Abstract
The precipitation process of the Nb-40Zr-10Ti alloy aged at 400° to 500°C was investigated by means of hardness measurements, and optical and electron microscopy. The results were discussed in relation to superconducting properties such as the critical current density vs applied transverse magnetic field and the transition temperature. The results obtained were as follows:
(1) In this alloy aged at about 500°C after a solution treatment, the β″ phase first precipitated continuously within β grains and then the α+β″ phases began discontinuously to precipitate in the grain boundary to expand into the region, in which the continuous precipitation had already occurred. The α+β″ lamella was a finally stable structure.
(2) From the result of an EPMA test, the Nb content in the continuously precipitated region were found to be relatively lower than those of the discontinuously precipitated region.
(3) The Vickers hardness in the α+β″ lamella was about 230, which corresponded to 3/5 of the hardness in the continuously precipitated region.
(4) Both the continuous and discontinuous precipitations were promoted by cold working.
(5) The critical current density increased with increasing ageing time. This result may be thought to be mainly due to the precipitation of the β″ phase.
(6) The superconducting transition temperature increased with increasing ageing time.
