Novel Processing Strategies for Laser Powder Bed Fusion to Reduce Defects in High Temperature TZM Alloy
Open Access
- Author:
- Hanagan, James
- Area of Honors:
- Materials Science and Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Edward William Reutzel, Thesis Supervisor
Robert Allen Kimel, Thesis Honors Advisor - Keywords:
- Laser powder bed fusion
TZM
Molybdenum
Additive Manufacturing
Microstructure
Refractory metals - Abstract:
- TZM is a high temperature molybdenum alloy that is of interest for aerospace, nuclear power, and medicine, and additive manufacturing (AM) offers the ability to generate novel designs for these applications, but there is little in the literature that investigates AM of TZM. In this work, the ability of TZM to be processed via laser powder bed fusion (LPBF) is investigated. Novel laser processing parameters, including double exposure of every layer and shorter hatch lengths, are utilized to influence melt pool morphology and solidification in attempting to create a defect free microstructure without the need to heat the build substrate to extreme temperatures. For each type of process strategy used, a variety of combinations for laser power, scan speed, and hatch spacing are tested. In addition, a novel specimen geometry is utilized to test the limits of TZM for processing fine features and support structures. With this set of laser parameters, relative densities as high as 99.76% and microhardness values as high as 400 HV are achieved. It is determined that the double exposure processing strategy is not shown to be effective as a method of processing TZM due to high defect quantities in the microstructure and high rate of build failures (e.g. due to cracking and distortion) among those specimens. Short hatch lengths, on the other hand, prove to be quite effective with 100% of specimens using a laser scan speed of 600 mm/s being built successfully to completion. These specimens had similar microstructures to the normal exposure specimens, so as a result it appears that hatch lengths anywhere from 0.5 mm to 5 mm showed potential for further optimization. Ultimately, this work shows that LPBF of TZM without high build substrate heating holds promise for producing TZM structures with minimal defects and limited cracking.