INTRODUCTION: Developing biodegradable implants is of growing interest to help fight antimicrobial resistance. Magnesium alloys are candidates for orthopaedic applications, but there is a need for improving their corrosion resistance[1]. Alloying reduces corrosion rates, but further improvement could be achieved by microstructural tuning using additive manufacturing (AM). However, process parameter optimization is time and resource consuming, motivating the use of numerical modelling to accelerate alloy development. The aim of this study was to predict the microstructure-temperature relationship for a MgCaZn alloy using the CALPHAD method as input for a classical nucleation and growth theory (CNGT) simulation. To achieve this, raw powder feedstock was characterized, along with a minimal number of printed samples.
METHODS: The powder composition was identified as Mg63.2Zn32Ca4.8 by Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) and compared to the results of ToF-ERDA (Time-of-Flight Elastic Recoil Detection Analysis). The composition of printed samples was also measured to estimate evaporation rates during printing.
X-ray diffraction (XRD) was used for phase identification. Differential Scanning Calorimetry (DSC) was used to characterize phase transitions and generate Time-Temperature-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams.
RESULTS: Three cold crystallizations were distinguished (see Figure 1) and analysed by XRD. Kissinger analysis[2] was done on four heating rates and the results are shown in Table 1 together with the transformation onset temperatures. Metastable phases were formed at the first (Tp1, phase Mg51Zn20) and third crystallisation (Tp3, IM4). Thermodynamic data and unit cell parameters from experimental results and literature[3] were used in a Python code to simulate CHT and TTT diagrams for comparison with the experimental results. The experimental data was used to validate the numerical model.
DISCUSSION & CONCLUSIONS: The overall transitions and phases agreed with previous literature, with only significant differences in the obtained energies of activation. The first simulated TTT diagram to our knowledge has been generated for this composition and phases. Synchrotron studies and more compositions should be tested for proper validation of the methodology.
REFERENCES:
[1] Radha, R., & Sreekanth, D. (2017), J. Magnes. Alloy, 5(3), 286–312.
[2] Kissinger, H. E. (1957) Anal. Chem., 29(11), 1702–1706.
[3] Mezbahul-Islam, M. et al. (2014) Calphad, 46, 134–147.
ACKNOWLEDGEMENTS: This work was supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation and the Swedish Research Council (grant numbers 2019-00191 and 2023-00155) supporting the Ion Technology Center.
2025.