Engineering Materials MCQ Questions & Answers | Mechanical Engineering

Gun metal, also known as red brass, is a type of bronze that is commonly used in casting and for making items like valves, gears, and bearings due to its resistance to corrosion and high strength.

It typically contains 85% to 92% copper, and the remainder is made up of tin, with small amounts of lead and sometimes nickel to improve its machinability and corrosion resistance.

Now let's look at why the other options are incorrect:

Option A: 70% copper and 30% zinc — This composition is closer to brass, not gun metal.

Option B: 90% copper and 10% tin — This is a typical composition of standard bronze, not gun metal specifically.

Option D: 70 - 78% copper and rest tin — This composition does not accurately reflect gun metal and lacks the small additions of lead and nickel that characterize gun metal.

Conclusion: The correct composition of gun metal is 85 - 92% copper, with the remainder being tin and small amounts of lead and nickel.

Hence, the correct answer is Option C.

Physical properties of wrought iron are listed below:
Soft and Tough
Ductile
Hight tensile Strength
High compressive strength
Easily forged and weldable

A crucible is a pot that is used to keep metals for melting in a furnace. Furnace crucibles are designed to withstand the highest temperatures encountered in the metal casting works. and it is made of graphite.

The correct answer is Option A: Nickel, copper and iron

Here's why:

Perminvar is a special type of alloy known for its exceptionally constant magnetic permeability over a wide range of magnetic field strengths.

This unique property is achieved through a specific combination of elements.

Key Takeaway: Perminvar alloys are primarily composed of Nickel (Ni), Copper (Cu), and Iron (Fe).

The other options contain different elements (like zinc, antimony, and bismuth) that are not used in the standard composition of Perminvar.

Tungsten is an important alloying element in steel, especially in high-speed tool steels.

Effect on properties: It forms very hard and stable carbides (tungsten carbides) that greatly enhance the wear resistance of the steel.

Cutting ability: Tungsten maintains hardness even at elevated temperatures (red hardness), which significantly improves the cutting ability of tools.

Toughness: Addition of tungsten also contributes to improved toughness of the steel, making it suitable for high-stress applications.

Conclusion: Therefore, tungsten in steel mainly improves wear resistance, cutting ability and toughness.

The hexagonal closest packed (hcp) has a coordination number of 12 and contains 6 atoms per unit cell. and it is found in Zinc, magnesium, cobalt, cadmium, antimony and bismuth

Body-centered cubic space lattice is found in Alpha iron, tungsten, chromium and molybdenum.
Body-centered cubic lattice (bcc or cubic-I), like all lattices, has lattice points at the eight corners of the unit cell plus additional points at the center of the cell.

allotropy is the existence of two or more crystalline or molecular structural forms of an element that have different chemical or physical attributes.

Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. and The surface hardness is achieved by nitriding operation at 1000 to 1100 VPN

creep is the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses.