A multi-element
composite object composed from first, second, and third
metal components is provided, wherein the first
metal and the third
metal are weld incompatible. The multi-element
composite object includes a first component fabricated from a first metal. A second component, fabricated from a second metal, is brazed to the first component A third component, fabricated from a third metal, is
inertia welded to the second component . The first metal may be provided as a
titanium alloy, e.g. a TiNi
alloy. The second metal may be provided as low-carbon mild or
alloy steel. The third metal may be provided as
alloy steel, e.g., 9310
nickel alloy steel. In an embodiment, the multi-element
composite object is a gear
assembly, with the first element of the gear
assembly object being a shaft and the third element of the gear
assembly being a gear member with hardened teeth surfaces. The first and second components can be mechanically keyed together via an anti-rotational element. The anti-rotational element can be provided as a pin-in-groove arrangement or a twist-fit arrangement A method of making a multi-metal composite object including a first component fabricated from a first metal, a second component fabricated from a second metal, and a third component fabricated from a third metal, wherein the first metal and the third metal are weld incompatible, is also disclosed. The first step of the method includes mechanically
keying the first component to the second component. Net, the first component is brazed to the second component. Finally, the third component is welded to the second component. Where the first metal is a Ti alloy and the second metal is low-
carbon steel, the step of
brazing the first component to the second component can include
brazing using a
brazing material such as Ag and Cu. Where the third component is heat-treated steel, the assembly can be stress-relieved after
inertia welding at a temperature sufficiently low so as not to degrade the heat-treated properties of the third component.