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Many additives are preferred to extend the usage of concrete constructions in order to increase durability. These compounds have to be non-poisonous and have no undesirable consequences on the environs. Out of all these concerns, amino acids are mainly used in food and drug industries as well as safe corrosion inhibitors in a number of acid solutions. Here, the corrosion inhibition efficacy of optimum concentration (50 ppm) of caffeine and L-arginine has been investigated for reinforcement steel in mixture water (MW) environment. This was performed for a duration of 2 h, 7, 28, 56 and 90 d using electrochemical impedance spectroscopy (EIS), dynamic EIS (DEIS), and potentiodynamic polarization (PDP) techniques. The surface of specimens was also investigated by atomic force microscopy (AFM), optical profilometer (OP) and scanning electron microscopy (SEM). DEIS results indicate that selected inhibitors protected reinforcement steel approximately up to 62% against corrosion till 7 d, then the effectiveness of the protection decreased to 30% on 90th day. It was also observed that L-arginine showed better inhibition efficiency than caffeine. Duzce University Research FundDuzce University [2019.06.05.1036] The authors acknowledge the financial support provided by the Duzce University Research Fund (Project No: 2019.06.05.1036). The authors also thank Dr. Marziya Rizvi (ORCID ID: 0000-0001-8928-529X) for his assistance in the interpretation of the EIS measurements. Africa Centre of Excellence in Future Energies and Electrochemical System, Federal University of Technology, Owerri, Nigeria is acknowledged for their contribution to this study. WOS:000650506200001 2-s2.0-85106258076

Orientation relationships (ORs) can form during solidification by a variety of mechanisms that are often difficult to distinguish after solidification. Here we study three ORs formed by the nucleation of Al3Ti on TiB2, and by the pushing and engulfment of TiB2 by growing Al3Ti facets in hyperperitectic Al-rich melts. The nucleation OR is identified by growing a relatively large TiB2 crystal, solidifying multiple small Al3Ti crystals on one (0001) facet of TiB2, and measuring the resulting OR by electron backscatter diffraction (EBSD). Pushing and engulfment ORs are investigated by statistical analysis of EBSD measurements, density functional theory (DFT) calculations of interface energies, and imaging of cross-sections of TiB2 particles being pushed and engulfed by Al3Ti facets. It is shown that the lowest energy OR is formed by nucleation as well as by pushing/engulfment. The higher energy ORs, formed by pushing and engulfment, correspond to local interfacial energy minima and can be explained by rotation of TiB2 particles on Al3Ti facets during pushing.

This paper provides insights into the effect of high thermal gradients and cooling rates on equiaxed grain nucleation and growth in conditions similar to those experienced during Additive Manufacturing (AM) processes. Bridgman type solidification is numerically simulated with columnar grains growing at a fixed pull rate under a user-imposed thermal gradient. Controlled inoculants of known nucleation undercooling were placed ahead of the growing columnar grains to allow quantitative analysis of nucleation events. At low thermal gradient and cooling rate only the inoculants with low nucleation undercooling were activated due to low melt undercooling driven by constitutional supercooling (CS). As the cooling rate is increased, for a given thermal gradient, a larger number of inoculants with higher nucleation undercoolings were activated. At higher cooling rates, thermal undercooling was generated by a lag in the growth rate of the solid-liquid (S-L) interface compared to the theoretical pull rate. Thus, thermal undercooling becomes dominant leading to the facilitation of nucleation on less potent substrates requiring higher undercooling. The results show a transition from solute-driven undercooling to cooling rate driven thermal undercooling which contributes to the undercooling that activates the nucleation events. Invoking the Interdependence model, it is also shown that the high cooling rate induced thermal undercooling reduces the size of the nucleation free zone substantially.

