Page 185 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

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

ing watches), is brittle at low temperatures, and offers poor resistance to oxidation.
As an alloying element, tungsten imparts strength and hardness to steels at elevated
temperatures.
Tungsten alloys are used for applications involving temperatures above
165O°C, such as nozzle throat liners in missiles and in the hottest parts of jet and
rocket engines, circuit breakers, welding electrodes, tooling for electrical-discharge
machining, and spark-plug electrodes. The filament Wire in incandescent light bulbs
(Section 1.1) is made of pure tungsten and is produced by the use of powder-
metallurgy and wire-drawing techniques. Tungsten carbide, with cobalt as a binder
for the carbide particles, is one of the most important tool and die materials.
Tungsten is processed from ore concentrates by chemical decomposition and is then
reduced. It is further processed by povvder-metallurgy techniques in a hydrogen
atmosphere.

6.8.4 Tantalum

Identified in 1802, tantalum (Ta, after the mythical Greek king, Tantalus) is charac-
terized by its high melting point (3000°C), high density, good ductility, and resist-
ance to corrosion. However, it has poor chemical resistance at temperatures above
15 O°C. Tantalum is used extensively in electrolytic capacitors and in various compo-
nents in the electrical, electronic, and chemical industries; it also is used for thermal
applications, such as in furnaces and in acid-resistant heat exchangers. A variety of
tantalum-based alloys are available in many forms for use in missiles and aircraft.
Tantalum also is used as an alloying element. It is processed by techniques similar to
those used for processing niobium.

6.9 Beryllium

Steel gray in color, beryllium (Be, from the ore beryl) has a high strength-to-Weight
ratio. Unalloyed beryllium is used in rocket nozzles, space and missile structures,
aircraft disc brakes, and precision instruments and mirrors. It is used in nuclear and
X-ray applications because of its low neutron absorption. Beryllium is also an al-
loying element, and its alloys of copper and nickel are employed in various applica-
tions, including springs (beryllium copper), electrical contacts, and nonsparking
tools for use in such explosive environments as mines and metal-powder production
(Section 17.2.3). Beryllium and its oxide are toxic; their associated dust and fumes
should not be inhaled.

6.l0 Zirconium

Zirconium (Zr) is silvery in appearance; it has good strength and ductility at elevated
temperatures and has good corrosion resistance because of an adherent oxide film.
Zirconium is used in electronic components and in nuclear-power reactor applica-
tions because of its low neutron absorption.

Low-melting Alloys
6.1 I

Low-melting alloys are so named because of their relatively low melting points. The
major metals in this category are lead, zinc, tin, and their alloys.