Cavitation and grain boundary sliding during creep of Mg-Y-Nd-Zn-Mn alloy

Creep of squeeze-cast Mg-3Y-2Nd-1Zn-1Mn alloy was investigated at the constant load in the stress range of 30-80 MPa. Tensile creep tests were performed at 300°C up to the final fracture. Several tests at 50 MPa were interrupted after reaching the steady state creep; and another set of creep tests was interrupted after the onset of ternary creep. Fraction of cavitated dendritic boundaries was evaluated using optical microscopy. Measurement of grain boundary sliding by observation of the offset of marker lines was carried out on the surface of the crept specimens after the test interruption by scanning electron microscopy and by confocal laser scanning microscopy. The results show that the dominant creep mechanism in this alloy is dislocation creep with minor contribution of the grain boundary sliding. Creep failure took place by the nucleation, growth and coalescence of creep cavities on the boundaries predominantly oriented perpendicular to the applied stress. Increasing amount of cavitated boundaries with time of creep exposure supports the mechanism of continuous cavity nucleation and growth.