A novel set of unified constitutive equations has been developed and validated to describe stress relaxation ageing (SRA) behaviour of 7xxx series aluminium alloys. The model, based on dynamic ageing and power-law creep relations, can predict the stress relaxation, age hardening response and their interactions at different temperatures, through considering the microstructure evolutions (precipitate radius, volume fraction and dislocation density) during SRA. In addition, the model newly incorporates the effects of prior plastic strain. This model was verified through T74 multi-step SRA experiments for different pre-strain conditions. Excellent agreement was achieved between the predicted and experimental results for stress relaxation and yield strength variation. The evolution of micro-internal variables (e.g. normalised precipitate radius) within the model were calibrated by observing transmission electron microscopy (TEM) images both performed in this work and available in literature. The advanced constitutive model developed predicts the mechanical properties and residual stresses in components after ageing. Therefore, the model provides a valuable tool to optimise manufacturing processes leading to many benefits including reduced scrap rates and financial losses.

Sn-Ag-Cu electronic solder joints typically solidify from a single nucleation event producing either a single βSn grain or twinned grains. With so few and variable βSn orientations, each joint is mechanically unique due to the anisotropy of tetragonal βSn. Here we explore the potential of increasing the number of βSn orientations in solder joints by promoting heterogeneous nucleation during solidification. It is shown that large (60 g) samples can be grain refined effectively by combining growth restricting solute with potent heterogeneous nucleant particles introduced by alloying additions of Zn, Ti, Co, Ir, Pd, or Pt. These mechanisms are discussed with reference to the grain refinement of structural casting alloys. In 500 μm solder balls, these grain refinement approaches were less effective and a relatively high cooling rate of 17 K/s combined with solute and nucleant particles were required to trigger multiple nucleation events. With this approach, up to 12 independent grains formed in 500 μm balls of Sn-3Ag-0.5Cu alloyed with Pt, Co, or Ti, compared with one independent grain in balls without nucleant particle additions.

The solution heat treatment (SHT) process resolving hardening precipitates in high strength aluminium alloys is a critical step for high-efficient forming processes, such as Hot Form Quench (HFQ®). SHT largely determines the overall cycle time of a forming process. However, effects of heating process parameters, such as the heating rate and soaking time, on the microstructure and the associated mechanical properties of aluminium alloy 6082, one of the most commonly used aluminium alloys, for HFQ applications, have not been systematically investigated. The aim of this study is to explore and understand the relationships among heat treatment conditions, grain microstructure and associated mechanical properties for AA6082. A series of uniaxial tensile tests conducted under various SHT conditions revealed significant variations on mechanical behaviour characterised by stress-strain curves. To correlate these stress-strain relationship with underlying microstructure, the grain and orientation distribution of each heat-treated sample were characterised by the electron backscatter diffraction (EBSD) technique. Due to the presence of a large number of microscopic variables, such as grain size, morphology, texture, grain boundary and etc., the crystal plasticity finite element (CPFE) modelling was employed to identify the key microscopic factors which determine the differences in the observed strength and ductility for all samples. A new CPFE model integrated with local strain criterion was proposed and validated to correlate the ductility and the strength with the material microstructure. This rigorous investigation provides more insights on how microstructure (grain size and texture) affects the mechanical behaviour for AA6082, which enables to enlarge the capability of HFQ for industrial applications.

Annealing behavior of Al-Mg-Sc-Zr alloy processed by equal-channel angular pressing (ECAP) at 325 degrees C to various strains and undergone subsequent cold rolling to similar to 80% reduction was investigated. ECAP to strain, e similar to 3 formed partially recrystallized structure with ultrafine-grain (UFG) mantle zone along the boundaries of initial grains of similar to 25 mm size in as-cast and homogenized condition, whilst ECAP to e similar to 8 and 10 resulted in nearly 1 mm grain size, with their volume fractions being 0.7 and 0.9, respectively. These structures after ECAP exhibited sufficient stability, within normal grain growth up to similar to 5 mm grain size only during annealing for 1 h in the temperature range of 350-520 degrees C. However, subsequent to ECAP cold rolling and further annealing at 425 degrees C and above revealed a distinct effect of prior ECAP. While the materials undergone ECAP to e similar to 3 and e similar to 8 and having lower UFG fractions revealed quite similar behavior, the material undergone ECAP to e similar to 10 (and nearly complete recrystallization at ECAP) exhibited abnormal grain growth. The sources of microstructure evolution at different stages of processing are analyzed along with their effects on hardness at ambient temperature. (C) 2016 Elsevier B.V. All rights reserved.

