ABSTRACTResistance ρ of an one-dimensional disordered system of length L has the log-normal distribution in the limit of large L. Parameters of this distribution depend on the Fermi level position, but are independent on the boundary conditions. However, the boundary conditions essentially affect the distribution of phases entering the transfer matrix and generally change the parameters of the evolution equation for the distribution P(ρ). This visible contradiction is resolved by the existence of the hidden symmetry, whose nature is revealed by the derivation of the equation for the stationary phase distribution and by analysis of its transformation properties.

ABSTRACTAfter solutionizing and aging at 980°C for various durations, the compressive deformation behaviour and mechanisms of the directionally solidified nickel-based superalloy CM247LC are investigated at room temperature. Experimental results show that the yield strength decreases gradually from 991 ± 1.2–672 ± 7.5 MPa with increasing the γ′ precipitate size from 145 ± 2–604 ± 19 nm. Transmission electron microscope observations on the slightly deformed specimens reveal that, in contrast to previous researches, plastic deformation of all the specimens is controlled by strongly coupled dislocations cutting through γ′ precipitates. Based on these experimental results, the relationship between the yield strength and precipitate size is discussed.

ABSTRACTRoom-temperature welding with gallium is regarded as a new strategy because of the low melting point of gallium and its affinity for forming intermetallic compounds with other metals. Benefitting from liquid gallium-based solder and an ultrasonic drive, the establishment of Cu/Cu diffusion-bond connections can be quickly completed. The underlying characteristics for the weld quality of room-temperature bonding were preliminarily clarified from the perspectives of welding process parameters and the solder composition. To further determine these characteristics, the research directions including features of welding product formed by ultrasonic-driven room-temperature bonding, the interface microstructure, the element distribution and the shear strength of the weld joint were then determined.

ABSTRACTThe plastic deformation of almost all solid polymers can be represented by a thermally activated rate process involving the motion of cooperative mobile elements over potential barriers, based on the Eyring activated rate theory. The present study shows that the governing equations for the Eyring rate theory can be completely derived based on the principle of microscopic reversibility in the framework of non-equilibrium dynamics.

ABSTRACTMicro- to nano-indentation hardness-based stress–strain computations made for Berkovich spherically-tipped impressions put into (001) MgO crystal surfaces show an exceptional plastic strain hardening that is attributed to reacted sessile-type Burgers vector dislocations. Additional evidence for the substantial strain hardening is provided in a compilation of Knoop hardness measurements. The combination of results is compared on the basis of an applied load dependence for an indentation size effect (ISE).

ABSTRACTFatigue pre-cracked four-point bend specimens of a rolled AZ31 Mg alloy are loaded asymmetrically and their mixed-mode (I and II) fracture behaviour is contrasted with pre-notched samples. In-situ mapping of displacement and strain fields is performed through optical imaging coupled with digital image correlation analysis. The fracture surface morphology and the deformed microstructure are also studied. The fracture toughness Jc for both types of specimens is highest for mode I and drops steeply with increase in mode II component. Furthermore, at the same level of mode-mixity, Jc for the notched samples is between two to three times the value pertaining to pre-cracked specimens. This is primarily attributed to quasi-brittle failure, irrespective of mode-mixity, for the latter, whereas the former display a combination of ductile and brittle fracture surface features. At the crack-initiation stage, more profuse tensile twinning is perceived at the far-edge of the ligament in the notched specimens, which also contributes to the observed toughness enhancement.

ABSTRACTIn this work, Ni-Ti shape-memory alloy (SMA) plates were laser welded using different laser powers. A systematic trend of decreasing deterioration in nanomechanical properties – including superelastic recovery – from the weld centre, through the interface region and the heat-affected zone to the base–metal regimes has been observed. The extent of the deterioration increases with increasing laser power. The observations are explained in terms of a decreasing cooling rate and increasing austenite finish temperature (Af) with an increase in laser power.

ABSTRACTIn the present study, the intelligent addition of Re and Al to TiZrHf equiatomic ternary alloy resulted in a new single-phase Ti30Zr30Hf30Re5Al5 HCP high entropy alloy. The XRD analyses show that the TiZrHfRex alloys have a single-phase HCP structure until x = 5 at.%. Subsequently, the TiZrHfRe5 retains its single-phase HCP microstructure with the addition of Al upto 5 at.%, leading to a new quinary TiZrHfRe5Al5 HCP HEA. Microstructural investigations using SEM revealed the formation of compositionally homogeneous single-phase HCP solid solution for TiZrHf, TiZrHfRe5 and TiZrHfRe5Al5 alloys. Vicker's microindentation measurements revealed that adding Re, followed by Al, increases the hardness of the TiZrHf ternary alloy from 7.85±0.37–8.35±0.42 GPa. In a nutshell, a novel quinary HCP alloy was developed based on transition metals, allowing HCP HEA compositional space to expand beyond rare-earth (RE) based HEAs.

