Influence of aluminium on the microstructure of Co based alloy coatings

Abstract

Coating contamination as a consequence of the diffusion of elements from the operating environment, accounts for the deterioration of a variety of mechanical components, and is particularly severe on those that operate at elevated temperatures. This study analysed the degradation of three Co based alloy coatings as a consequence of their contamination with Al. One Co–Cr–W and two Co–Cr–Mo–Si atomised alloy coatings, each with and without 5 wt-% aluminium powder, were deposited by plasma transferred arc on AISI 316L stainless steel plates. Accelerated aging at 600 and 1000°C contributed to the understanding of the effect of Al on the microstructure of coatings. Coatings with and without Al were characterised by laser confocal microscopy and microhardness. Dilution increased on coatings modified with Al due to the exothermic synthesis of aluminide compounds and the most significant microstructure modification was observed in the Co–Cr–Mo–Si coatings as primary Laves phase was almost suppressed. Accelerated aging tests showed that aluminium had a deleterious effect on the three Co based coatings although it was more pronounced in those processed with the Co–Cr–W alloy.

Keywords:

• Cobalt based coatings
• Plasma transferred arc hardfacing
• Accelerated aging

Thanks are due to CNPq (304070/2008-4) and FINEP/PROMOVE: ‘Engenharia de Superficies’ for the funding of this research. Special thanks are also due to Arotec and Ms Patricia Santos Biasotto from Olympus Latin America for helpful contributions with the confocal analysis.