Magnetic properties of tungsten composites
Janusz J. Bucki, Elżbieta Fortuna-Zaleśna, Maciej Kowalczyk, Zbigniew Ludyński
Quarterly No. 3, 2011 pages 268-273
DOI:
keywords: tungsten composites, tungsten heavy alloys, magnetic properties, microstructure
abstract The magnetic properties of three grades of tungsten composites (heavy alloys): W90.3Ni7Fe1.7Co1, W90Ni4Fe2Mo4 and W93Ni5Cu2 were examined. The dependence between the magnetic field and magnetic induction (hysteresis loop) was measured at room temperature. To determine the Curie temperature, the measurements of magnetic induction versus temperature were carried out (in temperature range 180÷700 K). In order to completely describe the materials, microstructural characterization of the composites was performed in terms of the size and volume fraction of tungsten particles and the chemical composition of the matrix. In the case of the W-Ni-Cu composite no hysteresis loop was registered. The dependency between the magnetic field and magnetization was linear. Moreover the measured (mass)magnetizations was at a constant, extremely low level of 0.0006 emu/g in the examined range of temperatures (180÷700 K). The results obtained for this grade confirmed that the material in the whole temperature range was in a paramagnetic state. The results obtained for two other grades: W90.3Ni7Fe1.7Co1 and W90Ni4Fe2Mo4 showed that they were slightly magnetic. In the case of these materials, the magnetization measured for the field 27000 A/m was at the relatively low level of 700 Gs. Both materials were difficult to saturate. The character of the hysteresis loops prove that at room temperature, the materials are close to ferro/paramagnetic transition. The Curie temperature is approached from the ferromagnetic side, which is confirmed by the plots of magnetization versus temperature. The Curie temperatures for these grades were estimated as 320 and 460 K, respectively. The results confirmed that the composite with a copper addition is a paramagnetic material whereas the two other grades are partially magnetic.