Method of manufacture of dual titanium alloy impeller

A method for fabricating an impeller having a first region and and a second region, the first region having predetermined strength properties, and the second region having a predetermined creep resistance properties, the method comprising the steps of:

• providing a first titanium alloy formulated to be capable of having the predetermined strength properties imparted thereto;
• forming the first titanium alloy into a bore subelement having a first mating surface including a first conical shape;
• heat treating the bore subelement;
• providing a second titanium alloy formulated differently than the first titanium alloy and to be capable of having the predetermined creep resistance properties imparted thereto;
• forming the second titanium alloy into a body subelement, the body subelement including a hollow portion defined by a second mating surface including a second conical shape corresponding to the first conical shape of the first mating surface;
• heat treating the body subelement;
• inertia welding the first mating surface of the bore subelement to the second mating surface of the body subelement so as to form an intermediate structure;
• stress relieving the intermediate structure to optimize a microstructure of the intermediate structure, to impart the predetermined strength characteristic to the bore subelement, and to impart the predetermined elevated temperature performance characteristic to the body subelement;
• and
• machining away excess material from the intermediate structure to form the impeller.