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The article presents a list of articles related to materials science published in volumes 39, 40, and 41. The articles include "Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials," "Observations of common microstructural issues associated with dynamic deformation phenomena: Twins, microbands, grain size effects, shear bands, and dynamic recrystal," and "Role of entropy of fusion in phase transformation and selfdiffusion."

This paper reports atomistic simulation studies of tensile and compressive behavior of nanowires of a model quinary high entropy face-centered cubic (FCC) alloy. The simulations employ empirical interatomic potentials and use massively parallel molecular dynamics techniques at the atomistic level to study the deformation mechanisms. The studies consider pristine cylindrical nanowires oriented along various crystallographic directions. The focus is the role that local composition fluctuations in the random alloy plays in the deformation response. The deformation behavior observed for the complex random alloy is compared with a corresponding "average atom" material that has the same average properties but no local compositional fluctuations. In all cases, deformation is governed by dislocations emitted from the free surface. Twinning was also found, depending on the crystallographic orientation and loading mode. We show that for all orientations, the high entropy alloy (HEA) wires show the onset of plasticity at lower stress levels than the average atom material. However, after the onset of plasticity, the HEA presents a higher strength, mostly driven by the fact that the dislocations emitted from the surface do not glide as easily in the random alloy as they do in the average atom material. [ABSTRACT FROM AUTHOR]

Al–Zn–Mg–Cu alloys can be fabricated by a series of thermo-mechanical processing methods (e.g., hot rolling, forging and extrusion), which is able to serve in aeronautic, automobile, and marine industries because of its excellent physical properties. However, reaching the balance between high strength and favorable ductility to present its high performance is still in progress, during which temperature and strain rate are two very important external variables. More importantly, the core lies in sophisticated microstructure evolution paths involved in hot deformation, which consists of different microstructure mechanisms and behaviors and can be expressed as various mechanical responses. Therefore, a fundamental review of microstructure mechanisms and behaviors, microstructure evolution and relevant mechanical responses of Al–Zn–Mg–Cu alloys during high-temperature deformation is of great significance. In present paper, first, various experimental methods have been introduced. Second, general trends of mechanical properties changing with temperature and strain rate have been summarized. Third, major microstructure mechanisms and behaviors have been discussed. Then, a schematic illustration originating from dislocations' movement has been depicted, which succeeding microstructure evolution and mechanical responses (including superplasticity) have been reviewed accordingly. Finally, further suggestions of hot deformation of Al–Zn–Mg–Cu alloys have been given. [ABSTRACT FROM AUTHOR]

Stacking fault energy (SFE) is an intrinsic material property whose value is crucial in determining different secondary deformation mechanisms in austenitic (face-centered cubic, fcc) steels. Considerable experimental and computational work suggests that the SFE itself is highly dependent-in a complex manner-on chemical composition and temperature. Over the past decades, there have been a large number of efforts focused on determining the composition dependence of SFE in austenitic steel alloys by means of experimental, theoretical or computational methods. Unfortunately, experimental methods suffer from the indirect nature of the methodologies used to estimate the value of SFE, while computational and/or theoretical approaches are either limited by the physics that they can incorporate into the predictions or have more practical limitations associated, for example, to the size of the systems that can be modeled or the assumptions that must be made. In this paper, we review the major experimental and computational approaches to determine SFE in austenitic steel alloys, and we discuss their limitations. We then demonstrate a data-driven machine learning technique to mine the literature of experimental SFE data in steels, while algorithms at the fore-front of machine learning have been used to visualize the SFE data and then construct a three-class classifier. The classifier is used then to predict likely secondary deformation mechanisms of untested compositions, while the classifier itself is presented as a valuable tool for the further development of austenitic steel alloys in which the specific secondary plastic deformation mechanisms are a feature to design for. The data as well as the entire analysis workflow are made available to the wider community through a public github repository. [ABSTRACT FROM AUTHOR]

This paper describes some technical limitations encountered in joining ceramics–ceramics or ceramics–metals, and how, to some extent, they have been practically overcome. The effect of the residual stresses on the strength of joints fabricated between alumina–alumina or alumina and the nickel base alloy HAYNES® 214™ using a solid-state bonding technique with Ni interlayer was studied. Finite element analyses (FEA) for the elastic–plastic and elastic–plastic–creep behavior have also been used to better design the joints and to predict their performance. It was found that the residual stresses caused by the thermal expansion mismatch between alumina (Al2O3) and the Ni-based superalloy (HAYNES® 214™) have severely deteriorated the joints compared to Al2O3–Al2O3 joint fabricated with the same solid-state bonding parameters. The high residual stresses zones obtained through the FEA simulation fitted well with the fractographic observations of the Al2O3/Ni/HAYNES® 214™ joints. Also, in order to use the joint material as a structural material, the study about the effect of geometrical parameters has been performed. Optimal geometries have been determined. [ABSTRACT FROM AUTHOR]

