The gage characteristics such as the strain gage factor
Gf, the electrical resistivity ρ, the temperature coefficient
Cf and the thermo-electromotive force relative to copper
Emf were investigated for Fe-15%Cr-5-40%Co+0-7%W and Fe-15%Cr-5-40%Co+0-7%Mo alloys cold-drawn by 30-99% reduction in cross-sectional area.
Fe-Cr-Co-W and Fe-Cr-Co-Mo alloys are scarcely varied in
Gf with the reduction in area. The values decrease with increasing Co content in the former quarternary alloys as previously reported for Fe-Cr-Co ternary alloys and show a maximum at 20%Co in the latter alloys. At more than 25%Co, the values of
Gf in these quarternary alloys range from 4.0 to 4.1 and is slightly larger than those of the Fe-Cr-Co ternary alloys. On the other hand, the dependence of
Gf on the W or Mo content becomes smaller with increasing Co content. Compared with other gage characteristics, the dependence of ρ,
Cf and
Emf on W content in the Fe-Cr-Co-W alloys and that of
Cf on Mo content in the Fe-Cr-Co-Mo alloys are small as is the case with
Gf. From the measurement of electrical resistivity at elevated temperatures up to 1273 K and X-ray diffraction analysis, it is clear that the micro-structures of both quarternary alloys in the cold-worked state consist of an α′ phase caused by the strain-induced transformation.
Fe-14.3%Cr-28.6%Co-4.8%W and Fe-14.7%Cr-29.4%Co-2.0%Mo alloys cold-drawn by 98% reduction in area show the following values: In the case of the former alloy,
Gf=4.1, ρ=0.93 μΩ·m,
Cf=7.8×10
−4 K
−1 and
Emf=+0.6 μV·K
−1; in the latter alloy,
Gf=4.1, ρ=0.86 μΩ·m,
Cf=4.0×10
−4 K
−1 and
Emf=+0.3 μV·K
−1. Despite a rather poor workability of cold-rolling, it is relatively easy for these alloys to be cold-drawn into fine wires. Therefore, the alloys can be used as strain gage elements in load cells and micro-strain sensors, etc.
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