Random solid solution alloys are a broad class of materials that are used across the entire spectrum of engineering metals, whether as stand-alone materials (e.g. Al-5xxx alloys) or as the matrix in ...precipitate-strengthening materials (e.g. Ni-based superalloys). As a result, the mechanisms of, and prediction of, strengthening in solid solutions has a long history. Many concepts have been developed and important trends identified but predictive capability has remained elusive. In recent years, a new theory has been developed that builds on one historical model, the Labusch model, in important ways that lead to a well-defined model valid for random solutions with arbitrary numbers of components and compositions. The new theory uses first-principles-computed solute/dislocation interaction energies as input, from which specific predictions emerge for the yield strength and activation volume as a function of alloy composition, temperature, and strain-rate. Being a general model for materials that otherwise have a low Peierls stress, it has broad application and has been successfully applied to Al-X alloys, Mg-Al, twinning in Mg alloys, and recently fcc High-Entropy Alloys. Here, the new theory is presented in a general and systematic manner. Approximations and limiting cases that reduce the complexity and facilitate understanding are introduced, and help relate the new model to various physical features present among the historical array of models, other recent models, and simulation studies. The quantitative predictions of the model in the various materials above is then demonstrated.
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•Pressure weakening unusual caged dynamics of metallic glass-forming liquid is illustrated.•The pressure causes the Al atoms to be less hindered by the surrounding atoms, enhancing the cage-breaking ...motion.•The dominant polyhedra under different pressures can affect the unusual caged dynamics.•The pressure increases the diversity of vibrational frequencies and weakens the difference in vibrational amplitudes.
Caged dynamics is the precursor of β-relaxation and is part of the complex relaxation dynamics of metallic glasses. However, limited by the lack of suitable experimental techniques, the pressure dependence of the caged dynamics of glass-forming metallic liquids and its underlying mechanism are still an open question to date. An unusual caged dynamics manifests a sudden drop near 0.1 ps in the partial non-Gaussian parameter of Al atoms in metallic alloy La80Al20 liquid was recently found by molecular dynamics simulations. The present work investigates the caged dynamics of the La80Al20 liquid with strong atomic interactions under different pressures again by molecular dynamics simulations. It is found that the dominant polyhedra are transformed from the stable icosahedral-like polyhedra to the unstable ones that are compatible with crystal symmetry, resulting in the promotion of the rearrangement of atoms. These changes in turn cause the central Al atoms to be less hindered by the surrounding atoms, enhancing the cage-breaking motion and weakening the unusual caged dynamics. In addition, the applied pressure not only increases the diversity of vibrational frequencies but also weakens the difference in atomic vibrational amplitudes, leading to the weakening of the unusual caged dynamics. These findings provide new insights into the caged dynamics under pressure from the perspective of microstructure and vibrational properties.
Failure of metals II: Fatigue Pineau, André; McDowell, David L.; Busso, Esteban P. ...
Acta biomaterialia,
04/2016, Letnik:
107
Journal Article
Recenzirano
Odprti dostop
In this interpretive review, fatigue in metallic systems is considered primarily from the perspective of interactions between the microstructure, the deformation mode and the mechanical state at both ...low and high temperatures. In Part 1 the development and early propagation of cracks is considered in terms of the basic damage mechanisms and the relative size of the crack with respect to applicable microstructural feature(s). In this section, a multistage grain scale approach to microstructure-sensitive fatigue crack formation and growth is presented which uses Fatigue Indicator Parameters (FIPs) to correlate these processes. Various FIPs parameters are discussed in terms of their indication of the state of fatigue. The development and early crack propagation is considered in the context of microstructure and notches, and probabilistic aspects of the notch fatigue problem are discussed. These features are integrated into a systematic approach for the selection of fatigue resistant microstructures for given applications. In Part 2, attention is focused on Ni-base superalloys and the interaction between oxidation, creep and microstructure (including coatings) in the formation and propagation of cracks. This part of the overview addresses both experimental and modelling aspects. Methodologies based upon fundamental physical processes are presented for understanding and predicting the development and propagation of fatigue cracks, including effects of sequential oxide type formation and of creep on either restraining or accelerating damage by oxidation. The variable fatigue resistance of discs in jet engines is seen to depend upon the variability of microstructure and its influence on the severity of creep/oxidation interactions. All of these factors are considered in the practical case where both temperature and loading parameters vary simultaneously (thermomechanical fatigue). A physics-based life prediction model considering the interactions of deformation and environmental damage is reviewed in terms of its applicability to life prediction of components.
