The Ever-Changing, Never-Ending Nature of Superalloy Development

The alloys that are currently used for aerospace applications are the result of a long series of innovations that trace their roots back to the earliest days of nickel-base alloys. Very rapid advances were made in the two decades following the introduction of the first aircraft turbine engine such that the generic wrought alloys of today bear a remarkable, though superficial, resemblance to the alloys available in the 1960’s. But alloy development did not stop there; new processes such as vacuum melting, directional casting, thermal barrier coating, isothermal forging and powder metallurgy opened up avenues to develop alloys with unique structures and enhanced properties for specific applications. The same thing is likely to happen in the future with additive manufacturing.  At the same time concepts of process control at all levels of alloy production facilitated differentiation of alloys into family groups with compositions often finely tuned to provide a narrow band of tailored properties produced on unique manufacturing equipment. Another force that has driven superalloy innovation in recent years is applications in new industries. Traditional nickel-base superalloys are being modified for: strength in corrosive environments (oil and gas), huge ingots (gas and steam turbine rotors), creep resistance and weldability (power generation), and molten salt resistance (solar-thermal power). Along the way the experimental tools used to develop alloys have evolved dramatically, from pure empiricism based on property responses, to electron microscopy, to statistically based alloy design, to thermodynamically based computational design. This paper will provide a brief overview of the nearly 100 years of progress on nickel-base superalloys from International Nickel Co. archives and provide a perspective on the future.