Corrosion behaviour of WC hardmetals with nickel - based binders

Cobalt is the standard binder in tungsten carbide (WC) hardmetals due to its compatibility with the WC phase, resulting in composites with exceptional hardness and wear resistance. However, their corrosion resistance is not satisfactory in many applications, leading to the early deterioration and failure of tools and equipment. In this work, the corrosion of WC hardmetals with three alternative binders (FeCoNi, NiCrCoMo and NiCrMo) is compared with a benchmark WC-Co composite, using electrochemical techniques such as open circuit potential (OCP) monitoring, polarisation curves and electrochemical impedance spectroscopy (EIS), assisted by scanning electron microscopy (SEM).publishe

Linking sintering stresses to nano modification in the microstructure of BaLa4Ti4O15 by transmission electron microscopy

High quality factor and a temperature stable resonant frequency make BaLa 4 Ti 4 O 15 (BLT) ceramics attractive materials for microwave applications. Aiming to exploit the effects of external stresses on the development of textured and anisotropic microstructures to optimise MW properties, the influence of applied external pressure during sintering of BLT ceramics is analysed. HRTEM and geometric phase analysis (GPA) showed that stresses applied during sintering, trigger the nucleation and growth of faults hypothesised to be due to the errors in the AO 3 layer (basal plane) stacking sequence of the hexagonal perovskite structure. The results reveal a strong correlation between the high concentration of structural defects and the development of anisotropic microstructures, which tune the properties of BLT. Stresses applied during sintering are therefore a promising tool to design material properties

Corrosion resistance of WC hardmetals with different Co and Ni-based binders

In this work, industrially relevant WC composites with alternative binders (Ni, CoNi, NiCr, CoCr, CoNiCr and NiCrMo) were produced and their corrosion resistance in 0.5 M NaCl was compared to conventional WC-Co system. The main objective is to develop hardmetals with higher corrosion resistance to extend the lifetime of tools and equipment, reducing the demand for new parts and maintenance, thus decreasing the total cost of the operation. The study includes different electrochemical techniques, namely corrosion potential monitoring, Electrochemical Impedance Spectroscopy (EIS) and polarization curves. The purpose is to evaluate the influence of each element on the corrosion resistance of the composites produced.publishe

Development of WC-NiCrMo hardmetals

The demand for improved components with a wide range of properties is a reality in today's hardmetal market. Furthermore, supply shortages of raw materials such as W and especially Co resulted in rapid price fluctuations. Combined with stricter environmental legislation and health protection, these facts prompt the demand for alternative or modified binders. Therefore, in this work, WC-NiCrMo composites were developed as a potential alternative to conventional WC-Co hardmetals. To evaluate this new hardmetal composite, prototypes of submicrometric WC with approximately 15 vol% of NiCrMo binder were produced by conventional powder metallurgy route. Thermodynamic assessment, wettability testing and constant heating rate dilatometry were performed to design an adequate sintering route. A detailed characterization of the mechanical properties (Young's modulus, Vickers hardness and fracture toughness), together with corrosion resistance assessment (OCP, polarization curves, EIS) and abrasive wear (ball-cratering) resistance evaluation were undertaken. Good wettability of molten NiCrMo binder on WC surface was observed, and highly dense compacts could be successfully attained by gas pressure sintering. The new WC-NiCrMo composite has lower hardness but higher corrosion resistance and better wear resistance than the conventional WC-Co hardmetals.publishe