On the improvement of the ductility of molybdenum by spinel (MgAl₂O₄) particles

In a 1967 patent, D. M. Scruggs found that the room temperature ductility of molybdenum is improved by adding several volume percent of MgAl2O4 spinel particles. The present work substantiates Scruggs' claim – with increasing MgAl2O4 volume fraction the ductility of Mo–MgAl2O4 is found to pass through a maximum near 2.5 vol%. Scruggs postulated that gettering of detrimental impurities was responsible for this effect. In the present work, fracture initiated at microcracks that formed on the Mo–MgAl2O4 specimen surfaces during tensile testing. The ductility maximum is interpreted in terms of the change in the microcrack size (which is assumed to scale with the grain size) and the ultimate tensile stress, as the MgAl2O4 volume fraction increases. Fracture occurs once a critical local stress-intensity factor, which is approximately independent of the MgAl2O4 volume fraction, is reached.