Premium
Grain Boundary Phases and Wake Zone Characterization in Monolithic Alumina
Author(s) -
Hay Jack C.,
White Kenneth W.
Publication year - 1995
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1995.tb08432.x
Subject(s) - materials science , toughening , softening point , grain boundary , thermal expansion , microstructure , composite material , softening , phase (matter) , anisotropy , phase boundary , mineralogy , toughness , geology , optics , chemistry , physics , organic chemistry
The postfracture tensile (PFT) technique has been used to characterize the wake zones of two alumina microstructures over a temperature range of 20° to 1280°C. Differing primarily in purity and grain size distribution, the behaviors of a commercial 99.7% alumina and a nominally pure alumina, Lucalox (General Electric, Cleveland, OH), were evaluated. Previously, the authors have demonstrated the dominant role of thermal expansion anisotropy in control of the toughening processes through 600°C. In this paper we relate microstructural aspects to those toughening mechanisms causing the behavioral change near 800°C, typical of commercial aluminas. This temperature coincides closely with the softening point of a glassy phase reported for some commercial aluminas. Since Lucalox exhibits the same behavior, but contains no added glassy phases, two possibilities remain: (1) trace quantities of a grain boundary phase are sufficient to promote the observed behavior, or (2) changes in toughening mechanisms result from more subtle microstructural transitions. Based upon studies of strain rate and time‐dependent behavior, we propose that the topographic changes of the fracture surface near this temperature may explain the increase in toughening behavior at high temperatures.