A. Hotloś

Ag Powders Consolidated by Reciprocating Extrusion (CEC)

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.

Bulk Nanomaterials and Powders Consolidation Produced by Cyclic Extrusion Compression

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.

Processing of Copper by Equal Channel Angular Pressing (ECAP) – Microstructure Investigations

The present study attempts to apply Equal-Channel Angular Pressing (ECAP) to 99.99% pure copper. ECAP process was realized at room temperature for 4, 8 and 16 passes through route BC using a die having angle of 90°. The microstructure of the samples was investigated by means both light and transmission electron microscopy. Additionally the microhardness was measured and statistical analysis of the grains and subgrains was performed. Based on Kikuchi diffraction patterns misorientation was determined. There were some different types of bands in the microstructure after deformation. The shear bands, bands and in the submicron range the microshear bands and microbands are a characteristic feature of the microstructure of copper. Also characteristic was increasing of the number of bands with increasing of deformation and mutually crossing of the bands. The intersection of a bands and microbands leads to the formation of new grains with the large misorientation angle. The measured grain/subgrain size show, that the grain size is maintained at a similar level after each stage of deformation and is equal to d = 0.25 – 0.32 μm.

Microstructure of AgNi and AgSnBi Powders Consolidated by CEC

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.