What Are nickel alloy UNS N07718 and nickel-molybdenum-chromium alloy UNS N10276?
nickel alloy UNS N07718 (UNS N07718) and nickel-molybdenum-chromium alloy UNS N10276 (UNS N10276) are both nickel-based alloys, but they are engineered for different jobs. nickel alloy UNS N07718 is a precipitation-hardenable alloy developed for high mechanical strength at elevated temperature, while nickel-molybdenum-chromium alloy UNS N10276 is a nickel-molybdenum-chromium solid-solution alloy developed for resistance to aggressive chemicals. Choosing between them is usually a question of whether the application demands load-bearing strength at high temperature or maximum corrosion resistance.
Chemical Composition and Standards
nickel alloy UNS N07718 has a nickel-chromium-iron base (nominally 50–55% Ni, 17–21% Cr) with niobium, molybdenum and titanium additions that form the hardening precipitates responsible for its strength; it is covered by specifications such as AMS 5662/5663 and ASTM B637. nickel-molybdenum-chromium alloy UNS N10276 carries significantly more molybdenum (15.0–17.0%) and tungsten (3.0–4.5%) with chromium (14.5–16.5%) and a balance of nickel; it is covered by ASTM B574/B575 and related ASME codes. The extra molybdenum and tungsten are exactly what gives C276 its exceptional resistance to pitting and crevice corrosion in reducing and mixed-acid media.
Mechanical Strength and Temperature Capability
nickel alloy UNS N07718 is age-hardened to tensile strengths above 1,200 MPa with yield strength over 1,000 MPa, and it retains useful strength and oxidation resistance up to roughly 1,300°F (704°C) for short periods, with long-term design usually limited to about 1,200°F (649°C). nickel-molybdenum-chromium alloy UNS N10276 is not precipitation-hardenable; in the annealed condition its yield strength is around 345 MPa and it is strengthened only by cold work. C276 is commonly cited for service from cryogenic temperatures up to about 750°F (400°C) in continuous chemical processing; for oxidation-dominated exposures, data sheets allow higher temperatures, so the appropriate limit must be matched to the actual environment and verified against the manufacturer's data.
Corrosion Resistance Profiles
nickel-molybdenum-chromium alloy UNS N10276 resists chloride-induced stress-corrosion cracking, pitting and crevice corrosion, and it performs well in wet chlorine, ferric and cupric chlorides, seawater, and sulfuric, hydrochloric and acetic acid media in both oxidizing and reducing conditions. nickel alloy UNS N07718 offers good general corrosion resistance in many environments, including chlorides, sulfides and mild oxidizers, but it is not a substitute for C276 in hot acids or highly corrosive chemical service, where local attack and cracking risk rise quickly.
Applications and Selection Guidance
nickel alloy UNS N07718 is the established material for jet engine discs and shafts, gas turbine fasteners, cryogenic pressure components and high-temperature structural hardware where strength-to-weight and fatigue life matter. nickel-molybdenum-chromium alloy UNS N10276 is the workhorse of chemical processing, flue-gas desulfurization scrubbers, pharmaceutical reactors, heat exchangers and marine systems handling harsh acids and chlorides. As a rule of thumb, choose 718 when the driver is mechanical strength at high temperature, choose C276 when the driver is corrosion resistance in aggressive media, and involve a corrosion engineer when both demands are present, because an overlay or a redesign is often more economical than forcing one alloy to do both jobs.
Frequently Asked Questions
Is nickel-molybdenum-chromium alloy UNS N10276 stronger than nickel alloy UNS N07718? No. In the aged condition nickel alloy UNS N07718 reaches tensile strengths above 1,200 MPa, while annealed nickel-molybdenum-chromium alloy UNS N10276 has a yield strength of about 345 MPa. C276 is selected for corrosion resistance, not for load-bearing strength at high temperature.
Can nickel alloy UNS N07718 replace nickel-molybdenum-chromium alloy UNS N10276 in chemical service? Only in mild media. In hot acids, chlorides and environments with stress-corrosion cracking risk, C276's higher molybdenum and tungsten content provides protection that nickel alloy UNS N07718 cannot match.
What is the maximum operating temperature of nickel-molybdenum-chromium alloy UNS N10276? For continuous chemical-processing service the commonly cited limit is about 750°F (400°C). Oxidation-dominated or short-term exposures may allow higher temperatures, so confirm the limit against the manufacturer's data sheet for the specific environment.
Which alloy is easier to weld? nickel-molybdenum-chromium alloy UNS N10276 is readily weldable with matching filler metal and retains its corrosion resistance when welding procedures are controlled. nickel alloy UNS N07718 welds acceptably in the annealed condition but is prone to strain-age cracking if welded in the age-hardened condition.
Is nickel alloy UNS N07718 or nickel-molybdenum-chromium alloy UNS N10276 magnetic? Both are essentially non-magnetic with low magnetic permeability, which is one reason they are accepted in instrument and magnetic-sensitive applications.
Which alloy should I choose for high-temperature structural parts? Choose nickel alloy UNS N07718 when the part must carry mechanical load at temperatures up to about 1,200–1,300°F (649–704°C). Choose nickel-molybdenum-chromium alloy UNS N10276 only when corrosion resistance, not load-bearing strength, is the dominant requirement at high temperature.
