Question 1
A spacing ‘’D’’ can be used to completely accommodate the lattice misfit in the one direction without any long-range strain field by a set of edge location. Calculate the value of D if the interplanar spacing’s of matching planes are given as 20mm, 19mm respectively? (Assume the misfit to be very small)
A. 390mm
B. 240mm
C. 795mm
D. 800mm
View Answer
Answer: Option A
Explanation:
The value of D is given as b/Δ. Where the value of b = (da+db)/2, in this case 20mm and 19mm and this is actually the Burgers vector for dislocation. And the value of Δ is given as (20-19)/20, that is 0.05 and hence substituting this we get the required solution.
Question 2
Ag-rich zones in an AI-4 atomic % Ag alloy is an example of GP zone (Guinier and Preston).
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
The above mentioned statement is true and these zones are silver rich FCC region within the aluminum-rich FCC matrix. And one more major thing to note is that the diameters of aluminum and silver differ only by 0.7% hence the coherency strains doesn’t make much contribution to the total free energy of the alloy.
Question 3
Assume that 5mm and 5mm are the unstressed interplanar spacing’s of matching planes in the α and ß phases respectively, the disregistry, or misfit between the two lattices (∆) is defined by__
A. 0
B. 0.5
C. 1
D. 2
View Answer
Answer: Option A
Explanation:
If dα and dβ are the unstressed interplanar spacing’s of matching planes in the α and β phases respectively, the disregistry, or misfit between the two lattices (Δ) is defined by Δ = (dα –dβ)/dα, here since the interplanar spacing’s are same, the misfit will be 0.
Question 4
Calculate the punching stress P, if the constrained misfit is given as 1/3 and the shear modulus of the matrix is given as 5Pa?
A. 5Pa
B. 3Pa
C. 2Pa
D. 7Pa
View Answer
Answer: Option A
Explanation:
The punching stress P is independent of the precipitate size and depends only on the constrained misfit Ɛ. If the shear modulus of the matrix is μ, the punching stress is given as P=3μƐ. Substitute the respective value we get the required solution.
Question 5
For small values of misfit ∆, the structural contribution to the interfacial energy is approximately proportional to the____ (Semi coherent interface).
A. Size and shape of dislocation
B. Density of dislocation
C. Texture
D. Position of dislocation
View Answer
Answer: Option D
Explanation:
As the misfit Δ increases the dislocation spacing diminishes. For small values of Δ the structural contribution to the interfacial energy is approximately proportional to the density of dislocations in the interface. However, the interfacial energy increases less rapidly as Δ becomes larger and it levels out at a particular value of Δ.
Question 6
From an interfacial energy standpoint it is favourable for a precipitate to be surrounded by____
A. High-energy coherent interfaces
B. High-energy incoherent interfaces
C. Low-energy incoherent interfaces
D. Low-energy coherent interfaces
View Answer
Answer: Option D
Explanation:
If we consider the interfacial energy standpoint it always favorable to be surrounded by low-energy coherent interfaces but when the crystal structures of the of the precipitates and matrix are different it is usually hard to find a plane in the lattice that is common to both planes.
Question 7
Fully coherent precipitate is also known as GP zone, GP stands for _______
A. Gaff and Pearl
B. Gas and Pressure
C. Gatsby and Prince
D. Guinier and Preston
View Answer
Answer: Option D
Explanation:
GP for Guinier and Preston who first discovered their existence. This discovery was made independently by Preston in the USA and Guinier in France, both employing X-ray diffraction techniques.
Question 8
HCP silicon-rich k phase and the FCC copper-rich α-matrix in Cu-Si alloys forms ___
A. A coherent interface
B. An incoherent interface
C. Mixed interface
D. A semi coherent interface
View Answer
Answer: Option D
Explanation:
Here it forms a fully coherent interface. This requires the two crystals to be oriented relative to each other in a special way such that the interfacial plane has the same atomic configuration in both phases, disregarding chemical species.
Question 9
If the dislocation network (Burger and Interfacial) glides into the FCC crystal it results in a transformation of_____
A. FCC->HCP
B. HCP->FCC
C. HCP->BCC
D. BCC->HCP
View Answer
Answer: Option A
Explanation:
The glide planes of the interfacial dislocations are continuous from the FCC to the HCP lattice and the Burgers vectors of the dislocation’s, which necessarily lie in the glide plane, are at an angle to the macroscopic interfacial. If the dislocation network (Burger and Interfacial) glides into the FCC crystal it results in a transformation of FCC->HCP.
Question 10
If the precipitate and inclusion have different elastic moduli the elastic strain energy is no longer shape independent.
A. FALSE
B. TRUE
View Answer
Answer: Option B
Explanation:
If the precipitate and inclusion have different elastic moduli the elastic strain energy is no longer shape independent but is a minimum for a sphere if the inclusion is hard and a disc if the inclusion is soft. The above statements are applicable to isotropic matrices.
Question 11
If μ is the shear modulus of the matrix and V is the volume of the unconstrained hole in the matrix and the elastic energy does not depend on the shape of the precipitate, if so, calculate the elastic strain energy? (Assume the poissons ratio to be 1/3 and Misfit-Δ)
A. ΔG=4μΔ2/V
B. ΔG=4μ/Δ2*V
C. ΔG=4μΔ2*V
D. ΔG=4μΔ2 – V
View Answer
Answer: Option C
Explanation:
In general, the total elastic energy depends on the shape and elastic properties of both matrix and inclusion. However, if the matrix is elastically isotropic and both precipitate and matrix have equal elastic moduli, the total elastic strain energy ΔG is independent of the shape of the precipitate and is given as ΔG=4μΔ2 *V.
