Page 182 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 6.6 Superalloys

Production. The main sources of nickel are sulfide and oxide ores, all of which
have low concentrations of nickel. Nickel metal is produced by preliminary sedimen-
tary and thermal processes, followed by electrolysis; this sequence yields 99.95%
pure nickel. Although nickel also is present in the ocean bed in significant amounts,
undersea mining is not yet economical.

6.6 Superalloys

Superalloys are important in high-temperature applications; hence, they are also
known as heat-resistant or high-temperature alloys. Superalloys generally have good
resistance to corrosion, mechanical and thermal fatigue, mechanical and thermal
shock, creep, and erosion, at elevated temperatures. Major applications of superal-
loys are in jet engines and gas turbines. Other applications are in reciprocating
engines, rocket engines, tools and dies for hot working of metals, and the nuclear,
chemical, and petrochemical industries. Generally, superalloys are identified by
trade names or by special numbering systems, and they are available in a variety of
shapes. Most superalloys have a maximum service temperature of about 1000°C in
structural applications. The temperatures can be as high as 1200°C for non-load-
bearing components.
Superalloys are referred to as iron-based, cobalt-based, or nic/eel-based.

° Iron-based superalloys generally contain from 32 to 67% Fe, from 15 to 22%
Cr, and from 9 to 38% Ni. Common alloys in this group are the Incoloy series.
° Cobalt-based superalloys generally contain from 35 to 65% Co, from 19 to
30% Cr, and up to 35% Ni. These superalloys are not as strong as nickel-based
superalloys, but they retain their strength at higher temperatures.
° Nickel-based superalloys are the most common of the superalloys and are avail-
able in a wide variety of compositions (Table 6.9). The proportion of nickel is
from 38 to 76%. These superalloys also contain up to 27% Cr and 20% Co.
Common alloys in this group are the Hastelloy Inconel, Nimonic, René, Udimet,
Astroloy and Waspaloy series.

TABLE 6.9
Properties and Typical Applications of Selected Nickel-based Superalloys at 8T0°C
(All Are Trade Names)
Elongation
Ultimate tensile Yield strength in 50 mm
Alloy Condition strength (MPa) (MPa) Typical applications
Astroloy Wrought 770 690 Forgings for high-temperature use
Hastelloy X Wrought 255 1 80 ]et engine sheet parts
IN-100 Cast 885 695 _let engine blades and Wheels
IN-102 Wrought 215 200 Superheater and jet engine parts
Inconel 625 Wrought 285 275 Aircraft engines and structures, chemical
processing equipment
Inconel 718 Wrought 340 330 jet engine and rocket parts
MAR-M 200 Cast 840 760 ]et engine blades
MAR-M 432 Cast 730 605 Integrally cast turbine wheels
René 41 Wrought 620 550 Jet engine parts
Udimet 700 Wrought 690 635 _jet engine parts
Waspaloy Wrought 525 515 jet engine parts