Materials Science Forum Vol. 1176

Abstract: The degradation behavior of adhesion between cycloaliphatic epoxy resin and copper under high temperature and high humidity conditions was investigated. The Cu/resin joints were aged at 175°C and at 85°C in 85% R. H. The degradation behavior of the joint interface was analyzed by tensile tests and Fourier infrared transform spectroscopy (FT-IR). As a result, it was confirmed that the adhesion strength was retained after aging at 175°C for 1000 h, while it decreased with an increase in the aging time by aging at 85°C in 85% R. H. Furthermore, the interfacial fracture mode increased with aging at 175°C. In contrast, cohesive fracture was the main fracture mode and hardly changed by aging at 85°C in 85% R. H. The FT-IR analysis results showed that the peak intensity of the carbonyl group increases and that of the methylene group decreases by aging at 175°C. The result indicates that the resin was oxidized. Moreover, the peak intensities of carboxy and hydroxyl groups increased and that of ester groups decreased by aging at 85°C in 85% R. H. The results suggest that ester groups may be hydrolyzed due to aging and thus the adhesion is degraded.

Abstract: The WC-Co cemented carbide is one of the metal-matrix composites produced by sintering hard tungsten carbide (WC) with Co as metallic binder at high temperatures, and has excellent hardness and wear properties. In recent years, the high-entropy alloys (HEAs), which contain at least five elements with equiatomic or near-equiatomic ratio, have gained significant attention. The HEAs possess unique properties, which cannot be achieved by conventional alloying approaches based on only one alloying element, such as enhanced mechanical properties at high temperatures induced by severe lattice distortion effect and sluggish diffusion effect. In this study, HEAs were applied to alternative binders for the WC-Co cemented carbide as an attempt to seek enhanced mechanical properties. In the experiment, HEA powders such as the CrMnFeCoNi and CrFeCoNiMo HEAs were used as binder to fabricate WC-HEA cemented carbides by the multi-beam laser directed energy deposition (L-DED). WC-Co cemented carbide powder was also used for a comparative study. Through the comparative study, the role of elements in the initial binders are discussed. The multi-beam L-DED is one of the additive manufacturing (AM) processes. The WC-HEA cemented carbide powders were processed as single beads and square-shaped samples. Phase identification of the samples was performed by the X-ray diffraction (XRD). Microstructural observations were performed by a scanning electron microscope (SEM). The experimental results suggested the possibility for controlling hardness easily than the conventional processing routes by tailoring formed carbides through controlling laser processing conditions and alloying elements in initial binder materials.