Material Matters – Additive Manufacturing of Metallic Alloys

Dr. Rajarshi Banerjee´s primary research focus is on identifying the underlying mechanisms and phase transformations governing microstructural evolution and microstructure-property relationships in complex multi-phase, multi-component materials systems, such as high entropy alloys (HEAs), titanium base alloys, nickel (and cobalt) base superalloys, and magnetic alloys. He works extensively on additive manufacturing (AM) technologies such as directed energy deposition (DED) and laser powder bed fusion (LPBF), as well as conventional thermo-mechanical processing.

Dr. Rajarshi Banerjee has pioneered efforts on AM of functionally/compositionally graded alloys using DED for the past twenty years. The use of advanced characterization techniques, spanning over a range of length scales, including scanning and transmission electron microscopy and atom probe tomography (APT), constitute a common thread tying his multiple research activities.

These techniques are used to identify the underlying mechanisms and phase transformations governing microstructural evolution and microstructure-property relationships in these complex multi-phase, multi-component materials systems.

Read more about Dr. Raj Banerjee Materials Science and Engineering >>

Abtract:

While there is an overwhelming amount of worldwide activity on 3D printing or additive manufacturing (AM) of alloys, the efforts have been largely focused on maturing this technology for fabricating near-net shape components. Microstructural investigations on such AM processed alloys is often limited to x-ray diffraction/tomography and optical/scanning electron microscopy (SEM).

While such investigations are useful as for preliminary scanning of larger scale defects and phases, they often miss critical features at finer length scales (tens of nm to Å) which can substantially impact the properties. In parallel there has been rapid development of advanced microscopy techniques, such as high-resolution SEM coupled with electron backscatter diffraction (EBSD), scanning/transmission electron microscopy (S)TEM, and atom probe tomography (APT). Applying these higher spatial and compositional resolution microscopy techniques to AM processed alloys can reveal novel microstructural features and the underlying fundamental mechanisms leading to such features. Furthermore, these features impact the mechanical and functional properties.

This talk will attempt to demonstrate these aspects in AM processed diverse metallic systems via the following examples:

1. Influence of thermo-kinetics associated with the AM process on fine scale omega and alpha precipitation and strain transformability in beta Ti alloys, highlighting the differences between laser powder bed fusion (LPBF) and directed energy deposition (DED) processing.
2. Ordering and clustering in a compositionally graded DED processed AlCo1-xCrxFeNi high entropy alloy and its impact on magnetic properties and microhardness.
3. Dislocation cell structure overlaid on compositionally segregated solidification substructure in LPBF processed Nb-base alloy C103 (Nb-10Hf-1Ti) and its impact on tensile yield strength.
4. Competing ordering/clustering (phase separation) tendencies in LPBF processed refractory high entropy alloys (RHEAs) leading to a nanoscale B2 + BCC mixture exhibiting very high strengths.

These representative examples will highlight the power of combining TEM, SEM-EBSD-ECCI and APT analysis, towards revealing the micro/nano-structure of AM processed metallic alloys and its influence on mechanical/functional properties.