Characterization of Ti–6Al–4V alloy foams synthesized by space holder technique

Ti–6Al–4V foams, biomedical candidate materials, were synthesized by powder metallurgical space holder technique as a result of evaporation of magnesium to achieve desired porosity content. Final products contained porosities in the range ∼43–64% with an average macropore size between 485 and 572 μm and a lamellar type Widmanstätten microstructure composed of α-platelets and β-laths. Unlike the case of bulk Ti–6Al–4V alloy tested under compression loading, compression stress–strain curves of manufactured Ti–6Al–4V foams were similar to those of elastic–plastic foams, which contain a linear elastic region; a plateau stage; and a densification stage. In the plateau region deformation bands perpendicular to the compression axis were developed and cell collapsing took place together with the buckling and fracture of some of the cell walls and edges in a ductile manner. Calculated elastic modulus and yield strength were in the range 1.42–14.7 GPa and 28.2–150 MPa, respectively, and the foam mechanical properties were found to be dependent on micro porous cell wall properties, which in turn depends on neck size between powder particles. Around 330 MPa yield strength value was calculated for porous cell walls by the use of Ti–6Al–4V alloy powder samples sintered in loose and compacted conditions, which were utilized to simulate the cell wall structure of foams. In addition, overall mechanical properties of foams were investigated considering macro porosity fraction, pmacro, and the yield strength of foams exhibited a power law dependence, similar to commonly used minimum solid area models, in the form of A * (1 − pmacro)n, where the proportionality constant “A” was found to be the yield strength of micro porous cell walls.