Modeling of Gibbs energies of pure elements down to 0K using segmented regression

A novel thermodynamic modeling strategy of stable solid alloy phases is proposed based on segmented regression approach. The model considers several physical effects (e.g. electronic, vibrational etc.) and is valid from 0K up to the melting temperature. The preceding approach has been applied for several pure elements. Results show good agreement with experimental data at low and high temperatures. Since it is not a first attempt to propose a "universal" physical-based model down to 0K for the pure elements as an alternative to current SGTE description, we also compare the results to existing models. Analysis of the obtained results shows that the newly proposed model delivers more accurate description down to 0K for all studied pure elements according to several statistical tests

Application of change-point analysis to the selection of representative data in creep experiments

The high volume of data resulting from a rapidly increasing number of experiments in materials science necessitates an efficient preparing of the data before any analysis. In addition, due to the large datasets in some experiments, it is essential to reduce the data sample to a small number of representative data points. In this study, three statistical methods for the change-point analysis are tested for the automated selection of representative creep data which provides large possibilities to speed up the data preparation for their further analysis. Moreover, this approach aids the practitioner to produce consistent and unique representative data for each experiment more efficiently

MultOpt++: a fast regression-based model for the development of compositions with high robustness against scatter of element concentrations

Abstract Alloys-by-design is a term used to describe new alloy development techniques based on numerical simulation. These approaches are extensively used for nickel-base superalloys to increase the chance of success in alloy development. During alloy production of numerically optimized compositions, unavoidable scattering of the element concentrations occurs. In the present paper, we investigate the effect of this scatter on the alloy properties. In particular, we describe routes to identify alloy compositions by numerical simulations that are more robust than other compositions. In our previously developed alloy development program package MultOpt, we introduced a sensitivity parameter that represents the influence of alloying variations on the final alloy properties in the post-optimization process, because the established sensitivity calculations require high computational effort. In this work, we derive a regression-based model for calculating the sensitivity that only requires one-time calculation of the regression coefficients. The model can be applied to any function with nearly linear behavior within the uncertainty range. The model is then successfully applied to the computational alloys-by-design work flow to facilitate alloy selection using the sensitivity of a composition owing to the inaccuracies in the manufacturing process as an additional minimization goal

The origins and spread of domestic horses from the Western Eurasian steppes

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: All collapsed and paired-end sequence data for samples sequenced in this study are available in compressed fastq format through the European Nucleotide Archive under accession number PRJEB44430, together with rescaled and trimmed bam sequence alignments against both the nuclear and mitochondrial horse reference genomes. Previously published ancient data used in this study are available under accession numbers PRJEB7537, PRJEB10098, PRJEB10854, PRJEB22390 and PRJEB31613, and detailed in Supplementary Table 1. The genomes of ten modern horses, publicly available, were also accessed as indicated in their corresponding original publications57,61,85-87.NOTE: see the published version available via the DOI in this record for the full list of authorsDomestication of horses fundamentally transformed long-range mobility and warfare. However, modern domesticated breeds do not descend from the earliest domestic horse lineage associated with archaeological evidence of bridling, milking and corralling at Botai, Central Asia around 3500 BC. Other longstanding candidate regions for horse domestication, such as Iberia and Anatolia, have also recently been challenged. Thus, the genetic, geographic and temporal origins of modern domestic horses have remained unknown. Here we pinpoint the Western Eurasian steppes, especially the lower Volga-Don region, as the homeland of modern domestic horses. Furthermore, we map the population changes accompanying domestication from 273 ancient horse genomes. This reveals that modern domestic horses ultimately replaced almost all other local populations as they expanded rapidly across Eurasia from about 2000 BC, synchronously with equestrian material culture, including Sintashta spoke-wheeled chariots. We find that equestrianism involved strong selection for critical locomotor and behavioural adaptations at the GSDMC and ZFPM1 genes. Our results reject the commonly held association between horseback riding and the massive expansion of Yamnaya steppe pastoralists into Europe around 3000 BC driving the spread of Indo-European languages. This contrasts with the scenario in Asia where Indo-Iranian languages, chariots and horses spread together, following the early second millennium BC Sintashta culture