Two types of A356 alloy castings in initial and modified with nanoparticles condition produced by gravitational casting were studied. Samples, as-cut from the castings, were subjected to light optical microscopy (LM), thermal analyses, Electron Backscattered Diffraction (EBSD) and Scanning Transmission Electron Microscopy (STEM) analyses. Results, obtained by EBSD, confirmed that there is grain refinement in samples from castings with added nanoparticles compared to the initial ones. STEM analysis shows agglomerates of nanoparticles in examined foils. Nanoparticles&rsquo, position in the microstructure confirms the hypothesis that they act as nucleating sites during the alloy solidification, which is the reason for observed fine-grained microstructure.

This paper investigates the effect of 0.05 wt.% Ni on the formation and growth of primary Cu6Sn5 in Sn-0.7 wt.%Cu solder paste soldered on a Cu substrate, using a real-time synchrotron imaging technique. It was found that small additions of Ni significantly alter the formation and growth of the primary Cu6Sn5 intermetallics, making them small. In contrast, without Ni, primary Cu6Sn5 intermetallics tend to continue growth throughout solidification and end up much larger and coarser. The primary effect of the Ni addition appears to be in promoting the nucleation of a larger amount of small Cu6Sn5. The results provide direct evidence of the sequence of events in the reaction of Ni-containing Sn-0.7 wt.%Cu solder paste with a Cu substrate, and in particular the formation and growth of the primary Cu6Sn5 intermetallic.

International audience; A three-stage mechanistic model for solidification cracking during TIG welding of steel is proposed from in situ synchrotron X-ray imaging of solidification cracking and subsequent analysis of fracture surfaces. Stage 1-Nucleation of inter-granular hot cracks: cracks nucleate inter-granularly in sub-surface where maximum volumetric strain is localized and volume fraction of liquid is less than 0.1; the crack nuclei occur at solute-enriched liquid pockets which remain trapped in increasingly impermeable semi-solid skeleton. Stage 2-Coalescence of cracks via inter-granular fracture: as the applied strain increases, cracks coalesce through inter-granular fracture; the coalescence path is preferential to the direction of the heat source and propagates through the grain boundaries to solidifying dendrites. Stage 3-Propagation through inter-dendritic hot tearing: inter-dendritic hot tearing occurs along the boundaries between solidifying columnar dendrites with higher liquid fraction. It is recommended that future solidification cracking criterion shall be based on the application of multiphase mechanics and fracture mechanics to the failure of semi-solid materials. (C) The Minerals, Metals & Materials Society and ASM International 2018

The purpose of the present work is to study on the effect of material properties tool on friction stir butt welding of AA2124-T4 alloy matrix MMC. Uncoated tool, coated tool with a CrN, and coated tool with AlTiN were used to weld aluminum MMC plates. Macrostructure and microstructure observations, ultimate tensile strength, wear resistance, and chemical analysis were carried out to determine the appropriate tool for joining these composite plates. Results showed that the good welded joints could be obtained when a tool is coated with AlTiN. (C) 2017 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license.

The work described in this paper concerns a novel method for directly forming curved profiles/sections from billets in one extrusion operation using two opposing punches. Its mechanics are based on internal differential material flow, and it has been given the acronym, differential velocity sideways extrusion (DVSE). A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was used for a series of experiments in which punch velocity ratio and extrusion ratio were process parameters. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Curvature of extrudate can be controlled and varied using a difference between the velocities of the two punches, defined by velocity ratio. Greater curvature is achieved with lower velocity ratio. Curvature is also dependent on extrusion ratio, an increase in which increases curvature, although curvature is less sensitive to it than to velocity ratio. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, has been identified. Severe plastic deformation of the extrudate occurs in a way similar to channel angular extrusion (CAE), thus a greatly promoted effective strain level is achieved, though it is not always uniform across a section. The inner bending region of an extrudate experiences maximum localised effective strain, which decreases with decrease in curvature. To the authors' knowledge this is the first publication in which extrudate curvature is deliberately induced using opposing punches with differential velocities. Although only fixed velocity ratio values have been used in the work described in this paper the ability to change during operation exists and the process has the potential for the production of a profile with different curvature along its length.

