Role In Alloys Research Articles

Role of alloying and heat treatment on microstructure and mechanical properties of cast Al-Li alloys: A review

Role of alloying and heat treatment on microstructure and mechanical properties of cast Al-Li alloys: A review

Alginic acid-functionalized silver nanoparticles: A rapid monitoring tool for detecting the technology-critical element tellurium

The increasing global demand for tellurium, driven by its critical role in alloys, photovoltaic devices, and electronics, has raised concerns about its environmental pollution and neurotoxicity. In response, the potential of alginic acid (AA), a renewable, low-cost, and sustainable biopolymer, was explored for the biosynthesis of ultra-small silver nanoparticles (AgNPs) and their application in the detection of tellurium (Te(IV)). The effect of key synthesis parameters on desired physicochemical properties and yield of AgNPs was established to ensure high specificity and sensitivity towards Te(IV). The purified AgNPs with AA surface ligands were utilized to demonstrate a ratiometric absorbance sensor that exhibits excellent linearity and nanomolar-level affinity. This approach achieved a high correlation coefficient of ∼ 0.982, with a low detection limit of about 22 nM. Further investigations into the effect of pH, ionic strength, and organic molecules were conducted to elucidate detection performance and molecular understanding. The detection mechanism relies on the coordination between Te(IV) ions and the carboxylate groups of AA, which initiates aggregation-induced plasmon coupling in adjacent AgNPs. The capability of this analytical method to monitor Te(IV) in real-world water samples features its rapidity, user-friendliness, and suitability for point-of-care monitoring, making it a promising alternative to more complex techniques.

Environment-Induced Degradation of Shape Memory Alloys: Role of Alloying and Nature of Environment.

Shape memory effects coupled with superelasticity are the distinctive characteristics of shape memory alloys (SMAs), a type of metal. When these alloys are subject to thermomechanical processing, they have the inherent ability to react to stimuli, such as heat. As a result, these alloys have established their usefulness in a variety of fields and have in recent years been chosen for use in stents, sensors, actuators, and several other forms of life-saving medical equipment. When it comes to the shape memory materials, nickel-titanium (Ni-Ti) alloys are in the forefront and have been chosen for use in a spectrum of demanding applications. As shape memory alloys (SMAs) are chosen for use in critical environments, such as blood streams (arteries and veins), orthodontic applications, orthopedic implants, and high temperature surroundings, such as actuators in aircraft engines, the phenomenon of environment-induced degradation is of both interest and concern. Hence, the environment-induced degradation behavior of the shape memory alloys (SMAs) needs to be studied to find viable ways to improve their resistance to an aggressive environment. The degradation that occurs upon exposure to an aggressive environment is often referred to as corrosion. Environment-induced degradation, or corrosion, being an unavoidable factor, certain techniques can be used for the purpose of enhancing the degradation resistance of shape memory alloys (SMAs). In this paper, we present and discuss the specific role of microstructure and contribution of environment to the degradation behavior of shape memory alloys (SMAs) while concurrently providing methods to resist both the development and growth of the degradation caused by the environment.

Electronic and excitonic properties of ultrathin (In,Ga)N layers: the role of alloy and monolayer width fluctuations.

We present an atomistic theoretical analysis of the electronic and excitonic properties of ultrathin, monolayer thick wurtzite (In,Ga)N embedded in GaN. Our microscopic investigation reveals that (i) alloy fluctuations within the monolayer lead to carrier localization effects that dominate the electronic and optical properties of these ultrathin systems and that (ii) excitonic binding energies in these structures exceed the thermal energy at room temperature, enabling excitonic effects to persist even at elevated temperatures. Our theoretical findings are consistent with, and provide an explanation for, literature experimental observations of (i) broad photoluminescence linewidth and (ii) excitonic effects contributing to the radiative recombination process at elevated temperatures. When accounting for small structural inhomogeneities, such as local thickness fluctuations of one monolayer, "indirect" excitons may be found, with electrons and holes independently localized in different spatial positions. This result also provides further arguments for experimentally observed effects such as (i) non-exponential decay curves in time dependent photoluminescence spectra and (ii) the "S"-shape temperature dependence of the photoluminescence peak energies. Overall, our results provide fundamental understanding, on an atomistic level, of the electronic and optical properties of ultrathin, quasi 2D (In,Ga)N monolayers embedded in GaN, and offer guidance for the tailoring of their properties for potential future device applications.

Quantification of APT physical limitations on chemical composition of precipitates in Fe–Cr alloys

Among the different nano-features at the origin of embrittlement of Fe–Cr alloys and steels, α′ precipitates play a major role in alloys with Cr content higher than about 10at.%. If Atom Probe Tomography (APT) is recognized as an efficient technique for characterizing α′ precipitates, discussions remain on its ability to measure the actual composition of small particles. Two APT limitations are at the origin of these discussions: its lateral resolution (and on a smaller scale the depth resolution) and local magnification effects due to the difference in field evaporations between the matrix and the particles. In this study, the impacts of these two limitations are quantified for the first time using numerical approaches and an analytical model. This will provide an overview of the interpretation for the α’ particles chemical composition experimentally measured by APT.The results show that: (i) the major effect of local magnification is ion focussing with no mixing in the core of the particles for particle radius larger than 1 nm, (ii) lateral resolution is the main contributor to the composition bias. Depending on the lateral resolution, the core of the small particles may be diluted by matrix atoms but the dilution does not exceed 5.2 at.%. The extent of the decrease in measured Cr concentration of the particles depends on the Cr concentration difference between particles and the surrounding matrix.

