This set of Phase Transformation Quiz focuses on “Solidification During Quenching from the Melt”.
1. Solidification can also occur at much higher rates of 104-107K/s. In which among the following it is not applicable?
a) Liquid metal atomization
b) Melt spinning
c) Roller quenching
d) Solidification of weld
View Answer
Explanation: Here except the fourth option rest everything can occur at much higher rates. Processes such as liquid metal atomization, melt spinning, roller-quenching or plasma spraying, as well as laser or electron beam surface treatment occur at this rate. By quenching melts, it is possible to achieve various metastable solid states not predicted by equilibrium phase diagrams.
2. Which among the following solidification can occur without microsegregation?
a) Crystalline solidification
b) Mixed solidification
c) Partial solidification
d) Revert solidification
View Answer
Explanation: Crystalline solidification can occur without microsegregation or with cells or secondary dendrites spaced much more finely than in conventional solidification processes. Whether the solid is crystalline or amorphous, rapid solidification processing offers a way of producing new materials with improved magnetic or mechanical properties.
3. The breakdown of solid/liquid interface at the local equilibrium can be due to___
a) Slow cooling
b) Slow heating
c) Rapid cooling
d) Rapid heating
View Answer
Explanation: One consequence of rapid cooling can be that local equilibrium at the solid/liquid interface breaks down. Melts can solidify with no change in composition, i.e. partition less solidification or solute trapping can occur.
4. It is seen that for crystal growth rate, R, to keep pace with the welding speed, 3m/s, the condition must be met that for this to happen is____ (wetting angle 60°)
a) R = 1.5m/s
b) R = 3m/s
c) R = 0
d) R = 1.33m/s
View Answer
Explanation: For this to happen it should satisfy the condition that R the crystal growth rate should be equal to V*cosφ (φ is the wetting angle), so here in this case φ = 60, hence cosφ equal to 0.5 hence the rate is given as 3*0.5 = 1.5 m/s.
5. Welding can be considered as a ______
a) Dynamic process
b) Static process
c) Rapid process
d) Explosive process
View Answer
Explanation: Welding is essentially a dynamic process in which the heat source is continuously moving. This means that the maximum temperature gradients are constantly changing direction as the heat source moves away.
6. An important effect of increasing the welding speed is that the shape of the weld pool changes from an elliptical shape to a ___________
a) Circular shape
b) Pear shape
c) Rectangular shape
d) Broad shape
View Answer
Explanation: Here the main change observed is in the shape of the weld pool, it changes from an elliptical shape to a narrower, pear shape. Corresponding to the angular geometry of the melt, the pear-shaped weld pool keep fairly constant thermal gradients up to the weld centre-line.
7. TIG welding of thin plates will give steeper thermal gradients than submerged arc welding of thick plates, the latter process will have the higher heat input.
a) True
b) False
View Answer
Explanation: The above mentioned statement is true. Here the base metal is an efficient heat sink and the temperature noticed directly underneath the arc is so high, hence as a consequence the degree of super cooling turns be so low.
8. Typical shielding gases in TIG welding includes ______
a) Helium
b) Carbon
c) Oxygen
d) Methane
View Answer
Explanation: Here the melting point of tungsten is fairly high and it is about 3140 degree Celsius hence it act as a good electrode. Argon, helium or the mixture of these gas elements act as the typical shielding gases.
9. Plasma arc welding is a special form of ____
a) TIG welding
b) Electron beam welding
c) Resistance welding
d) Submerged arc welding
View Answer
Explanation: Plasma arc welding (PAW) is a special type or form of gas tungsten arc welding in which the metal to metal joint takes place in molten state and in the weld area we have the a constricted plasma arc. It is extensively used in the electronic industries or for coating on the turbine blade we use this type of welding.
10. Which among the following is the first automated arc welding process?
a) TIG
b) Submerged arc welding
c) Plasma arc welding
d) Resistance arc process
View Answer
Explanation: This process, developed during the 1930s, was one of the first AW processes to be automated. Submerged arc welding (SAW) is an arc-welding process that uses a continuous, consumable bare wire electrode, and arc shielding is provided by a cover of granular flux.
11. Calculate the heat density if the power transferred is 1000W and the corresponding surface area is 10m2?
a) 100
b) 10
c) 1
d) 1000
View Answer
Explanation: Heat density can be calculated using the formula P/A, where P refers to the total power and A the corresponding area. So, in this case 1000/10 = 100W/m2. High-density heat energy is supplied to the faying surfaces, and the resulting temperatures are sufficient to cause localized melting of the base metals
12. In general dendritic and cellular substructures in welds tend to be on a finer scale than in casting.
a) False
b) True
View Answer
Explanation: The statement is true and this is mainly due to the comparatively high solidification rates of weld metal. Here the greater rates of solidification can be achieved by the higher welding speeds or thicker base metals, hence the finest and the smoothest substructures are associated with these welds.
13. How much impact does a nucleation barrier can create to the solidification when melt has approximately the same composition as the base metal, ‘wetting’ of the base metal is very efficient?
a) It can increase the undercooling
b) It can decrease the rate of undercooling
c) It can melt the base metal
d) No major effect
View Answer
Explanation: There is almost no nucleation barrier to solidification and hence very little undercooling occurs. Solidification is thus predicted to occur epitaxially, that means the nuclei will have the same lattice structure and orientation as the grains at the solid-liquid surface of the base metal.
14. Wire diameters in the Gas metal arc welding ranges from _______
a) 0.5-0.8cm
b) 1-3m
c) 1-4mm
d) 0.65-0.8mm
View Answer
Explanation: Wire diameters ranging from 0.8 to 6.5 mm are used in GMAW, the size depending on the thickness of the parts being joined and the desired deposition rate. Gases used for shielding include inert gases such as argon and helium, and active gases such as carbon dioxide.
15. General coarseness of the microstructure (Melt) is largely determined by the _______
a) Grain size of base metal
b) Composition of base metal
c) Texture
d) Nothing can be said
View Answer
Explanation: the general coarseness of the microstructure is largely determined at the melt by the grain size of the base metal. Unfortunately, the base metal at the transition zone receives the most severe thermal cycle and after high-energy welding in particular the grains in this zone tend to grow and become relatively coarse.
Sanfoundry Global Education & Learning Series – Phase Transformation.
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