While many aspects of electronics manufacturing are controlled with great precision, the nucleation of tin in solder joints is currently left to chance. This leads to a widely varying melt undercooling and different crystal orientations in each joint, which results in a different resistance to electromigration, thermomechanical fatigue, and other failure modes in each joint. Here we identify a family of nucleants for tin, prove their effectiveness using a novel droplet solidification technique, and demonstrate an approach to incorporate the nucleants into solder joints to control the orientation of the tin nucleation event. With this approach, it is possible to change tin nucleation from a stochastic to a deterministic process, and to generate single-crystal joints with their c-axis orientation tailored to best combat a selected failure mode., Control over the crystallographic orientation of solder joints based on βSn will improve the reliability of electronic interconnects. Using a technique based on droplet solidification and lattice matching, Ma et al. are able to control the βSn nucleation events, hence control the grain orientation.

Rapidly solidified nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy has previously shown outstanding tensile and compressive strength and microstructural stability up to elevated temperatures. Despite this, no study had previously assessed the effect of plastic deformation at elevated temperature to simulate thermal-mechanical forging processes for the production of engineering components. The present work analysed bars consisting of a nano-quasicrystalline Al93Fe3Cr2Ti2 at% alloy matrix, with the addition of 10 and 20 vol% pure Al ductilising fibres, produced through gas atomisation and warm extrusion. The microstructure was made primarily of nanometre-sized icosahedral particles in an α-Al matrix. Compression tests were performed across a range of temperatures and strain rates. The measured yield strength at 350 °C was over 3x that of “high strength” 7075 T6 Al alloy, showing outstanding thermal stability and mechanical performance. However, the microstructure was shown by XRD to undergo a phase transformation which resulted in the decomposition of the icosahedral phase around ~500 °C into more stable intermetallic phases. Serrated flow associated with dynamic strain ageing was observed and a semi-quantitative analysis matching elemental diffusion speeds with dislocation speed at specific strain rates was performed, which tentatively identified Ti as the solute species responsible within the selected range of temperatures and strain rates. Fil: Pedrazzini, S.. University of Oxford; Reino Unido. University of Cambridge; Reino Unido Fil: Galano, M.. University of Oxford; Reino Unido Fil: Audebert, Fernando Enrique. University of Oxford; Reino Unido. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Smith, G. D. W.. University of Oxford; Reino Unido

The microstructural patterns formed during liquid to solid phase transformations control the properties of a wide range of materials. We developed a novel methodology that enables in situ quantification of the microstructures formed during solidification of high temperature advanced alloys via synchrotron tomography. The patterns formed are captured in 4D (3D plus time) using a methodology which exploits three separate advances: a bespoke high temperature environment cell; the development of high X-ray contrast alloys; and a novel environmental encapsulation system. This methodology is demonstrated on Ni, Fe, and Co advanced alloy systems, revealing dendritic pattern formation. We present detailed quantification of microstructural pattern evolution in a novel high attenuation contrast Co-Hf alloy, including microstructural patterning and dendrite tip velocity. The images are quantified to provide 4D experimental data of growth and coarsening mechanisms in Co alloys, which are used for a range of applications from energy to aerospace. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Forming limit diagram of aluminum AA7075 and titanium Ti-6Al-4V alloys was examined. For this aim, various strain paths from uniaxial to equi-biaxial tensions were considered. It was established that titanium alloy stretching potential is more than of aluminum alloy due to higher average strain hardening exponent. Also, the average anisotropy factor of AA7075 is about five times lower than that of Ti-6Al-4V resulting in the reduction of resistance to thinning during sheet metal forming processes. Furthermore, employment of BBC2000 yield criterion for AA7075 and Hill’s 1993 for Ti-6Al-4V in determining numerical forming limit diagrams resulted in a closer coincidence with the experimentations. Finally, imperfection factors of 0.970 and 0.955 for AA7075, and 0.935 and 0.960 for Ti-6Al-4V are respectively attained by yield surfaces of BBC2000 and Hill’s 1993. Keywords: Bulge test, Strain paths, Imperfection factor, Strain hardening exponent, Strain hardening coefficient

