Computatioal Materials Design

Integrated Computational Materials Engineering (ICME) is built on the principle of linking materials processing, structure, properties, and performance through structure models, property models and performance models. It aims to accelerate materials development/design and optimize product performance.

Figure 1. Integrated Computational Materials Engineering (ICME) framework for precipitation-strengthened martensitic steels.

An ICME framework on precipitaion has been developed based on Cu precipitation in 15-5 PH maraging stainless steel:

• Cu precipitation kinetics using the Langer-Schwartz-Kampmann-Wagner approach coupled with CALPHAD thermodynamic and kinetic databases (tao-zhou-et-al-2018.pdf)(ze-sheng-et-al-2021.pdf) was calibrated by quantitative characterization of Cu precipitates including information of structure, size, volume fraction, number density and chemical composition as a function of ageing conditions measured using TEM (tao-zhou-et-al-2018.pdf), APT (ze-sheng-et-al-2021.pdf) and in situ SANS (tao-zhou-et-al-2022_2.pdf).
• Except for precipitation, models for other martensite microstructure characteristics like effective grain size and dislocation density were also calibrated by experiments, where the dislocation density was quantified using the modified Williamson-Hall and Warren-Averbach method (tao-zhou-et-al-2019.pdf) through analyzing the peak broadening of XRD data. The strain heterogeneity of the martensite matrix were modelled using a dislocation density-based crystal plasticity model (tim-fischer-et-al-2024.pdf).
• With regards to property modelling, yield strength of the material as a function of ageing treatment was modelled using semi-empirical models (tao-zhou-et-al-2019.pdf); the Cu precipitation hardening contribution to the stress-strain curves were modelled using an analytical flow stress model based on strain gradient plasticity theory (philip-crona-c-et-al-2022.pdf).

Computational Thermodyanimcs and kinetics were used to do the materials and process (heat treatment) desin to design the nanoscale MC and M2C carbides in cost of coarse M6C, M23C6, M7C3, M3C carbides:

Figure 2. Carbides precipitation engineering using computatational thermodynamics and kinetics for high performance stool steels, validated by advanced characterization.

• Cr, Mo, and V are widely used as alloying elements for carbon steels, especially tool steels and heat resistant steels, to increase hardenability, hardness, thermal stability,etc. They can potentially form carbide phases of V-rich MC, Mo-rich M2C and M6C, Cr-rich M7C3 and M23C6,etc., except for Fe-rich metastable carbides, depending on the chemical composition and process conditions. In our first works, mulitple carbides precipitation (tao-zhou-et-al-2020.pdf) and mechanical properties (tao-zhou-et-al-2020_2.pdf) of a high-performance tool steel were investigated, and it was found that coarse types of carbides were the dominant secondary phases at the tempering conditions, which is not ideal for the optimal performance.
• Therefore, carbides precipitation engineering were carried out to tailor the carbides precipitation using computational thermodynamics and kinetics (tao-zhou-et-al-2023.pdf) to achieve the precipitation of high number density of merely fine types of precipitates, as we know from open literature that the fine carbides precipitation has the merits of high precipitation strengthening, weak effects on toughness (also allowing the reduction in carbon content to improve toughness), H trapping for improved resistance to hydrogen embrittlement, higher thermal stability, increasing creep performance,etc.