Solid-state reactions between Cu and Al during mechanical alloying and heat treatment

High temperature in situ resistivity measurement was carried out to monitor the resistivity change of the Pd wire when annealed in the temperature range of 250–400°C in flowing N2. In the range of 250–350°C, the resistivity change with time can be fitted well by a bulk-diffusion model with infinite-long cylinder geometry, the derived apparent diffusion coefficient versus temperature matches the Arrhenius plot well, and the apparent activation energy for this process was derived to be 1.3 eV. The tensile test showed that the mechanical properties of the Pd wire annealed at 300°C in flowing N2 is better than those in air. The results disagree with the traditionally accepted conclusion: nitrogen is insoluble in the Pd below 1400°C (Hansen (1958) Constitution of Binary Alloys, McGraw-Hill, New York). Besides, the influence of superficial oxidation on the absorption and desorption behaviors of N atoms in Pd wire at different annealing temperatures (up to 400°C) was discussed in terms of the reversibility of resistivity change when the ambient atmosphere was changed between pure N2 and air.