Diffusion Creep and Grain Growth in Forsterite +20 vol% Enstatite Aggregates: 1. High‐Resolution Experiments and Their Data Analyses

We conducted uniaxial compression and grain growth experiments on fine‐grained (~1 μm) forsterite +20 vol% enstatite aggregates. Based on analyses of the sensitivity of the strain rate as a function of stress, we find power law creep at low stress, Newtonian creep at intermediate stress, and again power law creep at high stress, which correspond to interface‐controlled diffusion creep, grain boundary diffusion (Coble) creep, and a dislocation‐controlled process, respectively. The creep rate of these samples is well expressed by a combination of strain rates of these three mechanisms where interface‐controlled and Coble creep rates are combined as series‐sequential processes, while the rate of the dislocation process is added with them as a parallel‐concurrent process. Mechanical data collected continuously during the application of a constant load but while slowly changing temperature were decomposed into data for every 1 °C, which allowed consideration of >600 mechanical data points from 1054 to 1370 °C. The data were analyzed using Bayesian statistics implementing a Markov chain Monte Carlo method imposed on the above constitutive equation, resulting in the best fit flow law parameters for interface‐controlled and Coble creep. Samples were annealed for 500 hr at various temperatures. A comparison of the final grain sizes as a function of temperature on an Arrhenius plot resulted in an activation energy for grain growth similar to that observed for grain boundary diffusion during Coble creep of these materials.