Longitudinal graded porous titanium fabricated by spark plasma sintering: Design of layers, direction of crack path

Abstract

The design of layers and fabrication methods strongly affect the stress bearing capacity and crack propagation in functionally graded porous titanium (FGPT). Thus, in this study, uniform and functionally graded porous titanium (in three and five-layer structures) samples were fabricated using spark plasma sintering at 440 °C and 50%vol. space holder (NaCl). Compression results proved that selecting the highest NaCl in the center of five-layered samples, besides the smoothest porosity gradient, increases energy absorption up to ≅360 % compared with the uniform foam. The architectural design, along with the energy absorption, affects the crack direction and fracture pattern remarkably. Obviously, two types of cracks path, i.e., vertical and oblique, were detected in uniform and different graded samples, which the latter direction highlighted the Griffith rupture mechanism. Meanwhile, although trumpet-like and crushed/disc fracture patterns perceived in layered structures, promptly fragmented patterns were dominated in the uniform porous sample. This work provides an appropriate method with a suitable layers arrangement to fabricate FGPTs with incredible energy absorption due to crack arresting/deflecting and homogenizing strut thickness.