Development of solid reinforced porous femoral components made using electron beam powder bed fusion to meet endurance requirement

Solid stemmed femoral components are currently used, although they can be porous-coated. A highly porous component can enhance the long-term fixation of the implant through bone in-growth. Electron beam powder bed fusion (EBPBF) is capable of fabricating porous structures. However, a femoral component also needs to function under a highly critical loading condition. In this study, design/simulation, EBPBF and fatigue testing were conducted in order to develop satisfactory and highly porous Ti6Al4V femoral components. Loading during testing has closely followed that set by the international standard for femoral components. After the initial design, EBPBF and testing, a final design was made through topological optimisation and components were made. Tests have shown that two components have satisfied the requirement well (cycle number N > 5 x10 7 ) and two have failed each with a failure cycle number (N f ) slightly lower in logarithmic scale than the required (N f >5 x10 6 cycles). Then, an attempt has been made to explain the effect of EBPBF defect on N f using the Kitagawa-Takahashi (K-T) diagram approach through (a) tests to determine the threshold stress intensity factor, (b) fractography and micro-CT to locate the defects and measure the defect sizes, (c) close evaluation of stress in defect locations by simulation. It has been shown that the effect of defects affecting N f in a real component could approximately, although not highly accurately, be explained using the K-T diagram approach. The present findings may suggest how highly porous EMPBF femoral components can be designed, built and quality assured to satisfy the fatigue life requirement.