Sustainability in Materials

Sustainable Alloys

New Alloys for High Performance

Designing new alloys is critical to achieving sustainability goals because it enables the development of materials that are stronger, lighter, more durable, and more recyclable. Developing sustainable materials also supports new applications, such as developing first-wall materials for next-generation fusion reactors.

For example, the next generation alloys for the aerospace industry need to be lighter to accommodate greener and more efficient aerospace vehicles. In order to develop these high-performance alloys, a deeper understanding of titanium aluminide (TiAl) systems is needed. This was the purpose of the ADVANCE Project, founded by the European Union’s Horizon 2020 research and innovation program as part of the Clean Sky 2 initiative, whose goals are to reduce the aircraft noise and CO2 and NOX emissions in an effort to make tomorrow’s aircraft greener and more efficient.

How Thermo-Calc was Used

Partnering Thermo-Calc Software with Max-Planck-Institut für Eisenforschung GmbH (MPIE), Helmholtz-Zentrum hereon GmbH (Hereon), and Montanuniversität Leoben (MUL) and MTU Aero Engines AG, the ADVANCE project consisted of an extensive and ambitious experimental program to generate detailed and accurate phase equilibrium data for a series of homogenous Ti-Al-X alloys of high purity. The aim of the project was to resolve existing experimental controversies and to determine missing data points of relevance and ultimately support modeling activities consisting of assessing and re-optimizing individual subsystems and the development of cutting-edge CALPHAD databases for TiAl alloys.

New Alloys for Recycled Materials

One of the main strategies to reducing the carbon footprint associated with the production of, particularly primary steel and aluminum, is the emphasis on using recycled scrap where possible. Therefore, there is increasing interest in designing impurity‑tolerant, “recycling‑friendly” alloys that accommodate the variability of scrap inputs without compromising performance. Similarly, other development work is being performed to reduce the dependence on critical materials. Such examples are provided under the appropriate sub-sections on this page for aluminum, steel, and critical materials.

Examples of how Thermo-Calc has been used for this are provided under the appropriate sub-sections below on this page:

Design of Scrap-tolerant Aluminum Alloys

Design of Scrap Tolerant Steels

Critical Materials

Sustainable Processing

Sustainable processing focuses on designing and optimizing manufacturing processes to reduce environmental impact, conserve energy and resources, and minimize waste throughout a material’s lifecycle This includes selecting processes that use less energy (e.g., lower-temperature / shorter-duration heat treatments), enabling the use of recycled or scrap-based inputs, and reducing emissions of greenhouse gases and pollutants. Sustainable processing also involves minimizing material loss through improved casting yields, better joining techniques, or closed-loop recycling systems.

Refining

Primary nickel production using conventional methods such as rotary kiln-electric furnace (RK-EF) and high-pressure acid leaching (HPAL), emit up to 45 tons of CO₂ per ton of Ni and are highly energy intensive. Furthermore, the demand for nickel is projected to exceed 6 million tons annually by 2040, largely driven by the electrification of the transport sector.

How Thermo-Calc was Used

To address this, Manzoor et al [2] have proposed a method for producing nickel from low-grade laterite ores using a hydrogen-plasma smelting reduction (HPSR) process, which consolidates ore drying, calcination, reduction, and refining into a single furnace operation, offering up to 84% lower CO₂ emissions and 18% energy savings compared to RK-EF routes.

This process depends on the thermodynamic control of the reduction atmosphere, allowing selective reduction of nickel over iron from complex silicate matrices. The authors used Thermo-Calc to model the equilibrium behavior of molten laterite in an Ar–10%H₂ atmosphere at 1600 °C. These simulations helped determine the optimal oxygen removal window required for high-grade ferronickel formation (70–90 wt% Ni) and recovery (60–90 wt%). The Thermo-Calc results were validated through experiments showing Ni-rich nodules (up to 97.3 wt% Ni) and minimal impurities.

