Metallurgical Processes

Shot peening is a cold working process that bombards a surface with small spherical media to induce compressive residual stresses. These compressive stresses counteract tensile stresses during service, significantly delaying fatigue crack initiation and propagation in welds and springs. The other options (normalizing, spheroidizing, martempering) are heat treatments that primarily alter microstructure, not surface stress state.

This is True. Anodizing is indeed an electrolytic passivation process that increases the thickness of the natural oxide layer on metal parts, primarily aluminum. The process enhances corrosion resistance, surface hardness, and allows for dyeing. The anodized layer becomes integral to the metal substrate, not just a coating.

Passivation is indeed the spontaneous formation of a hard, non-reactive surface film (usually oxide) that inhibits further corrosion. This occurs naturally on metals like aluminum and stainless steel, creating a protective barrier. The statement correctly defines passivation, so 'True' (A) is the correct answer.

Superalloys are specifically designed for extreme environments like gas turbine engines where temperatures exceed 1000°C. They maintain strength at high temperatures, resist creep deformation, and withstand oxidation and corrosion. Common superalloys include Inconel, Waspaloy, and Rene alloys which contain nickel, cobalt, and other strategic elements.

Chemical milling is a specialized process used to create pockets, grooves, and contoured surfaces in aerospace sheet metal panels and bulkheads. It uses chemical etchants to remove material selectively from specific areas. This process is particularly useful for weight reduction in aircraft structures while maintaining structural integrity.

'Galvanize' originates from Luigi Galvani's experiments with electricity, meaning to stimulate with an electric current. In modern usage, it also means to shock or excite someone into action. The metallurgical meaning is coating metal with zinc for protection.

Japanese Type 97 Chi-Ha tanks had very thin armor (only 25mm maximum). Armor-piercing rounds would pass straight through without exploding. High explosive and incendiary rounds were more effective as they could ignite the tank or damage internal components despite the thin armor.

Rust is iron oxide (Fe2O3·nH2O), formed by oxidation of iron in the presence of oxygen and moisture. It is not a nitride (compound with nitrogen), cyanide (compound with CN-), or sulphide (compound with sulphur). The reddish-brown coating is oxidized iron.

Aluminum oxide (Al₂O₃) exhibits exceptional chemical inertness and high corrosion resistance, particularly against acids. This property, combined with its electrical insulation and high wear resistance, makes it valuable in applications like chemical processing equipment, crucible linings, and protective coatings. The sentence structure is awkward but the factual content is correct.

When iron rusts, it combines with oxygen from the air to form iron oxide (Fe2O3). This adds oxygen atoms to the iron, increasing the total mass. Therefore, iron weighs more after rusting, making True the correct answer.

Chromium is added to iron to produce stainless steel, which resists high temperatures and offers excellent hardness and abrasion resistance. This chromium steel is crucial for cutlery, industrial tools, and high-temperature applications.

The magnet test is a common field screening method for identifying stainless steel. Most stainless steel (austenitic grades like 304) is non-magnetic, so a magnet won't stick. However, some stainless steels (ferritic/martensitic grades) are magnetic, so this test isn't definitive but serves as a quick indicator.

Cold working introduces internal stresses and work hardening in materials due to plastic deformation. Annealing relieves these stresses by heating the metal above its recrystallization temperature and allowing controlled cooling, which enables new stress-free grains to form. This process restores ductility and reduces hardness. Hot working is a deformation process, not a stress-relief treatment, while normalising and temperpering serve different purposes.

Brasses and bronzes are copper-based alloys that are welded using a neutral flame, which has equal proportions of oxygen and acetylene completely burned. A neutral flame produces no chemical effect on the metal, preventing oxidation or decarburization, which is crucial for welding these non-ferrous alloys that are sensitive to chemical changes during heating.