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Analysis of microstructural changes with temperature of thermally sprayed WC-Co coatings by mechanical spectroscopy
Internal friction and mechanical spectroscopy : Selected, peer reviewed papers from the 16th International Conference on Internal Friction and Mechanical Spectroscopy (ICIFMS-16), July 3-8, 2011, Lausanne, Switzerland
Durnten-Zurich: Trans Tech Publications, 2012 (Solid state phenomena 184)
|International Conference on Internal Friction and Mechanical Spectroscopy (ICIFMS) <16, 2011, Lausanne>|
| Conference Paper|
|Fraunhofer IWS ()|
| cobalt; hardmetal; hardmetal coating; HVOF; tungsten carbide; W 6Co 6C; W 3Co 3C|
Thermally sprayed hardmetal coatings can be used to improve the wear or fatigue resistance of mechanical parts. Depending on the deposition conditions, their microstructure and phase composition are out of equilibrium at different levels due to the extreme heating/cooling rates. In the present study, the changes that occur with temperature variation are monitored by mechanical spectroscopy. Requirements to specimen of mechanical spectroscopy created the need to prepare WC-17%Co coatings of 1.2 mm thickness by high velocity oxy-fuel (HVOF) spraying. The coatings, separated from the substrate by spark erosion, were tested in a forced torsion pendulum between room temperature and 1570 K at a temperature scanning rate of 1K/min. The mechanical loss spectrum shows different features. At 800 K, a maximum M1 is observed in coincidence with a sudden increase of the elastic modulus. The change of the elastic modulus is due to a densification of the material possibly related to cobaltrecrystallization. A relaxation peak located at about 1100 K is typically found in WC-Co hardmetals. It is attributed to the movement of dislocations in the cobalt phase. A sharp peak is observed at 1510 K on heating and at 1410 K on cooling. Such peak is due to the reversible transition from W 3Co 3C at high temperature to W 6Co 6C at low temperature as proven by X-ray diffraction. The reversibility of such transformation was observed for the first time.