Al Recycling

The recycling of aluminum alloys is vital to sustainability efforts because it uses only about 5% of the energy required to produce primary aluminum, dramatically reducing greenhouse gas emissions. It also preserves natural bauxite resources and lowers landfill waste (red mud).

Design of Scrap-tolerant Aluminum Alloys

Considerable work has gone into developing scrap-tolerant aluminum alloys that meet industrial casting standards without additional refining. In a paper by Shurkin et al [3], an approach was described to developing high-strength aluminum alloys that are tolerant to Fe and Si impurities commonly found in recycled aluminum. In this case, the authors investigated six Al-8%Zn-3%Mg-based alloys doped with Ca, Fe, and Si to promote the formation of recycling-compatible microstructures.

How Thermo-Calc was Used

To guide alloy development, Thermo-Calc with the TCAl Database was used to predict solidification paths and equilibrium/non-equilibrium phase diagrams. These simulations predicted critical transformations such as the formation of beneficial phases like Al₁₀CaFe₂, Al₂CaSi₂, and (Al,Zn)₄Ca, as well as undesirable phases like Mg₂Si and Al₃Fe under different cooling conditions. Calculations were then used to customize a two-step heat treatment (450 °C, 3h + 520 °C, 3h) by locating phase transformation ranges and guiding spheroidization and dissolution of intermetallics. Among all the variants, the AlZnMg₁CaFeSi alloy exhibited the best performance, combining sufficient hardness, good ductility, and a refined microstructure compatible with high-reduction processing.

The plots below were recreated in Thermo-Calc based on Shurkin et al [3] and show the desirable heat treatment window in the alloys representing typical temperatures where such 7xxx series are heat treated. The Scheil simulation shows that the brittle phases Al₁₃Fe₄, and Mg₂Si along with the T_Phase will stabilize in the presence of Fe, Si, as pointed out by Shurkin et al [3].

Impurity Control in Secondary Aluminum Production

Fluxes to Refine and Protect Molten Al

In aluminum recycling, molten salts (typically NaCl, KCl, or mixed fluxes) are used to protect molten aluminum from oxidation and reduce dross formation, improving overall metal recovery. They also act as refining agents, helping remove impurities such as alkali metals, alkaline earth metals, and non-metallic inclusions by chemically binding them within the flux.

How Thermo-Calc Can Be Used

The TCSALT Database can be used to study how the flux composition impacts impurity removal during aluminum recycling. In the example shown below, the Ca and Na reduction in an Al-4.5% Mg melt with an initial amount of 200ppm Ca and 200ppm Na for a KCl-MgCl2 flux is presented. By increasing the MgCl2 content in the flux, Ca and Na can be removed from the Al melt (left) while simultaneously maintaining the Mg content (right).

Fe Impurities in Recycled Al Alloys

Another critical challenge in aluminum recycling is managing Fe impurities present in recycled aluminum scrap, which can form brittle, needle-like phases such as β-Al₉Fe₂Si₂, which reduce mechanical performance. By adding Mn (sometimes with Cr), Fe is “trapped” into forming α-Al₁₅Si₂Mn₄, a more compact and less detrimental intermetallic phase. These Mn-stabilized phases can either remain harmlessly in the microstructure or, under some conditions, be separated from the melt.

How Thermo-Calc Can Be Used

Thermo-Calc can be used to understand the chemical reactions and predict the Mn addition and processing temperature, as seen in the images below.

Steel Decarbonization

Today, an average 1.75 tons of CO₂ is emitted for every ton of steel produced and it is estimated that ~8% of global CO₂ emissions are derived from the steel industry. A broad range of strategies are being considered for the decarbonization of the steel industry, which primarily involve the use of more recycled steel [4].

