2. Experimental
2.1. Materials
The alloy chosen for the experiments was Pt–Rh8 added with
boron. In order to obtain a powder with a very small grain size, special
mixtures of metals and metal oxides were prepared, which contained
platinum-group minerals (PGM) and additives. The powder of the Pt–
Rh8 alloy had a mean grain diameter of 100 nm with above 90% of the
grain diameters falling within the range from 50 to 200 nm.
2.2. Methods
The powder was consolidated by isostatic pressing in a caoutchouc
mould at room temperature and a pressure of 2500 bar. The samples
thus obtained were 12 mm in diameter and 300 mm long. They were
subjected to annealing at 1200 °C for 8 h. After the annealing the
samples were subjected to multi-stage extrusion (drawing) with
inter-stage annealing. The final products of this combined thermoplastic treatment were wires with a diameter of 0.08 mm. Fig. 1 shows
the schematic representation of the proposed technological process.
At the consecutive stages of the extrusion, the microstructure and
mechanical properties, such as the microhardness and tensile
strength, of the wires were examined. The microstructure of the
samples was analyzed on transversal and longitudinal cross-sections
of the wires using transmission electron microscopy (TEM). The TEM
samples were prepared using the Focus Ion Beam system. The grain
size and porosity of the samples were determined based on the TEM
photographs.