Dispersion strengthened cobalt-chromium-molybdenum alloy produced by gas atomization

Claim 2

A high strength, corrosion-resistant, high temperature stable, ductile alloy having fine, equiaxed grain structure after high temperature exposure, produced by gas atomization and consisting essentially of the following percentage composition by weight: and the balance cobalt, apart from trace amounts of incidental impurities; in which the oxide-forming metal is a metal of Group IIA, IIIA, IIIB or IVB of the Periodic Table which forms high temperature-stable, non-accretive, fine oxide particles which oxide has a free energy of formation greater than the oxide of the matrix metal and is present in the dispersed phase; and said alloy after fabrication by gas atomization, thermomechanical processing and further high temperature exposure has an ultimate tensile-strength of 1103-1379 MPa (160-200 ksi), a 0.2% offset yield strength of 517-690 MPa (75-100 ksi), an elongation of 37 to 60%, and a fatigue strength at 10' cycles (Rotating Beam) of 483-655 MPa (70-95 ksi).

Claim 3

An alloy according to claim 1, in which the oxide-forming metal is aluminum, lanthanum or a mixture thereof. 3. An alloy according to claim 2, in which the percentage composition by weight is: and the balance cobalt, apart from trace amounts of incidental impurities.

Claim 4

An alloy according to claim 2, in which the percentage composition by weight is: and the balance cobalt, apart from trace amounts of incidental impurities, and said alloy after fabrication by gas atomization, thermomechanical processing and further high temperature exposure has an elongation of 58.7%.

Claim 5

An alloy according to claim 2, in which the percentage composition by weight is: and the balance cobalt, apart from trace amounts of incidental impurities, and said alloy after fabrication by gas atomization, thermomechanical processing and further high temperature exposure has an elongation of 51.0%.

Claim 6

A process for producing a high strength, corrosion-resistant, high temperature stable, ductile alloy having fine, equiaxed grain structure after high temperature exposure, which comprises melting under an atmosphere consisting substantially of nitrogen, an inert gas or a mixture thereof an alloy mixture consisting essentially of the following percentage composition by weight: and the balance cobalt, apart from trace amounts of incidental impurities, said oxide-forming metal being a metal of Group IIA, IIIA, IIIB or IVB of the Periodic Table which forms high temperature-stable, non-accretive, fine oxide particles which oxide has a free energy of formation greater than the oxide of the matrix metal and being present in the dispersed phase, wherein the cobalt, chromium, molybdenum and carbon are charged first, the resulting charge is flooded with nitrogen and/or inert gas and melted at a temperature within the range of 1454°C. (2650°F.) to 1538°C. (2800°F.), the manganese and silicon are then added, while maintaining the temperature of the molten mixture below 1510°C (2750 0 F), followed by addition of the oxide-forming metal, which acts as a getter for oxygen present in the original mixture and thus providing dispersed oxide, the nitrogen being present as nitride, derived from the nitrogenous atmosphere; subjecting the molten mixture to gas atomization to produce an alloy powder containing a fine oxide dispersion and then thermomechanically processing said alloy powder to provide an alloy having an ultimate tensile strength of 1103-1379 MPa (160-200 ksi), a 0.2% offset yield strength of 517-690 MPa (75-100 ksi), an elongation of 37 to 60%, and a fatigue strength at 10 7 cycles (Rotating Beam) of 483-655 MPa (70-95 ksi).

Claim 7

A process for producing a high strength, corrosion-resistant, high temperature stable, ductile alloy having fine, equiaxed grain structure after high temperature exposure, which comprises melting under an atmosphere consisting substantially of nitrogen, an inert gas or a mixture thereof an alloy mixture consisting essentially of the following percentage composition by weight: and the balance cobalt, apart from trace amounts of incidental impurities, said oxide-forming metal being a metal of Group IIA, IIIA, IIIB or IVB of the Periodic Table which forms high temperature-stable, non-accretive, fine oxide particles which oxide has a free energy of formation greater than the oxide of the matrix metal and being present in the dispersed phase, wherein the cobalt, chromium, molybdenum and carbon are charged first, the resulting charge is flooded with nitrogen and/or inert gas and melted at a temperature within the range of 1454°C. (2650°F.) to 1538°C. (2800°F.), the manganese and silicon are then added, while maintaining the temperature of the molten mixture below 1510°C (2750 0 F), followed by addition of the oxide-forming metal, which acts as a getter for oxygen present in the original mixture and thus providing dispersed oxide, the nitrogen being present as nitride, derived from the nitrogenous atmosphere; subjecting the molten mixture to gas atomization to produce an alloy powder containing a fine oxide dispersion and then thermomechanically processing said alloy powder to provide an alloy having an ultimate tensile strength of 1103-1379 MPa (160-200 ksi), a 0.2% offset yield strength of 517-690 MPa (75-100 ksi), an elongation of 37 to 60%, and a fatigue strength at 10 7 cycles (Rotating Beam) of 483-655 MPa (70-95 ksi).

Claim 8

A process according to claim 6, in which said oxide-forming metal is aluminum, lanthanum or a mixture thereof.

Claim 9

A process according to claim 6, in which the alloy powder after gas atomization has a percentage composition by weight of: and the balance cobalt, apart from trace amounts of incidental impurities.

Claim 10

A prosthesis made by forging a high-strength, corrosion-resistant, high temperature stable, ductile alloy having fine, equiaxed grain structure after high temperature exposure, produced by gas atomization and having a percentage composition by weight as set out in any one of claims 1 to 5.

Claim 11

A prosthesis according to claim 9 having a porous coating.