Scanning Electrical Resistivity Research Articles

Structural and soft magnetic properties of Fe 73.5Nb 3M 1Si 13.5B 9 (M=Cu, Mn, Pt)

The magnetic and the structural properties have been investigated for Fe 73.5Nb 3M 1Si 13.5B 9 (M=Cu, Mn, Pt) alloys in their as-received and heat-treated state. Differential scanning calorimeter and scanning electrical resistivity were used to study crystallization behaviour and to examine the influence of the nucleation elements Cu, Mn and Pt on the structural and magnetic properties of Fe-based nanocrystalline materials. The temperature coefficient of resistivity above Curie temperature was found to be very low (0.2×10 −4 K −1) in the Cu containing alloy as compared to the alloys which contained Mn or Pt. A broad exothermic DSC peak for the formation of Fe 3Si nanoparticles was absent when Cu was replaced by Mn or Pt. Instead, a sharp exothermic peak for the formation of Fe 3(SiB) phase was observed with an onset at 875 K. The magnetic properties of the three alloys measured after stress relaxed annealing were similar. However, after first-stage crystallization, the soft magnetic properties were further enhanced only in Cu containing alloys due to the formation of Fe 3Si nanoparticles. Such nanoparticles together with different intermetallic phases like FeMn 3 or FePt 3 were formed in Mn or Pt containing alloys. Moreover, the NbFeSi phase was also formed in the latter alloys after higher temperature annealing which reduced not only the amount of the Fe 3Si phase but also the grain refining effect due to the lesser amount of Nb available at the grain boundary. When Cu was replaced by Mn or Pt, the formation of different intermetallics reduced the volume fraction of Fe 3Si nanoparticles and the lesser amount of grain refining Nb made the materials magnetically inferior after annealing above 775 K.

A scanning electrical resistivity (SER) study of phase transformations in an Al-Cu alloy

Abstract The scanning electrical resistivity (SER) technique has been used as a method of investigating the phase transformations in an Al-Cu alloy during the formation and subsequent dissolution of fully coherent and/or semicoherent phases, resulting from an annealing at 190°C after solution treatment and quench. The dissolution of a structure of coherent precipitates produces an SER trace where the contribution to the resistivity of the Al matrix of the solute Cu atoms alone is not sufficient to explain the resistivity trend. The theory of Hillel-Edwards-Wilkes (HEW) is invoked to take into account the contribution of precipitated particles to the resistivity in terms of direct scattering of the conduction electron. Good agreement with experimental data is obtained. The SER results are compared with DSC traces, and it is shown that the two techniques are able to supply complementary information during the dissolution phenomena when coherent particles are involved. The results obtained suggest that the p...