Fatigue behavior and associated binder deformation mechanisms in WC-Co cemented carbides
Tipus de documentProjecte Final de Màster Oficial
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The mechanical integrity of WC-Co hardmetals has been studied by the occurrence of subcritical crack growth and strength degradation under cycling loading. The investigation is conducted on three WC-Co hardmetals grades with different binder content and/or grain size by assessing fatigue crack growth (FCG) behavior and fatigue life tests at room temperature. Experimental fatigue results are compared to fracture toughness and flexural strength data. An analysis of the results within a fatigue mechanics context permits to corroborate FCG threshold as the effective fracture toughness under cyclic loading. Mechanical tests were complemented by a fractographic inspection using field-emission scanning electron microscopy. Critical defects are evidenced to be agglomerates of coarse grains and abnormally coarse grains. Additionally, a roughness study is carried out by atomic force microscopy in order to optimize sample preparation for electron backscatter diffraction (EBSD) imaging. EBSD mapping on stable propagated cracks has been accomplished to characterize the crack-microstructure interactions within the cobalt phase. EBSD results suggest that martensitic transformation of cobalt phase (from fcc to hcp) is not exclusively associated with cyclic loading, as it had been postulated in the literature. On the other hand, it seems to be induced by rough grinding of the exposed surfaces. From the perspective of fatigue micromechanisms, they are clearly localized within the binder phase, although specific nature(slip/twining) of the crystallographic-like path observed may not be defined at this research stage.
MatèriesTungsten carbide-colbalt alloys -- Mechanical properties, Materials -- Fatigue, Fracture mechanics, Ceramic materials -- Mechanical properties, Metals -- Mechanical properties, Carbides -- Mechanical properties, Aliatges de carbur de tungstè i cobalt -- Propietats mecàniques, Materials -- Fatiga, Materials -- Fractura, Materials ceràmics -- Propietats mecàniques, Metalls -- Propietats mecàniques, Carburs -- Propietats mecàniques