Micromechanical testing of ultrathin layered material specimens at elevated temperature

Abstract

The mechanical characterisation of ultrathin specimens at very high temperature is challenging in terms of specimen preparation and mechanical testing under 'inert' atmospheres. An experimental procedure for the local characterisation of mechanical and thermal properties at elevated temperature is presented. Various common 'inert' atmospheres were investigated up to 1373 K in order to identify the most efficient environmental conditions to prevent surface reactivity and degradation of specimens. A NiCoCrAlYTa-coated monocrystalline Ni-based superalloy was used to exemplify the capabilities of the technique because of its high surface reactivity at very high temperature, i.e. oxidation and sublimation. Purified overpressured argon atmosphere combined with oxygen getters was found to be particularly suitable for the study of alumina-forming alloys at elevated temperature.

Alumina Failure and Post-failure Oxidation in the NiCoCrAlY Alloy System at High Temperature

“…The rods were sliced using electrodischarge machining to obtain 1-mm thick discs. Thin specimens were then prepared using a precision jig and a lapping machine in order to ensure good control over the thickness and surface finish [29]. Four specimens were prepared for each alloy: one "thick" (400-500 µm) used as a reference (series A in Table 2), and three "thin" (< 50 µm) used to rapidly trigger InCF (series B, C and D).…”

Oxidation of Thin Nickel-Based Superalloy Specimens: Kinetics Study and Mechanical Integrity

“…The samples for oxidation test with a 10 × 15 mm size were taken from a forged piece via electrical discharge machining and further drilled (Ø 1.5 mm) for holding during oxidation tests. Samples with thicknesses ranging from 15 to 500 μm with thickness deviations less than 2 μm were obtained by mechanical polishing using a precision polishing jig following the method detailed in previous work by Texier et al [11]. The samples were ground then polished using the jig on SiC paper down to a P2400/800 grit with sufficient material removal for each SiC paper to minimize residual stresses at the surface of the samples and produce a repeatable surface finishing.…”

Size effects on high temperature oxidation of MCrAlY coatings processed via APS and HVOF depositions

“…A particular care was paid on the precision jig stability to achieve low thickness variations over centimeter-size samples. The thinning procedure is fully detailed in Refs [46,48]. Samples with thickness ranging between 400 and 15 μm with less than  3 μm in thickness variation were prepared.…”

“…In the present study, oxidation experiments were conducted at 1150 C on ultrathin freestanding NiCoCrAlY coating specimens extracted from Air Plasma Spray (APS) and High Velocity Oxy Fuel (HVOF)-processed plates. The ultrathin specimens were prepared with a dedicated precision jig [46] in order to activate InCF for short-term high temperature exposures due to through-thickness Al depletion. Interrupted oxidation tests were performed to document the onset and progression of the generalized breakaway as a function of the exposure time.…”