Pure titanium and the titanium alloy Ti-6Al-4V have been foamed by expansion of small, high-pressure, argon-filled pores (1,4). To delay cell wall bursting, the foaming was carried out under conditions where the matrix exhibited transformation superplasticity. This mechanism does not depend on the grain size as in fine grained superplasticity but, instead, relies on internal stresses due to the density mismatch between the a and the ß phases that occurs during the allotropic phase transformation. Additional control experiments conducted at constant temperature where the material deforms by creep showed that superplastic foaming is more rapid (4). Mechanical properties and pore morphology can be correlated (2). The pores can be filled with nanofiber bioactive materials to encourage osseo-integration (3), making these foams very attractive as bone implant materials.
Please visit our website for more information on this topic.
If you want to learn more, please visit our website Ruiyun.
Open-pore titanium foams are produced using the so-called space holder method. The mechanical properties of titanium foams with porosities of 50-80% are studied. The stiffness and yield strength of the foams are found to encompass the property range between cancellous bone and cortical bone. The analyzed foams are found to be anisotropic due to the use of nonspherical space holder particles which rearrange during the compaction of the powder mixture. The titanium foams are stronger perpendicular to the compaction direction and weaker along the compaction axis. In view of the application as an implant material in the lumbar spine, an intermediate porosity of 60-65% is analyzed more in detail. The typical yield strength of titanium foam with 62.5% porosity is above 60 MPa in compression, bending, and tension. Stiffness values vary with the testing method from 7-14 GPa.