TEM INVESTIGATION OF PRECIPITATION PHENOMENA OCCURRING IN PH-15-5 ALLOY

The ageing of PH 15-5 alloy, previously quenched from 1050-degrees-C, is characterized by a hardness peak at 450-degrees-C, then by a soften ing and finally by a second increase in hardness from 650-degrees-C. T EM observations reveal the successive formation (between 450 and 650-d egrees-C) of coherent precipitates (A and B types) which become respec tively as rods (D) the growth directions of which have been determined and as partially coherent (C) globular precipitates. All these types of precipitates are enriched in copper. After tempering in temperature s higher than 650-degrees-C, new (E) precipitates are observed which a re coherent at first then become partially coherent after tempering at 750-850-degrees-C.