High temperature creep behaviour of nearly stoichiometric alumina spinel

Abstract

Creep behaviour of nearly stoichiometric spinel, (Al₂O₃)_n MgO, n=1.1, is investigated for compression axis [001], at temperatures 0.77 to 0.83 T _m and constant loads 88.2 to 117.6 MPa. Experimental observations, including the mechanical creep law and the dislocation substructures as imaged by TEM and Berg-Barrett X-ray topography support the following picture: {100} 〈110〉 slip is activated in the very early creep stage, while no evidence for {111} is found; on the other hand {111} slip planes are observed for stress orientation [110], in agreement with Schmid's law. (ii) When in edge orientation slip dislocations become sessile by pure climb splitting. Their dissociation plane has been determinated unambiguously and observed to be perpendicular to their Burgers vector. As a result, it is suggested that slip should be inhibited and further creep should occur by pure climb strain only. This expected “climb-creep” accounts for experimental rates and, tentatively, for their dependence on stoichiometry n since the latter is observed to change only pre-exponential terms, the creep energies being much the same whatever the value of n.