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We have investigated four models for calculating the contribution of an applied magnetic field to the free energy of Fe and Fe alloys—Weiss Molecular Field Theory (WMFT), Kuz’min, Arrott, and Curie-Weiss. On the basis of these models, the shifts in phase transformation including both ferromagnetic and paramagnetic phases as a function of magnetic field and alloy content can be predicted. The Kuz’min model is easiest to solve and is also best able to predict the trends in experimentally observed shifts in ferrite/austenite phase transformations for Fe-based alloys under an applied magnetic field both below and near the Curie temperature. For phase transformations above the Curie temperature, the predictions using the Curie-Weiss form with WMFT parameters, here extended to alloy systems, are in good agreement with experimental results. Different aspects of the four models have been discussed in detail with a view to developing a reliable methodology to predict shifts in phase diagrams as a function of alloy content.

Magnetic fields applied during electrodeposition are known to increase incorporation of inert second phase particles through field-induced convective forces. However, this incorporation was demonstrated in the bore of electromagnets, limiting application scope. Here we use low-cost permanent magnets to incorporate doped yttria particles that phosphoresce under ultraviolet radiation into a nickel coating. Negligible yttria amounts are observed in conventionally deposited coatings while a magnetic field perpendicular to the applied current successfully integrated enough yttria for a luminescent coating. These are useful for coating health monitoring applications; however, this magnetically assisted processing method is useful for other particle systems across multiple applications.

The electrodeposition of copper in the presence of a magnetic field has previously been shown to affect both electrochemical processes and the microstructure. In this work, we report a magnetically-induced anomalous second phase in thick films deposited with a current density of 500 mA/cm2 and 0.5 T magnetic field strength. Atom probe tomography suggests the phase is a combination of CuH and CuH2. Formation of the latter phases is likely induced by the applied magnetic field and indicates its role in promoting the hydrogen evolution reaction during deposition. Keywords: Electrodeposition, Magnetic field, Hydride, Hydrogen evolution reaction, Atom probe tomography

Cemented tungsten carbide materials are traditionally bonded using a cobalt matrix, resulting in a material that possesses a unique combination of exceptional properties. However, cobalt has been recently classified as “reasonably anticipated to be a human carcinogen,” and thus, removal of this hazardous phase is desired for many applications. This research focuses on the production of tungsten carbide bodies cemented with a non-hazardous iron-based alloy binder phase. This binder has roots in the previous transition metal binders and additives for tungsten carbide and is based on the principles of high-entropy alloys; however, it relies on a novel means of carbide formation and dispersion from prior investigations. Sintering studies were conducted through uniaxial hot pressing, field-assisted sintering techniques, and pressureless sintering techniques. While some of the results of hot pressing and field-assisted sintering technique were positive, the resultant mesostructure exhibited an undesired, graded, heterogeneous form. Pressureless sintering, on the other hand, was capable of producing a homogeneous microstructure with high theoretical density along with promising hardness and indentation toughness values.

Mathematical models in process engineering are becoming an essential part of accelerated materials by design, drastically shortening time to discovery by minimizing the vast experimental matrix. In this paper a combination of thermodynamic and analytical models have been used to develop an algorithm for visually guiding the rapid design of a nontoxic (cobalt free) liquid metal binder for WC based cermets. A method based on rapid screening method of key processing parameters is developed that significantly reduces the design space (here, to 27% of the initial alloy composition space). The parameters included represent heretofore unexamined considerations such as chemistry effects on capillary flow, viscosity, surface tension, and melting point which are less computationally intensive than the traditional thermodynamic modeling used in this problem to date. The results are presented in a series of easy to interpret atlases that enable quick identification of systems of interest for further study. Keywords: Cermet, Capillary, Materials by design

Tailoring microstructure evolution with the use of external forces (magnetic, electric, mechanical, etc.) can expand the ability to control material properties and performance through microstructure engineering. In particular, crystalline materials are comprised of a distribution of grains of differing sizes, crystallographic orientations (texture), and topologies, which may evolve differently under the influence of various fields and lead to changes in material properties, bounded by movable grain boundaries. In this work, simulations are used to demonstrate the effect of an applied field, in this case a magnetic field, on the evolution of microstructure at the grain scale. The simulation results show that fields can be used to control microstructure geometry and texture. They also show that a dynamic field application of the field, through a changing field direction over time, can create new microstructure features even in a system that does not seem as sensitive to as static field, and that temperature can play a key role in this evolution as well. This work overall demonstrates how unconventional processing techniques on polycrystalline microstructures can be impacted by applying fields, and ultimately be used to improve properties and performance through engineered microstructures.

