Preparation of Nb3Al superconductor by powder metallurgy and effect of mechanical alloying on the phase formation

Abstract

Adoption of powder-in-tube method to fabricate superconducting wire can realize a large application of Nb 3 Al prepared by powder metallurgy. Powder metallurgy was used to synthesize Nb 3 Al under various heat-treatment conditions, annealing temperature was varied from 700 to 1,000°C and heating time was varied from 10 to 50 h. X-ray diffraction patterns reveal that a reaction between Nb and Al took place and formed NbAl 3 phase. Under current heat-treatment conditions (annealing temperature was varied from 700 to 1,000°C and heating time was varied from 10 to 50 h), NbAl 3 was so stable that it did not further react with the unreacted Nb and was not sensitive to the heat-treatment condition. By mechanical alloying, adoption of high-energy ball milling significantly decreases particle size and enhances surface free energy, which promotes the formation of Nb 3 Al phase. X-ray diffraction patterns indicate that relatively pure Nb 3 Al phase was obtained under the same heat-treatment condition. Energy-dispersive X-ray analysis measurement demonstrates that the obtained samples were close to the right stoichiometry of A15 structure Nb 3 Al.

Studies on the formation of aluminides in heated Nb–Al powder mixtures

“…Since this is a solid state transformation based on diffusion, complete conversion to Nb 3 Al takes place slowly. Use of finer reactant particles and mechanical activation of the powder mixture could lead to faster reaction rates [8].…”

“…Nb 2 Al and Nb 3 Al are stable over a larger composition interval and decompose peritectically at 1940°and 2060°C respectively [3,7]. Niobium-rich compounds in general, and Nb 3 Al in particular, are refractory and superconducting materials which can be used for high-field and large-scale magnetic applications such as in nuclear fusion reactors or highenergy particle accelerators [8,9]. However, niobium aluminides are brittle and have low ductility at ambient temperatures.…”

Phase formation and superconducting properties of mechanically alloyed Nb3(Al1−xGex) system

“…According to previous reports [21][22][23], for each run, mixture powders of approximately 2.0 g and stainless steel balls of 20 g (ball-to-powder weight ratio = 10:1) were loaded into a stainless steel vial in an argon-filled glove box and milled for 3 h. Then, the mechanically alloyed powders were pressed into pellets and sealed into a vacuum quartz tube. Finally, the samples were put into a tubular furnace for sintering at 1100 °C for 5 h with flowing Ar atmosphere.…”

“…Material was usually formed by the continuous fragmentation and re-welding mechanism of grains in the process of the ball milling. Thus high-energy ball milling has been widely used for preparing Nb-Al alloy [14][15][16][17][18][19][20][21][22][23].…”

Microstructure and oxidation resistance of porous NbAl3 intermetallic prepared by thermal explosion reaction

“…Although the synthesis of intermetallics can be achieved by traditional methods such as powder metallurgy, mechanical alloying and sodiothermic reduction, the long sintering time (10-50 h) and additional forming process makes it uneconomical [5][6][7]. As a promising alternative, combustion synthesis (CS) provides a pioneering method for preparing porous intermetallics with a shorter processing time, higher energy efficiency and larger productivity [8].…”