In this paper, the plastic deformation behavior and strain homogeneity of the ZK60 Mg alloy during the multi-pass cyclic extrusion and compression (CEC) was simulated using the finite-element method (FEM) with a view to provide an insight into the mechanics of the process. Physical modeling (PM) experiment with same alloy was carried out to verify the results of the numerical simulations. The results show that two vortex flow regions with opposite flow direction are formed inside the cylindrical workpiece during CEC deformation. Although the deformation is inhomogeneous in both end regions of workpiece, a uniform region of equivalent strain exists, and the extent of uniform deformation increased with the increase in workpiece length. [ABSTRACT FROM AUTHOR]

The tensile properties of an ultrafine-grained Al–9%Si–3%Cu alloy deposited by the laser powder bed fusion process have been investigated in this work. The additively manufactured (AM) alloy was subjected to high-pressure torsion processing at room temperature successfully at different number of turns in HPT and then inspected through hot tensile testing at 298 and 573 K using strain rates ranging from 10–1 to 10–4 s−1. The processed alloy showed extensive refinement and high dislocation density that was associated with considerable strength at ambient temperature. The as-deposited and processed samples of the alloy exhibited significantly higher tensile strength and elongation under hot deformation conditions compared with their cast counterpart alloys. The room temperature-HPT processing presented ultrafine α-Al and well-distributed nanosized eutectic Si particles which significantly improved the tensile behaviour and thermal stability of the processed microstructures. The formation of fibrous structures has enhanced the flow behaviour and cavitation resistance at the elevated testing temperature. The current work indicates the impact of room temperature-HPT processing on the mechanical performance of the controllable AM-deposited alloy to meet industrial needs without further heat treatments or alloying additions. [ABSTRACT FROM AUTHOR]

Uniaxial hot tensile tests were carried out in the RD, 45°, and TD directions of cold-rolled Ti-6Al-4V alloy sheets. At 973 K-0.1 s−1, it shows apparent mechanical and fracture anisotropy. Increasing temperature or decreasing strain rate can reduce the anisotropic behavior and significantly improve its forming quality. The SEM-EBSD result indicates that there is a T-type texture in the initial microstructure. The yield anisotropy is closely related to the distribution of the Schmid factor caused by the texture. In the RD and 45° loading paths, the Schmid factors are large, and the basal and prismatic slip is easy to be activated. It is difficult to activate these two slip systems in the TD loading direction. Under high-temperature loading conditions, the rotation of grains leads to different orientation dispersion, which further affects the phase transformation and softening behavior. The primary mechanism affecting the softening behavior is dynamic recovery (DRV). In the case of the 45° loading direction, the orientation dispersion is the largest. Its DRV and phase transformation behavior is more prominent than the other two loading directions. The loading along 45° direction has the best forming quality, and it can be selected in the processing of Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

Isothermal torsion tests were performed on a Ti-6Al-4V alloy in the two-phase region. The results show that straining leads to an increase in the beta phase fraction, which increases slightly with strain rate. Transformation took place at 880, 940, 960, 980 and 1000 °C. The extent of this type of dynamic transformation (alpha to beta) was increased when the temperature approached the transus temperature. The reverse transformation (beta to alpha) occurred during isothermal holding after torsion and the volume fraction retransformed increased with time. The driving forces promoting dynamic and reverse transformation together with the energy barriers opposing these transformations were derived and compared. The critical stresses required to initiate dynamic transformation are calculated from the flow curves. This analysis confirms that the peak stresses are always higher than the critical stresses at the temperatures employed in the present tests, which makes it possible for the transformation to occur. [ABSTRACT FROM AUTHOR]

A nanostructured Al-1 %Si alloy containing a dispersion of Si particles in ultrapure aluminum (99.9996 %) was produced by heavy cold rolling to study the effect of second-phase particles on the occurrence of plastic instability during tensile testing of a nanostructured metal. Tensile tests were conducted on the as-deformed sample and on samples after recovery annealing treatments. Work hardening and strain rate sensitivity were studied by tensile test at different strain rates, and deformed and annealed samples were characterized by transmission electron microscopy. By comparing the observed behavior with that of nanostructured commercial purity Al, a significant increase in the tensile elongation was found. This is related to a homogenization of the deformation microstructure due to the presence of finely dispersed Si particles. As a result localized deformation is reduced and tensile ductility increased. [ABSTRACT FROM AUTHOR]

