Measurements of liquid-phase diffusion coefficients for dilute W and Mo in molten Ni were made using a pulsed ion-beam melting technique. A high-intensity beam of N ions was focused on the surface of a Ni substrate that was implanted with known concentration profiles of W and Mo. Melting of the surface to a depth of ~1μm allows broadening of the implant profiles while molten. Solute concentration-depth profiles were determined before and after melting using Rutherford back-scattering spectrometry. Using a series of numerical simulations to estimate the melt history and diffusional broadening at 1755 to 2022K, an effective diffusion coefficient was determined in each case by comparison to the measured depth profiles. This was found to be 2.4 x 10–5cm2/s for W and 1.6 x 10–5cm2/s for Mo, with an additional systematic uncertainty of some ±0.5 x 10–5 due to instrumental and surface effects.

J.P.Leonard, T.J.Renk, M.O.Thompson, M.J.Aziz: Metallurgical and Materials Transactions A, 2004, 35[9], 2803-7

Figure 29

Self-Diffusion of Ni in Ni and Alloys

(Filled squares: Ni, open squares: Ni80P20, triangles: Pd40Ni40P20,

open circles: Pd43Ni10Cu27P20, filled circles: Pd40Ni10Cu30P20)