Question 12
In a semi coherent interface, the disregistry is periodically taken up by _________
A. Coarsened structure
B. Proper fit
C. Misfit dislocations
D. Cross dislocation
View Answer
Answer: Option C
Explanation:
The misfit dislocations periodically take up the disregistry and it becomes energetically more favorable to replace the coherent interface with a semi coherent interface.The strains associated with a coherent interface raise the total energy of the system.
Question 13
In which among the following case there is only one plane that can form a coherent interface?
A. Simple cubic
B. BCC
C. Edge centered lattice
D. HCP
View Answer
Answer: Option D
Explanation:
Only a single plane can form a coherent interface in case of a HCP/FCC interface, no other plane is identical in both crystal lattices. However all the lattice planes are identical apart from the differences in the composition if the two adjoining phases have the same crystal structure and lattice parameter.
Question 14
Incoherent interface can also exist between crystals with an orientation relationship if the interface has a different structure in the two crystals.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In general, incoherent interfaces result when two randomly oriented crystals are joined across any interfacial plane. They may, however, also exist between crystals with an orientation relationship if the interface has a different structure in the two crystals and they have many features in common with high angle grain boundaries.
Question 15
The degree of coherency can be greatly increased if_______
A. Macroscopically irrational interface is formed
B. Microscopically rational interface is formed
C. Macroscopically rational interface is formed
D. Microscopically irrational interface is formed
View Answer
Answer: Option A
Explanation:
The degree of coherency can, however, be greatly increased if a macroscopically irrational interface is formed, that means the indices of the interfacial plane in either crystal structure are not small integers and the detailed structure is very complex in nature.
Question 16
The formation of martensite in steel and other alloy systems occurs by the motion of_______
A. Incoherent-dislocation interfaces
B. Cropped-dislocation interfaces
C. Mixed-dislocation interfaces
D. Glissile-dislocation interfaces
View Answer
Answer: Option D
Explanation:
The formation of martensite in steel and other alloy systems occurs by the motion of glissile-dislocation interfaces. These transformations are characterized by a macroscopic shape change and no change in composition.
Question 17
The interfacial energies of semi coherent interfaces are generally in the range of_______ (approximately)
A. 0-200 mJm-2
B. 200-500 mJm-2
C. 500-1000 mJm-2
D. 10000 mJm-2
View Answer
Answer: Option C
Explanation:
The energies of semi coherent interfaces are generally in the range 200-500 mJm-2. In general, coherent interfacial energies range up to about 200 mJm-2 and the incoherent interfaces are characterized by a high energy (500-1000 mJm-2).
Question 18
The interfacial energy of a semi coherent interface can be approximately considered as the sum of two parts. What are they?
A. Chemical and structural contribution
B. Chemical and bulk contribution
C. Magnetic contribution and structural
D. Physical and bulk contribution
View Answer
Answer: Option D
Explanation:
The interfacial energy of a semi coherent interface can be approximately considered as the sum of two parts: (a) a chemical contribution, same as for a fully coherent interface, and (b) a structural term, which is the extra energy due to the structural distortions caused by the misfit dislocations.
Question 19
The resultant lattice distortion to maintain the coherency is known as__
A. Strain rupture
B. Coherency strain
C. Rupture plane
D. Maintenance plane
View Answer
Answer: Option B
Explanation:
It is possible to maintain the coherency even when the distance between the atoms in the interface is not identical and this can be done by straining one or both of the two lattices and the lattice distortions which results from this is known as coherency strain.
Question 20
Under which circumstances does a glissile semi coherent interface gets formed?
A. If the dislocations do not have a Burgers vector that can glide on matching planes in the adjacent lattices
B. Depends on the extent of gliding
C. When the orientation of the plane is unmatching
D. If the dislocations have a Burgers vector that can glide on matching planes in the adjacent lattices
View Answer
Answer: Option D
Explanation:
It is however possible, under certain circumstances, to have glissile semi coherent interfaces which can advance by the coordinated glide of the interfacial dislocations. This is possible if the dislocations have a Burgers vector that can glide on matching planes in the adjacent lattices.
Question 21
What kind of misfit arises if the inclusion is the wrong size for the hole it is located?
A. Volume misfit
B. Lattice misfit
C. Vertical misfit
D. Lateral misfit
View Answer
Answer: Option A
Explanation:
When the inc1usion is incoherent with the matrix, there is no attempt at matching the two lattices and lattice sites are not conserved across the interface. Under these circumstances there are no coherency strains. Misfit strains can, however, still arise if the inclusion is the wrong size for the hole it is located in. In this case the lattice misfit has no significance and it is better to consider the volume misfit.
Question 22
When the value of (Δ) misfit is greater than 0.25, the kind of interface is known as _________
A. Coherent interface
B. Mixed interface
C. Semi coherent interface
D. Incoherent interface
View Answer
Answer: Option D
Explanation:
When Δ > 0.25, that is one dislocation every four interplanar spacing’s, the regions of poor fit around the dislocation cores overlap and the interface cannot be considered as coherent, and it is known as the incoherent interface.
Question 23
Within the bulk of each phase every atom has an optimum arrangement of nearest neighbours that produces a low energy. At the interface, however, there is usually a change in composition so that each atom is partly bonded to wrong neighbours across the interface.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
At the interface there is usually a change in composition so that each atom is partly bonded to wrong neighbours across the interface. This increases the energy of the interfacial atoms and leads to a chemical contribution to the interfacial energy.