NASA Technical Reports Server (NASA) · 1993 · 10 citations · 0 references
Natural SciencesMaterials EngineeringMaterials ScienceCeramic MaterialsMetallic MaterialsMetallurgyAlloysGrain Structure FormationMetalsMicrostructure ControlMicrostructure EvolutionPowder MetallurgyElectron Probe MicroanalysisGrain BoundariesMaterial Behaviour At Elevated TemperaturesMeltingMetal MicrostructureMicroanalysisMicrostructural ChangeZirconium Alloys
Microstructural evolution was studied in samples of wrought and vacuum plasma sprayed (VPS) NARloy-Z exposed to temperatures up to 970 C (1,780 F) for up to 60 h. Samples were heated in a vacuum furnace, followed by rapid quenching in helium (He) gas at a cooling rate of 166 C (300 F) per second. Microstructural analyses were conducted using optical microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). In both the wrought and VPS conditions, precipitates rich in silver (Ag) and zirconium (Zr) were present in the matrix and at the grain boundaries even after long exposure to elevated temperatures. Islands rich in oxygen (O2) and Zr were also observed, as well as incipient melting at the grain boundary triple points. Results indicated that the alloy cannot be homogenized by heat treatment at elevated temperatures.