Controlling microstructures during fusion-based metal additive manufacturing (AM) is often riddled with challenges, particularly with the growing complexity of multiprincipal element alloys (MPEA). New research focusing on the FeMnCoCr system reveals strategies for effective microstructure control, emphasizing the role of phase stability.
The study notes significant advances through the manipulation of manganese content within the alloy, which destabilizes the face-centered cubic (fcc) phase. This adjustment leads to pronounced grain refinement and prevents the undesirable growth of epitaxial columnar grains. By integrating advanced thermodynamic modeling, operando synchrotron X-ray diffraction, and multiscale microstructural characterizations, the team positions itself to elucidate the solidification physics impacting the structures within FeMnCoCr MPEA.
Multiprincipal element alloys have gained traction due to their superior mechanical properties, largely attributed to their unique configurations of 3D transition metals. While promising, their solidification behavior during additive manufacturing poses challenges similar to those faced with conventional alloys, such as the propensity for columnar grain growth, which arises from rapid cooling and thermal gradients.
The research team undertook rigorous experiments, elucidated by their findings, which highlight the advantages of alloy design wherein increasing manganese oxidizes the alloy, which resulted in remarkable grain size reductions exceeding 70%. Measurements indicated average grains sizes dropping to approximately 5.3 micrometers with precise control of solidification conditions. Such structural engineering is groundbreaking, paving the way for next-generation, high-performance AM components.
Mechanical testing also revealed enhanced yield strengths, linked closely to the grain refinement observed. Results indicated increases from 372.7 to 411.9 MPa as manganese content increased across the sampled alloys. While ductility showed slight reductions, the team attributes this to the unique characteristics of the sigma phase, which may hint at its complex interactions within the existing matrix.
Prior investigations have unveiled successful techniques for altering microstructural characteristics through various alloying strategies. This study emphasizes how fine-tuning compositions leads to controlled solidification pathways, fundamentally transforming grain structures and effective material properties. Importantly, the research reinforces the trends observed via the Scheil-Gulliver model, which supports the higher likelihood of bcc phase emergence with increasing manganese concentrations.
Moving forward, the findings set the foundation for systematic exploration within the expansive compositional space of MPEA. Future research is needed to optimize solidification conditions and fully unravel the intertwined relationships between phase stability, microstructure, and mechanical performance.