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What Are The Categories Of Superalloys

Sep 25, 2018

760 temperature High Temperature Alloy deformation Superalloy

Deformed superalloy is a kind of alloy with good mechanical properties, comprehensive strength and toughness, high oxidation resistance and corrosion resistance, which can be processed by hot and cold deformation, working temperature range - 253 ~ 1320 C. According to its heat treatment technology, it can be divided into solid solution strengthening alloy and age hardening alloy. The first digit after GH indicates the classification number, i.e. 1, solid solution hardening iron-base alloy 2, aging hardening iron-base alloy 3, solid solution hardening nickel-base alloy 4, and cobalt-base alloy GH, and the second, third and fourth digits indicate the sequence number.

1. Solid solution strengthened alloy

The temperature range is 900~1300 C, the highest oxidation resistance temperature is 1320 C. For example, GH128 alloy has a tensile strength of 850 MPa at room temperature, a yield strength of 350 MPa, a tensile strength of 140 MPa at 1000, an elongation of 85%, a stress life of 200 hours at 1000 and 30 MPa, and an elongation of 40%. Solid solution alloys are commonly used to make components such as combustor, casing and so on.

2. Age hardening alloy.

The operating temperature is - 253 ~ 950 C. It is generally used to make structural parts such as turbine discs and blades of aerospace engines. The alloy working temperature of turbine disk is - 253 ~ 700 ~C, which requires good high and low temperature strength and fatigue resistance. For example, the maximum yield strength of GH4169 alloy is 1000MPa at 650 C, and the alloy temperature of blade can reach 950 C. For example, the tensile strength of GH220 alloy at 950 C is 490 MPa, and the endurance life of 940 C and 200 MPa is longer than 40 hours.

Deformed superalloys mainly provide structural forgings, pies, rings, bars, plates, pipes, strips and wires for aerospace, aviation, nuclear and petroleum industries. [2]

760 degree 800MPa high temperature alloy cast superalloy

Casting superalloy is a kind of Superalloy that can or can only be molded by casting. Its main characteristics are:

1. With a broader composition range, the design of the alloy can concentrate on optimizing its serviceability because it does not need to take into account its deformation processing properties. For example, nickel-based superalloys, the content of gamma'can be up to 60% or higher by adjusting the composition, so that the alloy can still maintain good properties at temperatures up to 85% of the melting point.

  2. Because of the special advantages of casting method, superalloy castings with arbitrary complex structure and shape can be designed and manufactured according to the needs of parts.

According to the temperature of casting alloys, they can be divided into three categories:

Category I: equiaxed grain cast superalloys used at - 253 ~ 650 C have good comprehensive properties over a wide range of temperatures, especially at low temperatures to maintain strength and plasticity. For example, the K4169 alloy with a large amount of K4169 used in aerospace engine has a tensile strength of 1000MPa, a yield strength of 850 MPa and a tensile plasticity of 15%, and a durable life of 200 hours at 650 and 620 MPa stresses. It has been used to make diffuser casing in aero-engine and complex pump components in aero-engine.

The second type: equiaxed grain cast superalloys used at 650 ~ 950 C have higher mechanical properties and hot corrosion resistance at high temperatures. For example, the tensile strength of K419 alloy is greater than 700 MPa and the tensile plasticity is greater than 6% at 950 C, and the ultimate tensile strength is greater than 230 MPa at 950 C for 200 hours.  These alloys are suitable for aero engine turbine blades, guide vanes and integral turbine.

Category III: Directionally solidified columnar and single crystal superalloys used at 950 - 1100 C have excellent comprehensive properties, oxidation resistance and hot corrosion resistance in this temperature range. For example, the lifetime of DD402 single crystal alloy is greater than 100 hours under the stress of 1100 C and 130MPa. This is the highest temperature turbine blade material used in China, suitable for making a new type of high-performance engine turbine blade.

With the continuous improvement of precision casting technology, new special processes are emerging. Fine grained casting technology, directional solidification technology, CA technology of complex thin-walled structure have greatly improved the level of casting superalloy, and the application scope has been continuously improved.

760 degree 800MPa high temperature powder metallurgy superalloy

Superalloy powder is produced by atomizing superalloy powder, hot isostatic pressing or hot isostatic pressing followed by forging. Powder metallurgy process, because of fine powder particles, cooling speed, so that the composition is uniform, no macrosegregation, and small grain size, good hot working performance, high metal utilization, low cost, especially the yield strength and fatigue properties of the alloy have been greatly improved.

FGH95 powder metallurgy superalloy has a tensile strength of 1500MPa at 650 C and a rupture life of more than 50 hours at 1034 MPa. It is one of the disc powder metallurgy superalloys with the highest strength level at 650 C.  Powder metallurgy superalloy can meet the requirements of high stress engine, and it is the choice material of high thrust-weight ratio engine turbine disk, compressor disk, turbine baffle and other high temperature components.

It is a special superalloy formed by a unique mechanical alloying (MA) process, in which the ultra-fine (less than 50 nm) oxide dispersion strengthening phase is uniformly dispersed in the alloy matrix at high temperature. The strength of the alloy can be maintained near the melting point of the alloy itself. It has excellent high temperature creep property, excellent high temperature oxidation resistance, carbon and sulfur corrosion resistance.

There are mainly three kinds of ODS alloys that have been commercialized.

The service temperature of MA956 alloy can reach 1350 C in oxidizing atmosphere, ranking first in oxidation resistance, carbon and sulfur corrosion resistance of superalloy. It can be used for combustion chamber lining of aeroengine.

The MA754 alloy can be used at 1250 C in oxidizing atmosphere and maintains high temperature strength and resistance to medium alkali glass corrosion. It has been used to manufacture aero engine guide gear and guide vanes.

The tensile strength and yield strength of MA6000 alloy are 222 MPa and 192 MPa at 1100 and 127 MPa at 1000 hours. MA6000 alloy ranks first among superalloys and can be used for Aeroengine blades.