THE GROWTH OF GAMMA' PRECIPITATES IN A 53NI-20CO-15CR SUPERALLOY

The age hardening behavior and microstructural characteristics of a 53 Ni-20Co-15Cr-5Mo-4.9Al-1.3Ti alloy has been investigated by micro-Vick ers hardness test and transmission electron microscopy. The shape of g amma' precipitates was spherical at the early stage of aging and was c uboidal at the later stage. The aged hardness of the alloy closely rel ated to the size and the quantity of gamma' precipitates. The gamma' p recipitation cannot be suppressed by water quenching after solution tr eatment. It is necessary to cool the specimen at rates of higher than 10(4) K/s for restraining the precipitation of gamma' phase. The growt h kinetics of gamma' precipitates in the alloy followed the prediction of Lifshitz-Slyozov-Wagner (LSW) theory for growth under volume diffu sion control at all aging temperatures examined. The activation energy for the growth was estimated to be 266 kJ/mol which was close to thos e of diffusion of solute atoms such as Al, Ti and so on in Ni and Ni-b ase alloys. The actual particle size distribution of gamma' precipitat es was somewhat different from distributions predicted by the LSW and Brailsford-Wynblatt encounter modified (BWEM) theories.