Electric Arc Furnace Secondary Steelmaking Metallurgy

Electric Arc Furnaces (EAFs) are crucial to steel decarbonization because they primarily use recycled scrap and Direct Reduced Iron (DRI) instead of coal-based blast furnaces. When powered by renewable electricity and combined with low-carbon DRI, EAFs can reduce CO₂ emissions by up to 70%, enabling more sustainable, circular steel production at scale.

How Thermo-Calc was Used

Thermo-Calc can support steel decarbonization by modeling secondary-steelmaking in EAFs, including steel–slag–gas equilibria and solidification processes. Using the TCOX Database in conjunction with the Process Metallurgy Module, process engineers can optimize scrap/DRI blends, deoxidation and desulfurization practices, slag basicity, and temperature windows, and predict inclusion and tramp-element partitioning.

Using this approach, and as part of an initiative from Georgsmarienhütte GmbH (GMH) to advance Green Steel production,, Thermo-Calc Software and (GMH) have developed a fully automated physical model of secondary steelmaking metallurgy that simulates the entire production chain including tapping from the EAF, ladle furnace (LF), vacuum degassing (VD), and the final treatment process (FTP). The model has been used to gain insights into the metallurgical processes and significantly improved process understanding. Consequently, it facilitates the development of strategies, such as increasing ladle life.

Design of Scrap Tolerant Steels

One important challenge associated with the use of scrap steel is an increase in the residual content of elements such as Cu, Sn, Zn, and Ni with continual recycling, which negatively affects hot workability and mechanical performance. There are numerous papers in the published literature where CALPHAD-based tools have been used to study the effects of tramp elements on recycled steel, for example see references [6], [7], [8], where the goals are either to produce grades more tolerant to the tramp elements or identify ways of reducing them.

How Thermo-Calc was Used

For example, Mehta et al [6], investigated the impact of Cu and Sn on solidification microstructure and cracking. Traditional metallurgy cannot easily remove these impurities, and typical specifications limit Cu content in high-performance steels to <0.2 wt%. The authors investigated whether the cracking caused by micro-segregation of Cu and Sn during solidification could be controlled by limiting the alloy composition. Using Thermo-Calc’s Scheil Solidification calculator and the Diffusion Module (DICTRA) in conjunction with the TCFE and MOBFE Databases, they calculated that Cu and Sn can segregate up to 4–6 times their nominal addition. However, cracking only becomes problematic above certain threshold values: >3 wt% Cu or >0.15 wt% Sn in the alloys studied. Therefore, they recommend keeping compositions below Fe–3Cu and Fe–1Cu–0.15Sn for casting steels at typical cooling rates (around 10 K/s). This computationally guided, compositional control provides a practical guideline for recycling-friendly, scrap-tolerant steels to avoid cracking issues associated with higher impurity.

Removal of Tramp Elements

Removing tramp elements such as copper (Cu) from liquid steel is a major metallurgical challenge. Unlike many other impurities, copper does not readily oxidize under conventional steelmaking conditions and therefore cannot be removed through standard refining processes. Instead, it remains dissolved in the melt, where it can cause detrimental effects during downstream processing. Thermo-Calc can support the development of novel refining strategies by simulating thermodynamic equilibria and phase transformations, enabling researchers to identify conditions and materials that may promote the removal of tramp elements from liquid steel, as demonstrated in Filho et al [7].

How Thermo-Calc was Used

The paper by Filho et al [7] explored a novel thermodynamic approach to removing Cu from steel scrap. The authors demonstrate that evaporation of Cu from Fe–Cu–O melts can be effectively triggered when the melt reaches a critical oxygen concentration of ~22 wt%. Using hydrogen plasma-based reduction (HyPR) and inert plasma melting experiments, they show that Cu concentrations can drop from 1 wt% to <0.1 wt% without significant iron loss under optimized conditions. To support this, the study uses Thermo-Calc with the TCOX Database and SSUB Database to simulate equilibrium phase behavior, gas–liquid partitioning, and copper activity across temperature and oxygen gradients. Thermo-Calc was essential in identifying the critical O threshold for maximizing Cu activity and predicting Cu evaporation under various thermal and atmospheric conditions. This strategy enables scrap purification during primary iron production, allowing for Cu recovery.