Recombination of Frenkel defects is an important process that contributes to the performance of materials under irradiation. In this work, the recombination mechanisms of Frenkel defects in ...face-centered cubic Ni and Ni‒containing solid‒solution alloys are investigated based on interatomic potentials and ab initio calculations. It is found that, in pure Ni, the spontaneous recombination volume for a 100 dumbbell interstitial is 18Ω and 34Ω (Ω is the atomic volume) with the empirical potential and ab initio method respectively. Addition of Fe atoms increases the spontaneous recombination volume of Frenkel defects significantly. For those stable Frenkel defects that cannot recombine, a stronger attractive force between the interstitial and the vacancy is found in concentrated Ni‒Fe alloys compared to in pure Ni, which provides the driving force for enhanced recombination. The distribution of life-time for Frenkel defects at finite temperature suggests that recombination in Ni‒Fe alloys is delayed due to the sluggish diffusion of interstitials. Finally, recombination in Ni‒Fe‒Cr alloys is studied by substituting a portion of Fe in Ni‒Fe with Cr. A remarkable increase in recombination probability is observed in this case because of the presence of less stable Cr‒containing than Fe‒containing dumbbell interstitials and lower migration barriers of vacancies. This work reveals that higher defect recombination probability in concentrated alloys is responsible for the experimentally observed enhanced irradiation resistance.
The number of recombiantion sites increases signifiantly when alloying Fe into Ni, which can promote defect recombiantion and enhance irradiation tolerance. Display omitted
Femtosecond laser irradiation in Au@Ag, Ag@Au core@shell, and Au–Ag Janus-like nanoparticles are investigated using molecular dynamics simulations. Our results show that the morphology of Au@Ag ...core–shell and Au–Ag Janus-like nanoparticles tend to form hollow-like nanostructures due to the ultrafast energy transfer and the subsequent cooling process. In contrast, our results also shows that Ag@Au nanoparticles do not form a hollow structure due to the high diffusion of Ag atoms and the limited expansion of the Au shell. Besides, successive laser impacts on the Au–Ag Janus-like nanoparticle produce a structure that alternates from hollow to a solid nanoparticle and, at the same time, promotes atomic diffusion, favoring the alloying process of the Ag and Au atoms. In addition, the evolution of the crystalline structure is studied, observing a saturation of the planar defects due to the impossibility of forming a new crystalline phase. The energy variation between the initial and final step, it is not influenced by the presence of the hollow, however it is dominated by the increase of planar defects.
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•A novel method to produce alloy nanoparticles is proposed.•Ultrafast laser produce hollow and Janus AuAg nanoparticles.•Successive laser irradiation controls size and shape of the samples.
As a rapidly emerging class of metallic materials, high-entropy alloys (HEAs) provide the opportunity to develop novel alloys with superior mechanical properties through tackling the long-standing ...challenges, such as strength-ductility trade-off dilemma. Herein, C-doped CrMnFeCoNi0.8 alloys were produced by vacuum induction melting. The addition of C up to 0.1 at % strengthens the CrMnFeCoNi0.8 alloy without sacrificing ductility. Compared to the base alloy, the yield strength of the C0·1CrMnFeCoNi0.8 alloy was increased by ∼40% from 240.9 MPa to 334.2 MPa at no reduction in tensile ductility, mainly attributed to the formation of fully coherent carbide precipitates on the grain boundaries. The mechanical properties of the C0·1CrMnFeCoNi0.8 alloy can be further enhanced by annealing. The alloy annealed at 950 °C exhibits a yield strength of 517.8 MPa, an ultimate tensile strength of 914.6 MPa, and an appreciable ductility (20.5%), achieving an excellent combination of strength and ductility. Furthermore, the influence of C addition on the mechanical properties and electronic structures were explored using density functional theory (DFT) calculations to understand the enhanced strength-ductility synergy in the C0·1CrMnFeCoNi0.8 alloy.
•New application of LIBS in industry.•Hardness of metallic alloys estimation using LIBS calibration curves.•Linear correlation between the plasma temperature and the hardness of metallic alloys.•The ...shock wave is fast when the material is hard.
Surface hardness is a very important characteristic of metals. Its monitoring plays a key role in industry. In the present paper, using laser induced breakdown spectroscopy (LIBS), Fe–V18%–C1% alloys with different heat treatments have been used for making the correlation between surface hardness and laser-induced plasma temperatures. All investigated samples were characterized by the same ferrite phase with different Vickers surface hardnesses. The differences in hardness values were attributed to the crystallite size changes. A linear relationship has been obtained between the Vickers surface hardness and the laser induced plasma temperature. For comparison the relation between surface hardness and the ratio of the vanadium ionic to atomic spectral lines intensities (VII/VI) provided good linear results too. However, adopting the proposed approach of using the plasma temperature, instead, is more reliable in view of the difficulties that could be encountered in choosing the proper ionic and atomic spectral lines. To validate this approach we have investigated the shock wave speed induced by laser interaction with the used samples. It was found that harder is the material faster is the shock wave. The determination of the surface hardness via measuring Te shows the feasibility of using LIBS as an easy and reliable method for in situ industrial application for production control.
