In-Situ Study of Mechanical Properties of Diffusion Aluminide Bond Coating at Elevated TemperatureWednesday (28.09.2016) 17:45 - 18:00 Part of:
Diffusion aluminide bond coats are compositionally and microstructurally graded materials with significant variation in engineered mechanical properties across the cross-section, utilized for high-temperature protection of superalloys. These bond coatings exhibit three-layered microstructures: (a) the outer layer contains intermetallic PtAl2 and Cr-rich fine precipitates, (b) the intermediate layer contains B2-(Ni,Pt)Al and (c) the inner layer is interdiffusion zone containing coarse precipitates in B2-NiAl matrix. This study focuses on understanding the variation in mechanical properties and deformation mechanisms as a function of temperature. An in-situ SEM nanomechanical instrument, PI 87xR SEM PicoIndenter with an integrated high-temperature stage and an active tip heating was used to conduct uniaxial compression of pillar samples. Using the displacement-controlled feedback mode of the system, the pillars were compressed to 5-12% strain at a strain rate of 0.01 1/s at room temperature (RT) as well as several elevated temperatures up to 800°C. The stress-strain curves of bond coating indicate that the plastic response is characterized by major strain hardening at RT and limited strain hardening at higher temperature. The surface of the bond coating pillars shows evidence of grain boundary sliding at higher temperature. Elastic moduli of the bond coating remain nearly constant at RT to 800°C whereas yield stress of the coating decreases to ~50%. Transgranular fracture appears on the pillar surface at higher strain at room temperature whereas intergranular fracture dominates deformation at higher temperature. With combined analysis of chemistry and microstructural changes, the results are used to understand deformation mechanism and the variation in mechanical properties as a function of temperature.