Alloys Of Different Compositions Research Articles

Reverse ε→γ transformations of temperature-induced and stress-induced martensites in Fe–Mn–Si alloys with shape memory effect

In this work we argue that the reverse martensitic transformation (MT) of the stress-induced martensite (SIM) of Fe–Mn–Si-based alloys for moderate prestrains occurs in essentially thermoelastic-like way, in contrast to non-thermoelastic MT of temperature-induced martensite (TIM). We compare, using a number of complementary experimental techniques, the temperatures and the kinetics of the reverse ε→γ martensitic transformation of SIM and TIM for commercial and model Fe–Mn–Si alloys after various thermomechanical treatments. We claim that two studied phenomena are generic in Fe–Mn–Si-based alloys of different compositions and microstructure: first, opposite to the conventional effect of stabilization of martensite by prestrain, the reverse MT during heating of alloys prestrained in bending and tension starts well below (up to 100 K) the start temperature of the reverse MT for the TIM of the same alloy. The difference between engineering temperatures of the start of the reverse transformation, As, for SIM and TIM reaches ca. 50 K, pointing to a need to consider different As for TIM and SIM, AsTIM and AsSIM. Second, the reverse transformations of TIM and SIM show very different kinetics. The reverse MT of SIM is diffuse over the temperature range exceeding 100 K. The reverse MT of TIM, on the contrary, is well localized within the temperature range of ca. 20 K. The experimental observations can be interpreted assuming that, due to the differences in the formation mechanisms of SIM and TIM, the latter shows non-thermoelastic behaviour, whereas the SIM shows similarities with the thermoelastic martensites stabilized by prestrain.

Neural Network as a Tool for Design of Amorphous Metal Alloys with Desired Elastoplastic Properties

The development and implementation of the methods for designing amorphous metal alloys with desired mechanical properties is one of the most promising areas of modern materials science. Here, the machine learning methods appear to be a suitable complement to empirical methods related to the synthesis and testing of amorphous alloys of various compositions. In the present work, a method is proposed a method to determine amorphous metal alloys with mechanical properties closest to those required. More than 50,000 amorphous alloys of different compositions have been considered, and the Young’s modulus E and the yield strength σy have been evaluated for them by the machine learning model trained on the fundamental physical properties of the chemical elements. Statistical treatment of the obtained results reveals that the fundamental physical properties of the chemical element with the largest mass fraction are the most significant factors, whose values correlate with the values of the mechanical properties of the alloys, in which this element is involved. It is shown that the values of the Young’s modulus E and the yield strength σy are higher for amorphous alloys based on Cr, Fe, Co, Ni, Nb, Mo and W formed by the addition of semimetals (e.g., Be, B, Al, Sn), nonmetals (e.g., Si and P) and lanthanides (e.g., La and Gd) than for alloys of other compositions. Increasing the number of components in alloy from 2 to 7 and changing the mass fraction of chemical elements has no significantly impact on the strength characteristics E and σy. Amorphous metal alloys with the most improved mechanical properties have been identified. In particular, such extremely high-strength alloys include Cr80B20 (among binary), Mo60B20W20 (among ternary) and Cr40B20Nb10Pd10Ta10Si10 (among multicomponent).

Production and characterization of Al–Cu binary alloy produced by using novel continuous casting process

Abstract Aluminium (Al) and its constituent alloys has been consistently favoured as a promising material for industrial applications. In conventional casting technique of Al alloys, alloying elements are amalgamated in molten pool of Al melt followed by manual skimming. In contrast, batch type manufacturing includes intrinsic mixing and casting discontinuity, which negatively impacts the flexibility and cost-effectiveness of the process, resulting in a decline in the overall efficacy of the process. In the present study, a novel continuous casting processing route has been used to make Al–Cu binary alloys of different compositions. The newly designed technique makes use of a novel mechanical force convection technology, as well as bottom feeding of the molten metal and alloying element throughout the manufacturing process. The bottom feeding along with rotational swirl ensures better amalgamation of alloying element. Feed rates of Al melt and Al–Cu master alloy were mathematically modelled to obtain the desired alloy composition. The microstructural characterization of the developed alloys exhibit Al–Cu intermetallic phase invariably distributed throughout the sample, which concludes a better performing processing route to prepare Al–Cu binary alloys.

