ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2026 19 Power (a previous spin-off of General Electric Co.) adapted it for turbine wheels as well as spacers for large frame industrial gas turbines[7]. GE and its supply chain partners developed the capability to make rotors more than 10 times the size of the largest aircraft rotors. Triple melting (VIM-ESR-VAR), complex thermal cycles, and forging on the world’s largest hydraulic presses were required to prevent segregation, cracking, and grain growth. The technology developed in this program provided a template for producing large components out of alloy 718 and other superalloys. The gas alloy, designated as 706, lacked the delta phase responsible for the unique fine grain structure of alloy 718. Hence its fatigue strength and sonic inspectability could not be duplicated[6]. Inco did not heavily promote the alloy, and there were no notable applications until the early 1990s when GE TABLE 1 — NOMINAL COMPOSITION OF ALLOYS, WT% Alloy Type Ni Cr Fe Co Nb Al Ti Mo Other 718 B 53 18.5 18.5 5.1 0.6 0.9 3 625 MS 61 21.5 4 3.6 0.2 0.2 9 706 LC 42.5 16 38.5 3 0.2 1.7 Fenix700 LC 42 16 37 2 1.3 1.7 630 HT 50 18 18 6.5 0.5 1 3.2 3 W PWA 1472 HT 58 12 18 6 0.6 2 3 René 220 HT 56 19 12 5 0.5 1 3.2 3 Ta 718PLUS HT 52.5 17.5 9.5 9 5.5 1.5 0.7 2.7 1 W 780 HT 46 18 25 5 2 0.2 3 725 OG 57 21 9 3.5 0.2 1.3 8.2 625 Plus OG 60 21 6 3.5 0.2 1.3 8.2 625M OG 57 21.5 6 5 0.6 0.6 9 945 OG 47 20.5 22.5 3.1 0.1 1.5 3.2 2 Cu 945X OG 53.5 20.5 15 4.2 0.1 1.5 3.2 2 Cu AD955 OG 57.5 21.5 8.5 4.7 0.4 0.9 5.9 903/CTX-1 CTE 38 42 15 3 0.9 1.4 909/CTX-3 CTE 38 42 13 4.7 0.1 1.5 0.4 Si 908 CTE 49 4 41.5 3 1 1.5 Note: Table refers only to alloys mentioned in this article. Most alloys are defined with either nickel or iron as the balance element. All alloys contain some level of residual elements such as Mn, Si, Co, Cr, etc., thus, the calculated balance levels are approximate. For some alloys such as 718 or 625 there are many restricted compositions within the broader UNS definition. B = base alloy, CTE = coefficient of thermal expansion alloy, HT = high-temperature alloy, LC = low-cost alloy, MS = matrix-stiffened alloy, and OG = oil & gas alloy.
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