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Creep Characteristics of Tungsten Wires

Published online by Cambridge University Press:  25 February 2011

Wego Wang
Wego Wang*
Affiliation:
U.S. Army Research Laboratory, Materials Directorate, Watertown, MA 02172-0001
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Abstract

In this study heavily-drawn tungsten wires were tested for creep at a constant load of 115 MPa in a 10-3 torr nitrogen atmosphere. These fine wires had an elongated rectangular grain morphology with small average grain sizes, 1.6 to 2.2 µm. The typical test sample wire was about 2.54 m long and 130 µm in diameter. The test wire was heated to the test temperature by self-resistance. The creep elongation was monitored by a transducer. Steady state creep rates were determined from the creep curves for four specimens that were tested at 1673, 1553, 1453, and 1273K, respectively. Diffusional creep is the predominant deformation mode. The experimental data were analyzed and compared with several creep theories: Ashby's combined, Coble's grain boundary and Nabarro's lattice diffusional creep models. The effects of recrystallization, grain aspect ratio, grain growth, impurity contents, nitrification and oxygen contamination on creep behavior are discussed in detail. However, their influences on creep kinetics are minimized in this study by carefully controlled experimental conditions. At a stress of 115 MPa, the grain boundary diffusional creep model successfully predicts the creep behavior at temperatures below 1453K. The instantaneous creep rate is inversely proportional to the cube of grain size at 1453K. The lattice diffusional creep model becomes predominant when the test temperature rises to 1553K. It is concluded that the creep behavior is controlled by grain boundary diffusion at a temperature below 1453K, and lattice diffusion above this temperature. Diffusion controlled creep and grain boundary sliding with diffusional accommodation are coupled in tungsten wires.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 322: Symposium F – High-Temperature Silicides and Refractory Alloys , 1993 , 547
Copyright
Copyright © Materials Research Society 1994

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