Al-Cu-Li alloy (AA2195) was produced using vacuum induction melting (VIM) furnace under dynamic argon atmosphere. The as-cast billets were homogenized using a two-step homogenization cycle. The hot deformation behavior of homogenized and forged AA2195 alloy was studied by hot isothermal compression in a thermo-mechanical simulator. The contour maps of efficiency of power dissipation and instability maps have been generated within the temperature range of 250-450 degrees C and strain rate range of 10(-3)-10(2) s(-1). Various deformation mechanisms, which operate in different temperature-strain rate regimes, were identified with the aid of these maps and complementary microstructural analysis of the deformed specimens was carried out. Results indicate four distinct deformation domains within the range of experimental conditions examined. Out of these four domains, the optimum temperature and strain rate range for obtaining a completely reconstituted microstructure is T: 400 degrees C-450 degrees C and epsilon: 10(-2) 10(-1.5) s(-1) and epsilon: 10(-0.5)-10(1) s(-1). Instability mechanisms in the material are attributed to localized plastic flow and cracking. A constitutive equation that describes the flow stress of AA2195 alloy as a function of strain rate and deformation temperature was also established. (C) 2017 Elsevier B.V. All rights reserved.

A Cu6Sn5 layer is an integral part of many electronic interconnections. Here we show that, although primary Cu6Sn5 is not a potent nucleant for Sn, the Cu6Sn5 layer plays a key role in Sn nucleation and microstructure formation in solder joints. Combining thermal analysis, FIB-tomography and EBSD, we show that conical cavities are present between the scallops of the Cu6Sn5 layer that act as geometric nucleation sites for Sn, that Sn grows from the Cu6Sn5 layer, and that reproducible nucleation orientation relationships (ORs) exist between Cu6Sn5 and Sn. With these ORs, a near-random distribution of Sn orientations is predicted from joint to joint even for Cu6Sn5 layers with a strong [0001] fibre texture. It is shown that the nucleation undercooling is strongly affected by manipulation of the Cu6Sn5 layer shape, and that it is possible to prevent nucleation on the Cu6Sn5 layer by adding more potent nucleants.

International audience; Medium strength Al-Zn-Mg age hardening alloys are widely used when a low quench sensitivity is required. such as in welding applications. In this work we present a detailed characterization of the precipitate microstructures resulting from different quench rates from the solution treatment, and from the subsequent artificial ageing to the T6 state, in an Al-4.5Zn-1 Mg (wt%) alloy. This work is carried out using differential scanning calorimetry, transmission electron microscopy and in situ small-angle X-ray scattering. It is shown that for quench rate between 5 and 200 degrees C/min substantial heterogeneous precipitation is observed, nucleated on dispersoids and on grain boundaries, the former being of much larger size than the latter. During subsequent ageing, it is shown that the precipitation kinetics in the material unaffected by the quench-induced precipitates is independent on the quench rate used. (c) 2008 Elsevier B.V. All rights reserved.

