Consistency in material properties and performance is critical to the aerospace industry. Small variations in material chemistry or process windows can have a large impact on the final part performance. The ability to predict and adjust for these variations can reduce scrap and part re-work. Metallurgists and process engineers responsible for heat treatments must adapt their processes when input variables change.
In an article recently published in “Heat Treat Today”, Adam Hope and Paul Mason from Thermo-Calc Software Inc, discuss how modeling and simulation tools such as Thermo-Calc can support engineers in their research.
In the article “Predicting the Effects of Composition Variation for Heat Treatment of Aerospace Alloys”, Adam Hope and Paul Mason address questions that heat treaters are faced with and discuss how materials data is crucial to the decision-making process. Materials property data can be generated with experiments, but this can be costly and time consuming. Handbooks might have data for known alloys, yet often only for the nominal composition, which may not be suitable for material processed under a novel route. Fortunately, modeling and simulation tools can help fill this knowledge gap.
The examples in the article illustrate how modeling and simulation tools such as those based on the CALPHAD approach can be used to predict variability arising due to material composition. Hence, researchers and engineers can explore in-depth how materials will react and understand how to create correct materials for the aerospace industry.
Integrated Computational Materials Engineering (ICME) and CALPHAD
Integrated Computational Materials Engineering (ICME) is an approach to designing products, the materials they are comprised of and their associated materials processing methods. The article discusses this approach and explains how computational thermodynamics, specifically CALPHAD-based tools like Thermo-Calc, enable the prediction of the thermodynamic properties and phase stability of an alloy under stable and metastable conditions. The article then give several examples showing how the tools are currently being used.
Predicting Heat Treatments for Additively Manufactured Parts
Many additive manufacturing processes subject the material to rapid solidification with multiple subsequent reheat cycles. The effect of these thermal cycles on material properties is not always known. Typically, it does not result in the properties that a similar cast or wrought metal would have. In one study discussed in the article, the Scheil-Gulliver model for solidification in Thermo-Calc in conjunction with the Diffusion Module (DICTRA) was used to explore this issue. The Precipitation Module (TC-PRISMA) predicted the precipitation kinetics of the deleterious delta phase for nominal feedstock compositions, as well as the compositions measured at dendrite boundaries.
Gas Carburizing Highly-Alloyed Steels
Highly-alloyed stainless steels can be gas carburized to increase the surface hardness, as well as to improve the overall mechanical characteristics of the surface. CALPHAD-based tools can be used to identify suitable alloy compositions and heat treat windows, which are optimal for the application prior to testing in the laboratory. In one study, thermodynamic calculations performed with Thermo-Calc and diffusion simulations performed with the add-on Diffusion Module (DICTRA) were used to optimize a carburization heat treatment schedule for their specific steel composition.
Predicting β-transus Temperatures in Ti-Alloys
The β-transus temperature in Titanium alloys is sensitive to small changes in chemistry, especially oxygen content. Thermo-Calc and the Diffusion Module (DICTRA) can be used either to calculate β-transus temperature if the exact chemistry is known, or to determine the potential distribution of β-transus temperatures for a given chemistry range.
“Predicting the Effects of Composition Variation for Heat Treatment of Aerospace Alloys” written by Paul Mason and Adam Hope was published in “Heat Treat Today” in March 2020.