Microstructure evolution in an as-cast Na modified Al–7%Si (wt. pct.) alloy was examined during redundant and monotonic straining by repetitive equi-channel angular pressing (ECAP) under ambient temperature conditions, and during friction stir processing (FSP). Redundant straining during repetitive ECAP was accomplished by processing following route BC while monotonic straining employed route A. Single- and multi-pass FSP was conducted on this same as-cast material using an FSP tool having a threaded pin. The as-cast microstructure comprises equiaxed primary α dendrite cells embedded in the Al–Si eutectic constituent. The evolution of this microstructure during repetitive ECAP can be described by idealized models of this process. The primary and eutectic constituents can still be discerned and the Si particle distribution is not homogenized even during ambient temperature processing involving von Mises strains >9.0. In contrast, the primary and eutectic constituents cannot be distinguished in the stir zone after even a single FSP pass. Strain estimates based on the shape change of the primary α constituent indicate that the Si particle distribution has become homogeneous at local von Mises strains of 2.5–3.0 during the FSP thermomechanical cycle. Mechanical property data are consistent with strain path during SPD processing by repetitive ECAP and FSP. [ABSTRACT FROM AUTHOR]

The effect of homogenization treatment on the recrystallization process in a twin-roll cast AlFeSi alloy was investigated by means of calorimetry, microstructural analysis, electrical conductivity, and hardness measurements and cupping tests. The response to annealing of cold-rolled AlFeSi sheet processed with a homogenization treatment at the cast gauge is a typical two-stage, recovery and recrystallization process, while that processed without homogenization softens without recovery. The rather limited precipitation capacity in the former allows recrystallization to occur largely discontinously, favoring the annealing texture. The nucleation rate and the volume fraction of the discontinously recrystallized grains are largely reduced in the sheet processed without homogenization, owing to extensive dynamic precipitation. This reduces the strength of the annealing texture components and gives a more or less random crystallographic texture after annealing. With a relatively finer-grain structure and a nearly random crystallographic texture, AlFeSi sheet processed to soft temper at 1 mm without a homogenization treatment is an attractive foil stock material. [ABSTRACT FROM AUTHOR]

An Mg–12Gd–3Y (wt%) alloy was prepared by conventional casting method using permanent steel mold. Then this alloy was subjected to hot processing, involving hot extrusion and free forging. Tensile strength at room temperature can be improved, with the highest ultimate tensile strength (UTS) value of 390.2 MPa achieved by hot extrusion in comparison to that of as-cast alloy. Temperature dependence of tensile strength is distinguishable for the as-extruded alloy, while the relative stability in UTS values of the alloy after being freely forged should be ascribed to the inter-crossing among deformation bands located at various orientations and the accommodation effect of twining lamellas resulting from forging process on plastic deformation during tensile test at elevated temperatures. Further annealing after hot processing can only have adequate influence on the tensile strength of as-forged alloy. For the alloy freely forged and annealed at 523 K for 4 h, the highest UTS (441.1 MPa) at room temperature is found, which should be mainly related to an evolution from the original as-forged microstructure with subgrains to a more stable combination of large and refined grains through dynamic recrystallization during free forging, and the stress at offset yield YS (384.3 MPa) is also comparable to that relatively high value of 396.9 MPa after solution treatment and isothermal aging of the as-cast alloy. [ABSTRACT FROM AUTHOR]

The power law-creep behavior of superplastic Sn–40Pb–2.5Sb alloys with different grain sizes has been investigated at room temperature. Stress exponent values for these alloys have been determined by indentation creep, conventional creep and uniaxial tension tests in order to evaluate the correspondence of indentation creep results with conventional tests. In all cases, the indentation results were in good agreement with each other and with those of the tensile and conventional creep tests. The average stress exponent values of about 2.6 and 3.0 corresponding to the strain rate sensitivity (SRS) indices of 0.33–0.39, depending on the grain size of the materials, indicate that the grain boundary sliding is the possible mechanism during creep deformation of Sn–Pb–Sb alloys. Within limits, the indentation tests are thus considered useful to acquire information on the creep behavior of small specimens of these soft tin–lead–antimony alloys at room temperature. It is also demonstrated that the indentation creep test provides a convenient method to measure SRS and thereby to assess the ability of a material to undergo superplastic deformation. [ABSTRACT FROM AUTHOR]

