Effect of low pressure on discontinuous precipitation in Ni-7.5 at. % In and Ni-9 at. % Sn alloys

The kinetics and morphology of the discontinuous precipitation reaction have been studied by isothermal ageing under low pressures of 0.1 MPa (ambient), 10 MPa and 50 MPa at the following temperatures: Ni-7.5 at. % In at 713 and 763 K, and Ni-9 at. % Sn at 853 and 903 K. The migration rate of the reaction front increases by approximately a factor of 2 in this range of pressures, whereas the interlamellar spacing is not affected by these pressures. The applied low pressures increase the fraction of grain boundaries initiating the decomposition by about 50%. The results obtained can be explained by the assumption that the structure of grain boundaries and hence their mobility and ability to initiate the decomposition reaction is changed by the pressure.