Impression and Compression Creep of SiAlON Ceramics

Abstract

Concurrent impression and uniaxial compression creep studies were performed on three Yb‐SiAlON materials. Stress exponents were approximately 1 in compression and 2 in impression. The higher stress exponents were due to the complex stress field in the impression creep test, which caused microstructural dilation. The dilated multi‐grain junctions also became filled with additional intergranular glassy phase. Focused ion beam milling and in situ lift‐out specimen preparation combined with transmission electron microscopy was successful in identifying microstructural changes after creep testing. These observations have important implications in the design of creep‐resistant materials in complex stress fields.

Microstructure and Creep Behavior of Silicon Nitride and SiAlONs

“…The authors are aware of only three reports in the literature of impression creep testing of ceramics with a flat‐ended, cylindrical punch 90,95,96 . While the work by Petrovic et al 95 .…”

“…At the center of the impression, where stresses are mostly hydrostatic, additional glass was seen at many of the multigrain junctions in each of the three SiAlON compositions. The specimens extracted from the inside edge of the impression all showed evidence of grain boundary sliding in the form of strain whorls 96 …”

Viscosity of Ba–B–Si–Al–O glass measured by indentation creep test at operating temperature of IT-SOFC

“…The stress field under a flat-ended, cylindrical punch has been described by Fox et al [16]. Not only compressive stress but also tensile stress and shear stress exist in the testing system.…”

“…1. However, since tensile stress is induced "outside the contact area" during indentation [16], breakdown and rupture of the surrounding material may occur, which depends on the applied stress, temperature, and material itself. Such phenomenon has been reported by using SiAlON (Si 3 N 4 solid solutions containing Al 2 O 3 ) as specimen under a compressive stress of 300 MPa, which is significantly larger than the applied stress (0.08-0.51 MPa) in this study.…”

Silicon nitride compressive creep behavior in argon atmosphere

“…Its thermal expansion coefficient is around 2.9 × 10 −6 < α < 3.6 × 10 −6 K −1 for 20 < T < 1500 • C [1,3]. In each of its structural modifications, ␣ and ␤, silicon nitride has a unique combination of properties.…”