Online Lecture by prof. Sir Harry Bhadeshia

Diffusion-controlled growth in multicomponent steels, with steep concentration gradients

Speaker: prof. Sir Harry Bhadeshia, Cambridge University, United Kingdom.

Title:
Diffusion-controlled growth in multicomponent steels, with steep concentration gradients.

Abstract:
Since the work of Coates and others, it has been considered that diffusion-controlled growth in multicomponent systems occurs in one of two ways, assuming local equilibrium at the transformation front. Thus, the growth either involves the long-range partitioning of substitutional solutes, or a tiny amount of partitioning so that the product phase essentially has the same composition as that of the parent. But in the latter case, steep gradients in concentration are predicted at the transformation front.
Indeed, these phenomena are encoded in most popular algorithms for estimating growth rates and therefore, are applied widely.
Coates himself recognised the difficulty of steep gradients. I will present some quantitative arguments to demonstrate that local equilibrium with negligible partitioning cannot exist and show that there is no experimental evidence to suggest otherwise.

The session was chaired by prof. Maria Santofimia Navarro (TU Delft).