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Summary Cermets embrace the high hardness of a ceramic and the good ductility of a metal. Therefore, they potentially meet the ever-increasing demands of new materials for harsh environments in energy generation and conversion. However, cermet sintering faces many challenges, such as metal volatilization, grain coarsening, and poor wettability of the metal with the ceramic, which affect the microstructure and thus mechanical properties. Herein, we apply an ultrafast high-temperature sintering (UHS) method to sinter cermets at a high temperature in only seconds. The high temperature leads to good wettability of the metal with the ceramic, while the short sintering time limits the loss of metal components and accurately controls the grain growth. We demonstrate the UHS method using a model cermet composed of a Ni-based superalloy and aluminum oxide, where we obtain dense microstructure, minimal nickel loss, and uniform grain size. Owing to these merits, good mechanical properties and oxidation resistance are achieved.

Recuperators with design temperatures at and above 800 °C can further increase the thermal efficiency of supercritical CO2 power cycles by enabling higher turbine exhaust temperatures. Mar-M247 is a well-suited nickel-based superalloy for high temperature service due to its high creep strength that prevents excessive material thickness being required for pressure containment. Additive manufacturing using a high-speed laser-directed energy deposition (L-DED) process presents a promising solution, with build trials demonstrating the ability to produce nonconventional flow channels for enhanced heat transfer. A design process is presented that includes aerothermal and mechanical evaluation to maximize performance within the constraints of the manufacturing process. A 2-D heat transfer network and pressure drop code allows prediction of flow distribution and its effect on overall thermal performance. Established literature correlations, along with CFD simulation, inform the prediction of heat transfer coefficients and friction factors for the flowpaths and enhancement features in the heat exchanger core. Mechanical evaluation using finite element analysis (FEA) modeling with the intent of the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII, Div. 2 assesses the operational safety of the design. The detailed design features annular finned passages that take advantage of helical flow paths to distribute the flow from separated headers to shared heat transfer surfaces. Performance predictions for the recuperator at a 50 kW scale provide insights into the feasibility of the additively manufactured (AM) process to produce recuperators on a commercial scale that extend existing operating envelopes.

The alloying effects of Ni, W and Cr on the microstructural stability of CoNi-base alloys were investigated using a multicomponent diffusion multiple after being aged at 1000 °C for 1000 h. The diffusion multiple was carefully designed based on thermodynamic calculations. The relationships between alloy compositions and microstructural characteristics were established over a large compositional range using this single sample, and the alloying effects of Ni, W and Cr on the elemental partitioning behaviors between γ and γ′ two phases were thermodynamically analyzed using high-throughput calculation. The results together show that an increase of Ni content increases the γ′ volume faction in the long-term aged microstructures. However, the higher Ni content leads to the precipitation of the χ phase by promoting the partitioning of W from the γ′ phase to the γ phase. The decrease of W content dramatically reduces the γ′ volume faction, but the addition of Cr can properly counteract this effect by promoting the partitioning of Al and Ti from the γ phase to the γ′ phase. This study will be helpful for accelerating the development of novel γ′-strengthened multicomponent CoNi-base alloys, as well as providing experimental data to improve the thermodynamic database.

Welding of aluminum alloys to steel is increasingly important in manufacturing; however, the use of fusion welding is difficult because of disparate melting points and the possibility of intermetallic compound (IMC) formation. Here, an impact welding technique, vaporizing foil actuator welding, was utilized to produce solid-state joints between AA1100-O and 1018 mild steel. The relationship between weld processing conditions, microstructure, and mechanical properties was investigated. For this purpose, the welds were annealed between 300 °C and 600 °C and a combination of optical and scanning electron microscopy, along with image analysis was performed to characterize the weld microstructure and monitor IMC growth. Wedge testing was applied to understand the effect of annealing on the weld fracture toughness. A numerical model incorporating the Fick’s laws of diffusion, grain boundary diffusion, and grain growth kinetics was also developed to simulate the IMC growth. The heterogeneity in the original microstructure caused persistent differences in IMC growth, as initial IMC seemed to increase nucleation and growth. Simulation results indicated short circuit diffusion to be the major contributor to IMC growth since it is consistently faster then experimental IMC growths compared with the computational results that used lattice diffusion only. Wedge testing reveals increased weld toughness for modest anneals of 300 °C, possibly due to homogeneity at the weld interface while avoiding IMC growth.

