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Electrically exploding wire can be manipulated to produce nanometer-sized metal powder. Evolutionary characteristics directly affect the size of the grains formed in this process. Nanosecond laser pulses are adopted in this study to acquire photos of the explosion, wherein the explosive area has distinct margin lines within an interference fringe background. The lines are easily abstracted by recognizing disturbed sections of the stripes. The three-dimensional distribution of the metal powder at the measuring moment is determined according to the transmittance by which the laser beam penetrates the metal mist. Experimental results show that the diameter of metal wires expands from 0.3 mm to 4.7 mm 0.5 us after electrification, and expands to 28 mm by 18 us. The maximum concentration of particles decreases from 3×1021/cm3 to 1.1×1020/cm3. Throughout the expansion process, the particle concentration distribution presents multiple ring belts along the radial direction.

In some studies, the metal materials with different magnetic permeability and same chemical composition need to be prepared to avoid the interference caused by different compositions and make the parameter of magnetic permeability become the key variable directly. In order to prepare the metal materials with different magnetic and same component, the paper has considered other two commonly schemes, such as the casting method by adding some ferromagnetic elements and the heat-treatment process to increase its phase content of martensite or ferrite. Finally, it has been found that the cold working process was preferable if the austenitic stainless steel 1Cr18Ni9Ti with paramagnetic was selected as a raw material, because it got better control in forging ratio. The method of magnetic balance has been used to measure the relative magnetic permeability of every specimen with different hardness HB 165 (A), HRC 20 (B), HRC 25 (C) and HRC 30 (D). The metallurgical microscope, XRD, TEM and SEM has been put to use to analyse their microstructure before and after forging. The results show, the cold working process improved magnetic properties of 1Cr18Ni9Ti continuously and largely within limits by controlling different forging rate, as well as the process was not complicated. The relative rate of magnetic permeability for 1Cr18Ni9Ti and W18Cr4V (high-speed steel) could be up to 1:2.435 at 0.03 T. The 20.1 % maximum reduction of the austenite phase should be a main reason to improving magnetic permeability of 1Cr18Ni9Ti. The real magneto-crystalline anisotropy should be due to martensite or ferrite phases with strong magnetic property. The 1Cr18Ni9Ti after cold working still maintained high corrosion resistance. Furthermore, this process method was also applicable to other austenitic steels with paramagnetic and strong cold work hardening characteristics.DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9696

The paper introduces the current research on Magnetic-environment Dry Tribology (MDT), and proposes the necessity to study further on the coupled relations between permeability of material and MDT. The specimens with different permeability and same chemical composition were prepared by forging. The influence of permeability on dry sliding friction and wear property under DC magnetic field is studied. The results show the magnetic field can reduce friction and wear, and promote oxidation with major oxides Fe 2 O 3 and Fe 3 O 4 . The higher the permeability is, the better the wear resistance and the antifriction property are.