This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Postsintering Secondary Operations – Impregnation, Infiltration & Heat Treatment”.
1. Impregnation of sintered component is done using either a _______ or a ________
a) lubricant, resin
b) wax, resin
c) lubricant, aqueous medium
d) oil, wax
Explanation: Impregnation is the process of porosity sealing of sintered components. Impregnation of the sintered component is done using either a lubricant or a resin, the purpose is different in each case.
2. Porous bearings are impregnated with ______
Explanation: Porus bearings are generally impregnated with oil. The viscosity of oil prevents corrosion, the additives are used to increase film strength and to prevent oxidation.
3. What is the pressure in the vacuum chamber while carrying out oil impregnation of bearings?
a) ≈ 1mm H2O
b) ≈ 1mm Hg
c) ≈ 0.5mm Hg
d) ≈ -1mm Hg
Explanation: During impregnation, the bearings are placed in a vacuum chamber and evacuated to nearly 1mm of Hg pressure. Oil is allowed to enter into the chamber. Air or nitrogen at a pressure of 0.5 MPa is applied for 1 minute to complete the impregnation.
4. Which of the following SAE standards give deatils regarding the impregnation of porous castings and sintered metal components?
Explanation: The SAE standard AMS03_1A specifies the processes and type of impregnant which can be used when impregnating castings for the following purposes: (1) Eliminating microporosity in castings, for applications requiring pressure tightness. (2) For sealing castings/sinter metal components to improve corrosion resistance and/or to render surface uitable for subsequent surface treatment.
5. _______ is widely practiced for valves, pumps, and compressor parts.
a) Lubricant impregnation
b) Grease impregnation
c) Oil impregnation
d) Resin impregnation
Explanation: Resin impregnation is used for valves, cylinder heads, pistons, pumps, and compressor housing requiring pressure tightness. Gun compnonets are typically resin impregnated to seal the pores.
6. Which of the following is not a benefit of impregnation?
b) Dimensional tolerance
c) Porosity elimination
d) Improved machinability
Explanation: The benfits of impregnation include- (1) self lubricating ability, (2) Increase in mechanical properties, (3) Pressure-tightness due to sealing off the porosity, (4) Prevention of the entry of corrosive salts into pores during plating, and (5) Improvement in machinability.
7. Which of the following baths are not used during heat treating P/M steel parts?
a) Oil baths
b) Water baths
c) Cyanide baths
d) Polymer quench
Explanation: While heat-treating P/M steel parts, salt baths and cyanide baths are generally not used for austenizing to avoid the possibility of trapping salt in the porous structure.
8. Which of the following quenching medium is used for quenching of P/M parts?
b) Brine solution
Explanation: The typical quenching medium used for P/M parts include plain water, brine solution and oil. However, oil is the preferred medium since it avoids cracking (occurs due to drastic cooling) as well as corrosion.
9. Which of the following treatment fives a ferrito-pearlitic structure in P/M steel forgings?
Explanation: The main purpose of annealing heat treatment is to obtain a ferrito-pearlitic structure which gives good machining characteristics. The temperature employed for annealing depends on the carbon content.
10. Which of the following heat treatment for sintered component is carried out in range of 500-570°C?
Explanation: Nitrocarburizing treatment is carried out on sintered components at temperature between 500-570°C. Carbonitriding is usually carried out at temperatures of 790°C whereas carburizing and gas- carburizing is carried out at still higher temperature ranges of 800-900°C.
11. Which of the following process gives a case with microstructure consisting of iron carbonitride and iron nitride?
Explanation: In nitrocarburizing, the microstructure of the case (after quenching in oil) consists of a thin layer of iron carbonitride and iron nitride (white layer), with a diffused layer of iron nitride, alloy nitrides and nitrogen.
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