Corrosion Behaviour of Cemented Carbides with Co- and Ni-Alloy Binders in the Presence of Abrasion

Abstract

More and more often, cemented carbides are employed for the production of wear resistant components and have to face highly demanding service conditions that combine different damage mechanisms. A key example is the range of tetraphasic (sea water, sand, liquid and gaseous hydrocarbons) flows encountered in the Oil and Gas extraction industry. Notwithstanding the importance of operating regimes of this type, the availability of fundamental and quantitative information on the corrosion performance of cemented carbides in the presence of abrasion is still limited. In this paper, we report a systematic study of the corrosion behaviour of cemented tungsten carbide grades with binders containing different amounts of cobalt (Co), nickel (Ni), chromium (Cr) and noble metal additions, subjected to controlled mechanical abrasion, impacting the stability and nature of pseudopassivation films. In this work, special attention is devoted to Cr, a classical of additive that inhibits the Ostwald ripening of tungsten carbide (WC) particles and notably improves the corrosion resistance of grades with ultrafine-to-fine WC grain size and low-to-medium binder content. We assessed the impact of binder composition on the anodic behaviour by means of linear-sweep voltammetry and chronopotentiometry as well as on the mechanical properties. The application of controlled abrasion conditions under electrochemical control is carried out with an in-house modified ASTM B611 apparatus, equipped with a three-electrode system, enabling the systematic investigation of the synergy of electrochemical and mechanical damaging conditions. Increased corrosion resistance in environments without and with added chloride—both in the absence and in the presence of abrasion—was observed in all the Co- and Ni-based grades to which growing quantities of Cr were added. Moreover, doping with ruthenium (Ru) further enhances corrosion resistance. Regarding corrosion in the presence of abrasion, the addition of Cr and Ru increases the ability of regenerating the pseudopassivation film. The optimized compositions of the binder have been highlighted that open up attractive opportunities of improved service behaviour and deployment in new applications.

In-Depth Understanding of Hardmetal Corrosion Performance Reveals a Path to the Electrochemical Demolition of Scrap

“…Firstly, the Co-rich HMs (Co-Ni and Co-Ni-Cr-Mo) are much less resistant than the Ni-rich ones (Ni-Co, Ni-Co-Cr-Mo) and addition of Cr + Mo (Co-Ni-Cr-Mo and Ni-Co-Cr-Mo) enhances dramatically the corrosion resistance of both grades. This quantitative outcome is coherent with the literature on the corrosion-resistance enhancement of grades with these additives[43,44,65,66,71]. The voltammetric behavior of the Cr + Mo containing Co-rich grade (Co-Ni-Cr-Mo) is similar to that of the Ni-rich (Ni-Co) one without binder additives.Focusing on the details of the CVs of Figure1a-d-in combination with the evolution of the anodic charge with ATV and number of cycles, analyzed in FigureS1in the Supplementary Material-it can be noticed that there are classes of the CV pattern group in specific potential ranges, as detailed in FiguresS2-S5in the Supplementary Material.…”

“…The compositions of HM samples used in this work are reported in Table 1. CoNibased metallic binders demonstrate high versatility in a wide range of applications, as they show improved chemical stability in aggressive environments, while keeping mechanical properties comparable to those of Co-based HMs [44,65]. We considered four different compositions of the metallic matrix, reversing the Co/Ni ratio, without or with the presence of Cr and Mo as alloying elements, at a fraction not far from solubility limits [66].…”

“…Coherently with literature findings [67,68], the OCP time-series of Figure 1e exhibit a denobling trend for the Co-rich samples (Co-Ni and Ni-Co) and progressive ennobling for the Ni-rich ones (Co-Ni-Cr-Mo and Ni-Co-Cr-Mo). The CVs of grade Co-Ni (Figure 1a) exhibit an active corrosion range, followed by an evident pseudopassivation feature that is typical of Co-rich grades [69,70], while the other grades (Panels (b-d)) have achieved the pseudopassivated state under environmental exposure.…”

“…Among attempted HM recovery routes, controlled electrochemical corrosion has been proposed since the 1950s as a cheap, safe and environmentally friendly approach [22]. The corrosion of HMs has been described in a series of papers, that have enabled a general, though not conclusive, understanding of the process, the key feature of which is the formation of poorly understood pseudopassivation layers [24][25][26][27][28][29][30][31][32][33][34]. It is worth recalling here that the formation of pseudopassivation layers, though playing a crucial role in lowering the corrosion rate but not the practical corrosion-induced overall HM damage, is not its only cause.…”

Influence of Corrosion-Induced Damage on Mechanical Integrity and Load-Bearing Capability of Cemented Carbides

“…In this regard and considering the ceramic-metal composite nature of hardmetals, it is now well-established that the metallic binder is preferentially attacked in acid and neutral media, whereas the ceramic phase is the one corroded in alkaline solutions (e.g., Refs. [5][6][7][8][9][10][11]). Under these conditions, it has been shown that accelerated failures induced by applied loads may lead to a significant reduction in service life.…”