Critical Materials

Critical raw materials (CRMs) such as rare earths, Nb, Ta, and Co are essential for modern technologies, from renewable energy systems like wind turbines and solar panels to electric vehicles and advanced electronics. The sustainability importance of critical raw materials stems from three key factors: availability, environmental impact, and supply chain resilience. Additionally, extraction and refining often involve high energy consumption, water use, and environmental degradation, so efficient use, recycling, and substitution are crucial. Mitigating dependence on CRMs is a major focus for sustainability and supply chain resilience and key strategies include a) material substitution to reduce the amount of or completely eliminate the need for CRMs and b) recycling CRMs from end-of-life products and industrial waste.

How Thermo-Calc was Used

As an example of material substitution to reduce critical raw materials, Singh et al [8] developed a computational framework for designing high-performance multi-principal element alloys (MPEAs) that eliminate the use of CRMs while retaining desirable mechanical properties. Integrating CALPHAD-based predictions from Thermo-Calc and the TCHEA Database with machine learning (ML), a dataset of 3,608 entries was generated using Thermo-Calc’s Property Model Calculator, predicting Vickers hardness for unary and binary alloys without relying on experimental data. This was then used to train multiple regression models. Novel CRM-free alloy compositions were then inversely predicted using five metaheuristic algorithms. An experimental validation with Al_6.25Cu_18.75Fe₂₅Co₂₅Ni₂₅ showed strong agreement with both ML and Thermo-Calc predictions, confirming the framework’s utility for sustainable alloy discovery

Green Energy

From a broader sustainability perspective, the energy sector’s focus includes key areas such as electrification of energy use (including permanent magnets for electric motors), energy storage solutions (such as batteries, thermal energy storage, and hydrogen storage) and nuclear energy (fission and fusion).

Permanent Magnets

Anisotropic bulk permanent magnets based on Nd-Fe-B alloys are the most widely used types of rare earth magnets, and their fabrication requires precise control of their microstructure. The TCPMAG Database is our thermodynamic and properties database for applications to permanent magnetic NdFeB-based alloys and can be used, for example, to predict the Curie temperature of such materials as a function of composition and temperature.

Thermal Energy Storage

Metallic Phase Change Materials (mPCMs) are thermal energy storage technologies that use metals and their alloys to store and release heat through solid–liquid transitions. Their high thermal conductivity and volumetric energy density enable rapid heat transfer and compact storage, making them ideal for high-temperature applications. These systems are particularly important for concentrated solar power, industrial waste heat recovery, and high-temperature thermal batteries, where efficient, reliable, and long-lasting energy storage is critical.

How Thermo-Calc was Used

Villada et al [9] have explored the feasibility of using mCPMs based on Al–Si alloys derived from scrap metal for thermal energy storage in the 500–600 °C range. Four Al–12.6 wt% Si alloys were synthesized with varying impurity levels (Fe, Cu, Mg, Mn, Zn) as surrogates for different recycled aluminum grades and Thermo-Calc was used as part of the alloy design and preliminary evaluation. Using the TCAL Database, the authors simulated how individual impurities affect solidus and liquidus temperatures and latent heat. Thermo-Calc also provided density data for calculating thermal conductivity. Results revealed that although impurities strongly influenced melting behavior and thermal diffusivity at lower temperatures, their effect on heat capacity and liquid-state properties was minor, thus providing a potential market for scrap aluminum.

The plot below is a parallel property plot based on the work by Villada et al [9] showing the effect of the addition of Fe, Cu on Al-12.4Si alloy. From the alloys selected (red), it is seen that Fe positively affects heat capacity and Cu negatively affects thermal conductivity and heat capacity. Calculations were conducted at a constant temperature of 500 ⁰C.