Papers by Keyword: CALPHAD

Abstract: AZ91 magnesium injection molding is suitable for manufacturing complex-shaped electronic product frames or thin plates. However, the strengthening effect of the Mg₁₇Al₁₂ precipitate in AZ91 is limited, and it tends to dissolve during heat treatment, leading to a lack of particles that can pin grain boundaries and prevent grain growth. To address these challenges, the LAZ561Ca alloy has been developed, offering a reduced density (83% of AZ91), AlLi nanoprecipitates with strong strengthening capabilities, and thermally stable Ca-bearing intermetallics that effectively pin grain boundaries, maintaining a fine-grained structure (~8 μm) even after heat treatment. Experimental results demonstrate that AZ91 undergoes abnormal grain growth after solution treatment at 400°C due to a significant reduction in Zener pinning forces. In contrast, the LAZ561Ca alloy, with stable Al₂Ca precipitates, resists such growth during two-stage heat treatment at 370°C – 400°C. Through the coupling between Thermo-Calc and MICRESS software, multiphase field modeling reasonably reproduced the microstructure evolution during injection molding and heat treatment processes, highlighting its value in establishing digital physical metallurgy models. This study reveals the microstructural mechanisms of magnesium alloys, confirming the critical role of Ca-bearing precipitates in grain growth suppression. It provides a foundation for further optimization of alloy compositions and heat treatment conditions, paving the way for advanced magnesium alloys with enhanced performance in injection molding applications.

Abstract: The development of tailored alloys is an important aspect for enhancing efficiency across diverse applications in mechanical engineering. The use of computer-aided modelling offers an opportunity to enable a more efficient and targeted material development. In the present work, new iron-based alloys with specific properties were developed using the CALPHAD method. The alloy design developing process was carried out by using the simulation software JMatPro® and the data evaluation software EDA®. Using a full factorial plan, various alloys were modelled on the basis of the elements iron, nickel, vanadium, carbon, niobium and chromium. Afterwards, the alloys were narrowed down with regard to the criteria of carbide phase content, formability, and corrosion resistance. Subsequently, two final alloys were chosen based on their properties. Afterwards the selected final alloys were produced by mechanically blending different powder alloys and elements. These alloys were welded onto unalloyed steel using Plasma Transferred Arc welding and were characterised by using x-ray diffraction, scanning electron microscopy, hardness measurements, spark spectrometry and metallography. Subsequently, a verification of the welded samples regarding to chemical composition, phases, and corrosion resistance was carried out. The investigations showed that it was possible to simulate alloys with specific properties using computer-based software, which corresponded with the experimental studies.

Abstract: In this study, the phase formation, microstructure and microhardness of nickel-based superalloy fabricated using a spark plasma sintering technique were evaluated. The microstructure and microhardness of the nickel-based superalloy were explored at diverse sintering temperatures (600 °C - 1050 °C). The phase formations and volume fraction with respect to temperature were predicted by using CALPHAD-based software. The microstructure, phase constitution, and microhardness were evaluated via scanning electron microscope (SEM), X-ray diffraction (XRD), and Vickers hardness tester. The findings indicated that the spark plasma sintering technique enables the development and growth of the necking of particles, enhancing elemental bonding and alloy densification as the temperature increases. The hardness value increases at increasing temperatures, with a maximum value of 353 HV attained at a temperature of 1050 °C.

Abstract: The excellent biocompatibility of Ti and Zr alloys makes them the best candidates for orthopedic implantations. The design of high Ti and Zr-containing alloys that show low Young's modulus for implant manufacturing is the objective of this work. Here, a feed-forward-back propagation neural network was used to speed up the design process and optimize alloy composition. The β-typeTi₄₅-Zr₃₉-Nb₁₂-Mo₄ alloy is designed and showed promising properties. The alloy showed a low elastic modulus of 78 GPa and a high yield strength of 891 MPa resulting in a high elastic admissible strain that made it suitable for orthopedic applications.

Abstract: Phase boundaries of the pseudo-binary Fe-C diagram are key inputs for the prediction and understanding of matrix phase transformation in steels. The mechanical properties, of such steels, however, are often not dictated by the individual phase fractions, accessible through CALPHAD calculations, but by the arrangement of the phases, i.e., the steel’s microstructure. The prediction of these microstructural constituents requires the application of additional models, which are reviewed in the present contribution. Additionally, the current use and limitations for industrial application are presented together with an outlook to future challenges and opportunities in this field of research.

