MCQOPTIONS
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MCQOPTIONS
This section includes 15 Mcqs, each offering curated multiple-choice questions to sharpen your Phase Transformation knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The maximum velocity at the tip of growing dendrite occurs when ______ (r* is the critical radius) |
| A. | R = 2r* |
| B. | R = 3r* |
| C. | R = r* |
| D. | R = 4r* |
| Answer» B. R = 3r* | |
| 2. |
Calculate the value of latent heat of fusion per unit volume if the thermal conductivities of solid and liquid are given as 15 and 20 kW/mK respectively and the temperature gradient of liquid and solid are given as 2K/m and 1.5K/m respectively? (Assume the rate of growth as 5m/s) |
| A. | 0 |
| B. | 5 |
| C. | 25 |
| D. | 100 |
| Answer» B. 5 | |
| 3. |
When the solidification takes place from the mould wall (cooler than melt), this leads to the heat conduction through the solids. However the heat flow into the liquid arises if a certain condition is satisfied. Which among the following corresponds to the same? |
| A. | If the liquid is supercooled below Tm |
| B. | If the liquid is brought in contact with mould wall |
| C. | If the liquid is supercooled at any temperature |
| D. | Superheated above Tm |
| Answer» B. If the liquid is brought in contact with mould wall | |
| 4. |
Let s take the tip of a growing dendrite. Here in this case it can be seen that the tip velocity tends to zero for a particular value of r known as______ |
| A. | Critical radius |
| B. | Open radius |
| C. | Closed radius |
| D. | Extended radius |
| Answer» B. Open radius | |
| 5. |
Let us now take a closer look at the tip of a growing dendrite. The situation is different from that of a planar interface because heat can be conducted away from the tip in three dimensions. As a result of the Gibbs-Thomson effect equilibrium across a curved interface occurs at an undercooling Tr below Tm given by______ (Latent heat of fusion per unit volume) |
| A. | Tr = 2 Tm/(L*r) |
| B. | Tr = 2Tm/(L*r) |
| C. | Tr = 2Tm/(L* *r) |
| D. | Tr = 2 Tm/L |
| Answer» B. Tr = 2Tm/(L*r) | |
| 6. |
In pure metals solidification is controlled by the rate at which the latent heat of solidification can be conducted away from the solid/liquid interface. Which among the following equation satisfies the heat flow and the interface stability? (Kl, Ks are respective thermal conductivities of liquids and solids, L the latent heat of fusion per unit volume, v growth rate). |
| A. | KsTs = Kl*Tl /(v*L) |
| B. | KsTs = Kl*Tl v*L |
| C. | KsTs = Kl/(Tl +v*L) |
| D. | KsTs = Kl*Tl +v*L |
| Answer» E. | |
| 7. |
In solidification it is quite common for materials showing faceting to solidify as two crystals in twin orientations. |
| A. | False |
| B. | True |
| Answer» C. | |
| 8. |
If the solid contains dislocations that intersect the S/L interface the problem of creating new interfacial steps can be circumvented. A complete theoretical treatment of this situation shows that for spiral growth the normal growth rate v and the undercooling of the interface Ti are related by an expression given as_______ (K material constant) |
| A. | R = K( Ti) |
| B. | R = K( Ti)<sup>3</sup> |
| C. | R = K( Ti)<sup>2</sup> |
| D. | R = K/( Ti)<sup>2</sup> |
| Answer» D. R = K/( Ti)<sup>2</sup> | |
| 9. |
Calculate the extent of interfacial undercooling if the value of k (Mobility) is given as 0.05(m/ (sec*Kelvin)) and the rate of solidification(R) is given as 5m/sec? |
| A. | 100K |
| B. | 1000K |
| C. | 200K |
| D. | 2000K |
| Answer» B. 1000K | |
| 10. |
Calculate the interfacial undercooling if the melting temperature is 600K and the latent heat of melting is given as 30kJ/kg? (Assume the driving force for solidification as 45kJ/kg? |
| A. | 150K |
| B. | 600K |
| C. | 900K |
| D. | 450K |
| Answer» D. 450K | |
| 11. |
Materials with a high entropy of melting prefer to form atomically smooth, close-packed interfaces. For this type of interface the minimum free energy also corresponds to the minimum internal energy. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 12. |
The surface nucleation rate governs the rate of growth normal to the interface .A theoretical treatment shows that this is proportional to_______ |
| A. | Ti |
| B. | Exp (k/ Ti) |
| C. | 1/ Ti |
| D. | Exp (-k/ Ti) |
| Answer» E. | |
| 13. |
The equation related to the net rate of solidification is given as_______ (K has the properties of boundary mobility) |
| A. | R = K* Ti |
| B. | R = K* Ti/Tm |
| C. | R = K*Tm |
| D. | R = K*(Tm/ Ti) |
| Answer» B. R = K* Ti/Tm | |
| 14. |
In the continuous growth process the driving force for solidification G is given as ______ |
| A. | G= L( Ti/Tm) |
| B. | G= L(Tm/ Ti) |
| C. | G= Ti/(Tm*L) |
| D. | G= Tm/(L* Ti) |
| Answer» B. G= L(Tm/ Ti) | |
| 15. |
Name the process by which the migration of rough interfaces takes place? |
| A. | Lateral growth |
| B. | Vertical wipe |
| C. | Batch growth |
| D. | Continuous growth |
| Answer» E. | |