Thermal stability of nanocrystalline nickel–18 at.% tungsten alloy investigated with the tomographic atom probe

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2003-07, Vol.353 (1), p.74-79
• Main Authors: Choi, P., Al-Kassab, T., Gärtner, F., Kreye, H., Kirchheim, R.
• Format: Article
• Language: English
• Subjects: Atom probe; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Nanocrystalline; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nickel alloys; Other heat and thermomechanical treatments; Physics; Plating; Treatment of materials and its effects on microstructure and properties
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/S0921-5093(02)00670-6

The microstructure of commercially available electrodeposited and thermally aged Ni–W layers with a composition of 18 at.% W was studied by means of field ion microscopy and the tomographic atom probe. In comparison with standard Ni–P or hard chrome coatings, Ni–W layers have a promising application field owing to their specific tribological and electro-erosion properties and in particular because they are manufactured at low cost without harm to the environment. The as-plated state is characterized by the presence of nanocrystalline grains of the Ni-rich fcc phase, with the nanocrystalline structure being preserved up to 700 °C. At this temperature the formation of the ordered Ni 4W-phase (D1a structure) is observed and finally, after aging at 800 °C, the specimens are completely ordered. Whereas in Ni–P the continuous segregation of P and the grain boundaries is responsible for the thermal stability, in Ni–W grain growth is inhibited by the low mobility of the W atoms.