Fatigue behaviour of additive manufactured Nb-48Ti alloy parts from powders produced by Plasma Atomization (PA) and Hydride-Dehydride (HDH) process

Abstract

Fatigue behaviour of bcc Nb-48 wt%Ti (Ti-36at%Nb) alloy parts processed by Laser Powder Bed Fusion (L-PBF) using as raw material two different types of powders, spherical powder produced by Plasma Atomization (PA) and irregularly shaped powder produced by Hydride-Dehydride (HDH) process, are compared. Laser power and scanning speed were selected to obtain rods with porosity below 0.5 vol%. All rods were produced using the same scanning strategy (chessboard with shift). The building platforms were heat treated for stress relieving at 650 °C for two hours before removing the rods using wire electro-discharge machining. The heat-traded rods were machined to obtain specimens for rotate bending fatigue tests, and S-N curves were plotted. Fatigue behaviour for PA and HDH sets were similar but with higher dispersed results for the specimens produced from the HDH powder. The fracture was nucleated in porosities near the machined sample surface, mostly on lack-of-fusion type pores. The fatigue cracks propagated in a “zigzag” mode with peaks and valleys parallel to the L-PBF building direction (BD) in both sets. One of the analysed samples, produced from HDH powder and with a lower fatigue life than average, showed a significantly higher number of pores, indicating the existence of a laser process parameter yet to be controlled.