Transmission electron microscopy of low pressure plasma sprayed CoNiCrAlY coating

Investigation of an as-sprayed NiCoCrAlY overlay coating - microstructure and evolution of the coating

“…XRD results confirm earlier observations [10] that the c phase dominates the microstructure in the as-sprayed state at the expense of brittle b phase as this structure is compared to the heat-treated/equilibrated state; the high portion of the fcc c phase also accounts for enhanced low temperature ductility of LPPS structures reported [4]. Besides the submicron grain size of typically 0.5 lm in LPPS NiCoCrAlY coatings may also contribute to higher ductility.…”

“…The respective diffusivities (relatively high ¼ thick arrow, relatively low ¼ thin arrow) of Ti are compared to the other metallic elements in the crystalline and the amorphous sections. The concentration profiles of the two elements Cr and Ti (arbitrary scale), which are estimated to be most important for melting point depression and glass formation in this coating, are given at the bottom phase suppression was also observed in LPPS CoNiCrAlY coatings before homogenization [10]. A NiCoCrAlY coating of slightly different composition is reported to be even fully c and devoid of b-NiAl in the as-sprayed state [10].…”

“…The concentration profiles of the two elements Cr and Ti (arbitrary scale), which are estimated to be most important for melting point depression and glass formation in this coating, are given at the bottom phase suppression was also observed in LPPS CoNiCrAlY coatings before homogenization [10]. A NiCoCrAlY coating of slightly different composition is reported to be even fully c and devoid of b-NiAl in the as-sprayed state [10]. All these observations originate from the same cause: preferential formation of c phase attributable to higher solidification rates of c on cooling whereas growth of the b phase is kinetically delayed as will be detailed later.…”

“…In either case c 0 will not have formed under equilibrium conditions. The presence of metastable tiny c 0 particles of typically 3 nm is reported for an assprayed CoNiCrAlY, which also represents a coating composition too rich in Co to account for stable c 0 formation from the melt [10]. In this case they are judged to have formed by a solid state precipitation reaction from supersaturated c with reference to their minute sizes.…”

Temperature Estimation and Al Content Prediction Focusing on Microstructural Change in a Thermal Barrier Coating

“…It clearly points out that the two phases are b-(Ni(Co), Al) and c-(Co(Ni), Cr) rich. The authors compare the elemental distribution in this study with that reported in the previous studies (Ref 13,15) to determine the phase constitution. Aluminum oxide is formed along the boundary.…”