Nanosilver-Reinforced AgSn Alloys for Dental Applications: Mechanical Behavior and Hardness

Aim: AgSn alloys of different compositions were prepared by direct mixing with silver nanoparticles, synthesized, in turn, by an environmentally-friendly method. Method: The procedure was carried out by following the standard technique for preparing dental materials and devices. A detailed mechanical characterization, including the maximum elongation at break, the ultimate tensile strength and the hardness of the resulting nanocomposites, was obtained and numerically fitted by statistically-significant equations Result: The results show improved mechanical performance, as compared to standard materials used in dentistry, in particular amalgams. Conclusion: The procedure described allows to produce low cost materials with tailored mechanical properties.

Пластическое течение в твердых растворах Cu-Ni как автоволновой процесс

The influence of Ni content in Cu-Ni alloys on the localization of plastic flow under uniaxial tension has been studied. The regularities of localization of plastic deformation during linear and parabolic deformation hardening, as well as at the yield point, depending on the Ni content in the solid solution, have been studied by the speckle photography method. The influence of the Ni content on the duration of the stages of parabolic deformation hardening in alloys of different composition was found. The dependence of the spatial period of localization of plastic deformation (the length of the localization autowave) on the Ni content in the studied alloys is established. Keywords: localization of plastic deformation, autowaves, copper-nickel alloys, structure, mechanical properties, deformation and impurity hardening.

Plastic flow in Cu-Ni solid solutions as an autowave process

The influence of Ni content in Cu-Ni alloys on the localization of plastic flow under uniaxial tension has been studied. The regularities of localization of plastic deformation during linear and parabolic deformation hardening, as well as at the yield point, depending on the Ni content in the solid solution, have been studied by the speckle photography method. The influence of the Ni content on the duration of the stages of parabolic deformation hardening in alloys of different composition was found. The dependence of the spatial period of localization of plastic deformation (the length of the localization autowave) on the Ni content in the studied alloys is established. Keywords: localization of plastic deformation, autowaves, copper-nickel alloys, structure, mechanical properties, deformation and impurity hardening.

Study on the electrochemical behaviour of Al3+ in LiCl‐KCl‐AlCl3 melt

AbstractThe electrochemical behaviour of Al3+ reduction on a tungsten electrode in LiCl‐KCl‐AlCl3 molten salt was investigated by electrochemical techniques. Using cyclic voltammetry (CV) and square wave voltammetry (SWV), Al3+ was reduced to Al in one step, and Li was deposited on Al to form Al‐Li alloys of different compositions. According to chronoamperometry (CA), co‐deposition of Li‐Al alloys can be obtained at cathode current densities greater than 0.045 A cm−2 or cathode potentials lower than −2.28 V (vs. Ag/AgCl). The apparent standard potential was calculated using the equilibrium electrode potential obtained from the open‐circuit chronopotentiometry. Al3+ diffusion coefficient calculated by CV at 703 K is 0.82 × 10−5 cm2/s. In addition, the diffusion activation energy of Al3+ in LiCl‐KCl‐AlCl3 molten salt was also obtained using the Arrhenius equation. The linear polarization was used to calculate exchange current density at different temperatures. Based on the theoretical model of metal nucleation deposition developed by Scharifker and Hills, the nucleation process of Al3+ involves instantaneous nucleation in the range of 673~763 K.

Role of Ni, Si and P on the formation of solute-rich clusters under irradiation in Fe-Cr alloys

After irradiation of Fe-Cr alloys of low purity (model alloys of F-M steels), minor solute elements as P, Ni and Si have been shown to create solute clusters which significantly contribute to hardening and might be associated with small dislocation loops. In order to understand the role of each impurity on the formation of the nano-features formed under irradiation and the eventual synergies between the different species, Fe-15at.%Cr-X (X = Si, Ni, P, NiSiP) alloys of different composition have been ion irradiated and characterized using atom probe tomography. Irradiation were performed at 300 °C up to 2.5 dpa in four alloys: Fe15CrNi, Fe15CrSi, Fe15CrP and Fe15CrNiSiP. Influence of C atoms implanted during irradiation on the nanostructure evolution is also discussed. The study of the evolution of the nanofeatures formed under irradiation with the dose as a function of the composition highlights the role of P and C on the formation of the nano-clusters and confirm the radiation-induced nature of solute-rich clusters.

