Rapid Hot‐Pressing of Ultrafine PSZ Powders

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Abstract
The process of compaction and densification of ultrafine (40‐ to 60‐nm grain size) powder of partially stabilized zirconia with 3 mol% of Y 2 O 3 (Y3‐PSZ) during rapid hot‐pressing was investigated. A special apparatus was designed to allow rapid application of 1.6 GPa of quasi‐isostatic pressure at temperatures of 1100° to 1300°C to powder compacts encapsulated in glass under vacuum. Pressure was applied for 10 s, then the samples were rapidly cooled to room temperature, removed from the encapsulating glass, and characterized using SEM, TEM, and X‐ray diffraction. Density and mechanical properties of the prepared materials were measured and compared with those of similar materials fabricated using conventional hot‐pressing. SEM and TEM observations revealed that the ultrafine grains of the starting powder coarsened rapidly during the initial heating, and the compacts developed large (> 10 μm) and small (< 1 μm) pores. The process of densification under pressure consisted of closing of the large pores, whereas the small pores were relatively unaffected by the application of pressure at all investigated temperatures. The major mechanism of densification during the rapid pressing appears to be rearrangement and sliding of grains around the large pores. The material prepared by rapid pressing at 1300°C had higher hardness ( H v = 1400 versus 1300 kg/mm 2 ) but somewhat lower fracture toughness ( K I C = 5.5 versus 6.0 MPa · m 1/2 ) compared with the conventionally hot‐pressed Y3‐PSZ. Density of the material pressed at 1300°C was 97% of theoretical density.

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