Mechanical and tribological properties of compacts obtained by pulse pressing from a mixture of iron micropowder and molybdenum nanopowder

Experimental data on the structure, hardness and wear resistance of compacts obtained from mixtures of reduced iron micropowder Fe (average particle size 2–8 μm) and molybdenum nanopowder Mo (average particle size 20–25 nm) are presented. Such materials are used in many promising areas of applica-tion, including the manufacture of parts and structural elements in brake systems, in micromachine units and micromechanisms. Two powder compositions were studied – Fe + 10 % Mo and Fe + 15 % Mo. The mass fraction of molybdenum in these mixtures was 10 % and 15 % of the total mass. Pulse pressing was carried out using a modified Kolsky technique convenient for practical application and research into the mechanics of the dynamic compaction process of powder materials. This scheme allows obtaining high-quality compacts with a uniform structure and high density. The kinematic parameters – the amplitude and duration of the pressure pulses – were within 1000–2000 MPa and 100–400 μs, respectively. The optimal compaction modes were experimentally established and high-quality compacts with a relative density of 85 % for the mixture (Fe + 10 % Mo) and 89 % for (Fe + 15 % Mo) were obtained. Metallographic studies were carried out on a TESCAN VEGA II electron microscope. It was found that the obtained compacts have a fairly uniform fine-grained structure. The over-all pore distribution pattern is fairly uniform, the observed pore shapes are diverse and mostly close to spherical. X-ray spectral microanalysis was carried out on an INCA Energy 250 energy-dispersive spec-trometer in the scanning mode along the surface line of the obtained compacts. It is shown that dynamic pressing does not lead to a noticeable change in the distribution of Fe, Mo and O elements over the volume of the samples. The microhardness of the compacts was measured with a standard PMT-3 hardness tester. The density of the compacts was determined by measuring their mass and volume. The volume was calcu-lated by hydrostatic weighing. The initial mass of the compacts and the mass loss of the samples due to wear were determined by weighing them on an Ohaus Explorer EX124 analytical balance with an accuracy of 0.1 mg. The results showed that with an increase in the mass fraction of Mo, the density of the iron-based material increases, and the hardness shows a tendency to increase. The wear resistance of the compacts was tested in the dry friction mode according to the “rotating disk – stationary sample” scheme. The dependen-ces of the mass loss of the compacts on the test time are presented. It was experimentally established that the maximum wear resistance is observed in Fe + 15 % Mo compacts.