An Al-5 at. pct Cr alloy was produced by high-energy ball milling at liquid nitrogen temperature followed by consolidation using equal-channel axial extrusion at 200 °C, 300 °C and 450 °C. The microstructure and corrosion response were compared with a cast alloy of the same composition. Rather than the intermetallics expected by the phase diagram and seen in the cast alloy, consolidated HEBM alloys exhibited extended solid solubility of Cr in the aluminum matrix in addition to a finely dispersed Cr-rich phase. This led to improvement in the corrosion behavior as investigated via potentiodynamic polarization and constant immersion tests in NaCl solution. Hardness and tensile tests were performed to evaluate the mechanical properties. The highest consolidation temperature (450 °C) contributed to significant grain growth and Cr diffusion, lessening the beneficial effects of processing with HEBM.

Processing of materials under an externally applied magnetic field could enable exploitation of broader processing spaces, affecting the relative stability of phases. To properly predict how a material will react to an applied field, the magnetic properties must be incorporated into the free energy calculations. Previous works assumed alloy composition played a negligible effect on the magnetization term; however, this assumption is not valid for all systems. Here, we assess twelve binary iron systems to quantify the shifts of magnetic moment and Curie temperature with respect to alloy content. Descriptive magnetic property equations for these binary systems were assessed in conjunction with experimental data and prior descriptions obtained from literature. To showcase the impact of using the compositionally dependent magnetic property predictions, the austenite loops for Fe–Si and Fe–Mo were re-calculated under an applied magnetic field. Further, the magnetic property data summarized herein can also be used for future assessments or re-assessments of the iron alloy systems reported, in addition to the current goal of processing under magnetic fields.

Grain refinement through surface plastic deformation processes such as surface mechanical attrition treatment has shown measureable benefits for mechanical properties, but the impact on corrosion behavior has been inconsistent. Many factors obfuscate the particular corrosion mechanisms at work, including grain size, but also texture, processing contamination, and surface roughness. Many studies attempting to link corrosion and grain size have not been able to decouple these effects. Here we introduce a preprocessing step to mitigate the surface contamination effects that have been a concern in previous corrosion studies on plastically deformed surfaces; this allows comparison of corrosion behavior across grain sizes while controlling for texture and surface roughness. Potentiodynamic polarization in aqueous NaCl solution suggests that different corrosion mechanisms are responsible for samples prepared with the preprocessing step.

Ionic liquids have many advantages over traditional aqueous electrosynthesis for fabrication of functional nanoarchitectures, including enabling the integration of nanoparticles into traditional coatings, superhydrophobicity, nanofoams, and other hierarchical structures. Shape and size control through ionic liquid selection and processing conditions can synthesize nanoparticles and nanoarchitectures without the use of capping agents, surfactants, or templates that are often deleterious to the functionality of the resultant system. Here we give a brief overview of some recent and interesting applications of ionic liquids to the synthesis of nanoparticles and nanoarchitectures.

For many years 5000 series aluminum alloys have played an important role in weight reduction of air, land and sea vehicles. However, sensitization of these alloys has been a major concern regarding the performance of aging vehicles. As the aluminum ages, magnesium, supersaturated in the matrix, segregates out to grain and precipitate boundaries as Al3Mg2 (β phase). The β phase is more electrochemically active than the solid solution, leading to increased sensitivity to corrosion including stress corrosion cracking and costly repairs or replacement (Lim et al., Corrosion 72:198–220, 2015). Studies have mostly focused on the effectiveness of various methods (grain boundary engineering, stabilization, coatings) in reducing corrosion but very little work has been performed on the high rate mechanical response of sensitized aluminum. This study will try to elucidate the effect of sensitization on the mechanical response of AA5083-H131. Specimens will be conditioned up to 28 days at 100 °C. Tension and compression tests will be performed at various loading rates to examine strength and elongation to failure. Results from this study will correlate mechanical response to corrosion criteria while aiding in the development of new alloys resistant to the effects of sensitization.

Small-scale shear punch testing has been applied to a butt joint created by friction stir welding of two adjoining AA2139-T8 plates. Advantages of this technique include the ability to perform a large number of independent tests on a given volume of material and the ability to measure site-specific differences and variations in local material properties. As such, combined with a simultaneous evaluation of the weld morphology, a series of 144 shear punch tests were carried out in a 12×12 grid pattern on the retreating half of the weld. The overlay of the grid pattern onto the etched surface allowed a correlation of the microstructure and mechanical properties measured across the weld at each shear punch site. Two-dimensional color enhanced property maps were generated to provide a powerful site specific visualization of the unique or distinctive microstructural features and how they correlate with the local mechanical response across the weld. One of the more insightful discoveries was the weld nugget region undergoing 2.5 times more strain-hardening than the base plate material, while simultaneously experiencing the Portevin-LeChatelier effect. Aspects of the technique and results of our experiments are described.

