Plastic deformation localization study of metal-intermetallic layered composites under dynamic channel-angular pressing

The method of mathematical modeling has been used to study the processes of plastic deformation localization of layered metal-intermetallic composites under dynamic channel-angular pressing. The deformation patterns of single-phase intermetallic samples and layered composites samples with the different arrangement of layers relative to the compression axis have been compared. The calculated stress-strain curves have been obtained. Three-dimensional modeling has been carried out on the basis of an approach combining two methods for the plastic flow description through the kinetics of deformation defects storage and the solid state mechanics. The numerical solution of the model equations has been carried out by the finite element method.

Durability of Mo-Ni Intermetallic Compounds in the Hydrogen Evolution Reaction

Molybdenum-nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). This contribution investigates the potential influence of ordered crystal structures on the catalytic activity. Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel, whether crystallographic ordering affects the activity. Due to their intrinsic instability, molybdenum is leached resulting in higher specific surface areas and nickel-rich surfaces. The gain in surface area scales with the applied potential and the molybdenum content of the pristine samples. The nickel-enriched surfaces are more prone to form Ni(OH)2 layers, which leads to deactivation of the Mo-Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. The earlier as durable identified Ni7Mo7 proves to be highly unstable in the applied ADTs. The results indicate that the enhanced activity of unsupported bulk Mo-Ni electrodes can solely be ascribed to increased specific surface areas.

Durability of Mo-Ni Intermetallic Compounds in the Hydrogen Evolution Reaction

Molybdenum-nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). This contribution investigates the potential influence of ordered crystal structures on the catalytic activity. Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel, whether crystallographic ordering affects the activity. Due to their intrinsic instability, molybdenum is leached resulting in higher specific surface areas and nickel-rich surfaces. The gain in surface area scales with the applied potential and the molybdenum content of the pristine samples. The nickel-enriched surfaces are more prone to form Ni(OH)2 layers, which leads to deactivation of the Mo-Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. The earlier as durable identified Ni7Mo7 proves to be highly unstable in the applied ADTs. The results indicate that the enhanced activity of unsupported bulk Mo-Ni electrodes can solely be ascribed to increased specific surface areas.

Mechanical Properties of Rapidly Solidified Ni3Ge and Ni5Ge3 Intermetallic Compounds

The congruently melting, single phase, intermetallic compounds β-Ni3Ge and ε-Ni5Ge3 were produced by arc melt. Each was subject to rapid solidification via drop-tube processing. Each compound remained fully single phase (either β-Ni3Ge or ε-Ni5Ge3) irrespective of the imposed cooling rate. In the investigation of β-Ni3Ge compound, droplets spanning the size range ≥850 to ≤38 μm diameter particles, with corresponding cooling rates of <700 to >54500 K s−1, were subject to microstructural investigation using SEM. Six dominant solidification morphologies were identified with increasing cooling rate, namely; (i) spherulites, (ii) mixed spherulites and dendrites, (iii) dendrites-orthogonal, (iv) dendrites-non-orthogonal, (v) recrystallized, and (vi) dendritic seaweed, are observed imbedded within a featureless matrix. For the ε-Ni5Ge3 compound, four dominant solidification morphologies were observed, namely; (i) partial plate and lath, (ii) plate and lath microstructure (iii) isolated hexagonal crystallites, and (iv) single crystal imbedded within a featureless matrix. Micro-Vickers hardness test result of both compounds showed a complex dependence of micro hardness upon cooling rate. At 700 K s−1 the hardness was significantly lower in both compounds than the reported equilibrium value, although in both cases this subsequently increased with further increases in cooling rate. Moreover, in both cases, microstructural transition, such as change in growth direction, led to abrupt drops in hardness. The micro-Vickers hardness results confirmed that the ε-Ni5Ge3 is significantly harder (maximum 1021 Hv0.01) than the β-Ni3Ge compound (maximum 526 Hv0.01).