Influence of heat treatment on the structure and properties of VT1 titanium and the OT4 alloy

Conclusions

• 1. Sheets of technically pure commercial VT1 titanium as delivered have a small grained structure with the grain size corresponding to grade 7-6.

• 2. Heating in air at 650°C leads to a considerable increase in the surface hardness of VT1 titanium. The microhardness on the surface of the sheet is H 405; it is H 196 in the center.

• 3. Heating of VT1 titanium and the OT4 alloy for 2 h at 750–850°C leads to the saturation of the surface layer with gases and, as the result, a gray oxide film 15 microns thick is formed with a hardness of H 727 in the case of VT1 titanium and H 1030 in the case of the OT4 alloy.

• 4. Heating above the temperature of allotropic transformation (from 950 to 1050°C) leads to the formation of a white oxide film with a higher hardness on the surface of VT1 titanium and the OT4 alloy: H 1079 in the case of titanium and H 1300–1410 in the case of the OT4 alloy. Under the oxide layer there is a very hard diffusion layer. The depth of penetration of oxygen into the metal depends on the temperature and heating time.