Thermo-Calc Used to Predict Phase Fractions when Partially Substituting Cobalt

Cobalt symbol on blue background with the words Thermo-Calc used to predict phase fractions when Partially Substituting Cobalt

A new publication in Acta Materialia investigates the possibility to partially substitute Cobalt with entropic alloys, focusing on the relative stabilities of the fcc and hcp structures.

Cobalt-base alloys are important for high temperature applications due to their possibility to form duplex fcc + hcp structures and their low stacking fault energy. However, there is an interest in substituting cobalt for economical, ethical and health reasons.

Both the thermodynamic and kinetic calculations in this publication were performed with Thermo-Calc software and the Diffusion module (DICTRA) together with the thermodynamic database TCHEA and the kinetic database MOBNI. Thermo-Calc was used to predict the phase fractions of fcc and hcp which were compared with experimental results. In the article, it is stated that the calculated thermodynamic values correlate relatively well with the experimental values. The authors concluded that designing duplex fcc + hcp Co-based alloys with computational tools is feasible.

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Thermo-Calc used to Estimate Critical Temperatures in Type 410 Steels

A person welding with the words Thermo-Calc used to estimate critical temperatures in type 410 steels written on top

In the paper Alloy Composition and Critical Temperatures in Type 410 Steel Welds, Thermo-Calc was used to evaluate the effect of alloy composition on critical temperatures (A1 and A3) in Type 410 steels.

Type 410 steels are typically welded by using consumables with matching composition. However, this type of steel has shown to have poor weldability which is related to formation of hard and brittle martensite in the weld zone, hydrogen-included cracking or retention of δ-ferrite which affects the toughness. One theory that explains the inconsistent toughness is that the wide composition ranges of the base metal results in wide variations of the A1-temperature. In the paper, this theory was investigated with the design of experiment (DoE) approach using Thermo-Calc to perform thermodynamic simulations. Thermo-Calc together with the TCFE8 database was used to predict A1 and A3 temperatures for various compositions.

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Paper Investigates Carbon Behavior in the Heat-Affected Zone of Grade 91 Steel using DICTRA

A macro view of the weld metal, heat affected zone and base metal from section with the words "investigation of carbon behavior in the heat-affected zone of grade 91 steel using DICTRA".
A macro view of the weld metal, heat affected zone and base metal from section.

In a paper out of Ohio State University, the mechanism of δ-ferrite retention in the coarse-grained heat-affected zone is studied.

The efficiency of fossil-fired and nuclear power plants has caused raised operating temperatures, which requires use of creep-resistant stainless steels in the hottest regions of the plant. Grade 91 steels are used in the lower-temperature heat recovery steam generators. To be able to join the high- and low-temperature sections, dissimilar metal welds (DMWs) are necessary. The problem with using DMWs is that it often results in extensive carbon diffusion near the fusion boundary which creates brittle and large carbides that make the welds weaker.

Creep strength-enhanced ferritic (CSEF) steels are today welded with Ni-based filler metals to reduce the carbon diffusion between the dissimilar steels, which reduces the formation of hard and soft zones that negatively affects the creep strength. However, the high concentration of carbide forming elements in Ni-based alloys still creates a driving force for carbon diffusion toward the filler metal.

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Applications of Thermo-Calc to Additive Manufacturing of Metals

A few pieces of 3D printed metal components.Additive manufacturing of metals is transforming materials design and processing in ways unimaginable even 10 years ago, offering the freedom to produce complex parts without the restraints of traditional manufacturing. 

However, Additive Manufacturing is a complex process and the mechanical properties of these materials and the parameters which control their reproducibility are not yet well understood. For example, additive processes are typically associated with rapid cooling rates and large thermal gradients. This can give rise to high levels of residual stress in the final part and local inhomogeneities in alloy composition during solidification. Also, the effect of multiple thermal cycles on material properties is sometimes unknown and typically does not result in the properties of a similar cast or wrought metal.

A lot of research is now being published in this area by members of our community using Thermo-Calc and we want to share some of this work with you. Below you will find a sampling of some of the work that is being done using Thermo-Calc and our add-on modules for diffusion and precipitation to research additive manufacturing of metals. Continue reading

DICTRA used to model changes to Ni-based superalloy during Interdiffusion

In a  paper published in the January 2016 issue of Journal of Phase Equilibria and Diffusion , Vol. 37 No. 2 2016, the homogenization model within DICTRA together with the TCNI and MOBNI databases were used to model the interdiffusion processes in the Ni-based superalloy CMSX-10 and was shown to have good agreement with experimental values. Continue reading

TC-Toolbox for MATLAB® with Thermo-Calc Used to Optimise a Nickel-based Superalloy

In a 2015 issue of Metallurgical and Materials Transactions A a group at Michigan University, Department of Materials Science & Engineering used TC-Toolbox for MATLAB® in conjunction with Thermo-Calc to optimise a nickel-based alloy, resulting in a lower cost alloy with 25% improvement in properties when assessed with their utility function. Continue reading