Structure-processing correlations and mechanical properties in freeze-cast Ti-6Al-4V with highly aligned porosity and a lightweight Ti-6Al-4V-PMMA composite with excellent energy absorption capability

Abstract

In contrast to freeze-cast ceramics and polymers, few freeze-cast metals have been described, to date. Our systematic study on structure-processing correlations in freeze-cast Ti-6Al-4V scaffolds reports, how processing parameters determine the architecture formed during the directional solidification of water-based metal slurries, and after sintering. In addition, sedimentation in the slurry during freezing and volume shrinkage during burnout and sintering were found to significantly affect both structure and properties of the scaffolds. Using two freezing rates, 1 and 10 °C min−1, two water-based polymer solutions as binders (chitosan and carboxymethyl cellulose) and two different metal volume fractions in the slurry, 20 and 30 vol%, Ti-6Al-4V scaffolds could be prepared with pore length, width, and porosity ranging from 41 to 523 μm, 14.5 to 76.5 μm, and 65 to 34%, respectively. Their compressive strength, stiffness, and toughness (work to 20% strain) fall in the range of 83–412 MPa, 7–29 GPa, and 14–122 MJ m−3, respectively. To further improve the properties, a select composition was infiltrated with poly(methyl methacrylate). This increased the average yield strength by a factor of 2.3 from 83 to 193 MPa and the average toughness (work to 50% strain) by a factor of 2.7 from 28.1 to 76.8 MJ m−3.