Mingard, K P; Roebuck, B (2009) Electrical and magnetic measurements of hardmetals with Ni binder phase. NPL Report. MAT 33

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Abstract

Methods of measuring resistivity and magnetic properties on a small scale in hardmetals have been assessed, with particular attention to measurements of hardmetals with Ni binders where conventional magnetic property measurement gives little or no information.

Miniaturised four-point probe can be used to give measurements of resistivity of hardmetal components which do not have a conventional rod or bar geometry. Absolute values can only be obtained by this means from thick samples away from edges, but comparative measurements can be made on any component if the geometry of the probe and component are kept constant. A reference sample should be used to detect drift in values whether absolute or comparative measurements are being made.

Resistivity has been found to correlate well with coercivity in conventional Co binder hardmetals. In Ni binder hardmetals resistivity would appear to discriminate well between samples produced under different conditions where magnetic measurements are not possible. However it has not yet been established what differences in microstructure are being discriminated by these measurements.

As an alternative to the four-point probe, a small eddy current probe has been shown to be capable of measuring differences between hardmetal samples, with very good correlation between the probe inductance and magnetic moment for Co binder hardmetals. With Ni binder materials the eddy current probe output gives information which is complementary to resistivity data and appears to distinguish between materials with different binder phase grain size and WC grain size, but further work is needed on more samples to understand this information fully.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	MAT 33
Keywords:	hardmetal, resistivity, magnetic moment, eddy current, magnetic saturation, binder phase
Subjects:	Advanced Materials Advanced Materials > Powder Route Materials
Last Modified:	02 Feb 2018 13:15
URI:	http://eprintspublications.npl.co.uk/id/eprint/4495

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