Abstract
In this work, the shielding performance of (97.3–x)Pb–xCd–2.7Ag (x = 10, 18, and 30) ternary alloys against neutrons and gamma rays has been investigated. The microstructure, thermal and ...mechanical properties of the ternary alloys were examined. The total mass attenuation coefficients,
μ
/
ρ
,
for prepared alloys were determined at 662, 1173, and 1332 keV photon energies using NaI (Tl) scintillation detector. The theoretical values of
μ
/
ρ
were calculated using WinXCom program depending on the mixture rule. The estimated values were compared with the measured values for all investigated alloys. Atomic cross-section,
σ
a
, electronic cross-s
e
ction,
σ
e
, effective atomic number,
Z
eff
, effective electron number,
N
eff
, and GP fitting parameters (b, c, a, X
k
, and d) were determined. The exposure buildup factor, EBF, have been also calculated. Fast neutron attenuation for the prepared samples have been investigated via the macroscopic effective removal cross-section (
∑
R
) calculation. Also, thermal neutron attenuation has been evaluated via neutron scattering calculator. The results show that the alloys containing 10 and 30% Cd compromise between superior tensile strength and Young modulus, while the pasty range, heat of fusion and ductility decreased with increasing Cd content. Moreover, the prepared ternary alloys have a high attenuation ability for gamma rays as the standard Pb. The increase of Cd ratio also significantly enhances the thermal neutron attenuation by amazing way along with the increase in the attenuation rate of fast neutrons.
Cashew Nut Shell Liquid (CNSL) has been explored in several applications within the sustainability principles and circular economy of agro-industrial product waste. To understand the anticorrosive ...and lubricant properties of CNSL solutions, a multi-faceted approach, incorporating electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for mild steel AISI 1012, stainless steel AISI 420 and Aluminium Alloy 6061. Electrochemical analyses reveal a positive impact of CNSL, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current, indicating effective corrosion inhibition for stainless steel and aluminium alloy. In mild steel, CNSL exhibits a mixed-type inhibition with efficiency increasing in correlation with oil concentration. The lubricating properties of CNSL are evident according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests. Tribochemical tests demonstrate a reduction in wear and an improvement in tribocorrosion behavior under sliding conditions. CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits. The concentration-dependent effects highlight the need for optimization in specific applications, particularly for passive materials. CNSL not only inhibits corrosion through film formation but also provides effective lubrication, reducing friction, wear, and chemical-mechanical degradation. This research contributes valuable insights to corrosion science. It proposes practical applications for CNSL in diverse industrial contexts, showcasing its potential as an environmentally friendly and sustainable solution for tribocorrosion challenges.
•The influence of Cashew Nut Shell Liquid (CNSL) on the tribocorrosion behavior across three metallic alloys (mild steel, stainless steel, and aluminium) is explored.•Electrochemical analyses, immersion test, tribological measurements, and tribochemical characterization was carried out for AISI 1012, AISI 420 and AA6061.•CNSL exhibited a positive impact on corrosion inhibition for stainless steel and aluminium alloy, inducing a shift in corrosion potential to more positive values and a decrease in corrosion current.•CNSL demonstrated lubricating properties according to the coefficients of friction (COF) obtained and the elastohydrodynamic lubrication regime observed during tribological tests.•CNSL emerges as a promising tribocorrosion mitigator, demonstrating multifaceted benefits.
With an aim of efficiently using radiations in different fields, radiation physicists are continuously exploring different type of materials in terms of visualizing various parameters. Besides ...physical parameters viz. density, hardness/structural strength; special emphasis has been given to radiation shielding parameters which includes mass attenuation coefficient (μm), effective atomic number (Zeff), electron density (Ne), mean free path (mfp), half value layer (HVL), tenth value layer (TVL), exposure buildup factor (EBF) and energy exposure buildup factor (EABF). In the present work, an attempt has been made not only to summarize the various investigations made so far on visualizing the feasibility of alloys as radiation shielding material; but also to provide comparative study for further consideration to be used in other fields.
•Summarized the feasibility of using various alloys as gamma radiations shielding material.•Comparative study on the basis of some shielding parameters for selective metallic alloys.•Besides physical parameters, economical factors were also considered.•Finds applications at experimental nuclear labs, storing, shielding and collimating radioactive sources.
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