The diffusion behavior and phase equilibria in the Cu-Zn binary system were investigated using solid–solid and solid–liquid diffusion couples. Heat treatments at temperatures ranging from 100 to 750 °C were performed and the samples were examined using optical microscopy, energy dispersive x-ray spectroscopy, and electron probe microanalysis to identify the phases and to obtain composition profiles. Solubility limits of both solid solution and intermetallic phases were then evaluated, and a forward-simulation analysis (FSA) was applied to extract interdiffusion coefficients. The composition profiles from Hoxha et al. were also re-analyzed using FSA to obtain more reliable diffusion coefficient data without the assumption of constant diffusion coefficients for the intermetallic phases. A comprehensive assessment of the interdiffusion coefficients in three intermetallic phases of the Cu-Zn system was performed based on the results from the current study as well as those in the literature. Activation energies and Arrhenius pre-factors were evaluated for each phase as a function of composition. The fitted equations based on the comprehensive assessment have the capabilities of computing the interdiffusion coefficients of each of the phases at a given composition and temperature. Suggested modifications to the Cu-Zn binary phase diagram were presented based on the new experimental information gathered from the present study. A clear explanation is provided for the puzzling low Zn concentrations often observed in the Cu-rich fcc phase of Cu-Zn diffusion couples in comparison with the expected high solubility values based on the equilibrium Cu-Zn phase diagram.

This article highlights the capabilities of dual-anneal diffusion multiples (DADMs) in performing high-throughput and systematic studies of phase transformations and metastability. DADMs create wide ranges of solid solution compositions through elemental interdiffusion during a first anneal at a high temperature. After quenching to ambient temperature, each diffusion multiple can be cut into several slices, and each slice is further annealed individually at a lower/second temperature. Phase transformations take place in the supersaturated regions of the solid solution compositions that are formed during the first anneal, leading to various precipitates due to different driving force, interfacial energy, and other factors as composition varies across the regions in the sample. By subjecting the sliced diffusion multiples individually to different anneal durations and different second anneal temperatures, very large datasets can be collected on phase transformation kinetics and evolution of precipitate morphology as a function of composition, time, and temperature. Metastable phases and their transitions to more stable phases have been systematically observed in the Fe-Cr-Mo ternary system across a wide range of composition, temperature, and anneal time, thus providing a large amount of information on metastability of the phases. The solvi of the metastable and stable phases can be systematically collected for more reliable CALPHAD assessments of the Gibbs free energy of the metastable phases. By adjusting the interfacial energy value in simulations using models such as the Kampmann–Wagner Numerical (KWN) model and matching the simulated precipitate sizes at different compositions with experimentally measured sizes of the corresponding compositions in a DADM, the interfacial energy value can be obtained. Opportunities and challenges in using DADMs to collect large datasets on precipitation kinetics and morphology will be explained to enable full utilization of the capabilities of DADMs in the future. This review not only presents experimental results collected to date, but also explains the vast more datasets that can be collected from DADMs in the future. An approach that iteratively and holistically integrates experimental results with model predictions is advocated as a very effective means to advance the understanding of various phase transformation mechanisms. In this way, the new mechanistic understanding can be integrated to more robust models to simulate the “abnormal” behaviors that are observed in DADMs, especially related to sequential precipitations of phases that are common in engineering alloys. Examples are also shown to illustrate the systematic nature of DADMs as a result of their continuously varying composition regions in catching unusual phenomena and emergent trends that are easily missed during studies using discrete compositions afforded by individual alloys.

A new technique to calculate spatial variations of grain shape, grain size, and grain boundary curvature in the fusion zone (FZ) of refractory metal alloys has been developed. This technique was applied to quantitatively evaluate changes in microstructures of simulated molybdenum welds available in the literature. Use of this technique showed that a 50% increase in weld speed more than doubled the fraction of grain segments oriented between 0° and 30° to the normal to the weld direction along with a decrease in grain size from approximately 120 µm to 84 µm in the weld direction at the FZ centerline.

Diffusion between Al and Mg was investigated comprehensively using both high-throughput experiments and density functional theory (DFT) calculations. Experimental diffusion coefficients in fcc Al, hcp Mg, β–Mg17Al12, γ–Mg2Al3 and e − Mg23Al30 phases were collected by combining diffusion multiples with forward-simulation analysis together with a critical review of the experimental studies in the literature. The best settings to compute the dilute (impurity) diffusion coefficients of Al and Mg using DFT were tested by comparing the computed data using various DFT settings with the critically assessed experimental diffusion coefficients in stable phases (fcc Al and hcp Mg). The optimal DFT settings were employed to calculate the dilute diffusion coefficients of Al and Mg in metastable (hypothetical) phases (hcp Al and fcc Mg) where experimental measurements were impossible. The atomic mobilities of Al and Mg in the Al–Mg binary system across the entire composition range were then reliably optimized for both the fcc and hcp phases based on the comprehensive diffusion data obtained from both experimental measurements for the stable phases and DFT calculations for the metastable phases. This study demonstrates an efficient and reliable way to develop fundamental mobility databases using integrated experimental and computational methods.