Effect of Grain Size on the Properties of Aluminum Matrix Composites with Graphene

The structure and mechanical properties of composites consisting of a metal matrix based on aluminum and its alloys of different compositions (AA-3003 and AA-5154) and graphene synthes sized in situ under a layer of molten salts were investigated depending on the chemical composition and grain size of the matrix. Aluminum matrix composites of three compositions were studied in as-cast coarse-grained, deformed fine-grained (grain size < 1 mm), and deformed sub microcrystalline (grain size < 1 μm) states in order to compare the structural characteristics of composites with different grain sizes. The composites were subjected to deformation with a split Hopkinson (Kolsky) bar and to dynamic-channel angular pressing. The hardness and dynamic mechanical properties of the composites were measured at strain rates ε˙ from 1.8 − 4.7 × 103 to 1.6 − 2.4 × 105 s−1. It was found that grain refinement induced a sharp increase in the hardness of composites with various compositions (by a factor of 1.6–2.6). A correlation of the elastic-plastic properties of the aluminum matrix composites with the grain sizes and chemical compositions of the matrices was established. A transition from coarse-grained to sub microcrystalline structure was shown to improve the elastic-plastic properties on average by a factor of 1.5. It was proved that the reinforcing effect of graphene increased with the decreasing grain size of the matrix. Mechanisms of reinforcement of the aluminum matrix composites using graphene were proposed.

Wigner-Weyl description of light absorption in disordered semiconductor alloys using the localization landscape theory

The presence of disorder in semiconductors can dramatically change their physical properties. Yet, models faithfully accounting for it are still scarce and computationally inefficient. We present a mathematical and computational model able to simulate the optoelectronic response of semiconductor alloys of several tens of nanometer sidelength, while at the same time accounting for the quantum localization effects induced by the compositional disorder at the nano-scale. The model is based on a Wigner-Weyl analysis of the structure of electron and hole eigenstates in phase space made possible by the localization landscape theory. After validation against eigenstates-based computations in 1D and 2D, our model is applied to the computation of light absorption in 3D InGaN alloys of different compositions. We obtain the detailed structures of the absorption tail below the average bandgap and the Urbach energies of all simulated compositions. Moreover, the Wigner-Weyl formalism allows us to define and compute 3D maps of the effective locally absorbed power at all frequencies. Finally the proposed approach opens the way to generalize this method to all energy-exchange processes such as radiative and non-radiative recombination in realistic devices.

Coating of aluminum substrates with nanostructured Pd–Ni alloys by electrodeposition

Pd–Ni alloys are electrodeposited onto low-purity aluminum substrates varying both the composition of the feeding solution and the applied electrodeposition potential. It is found that the initial nucleation-and-growth mechanism in every case is well described by a 3D-type nucleation process. The resulting deposits consist of Pd–Ni alloys of different compositions, all electrocrystallized in a disordered fcc phase; depending on the electrodeposition parameters, different morphologies and compositions are obtained. It is found that when the electrodeposition potential is high and the Pd content in the feeding solution is low, the substrate coating is more efficient and the deposit morphology tends to refine into dendritic-like structures, making this kind of deposit quite interesting for using as electrodes in electrochemical devices. Room temperature magnetic measurements indicate that the samples are soft ferromagnetic with negligible demagnetizing effects. Dendritic and spheroidal-like Pd-rich deposits exhibit larger remanence values and are more coercive than those with higher Ni content due to the dependence of the anisotropy constant on the alloy composition.

Metallurgical processing of Mg alloys and MgH2 for hydrogen storage

The reversible reaction of hydrogen with metallic Mg to form MgH2 has been evaluated by more than 70 years, with particular attention in the last 20–30 years for the exceptional properties of this hydride to store energy. The main challenges to the practical use of these properties were soon identified; the high thermodynamical stability of the hydride, resulting in high temperatures for absorption / desorption of hydrogen; the low diffusion rate of hydrogen in Mg and in MgH2, which requires short diffusion distances and therefore, large surface, interface or interphase areas and the presence of catalyst to improve the absorption and desorption kinetics. Thermodynamic stability cannot be modified by the microstructure, which can, however, affect the other above-mentioned challenges. The first Mg samples to react with hydrogen were prepared by conventional metallurgical routes, but with the important addition of being crushed to be smaller than a certain particle size. Turnings of bulk Mg or Mg alloys samples were also used, resulting in the same increase in surface and interfaces area as the crushed particles. Alloys of different compositions, including eutectic alloys were designed to result in a combination of phases, with one of them in conditions to form a hydride and the other to act as catalyst, or most likely just supplying extra interphases for hydrogen diffusion. But since melting of Mg and Mg alloys is not a friendly process, mechanical alloying was considered simpler and more adequate to prepare Mg powders, resulting in the identification of the exceptional properties of nano powders to improve kinetics but also stressing the difficulties of handling nano powders and the deleterious effect of surface contamination. Severe plastic deformation was then used to prepare “bulk” nanograined material with the expectation to design microstructures with special textures and special types of grain boundaries and to avoid the problem associated with surface reactivity. Because of kinetics limitation, the SPD techniques had to be combined with other processing step, such as filing, cold rolling or milling, basically to increase the surface / interface area. Extensive plastic deformation via co-lamination had already been used but the necessity to complement SPD processing led to the use of conventional metallurgical processing such as cold rolling and cold forging to process Mg and MgH2. Such metallurgical routes prove to be simpler and cost-effective to deliver microstructures satisfying the requirement for Mg and MgH2 to act as hydrogen storage material. Other processing routes or combination of routes that could result in refined microstructure have also been studied, including melt spinning, melt spinning combined with HEBM or with cold-rolling, friction stir welding, mechanical grinding and filing and chips from lathe turnings. In this review we discuss the evolution of metallurgical processing of Mg and MgH2 based hydrogen storage material and how each processing route can lead to microstructures with the required characteristics.

