Use of indentation test methods for additive manufacturing build verification for Ti-6Al-4V

Additive Manufacturing (AM), commonly called 3D printing, has increased significantly for medical device production since 2010. Despite ongoing technological improvements, the variability of mechanical properties for AM parts tends to exceed the variability in parts built using traditional manufacturing techniques. To assess this variability, the current approach is to perform tensile tests to verify the mechanical performance of each build. While this approach has a long history of use, tensile coupons are often taller than the devices being produced, which leads to longer build times to account for the additional height and potentially the need to machine these coupons before testing. While several AM build verification approaches have been proposed, this effort focuses on assessing a traditional indentation technique (Vickers micro-hardness) with a new indentation technique based on plastometry, Profilometry-based Indentation Plastometry (PIP), which is cost effective and time efficient. AM and conventional wrought titanium alloy tensile coupons (per ASTM E8) were obtained from multiple vendors and tested. After testing, indentation coupons were cut from the grip sections of the tensile coupons. Vickers and PIP testing were then conducted to obtain the most accurate comparison between tensile and indentation results. A linear regression analysis was performed to evaluate the two indentation methods and their feasibility for build verification by comparing their results to tensile test outcomes. While there were a few outliers, attributed to anisotropy in those samples, the correlation between measured tensile results and those predicted by PIP was similar for the AM and wrought specimens for yield strength (0.48 and 0.22) and ultimate tensile strength (0.85 and 0.84), respectively. Measurements predicted from Vickers micro-hardness showed a better correlation to the measured tensile results for AM specimens than wrought, based on the coefficients of determination for yield strength (0.59 and 0.14) and ultimate tensile strength (0.70 and 0.17), respectively. These results indicate that, with sufficient validation, indentation techniques could be utilized in future AM build verification testing.