A newly developed micro-kolsy bar system at the Army Research Laboratory has made it possible to test materials in compression at strain rates greater than 104 s−1. Opening up a new realm for testing of materials at high strain rates. In order to reach these high strain rates, sample diameters must be on the order of tens to hundreds of microns. Fabrication of these micro-samples is done using a femtosecond laser, since the ultrashort pulse width of this laser does not produce any appreciable damage layer. The high strain rate (103–105 s−1) behavior and resulting microstructure of electrodeposited nickel was investigated using this micro-kolsy bar system. The microstructure of the as-deposited and tested samples was examined with electron backscatter diffraction and transmission electron microscopy. Tested samples show evidence of dynamic recrystallization and formation of a large number fraction of high angle, Σ3 boundaries.

Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is shallower in the cryogenic SMAT process. The tensile ductility of the grain size gradient remains low (

It is a new beginning for innovative fundamental and applied science in nanocrystalline materials. Many of the processing and consolidation challenges that have haunted nanocrystalline materials are now more fully understood, opening the doors for bulk nanocrystalline materials and parts to be produced. While challenges remain, recent advances in experimental, computational, and theoretical capability have allowed for bulk specimens that have heretofore been pursued only on a limited basis. This article discusses the methodology for synthesis and consolidation of bulk nanocrystalline materials using mechanical alloying, the alloy development and synthesis process for stabilizing these materials at elevated temperatures, and the physical and mechanical properties of nanocrystalline materials with a focus throughout on nanocrystalline copper and a nanocrystalline Cu-Ta system, consolidated via equal channel angular extrusion, with properties rivaling that of nanocrystalline pure Ta. Moreover, modeling and simulation approaches as well as experimental results for grain growth, grain boundary processes, and deformation mechanisms in nanocrystalline copper are briefly reviewed and discussed. Integrating experiments and computational materials science for synthesizing bulk nanocrystalline materials can bring about the next generation of ultrahigh strength materials for defense and energy applications.

Development of ultra-high strength and corrosion-resistant aluminum (Al) alloys is demonstrated by a combination of suitable alloying elements and processing technology able to cause extended solid solubility and nanocrystalline structure. Binary Al-transition metal (M: Cr, Ni, Mo, Si, Ti, Mn, V, Nb) alloys, produced by high-energy ball milling and subsequent cold compaction, have exhibited significantly high hardness and corrosion resistance compared to any commercial Al alloy. The cyclic potentiodynamic polarization tests revealed a significant improvement in pitting and repassivation potentials. X-ray diffraction analysis revealed the grain refinement IMPACT STATEMENT High-energy ball-milled Al alloys, owing to excellent corrosion resistance and high hardness, are expected to be a new class of Al alloys and initiate a multidisciplinary research direction.

Ion implantation was used to modify the surface chemistry of magnesium in order to improve the corrosion resistance. Metalloids which have recently been shown to reduce the cathodic reaction kinetics in magnesium alloys, were implanted into high purity polycrystalline magnesium at varying doses and the composition gradient, microstructure, and electrochemical behavior were characterized. The primary chemical reactions at a magnesium alloy surface during corrosion are water reduction, wherein water is split to evolve hydrogen, and oxidation of Mg to Mg2+. Recently, germanium and arsenic have been reported to have a significant impact on the kinetics of the cathodic water reduction reaction by inhibiting the recombination of hydrogen atoms and subsequent evolution of H2 gas from the Mg surface.(1, 2) Density functional theory (DFT) has provided support for these observations indicating unfavorable enthalpy changes for adsorbed hydrogen atom diffusion toward several metals and metalloids alloyed on a magnesium surface.(3) The DFT results also showed that the reaction enthalpy of diatomic hydrogen evolution was unfavorable on a dilute Mg-metalloid surface. Ion implantation into the surface of metals has been known to improve wear and corrosion resistance, alter conductivity and optical properties, and improve thermal oxidation resistance. For example, the corrosion resistance of 1070 and 52100 steels has been improved by implanting Ta or Ti. Although lesser studied than some substrates, implantation into Mg and Mg alloys has been examined for corrosion and wear in implantable medical devices.(4-6) Implantation of Y into Mg and of Al into AZ31 is known to increase open circuit potential (OCP) and co-implantation of Cr and O is known to form a protective oxide film. This study examines the role of ion implantation in forming protective, corrosion resistant magnesium surface alloys. Germanium and arsenic ions were implanted at 1532 keV into high-purity Mg samples using a National Electrostatics 5SDH-2 positive ion accelerator at doses sufficient to achieve 1-micrometer thick doped layers with peak concentrations of 0.01-0.3 atomic percent at approximately 1.5 micrometers beneath the surface. The depth of implantation and concentration were verified using Rutherford backscattering spectrometry, and were consistent with what had been expected from the ion implantation simulation program SRIM. Energy dispersive spectroscopy, and x-ray photoelectron spectroscopy were used to characterize surface chemistry. Surface morphology was characterized using scanning electron microscopy, tunneling electron microscopy, and atomic force microscopy. Higher concentrations of Ge and As were both observed to roughen the alloy surface, generating a thick MgO surface film, whereas low doses had a minimal effect. The corrosion behavior was evaluated using potentiodynamic polarization and immersion in quiescent NaCl. In order to de-convolute the effect of surface oxide thickness from the chemical effect of the alloying addition, Mg was also implanted into the Mg substrate as a reference. 1. R. Liu, M. Hurley, A. Kvryan, G. Williams, J. Scully and N. Birbilis, Scientific Reports, 6(2016). 2. N. Birbilis, G. Williams, K. Gusieva, A. Samaniego, M. A. Gibson and H. N. McMurray, Electrochemistry Communications, 34, 295 (2013). 3. K. R. Limmer, K. S. Williams, J. P. Labukas and J. W. Andzelm, CORROSION, 73, 506 (2017). 4. C. Liu, Y. Xin, X. Tian, J. Zhao and P. K. Chu, Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 25, 334 (2007). 5. Y. Z. Wan, G. Y. Xiong, H. L. Luo, F. He, Y. Huang and Y. L. Wang, Applied Surface Science, 254, 5514 (2008). 6. R. Xu, G. Wu, X. Yang, T. Hu, Q. Lu and P. K. Chu, Materials Letters, 65, 2171 (2011).