Al Composition Dependence of Band Offsets for SiO2 on α-(AlxGa1−x)2O3

Valence band offsets for SiO2 deposited by Atomic Layer Deposition on α-(AlxGa1-x)2O3 alloys with x = 0.26–0.74 were measured by X-ray Photoelectron Spectroscopy. The samples were grown with a continuous composition spread to enable investigations of the band alignment as a function of the alloy composition. From measurement of the core levels in the alloys, the bandgaps were determined to range from 5.8 eV (x = 0.26) to 7 eV (x = 0.74). These are consistent with previous measurements by transmission spectroscopy. The valence band offsets of SiO2 with these alloys of different composition were, respectively, were −1.2 eV for x = 0.26, −0.2 eV for x = 0.42, 0.2 eV for x = 0.58 and 0.4 eV for x = 0.74. All of these band offsets are too low for most device applications. Given the bandgap of the SiO2 was 8.7 eV, this led to conduction band offsets of 4.1 eV (x = 0.26) to 1.3 eV (x = 0.74). The band alignments were of the desired nested configuration for x > 0.5, but at lower Al contents the conduction band offsets were negative, with a staggered band alignment. This shows the challenge of finding appropriate dielectrics for this ultra-wide bandgap semiconductor system.

Properties improvement of titanium alloys scaffolds in bone tissue engineering: a literature review

Owing to their excellent biocompatibility and corrosion-resistant properties, titanium (Ti) (and its alloy) are essential artificial substitute biomaterials for orthopedics. However, flaws, such as weak osteogenic induction ability and higher Young’s modulus, have been observed during clinical application. As a result, short- and long-term postoperative follow-up has found that several complications have occurred. For decades, scientists have exerted efforts to compensate for these deficiencies. Different modification methods have been investigated, including changing alloy contents, surface structure transformation, three-dimensional (3D) structure transformation, coating, and surface functionalization technologies. The cell-surface interaction effect and imitation of the natural 3D bone structure are the two main mechanisms of these improved methods. In recent years, significant progress has been made in materials science research methods, including thorough research of titanium alloys of different compositions, precise surface pattern control technology, controllable 3D structure construction technology, improvement of coating technologies, and novel concepts of surface functionalization. These improvements facilitate the possibility for further research in the field of bone tissue engineering. Although the underlying mechanism is still not fully understood, these studies still have some implications for clinical practice. Therefore, for the direction of further research, it is beneficial to summarize these studies according to the basal method used. This literature review aimed to classify these technologies, thereby providing beginners with a preliminary understanding of the field.

Mechanical Alloying of Elemental Powders into Nanocrystalline (NC) Fe-Cr Alloys: Remarkable Oxidation Resistance of NC Alloys

Mechanical alloying is among the few cost effective techniques for synthesizing nanocrystalline alloy powders. This article reviews mechanical alloying or ball-milling of (NC) powders of Fe-Cr alloys of different compositions, and the remarkable oxidation resistance of the NC alloy. The article also reviews challenges in thermal processing of the mechanically alloyed powders (such as compaction into monolithic mass) and means to overcome the challenges.