Modeling thermodynamical properties by segmented non-linear regression

Die spezifische Wärme von festen Phasen als Funktion der Temperatur von 0 Kelvin bis zum Schmelzpunkt wird mit einem neuartigen, physikalisch-basierten, segmentierten mathematischen Modell dargestellt. Es basiert auf dem Debye Modell der spezifischen Wärme und berücksichtigt weitere physikalische Effekte, die in verschiedenen Temperaturbereichen auftreten können. Das Model wird auf experimentell ermittelte Wärmekapazitäten von purem Cr, Fe und Al angewendet. Ein wichtiges Element dieses Models ist das so-genannte Bent-Cable Modell, für welches die asymptotische Theorie der Schätzung der kleinsten Quadratabweichungen der Modellparameter entwickelt wird. Basierend auf dieser Theorie werden optimale Designs für das segmentierte Regressionsmodell der betrachteten Wärmekapazitäten konstruiert. Hinweise für die Sammlung der Wärmekapazitätsmessungen aus Literaturquellen werden entwickelt, bei deren Berücksichtigung die Parameter des segmentierten Modells zuverlässig festgelegt werden können

Thermodynamic descriptions of quaternary Mg–Al–Zn–Bi system supported by experiments and their application in descriptions of solidification behavior in Bi-additional AZ casting alloys

16 Mg–Al–Zn–Bi quaternary alloys were utilized to measure the phase equilibria and transformation temperatures in the Mg-rich Mg–Al–Zn–Bi quaternary system by means of the X-ray diffraction, electron probe micro-analysis and differential scanning calorimetry techniques. The isothermal section at 400 °C and three vertical sections along Mg–8 wt%Al–0.75 wt%Zn–xBi, Mg–3.4 wt%Al–0.5 wt%Zn–xBi and Mg–6.9 wt%Al–2.3 wt%Zn–xBi in the Mg–Al–Zn–Bi quaternary system were constructed. Based on the literature data, the ternary Mg–Al–Bi and Mg–Bi–Zn systems were re-assessed using the CALculaiton of PHAse Diagram (CALPHAD) approach. The calculated phase equilibria agree well with the measured data. By directly extrapolating the constituent sub-ternary systems, the thermodynamic database for the Mg–Al–Zn–Bi quaternary system was developed. The remarkable consistency between the predicted phase equilibria and the presently measured data in Mg–Al–Zn–Bi quaternary system further demonstrated the accuracy and reliability of the established thermodynamic database. After that, by using the newly developed thermodynamic database, the growth restrict factors and the solidification curves in Bi-containing AZ series magnesium alloys were calculated and analyzed. It was confirmed that the grain size of AZ alloys can be refined with the addition of Bi, and the component Al had larger grain refinement effect than Bi. Besides, the amount of Bi had also noticeable effect on the solidification sequence of the AZ alloys

Including state-of-the-art physical understanding of thermal vacancies in Calphad models

A physically sound thermochemical model accounting for explicit thermal vacancies in elements and alloys is presented. The model transfers the latest theoretical understanding of vacancy formation into the Calphad formalism where it can extend currently available thermodynamic databases to cover vacancy concentrations without a complete re-assessment. The parametrization of the model is based on ab initio-calculated enthalpy of vacancy formation and two model parameters describing the excess heat capacity of vacancy formation. Excellent agreement is obtained with temperature-dependent vacancy concentrations and elemental heat capacities while reasonable extrapolation of phase stability to high temperatures is ensured. Extrapolation to multicomponent systems is reasonable and the long-standing Neumann–Kopp related problem in the Calphad community is solved since multicomponent solid solutions will no longer show fingerprints of elemental heat capacity peaks at their melting points. FCC-Ag, FCC-Al and FCC-Cu, FCC-Zn, FCC-Ni, BCC-Ti, and BCC-W are used as a demonstration, along with the Cu–Zn binary system