This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Melting of Titanium Alloys”.
1. In general, titanium is denser than steel due to compactness in grain structure of titanium.
a) True
b) False
View Answer
Explanation: Titanium is a low density material which is approximately 60% of the density of steel. It is mainly strengthened by alloying and deformation methods. It is a nonmagnetic metal which has low thermal conductivity. Its coefficient of thermal expansion is generally less than that of steel and less than half that of aluminium.
2. Titanium alloys have melting point greater than that of steels.
a) True
b) False
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Explanation: Titanium alloys have melting point greater than that of steels, but maximum temperatures for various applications normally range from 428 °C to approximately 540 °C. It mainly depends upon the composition and its characteristics. Titanium aluminide alloy can achieve temperature up to 760 °C for some applications.
3. Titanium is a toxic material which can also be affected by the attack of chlorides or mineral acids.
a) True
b) False
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Explanation: Titanium has the ability to un-react with any coating or material, so thereby it shows a high degree of resistance against the attacks of chlorides and mineral acids. Pure titanium is a nontoxic material, so its alloys and it can be compatible with human tissues and bones biologically without any significant effects to the human body.
4. The properties of titanium can remain constant with abrupt variations in the temperature of a material.
a) True
b) False
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Explanation: Titanium has good properties like strength, low-thermal expansion with low modulus with respect to its low-high cycle of fatigue strength, corrosion resistance, and weld-ability. Titanium is the only material that includes this combination of properties over a temperature range starting from the surrounding temperature to approx 550 ⁰C.
5. Which of the following materials is the most dominant in aero engine applications?
a) Iron
b) Brass
c) Titanium
d) Copper
View Answer
Explanation: Titanium is the single material which is very dominant in compressor stages of aero engine applications. Aluminium and steel can also be used, but the use of titanium is very effective. Its alloys greatly improve the aerodynamic cycle and propulsive efficiency also with improvements in thrust to weight ratio.
6. Melting and casting of titanium are very difficult due to its high chemical reactivity with mould materials.
a) True
b) False
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Explanation: Many problems arise in process of melting and casting of titanium due to its great chemical reactivity with mould material and its great affinity for surrounding gases. To avoid such problems, graphite or investment moulding is preferred which are also difficult but possible to produce equipment in aero engine and biomedical applications.
7. In general, titanium castings exhibits excellent fatigue strength due to its high rigidity.
a) True
b) False
View Answer
Explanation: Titanium castings generally have beta structure which is combined with excellent creep resistance, fatigue crack resistance and tensile properties. But the titanium castings exhibits very low fatigue strength due to the presence of porosities in the castings. These porosities can be treated by isostatic pressing to improve properties of the titanium castings.
8. Refractory oxides do not have any effect on molten titanium metal at the time of casting process.
a) True
b) False
View Answer
Explanation: Most of the refractory oxides like zirconia and alumina react with molten titanium to generate a layer which is enriched in oxygen or inter-metallic compounds of titanium. The oxide mixes in molten titanium which gives rise to a contaminated layer that can be considered as precipitate as a separate phase on cooling.
9. Which of the following methods of melting is not used for melting titanium metal?
a) Induction method
b) Vacuum arc method
c) Electron beam melting
d) Cupola furnace melting
View Answer
Explanation: Various melting methods are used for melting of titanium metal. For example, induction, vacuum arc and electron beam melting, in which vacuum arc and electron beam melting methods are widely used, though efforts are made continuously for producing other different methods to gain better control on melting and to have better utilization of scrap materials. And cupola furnace is basically used for melting iron alloys.
10. Titanium metal generally has a high melting point and low thermal conductivity.
a) True
b) False
View Answer
Explanation: Titanium metal has a high melting point and low thermal conductivity which is responsible for producing a steep thermal gradient in the casting during solidification. The reaction with mould materials forms surface layers which include oxygen and other elements taken from the mould. This affects the mechanical properties of the castings. So to avoid such problems, graphite or investments moulds are used instead of simple moulds.
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