Entropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy

Muskox Health Ecology Symposium 2016: Gathering to Share Knowledge on Umingmak in a Time of Rapid Change

The Muskox, Ovibos moschatus, also known as Umingmak ‘the Bearded One,’ is a taxonomically unique, cold-adapted, ice-age survivor. Originally native to Canada and Greenland, it has established a circum-Arctic distribution via introduced populations. As a key resident herbivore in northern ecosystems, the muskox has importance that should not be underestimated. Muskoxen play an important role in the cultural identity of Arctic Indigenous peoples and provide a healthy source of country food. More recently, recognition of the economic potential of the species through tourism, sport hunting, and the traditional sale of handicrafts has generated renewed interest in muskoxen and their ecology. Recent documentation of diseases, including several zoonoses, regional mortality events, and population declines have highlighted knowledge gaps in both our understanding of the drivers of muskox population fluctuations and the potential sensitivity of this species to a rapidly changing climate (Kutz et al., 2013, 2015; Handeland et al., 2014; Ytrehus et al., 2015; Tomaselli et al., 2016c; Afema et al., 2017)

Quantification of Solid Solution Strengthening and Internal Stresses through Creep Testing of Ni-Containing Single Crystals at 980 °C

Various alloy compositions were cast as single crystals in a Bridgman vacuum induction furnace and creep tested at 980 °C: pure Ni, the equiatomic alloys CoCrNi and CrMnFeCoNi (Cantor alloy), single-phase fcc (Ni) solid solution alloys (with the composition of the matrix-phase of CMSX-3 and CMSX-4), and two-phase Ni-based superalloys CMSX-3 and CMSX-4. Due to the single-crystal state, grain size effects, grain boundary sliding, and grain boundary diffusion can be excluded. The results identify two major strengthening mechanisms: solid solution strengthening and other mechanisms summarized as precipitation hardening. Configurational entropy does not increase creep strength: The Cantor alloy, with the highest configurational entropy of all alloys tested, shows a weak and similar creep strength at 980 °C in comparison to pure Ni with zero configurational entropy. The element Re is a very effective strengthener, both in single-phase fcc (Ni) solid solution alloys as well as in two-phase superalloys. Quantitative estimations of different strengthening mechanisms: internal back stress, misfit stresses, Orowan bowing, and γ′-phase cutting (in the case of two-phase superalloys) are presented. Finite element simulations allow estimating the influence of solid solution strengthening of the matrix on the creep behavior of the two-phase superalloys

Entropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy

Muskox status, recent variation, and uncertain future

Muskoxen (Ovibos moschatus) are an integral component of Arctic biodiversity. Given low genetic diversity, their ability to respond to future and rapid Arctic change is unknown, although paleontological history demonstrates adaptability within limits. We discuss status and limitations of current monitoring, and summarize circumpolar status and recent variations, delineating all 55 endemic or transl ocated populations. Acknowledging uncertainties, global abundance is ca 170 000 muskoxen. Not all populations are thriving. Six populations are in decline, and as recently as the turn of the century, one of these was the largest population in the world, equaling ca 41% of today’s total abundance. Climate, disease s, and anthropogenic changes are likely the principal drivers of muskox population change and result in multiple stressors that vary temporally and spatially. Impacts to muskoxen are precipitated by habitat loss/degradation, altered vegetation and species associations, pollution, and harvest. Whi ch elements are relevant for a specific population will vary, as will their cumulative interactions. Our summaries highlight the importance of harmonizing existing data, intensifying long-term monitoring efforts including demographics and health assessments, standardizing and implementing monitoring protocols, and increasing stakeholder engagement/contributions. Abundance Circumpolar Drivers Ovibos Population status TrendspublishedVersio

Hair element profile as an indicator of wildlife population health and demographics

International audienc

Muskox Health Ecology Symposium 2016: Gathering to Share Knowledge on Umingmak in a Time of Rapid Change

The Muskox, Ovibos moschatus, also known as Umingmak ‘the Bearded One,’ is a taxonomically unique, cold-adapted, ice-age survivor. Originally native to Canada and Greenland, it has established a circum-Arctic distribution via introduced populations. As a key resident herbivore in northern ecosystems, the muskox has importance that should not be underestimated. Muskoxen play an important role in the cultural identity of Arctic Indigenous peoples and provide a healthy source of country food. More recently, recognition of the economic potential of the species through tourism, sport hunting, and the traditional sale of handicrafts has generated renewed interest in muskoxen and their ecology. Recent documentation of diseases, including several zoonoses, regional mortality events, and population declines have highlighted knowledge gaps in both our understanding of the drivers of muskox population fluctuations and the potential sensitivity of this species to a rapidly changing climate (Kutz et al., 2013, 2015; Handeland et al., 2014; Ytrehus et al., 2015; Tomaselli et al., 2016c; Afema et al., 2017)

Muskox status, recent variation, and uncertain future

Muskoxen (Ovibos moschatus) are an integral component of Arctic biodiversity. Given low genetic diversity, their ability to respond to future and rapid Arctic change is unknown, although paleontological history demonstrates adaptability within limits. We discuss status and limitations of current monitoring, and summarize circumpolar status and recent variations, delineating all 55 endemic or transl ocated populations. Acknowledging uncertainties, global abundance is ca 170 000 muskoxen. Not all populations are thriving. Six populations are in decline, and as recently as the turn of the century, one of these was the largest population in the world, equaling ca 41% of today’s total abundance. Climate, disease s, and anthropogenic changes are likely the principal drivers of muskox population change and result in multiple stressors that vary temporally and spatially. Impacts to muskoxen are precipitated by habitat loss/degradation, altered vegetation and species associations, pollution, and harvest. Whi ch elements are relevant for a specific population will vary, as will their cumulative interactions. Our summaries highlight the importance of harmonizing existing data, intensifying long-term monitoring efforts including demographics and health assessments, standardizing and implementing monitoring protocols, and increasing stakeholder engagement/contributions. Abundance Circumpolar Drivers Ovibos Population status Trend