Grain refinement via semi-solid deformation is desired to obtain superior mechanical properties of cast components. Using quantitative in situ synchrotron X-ray tomographic microscopy, we show an additional mechanism for the reduction of grain size, via liquation assisted transgranular cracking of semi-solid globular microstructures. Here we perform localized indentation of Al-15wt.%Cu globular microstructures, with an average grain size of ∼480 μm, at 555 °C (74% solid fraction). Although transgranular fracture has been observed in brittle materials, our results show transgranular fracture can also occur in metallic alloys in semi-solid state. This transgranular liquation cracking (TLC) occurs at very low contact stresses (between 1.1 and 38 MPa). With increasing strain, TLC continues to refine the size of the microstructure until the grain distribution reaches log-normal packing. The results demonstrate that this refinement, previously attributed to fragmentation of secondary arms by melt-shearing, is also controlled by an additional TLC mechanism., Nature Communications, 6, ISSN:2041-1723

International audience; The two surfaces of a 40% cold-rolled tricrystal of aluminium were scratched to stimulate recrystallization nucleation. Serial sectioning combined with electron backscatter diffraction was used to characterize the nuclei in three dimensions. It was found that the largest nuclei have a 40 degrees < 1 1 1 > relationship to the matrix, but there are also many nuclei of this orientation relationship which do not grow to large sizes. It is shown that local variations in the deformation microstructure determine where preferential growth occurs. (C) 2013 The Authors. Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.

International audience; The bendability of AA6016 sheets is a critical parameter for many automotive applications. In this experimental study the origins of damage and its evolution are characterized using interrupted and in-situ bending tests to correlate microstructural evolution with damage development. Local strains were estimated by optical and scanning microscopy (EBSD). Together with the load-displacement plots, they provided a set of physical parameters characterizing crack initiation. In particular, it is shown that (1) crack initiation occurs at the maximum of the rigidity-displacement curve; (2) cracking is preceded by strain localization in the form of macro-shear bands which induce surface roughening. Local necking then occurs in some surface grains and leads to ductile intergranular crack propagation. The sequence of microscopic changes at the grain scale up to and beyond crack initiation have been characterized and quantified in terms of local grain strains, coarse intragranular slip and shear band evolution over several grains. (C) 2012 Elsevier B.V. All rights reserved.

International audience; The composition of precipitates in three alloys of the Al-Zn-Mg-Cu system has been investigated for different heat treatments, including peak-aged and over-aged states as well as near-equilibrium conditions, by combining atom probe tomography and systematic anomalous small-angle X-ray scattering experiments. We show that the concentration of Cu in the precipitates changes during heat treatments and is alloy dependent. At low ageing temperature (120 degrees C) the Cu content in the precipitates is close to the alloy content. The precipitate Cu content is shown to increase with increasing temperature and Cu alloy content. We show that in near-equilibrium conditions the precipitate compositions are 33 at.% in Mg, about 15 at.% in Al, about 13 at.% in Cu and balance Zn. Our results strongly suggest that the gradual incorporation of Cu in the precipitates during the heat treatment is essentially related to the slower diffusivity of this element in aluminium.

A set of unified constitutive equations is presented that predict the asymmetric tension and compression creep behaviour and recently observed double primary creep of pre-stretched/naturally aged aluminium-cooper-lithium alloy AA2050-T34. The evolution of the primary micro- and macro-variables related to the precipitation hardening and creep deformation of the alloy during creep age forming (CAF) are analysed and modelled. Equations for the yield strength evolution of the alloy, including an initial reversion and subsequent strengthening, are proposed based on a theory of concurrent dissolution, re-nucleation and growth of precipitates during artificial ageing. We present new observations of so-called double primary creep during the CAF process. This phenomenon is then predicted by introducing effects of interacting microstructures, including evolving precipitates, diffusing solutes and dislocations, into the sinh-law creep model. In addition, concepts of threshold creep stress σ t h and a microstructure-dependant creep variable H, which behave differently under different external stress directions, are proposed and incorporated into the creep model. This enables prediction of the asymmetric tension and compression creep-ageing behaviour of the alloy. Quantitative transmission electron microscopy (TEM) and related small-angle X-ray scattering (SAXS) analysis have been carried out for selected creep-aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to creep age forming of other heat-treatable aluminium alloys.