Titanium and titanium alloys are used chiefly for parts that require good corrosion resistance, moderate strength up to 600F, and lightweight.

TYPES, CHARACTERISTICS, AND USES. -Titanium alloys are being used in quantity for jet engine compressor wheels, compressor blades, spacer rings, housing compartments, and airframe parts such as engine pads, ducting, wing surfaces, fire walls, fuselage skin adjacent to the engine outlet, and armor plate. In view of titaniums high melting temperature, approximately 3,300F, its high-temperature properties are disappointing. The ultimate and yield strengths of titanium drop fast above 800F. In applications where the declines might be tolerated, the absorption of oxygen and nitrogen from the air at temperatures above 1,000F makes the metal so brittle on long exposure that it soon becomes worthless. Titanium has some merit for short-time exposure up to 2,000F where strength is not important, as in aircraft fire walls.

Sharp tools are essential in machining techniques because titanium has a tendency to resist or back away from the cutting edge of tools. It is readily welded, but the tendency of the metal to absorb oxygen, nitrogen, and hydrogen must never be ignored. Machine welding with an inert gas atmosphere has proven most successful.

Both commercially pure and alloy titanium can absorb large amounts of cold-work without cracking. Practically anything that can be deep drawn in low-carbon steel can be duplicated in commercially pure titanium, although the titanium may require more intermediate anneals.

IDENTIFICATION OF TITANIUM. -Titanium metal, pure or alloyed, is easily identified. When touched with a grinding wheel, it makes white spark traces that end in brilliant white bursts. When rubbed with a piece of glass, moistened titanium will leave a dark line similar in appearance to a pencil mark.

Most commercial copper is refined to a purity of 99.9 percent minimum copper plus silver. It is the only reddish-colored metal, and it is second only to silver in electrical conductivity. Its use as a structural material is limited because of its great weight. However, some of its outstanding characteristics, such as its high electrical and heat conductivity, in many cases overbalance the weight factor.

Because it is very malleable and ductile, copper is ideal for making wire. In aircraft, copper is used primarily for the electrical system and for instrument tubing and bonding. It is corroded by salt water, but is not affected by fresh water. The ultimate tensile strength of copper varies greatly. For cast copper, the tensile strength is about 25,000 psi; and when cold-rolled or cold-drawn, its tensile strength increases, ranging from 40,000 to 67,000 psi.

BRASS. -Brass is a copper alloy containing zinc and small amounts of aluminum, iron, lead, manganese, magnesium, nickel, phosphorous, and tin. Brass with a zinc content of 30 to 35 percent is very ductile, while that containing 45 percent has relatively high strength. "Muntz metal" is a brass composed of 60 percent copper and 40 percent zinc. It has excellent corrosion-resistant qualities when in contact with saltwater. Its strength can be increased by heat treatment. As cast, this metal has an ultimate tensile strength of 50,000 psi and can be elongated 18 percent. It is used in making bolts and nuts, as well as parts that come in contact with salt water.

"Red brass," sometimes termed bronze because of its tin content, is used in fuel and oil line fittings. This metal has good casting and finishing properties and machines freely.

BRONZES. -Bronzes are copper alloys containing tin. The true bronzes have up to 25 percent tin, but those below 11 percent are most useful, especially for such items as tube fittings in aircraft.

Among the copper alloys are the copper aluminum alloys, of which the aluminum bronzes rank very high in aircraft usage. They would find greater usefulness in structures if it were not for their strength/weight ratio as compared with alloy steels. Wrought aluminum bronzes are almost as strong and ductile as medium-carbon steel, and possess a high degree of resistance to corrosion by air, salt water, and chemicals. They are readily forged, hot- or cold-rolled, and some react to heat treatment.

These copper-based alloys contain up to 16 percent of aluminum (usually 5 to 11 percent) to which other metals such as iron, nickel, or manganese maybe added. Aluminum bronzes have good tearing qualities, great strength, hardness, and resistance to both shock and fatigue. Because of these properties, they are used for diaphragms and gears, air pumps, condenser bolts, and slide liners. Aluminum bronzes are available in rods, bars, plates, sheets, strips, and forgings.

Cast aluminum bronzes, using about 89 percent copper, 9 percent aluminum, and 2 percent of other elements, have high strength combined with ductility, and are resistant to corrosion, shock, and fatigue. Because of these properties, cast aluminum bronze is used in gun mounts, bearings, and pump parts. These alloys are useful in areas exposed to salt water and corrosive gases.

Manganese bronze is an exceptionally high-strength, tough, corrosion-resistant copper zinc alloy containing aluminum, manganese, iron, and occasionally nickel or tin. This metal can be formed, extruded, drawn, or rolled to any desired shape. In rod form, it is generally used for machined parts. Otherwise it is used in catapults, landing gears, and brackets. Silicon bronze is composed of about 95 percent copper, 3 percent silicon, and 2 percent mixture of manganese, zinc, iron, tin, and aluminum. Although not a bronze in the true sense of the word because of its small tin content, silicon bronze has high strength and great corrosion resistance and is used variably.

BERYLLIUM COPPER. -Beryllium copper is one of the most successful of all the copper-based alloys. It is a recently developed alloy containing about 97 percent copper, 2 percent beryllium, and sufficient nickel to increase the percentage of elongation. The most valuable feature of this metal is that the physical properties can be greatly stepped up by heat treatment-the tensile strength rising from 70,000 psi in the annealed state to 200,000 psi in the heat-treated state. The resistance of beryllium copper to fatigue and wear makes it suitable for diaphragms, precision bearings and bushings, ball cages, spring washers, and nonsparking tools.

Monel, the leading high-nickel alloy, combines the properties of high strength and excellent corrosion resistance. This metal consists of 67 percent nickel, 30 percent copper, 1.4 percent iron, 1 percent manganese, and 0.15 percent carbon. It cannot be hardened by heat treatment; it responds only to cold-working. Monel, adaptable to castings and hot- or cold-working, can be successfully welded and has working properties similar to those of steel. It has a tensile strength of 65,000 psi that, by means of cold-working, may be increased to 160,000 psi, thus entitling this metal to classification among the tough alloys. Monel has been successfully used for gears and chains, for operating retractable landing gears, and for structural parts subject to corrosion. In aircraft, Monel has long been used for parts demanding both strength and high resistance to corrosion, such as exhaust manifolds and carburetor needle valves and sleeves.

K-Monel is a nonferrous alloy containing mainly nickel, copper, and aluminum. It is produced by adding a small amount of aluminum to the Monel formula. It is corrosion resistant and capable of hardening by heat treatment. K-Monel has been successfully used for gears, chains, and structural members in aircraft that are subjected to corrosive attacks. This alloy is nonmagnetic at all temperatures. K-Monel can be successfully welded.