Microstructural Analysis of Intermetallic Ni5Al3 Thin Films

The possible magnetic transition phenomenon obtained is postulated particularly on the Nickel Aluminum (Ni5Al3) thin films of different thickness. It was found that the film resistance exhibits a linear but mild increase over the initial temperature range, followed by a transition to a relatively rapid decline in the resistance after attaining maximum at ~170ºC. This positive temperature coefficient of resistance (TCR) makes this material suitable for magneto resistor applications. The same observations were made on two different sputtering systems with different deposition conditions, indicating that the magnetic transition is a highly reproducible phenomenon

Superplasticity of a nano-grained Mg-Gd-Y-Zr alloy processed by high-pressure torsion

While most of the reports on Mg-Gd-Y-Zr alloys report superplasticity after extrusion or friction stir processing, it is important to investigate superplasticity in these alloys after other severe plastic deformation processes having greater grain refinement capability. Accordingly, superplasticity was studied in an Mg–9Gd–4Y–0.4Zr (GW94) alloy after different high-pressure torsion (HPT) conditions. The HPT was performed at room temperature under an applied pressure of 6.0 GPa for up to 16 turns. TEM microstructural characterization revealed that the grain size was reduced from an initial value of ?8.6 ?m in the extruded condition to ?95±10 and ?85±10 nm after 8 and 16 turns, respectively. A shear punch testing method was used for evaluation of superplasticity at 573, 623, 673 and 723 K. Maximum strain rate sensitivities of ?0.51±0.05 and ?0.48±0.05 were obtained at 623 K for the material processed through 16 and 8 turns, respectively. This strain rate sensitivity and an activation energy of ?100±5 kJ mol–1 suggests the occurrence of grain boundary sliding in the superplastic regio

NANOSTRUCTURAL STUDIES OF SPUTTER-DEPOSITED NixAl1-x (0.5 ≤ x ≤ 1.0) ALLOY THIN FILMS

The nanostructural characteristics of direct-current magnetron sputter-deposited NixAl1-x (0.5 ≤ x ≤ 1.0) alloy films were studied during in situ isothermal annealing in a transmission electron microscope. An expansion of the lattice by nearly 5% was observed for the Ni0.5Al0.5 and the Ni0.8Al0.2 films in their low-thickness and as-deposited state. The lattice size approaches the bulk value when the film thickness increases or after vacuum annealing heat-treatment. The Ni0.8Al0.2 films have a nanocrystalline structure in which the ordered L12 phase appears upon annealing at above 500°C. The ordered B2 phase for Ni0.5Al0.5 and Ni5Al3 phase with orthorhombic structure for Ni0.65Al0.35 were found

Probabilistic nature of the nucleation of dislocations in an applied stress field

The nucleation of dislocations under applied stress exhibits significant statistical scatter, as well as time and size dependence. In this work, a general probabilistic theory is proposed to explain these. The predicted survival probability under nanoindentation loading is found to be in excellent agreement with experimental results in Ni3Al

Microstructural Analysis of Intermetallic Ni5Al3 Thin Films

Abstract

Microstructural evolution during hot shear deformation of an extruded fine-grained Mg–Gd–Y–Zr alloy

Mg–Gd–Y–Zr alloys are among recently developed Mg alloys having superior mechanical properties at elevated temperatures. Dynamic recrystallization (DRX) and rare earth (RE)-rich particles play important roles in enhancing the high temperature strength of these alloys. Accordingly, the microstructural evolution of a fine grained extruded Mg–5Gd–4Y–0.4Zr alloy was investigated after hot shear deformation in the temperature range of 350–450 °C using the shear punch testing (SPT) method. The results reveal the occurrence of partial dynamic recrystallization at the grain boundaries at 350 °C while the fraction of DRX grains increases with increasing deformation temperature. A fully-recrystallized microstructure was achieved after SPT at 450 °C. The Gd-rich and Y-rich cuboid particles, having typical sizes in the range of ~50 nm to ~3 m, show excellent stability and compatibility after hot shear deformation and these particles enhance the high temperature strength during hot deformation at elevated temperatures. The textural evolution, examined using electron backscattered diffraction (EBSD), revealed a non-fibrous basal DRX texture after SPT which is different from the conventional deformation texture