Work softening in stoichiometric spinel (MgAl₂O₄)

Dislocations and Mechanical Properties of MgO‐Al2O3 Spinel Single Crystals

“…The work-softening phenomenon is then due to a decrease in dislocation density with increasing strain. This has been shown clearly by Donlon et al, 17 who measured the dislocation density, , by transmission electron microscopy (TEM). Their results are shown in Fig.…”

Microstructural examination in high-strain-rate superplastically deformed tetragonal ZrO2 dispersed with 30 vol% MgAl2O4 spinel

“…For ceramic materials, it has generally been explained that the accommodation process predominantly occurs through the diffusional processes. Indeed, the superplastic flow stress level of ഛ120 MPa is smaller than that of the slip deformation in ZrO 2 and spinel single crystals, 47,48 where the yield stress is on the order of 200-300 MPa at 1773 K. The existence of intragranular dislocations indicates, however, that the stress concentrations cannot be fully relaxed only by diffusional processes. Thus, it is reasonable to explain that the dislocations observed frequently around boundaries would act as the accommodation process of significant stress concentrations, 32 which are exerted due to the predominant GBS process.…”

“…As mentioned above, however, the smaller flow stress is not compatible with those reported in the slip deformation. 47,48 Although detailed examinations are necessary for further discussion, the transition of the m value may arise from an intervention of slip deformation, which would work at higher stresses. 51…”

Dislocations in Ceramics

“…The mechanical properties of MgO-Al 2 O 3 spinel single crystals have been studied extensively by both creep and constant strain-rate compression tests at high temperature [18-20, 26, 127-148], as well as by indentation testing [21,142,149]. Studies have also been conducted on other oxides with the spinel structure, such as magnetite (Fe 3 O 4 ) [150], manganese zinc ferrite (Mn 0.7 Zn 0.2 Fe 2.1 O 4 ) [151,152], manganese aluminum spinel (Mn 1.8 Al 1.2 O 4 ) [153], nickel ferrite (Ni 0.7-Fe 2.3 O 4 ) [154][155][156], and chromite (FeCr 2 O 4 ) [157].…”

“…This should be compared with the value of q $ m/300 for stage II hardening in fcc metals. The high initial hardening rate in spinel has been ascribed to a rapid build-up in the dislocation density, to a value of about 10 13 m À2 at a strain of less than 1% [142]. Such rapid buildup is due to the small slip distance, which in turn is due to the formation of a threedimensional dislocation network by climb.…”