Thermal residues stresses and microstructural characterisation of functionally graded WC-Co composites
(English)Manuscript (preprint) (Other academic)
X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC-Co composite. The gradient was continuous within a distance of about 40 Jlm below the surface and consisted of varying WC and Co phase volume fractions. The composite was characterised by scanning electron microscopy, optical microscopy and X-ray diffraction. Thermal residual stresses develop due to the thermal mismatch between the WC and the Co phase during cooling from the liquid-phase sintering temperature (1450°C). Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. Stresses were measured in both WC and Co phases at various depths. For WC, the in-plane compressive residual stresses varied approximately between -300 MPa to -500 MPa with depth below the surface. For the low volume fraction Co phase, the tensile residual stresses were approximately 600 MPa. The changes in the magnitude of the residual stresses can be related to the changes in the Co phase content through the graded zone. Microstresses in the graded zone are attributed to the thermal mismatch between WC and the Co phase. The compressive macrostresses were determined to be a result of the compositional gradient. This conclusion is strongly supported by the result that almost no macrostresses were measured in a similar homogenous sample i.e., without the corresponding compositional gradient. Therefore, varying the composition gradient during fabrication is expected to directly affect the macrostresses.
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-102051OAI: oai:DiVA.org:liu-102051DiVA: diva2:668023