ABSTRACTLZ7C3 fibres with nanostructures have been synthesised by the sol–gel method combined with electrostatic spinning technology and a high-temperature-resistant LZ7C3 ceramic material prepared by high-temperature calcination. The formation process of the ceramic fibre was studied and its properties characterized by differential thermal analysis, X-ray diffraction and infrared spectroscopy. The microstructure of the fibre was analysed by scanning electron microscopy and transmission electron microscopy, and the properties of the fibre were determined. The results showed that many conditions, such as calcination temperature and silica-sol content, have a pivotal influence on the crystal phase composition and morphology. By comparing the effects of these conditions, ceramic materials with exceptional properties have been prepared.

ABSTRACTThis experimental study deals with the effect of modifying an Si-rich LM6 cast alloy by ball milling with Si/Al powder particulates in which alloying was conducted via semi-solid liquid processing. The cast alloys were analyzed via their tensile properties with a microstructural evaluation of their fractured surfaces. The tensile results reveal the influence of ball-milled Si-rich powdery chips on the cast materials and demonstrate an improvement in tensile properties for 10% (R = 0.1) and 25% (R = 0.25) addition of reinforcement particulates. The combined effect of processing and the presence of Si-rich particulates is identified on the fractured surfaces. The results also show that higher values of tensile stress and Young’s modulus are obtained for the R = 0.1 samples but that the strain was higher for the R = 0.25 samples. A mechanism and model for the tensile fracture, and particle and interface cracking are proposed according to microstructure and EDX observations.

ABSTRACTGrain refinement is significant for the mechanical properties of engineering alloys. We achieved a bi-ultrafine microstructure in an Mg–12Gd–3Y–0.5Zr alloy through equal channel angular pressing (ECAP) at 300°C. The ECAP not only refined the matrix grains but also broke the large intermetallic particles into fine secondary particles and then rearranged them at the grain boundaries. These fine particles can suppress the growth of the recrystallised grains, as well as promote nucleation for recrystallisation. After four passes of ECAP, a uniform microstructure with both the matrix grain (∼500 nm) and the particle size (∼300 nm) in the ultrafine range was obtained. This unique microstructure resulted in a good combination of strength (>300MPa) and elongation to failure (>35%) at 200°C, which sheds new light on refining microstructure to obtain good mechanical performance at elevated temperatures for Mg alloys.

ABSTRACTIn the present study, to achieve grain refinement and enhance the mechanical properties of Al-2Mg alloy, ultrasonic treatment (UT) has been applied to the melt. The effects of this treatment on the microstructure, porosity alleviation, and mechanical properties of Al-2Mg have been thoroughly investigated. A microstructure study of the Al-2Mg UT alloy has revealed a noteworthy enhancement in grain refinement, resulting in a 3-to-4-fold reduction in grain size as compared to a non-UT Al-2Mg alloy. After UT, the yield tensile strength, the ultimate tensile strength, and the microhardness of Al-2Mg alloy are increased by 21%, 34%, and 36% respectively, with a large improvement of 143% in the ductility.

ABSTRACTThe hydrogen evolution process in the as-cast Mg-0.6Ca alloy was investigated using real-time optical imaging of the corroding surface. It was revealed that hydrogen evolved as large stable bubbles and continuous streams of tiny bubbles because of high localised current density. To the best of the author’s knowledge, this is the first attempt to characterise the hydrogen evolution behaviour of Mg-Ca binary alloy employing a mechanistic model based on real-time imaging.

ABSTRACTThe objective of this technical note is to illustrate twofold. The first issue is devoted to the ability of the recently developed smoothing gradient-enhanced damage model (SGDM), which is associated with the modified von Mises equivalent strain in modelling mixed-mode fracture problems, in particular the common Nooru–Mohamed's test. We show that the developed approach works pretty well for this test, yielding appropriate structural damage response and crack paths for all three specimen sizes, i.e. 200×200,100×100 and 50×50. The second issue is, in a similar manner, to discuss the less accuracy of another damage model, the localising gradient damage scheme recently studied by Shedbale et al. Int. J. Mech Sci 2021, 199:106410, in reproducing crack paths and structural responses for the same mixed-mode problem.

