloy containing 0.68 wt% Mg and extruded at 200 °C are enhanced for degradable load-bearing applications, addressing a crucial need in the field. The material exhibits a bimodal grain size distribution that is random texture, consisting of secondary phases, grains, and sub-grains. With an elongation to failure of 16 %, the yield and ultimate tensile strengths are 325.9 and 414.5 MPa, respectively, and the compressive yield strength is 450.5 MPa.The “grafting-from” method was used to coat a few micrometers thick of PMMA on both bulk and scaffold Zn alloys to mitigate the corrosion rate. The last one is a porous structure, with a porosity of 65.8 %, considered as in the first approach of an orthopedic implant. After being immersed for 720 h, the PMMA-grafted bulk alloy's corrosion rate decreased from 0.43 to 0.25 mm/y. Similarly, the scaffold alloy's corrosion rate reduced from 1.24 to 0.49 mm/y. These results indicate that the method employed could be used for future orthopedic applications.

Effects of sintering temperature on the microstructure and mechanical properties of Ni-based alloy

Ni-based alloys were prepared at different sintering temperatures in this study. The effects of sintering temperature on the volume fraction, morphology, and distribution of precipitates in Ni-based alloys, and its impact on mechanical properties were studied. The results show that the microstructure contains γ-Ni, Ni3Si, M7(B, C)3, M23(B, C)6, and a Si-rich multi element phase. The morphology of M7(B, C)3 particles undergoes an evolution of small particles → mainly strip shape → mainly small block shape and nearly spherical shape, accompanying with the dissolution-reprecipitation process of M7(B, C)3 particles caused by the diffusion of Cr element with the increasing of sintering temperature. Meanwhile, the M23(B, C)6 particle is keeping aggregating and growing. The relative density, microhardness, and bending strength of Ni-based alloys also increase. Especially these properties are found to be increase quickly between 1025 °C and 1050 °C. The increase in microhardness and bending strength is attributed to the reduction in the number of residual sintering pores and the increase in the volume fraction and size of precipitates. In addition, the transition of fracture morphology from intergranular fracture mode to a combination of intergranular and partially transgranular fracture mode also contributes to the rise in bending strength.

Achieving Equiaxed Transition and Excellent Mechanical Properties in a Novel Near-β Titanium Alloy by Regulating the Volume Energy Density of Selective Laser Melting.

This research investigated the relationship between volume energy density and the microstructure, density, and mechanical properties of the Ti-5Al-5Mo-3V-1Cr-1Fe alloy fabricated via the SLM process. The results indicate that an increase in volume energy density can promote a transition from a columnar to an equiaxed grain structure and suppress the anisotropy of mechanical properties. Specifically, at a volume energy density of 83.33 J/mm3, the average aspect ratio of β grains reached 0.77, accompanied by the formation of numerous nano-precipitated phases. Furthermore, the relative density of the alloy initially increased and then decreased as the volume energy density increased. At a volume energy density of 83.33 J/mm3, the relative density reached 99.6%. It is noteworthy that an increase in volume energy density increases the β grain size. Consequently, with a volume energy density of 83.33 J/mm3, the alloy exhibited an average grain size of 63.92 μm, demonstrating optimal performance with a yield strength of 1003.06 MPa and an elongation of 18.16%. This is mainly attributable to the fact that an increase in volume energy density enhances thermal convection within the molten pool, leading to alterations in molten pool morphology and a reduction in temperature gradients within the alloy. The reduction in temperature gradients promotes equiaxed grain transformation and grain refinement by increasing constitutive supercooling at the leading edge of the solid-liquid interface. The evolution of molten pool morphology mainly inhibits columnar grain growth and refines grain by changing the grain growth direction. This study provided a straightforward method for inhibiting anisotropy and enhancing mechanical properties.