A dual-anneal diffusion multiple was utilized to generate a composition gradient via a first anneal at a high temperature followed by a second anneal at a lower temperature to induce phase precipitation as a function of composition/supersaturation. By adjusting the interfacial energy value in simulations using the classical nucleation and growth theories as implemented in the Kampmann-Wagner numerical (KWN) model and matching the simulated average precipitate sizes at different compositions with the experimental measurements along the composition gradient, the Ni3Al/fcc interfacial energy in the Ni-Al system at 700 °C was effectively determined to be ~12 mJ/m2.

Powder to bulk processes, such as additive manufacturing and metal injection molding (MIM), have enabled great potential for complex metal designing and manufacturing. However, additive manufacturing process normally introduces a high residue stress and textures due to the locally intense temperature. MIM is an excellent batch manufacturing process; nevertheless, it is not suitable for rapid screening and development of new metal compositions and structures due to the slow sintering process. Herein, an ultrafast high‐temperature sintering (UHS) process is reported that enables the rapid synthesis and sintering of bulk metals/alloys and intermetallic compounds. In this process, elemental powders are mixed and pressed into pellets, followed by UHS sintering in just seconds at a temperature between 1000 and 3000 °C. Three representative compositions, including pure metals, intermetallics, and multielement alloys, are demonstrated with a broad range of melting points. The UHS process for metal sintering is nonmaterials specific, in addition to being extremely rapid, which make it suitable for materials discovery. Furthermore, the sintering method does not apply pressure to the samples, making it compatible with 3D printing and other additive manufacturing processes of complex structures. This rapid sintering technique will greatly facilitate the development and manufacturing of metals and alloys., An ultrafast high‐temperature sintering (UHS) process is developed to sinter a wide range of metals/alloys from compacts of elemental or prealloyed powders. Joule‐heated carbon heaters provide a uniform high‐temperature environment (up to 3000 °C) for a rapid sintering in just ≈10 s.

Sn and Zr are two important alloying elements in low-modulus biomedical titanium alloys, yet experimental data on Sn diffusion in bcc Ti and bcc Zr are still very limited in the literature, and thus were systematically measured in the present study using solid–solid diffusion couples (SSDCs) and novel liquid–solid diffusion couples (LSDCs). Both interdiffusion and impurity diffusion coefficients in the bcc phase of the Ti-Sn and Zr-Sn systems were extracted with forward-simulation analysis (FSA), and show good agreement with existing literature. The interdiffusion coefficients in the Ti-Sn system at six temperatures, from 950 °C to 1200 °C, extend experimental measurements to a much wider composition range, and the interdiffusion coefficients in the Zr-Sn system at 1200 °C, 1150 °C, and 1100 °C are the first such data experimentally measured. The data obtained from this study, together with our previous data for the Ti-X (X = Cr, Hf, Mo, Nb, V, Zr) systems, provide reliable experimental inputs to improve the mobility databases for advanced Ti alloys development. In addition, the excellent agreement between the LSDCs and SSDCs results validates the reliability of this novel approach by combining LSDC experiments and FSA in evaluating diffusion coefficients at elevated temperatures.

First-principles calculation of diffusion coefficients between Mg and Al is investigated comprehensively using density functional theory (DFT). The effect of different uncertainty sources arising from first principles calculations has been investigated systematically. These sources include the diffusion model, energetic, entropic and attempt frequency calculations. Variation in self and impurity diffusion coefficients of Mg and Al in stable phases are quantified using different DFT settings and compared with the experiments. Using the optimal DFT settings, diffusion coefficients in metastable phases of Al and Mg are predicted. The dataset refers to "An integrated experimental and computational study of diffusion and atomic mobility of the aluminum-magnesium system" [1].

An easy-to-implement gradient temperature heat treatment process was developed to effectively study the phase precipitation in a Fe-Cr-Mo high-temperature ferritic steel over a wide range of temperatures. The natural temperature gradient across a Fe-Cr-Mo steel bar that was placed at an open-end of a tube furnace led to microstructure variations and hardness changes as a result of the difference in phase precipitation. SEM and TEM characterizations showed that the Chi-phase was the dominant phase at temperatures higher than 785 °C and a metastable Laves phase precipitated prior to the Chi-phase at temperatures below 785 °C. Vickers microhardness was measured at locations across the steel bar, and the Ashby-Orowan equation was found to hold well in correlating the microhardness values to the average particle size and inter-particle spacing obtained from quantitative image analysis.

