A study on the hardness variation of α- and β-pure titanium with different grain sizes

In this study, the hardness and the microstructure of α- and β-pure Ti treated with different grain sizes were investigated. The α-Ti specimens were obtained by heating pure Ti at 750 °C for various periods and then quenched in water, while the β-Ti specimens by heating at 1000 °C for various periods and then quenched in water. Experimental results show that the hardness of α-Ti decreased with increasing the grain size; whereas, the hardness of β-Ti tends to increase with increasing grain size. From the microstructures examined with transmission electron microscope, it can be realized that the strengthening mechanisms of α- and β-Ti are quite different. Grain boundary could be the main strengthening microstructure of α-Ti and the smaller grain size the higher hardness. The major strengthening microstructure of β-Ti was martensitic twin with a very high dislocation density. The amount of martensitic twin increased with increasing the grain size of β-Ti and, therefore, the larger grain size the higher hardness.