Grain boundary segregation provides a method for stabilization of nanocrystalline metals—an alloying element that will segregate to the boundaries can lower the grain boundary energy, attenuating the driving force for grain growth. The segregation strength relative to the mixing enthalpy of a binary system determines the propensity for segregation stabilization. This relationship has been codified for the design space of positive enthalpy alloys; unfortunately, quantitative values for the grain boundary segregation enthalpy exist in only very few material systems, hampering the prospect of nanocrystalline alloy design. Here we present a Miedema-type model for estimation of grain boundary segregation enthalpy, with which potential nanocrystalline phase-forming alloys can be rapidly screened. Calculations of the necessary enthalpies are made for ~2500 alloys and used to make predictions about nanocrystalline stability., United States. Army Research Office (Contract W911NF-09-1-0422), United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center DE-SC0001299)

Grain boundary segregation has been established through both simulation and experiments as a successful approach to stabilize nanocrystalline materials against grain growth. However, relatively few alloy systems have been studied in this context; these vary in their efficacy, and in many cases the stabilization effect is compromised by second phase precipitation. Here we address the open-ended design problem of how to select alloy systems that may be stable in a nanocrystalline state. We continue the development of a general “regular nanocrystalline solution” model to identify the conditions under which binary nanocrystalline alloy systems with positive heats of mixing are stable with respect to both grain growth (segregation removes the grain boundary energy penalty) and phase separation (the free energy of the nanocrystalline system is lower than the common tangent defining the bulk miscibility gap). We calculate a “nanostructure stability map” in terms of alloy thermodynamic parameters. Three main regions are delineated in these maps: one where grain boundary segregation does not result in a stabilized nanocrystalline structure, one in which macroscopic phase separation would be preferential (despite the presence of a nanocrystalline state stable against grain growth) and one for which the nanocrystalline state is stable against both grain growth and phase separation. Additional details about the stabilized structures are also presented in the map, which can be regarded as a tool for the design of stable nanocrystalline alloys., United States. Army Research Office (Contract W911NF-09-1-0422), United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center DE-SC0001299)

Metal Manipulation Reducing the grain size below 100 micrometers can vastly improve the properties of a metal. However, these nanocrystalline metals are not thermally stable; at elevated temperatures the grains will grow and merge. Alloying with a second metal to slow grain growth can slow down this process, which has shown some success on a trial-and-error basis. Chookajorn et al. (p. 951 ; see the Perspective by Weertman ) now provide a theoretical framework to create stability maps to identify potential alloys with the greatest thermal stability. For tungsten, counterintuitively, the theory suggests that atoms with the largest size differential or lowest solubility are not the best alloying choice. Indeed, an alloy of tungsten and titanium was processed more easily than pure nanocrystalline tungsten and also showed better stability at high temperatures.

The present paper analyses the effect of crystallographic texture on the electromechanical interactions of polycrystalline PZT films. These interactions are responsible for inducing local enhancements of the remnant polarisation. Built-in stresses and electric fields are responsible for asymmetries in the local shape of the hysteretic loop that are as large as 25% in the coercive field and 10% in the out-of-plane remnant polarisation. Simulations show two types of 180° domain walls are favoured: stress-free and mechanically tensile polarisation interfaces. For [001] fibre textured grains a texture of 37 MRDs (r = 0.3) will maximise the performance of individual memory units.