Boronizing of Monel K500 alloy: Microstructural characterization and modeling of boron diffusion

In this study, the thermochemical treatments were carried out using the powder-pack boronizing method at temperatures ranging from 1123 K to 1223 K for durations of 2 to 6 h, with the aim of improving the surface properties of Monel K500 alloy. Microstructural investigation of the boride layers, conducted using optical microscopy (OM) and scanning electron microscopy (SEM), revealed a needle-like layer structure with high porosity homogeneously distributed on the surface. The results of XRD analysis showed that the boride layer contained different nickel borides (Ni2B, Ni3B, Ni4B3 and NiB12), iron borides (Fe2B and Fe3B) and complex borides (Fe4.5Ni18.5B6 and Fe3Ni3B). The presence and amount of elements in the boride layer were determined by EDS analysis. This study focused mainly on diffusion kinetics studies of boronized Monel K500 alloy. Growth kinetics of the boride layer were investigated using three different approaches such as parabolic growth model, regression model and mean diffusion coefficient (MDC) model. Boron activation energy values were calculated and found to be quite similar, at 266.14 kJ mol−1 and 266.17 kJ mol−1 using the MDC model and parabolic growth model, respectively. These values were compared with similar results reported in the literature.

Crystal structure, stability, and transport properties of Li2BeAl and Li2BeGa Heusler alloys: a DFT study

In this study, the structural, elastic, electronic, and thermoelectric properties of full Li2BeAl and Li2BeGa Heusler alloys were explored using density functional and the Boltzmann transport theories. The GGA and HSE approximations have been used for the exchange–correlation potential. Results indicated that these two compounds are more energetically stable in the inverse Heusler structure. Additionally, both Li2BeAl and Li2BeGa Heusler alloys were found to be mechanically stable due to the positive values of the elastic constants. Also, the high values of the Young's modulus indicate that these compounds are stiff and exhibit a semi-metallic nature. The band gaps were determined to be 0.13 eV and − 0.22 eV for Li2BeAl and Li2BeGa alloys, respectively, using the GGA approximation. By employing the HSE hybrid functional, however, the band gap for Li2BeAl increased to 0.26 eV, and for Li2BeGa, it decreased to − 0.16 eV. Regarding thermoelectric properties, Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, power factor, and the figure of merit have been calculated for both Li2BeAl and Li2BeGa Heusler alloys at different temperatures. Seebeck coefficient in both alloys decreases with increasing the temperature and has the highest value at 300 K. Thermal conductivity and electrical conductivity increase with increasing the temperature, which confirms the intermetallic behavior of the Heusler alloys. The results obtained for both alloys show that n-type doping has better thermoelectric properties than p-type doping. The maximum value of the figure of merit (ZT) was obtained for n-type doping, which was 1.43 at 660 K for Li2BeAl and 0.39 at 1000 K for Li2BeGa alloy. The high values of ZT especially for electron-dopped Li2BeAl suggest the great potential of this material for use in thermoelectric devices. This study suggests that the proposed materials have potential applications in spintronic devices and thermoelectric materials due to their intermetallic character and effective thermoelectric coefficients.

Effect of Niobium on Mechanical Properties of Steels and High-Entropy Alloys

Effect of Niobium on Mechanical Properties of Steels and High-Entropy Alloys

Influence of thermocycling on the functional properties of the NiTi alloy produced by wire arc additive manufacturing

The influence of the thermocycling under a stress of 200 and 300 MPa on the martensitic transformation temperatures, recoverable and irreversible strain was study in the NiTi samples produced by wire arc additive manufacturing (WAAM). Two types of samples were used: the T1 sample including the Ti-rich NiTi and Ni-rich NiTi layers in the working length and the T2 sample including only the Ni-rich NiTi layers. It was found that the variation in the martensitic transformation temperatures on thermal cycling depended on the chemical composition of the layer. The transformation temperatures decreased on thermal cycling in the Ti-rich NiTi layer (in T1 sample), whereas they were constant in the Ni-rich NiTi layers (in T1 and T2 samples). The recoverable strain in both samples did not change during thermal cycling. The irreversible strain was found in the T1 sample regardless of stress acting on thermal cycling, while T2 sample showed the plastic strain only in the first cycle under 300 MPa. It was shown that the difference in a functional behavior of the T1 and T2 samples on thermocycling was due to that the T1 sample contained the Ti-rich NiTi layer, that was characterized by a low dislocation slip limit contrary to the Ni-rich layers which were hardened by the Ni4Ti3 precipitates.

