Malik A. Blackman
Advisor: Prof. Meisha L. Shofner & Dr. Camden A. Chatham

will defend a doctoral thesis entitled,

Exploring Calorimetry as a Materials Screening Tool for Laser Based Powder Bed Fusion

On

Monday, June 15th at 12:00 p.m.
IBB Suddath Seminar Room 1128

And via

MS TEAMS

 https://teams.microsoft.com/meet/27836548204445?p=pguBE8RkBhzN3cCbiX 

Committee
            Prof. Meisha L. Shofner – School of Materials Science and Engineering (advisor)
            Prof. Natalie Stingelin – School of Materials Science and Engineering 
            Prof. Donggang Yao – School of School of Materials Science and Engineering

            Prof. Tequila A. L. Harris – School of School of Materials Science and Engineering 
            Dr. Camden A. Chatham –Savannah River National Laboratory (co-advisor)

Abstract

Developing unique temperature protocols in fast scanning calorimetry (FSC) to screen for material compatibility with laser powder bed fusion (PBF-LB) is suggested to be a key factor for increasing this additive manufacturing (AM) technique’s material library. PBF-LB printing is utilized across industries such as automotive and aerospace, which require high performance materials under intense environmental conditions. Unsurprisingly, investigations into polymeric printing reveal Polyamide 12’s (PA12) domination of the research literature and application space - whereas studies into high-temperature, unique crystal structure polymers are far less common for PBF-LB. Therefore, further advancements in the utilization of this AM technique require exploration into a wider range of thermoplastics and thermosets by characterizing materials at heating rates comparable to PBF-LB to screen their compatibility with PBF-LB. In this work, unique temperature protocols in FSC were developed to mimic the thermal environment in PBF-LB, such as energy input from the laser and particle coalescence, as well as solidification under varying printing conditions. Thermal analysis of the selected polymers during rapid heating and cooling with FSC compared to conventional heating rates such as differential scanning calorimetry (DSC) revealed a clear distinction in physical reactions associated with crystallinity and chemical reactions associated with crosslinking.

To investigate the influence of pre-processing and laser parameters emulation on thermoplastics during PBF-LB, unique temperature protocols were developed and experimented with FSC. A model polyester powder was initially studied, where its exothermic enthalpy was explored at various rates to then model the extent of crosslinking as a function of activation energy with Isoconversional methods and compared to conventional rates seen in DSC. A selection of thermoplastics where then used to explore classic thermal environments in PBF-LB such as isothermal heat exposure at bed temperature and particle coalescence by rapid melting, where thermal analysis in FSC was compared with actual PBF-LB single-layer prints and post-print characterization. Finally, two methodologies in powder aging and powder recycling were studied on high temperature and high molecular weight thermoplastics, using the Avrami equation to quantify the kinetics of crystallization’s dependence on thermal exposure at industrial fabrication times.

Overall, this work attempts to fill the gap present in literature surrounding the comprehension of the process-structure relationship between powders and laser parameters in PBF-LB to predict material compatibility with the use of FSC. Through a more expansive use of this thermal characterization method, a greater potential to improve the material library for this AM technique is possible.