May 2026 Volume 8

MATERIALS

The Jet Engine Nickel Alloy Quality Committee (JENQC) was formed in the years leading up to 2011, created to establish manufacturing standards for nickel-based alloys in rotating engine parts. It operates similarly to the earlier Jet Engine Titanium Quality Committee (JETQC), focusing on alloy quality improvements. Members include Turbine Engine OEMs, Nickel Melters/Forgers, FAA and Foreign Regulators. The committee focuses on the quality of nickel alloys used in jet engine rotating parts, often in coordination with Federal Aviation Administration and NTSB safety recommendations. Their work aligns with Federal Aviation Administration Advisory Circular 33.15-2, issued on February 4, 2011, which covers manufacturing processes for premium quality nickel alloys 6 . The Nickel Billet Inspection Program, which was driven by 2 NTSB recommendations from the AA 383 event (Figure 12) includes the evaluation of current and enhanced inspection technologies for nickel alloys and issue guidance; and requiring subsurface in-service inspection for all engines. The FAA’s Rotor Integrity Program consists of two requirements that focus on Damage Tolerance (DT) and Nondestructive Evaluation (NDE) research, which complement each other. Note: The JETQC (Jet Engine Titanium Quality Committee) for titanium mill products and components. This was discussed in August 2025 FIA Magazine.

Alloys The nickel-chromium and nickel-chromium-iron series of alloys led the way to higher strength and resistance to elevated temperatures (see Figure 10). Today they also form the basis for both commercial and military power systems. One of the earliest developed Ni-Cr and Ni-Cr-Fe alloys is Alloy 600 (76Ni-15Cr-8Fe). A popular high-temperature variant is Alloy 718. Titanium and niobium additions to overcome strain-age cracking (SAC) during welding and weld repair. The work horse corrosion-resistant variant in the Ni-Cr-Fe system is: Alloy 625. The addition of 9% Mo plus 3% Nb offers both high-temperature and wet corrosion resistance; resists pitting and crevice corrosion. Nickel-base high-temperature alloys are basically of two types: solid solution and precipitation-hardenable. The solid-solution alloys typically contain little or no aluminum, titanium, or niobium; the precipitation-hardenable alloys typically contain several percent aluminum and titanium, and a few contain substantial niobium. The age-hardenable alloys are typically strengthened by γ ' precipitation by the addition of aluminum and titanium, by carbide, and by solid-solution alloying. The nature of the γ ' is of primary importance in obtaining optimum high-temperature properties. Compositionally, the aluminum and titanium content and the aluminum/titanium ratio are very important, as is heat treatment. Increasing the aluminum/titanium ratio improves high temperature properties. The volume fraction, size, and spacing of γ ' are important parameters to control. Alloys with low amounts of γ ' require greater attention to γ ' spacing than alloys with high amounts. Other factors, such as coherency strain due to the lattice mismatch between γ and γ ', appear to be important in certain alloys, such as Waspaloy. Premium Quality Melting The production of Nickel Alloy from reduction of ore through melting was discussed previously. However, for flight applications, a premium quality (PQ) level is required. PQ materials typically are produced via triple melting (VIM-ESR-VAR or VIM-VAR-VAR) as shown in Figure 11.

Figure 12: Example: AA Flt 383 (Nickel Anomaly) in 2016 6 Forging is one of the most popular methods for forming nickel alloy components and the forging temperature has a critical impact on the microstructure and properties of the forged component. The forging of Nickel alloys is typically divided into two temperature bands by alloy type 4 : • Alloy 718 - has good hot working characteristics. Recommended forging furnace temperatures for initial forgings are 2,050° F (1,121° C) maximum for initial forging and 1,775-1,800° F (968 - 982° C) minimum for finish forging. A reduction of 25% minimum during final forging, together with a low finishing temperature, is required to avoid a duplex grain structure and to establish proper mechanical properties. • Alloy 625 – also has good hot workability characteristics within the 1,250 - 1,850°F (677 - 1,010°C) range. Reductions of 15 to 20 percent at temperatures approaching 1,850°F (1,010°C) are recommended for good grain refinement. Following forging the final properties of nickel alloy forging are set by the heat treat process. The specific heat treatment parameters for an IN718 and IN625 are shown below 4 :

Figure 11: Nickel Alloy Manufacturing Steps

FIA MAGAZINE | MAY 2026 49