Assessing the Feasibility of Statistical Design Allowables for L-PBF Ti64 for the DoD – a Study Across the Industrial Base

Conference Abstract: In applications where a combination of high specific strength and excellent corrosion resistance is required, Ti-6Al-4V (Ti64) alpha-beta titanium alloy is a common material choice, particularly in Naval and aerospace applications. This alloy is traditionally processed through a combination of casting, rolling, and machining. A variety of heat treatments are used to anneal and age the alloy for tailored properties. While additive manufacturing removes many geometric design constraints from these traditional forming processes, until recently, structures fabricated via laser powder bed fusion (L-PBF) were porous and contained undesirable columnar grain structures that contributed to unpredictable and anisotropic mechanical properties. Recent advances in L-PBF processing technology including improved gas flow, powder atomization, and print parameter optimization enable printing of high-quality AM Ti64 with properties that are comparable and consistent to traditionally processed material. Currently, the DoD is looking for rapid adoption of AM Ti64 for part replacement of legacy components and unlocking the potential of AM for future applications. With the ultimate goal of establishing mechanical property design allowables involving numerous L-PBF processes, seven vendors fabricated samples of Ti64 for tensile testing using a variety of machines. Ultimately, 198 samples were tested and properties across builds fell within a normal distribution, allowing for reasonable A and B Basis calculations. While two vendors did provide material that was significantly different than the other five, these out of family materials were easily detected in statistical analysis of mechanical testing, and the root cause determined with routine microscopy. Electron microscopy indicated the presence of significant porosity and contamination in one vendor’s samples, and an out-of-specification heat treatment in another. Given the consistency in properties without a traditional anneal + age heat treatment or powder chemistry specification, this study demonstrates great promise for DoD of L-PBF Ti64 materials maturity.

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