Influence of Processing on the Microstructure and Properties of CoCrMoSi Alloy PTA Coatings

Influência do Processamento sobre a Microestrutura e Propriedades de Revestimentos da liga CoCrMoSi por PTA

Abstract

Wear performance as well as the low toughness of CoCrMoSi alloys is associated with the presence of Laves phase. In light of this, alloying elements have been altered in order to reduce the brittleness of newly-cast alloys. This study evaluated coatings by Plasma Transferred Arc (PTA) with different interactions with the AISI 316L substrate. The higher the dilution, it was hypothesized, the higher Iron, Chromium and Nickel contents proceeding from substrate and, therefore, the lower hard Laves phase fraction. Coatings were characterized by light and scanning electron microscopy, X-ray diffraction and Vickers hardness. Wear behavior was assessed by pin-on-disc and ball-on-flat tests. Laves phase and Cobalt solid solution eutectic lamellar microstructure was observed for coating processed with 120A (18% dilution). The chemical composition was displaced to hypoeutectic, showing Cobalt solid solution dendrites and interdendrictic eutectic lamellar for the coatings processed with higher current intensity (150 / 180A), due to the higher interaction with the substrate (26 / 38% dilution). Dilution increased with the deposition current, causing hardness to decrease from 702 – 526 HV_0.5. Wear mass loss rate increased by up to 41.7% and friction coefficient (μ) ranged from 0.45 – 1.06 as the chemical composition changed.

Key-words: CoMoCrSi alloy; Plasma transferred arc; Dilution; Microstructure; Wear behavior