SMALL-SCALE ASSESSMENT OF CORROSION-INDUCED DAMAGE IN HARDMETALS Y. F. Zheng 1,2,*,Φ , G. Fargas 1,2 , H. Besharatloo 1,2 , J. J. Roa 1,2 , O. Lavigne 3 , L. Llanes 1,2 1 CIEFMA, Departament de Ciència dels Materials i Enginyeria Metal∙lúrgica, Universitat Politècnica de Catalunya, EEBE, Barcelona 08019, Spain 2 Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Barcelona 08019, Spain 3 Hyperion Materials & Technologies, 08107 Martorelles, Spain * Corresponding author, e-mail: yafeng.zheng@upc.edu Φ Current address: Escola d'Enginyeria de Barcelona Est (EEBE), Campus Diagonal Besòs, Edifici I, Av. Eduard Maristany 16, 08019 Barcelona Abstract In this work, the effect of corrosion-induced damage on mechanical response of hardmetals was evaluated at small-scale level by nanoindentation and nanoscratch techniques. Immersion tests in acidic solution were performed to induce corrosion damage in a controlled way. Results pointed out that the corroded zone led to a strong reduction of hardness and elastic modulus compared to the non-corroded samples. Significant differences were also observed in nanoscratch tracks not only regarding width and depth but also deformation mechanisms developed, as scratching load increased. Corroded surfaces displayed relevant damage even a quite low loads (~45 mN). Cracking and fragmentation of individual WC grains took place together with chipping of fine WC fragments at the track edges. Such microstructural degradation was detected for non-corroded specimens at much higher loads (~400 mN). Keywords: Hardmetals, corrosion, nanoindentation, nanoscratch. 1. Introduction Cemented carbides, also simply referred to as hardmetals, has been extensively used as a tooling material in manufacturing and mining industries due to their outstanding combination of hardness, wear resistance and toughness [1-3]. They are composite materials comprising hard ceramic phase (generally WC) in a more ductile metallic binder. In general, the preferential choice for the ductile binder is Co. However, it is also common to choose binders of different chemical nature (e.g. Ni, CoNi) for applications demanding enhanced performance when subjected to severe working conditions, such as corrosive environment and high temperature [4]. Additionally, the mechanical and in-service performance can be tuned by adjusting the carbide grain size, binder content and composition [1,4,5]. As a rule, poor corrosion resistance of cemented carbides is a key factor limiting its application in chemically aggressive environments [6-8]. For this reason, the corrosion behaviour of hardmetals has been intensively investigated in recent decades [5-11]. It has been demonstrated that corrosive media preferentially attacks the binder phase when exposed to acidic and neutral environments, due to the galvanic coupling between the carbides and binder phase [9-12]. In alkaline solution, Co binder exhibits stable passivation, while WC phase is readily dissolved [5, 10-12]. Normally, corrosion damage induced by acidic media is much more severe than that from neutral and basic ones, which can be reflected in much higher current density [10] and wear rate [11,12]. A greater amount of binder phase dissolution in acidic solution ultimately results in the formation of W oxide layer and Co-depleted region, compared to exposure in neutral and basic solutions [9]. The formed corroded layer is no longer present in the compact form as shown in the uncorroded hardmetals, which leads to a pronounced deterioration in the mechanical and in-service performance of cemented carbides. In this regard, numerous investigations have been done for determining the detrimental effects of aggressive acidic environment on flexural strength [6], wear resistance [8, 11, 12] and fatigue resistance [13]. However, scarce information can be found regarding microstructural degradation phenomena occurring on the surface and its influence on mechanical response of cemented carbides. In recent years, nanoindentation and nanoscratch techniques have drawn much attention and have been extensively used to comprehend the mechanical behavior of materials at micron- and submicron length scale. Concerning this study, implementation of nanoindentation technique has mainly focused on the measurements of Young’s modulus (E) and hardness (H) in constituent phases of hardmetals, as well as on the evaluation of crystal orientation effects for WC single