Essentially all diffusion coefficients, except for a tiny fraction from tracer experiments, are evaluated from diffusion concentration profiles that are predominantly measured via wavelength or energy dispersive spectroscopy of characteristic X-rays of the pertinent elements. X-ray generation (interaction) volume simulation and an analysis of experimental profiles show that the extracted diffusion coefficients can be inflated by up to three orders of magnitude in very steep gradient regions due to artificial broadening of the concentration profiles. A recommendation is made to trust only diffusion coefficients from concentration gradients less than 1 at% per micron unless very special corrections are made.

The thermal conductivity (κ) and heat capacity (Cp) of the magnetocaloric AlFe2B2 compound were investigated to assess its room temperature heat transfer and thermal management potential relative to other magnetocaloric materials such as FeRh, Gd, Gd5(Si,Ge)4 La(Fe,Si)13 and (Mn,Fe) (P,As). The room temperature thermal conductivity was determined along the three principal crystallographic directions of AlFe2B2 using the time-domain thermoreflectance (TDTR) method on six randomly oriented AlFe2B2 grains, resulting in an observed anisotropic thermal conductivity with a 40% larger κ along the c-axis: κx = 4.7 ± 0.1 W/mK, κy= 4.4 ± 0.1 W/mK, and κz= 6.8 ± 0.3 W/mK.

Residential combined heat and power (CHP) systems produce electricity onsite while utilizing waste heat to supplement home heating requirements, which can lead to significant reductions in CO2 emissions and primary energy consumption. However, the current deployment of such CHP systems in the U.S. residential sector is extremely low primarily due to their high cost, short system life, and low system efficiency. Based on an analysis of average energy consumption of representative single-family homes in 10 U.S. cities across 7 different climate zones, it is concluded that there is no one-size-fits-all residential CHP system, but that a range of products are more likely to reflect consumer preferences. It is further identified via a systematic techno-economic analysis (TEA) that high-efficiency (e.g., 30–40% fuel to electricity), long-life (e.g., 15 years), low-cost (preferably less than U.S. $2,500 installed price), and low emissions are key requirements to enable widespread deployment of CHP systems in the U.S. residential sector. This article analyzes how the payback period would change for each city by varying nearly a dozen parameters and concludes with an evaluation on maximum market penetration based on a given set of parameters, and the resulting energy and emissions savings that can be practically achieved in some scenarios.

Diffusion in the Ti-Al-V system is studied and a CALculation of Phase Diagrams (CALPHAD) diffusion mobility description is developed. Diffusion couple experiments are performed to obtain diffusion paths in the hcp phase at 923 K, 1023 K and 1123 K. The diffusion coefficient of V in the hcp-Ti phase is found to decrease with increasing Al alloying. A forward-simulation analysis is used to evaluate the impurity diffusion coefficient for Al and V diffusion in the hcp Ti-V and the Ti-Al systems which are used as input in the mobility modeling. The composition dependency for the diffusion in the hcp phase in the ternary system is accounted for and a CALPHAD diffusion mobility description is obtained by directly optimizing the mobility parameters as a function of the experimental composition profiles from the diffusion couples. Both experimental data and previous diffusion mobility descriptions in the literature for the bcc Ti-Al-V phase are adopted. A complete description of diffusion in both the hcp and bcc phases for the Ti-Al-V system is presented with the aim to be used for design of Ti alloys and processes.

Titanium alloys are great candidates for applications such as biomedical implants that require biocompatibility, a low Young's modulus and a high strength. However, the properties of Ti alloys are highly dependent on phase stability. In the present work, a database for the Ti-Mo-Nb-Ta-Zr system has been evaluated using the CALPHAD (CALculation of PHAse Diagram) approach. The database was completed by evaluating the accuracy of previously modeled systems from literature and modeling systems that, to the best of the authors’ knowledge, had no modeling available in literature. All of the binary systems that make up the Ti-Mo-Nb-Ta-Zr system had previously modeled thermodynamic descriptions available in the literature and in most cases had multiple different descriptions available, which meant determining which previous thermodynamic description most accurately modeled the binary system with a direct focus on the bcc phase. In order to determine the accuracy of the multiple available thermodynamic descriptions from literature a combination of experimental data (also obtained from the literature) and computed thermochemical properties of the bcc phase from DFT (Density Functional Theory)-based first-principles calculations (present work) were used. Once the thermodynamic descriptions for the binary systems were chosen, focus shifted to the Ti-containing ternary systems. The Ti-Mo-Zr, Ti-Nb-Zr and Ti-Ta-Zr systems had previous thermodynamic description available in literature, which were incorporated without changes into the working database. The Ti-Mo-Ta, Ti-Nb-Ta and Ti-Mo-Nb systems had, to the authors’ knowledge, no descriptions available in the literature. Interaction parameters were determined for the Ti-Mo-Ta and Ti-Nb-Ta systems, and no interaction parameters were introduced for the Ti-Mo-Nb system. The database introduced by this work satisfactorily predicts the thermodynamics of the Ti-Mo-Nb-Ta-Zr system.