Zr and V-doped effect on Martensitic transformations and magnetic properties of NiMnIn shape memory alloy

In this study, the elements vanadium (V) and zirconium (Zr) were doped separately as a fourth element to the ternary NiMnIn Heusler magnetic shape memory alloy and the alloys were produced as ingots by arc-melting method. The shape memory properties, microstructures, magnetic and microstructural changes of these new alloys were investigated in detail. The vanadium (V) and zirconium (Zr) elements doped into the alloy caused a decrease in the transformation temperature values of the alloy, but did not cause a significant change in its magnetic properties. The master sample, which has low hysteresis, undergoes a phase transition from the martensite phase to the austenite phase due to an increase in the nucleation of austenite phases at the twinning boundaries. Here, the vanadium and zirconium doping of the alloy caused an increase in the strength and ductility values of the alloy and this caused the formation of the second phase. Due to the increase of this phase formation in the alloy, it can be said that there is a slight decrease in the shape retention of the alloy.

Effect of Heat Treatment on Some Thermodynamics Analysis, Crystal and Microstructures of Cu-Al-X (X: Nb, Hf) Shape Memory Alloy

Heat treatment is an important technique that can improve the properties of shape memory alloys. In this study the effect of heat treatment at three different temperatures (973 K, 1073 K and 1173 K) on some thermodynamics parameters, crystal structure, and microstructure of Cu_86 Al_12 Nb_2 and Cu_86 Al_12 Hf_2 (mass %) Shape Memory Alloy has been investigated. After heat treatment, the change in the thermal properties of the samples was determined using Differential Scanning calorimetry (DSC). The effect of heat treatment on the crystal and microstructure of the alloy samples were determined at room temperature using X-ray diffraction (XRD), Scanning Electron microscopy (SEM) device. The DSC result showed that in both samples the temperature hysteresis was decreased after heat treatment. Also grain size was decreased by increasing the treatment temperature in both samples. And finally, optical images represented that Hafnium (Hf) is more dissolved in the alloy compared to Niobium (Nb).

Effects of Ti addition and annealing on microstructure and mechanical properties of CoCrFeMnNi high-entropy alloy

Effects of Ti addition and annealing on microstructure and mechanical properties of CoCrFeMnNi high-entropy alloy

Influence of Jewelry Surface Vibromechanical Processing on the Structure and Mechanical Properties of TiNi Alloy

Influence of Jewelry Surface Vibromechanical Processing on the Structure and Mechanical Properties of TiNi Alloy

Nd-, La-induced precipitate/defect in cobalt-iron magnetic alloy for strong and broadband microwave absorption

Soft magnetic microwave absorbents have merits of sufficient magnetic loss and unique magnetism-frequency response characteristics, yet are limited by the low natural resonance frequencies and simplex loss mechanism. Introducing second phase has been proven to be efficient in evoking structure, magnetism and conductivity changes, but the effects on the microwave absorption is still unbeknown. In this work, the Co0.72Fe0.28 alloy magnetic absorbents with dispersedly distributed NdCo5/LaCo5 nano precipitates were prepared. By fine-tuning the doping ratios of the rare earth (RE) of Nd/La, the coercivity and conductivity show an upward trend with enhanced magnetic and dielectric losses on 2–18 GHz. On one hand, the high magneto-crystalline anisotropic RECo5 phases uplifted the holistic resonance frequency ranges and enhanced the C/X/Ku band attenuations. On the other hand, the as-spawn vacancies, heterogeneous interfaces and dislocations boosted the conductive/polarization losses of the individual magnetic alloys. As a result, the high-frequency performance was significantly improved when ensuring the impressive low-frequency loss. A remarkable minimum reflection loss (RLmin) of −76 dB was achieved in the S band, and the effective absorption bandwidth (EAB) of 7.34 GHz was obtained at only 1.7 mm, covering most of the X/Ku bands. The performance sets it apart as the highest among the reported RE-transitional alloy absorbents so far. Overall, this work provides a feasible way and novel strategy for improving the microwave absorption properties for the traditional metal alloys and their compounds.

