In this work, the influence of chloride and sulfate ions on the corrosion behavior of WC-Co and WC-Ni cemented carbides is investigated using open circuit potential monitoring, potentiodynamic polarization, electrochemical impedance spectroscopy, and surface analytical techniques. Results reveal that the corrosion resistance of WC-Co cemented carbide is significantly compromised in the presence of chloride ions, with more negative corrosion potentials and higher corrosion current densities compared to the alloy in presence of sulfate ions. In contrast, due to its lower corrosion sensitivity, WC-Ni cemented carbide exhibits only slight dissolution behavior in both media, especially in the less aggressive sulfate-containing environment, where it demonstrates an outstanding corrosion resistance. WC-Ni cemented carbide also displays higher polarization charge transfer resistance than WC-Co counterparts. This is primarily attributed to the stable passivation layer of the WC-Ni hardmetal surface, which slows the charge transfer at the interface, impeding the oxidative reaction processes and effectively preventing corrosion. This different corrosion response is supported by small-scale hardness changes observed in WC-Co and WC-Ni cemented carbides, after corrosive immersion of both materials, especially in chloride-containing environments.
In this work, fatigue life and fatigue crack growth (FCG) testing, using pristine and pre-cracked samples respectively, are combined for studying the mechanical behavior of a fine-grained WC-Co cemented carbide. The main objective is to correlate fatigue lives measured with estimated and experimentally determined FCG data for natural and long through-thickness cracks respectively. It is done on the basis that fatigue failure, within the finite fatigue life regime, is controlled by the subcritical propagation of pre-existing flaws. In doing so, fatigue strength for the finite life defined as run-out (200,000 cycles) is first evaluated using two protocols based on the stair-case methodology. Then, strength data experimentally measured under monotonic and cyclic loading are correlated to each other for estimating FCG data for intrinsic defects. As a result, the dependence of FCG rates with the maximum applied stress intensity factor estimated for natural small flaws is found to follow trends similar to those experimentally determined for artificial long cracks. However, FCG rates and effective threshold for crack extension for the former are determined to be significantly lower than for the latter. The similitude found by both crack types regarding fatigue and fracture micromechanisms, as discerned from scanning electron microscopy inspection of stable and unstable crack extension phenomena, points out that distinct FCG behavior exhibited by small and long cracks is a consequence of extrinsic issues, such as length-scale of crack size or environmental aspects linked to location of the flaw either in the bulk or at the surface, rather than physicallybased intrinsic ones.
WC-Co cemented carbides, commonly known as hardmetals, are composite materials constituted by hard ceramic particles embedded in a ductile metal matrix. Due to their unique microstructural assemblage, these materials exhibit excellent combinations of hardness, strength, and toughness, consolidating them as a first choice for tools, structural and wear components. During recent decades, extensive research and technological advancements have driven the development of alternative cemented carbide grades, where traditionally used WC or Co are partially or entirely replaced. Within this context, hardmetals containing a third γ-phase (mixed cubic carbides) represent an interesting alternative. However, accurate evaluation of their fracture toughness remains a significant issue, especially as conventional methods using either indentation or precracking approaches are limited by either restricted implementation of fracture mechanics analysis or testing challenges. Within this context, this study proposes, implements, and validates the use of a novel laser-micronotching methodology to evaluate the fracture toughness of a γ-phase containing cemented carbide grade. For comparison purposes, the investigation also includes assessment of such a property by means of two other well-established testing methodologies. Moreover, similar experimental work was conducted in a plain WC-Co system with similar microstructural features. It is shown that machining of a through-thickness micronotch by means of ultra-short pulsed laser ablation is a reliable and efficient method for fracture toughness evaluation of γ-phase containing hardmetals. The main reason behind this is its capability for providing a precise and reproducible micronotch, with minimal thermal damage, that finally acts as a real through-thickness crack for which a stress-intensity factor is well-defined under flexural testing. Furthermore, toughness values obtained are in satisfactory agreement with those determined using precracked specimens with machined large notches and/or indentation techniques.
In this paper, a systematic investigation of friction and wear properties of industrial lubricants is carried out by varying the parameters of speed and temperature. Novel bootstrap-based likelihood ratio trend tests have been applied to analyze the results of such experiments. Speed is varied at 600 and 1200 rpm, whereas temperature is varied at 30 and 75 degrees C. Properties like the coefficient of friction, wear scar diameter, wear scar surface roughness, and wear depth values have been measured for each test condition. Orderings of the best oils and test conditions have been obtained to determine the optimal oil and speed. The results of statistical analysis and experiments are seen to be in perfect concordance. Experimental observations indicate the optimal speed as 1200 rpm and temperature as 30 degrees C. This combined experimental and statistical approach can be of immense help in lubricant optimization in achieving improved service life and performance of industrial machinery, automotive, etc.
As one kind of important lithium-ion battery electrolyte, fluoroethylene carbonate (FEC) holds significant importance in improving battery performance. In response to the lack of research on the melt crystallization purification of FEC, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were used to determine the thermodynamics and the nonisothermal crystallization kinetics of FEC. The binary solid-liquid phase equilibrium data for FEC-ethylene carbonate (EC) and FEC-vinylene carbonate (VC) systems were measured, calculated, and fitted by ideal solution, Van't Hoff, Apelblat, lambda h models, non-random two-liquid (NRTL) model, and Wilson models. The results indicate that both FEC-EC and FEC-VC systems are eutectic mixtures, and the Apelblat model can give the best fitting results for the phase diagram data of both systems. The kinetics of the FEC melt crystallization process were also investigated. It was found that a faster cooling rate could result in higher supercooling.