Diffusion coefficients of seven binary systems (Ti-Mo, Ti-Nb, Ti-Ta, Ti-Zr, Zr-Mo, Zr-Nb, and Zr-Ta) at 1200 °C, 1000 °C, and 800 °C were experimentally determined using three Ti-Mo-Nb-Ta-Zr diffusion multiples. Electron probe microanalysis (EPMA) was performed to collect concentration profiles at the binary diffusion regions. Forward simulation analysis (FSA) was then applied to extract both impurity and interdiffusion coefficients in Ti-rich and Zr-rich part of the bcc phase. Excellent agreements between our results and most of the literature data validate the high-throughput approach combining FSA with diffusion multiples to obtain a large amount of systematic diffusion data, which will help establish the diffusion (mobility) databases for the design and development of biomedical and structural Ti alloys.

Phase stability information regarding the formation of the topologically close packed (TCP) phases is critical for the design of advanced Ni-based and Co-based superalloys that contain high concentrations of refractory elements. Isothermal sections of the Co-Ni-W, Co-Ni-Mo, Co-Ni-Nb and Co-Ni-Ta systems at both 900 °C and 800 °C were constructed for the first time from electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD) measurements on two Co-CoAl-Cr-Mo-Ni-Nb-Ta-W diffusion multiples. The new data will serve as experimental input to future thermodynamic assessments of the Co-Ni-X ternary systems in order to improve the thermodynamic databases for the design and development of advanced Ni-based and Co-based superalloys.

Titanium alloys are great implant materials due to their mechanical properties and biocompatibility. However, a large difference in Young’s modulus between bone (∼10–40 GPa) and common implant materials (ie. Ti-6Al-4V alloy ∼110 GPa) leads to stress shielding and possible implant failure. The present work predicts the single crystal elastic stiffness coefficients (cij’s) for five binary systems with the body centered cubic lattice of Ti-X (X = Mo, Nb, Ta, Zr, Sn) using first-principles calculations based on Density Functional Theory. In addition, the polycrystalline aggregate properties of bulk modulus, shear modulus, Young’s modulus, and Poisson ratio are calculated. It is shown that the lower Young’s modulus of these Ti-alloys stems from the unstable bcc Ti with a negative value of (c11–c12). The data gathered from these efforts are compared with available experimental and other first-principles results in the literature, which set a foundation to design biocompatible Ti alloys for desired elastic properties.

This study extends a 1-parameter Z-Z-Z binary diffusion coefficient model to ternary and multicomponent systems. The cross-binary and ternary interaction parameters in atomic mobility (diffusion coefficient) assessments were systematically tested on 4 ternary solid solutions: fcc Ag-Au-Cu, fcc Co-Fe-Ni, fcc Cu-Fe-Ni, and bcc Nb-Ti-V. A simple combination of the Z-Z-Z binary model parameters without any additional fitting parameters already provides impressive predictions of the ternary diffusion coefficients when the 3 cross-binary parameters are set to be the corresponding binary Z-Z-Z model interaction parameters, leading to a robust Z-Z-ternary diffusion model. Employment of 3 independent cross-binary fitting parameters leads to an even better binary and cross-binary parameters only (BCBPO) model. Recommendations are rendered based upon the amount of available experimental ternary diffusion coefficients. These recommendations will substantially reduce the number of fitting parameters and improve the robustness of the resultant atomic mobility and diffusion coefficient databases for computational materials design.

The effects of substituting W with γ′ formers (Al, Ti, Ta, Mo and Nb) on the microstructural stability of a base model superalloy Co-20Ni-7Al-8W-1Ta-4Ti were studied using a high-throughput diffusion-multiple approach. A substantial amount of composition-microstructure data was obtained from a single sample, enabling deeper understanding of the alloying effects. It was found that alloy 15Al0W still contains stable γ′ phase at 1000 °C for 1000 h even with a W content of zero. However, the γ′ volume fraction of this alloy was far lower than other W-containing alloys, indicating that W plays an important role on retaining the stability of the γ′ phase. Except for Ti, substituting W with other γ′ forming elements promotes the precipitation of detrimental phases, with a potency of Nb > Ta≈Al > Mo > Ti. The Nb content should be carefully controlled due to its strong effect on inducing the precipitation of the χ phase. The literature data for W-free alloy systems were discussed in comparison to the current W-containing alloy system in order to analyze the role of W in stabilizing the γ′ phase at high temperatures. Furthermore, the γ′ strength and density of more than 300 alloys from the investigated diffusion multiple were analyzed using classic models established for Ni-base superalloys, to guide the alloy design aiming to achieve higher strength to weight ratio. The substitution of W with Ti or Al could significantly reduce the alloy density, but would also decrease the γ′ strength to some extents. These negative effects could be counterbalanced by moderate additions of Ta and Nb. This study will be helpful for the accelerated design of multi-component CoNi-base superalloys to achieve light weight and high strength.