Atomic force microscopy has been used to study slip step patterns, which form around indentations in FCC alloys. These patterns form in a consistent and repeatable manner. From these observations it has been determined that slip steps increase in height only in the outer region of the plastic zone leading to the cessation of their growth as the plastic zone expands outward. Electron backscatter diffraction techniques are used to map grain orientation and the effect of different surface orientations as well as different tip geometries on slip step behavior is explored. Changes in resolved shear stress on different slip planes can be observed qualitatively from changes in the slip step patterns as surface orientation and tip geometry are varied. Pile up is shown to form above the regions with the largest amounts of strain downward into the bulk. Changes in slip step patterns can be predicted based on changes in resolved shear stress. Discreet dislocation dynamics simulations have been performed to support these observations. [ABSTRACT FROM AUTHOR]

The hot working behavior of a as-homogenized Mg–Zn–Y–Zr alloy has been investigated in the temperature range 200–400°C and strain rate range 0.0015–7.5 s−1 using processing map. The power dissipation map reveals that a domain of dynamic recrystallisation (DRX) in the temperature range 300–400°C and strain rate range 0.0015–0.15 s−1, with its peak efficiency of 38% at 350°C and 0.0015 s−1, which are the optimum hot working parameters. The apparent activation energy in the hot deformation process is 148 ± 3 KJ/mol that is larger than that of ZK60 alloy because of the obstruction of Y atoms for diffusion. DRX model indicates that DRX of Mg–Zn–Y–Zr alloy is controlled by the rate of nucleation, which is lower one order of magnitude than growth. And the rate of nucleation depends on the process of mechanical recovery by cross-slip of screw dislocations. [ABSTRACT FROM AUTHOR]

Deformation introduced by punching had a big impact on the response of the 6061 alloy to DSC heating. Clustering at low temperatures was suppressed while the precipitation of the metastable precursors of the equilibrium β-Mg2Si phase were accelerated. The β″ peak in the DSC curve has transformed into a doublet when the samples were punched after the solution treatment. This change in the peak arrangement was accounted for by the operation of two distinct mechanisms for the formation of the β″ phase. While a fraction of the β″ needles has formed through evolution of the GP-1 zones, the rest had to form in the solid solution matrix. Acceleration in the kinetics of β″ precipitation and its transformation to β′ was confirmed by hardness measurements. [ABSTRACT FROM AUTHOR]

The effects of displacement rate on fracture behaviors of 100Sn solder and 63Sn37Pb solder alloys have been investigated by SEMin-situtesting. It was found that for the 100Sn solder, grain boundary sliding was the dominant deformation mechanism at lower tensile rate regime, while a large area of slip lines crossing grains were detected at the surface of specimens at higher tensile rate regime. For the 63Sn37Pb eutectic alloy, however, because of existence of the second phase, fracture behavior depended on the growth and linkage of cavities ahead of crack tip, and the crack paths changed from intergranular to transgranular with the increasing of loading rate. [ABSTRACT FROM AUTHOR]

Thixocast samples of an Al-Si-Cu alloy were solution treated at 500°C for 4 h, aged at 170°C for different times and tensile tested at room temperature. Statistical analysis on the fractured Si particles has pointed out how the fraction of damaged particles is influenced by the ageing treatments performed before deformation. The damage accumulation per unit of strain decreases with increasing ductility of the samples. The Considére criterion for plastic instability shows no significative necking. [ABSTRACT FROM AUTHOR]

The compression strength of an Ir-15at%Nb alloy at 1473 and 2073 K was investigated. A coherent two-phase fcc L12 structure was found in the Ir-15Nb alloy. The L12 precipitate morphology depended on the heat treatment. Cuboidal L12 precipitates with a size of 100 nm and a plate-like fcc phase inside (type A) were found after heat treatment at 1773 K. The plate-like fcc phase disappeared after heat treatment at 2073 K for 24 h, and only a cuboidal L12 phase remained (type B). Coarse rectangular L12 precipitates with a length of 400 nm (type C) were found after heat treatment at 2073 K for 168 h. The influence of L12 precipitate morphology on the high-temperature strength and dislocation structure was investigated after the compression test. A bypass mechanism in which dislocations spread in the narrow fcc phase was dominant in the type A and B structures during deformation at 1473 K. In the type C structure, bypassing of precipitates was found to be dominant. At 2073 K, deformation by a shearing mechanism was dominant in the type A and B structures, while deformation by a bypassing mechanism was dominant in the type C structure. When the precipitate size was large and the fcc channel width was wide in the type B structure, a bypassing mechanism was dominant. The deformation mechanisms are discussed in terms of the precipitate morphologies. [ABSTRACT FROM AUTHOR]

