Committee Members: 

• Prof. Surya R. Kalidindi, Advisor, ME/MSE
• Prof. Joshua P. Kacher, MSE
• Prof. David L. McDowell, ME/MSE
• Prof. Richard W. Neu, ME/MSE
• Prof. Aaron Stebner, MSE/ME
• Prof. Naresh N. Thadhani, MSE
• Brad L. Boyce, Ph.D., Sandia National Laboratory

Exploration of the Additive Manufacturing Process Development Space using High-throughput Mechanical Property Assays

Abstract:

Additive Manufacturing (AM) of metals is a breakthrough technology that may fabricate parts more quickly and allow for the development of novel materials. Recently, AM has been of growing industrial significance for aerospace applications. Laser Powder Bed Fusion (L-PBF) has been a subject of research over the past decade for aero-engine applications. This research has uncovered a variety of discrepancies in the development of AM processes which must be addressed so these processes may meet their true industrial potential. One such discrepancy is in the mechanical testing of AM samples, so they may be qualified and certified. This is mainly due to the highly anisotropic nature of AM builds and the costs associated with fabricating and testing mechanical test coupons. Due to the cost-prohibitive nature of mechanical testing of AM builds, it is common for build parameters and post-build processing conditions to be fully developed based on density and metallography before mechanical tests are performed at the tail end of the development process. This method has been met with relative success, but in many scenarios, leads to a non-optimized final processing map. To mitigate this issue and find processing parameters that produce a sample with optimal mechanical properties, lower cost, high-throughput mechanical testing protocols must be employed.

Indentation-type mechanical testing protocols are ideal for mitigating the discrepancy in AM process or alloy development. Two primary benefits of indentation-type mechanical testing present themselves. 1). A significantly reduced sample volume compared to ASTM-E8 standard samples, and 2). A configuration that is highly conducive to high-throughput automation. These two benefits lead to cost reductions to generate the relevant mechanical property data necessary to down-select AM process parameters or alloys. This cost reduction has the potential to convince AM developers to apply mechanical testing earlier in their development cycle, so they can reduce the number of builds or heat treatment cycles necessary to determine optimal processing windows.

 A primary challenge to the application of indentation-type mechanical testing protocols to AM development is their limited historical use in the qualification of wrought or cast metals. This leads to a hesitancy throughout industry to adopt these methods for the development of their processes. While this is true, an explosion in research has been ongoing over the past decade to prove indentation-type testing as a viable and reliable mechanical testing solution. Since these types of testing processes are low-cost and highly conducive to automation, the amount of test data necessary to build reliable confidence intervals will be produced much more quickly and at a much lower cost than was necessary to produce similar test data using uniaxial tensile testing.

The proposed research will focus on adding to the already growing amount of indentation-type test data from spherical microindentation and Small Punch Test (SPT). It will align specifically with additive manufactured alloys relevant to aeronautical and astronautical applications. Known issues with AM of aerospace relevant materials, such as microstructural and property heterogeneity, will be addressed by performing tests in multiple planes with respect to the build orientation of samples. SPT will be of significant focus in the proposed work due to its ability to predict plastic mechanical properties such as yield and ultimate tensile strength. The data produced with indentation-type tests will be validated, in part, by standard ASTM-E8 tensile tests. The two primary end goals of the proposed work will be to produce reliable correlations between indentation-type mechanical test results and microstructural features in AM samples and to develop high-throughput experimental protocols for SPT.