This study is the most comprehensive test to date aiming at defining the optimal number of fitting parameters for a reliable mathematical description of the diffusion behavior of a binary solid solution. Our systematic test of 18 diverse binary systems has yielded a surprisingly simple model with only one fitting parameter/constant which can be evaluated from experimental diffusion data. The rest of the quantities in the model are the self-diffusion and impurity (dilute) diffusion coefficients of the pure elements and the thermodynamic factor which can be computed from a CALPHAD thermodynamic assessment of the pertinent binary system. The 1-parameter Z-Z-Z model has been demonstrated to be very reliable and robust since the 18 binary systems tested in this study include very asymmetrical systems such as Co-Pd and Fe-Pd as well as Nb-Ti whose experimental diffusion coefficient data cover ~9 orders of magnitude and over a temperature range spanning ~1200°C (from ~800°C to ~2000°C). The Z-Z-Z model allows both tracer and intrinsic diffusion coefficients to be reliably computed for any composition at any temperature after the sole constant is evaluated from the interdiffusion or all experimental diffusion data. Extension of such a simple and robust model from binary to ternary and higher order systems will lead to a substantial reduction of fitting parameters and an enhancement of the reliability of future multicomponent diffusion (atomic mobility) databases for simulation of kinetic processes in materials.

Titanium alloys are being investigated as suitable materials for load-bearing implants because of their biocompatibility and mechanical properties. Stress shielding, a common issue with the current load-bearing implant materials, occurs due to a Young’s modulus (E) mismatch between bone (∼10–40 GPa) and implants (such as Ti-6Al-4V ∼110 GPa), which leads to bone dying around the implant and ultimately implant failure. Reducing the Young’s modulus of Ti alloys may overcome the issues of stress shielding and improve implant materials. In the present work, first-principles calculations have been used to predict the single crystal elastic stiffness coefficients (cij’s) for the Ti-containing ternary alloys Ti-X-Y (X ≠ Y = Mo, Nb, Sn, Ta, Zr) in the bcc lattice. It is found that the ternary Ti-X-Y (X ≠ Y = Mo, Nb, Ta) alloys behave similarly; so do the ternary Ti-X-Sn (X = Mo, Nb, Ta) alloys and the Ti-X-Zr (X = Mo, Nb, Ta) alloys. This is expected due to the similarity between the Mo, Nb and Ta elements. The results also show that the Ti-Zr-X alloys stabilized the bcc phase at lower alloying concentrations. The polycrystalline aggregate properties are also estimated from the cij’s, including bulk modulus, shear modulus and Young’s modulus. The results show that Ti-alloys with compositions close to the bcc stability limit have the lowest E. In combination with previous predictions, a complete elastic database has been established using the CALPHAD (CALculation of PHAse Diagram) based modeling approach. The database results are compared with the E of higher order Ti alloys and shown to be able to predict the E accurately. This complete database forms a foundation to tailor Ti alloys for desired elastic properties.

Forward-simulation analysis was performed on composition profiles collected from liquid-solid and solid-solid diffusion couples to obtain diffusion coefficients of Mg-Sn, Mg-Y, and Mg-Zn. Reliable impurity diffusion coefficient of Y in Mg is obtained for the first time, showing that Y diffusion in Mg is about the same as Sn below 390 °C. The first sets of interdiffusion coefficients of Mg-Sn and Mg-Y are also obtained together with wider temperature-range data for Mg-Zn.

We extended and updated Mott's two-band model for the composition-dependence of thermal and electrical conductivity in binary metal alloys based on high-throughput time-domain thermoreflectance (TDTR) measurements on diffusion multiples and scatterer-density calculations from first principles. Examining Au-Cu, Au-Ag, Pd-Ag, Pd-Cu, Pd-Pt, Pt-Rh, and Ni-Rh binary alloys, we found that the nature of the two dominant scatterer-bands considered in the Mott model changes with the alloys, and should be interpreted as a combination of the dominant element-specific s - and/or d -orbitals. Using orbital and element-resolved density-of-states values calculated with density functional theory as input, we determined the correct orbital mix that dominates electron scattering for all examined alloys and found excellent agreement between fitted models and experimental results. This general model of the composition dependence of the thermal and electrical resistivity can be readily implemented into the CALPHAD framework.

