This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Postsintering Secondary Operations – Steam Treatment, Machining, Joining & Plating – 1”.
1. Which of the following process consists of heating the P/M part in air at temperature (200-250°C) and is not as effective as steam treatment?
a) Low- temperature treatment
b) Hot treatment
c) Blowing
d) Blueing
View Answer
Explanation: Blueing refers to heating the P/M part in air at a lower temperature (200-250°C) to provide a thin magnetite layer that gives some increase in corrosion resistance, but this treatment is not as effective as steam treatment.
2. What is the temperature range for steam treatment process?
a) 600-700°C
b) 350-400°C
c) 500-550°C
d) 400-470°C
View Answer
Explanation: The steam treatment process is very unique to P/M parts, and it involves exposing the part at a temperature around 500-550°C to high pressure steam. The steam reacts with the outer surface as well as the inner surfaces of the open pores exposed to the steam.
3. ________ layer forms during steam treatment.
a) Oxide
b) Hydride
c) Carbide
d) Nitride
View Answer
Explanation: Steam treatment of P/M parts leads to the formation of a layer of magnetite (oxide layer) on all accessible surfaces. The oxide layer so formed increases the surface hardness and particularly the wear resistance of the part.
4. Steam treatment is not applicable for ________
a) normalized parts
b) hardened and tempered parts
c) annealed parts
d) stress relived parts
View Answer
Explanation: Seam treatment is not generally applicable to hardened and tempered powder metallurgical parts because the exposure to high temperatures will result in over tempering of the parts.
5. _________ of P/M parts is carried out to add holes, threads, undercuts, grooves.
a) Joining
b) Plating
c) Machining
d) Impregnation
View Answer
Explanation: Machining of P/M parts is carried out to add holes, threads, undercuts, grooves as well as special features that cannot be incorporated into the die design. When holes at an angle to the direction of pressing or tapped holes are needed, machining is done.
6. Which of the following P/M part exhibit a short cutting tool life?
a) Sintered
b) Porous
c) Dense
d) Very dense
View Answer
Explanation: The presence of porosity alters the machining characteristics thus porous powder metallurgical part exhibit a low-thermal conductivity and hence the cutting tool life is short due to heat erosion.
7. The stress at the cutting tool tip while machining porous parts is ________
a) cyclic
b) non-cyclic
c) constant
d) linear
View Answer
Explanation: The stress at the cutting tool tip while machining porous parts is cyclic this is because the tool is stressed while in contact with solid and stress is relieved in contact with a pore.
8. Which type of failure occurs due to cyclic loading?
a) Plastic
b) Creep
c) Fatigue
d) Ductile
View Answer
Explanation: The stress at the tip of the cutting tool while machining porous parts is cyclic and this cyclic loading leads to fatigue failure of the tool. This fatigue failure becomes more prominent when the pores are open and connected.
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