No abstract

Two different Nb,Sn strands have been processed a t GEC ALSTHOM using the internal tin process. Conductors were composed with seven sub-elements, made u p with NbTa7,5wt% filaments, surrounded by a Nb/Ta diffusion barrier to isolate the core from the copper shell. Effects of 9 different heat treatments (HT) on superconducting properties such as critical current densities, critical temperatures, critical magnetic fields and hysteresis losses have been investigated. The use of heat treatments adapted to the strand design showed a n increase in critical current up to 48 % with only a slight increase in the level of hysteresis losses. The low variation of losses is correlated to filament locations and bridging distributions across the conductor section. The critical current enhancement is achieved under a more complete transformation of the filaments into Nb,Sn and also by the refinement of Nb,Sn grains controlled by particular conditions of germination. As a result, critical current density Jc,,, = 800 A h " a t 12 T with hysteresis losses Q,,, cu *, -, = 490 mJ/cm3 have been measured.

No abstract

Precipitation-hardened aluminum alloys need to be heat treated to achieve the mechanical properties required for their application. The production of these materials can be optimized to make them more attractive and competitive comparing to other materials such as composites that have a growing and large market share in aeronautics field. One way to do this is by controlling the artificial aging of precipitation-hardenable aluminum alloys, such as the 2000 series Al-Cu alloys. These alloys can be monitored in real time by analyzing their conductivity behavior inside the furnace. The objective of this work is to evaluate the electrical conductivity behavior in real time of the 2024 alloy during the artificial aging at 190 °C. For this, analyses were made in order to assess the behavior of the microhardness curve by aging time and its microstructural characterization with thermal treatments in the times of 1 h to 9 h interrupted every 1 h. The results of the electrical conductivity versus hardness curve showed a significant correlation and indicate that this measure has great potential to be used as a tool to control the thermal treatment of aging.