Solute Diffusion in Liquid Nickel Measured by Pulsed Ion Beam Melting

Abstract

Measurements of liquid-phase diffusion coefficients for dilute tungsten and molybdenum in molten nickel were made using a pulsed ion-beam melting technique. A high-intensity beam of nitrogen ions is focused on the surface of a nickel substrate that was implanted with known concentration profiles of W and Mo. Melting of the surface to a depth of 1 m allows broadening of the implant profiles while molten. Solute concentration-depth profiles were determined before and after melting using Rutherford backscattering spectrometry. Using a series of numerical simulations to estimate the melt history and diffusional broadening for mean liquid temperatures in the range 1755 to 2022 K, an effective diffusion coefficient is determined in each case by comparison to the measured depth profiles. This is found to be (2.4 0.2) 10^-5 cm²/s for W and (1.6 0.4) 10^-5 cm2/s for Mo, with an additional systematic uncertainty of 0.5 10 5 due to instrumental and surface effects.