Session: 03-02-03: Advanced Manufacturing

Paper Number: 121678

121678 - Contribution of Defects in Laser Powder Bed Fusion of Ti6al4v to the Variability in Mechanical Properties Within and Across Machines 

Laser powder bed fusion (LPBF) of metallic structures has nearly unlimited potential in the aerospace industry. Key to its adoption and projected widespread application are the ability to produce components with unprecedented complexity and with substantially lower buy-to-fly ratio than subtractive manufacturing processes. However, the advantages of LPBF are tempered by the fact that process-inherent defects, such as lack of fusion voids and keyhole porosity, are not uncommon. The potential for these anomalies to be introduced during the manufacturing process can necessitate the use of costly and time-consuming quality control. As such, substantial work has been performed to understand the relationships between the LPBF process parameters and resulting metal quality and defect density enroute to maximizing quality. But there is a limitation to prior work in this area.  Past investigations conducted in pursuit of maximizing metal quality are often conducted using a single machine and a single build, which overlooks the potential for process variability within and between machines. In fact, limited effort has been focused on understanding differences in metal quality and defect density when comparing between multiple identical machines performing the same build but conducted at different organizations and under the control of different operators. Unique aspects of process control, build execution and environment could contribute to powder characteristics (e.g. packing density, size distribution), metal quality and its mechanical behavior.  

This presentation will describe an experimental investigation that is presently underway and focused on understanding the variability in metal quality among multiple identical LPBF machines producing components with Grade 5 Ti6Al4V. Six partners produced identical builds using an EOS M290 LPBF that consisted of an array of tensile coupons representing both vertical and horizontal orientations that conformed to ASTM E8.  The coupons were subjected to a stress relief heat treatment and machined to net-shape after printing prior to tensile testing. A subset of the specimens were subjected to hot isostatic pressing (HIP) treatment and then machined to net-shape. The metal quality was characterized using micro computed tomography microCT and root cause defects contributing to variability in the mechanical properties were identified by fractographic analyses. Results showed that there were significant difference in metal quality and mechanical properties between the partners. Interestingly, the differences were a function of the metal orientation. While there were significant differences in strength, the largest differences in the mechanical properties evaluated were reflected in the strain at failure. Differences in the family of defects and the corresponding reliability were evaluated using Weibull statistics in terms of two-parameter models. These results reflected some unique qualities of the metal of each partner and on the strain at failure data from each tested coupon.  Details of the program will be discussed, including contributions to metal quality variability and the importance of the findings to the development of a reliable set of design allowables for LPBF conponents.

Presenting Author: Rick Schleusener University of Washington

Presenting Author Biography: Rick Schleusener is a fourth year PhD student at the University of Washington originally from Rapid City, South Dakota. His research is focused on understanding mechanical property variability in components produced by laser powder bed fusion systems under the advisement of Professor Dwayne Arola in the department of Materials Science and Engineering.