ABSTRACTOne of the primary candidate materials used in 650°C ultra-supercritical (USC) thermal power plant units is a novel thick grade of heat-resistant steel, 08Cr9W3Co3VNbCuBN (G115), for which China has complete intellectual property rights. In this study, G115 steel with a 115 mm thick wall was successfully welded using gas tungsten arc welding (GTAW) + shielded metal arc welding (SWAM), which was a significant step toward achieving its application in large-diameter boiler tubes. The influence of the welding process on the microstructure and mechanical properties of the G115 welded joint after post-weld heat treatment (PWHT) at 770°C for 11 h was investigated. The findings demonstrate that the weld zone (WZ) after PWHT was composed of martensite and ferrite, and M23C6 was the precipitate. The average hardness of WZ was 273.1 HV, and the average impact toughness was above 39J, which was sufficient for actual production applications. It offered the necessary theoretical foundation for the practical development of thick-walled G115 heat-resistant alloy steel during welding.

ABSTRACTOur studies formulate a classical theory to study the influence of in-plane electric field on electron-impurity scattering process and magnetotransport in a two-dimensional space, in the presence of a strong out-of-plane magnetic field. Our studies connect classical scattering and quantum Landau Level broadening, as will be reviewed in this report. We derived an electric current formula in agreement with the current derived from the Drude theory under a strong magnetic field. Our electric current formula is derived microscopically from the migration of the guiding centres at strong magnetic field regime ωτ>1. The electron-impurity scattering under electromagnetic field not only shifts the guiding centre coordinates X and Y, but also changes cyclotron radius R. The change of cyclotron radius R compensates the change of the electric potential energy during the scattering process. The broadening of cyclotron radius is a classical manifestation of Landau Levels broadening. Our conductivity mnB2τ derived from our current formula in the linear response regime results in the same as the current derived from Kubo current fluctuation theory, providing a special case of the fluctuation-dissipation theorem.

ABSTRACTA friction-stir welded Al–Cu–Li alloy plate with desirable mechanical performance has been obtained using specific parameters. The microstructures of the nugget zone were systematically characterised and nano-sized phases, including δ′, θ′ and T1 were found in its matrix. These phases enhance the strength of the joint to a level comparable with the base metal. The results provide the means of obtaining a reliable and low-cost friction-stir weld (FSW) joint for T3-tempered Al–Cu–Li alloy plates without any post-welding heat treatments. This study shows that, by using appropriate parameters of FSW, the microstructures and mechanical precipitates of the nugget zone can be controlled to enhance the weld quality.

ABSTRACTAn efficient alternative approach for detecting missing boundaries in micrographs is presented in the current work. By treating the missing boundaries as a class of object, a suitable detection algorithm is extended to realise discontinuities in interfaces separating phases and grains. The metrics, including precision and recall, estimated during the development of the model indicate noteworthy performance. Moreover, a direct comparison with actual situations attests to the accuracy of the current approach in detecting missing boundaries across different multiphase polycrystalline micrographs.

ABSTRACTAl–Cu melts were used to study interdiffusion under a transverse magnetic field (TMF) using X-ray imaging. A novel gravity-assisted automatic docking device was used to create a long capillary of the diffusion couple. Compared with the results acquired using energy-dispersive spectroscopy, X-ray imaging is more convenient and accurate to determine concentration profiles along long capillaries using the numerous gray value intensities in the imaging. Because a TMF can inhibit melt convection, the interdiffusion coefficient (DAlCu) was reduced after applying a TMF of 2 T. Our results demonstrate that the application of X-ray imaging is an efficient way to study ex-situ diffusion in liquid melts.

ABSTRACTA quasicrystalline approximate monoclinic phase η-Al5(Mn,Cr) with a plate-like or rod-like morphology in AA5083 aluminium alloy was investigated using transmission electron microscopy. Several types of orientation relationships (ORs) between the η-Al5(Mn,Cr) phase and the α-Al matrix were observed and these ORs could be correlated with a rotation operation around the axis [001]η with an angle that is an integer times 18.5°. These multiple ORs were interpreted by utilizing an invariant deformation element model – a simplified version of three-dimensional invariant line strain analysis.