Most impurity diffusion coefficients were measured in the 1960s and 1970s using tracer experiments with only 14 sets of tracer measurements performed worldwide in the past 15 years. It is thus impractical to rely on tracer experiments to obtain the missing thousands of impurity diffusion coefficients. A recently developed forward-simulation analysis can change the scenario by reliably extracting impurity diffusion coefficients from regular diffusion couple profiles. A comparison of 51 values obtained from the forward-simulation analysis with tracer experiment values in the literature shows an excellent agreement, thus validating the reliability of the forward-simulation analysis in obtaining accurate impurity diffusion coefficients.

As a new class of promising high-temperature materials, Co–Al–W-base alloys have been developed by alloying additions to improve the microstructure stability and other properties. However, the optimization of Co–Al–W-base alloys becomes more complicated with increasing variety and content of alloying elements. In this study, an accelerated approach to design γ′-strengthened Co–Ni-base superalloys with well-balanced properties was developed, by integrating the diffusion-multiple approach and machine-learning tools. A large amount of experimental data was obtained using the diffusion-multiple approach and fed into machine learning tools to establish the relationship between alloy compositions and important thermodynamic and microstructural parameters such as the phase constituent, the γ′ phase fraction (Fγ′) and the γ′ solvus temperature (Tγ′). The established machine-learning models were then employed to predict the characteristic parameters of multicomponent Co-Ni-base superalloys containing up to nine elements (Co, Ni, Al, W, Ta, Ti, Cr, Mo, Nb), even though most of the collected compositions from experiments were quinary to septenary alloys. Using the predicted results from the models and the computational thermodynamics tools, a multicomponent Co–Ni-base superalloy aimed at the application as single crystal blades was designed and characterized to test the reliability and robustness of the novel design approach.

The full elastic constants of Ni-based superalloy Rene 88DT were measured for the first time using a recently developed method that matches the computed surface acoustic wave (SAW) velocities from an elastodynamic model with experimental velocities of SAWs that are generated and detected with a femtosecond laser. The experimental measurements were performed on several grains of a polycrystalline sample without the need of growing a single crystal. The computed Young's modulus from the resultant elastic constants agrees with the literature values, lending confidence on our measured elastic constants: C11 = 267.1, C12 = 170.5, and C44 = 107.6 (GPa).

The Materials Genome Initiative (MGI) advanced a new paradigm for materials discovery and design, namely that the pace of new materials deployment could be accelerated through complementary efforts in theory, computation, and experiment. Along with numerous successes, new challenges are inviting researchers to refocus the efforts and approaches that were originally inspired by the MGI. In May 2017, the National Science Foundation sponsored the workshop “Advancing and Accelerating Materials Innovation Through the Synergistic Interaction among Computation, Experiment, and Theory: Opening New Frontiers” to review accomplishments that emerged from investments in science and infrastructure under the MGI, identify scientific opportunities in this new environment, examine how to effectively utilize new materials innovation infrastructure, and discuss challenges in achieving accelerated materials research through the seamless integration of experiment, computation, and theory. This article summarizes key findings from the workshop and provides perspectives that aim to guide the direction of future materials research and its translation into societal impacts.

Insight in phase equilibria is very valuable for the design of Co-based superalloys that have the potential of 50 °C higher temperature capability than Ni-based superalloys. The Co-rich part of the Co-Al-X (X = W, Mo, Nb, Ni, Ta) ternary systems is especially important and was thus investigated using two sets of diffusion multiples (Ni-Co-CoAl-Cr-Mo-Nb-Ta-W and Ni-Co-NiAl-Si-Zr). Isothermal sections of the Co-Al-W and Co-Al-Nb systems at 900 °C as well as the Co-Al-Mo, Co-Al-Ni and Co-Al-Ta systems at both 900 °C and 800 °C were constructed from the results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The data can be used as experimental input to future thermodynamic assessments of the Co-Al-X ternary systems in order to improve the relevant thermodynamic databases for the design and development of Co-based superalloys.

A novel liquid-solid diffusion couple enables effective measurements of composition profiles at high temperatures. A forward-simulation analysis is then performed to extract both interdiffusion and impurity diffusion coefficients. The combined method enables measurement of the first ever set of impurity diffusion coefficients of Ca in Mg and reliable high-temperature diffusion data of Al in Mg. The results show that Ca diffuses faster than the Mg self-diffusion which is faster than the Al impurity diffusion in Mg; thus Ca may not be an ideal element for the enhancement of high-temperature creep strength of Mg alloys as has been often assumed.

