Some papers from scripta

September 10, 2010

[1] Single-Phase Interdiffusion in Ni3Al–Mo Ternary System

H Wei et al

Interdiffusion behavior of Ni3Al-Mo ternary system at 1423, 1473 and 1523 K were studied using Ni3Al/Ni3Al-Mo single-phase diffusion couples. The concentration dependent interdiffusion coefficients were calculated over whole diffusion range, and average ternary interdiffusion coefficients were carefully determined in the middle of the diffusion zone. These ternary coefficients were also examined to estimate tracer diffusion coefficients of Mo in Ni3Al phase. Furthermore, the results were utilized to explain the diffusion behavior of Mo in Ni3Al-based superalloys IC-6.

[2] Stabilizing force on perturbed grain boundaries using dislocation model

X Zhu and Y Xiang

In this paper, we study the glide force due to stress on the constituent dislocations of slightly perturbed symmetric low angle tilt boundaries. We show that the stabilizing force comes from both the long-range interaction of the constituent dislocations and their local line tension effect. We also present a continuum model for such glide force. The obtained results and continuum model provide a basis for further understanding of the stress-driven migration of distorted grain boundaries.

[3] Stress Driven Grain Growth in Nanocrystalline Pt Thin Films

J A Sharon et al

Micro-tensile experiments and electron microscopy have been utilized to characterize the mechanical behavior of nanocrystalline Pt films. The behavior can be described as high strength with limited strain to failure. The tensile deformation triggers a microstructural evolution increasing the grain size from 20nm in the initial state to 33nm in the deformed state. This observation of grain growth at a homologous temperature of 0.146 provides further evidence of the role of mechanical stress in initiating grain growth in nanocrystalline metals.

[4] Morphological evolution of the interface microstructure in the presence of bubbles during directional solidification

H Xing et al

The evolution of morphology during directional solidification is investigated in terms of the interaction between bubbles and the solid–liquid interface. The results reveal that the solid phase grows along the bubble boundary to form solid envelopes and a liquid gap. As the interface velocity increases, the expansion coefficients of bubbles increase continually, and then decrease. The solidification microstructures of bubbles transform in the sequence water-drop→elongated→irregular with increasing interface velocity.

[5] Direct observations of silver nanoink sintering and eutectic remelt reaction with copper

J W Elmer and E D Specht

Ag nanoink sintering kinetics and subsequent melting is studied using in situ synchrotron-based X-ray diffraction. Direct observations of Ag nanoink sintering on Cu demonstrate its potential for materials joining since the Ag nanoink sinters at low temperatures but melts at high-temperatures. Results show low expansion coefficient of sintered Ag, nonlinear expansion as Ag densifies and interdiffuses with Cu above 500 °C, remelting consistent with bulk Ag, and eutectic reaction with Cu. The results demonstrate the usefulness of Ag nanoink as a high-temperature bonding medium.

[6] Deviation of the magnetization change from the structural phase transition temperature in polycrystalline Ni–Mn–Sn in low magnetic fields

P J Shamberger et al

Magnetization and resistivity were measured as a function of temperature in polycrystalline Ni–Mn–Sn Heusler alloys with a magnetocrystalline first order phase transition. At external magnetic fields <0.2 T the magnetization change associated with the phase transition happened at a temperature up to not, vert, similar5 K lower than the true phase transition temperature measured by electrical resistivity or predicted by thermodynamic theory. We associate this anomaly with magnetic exchange coupling between austenite and martensite phases coexisting near the transition.

[7] On the retardation of grain boundary motion by small particles

G Gottstein and L S Shvindlerman

The drag effect by second-phase particles on grain boundary motion is considered with regard to the triple line particle–grain boundary that is formed during the interaction between a particle and a grain boundary. A quantitative analysis of this effect has become possible due to recent measurements of the triple line energy. In the limit of large particles (dp > 50 nm) the particle is wet by the boundary (Zener approximation) whereas smaller particles are repelled by the grain boundary.

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