Microstructure of SLM Ti-6Al-4V parts subjected to electropulsing assisted ultrasonic impact treatment.

The regularities of the microstructure modification in the surface layer of 3D-printed Ti-6Al-4V parts subjected to the Electropulsing Assisted Ultrasonic Impact Treatment (EAUIT) have been studied. It is shown that the EAUIT parameters exerted a significant impact on the surface morphology and microstructure of the 3D-printed Ti-6Al- 4V samples. Metallographic analysis of etched lateral face of the studied samples has been performed. It is shown that the mode 1 EAUIT resulted in structure refinement of a thin surface layer ∼50 µm thick while in the mode 2 EAUIT treated ones the depth of the modified layer had increased up to ∼80 µm. The modes 1 and 2 EAUIT resulted in increasing surface hardness of the SLM samples from 252 to 256 and 300 HV, respectively. The gradient hardening pattern of the surface layer structure in the SLM Ti-6Al-4V samples through measuring the cross-section microhardness distribution was demonstrated. It is suggested that the revealed bulk microhardness increase in the SLM Ti-6Al-4V sample also resulted from its heating during passing the pulsed electric current. [ABSTRACT FROM AUTHOR]