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Views: 5 Author: Wang Publish Time: 2024-03-07 Origin: Site
Alloy 718 is a precipitation hardened nickel-chromium alloy with additions of niobium, molybdenum, aluminum and titanium for improved corrosion resistance combined with extremely high strength and excellent weldability, including resistance to cracking after welding. Alloy 718 has excellent creep rupture strength at temperatures up to 700 °C. Alloy 718 achieves its strength through a precipitation hardening heat treatment and can be supplied in a ready-to-anneal solution to facilitate processing, after which it is heat treated to achieve full strength, or the material can be supplied in the fully precipitation-hardened state.
Alloy 718, often referred to as Inconel 718, is precipitation hardened to give maximum strength and high creep-stress rupture strength. The alloy can be supplied in the annealed condition to enhance machinability followed by subsequent appropriate heat treatments. Capability tests are completed on test samples which have had the precipitation hardening process completed. Alloy 718/Inconel 718, demonstrates outstanding weldability including resistance to post-weld cracking. The major applications are components for gas turbines, aircraft engines, fasteners and other high strength applications. Its available in round bar, wire and sheet and plate.
High mechanical strength
For most applications, Inconel 718 is specified as: solution annealed and precipitation hardened (precipitation hardening, age hardening, and precipitation heat treatment are synonymous terms). Alloy 718 is hardened by the precipitation of secondary phases (e.g. gamma prime and gamma double-prime) into the metal matrix. The precipitation of these nickel- (aluminum, titanium, niobium) phases is induced by heat treating in the temperature range of 1100 to 1500°F. For this metallurgical reaction to properly take place, the aging constituents (aluminum, titanium, niobium) must be in solution (dissolved in the matrix); if they are precipitated as some other phase or are combined in some other form, they will not precipitate correctly and the full strength of the alloy with not be realized. To perform this function, the material must first be solution heat treated (solution annealed is a synonymous term).
Exceptional welding quality
Other Inconel alloys are difficult to weld due to brittleness and cracking at the exact welding point. However, Inconel 718 has been created to address this issue, whether electron-beam or arc welding is used.
Good malleability and machining quality
Most Inconel alloys tend to experience strain hardening when machining or shaping is attempted. Inconel 718 is different-- it’s easier to machine using a hard cutting implement through a slower cutting mechanism.
Inconel 718 alloy is a nickel-based high-temperature alloy consisting mainly of approximately 50% nickel, 20% chromium, 15% iron, 5% molybdenum, and 3% aluminium. This alloy has excellent corrosion resistance and high-temperature strength and can be used long in high-temperature environments. The addition of Nb, Ti, Al and Ni forms a series of precipitates during the controlled solution annealing and ageing process steps. This results in a significant increase in strength and hardness compared with alternative nickel alloys. These tensile and creep rupture properties are maintained from cryogenic to elevated temperatures. These properties make it suitable for applications between -250oC – 650oC.
It is mostly chosen by design engineers thanks to its high strength in extreme temperature conditions at both ends of the spectrum. It can be used in environments from cryogenic all the way up to 1300°F/704°C. Throughout this entire range it exhibits exceptionally high yield, tensile and creep-rupture properties. It also shows excellent tensile and impact strength.
The alloy is made up of 50-55% nickel+cobalt (with cobalt limited to 1% max) and 17-21% chromium. This combination gives the material its corrosion-resistance properties. This includes good resistance to oxidation, enabling it to withstand corrosive media present in many of its applications. The remainder of the composition includes niobium+tantalum (4.75-5.5%), molybdenum (2.8-3.3%) and titanium (0.65-1.15%), plus other balancing elements. It’s a potent and well-balanced combination of elements, responsible for the superalloy’s desirable technical properties.
Alloy 718 finds widespread utility owing to its outstanding mechanical properties, encompassing high tensile strength, resistance to creep, extended fatigue life, as well as impressive oxidation and corrosion resistance. This versatile alloy is integral in various applications, playing a pivotal role in the aerospace industry with uses ranging from landing gear components to automotive applications like exhaust manifolds. WR.Nr 2.4668 Alloys also find a place in critical sectors such as medical devices, particularly in orthopedic surgery screws. Its adaptability extends to nuclear power plants, gas turbines, oil refineries, industrial valves, pressure vessels, heat exchangers, and fasteners like bolts and nuts. Notably, its exceptional heat resistance positions it as an ideal material for elevated temperature operations, making it indispensable for applications such as jet engines and combustion chambers in automobiles and motorcycles.