Abstract: Additive manufacturing (AM) provides numerous advantages compared to conventional manufacturing methods, such as high design freedom and low material waste. Among the available materials, precipitation-hardenable aluminum alloys are highly attractive for AM due to their high specific strength and low density. Precise control of the processing conditions during AM and post heat treatment (HT) is required to tailor the final mechanical properties. Consequently, many variables, such as the chemical composition and process and HT parameters, must be considered to design suitable alloys for AM. Experimental investigations are, however, limited in variation of these variables. Therefore, computational alloy design approaches allowing for a faster evaluation of many possible variations must be developed. This work presents a high-throughput approach to determine the precipitation kinetics and thermodynamic properties based on the CALculation of PHAse Diagrams (CALPHAD) method. The developed approach is successfully validated for an Al-Mg-Si-Ti-Fe alloy and is applied to screen 243 combinations of chemical compositions and HT parameters. The results confirm the microstructural stability of the Al-Mg-Si-Ti-Fe system to small composition variations.

Abstract: Steel alloys with high Mn and low C, low Cr wt.%, were designed based on the composition system for traditional high toughness, creep resistance, and longevity for high-temperature applications. In terms of energy resource utilization during production and refining, CALPHAD strategical optimization is preferable for all steel alloys. Thermo-Calc software calculates the phase diagrams α-BCC (Ferrite), and M₂₃C₆ (carbide) phases. The vital temperatures which are highlighted in this work are Ac₃ (threshold temperature at which ferrite is fully transformed into austenite (α→γ)), and A₄ (the threshold temperature at which austenite is fully transformed into Delta ferrite (γ→δ)) are essential for phase transformations. JMatPro software is used to predict the mechanical properties of steel alloys. The interfacial energies with regards to alloying elements for M₂₃C₆ are calculated to be between ~0.272 J/m^-2 to ~0.328 J/m^-2 for α-BCC) matrix, while γ-FCC has interfacial energy ranges to be between ~0.132 J/m^-2 to ~0.168 J/m^-2. This paper focuses on investigating the effect of alloying elements on phase transformations, interfacial energy, coarsening rate of carbides, and many other mechanical properties such as toughness at high-temperature applications using CALPHAD strategies.

Abstract: β titanium alloys have been widely used as implantation inside the human body. Based on this, two β Ti-based medium entropy alloys (namely; Ti₄₅Zr₃₃Nb₂₂ and Ti₄₀Zr₃₃Nb₂₂Mn_5, at. %) were designed using mean bond order (Bo) and mean d-orbital energy level (Md) diagram along with the CALPHAD approaches. The two alloys showed single β phase composed of a dendritic structure. When 5 at. % of Ti was replaced by Mn in Ti₄₅Zr₃₃Nb₂₂ alloy, the compressive yield strength has increased. Furthermore, the hardness was increased upon the addition of Mn. Finally, Ti₄₅Zr₃₃Nb₂₂ alloy showed good cold workability and slight hardness increase upon cold rolling up to 90% reduction.

Abstract: Identification of critical temperatures is paramount for semisolid processing. Application of the principles of differential calculus to identify these temperatures on semisolid transformation curves allows the semisolid metal (SSM) processing window to be determined. This paper synthesizes and organizes a methodology that can be used to this end, namely the differentiation method (DM). Examples are given of the application of the method to 356, 355, and 319 aluminum alloys, which are commonly used in SSM processing, and the results are compared with those of numerical simulations performed with Thermo-Calc^® (under the Scheil condition). The DM is applied to experimental differential scanning calorimetry (DSC) heat-flow data for cooling and heating cycles under different kinetic conditions (5, 10, 15, 20, and 25 °C/min). The findings indicate that the DM is an efficient tool for identifying critical points such as the solidus, liquidus, and knee as well as tertiary transformations. The results obtained using the method agree well with those obtained using traditional techniques. The method is operator-independent as it uses well-defined mathematical/graphical criteria to identify critical points. Furthermore, the DM identifies an SSM processing window defined in terms of a higher and lower temperature for rheocasting or thixoforming operations (T_SSML and T_SSMH) between which the sensitivity is less than 0.03 °C^-1 and, consequently, the process is highly controllable. This DM has already been published in a partial and dispersed way in different works in the past and the aim here is to present it in a more cohesive and didactic way, synthesizing the presented data and comparing them.

Abstract: According to the results of thermodynamic calculations, it has been determined that the usage of alloys with Hf content near to its maximum possible value solubility in the copper matrix is not appropriate. It is more appropriate to use alloy compositions with lower Hf content. With the help of calculations and analysis of experimental data, it has been established that in order to ensure the thermal stability of SPD-formed structures it is sufficient to obtain a concentration of dissolved in copper matrix Hf of about 0.01 at.%. It has also been shown that the average grain size formed by the SPD is a determining factor in the strength properties of these alloys; an increasing Hf concentration in the copper matrix is not always a condition for higher hardness values. However, higher concentrations of dissolved hafnium in the copper matrix will determine the higher mechanical characteristics of precipitation hardening of the alloys after heat treatment.