Irradiation-Induced Nanoprecipitation in Ni-W Alloys

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2015-03, Vol.46 (3), p.1046-1061
• Main Authors: Lee, Jaeyel, Lear, Calvin R., Zhang, Xuan, Bellon, Pascal, Averback, Robert S.
• Format: Article
• Language: English
• Subjects: Alloys; Annealing; Blocking; Carbides; Characterization and Evaluation of Materials; Chemical precipitation; Chemistry and Materials Science; Density; Irradiation; Materials Science; Metallic Materials; Metallurgy; Nanostructure; Nanotechnology; Nickel base alloys; Structural Materials; Surfaces and Interfaces; Thin Films
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-014-2704-4

The evolution of Ni-W alloy thin films subjected to Kr irradiation at room temperature and subsequent annealing at 1123 K (850 °C) was studied by X-ray diffraction and transmission electron microscopy. Irradiation resulted in significant increase in grain size, from ~20 nm in the as-grown state to over 300 nm after irradiation and annealing. The compositions selected for the study, 18 and 23 at. pct W, resulted in the formation of an ordered Ni 4 W matrix after annealing. Remarkably, in the Ni-23 at. pct W films, irradiation followed by annealing induced the precipitation of two families of Ni 2 W 4 C carbides, large blocky ones at grain boundaries, and intragranular nanocarbides, ~5 to 20 nm in size and with a high number density, 9.0 × 10 22  m −3 . In contrast, only blocky Ni 6 W 6 C carbides formed in control specimens directly subjected to annealing. The intragranular Ni 2 W 4 C nanocarbides displayed an orientation relationship with the Ni 4 W matrix, and they appear to be effective traps for implanted Kr ions, since nanobubbles formed on their periphery. The results suggest that non-equilibrium processing can be used to nucleate nanocarbides in the grain interiors of Ni-W alloys, and that this may improve alloy properties, including radiation resistance.