The following points highlight the five main alloying elements that are used to improve the properties of metals. The alloying elements are: 1. Titanium 2. Zirconium 3. Beryllium 4. Halnium 5. Niobium.
Alloying Element # 1. Titanium:
It is becoming an important structural material. Commercially pure titanium melts at about 1660°C. It has good weight to strength ratio, high temperature properties and it is very corrosion resistant. It is about 67% heavier than aluminium, and about 409?’ lighter than stainless steels. It retains its strength very well upto 540°C.
Titanium-carbon alloys (with carbon varying from 0.015 to 1.1%) are finding wide acceptance. With increase in carbon content, these become more brittle but also become more corrosion resistant.
Maximum tensile strength of 7500 kg/cm2 is reached with 0.4% carbon. However, 0.04% carbon alloy has a strength of about 6150 kg/cm. Titanium alloys using tungsten and carbon have a tensile-strength of about 8700 kg/cm2.
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These fine wide applications in aircraft industry as titanium-manganese alloys with 8% Mm. The extraction of titanium from its ore is difficult, because of the great affinity of titanium for oxygen.
Alloying Element # 2. Zirconium:
It is a rare metal which is found in nature combined with silicon as zirconium silicate (ZrSiO4). It melts at 1852°C whereas Zirconium oxide melts at 2700°C and is used as lining for high temperature furnaces. It is difficult to separate from its ore. It is silvery-white in colour and reasonably strong.
Zirconium oxidises easily. Its strength is affected by oxygen, nitrogen and hydrogen with which it combines. It is used as air alloying element in alloy steels. Zirconium alloys with tin, nickel, Cr and iron have improved corrosion resistance and higher strength than unalloyed Zirconium. It is also used as a nuclear engineering material.
Alloying Element # 3. Beryllium:
It is a rare metal which is expensive to produce. It is light metal having density of 1.845 gm/cc. (lighter than aluminium). It is often used as an alloying clement with other metals (like copper and nickel to increase elasticity and strength characteristics). It is a hard, steel- grey metal that melts at about 1285°C. It does not react to any marked degree with neutrons which pass through it.
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It has high thermal and electrical conductivity and high heat absorption rate. It has good strength at high temperatures.
Some beryllium copper alloys are very strong and are used to replace forged steel tools in places when an explosive atmosphere may be present since these alloys are non- sparking. Because of its low density and high modulus of elasticity, beryllium also finds use in high speed aircrafts and rockets.
Beryllium is mixed with magnesium to reduce its tendency to burn during melting and casting. This metal and its compounds are reported to have dangerously poisonous properties and as such special precautions are needed in working with it.
Alloying Element # 4. Halnium:
This is similar to zirconium. Its melting point is 2120°C. It is heavy and slightly stronger than beryllium. Because of its high strength and corrosion resistance, capacity to absorb neutrons and free radiation attack, it is used as a control-rod material for pressurised water cooled reactors.
Alloying Element # 5. Niobium:
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This is a silvery white metal which is extremely ductile and soft. Its melting point is 2468°C. It is slightly weaker than iron. Since its ductility is affected by small amounts of oxygen and carbon, hot working and heating in air should be avoided. It is used in nuclear engineering applications and for gas-turbine blades.