Effect of Si Addition on the Weibull Distribution of Tensile Properties of Fe-bearing Al-Cu Alloys

Effect of Si Addition on the Weibull Distribution of Tensile Properties of Fe-bearing Al-Cu Alloys

Understanding grain boundary segregation and solute drag using computational and machine learning studies

Grain boundary (GB) solute segregation has been used as a strategy to tailor the properties and processing pathways of a wide range of metallic alloys. GB solute drag results when segregated alloying elements exert a resistive force on migrating GBs hindering their motion. While GB segregation has been the subject of active research, a detailed understanding of solute drag and the migration kinetics of doped boundaries is still lacking, especially in technologically-relevant alloys. Through theoretical analysis, mesoscale modeling, and machine learning studies, we investigate GB segregation and solute drag and establish design maps relating drag effects to relevant alloy and GB properties, i.e., the complete alloy design space. We find that solute drag is dominant in immiscible alloys with far-from-dilute compositions in agreement with experimental observations of GB segregation in metallic alloys. Our analysis reveals that solute–solute interactions within the GB and the degree of segregation asymmetry greatly influence solute drag values. In broad terms, our work provides future avenues to employ GB segregation to control boundary dynamics during materials processing or under service conditions.

Optimizing the mechanical performance of A356–Sc–Sr alloy via combining machine learning and mechanical stirring under vacuum

In this study, a machine learning design system (MLDS) with a property-oriented optimization strategy was first established to predict the mechanical properties of the A356 alloys with adding Sc and Sr elements. Based on the experimental verification from the MLDS, the addition of 0.2 wt% Sc and 0.067 wt% Sr elements led to the refinement of α-Al grains and eutectic Si phases. Then, the vacuum–stirring was introduced to obtain the semi-solid microstructure of the A356–0.2Sc–0.067Sr alloy. The α-Al grains displayed the spherical morphology and the reduction in pores helped improve the mechanical properties of the alloy. In addition, the effects of stirring time and stirring temperature on the microstructure and mechanical properties of the alloy were investigated. The results demonstrated that the α-Al grains of the alloy were further spheroidized, resulting in the improved mechanical properties. The ultimate tensile strength and elongation of the alloy were 220 MPa and 6.0%, respectively, which were increased by 16.8% and 26.7% in comparison to those of the alloy without vacuum–stirring. The aim of this work is to provide a new method to prepare high-performance A356 alloy through composition design and microstructural control.

Effect of thermal treatments on the surface electrical conductivity of AlSi7Mg produced by laser powder bed fusion

In the last years, the production of hypoeutectic Al-Si waveguide components by metal additive manufacturing has gained increasing attention in the telecommunications industry. The performances of waveguide components are influenced primarily by dimensional tolerances, surface electrical conductivity, surface roughness, and dimensional accuracy. Among these properties, electrical conductivity is known to be strongly influenced by the structural and microstructural characteristics of the alloys.In this work, microstructural and structural properties of an hypoeutectic Al-Si alloy, namely the AlSi7Mg alloy, were studied using FESEM, DSC, and XRD to understand how different thermal treatments (stress relieving, T5, and T6) affect the surface electrical conductivity. In the end, the most suitable thermal treatment to be applied to this alloy to maximize its electrical conductivity and, therefore, its appeal for microwave waveguide components is identified.

Enhancing strength-ductility synergy in 316L stainless steel through pre-straining at 4.2K

In this study, we introduce a novel approach to enhance the strength of face-centered cubic (FCC)-structured 316L austenitic stainless steel (ASS) while preserving its tensile ductility. The proposed method involves subjecting the 316L ASS to a pre-strain of 3.5 % at a cryogenic temperature of 4.2 K, resulting in the formation of multiple-fine-defects, including mechanical twins, stacking faults, hexagonal close-packed phases, and body-centered cubic (BCC) phases, which act as BCC martensite seeds. The formation of multiple-fine-defects in 316L ASS through pre-straining at 4.2 K leads to a substantial increase in the yield strength of approximately 45 %, while also maintaining tensile ductility during the subsequent tensile testing at room temperature. Moreover, these pre-existing defects can effectively suppress cross-slip, resulting in a high fraction of planar BCC martensite, which lead to a higher strain-hardening ability than that of the as-annealed 316L ASS. These findings suggest that the mechanical properties of metastable FCC alloys with low to medium stacking fault energies can be effectively enhanced by facilitating martensite seeds via pre-straining at cryogenic temperatures.