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

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. Influência do Processamento sobre a Microestrutura e Propriedades de Revestimentos da liga CoCrMoSi por PTAResumo: O desempenho em desgaste e a tenacidade das ligas CoCrMoSi estão associados à presença de fase de Laves. Neste sentido, o teor de elementos de liga vem sendo alterado para reduzir a fragilidade em algumas ligas recentemente propostas. O presente estudo avaliou revestimentos por Plasma com Arco Transferido (PTA) para diferentes graus de interação com o substrato de aço AISI 316L. Por hipótese, uma maior diluição promoverá maior teor de ferro, cromo e níquel oriundos do substrato e, portanto, uma menor fração de fase dura de Laves. Os revestimentos foram caracterizados por microscopia ótica e eletrônica e varredura, difração de raios-X e dureza Vickers. O comportamento em desgaste foi avaliado a partir de ensaios tipo pino sobre disco e esfera sobre superfície plana. Microestrutura eutética lamelar composta por fase Laves e solução sólida em Cobalto foi observada para a deposição com corrente de 120 A (18% diluição). A composição química foi deslocada para hipoeutética, mostrando dendritas de solução sólida em Cobalto e região eutética lamelar para os revestimentos depositados com correntes de 150 e 180 A (26 e 38% diluição). A diluição aumentou com a corrente e deposição, levando à redução na dureza de 702 -526 HV 0.5 . A taxa de perda de massa em desgaste aumentou em 41.7% enquanto o coeficiente de atrito (μ) variou entre 0.45 -1.06 à medida que a composição química foi alterada.Palavras-Chave: Liga CoMoCrSi; Plasma com arco transferido; Diluição; Microestrutura; Comportamento em desgaste.

Effect of Dilution on the Microstructure and Properties of CoCrMoSi alloy Coatings Processed on High-Carbon Substrate

“…Thus, to promote distinct dilution, coatings were prepared by PTA-P as single beads with four distinct deposition currents: 120, 150, 180 and 200 A. The procedure is in agreement with previous experience and results presented in the literature for such an approach 11,13,24,[26][27][28] . Table 2 shows the main deposition parameters utilized.…”

“…6 and 7). Opposed to what has been previously observed regarding the effect of dilution with iron-base alloy substrates on the T400 alloy, in which a decrease in hardness was found [24][25][26] , the processing on highcarbon cast iron was able to maintain or even increase the high coatings hardness. From the nanoindentation tests, it can be noticed that labyrinth-like eutectics (120 and 150 A) presented a slight hardness increase from 7.1 and 7.7 GPa, respectively.…”

“…For the coatings deposited with 120 A, the microstructure indicated two different primary phases embedded in an eutectic lamellar: Laves and carbides. Bohatch et al 24 notably found a completely eutectic microstructure for CoCrMoSi (T400) coatings with 18% dilution on AISI 316L…”

“…Many studies have being carried out to improve corrosion and wear resistance selecting Ni-based alloys, [17][18][19][20] , TiC-W-Cr alloying 21 [23][24][25] , there is an evident gap concerning the effect of processing CoCrMoSi alloys coatings on Fe-C-Si alloy substrates. Hence, the aim of this investigation is to evaluate the effect of simultaneous introduction of iron, carbon and silicon (due to welding dilution) on the microstructure and properties of the Co base T400 alloy coatings processed by PTA on highcarbon content GGG40 ductile Iron.…”

Effect of Bead Overlapping on the Microstructure and Mechanical Properties of CoCrWC Alloy Coatings

“…Moreover, the hardfacing of steel substrates has been considered for their attractive properties and relatively low cost. In fact, dilution should be kept as low as possible, since higher dilution induces a decrease in hardness often associated with microstructure changes, that is, a lower fraction of strengthening carbides and lower alloying in the Co-SS 8,[11][12][13][14][15] . Halstead and Rawlings 16 have investigated the effect of iron additions on Co-based alloys microstructure, and many recent welding papers 8,12,14,15 have confirmed a larger fraction of Co-rich solid solution phase as higher dilution in the steel substrate is achieved 8 .…”