Fe/Ni-based superalloys

All Ni and Fe—Ni-based superalloys are alloyed with Al. This leads to a two-phase matrix consisting of the y-(Ni, Fe, Al) solid solution phase (fee, Al stmeture) and the intermetallic y -NisAl phase (LI2 stmeture), which has a superlattice structure relative to the fee stmeture of the y phase. The binary Al—Ni phase diagram in Fig. 3.1-128 shows clearly that the y phase is stable up to the melting range. The matrix phase y is solid solution strengthened by allo3dng additions of Cr, Mo, W, and... 

The Incoloy alloys 800 and 800H are excellent examples of the effect of carbon content on creep strength. These two wrought, Fe-Ni-base superalloys contain nominally 30-35% Ni and 19-23% Cr, and so are relatively free from crformation and have good oxidation-resistance up to ca. 1100 °C. The maximum nominal carbon content of alloy 800 is 0.1%, with no lower limit. The nominal carbon content of alloy 800H is 0.05-... 

For Fe/Ni-based superalloys, a minimum of 20-25% chromium is required to ensure the formation of a protective Cr203 layer. Some cobalt-based alloys require 25-30% Cr203 and do not contain any aluminium. These alloys are resistant to high temperature and possess slower oxidation kinetics. Anyhow, their disadvantage is larger thermal CTE as compared to the iron-based alloys. 

Gas Atomization 50-300 Standard deviation 1.9-2.5 <10-50 at high gas pressures with close-coupled atomizer Solder materials. Precious metals, Cu, Fe, Al, Mg, Co, Ti, Zn, Al-6Cr-3Fe-2Zr alloy. Low-alloy steels. High speed steels. Stainless steels, Specialty alloys, Ni-base superalloys, Alumina, Intermetallics io3-.o5 1-70 Spherical smooth particles. Cleanliness, Rapidly-solidified structures, Acceptable production rates High cost, Low 1 volume, Low energy efficiency (EE), Gas-filled porosity in particles H... 

As discussed before, hard metal-like composites can be prepared by pressureless sintering of ternary borides with Fe, Ni, or Co melts. Materials with x-phase (M21M2 Bg, where = Fe, Ni, or Co, and M = Zr, Hf, Nb, Ta, or W with M as the matrix phase) have not been developed for technical use but Ni-based alloys with x are in applications as wear- and corrosion-resistant coatings on steels [355]. The x phase is also used for the improvement of the creep resistance of Ni-based superalloys. 

Table 3.1-95 Nominal compositions of Fe—Ni-based and Ni-based wrought superalloys, cont.

The superalloys are strengthened by addition of both solid-solution hardening and precipitate-forming elements. The Fe-Ni-base alloys can be strengthened the least and the Ni-base alloys the most (Fig. 5-8). The... 

Nanocrystalhzation has been shown to decrease the carrier density of the semiconductive passive film, such as Fe-lOCr, Fe-20Cr, 309 stainless steel, 304 stainless steel, AZ91D magnesium alloy and Ni-based superalloys. " - However, for pure Al, whether in solution with or without Cl", nanocrystalhzation... 

Cobalamin, 25 803 folic acid and, 25 802 Cobalt (Co), 7 207-228. See also Co-base superalloys 60Co isotope 60Co nucleus Fe-Ni-Co alloys Dicobalt octacarbonyl Tetracobalt dodecacarbonyl analysis, 7 215-216 in ceramic-matrix composites, 5 554t coke formation on, 5 266 colloidal suspensions, 7 275 economic aspects, 7 214-215 effect on copper resistivity, 7 676t environmental concerns, 7 216 health and safety factors, 7 216-218 in M-type ferrites, 11 66, 69 occurrence, 7 208... 

Ni,Fe)4>ased superalloys. Ni,Fe-based siqieralloys, such as 718, can behave in a complex fashion, which is associated with the formation of various carbides and the interplay between three major precipitated phases S based on NisNb, 7 based on Ni3Al and a metastable phase 7" which is related to the 6 phase. Inconel 625 (IN625) was the prototype for the Nb-hardened NiFe-type superalloys and it is instructive to look at the complex precipitation phenomena which occur in this alloy which has the composition Ni-21.5Cr-9Mo-3.6Nb-5Fe-0.2Al-0.2Ti-0.05C (in wt%). 

Mishra SB, Chandra K, Prakash S and Venkataraman B, Characterization and Erosion Behaviour of a Plasma Sprayed Ni A1 Coating on a Fe-Based Superalloy. Mater Lett, 2005, 59 3694—3698. 

Iron-based superalloys. The influence of solution treatment temperature on flie mierostrueture, fiaeture surface, composition and amount of precipitates, tensile properties of hot-rolled speeimens of Cr-Fe-Ni alloys were studied by [2003Cai]. It is reported that optimum meehanieal properties can be obtained by solution-treatment at 1000°C followed by conventional aging. 

Material of the heat transfer tubes and the hot header is Hastelloy XR, and inner and outer shells is made of 2 1/4Cr-1Mo. The Ni-base Cr-Mo-Fe superalloy Hastelloy XR was so developed as to have a superior corrosion resistance under the exposure to... 

Coatings based on MCrAlY (M = Fe, Ni, Co) are particularly interesting because they contain the same elements as the superalloys. As they are not required to sustain mechanical load, their composition can be chosen uniquely to optimize their corrosion resistance. For example, by increasing the concentration of active elements such as A1 and Y one improves the adhesion of the oxide scales. 

A distinction is often made between those alloys that are primarily used for high-temperature strength, commonly referred to as superalloys, and those that are primarily used for corrosion resistance. Hi -performance alloys are defined, in the present context, as Ni-, Ni-Fe-, and Co-base alloys able to operate at high temperatures, > 550°C, and pressmes. Fe, Co, and Ni are transition metals with consecutive positions in the periodic table. The relative order of abimdance decreases as Fe, Ni, Co. 

Tiwari, S. N. (1997), Investigations on Hot Corrosion of Some Fe-, Ni- and Co-Base Superalloy in Na2S04-V205 Environment under Cyclic Conditions, PhD Thesis, Met. and Mat. Eng. Dept, UOR, Roorkee, India. 

The superalloys are typically Ni, Ni-Fe, and Co based alloys with Cr, Ti, W, A1 additions. They were originally used for high temperature applications (over 810 °C) or in severe corrosive media. Superalloys can be distinguished from high alloyed steels (see definition in Section 2.1.3). Since iron is not the major compound (as defined in [201, CEN, 2000]), they are considered non-ferrous materials. The casting of superalloys may occur in certain investment casting foundries, as well as partly in foundries which specialise in high alloyed steel qualities. 

Some superalloys, particularly Ni-Fe and Co based alloys, are directly melted in electric furnaces by classical methods usually applicable to stainless steels. However for Ni and special Ni-Fe superalloys, vacuum induction melting is required in order to reduce the content of interstitial gases (O, H, N) to a very low level. This enables foundries to achieve high and controlled contents of oxidisable elements such as Ti or Al. 

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