Screening for O phase in advanced γ–TiAl alloys

This is a screening study using high-energy X-ray diffraction measurements to determine whether an orthorhombic phase forms in γ-based TiAl alloys of different compositions. The 13 alloy compositions investigated were chosen to be either close to commercial alloys or to identify the effects of different single alloying elements on the formation of orthorhombic phase. The orthorhombic O phase with Cmcm structure was found in several of those γ-TiAl alloys after an aging heat treatment at 550 °C for 20 h. The presence of different β-stabilising elements such as niobium, tantalum, molybdenum or vanadium did promote the formation of orthorhombic phase, while micro alloying elements such as carbon or boron were neutral in this respect. Furthermore, a limit for aluminium was also found, below which the orthorhombic O phase is formed in the alloys investigated. This limit lies between 46 at.% and 47 at.%.

Hardness characteristics of as-cast Ni-Ru-Zr alloys

The Vickers hardness of 21 as-cast Ni-Ru-Zr alloys of different compositions were studied, and nanohardness indentations were done on the individual phases. The results were used to explain the brittleness by assessing the proportions of the phases, and their morphologies. The compound hardness varied between 704 - 1289 HV, with ~ZrRu2 being the hardest phase, and ~Zr2Ni7 being the least hard phase. The sample hardness was 300 - 1015 HV. Most of the samples were brittle, although there were regions of toughness around Ni36:Ru13:Zr51 and Ni20:Ru5:Zr75 (at.%). No alloy was identified to have potential good mechanical properties.

Structural Characteristics of Multilayered Ni-Ti Nanocomposite Fabricated by High Speed High Pressure Torsion (HSHPT)

It is generally accepted that severe plastic deformation (SPD) has the ability to produce ultrafinegrained (UFG) and nanocrystalline materials in bulk. Recent developments in high pressure torsion (HPT) processes have led to the production of bimetallic composites using copper, aluminum or magnesium alloys. This article outlines a new approach to fabricate multilayered Ni-Ti nanocomposites by a patented SPD technique, namely, high speed high pressure torsion (HSHPT). The multilayered composite discs consist of Ni-Ti alloys of different composition: a shape memory alloy (SMA) Ti-rich, whose Mf > RT, and an SMA Ni-rich, whose Af < RT. The composites were designed to have 2 to 32 layers of both alloys. The layers were arranged in different sequences to improve the shape recovery on both heating and cooling of nickel-titanium alloys. The manufacturing process of Ni-Ti multilayers is explained in this work. The evolution of the microstructure was traced using optical, scanning electron and transmission electron microscopes. The effectiveness of the bonding of the multilayered composites was investigated. The shape memory characteristics and the martensitic transition of the nickel-titanium nanocomposites were studied by differential scanning calorimetry (DSC). This method opens up new possibilities for designing various layered metal-matrix composites achieving the best combination of shape memory, deformability and tensile strength.

Effect of high pressure processing in the formation of castings of aluminum alloys

The effect of high pressure on the formation conditions of aluminum castings has been investigated. It was established experimentally that the crystallization of castings under high mechanical pressure proceeds at a higher temperature difference across the cross section than at atmospheric pressure. The cooling rate of a cylindrical casting in various zones on the section, which is characteristic for cooling alloy in the crystallization range, is determined. The formula for calculating the solidification time of a casting and the time of its holding pressure during piston compression is recommended. The influence of the scale factor on the solidification time of cylindrical castings is considered. It is shown that with increasing height at a constant diameter of the casting, the relationship between the solidification time and diameter of the casting is linear. It has been experimentally established that the solidification coefficient of an alloy depends on its thermophysical properties of the alloy and the applied pressure. Its value increases with decreasing silicon content in the alloy and increasing pressure. The pressure significantly reduces the difference in the values of the solidification coefficient of castings from alloys of different compositions.

Abrasive wear of metal surface modified with mineral particles

The resistance of mineral coatings created on the surface of specimens of 20X13 steel (Russian analogue of steel 20Cr13 (EU)) modified with ultradispersed mineral particles to abrasive wear during friction against fixed particles was determined, and the wear parameters of layers modified with mineral particles were compared with the parameters of surface layers created by laser cladding of alloys of different compositions. The studies were carried out on an experimental setup for testing abrasive wear under a static load of 60 N and 160 N and determined the weight wear, the average wear rate and the average wear rate of the surface layer of three samples with different mineral coatings. According to the results of measurements at a pressure on the wear surface of 0.5 MPa, a sample was determined with an indicator of weight wear comparable to a coating made of cobalt alloy, created by the method of laser cladding and about four times inferior in this indicator, to a coating of a nickel alloy, created by the method of laser cladding and tool steel. The practical use of various methods of protecting parts from abrasive wear is determined, along with the physical and technical characteristics of the layers, by the economic feasibility in specific operating conditions.