Formation of denuded zones in crept Mg–2.5Gd–0.1Zr alloy

Denuded zones formed in a Mg–2.5Gd–0.1Zr (at.%) alloy crept under 40, 60 and 80 MPa at 300 °C are systematically studied using electron backscattered diffraction and transmission electron microscopy. The denuded zones are found in matrix regions adjacent to grain boundaries lying approximately perpendicular to the applied stress direction, and they widen mainly in the tertiary creep stage of the creep tests. The majority of the denuded zones are characterized by the distribution of an array of grain boundary particles on one side and a misorientation between the denuded zone and the grain interior. The misorientation is caused by the formation of a dislocation wall between the denuded zone and the grain interior, and it leads to a loss of coherent matching between the otherwise coherent precipitates and the surrounding matrix in this region, which in turn results in the dissolution of the precipitates in this region and hence the formation of a denuded zone.