Surface-hardened titanium material, surface hardening method of titanium material, watchcase decoration article, and decoration article

A method of surface hardening a titanium material, comprising

• bringing only titanium-aluminum alloy powders containing not lower than 30 at % but not higher than 70 at % of aluminum and having an average grain size of not greater than 30 μm into contact with a surface of a pure titanium material, and
• applying a heat treatment thereto at a temperature within the range of 800° C. to 900° C.,
• so as to form a first phase composed of TiAl, a second phase composed of TiAl and Ti3Al, a third phase composed of Ti3Al, and a fourth phase composed of Ti3Al and Ti sequentially from the surface towards an interior zone of the pure titanium material, such that a percentage of aluminum in relation to pure titanium is caused to decline sequentially by a gradient from the surface to the interior zone of the pure titanium material.

A surface-hardened titanium-base material wherein a first phase composed of TiAl, a second phase composed of TiAl and Ti3Al, a third phase composed of Ti3Al, and a fourth phase composed of Ti3Al and Ti are formed sequentially from a surface towards an interior zone of pure titanium material, such that a percentage of aluminum in relation to pure titanium declines sequentially by a gradient from the surface to the interior zone of the pure titanium material, and oxygen concentration also declines sequentially by gradient from the surface to the interior zone of the pure titanium material.

A method of surface hardening a titanium material, comprising

• bringing only aluminum oxide (Al2O3) powders having an average grain size in the range of 0.1 to 50 μm into contact with a surface of a pure titanium material, and
• applying a heat treatment thereto at a temperature within the range of 800° C. to 900° C. and in a reduced-pressure atmosphere of an inert gas,
• so as to form a first phase composed of TiAl, a second phase composed of TiAl and Ti3Al, a third phase composed of Ti3Al, and a fourth phase composed of Ti3Al and Ti sequentially from the surface towards an interior zone of the pure titanium material, such that a percentage of aluminum in relation to pure titanium declines sequentially by a gradient from the surface to the interior zone of the pure titanium material, and oxygen concentration also declines sequentially by gradient from the surface to the interior zone of the pure titanium material.