First-principles study of phase stability and solubility in Al-(Cu, Zr) alloys

ABSTRACTThe solubility limit of elements plays a crucial role in alloy designing, as well as in the understanding of kinetic processes in alloys. Using first-principles calculations, we calculated the ground states of Al-Cu and Al-Zr compounds, and predicted the stable and metastable structures of these two binaries. The results indicate that the stable structures for Al-Cu compounds are Al2Cu(cF12), AlCu(mC20), Al4Cu9(cP52) and AlCu3(tI8), and those for Al-Zr binary are Al3Zr(tI16), Al2Zr(hP12), Al3Zr4(hP7) and AlZr3(cP4). Based on the statistical-thermodynamic theory of dilute lattice gas, we presented a systematic series of calculations of the solubility limits of Cu and Zr in Al as a function of temperature. It is found that the solubility of Cu is much higher than Zr over the whole investigated temperature range.

First-Principles Study of Phase Stability and Solubility in Fe-RE (Y, La, Ce) Alloys

The solubility limit of elements plays a crucial role in alloy designing, as well as in the understanding of kinetic processes in alloys. Using first-principles calculations, we calculated the ground states of Fe-RE compound, and predicted the stable and metastable structures of Fe-Y and Fe-Ce. The results indicate that the stable structures for Fe-Y compounds are Fe 12 Y.tI26, Fe 17 Y 2 .hP38 and Fe 2 Y.cF24, and those for Fe-Ce binary are Fe 17 Ce 2 .hP38, Fe 19 Ce 5 .hR24 and Fe 2 Ce.cF24. Based on the statistical-thermodynamic theory of dilute lattice gas, we presented a systematic series of calculations of the solubility limits of RE in α -Fe as a function of temperature. It is found that the solubilities are sorted in the following order: S La > S Ce > S Y , corresponding to the trend in the solubility formation enthalpies: H sol (La)< H sol (Ce)< H sol (Y).

Analysis of the various processes downstream cathodic hydrogen charging, II: Charging transients, precharging and natural permeation

The new views of the subject since 2000 on cathodic hydrogen charging are introduced through the numerical modelling of the downstream hydrogen diffusion, and this Part II deals with other experimental issues not covered in the laboratory permeation described in Part I: these include HIC testing of plane sheet in two-face exposure, SSC testing and cylindrical tensile specimen, necessarily imperfect quenching of precharged specimens, impossible confusion between trapping and poor degassing, and natural permeation in the field. Orders of magnitude are given for the practical application of present calculations, and the role of alloying is also mentioned, as well as that of corrosion layers. An example of what should no longer be done is also discussed, namely the re-use of all the historical calculation tools available in the literature, since they are strictly incompatible with the present views on cathodic charging. Actually, such “approximation” would range from good or fair to awfully poor, but this depends on each calculation type. The method of airstream measurement is also discussed in the light of this new modelling, as well as the basic principles of fitness-for-purpose and application specific testing for full HIC-resistance.

Phase and structural transformations in corrosion-resistant steels upon high-pressure torsion and heating

High-pressure torsion (HPT) at a pressure of 6 GPa and room temperature is found to form a nanocrystalline structure in corrosion-resistant austenitic 05Kh15N9D2TAMF and 08Kh18N10T steels and a submicrocrystalline structure in corrosion-resistant ferritic 08Kh18T1 steel and armco iron. X-ray diffraction analysis of both austenitic steels reveals the γ → α and γ→ ɛ→ α martensitic transformations during HPT at room temperature. After HPT, the strain hardening in the austenitic and ferritic steels is approximately the same and mainly determined by nano- and submicrocrystalline structures, and the role of alloying and phase composition weakens. The thermal stability of the hardening in the austenitic and ferritic steels is almost the same, ∼400°C. As a result of HPT, the austenitic 08Kh18N10T and ferritic 08Kh18T1 steels acquire an axial texture with the predominant 〈211〉γ direction in austenite and the 〈110〉α and 〈311〉α directions in martensite and ferrite, respectively. The axial texture is retained in both steels up to a heating temperature of 750°C.

Spin–orbit coupling: a recursion method approach

Relativistic effects play a significant role in alloys of the heavier elements. Majority of earlier works on alloys had included the scalar relativistic corrections. We present here a methodology to take into account the spin–orbit coupling using the recursion method. The basis used for representation of the Hamiltonian is the TB-LMTO (Phys. Rev. B 12 (1975) 3060, Phys. Rev. Lett. 53 (1984) 2571), since its sparseness is an essential requirement for recursion. The recursion technique (J. Phys. C 5 (1972) 2845; Surf. Sci. 38 (1973) 139; J. Phys.: Condens. Matter 6 (1994) L245, Phys. Rev. B 51 (1995) 3413) can then be extended to augmented space to deal with disordered alloys.

Role of alloys in the thermal decomposition and combustion of ammonium perchlorate

The participation of aluminum in the decomposition reaction of ammonium perchlorate (AP) is enhanced if magnesium is added—either as a mixture of Al and Mg powders or as an alloy of Mg in Al. The differential thermal analyses of the compositions show a sensitization in the temperatures of decomposition, as well as increase in the heat of reaction. The AP-Mg and Ap-(MgLi) alloy pellets also show increased reactivity. The burning rates of AP-(Al-10% Mg) alloy pellets increase with increase in the alloy content, while calorimetric values peak at 40% alloy content. The combustion product gases of AP-40% (Al-10% Mg) alloy contain large quantities of hydrogen.

Microstructural control in lead alloys for storage battery application

The role of alloying and thermomechanical processing in direct microstructural control in lead-base storage battery alloys is reviewed. Strength, corrosion, and electrochemical correlations are discussed for conventional and emerging lead alloy systems.