Dissolution of precipitates heated above the solubility line: A Monte Carlo simulation

Abstract

The use of precipitate hardened alloys at high temperatures is often limited by the thermal stability of the precipitates. To improve the understanding of precipitate dissolution after a rapid increase of temperature, we used computer simulation to study a binary A -5 at. % B model alloy. The system consisted of A and B atoms on a quadratic lattice with nearest-neighbor attractive interactions between like atoms. The dynamics was provided by a single vacancy moving across the lattice by exchanges with neighboring atoms. The evolution of the precipitates was studied as a function of time at various temperatures T a , starting from a given initial configuration, which was prepared by ''annealing'' a random mixture of A and B atoms at a low temperature inside the miscibility gap of the alloy. Depending on the new temperature T a , different processes were observed. For T a inside the miscibility gap, the precipitates stayed compact and dissolved partially at first, but afterwards their average size increased again by a coarsening process. For T a outside the miscibility gap, but below the critical temperature T c , the precipitates stayed compact and dissolved completely by evaporation of atoms from their surfaces. Above T c , they decomposed rapidly into many smaller particles in a process that resembles an explosion. A theoretical description of these various processes, based on a phase field model, is presented.

Reversion of precipitates in phase separated soda lime silica glass

“…However, the scattering term K2 increases with increasing dissolution of the precipitates. These findings are in good agreement with results obtained experimentally for the reversion of Guinier-Preston zones in Al-Zn alloys (Okuda, Tanaka, Osamura & Amemiya, 1997) and those obtained from Monte Carlo simulations of the reversion process performed for T<Tc (Zizak, Fratzl & Penrose, 1997). Distance distribution functions calculated from the SAXS curves shown in Fig.…”

“…Afterwards, the largest droplets grow again by slow coarsening. These findings are completely confirmed by the results of Monte Carlo simulations (Zizak, Fratzl & Penrose, 1997) performed for about the same reversion conditions: T < Tb and T /Tc = 0.65. SAXS studies, including in situ experiments, are in progress to investigate the kinetics of the observed coarsening process in more detail.…”

Using Kinetic Monte Carlo simulations to study phase separation in Alloys

“…(2)) (Porta et al, 1997). The dissolution of precipitates when heated above the solubility line occurred depending on the temperature either by an evaporation of atoms or by a process resembling an explosion (Zizak et al, 1997). Starting from a completely phase separated initial configuration, i.e., pure A and B domains separated by a planar interface, the disordering at T ¼ 1 occurred via a different path when using vacancy dynamics compared to Kawasaki dynamics (Aspelmeier et al, 2001).…”

Magnetização e magnetorresistência em ligas granulares

“…(79-84) com Eqs. (54)(55)(56)(57)(58)(59)(60), determinam-se as seguintes relações entre os correspondentes parâmetros:…”

“…Logo depois, os precipitados param de encolher e crescem novamente, o que é um comportamento típico da liga no intervalo de miscibilidade. [56] O aumento de tamanho predomina sobre a dispersão de aglomerados até T = 600 K, os precipitados tornam-se maiores e mais compactos, enquanto a sua concentração cai. A temperaturas mais elevadas, a dissolução de pequenos grãos rapidamente aumenta a concentração de átomos de Co isolados na matriz.…”