Page 189 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

|68 Chapter 6 Nonferrous Metals and Alloys: Production, General Properties, and Applications

W yy* into molten metal and tapping the froth that forms at the surface; this froth then
solidifies into a foam. Other approaches to producing metal foam include (a) chem-
ical vapor deposition (Section 34.6.2) onto a carbon foam lattice, (b) depositing
metal powders from a slurry onto a polymer foam lattice, followed by sintering
(Section 17.4) to fuse the metals and burn off the polymer, (c) doping molten or
powder metals (Chapter 17) with titanium hydride (TiH2), which then releases
hydrogen gas at the elevated casting or sintering temperatures, and (d) pouring
molten metal into a porous salt and, upon cooling, leaching out the salt with acid.
Metal foams have unique combinations of strength-to-density and stiffness-to-
density ratios, although these ratios are not as high as the base metals themselves.
However, metal foams are very lightweight and thus are attractive materials for aero-
space applications. Because of their porosity, other applications of metal foams are
filters and orthopedic implants. Recent developments include nicl<el-manganese-
gallium metal foams with shape-memory characteristics (Section 6.13).
FIGURE 6.3 Microstructure
of a metal foam used in ortho-
pedic implants to encourage
bone ingrowth. Source: Cour- SUMMARY
tesy of Zimmer, Inc.
° Nonferrous metals and alloys include a very broad range of materials. The most
common are aluminum, magnesium, and copper and their alloys, which have a
wide range of applications. For higher temperature service, nonferrous metals in-
clude nickel, titanium, refractory alloys (molybdenum, niobium, tungsten, tanta-
lum), and superalloys. Other nonferrous metal categories include low-melting
alloys (lead, zinc, tin) and precious metals (gold, silver, platinum).
° Nonferrous alloys have a wide variety of desirable properties, such as strength,
toughness, hardness, and ductility; resistance to high temperature, creep, and
oxidation; a wide range of physical, thermal, and chemical properties; and high
strength-to-weight and stiffness-to-weight ratios (particularly for aluminum
and titanium). Nonferrous alloys can be heat treated to impart certain desired
properties.
° Shape-memory alloys (smart materials) have unique properties, with numerous
applications in a variety of products and manufacturing operations.
° Amorphous alloys (metallic glasses) have several properties that are superior to
other materials, available in various forms, they have numerous applications.
° Metal foams are very lightweight and thus are attractive for aerospace as well as
various other applications.
° As with all materials, the selection of a nonferrous material for a particular appli-
cation requires a careful consideration of many factors, including design and
service requirements, long-term effects, chemical affinity to other materials, envi-
ronmental attack, and cost.

KEY TERMS

Amorphous alloys Low-melting alloys Precious metals Smelting
Babbitts Metal foam Pyrometallurgy Superalloys
Brass Metallic glasses Refractory metals Temper designation
Bronze Nonferrous Shape-memory alloys
Galvanizing Pewter Smart materials