| Abstract: | The variations of the structure and the mechanical properties had been investigated by means of TEM investigations and determination of the microhardness number in the Ta range between 0 °C and 180 °C. The main results are the following: – At the starting period of the isothermal ageing an incubation time, tinc, occurs. tinc plotted versus Ta yields two intersecting C curves at about 100 °C. – At Ta = 70 °C the only decomposition product are G.P. zones. – At 70 °C <Ta <100 °C the G.P. zones formed in the first period of decomposition can be transformed into η-phase or spherical hexagonal (S.H.) zones. – Above about 110 °C the precipitates present in the matrix are quasi-homogeneously formed at nucleation sites delivered by clusters of impurity atoms. |
