Effect of powder layer thickness and scan orientation on the deformation and failure of selectively laser melted Ti-6Al-4V alloy over six decades of strain rates

The plastic deformation and failure behavior of additively manufactured Ti-6Al-4V coupons via selective laser melting (SLM) are investigated over 6 decades of strain rates i.e., 10(-3), 10, 2000, and 7000 s(-1). Four different types of mesostructures are generated by varying the powder layer thickness and scan rotation in the SLM process. A scan rotation, Psi, 90 degrees produces mesostructures having cuboidal grains along the build direction and columnar prior beta grains on the scanned direction, while Psi of 67 degrees produces nearly equiaxed grains along the build and scanned directions. All the mesostructures, independent of Psi, consists of fine acicular martensitic alpha' laths. Experimental results show that the flow stress increases with strain rate suggesting that all the samples exhibit positive strain rate sensitivity. Post deformation macroscopic images of the failed samples show that plastic strain localization increased with strain rate. At high strain rates, the deformation is dominated by adiabatic shear bands (ASBs) and significant macro-cracks are observed along with the shear bands particularly at high strain rates. The ASBs are more tortuous in the samples fabricated using scan rotation of 67 degrees as compared to 90 degrees suggesting that the nature of mesostructure has a pronounced effect on the deformation characteristics. Further, the fractographs analyzed using a scanning electron microscope clearly show both ductile and brittle features.

Automated summary

The study investigates the plastic deformation and failure behavior of additively manufactured Ti-6Al-4V coupons via selective laser melting at different strain rates. The results show positive strain rate sensitivity with increasing flow stress, along with increased plastic strain localization at higher strain rates. Deformation is dominated by adiabatic shear bands at high strain rates, with significant macro-cracks observed. The mesostructure nature has a pronounced effect on the deformation characteristics, with different scan rotations resulting in varying tortuosity of ASBs.