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The in vitro response of the mouse fibroblast cell line 3T3 on the surface of ultrafine grained titanium [produced by a severe plastic deformation (SPD) process] has been studied in this work. SPD Ti showed much higher strength than the coarse grained Ti and equivalent to that of Ti-6Al-4V alloy. Better cell proliferation was observed on SPD Ti compared to conventional Ti and Ti-6Al-4V alloy. This could be attributed to the increased surface free energy by reduction in the grain size and possibly the presence of a large number of nano size grooves at the triple point junctions in SPD Ti sample. There was no significant difference in the results of cytotoxicity tests of fine and coarse grained materials.

The ␤ → ␣ transformation kinetics of CP-Ti during continuous cooling was measured using a fully computer-controlled resistivity-temperature real-time measurement apparatus. Unlike the pure Ti case, the massive transformation occurs at medium cooling rates, about 90 ЊC/s to 600 ЊC/s. Its start temperature is estimated to be about 890 ЊC, which is close to the T 0 temperature. The reason for the appearance of massive transformation in CP-Ti is because CP-Ti contains a significant amount of Fe as an impurity, which leads to the T 0 (␤ → ␣ ) vs composition curve being parallel to the composition axis due to its retrograde solubility. The martensitic transformation starts to occur at a cooling rate of about 500 ЊC/s, which is much slower than that (about 3000 ЊC/s) reported in a pure Ti case. This retardation effect of martensitic transformation is also believed to arise from the presence of Fe in CP-Ti, which is a strong ␤ stabilizer.

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