High-Throughput and Systematic Study of Phase Transformations and Metastability Using Dual-Anneal Diffusion Multiples

Abstract

This article highlights the capabilities of dual-anneal diffusion multiples (DADMs) in performing high-throughput and systematic studies of phase transformations and metastability. DADMs create wide ranges of solid solution compositions through elemental interdiffusion during a first anneal at a high temperature. After quenching to ambient temperature, each diffusion multiple can be cut into several slices, and each slice is further annealed individually at a lower/second temperature. Phase transformations take place in the supersaturated regions of the solid solution compositions that are formed during the first anneal, leading to various precipitates due to different driving force, interfacial energy, and other factors as composition varies across the regions in the sample. By subjecting the sliced diffusion multiples individually to different anneal durations and different second anneal temperatures, very large datasets can be collected on phase transformation kinetics and evolution of precipitate morphology as a function of composition, time, and temperature. Metastable phases and their transitions to more stable phases have been systematically observed in the Fe-Cr-Mo ternary system across a wide range of composition, temperature, and anneal time, thus providing a large amount of information on metastability of the phases. The solvi of the metastable and stable phases can be systematically collected for more reliable CALPHAD assessments of the Gibbs free energy of the metastable phases. By adjusting the interfacial energy value in simulations using models such as the Kampmann-Wagner Numerical (KWN) model and matching the simulated precipitate sizes at different compositions with experimentally measured sizes of the corresponding compositions in a DADM, the interfacial energy value can be obtained. Opportunities and challenges in using DADMs to collect large datasets on precipitation kinetics and morphology will be explained to enable full utilization of the capabilities of DADMs in the future. This review not only presents experimental results collected to date, but also explains the vast more datasets that can be collected from DADMs in the future. An approach that iteratively and holistically integrates experimental results with model predictions is advocated as a very effective means to advance the understanding of various phase transformation mechanisms. In this way, the new mechanistic understanding can be integrated to more robust models to simulate the ''abnormal'' behaviors that are observed in DADMs, especially related to sequential precipitations of phases that are common in engineering alloys. Examples are also shown to illustrate the systematic nature of DADMs as a result of their continuously varying composition regions in catching unusual phenomena and emergent trends that are easily missed during studies using discrete compositions afforded by individual alloys.

Microstructure and Properties after Friction Stir Processing of Twin-Roll Cast Al–Mn–Cu–Be Alloy

“…In the HAZ, only the dissolution of θ'-precipitates can dissolve in the matrix. The solvus temperature for these precipitates is about 400 • C [36]. Thus, at 3 mm from the TMAZ-HAZ interface, the temperature was at least 400 • C. Thus, the alloy was relatively stable through short time exposure to temperatures at least up to 400 • C.…”

A Novel Approach for Rapid Material Library Generation Using Laser‐Remelting

“…Such material libraries have effectively been used to investigate phase stabilities and microstructures for the determination of phase diagrams. [28,[30][31][32][33] Mechanical properties such as hardness, yield stress, and elastic properties can be determined using nanoindentation (for example, for the CrCoNi system [34] ) and can be correlated for example to solid solution hardening in single-phase compositions. [35] Time-domain thermo-reflectance was also employed to measure micron resolution spatially resolved thermophysical properties such as thermal conductivity and heat capacity.…”

High-throughput compositional mapping of phase transformation kinetics in low-alloy steel

“…Alternatively, they can be estimated using models, but these require refining and calibrating with plenty of experimental data before they can be applied to practical cases with sufficient accuracy. Consequently, there is a strong appeal to novel methods for highthroughput measurement of phase transformation kinetics, which could dramatically speed-up the development of future high-performance grades [7][8][9][10].…”