Selective cobalt etching from WC–Co composite usually carry out prior diamond deposition was investigated. Diluted Caro’s acid as primarily utilized etching reagent was used. The cobalt and tungsten dissolution from hardmetals (HM) were determined as a function of time and a comparison were done in case of different grade hardmetals. For comparison beside the hardmetals the pure metallic cobalt and binderless, plasma sprayed tungsten carbide dissolution also has been tested. Hot filament chemical vapor deposition (HFCVD) technic was used to investigate the diamond nucleation on the differently pre-treated samples. The investigation highlighted for that: a) the selective cobalt etching can due to the different rate of dissolution of the two components, however the dissolution of the WC was not zero, b) the dissolution rate governed by the composite substance structure by the pore size which has formed during the selective dissolution process, therefore the dissolution rate of both components was found to be influenced by the grain size of WC and the cobalt content of the hardmetal. c) The removed cobalt quantity from the hardmetal surface has strong effect on the diamond nucleation during HFCVD method. Based on this research a better understanding of the mechanism of the pre-treatment and a chance for optimizing the selective cobalt etching from hardmetals prior diamond deposition will be achieved.

The behaviour of TiB2 coated steel in Sn-Ag–Cu based solder melt was investigated. The samples were subjected to immersion tests in static solder melt for 40 days at 593 K. The reactions at the solder/native oxide layer covered TiB2/substrate and solder/oxide layer-free TiB2/substrate interfaces were investigated with X-ray diffraction, secondary neutral mass spectrometry, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. The thermodynamic background of possible reactions is also presented. It was found that neither oxide covered, nor oxide layer-free TiB2 showed any observable reaction with the Sn-Ag–Cu solder melt.

The cobalt depleted layer of WC–Co composite materials was investigated after selective cobalt etching in diluted Caro’s acid. The time dependence of Co etching and the thickness of the etched layer was determined by using Glow Discharge Optical Emission Spectrometer (GD-OES) depth profiling as well as by calculation method based on determination of the dissolved Co by Atomic Absorption Spectrophotometric (AAS) measurement. The integrity of the modified outermost layer of the WC–Co composite materials were qualified using Rockwell C indentation test. This test methods were found usable for optimisation of the pre-treatment applied before the diamond thin film deposition.

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