Thermomechanically influenced dynamic elastic constants of laser powder bed fusion additively manufactured Ti6Al4V

This paper reports the dynamic elastic constants of laser powder bed fusion additively manufactured Ti6Al4V alloy by recently developed effective bulk modulus elastography technique and compares them with the static elastic constants evaluated using the nanoindentation technique. With this elastography technique, two ultrasound frequencies (10 MHz and 20 MHz) were employed, which distinctly identified spatially varying the dynamic elastic constants and effective density in additively manufactured Ti6Al4V while comparing to the wrought Ti6Al4V. The spatial resolution of elastic constants and effective density of the scanned region significantly improved at 20 MHz ultrasound frequency. The dynamic elastic constants were 5$\text{\%}$–8$\text{\%}$ lower than static elastic constants obtained for the additively manufactured Ti6Al4V and wrought Ti6Al4V. In addition, the present study compares the elastic moduli of additively manufactured Ti6Al4V, wrought Ti6Al4V, and solutionized and water quenched wrought Ti6Al4V. The microstructural examination of additively manufactured Ti6Al4V using scanning electron microscopy revealed a high density of internal twins within martensite laths contrary to scarcely twinned martensite lath in water quenched wrought Ti6Al4V. The origin of such high defect density was realized by a thermo-mechanical computational model that predicted rapidly changing alternating tensile-compressive stresses in the range of 49–720 MPa that, in turn, affected the dynamic and static elastic constants.