Papers by Author: Jan Richert

Abstract: The Cyclic Extrusion – Compression - reciprocating extrusion process (CEC) is one of severe plastic deformation methods (SPD), which allow to produce bulk nanomaterials without changing the initial shape of deformed samples. The results are presented showing that the average grains size and microbands thickness in aluminium alloys decrease below 100 nm. The investigations revealed that the average grains size is about 250 nm and 200 nm in polycrystalline and monocrystalline copper, respectively.The Cyclic Extrusion Compression method is also used to produce bulk materials by powder consolidation. The subgrains/nanograins inside the silver powder particles after the consolidation processes achieved the mean size of about 100 nm. Moreover, it has been found that inside structure observed by TEM, the consolidated powder granules consisted from nanometric twins of about 10 – 20 nm. This silver based powder consolidated by CEC method were extruded by hydrostatic extrusion method. The final product were the wires with a diameter of 3 mm, which were used to electrical contacts production.

Abstract: Powder metallurgy is widely used to the production of AgNi and AgSnBi powders employed for electrical contacts. In the work AgNi and AgSnBi powders were consolidated by the cyclic extrusion compression (CEC) method enabling cyclic unlimited deformation. In the initial stage the AgNi powder contained the two phases Ag and Ni, recognized by the EDX technique using scanning electron microscopy (SEM). The investigations shown that the Ni phase is distributed in the form of small granules around larger Ag granules. In the AgSnBi powder phases Ag + Bi + Ag3Sn (ξ) were distributed uniformly. It was found that after the CEC consolidation phases were excellently joined without cavities and cracks. Detailed observations of microstructure have been performed by the transmission electron microscopy (TEM) and revealed inside the consolidated granules nanometric grains with the nanometric twins inside.

Abstract: CEC has unique characteristic. These are applicability of very large strain and deformation under high hydrostatic pressure. Due to these abilities of CEC, several unique phenomena have been observed. One of them is the possibility of consolidation of metallic powders in room temperature to the form of bulk material. In the present paper the consolidation of AgSnBi and AgNi to bulk composites was presented. Applying the deformation of  = 0.42 in the single cycle of CEC, under high hydrostatic pressure, the samples without pores and discontinuities were fabricated. The microstructure observations were performed by optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). They show refinement of microstructure at all levels of observation. The nanometric-size subgrains/grains were found inside consolidated granules. The microhardness level of AgSnBi in average achieved level 110 μHV100, and AgNi of about 90 μHV100. The AgSnBi samples consolidated by CEC and additional hydrostatically extruded to wires with 3 mm in diameter average showed 500 MPa yield point.

Abstract: In the work the distribution of stresses and strains as well as temperature field within the welding chamber of the porthole die were determined. The analysis was performed by the use of the computer program DEFORM based on a finite element method. The direct hot extrusion of 2024 aluminum alloy was investigated with the use of the porthole dies of different geometry. Particularly, a different height of the welding chamber was adopted in calculations. The calculations allowed determining both pressure and temperature levels and their distributions within the welding chamber leading to the best welding conditions for the alloy tested.