| Popis: |
Consolidation of N2 gas atomized powders of Al-9 mass%Fe alloy was done by cold pressing, degassing, hot pressing and extrusion at a reduction ratio of 7 to 1. The degassing was carried out at various temperatures between room temperature and 500°C, while both hot pressing and extrusion were carried out at a fixed temperature of 300°C at which no coarsening of intermetallic compounds occurs at all. The dehydration of surface oxide film on the powder particles is accelerated with increase in the degassing temperature, making the oxide layer more brittle. When the degassing is carried out below 300°C, the room temperature strength of the extruded rod is high, but the toughness remains low showing rapid decrease with slight increase of strength (or with decrease of degassing temperature). On the contrary, the strength decreases and the toughness increases with increasing degassing time and temperature above 400°C, and this is attributed to the coarsening of Al-Fe compounds during degassing. One reason why low temperature degassing brings about a low toughness is that the strength of extruded rod is kept at high level, and another can be that cracks propagate preferentially along the prior powder particle boundaries where exist continuous oxide layers which were broken-up neither by degassing nor by extrusion. |