A new technique for Scanning Electron Microscopy (SEM), which provides a mesoscopic coordinate system inscribed on the surface of the center of a tension test specimen has been proposed. Such technique allows to establish in a repeatable way any angle relative to any axis of any coordinate system, or distances between grains, or to measure local or global true deformation in parallel or perpendicular directions relatives to the tension axis. The application of such technique for a Zn-20.2%Al - 1.8% Cu alloy tension test specimen with a total length between shoulders of 412 μm length and a gage length of 371 μm, deformed at room temperature, allows to obtain: The mapping of the granular flow during superplastic deformation; this result is in qualitative agreement with similar flow-diagrams obtained previously by Ashby and Verral ( Acta Metall. 21, 1973, p. 149) from their oil-emulsion model. [ABSTRACT FROM AUTHOR]

Texture resulting from micromechanical processing plays an important role in the anisotropy of materials. The determination of texture components is a useful way to present texture data. The types of components present in the texture of a material can be related to other material aspects including predictions of yield loci using polycrystal methods. Al-Cu-Li 2195 thick plate was cold rolled to produce various reductions in thickness. Texture analysis was performed on the various rolled materials at different positions through the thickness of the plates. The texture components are consistent among the various rolled specimens at equivalent thickness positions. A texture gradient is observed to exist through the plate thickness that may indicate other microstructural information about the alloy. This texture gradient evidences the effects of increasing amounts of deformation on texture intensity, texture components observed, and changing modes of deformation. [ABSTRACT FROM AUTHOR]

The details of structure modification on α2/γ interface induced by deformation in a hot-deformed Ti-45Al-10Nb alloy were investigated by conventional and high-resolution transmission electron microscopy. A new type of dislocation ledge containing 1/3[111] partials was identified. The Burgers vectors of these dislocation ledges were determined to be 1/2[110] or 1/2〈101]. The formation mechanism of this new type of dislocation ledge is discussed. Also, two types of hot deformation induced α2/γ interfaces, coherent interfaces with high density of ledges and misoriented semi-coherent α2/γ interfacial boundaries were observed. For the misoriented semi-coherent α2γ interfaces, the density of dislocation ledges in these interfaces increases with the misoriented angle between the (111) $$_\gamma $$ and (0001) $$_{\alpha 2} $$ planes, and 1/3[111] partial dislocations were involved in all the dislocation ledges. The formation mechanism of these deformation-induced α2/γ interfaces were discussed related to the role of α2/γ interfaces adjusting the deformation as a dislocation sink absorbing the slipping dislocations in the γ phase. Moreover, misoriented semi-coherent α2γ interface related deformation twinning and structure transformation induced by deformation were analyzed and discussed related to the role of α2/γ interfaces as a dislocation source during deformation. [ABSTRACT FROM AUTHOR]

Deformation microstructures of the γ-TiAl Phase in two-phase (α2 + γ) alloy, Ti-46Al-2V-0.4Er (all compositions are given in atomic percent), have been studied by transmission electron microscopy. Heat treated samples of this alloy were subjected to 3% plastic strain in compression at room temperature, 600°C, and 900°C. Majority of dislocations present in the as heat treated and deformed samples are of b = 1/2 < 110] type. Formation of loops from the dislocations are also observed. Isolated super dislocations and faulted dipoles are seldom seen in the microstructures. Plenty of twins are present in these samples and it appears that their density increases with increasing deformation temperature. The deformation microstructures of the alloy studied here are quite similar to those in the binary two-phase titanium aluminides or the V containing two-phase titanium aluminides. It appears that Er does not significantly change the deformation microstructure of this two-phase alloy, although Er has a significant effect on the deformation microstructure of the single-phase γ-TiAl alloys. [ABSTRACT FROM AUTHOR]

New method to estimate quantitatively the strain-rate sensitivity of a superplastic material is suggested. It is based upon measurements of the initial slopes of the stress–strain curves. In contrast with known techniques the method suggested is appropriate to apply to small deformations, so that the result obtained are to be assigned to the initial structural state of the material under consideration. The experimental verification of the method suggested is fulfilled in practice for the example of Wood's alloy. It is shown that the strain-rate sensitivity of this alloy decreases monotonically with increasing strain, ε the value of m determined by means of the method suggested are in good agreement with that determined independently using standard techniques. An important feature of the method suggested is that in contrast with standard techniques its accuracy improves as the value of strain, ε, becomes smaller, since the tilts of σ–ε curves have a maximum when ε→0. © 1998 Chapman & Hall [ABSTRACT FROM AUTHOR]