The design and development of novel titanium alloys for structural and biomedical applications require reliable thermodynamic and kinetic databases. In this study, diffusion behaviors of six Ti–X (X = Cr, Hf, Mo, Nb, V, Zr) binary systems were systematically investigated at temperatures from 800 to 1200 °C using a set of five Ti–TiAl–Cr–Hf–Mo–Nb–V–Zr diffusion multiples. Concentration profiles of the six Ti–X binary systems were collected from binary regions of the diffusion multiples using electron probe microanalysis (EPMA). Both interdiffusion and impurity (dilute) diffusion coefficients in the Ti-rich bcc phase of these systems were extracted from the concentration profiles using the forward-simulation method. Twenty impurity diffusion coefficients of all the six elements in bcc Ti as well as Ti in bcc Zr at different temperatures obtained from this study are in excellent agreement with the literature data. The interdiffusion coefficients obtained from this study are also in good agreement with previous literature results. The large amount of new experimental data obtained from this study will be essential for establishing the mobility databases for the design and development of advanced titanium alloys.

SnSe is a semiconductor compound reported to possess very high thermoelectric ZT values at 600 °C–700 °C. Oxidation and sublimation are of significant concern at such temperatures. The oxidation behavior of SnSe at four temperatures between 600 °C and 700 °C in atmospheric air was investigated by monitoring the weight change as a function of time, as well as by characterizing the oxidized samples using optical microscopy, SEM with EDS, and powder XRD. The results show that SnSe oxidizes very rapidly at 600 °C–700 °C to form SnO 2 and possibly Sn(SeO 3 ) 2 . Sublimation of Se and Se oxides is also observed. At 600 °C the consumption of Sn from SnSe to form SnO 2 drives the composition to be Se rich. A layer of SnSe 2 forms between the oxides and SnSe. At ≥ 650 °C, the consumption of Sn likely leads to the formation of a transient liquid phase, which significantly accelerates both oxidation and sublimation. It is concluded that SnSe needs to be used under vacuum or with a protective coating such as pure Si.

A recently developed dual-anneal diffusion-multiple approach is employed to the determination of the Fe-Cr-Mo phase diagram at intermediate temperatures. Diffusion multiples of Fe-Cr-Ni-Co-Mo were first annealed at 1200 °C for 500 h to create wide ranges of solid solution compositions. Subsequent annealing of the diffusion multiples at individual intermediate temperatures induced various precipitate phases. Electron probe microanalysis (EPMA) across the interface between large precipitates and the matrix phase provided local equilibrium information for the establishment of equilibrium tie-lines which are utilized to construct the Fe-rich part of the Fe-Cr-Mo isothermal sections at 900 and 800 °C. The Mo-rich part of the isothermal sections at intermediate temperatures was not obtained due to the sluggish kinetics of precipitation and growth, resulting in too small precipitates for reliable EPMA composition evaluation. A complete 1200 °C isothermal section of the Fe-Cr-Mo system is also established from EPMA data on a water quenched diffusion multiple that was annealed at 1200 °C for 500 h only without a second anneal.

A combined heat and power (CHP) system typically employs a prime mover generator that produces electricity on-site and utilizes waste heat energy to supplement a site’s thermal load requirements. Micro-CHP, notionally defined as CHP systems with a capacity lower than 50 kW, offers an alternative, and in some cases a complementary, solution to centralized power generation. A micro-CHP system would be typically installed at a residential or small commercial site where it would consume fuel such as diesel or natural gas to generate electricity locally and further use the rejected waste heat for local heating, air-conditioning, and/or humidification needs. This is in contrast to the rejected heat being dissipated at centralized power plants using cooling towers. The combined efficiency of primary energy usage for such systems can be higher than 90% on a fuel lower heating value (LHV) basis. Since a large fraction of the electricity generated from all the centralized power plants is consumed by the residential and commercial sectors, CHP implementation in these sectors can have a huge impact on both energy savings and carbon dioxide (CO2) emissions’ reduction. Apart from these benefits, decentralized CHP as a form of distributed electricity generation offers numerous advantages such as reduced electrical grid stress, reduced electricity transmission and distribution losses, and potentially improved resiliency of the electricity grid. Various technologies including reciprocating internal combustion engines, Stirling engines, Brayton cycle engines, Rankine cycle engines, fuel cells, and solid-state devices such as thermoelectric generators and thermionic generators can be used as micro-CHP systems. This chapter provides a detailed technological review of engine-based micro-CHP systems and further presents the challenges and opportunities for achieving high fuel conversion efficiency.