Phase Transformation Interview Questions and Answers for Experienced people on “Interphase Interfaces in Solids – 2”.
1. 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
Answer: d
Clarification: 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.
2. Ag-rich zones in an AI-4 atomic % Ag alloy is an example of GP zone (Guinier and Preston).
a) True
b) False
Answer: a
Clarification: 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.
3. 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
Answer: d
Clarification: 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.
4. Which among the following are most unlikely to arise when a second-phase particle is located on a grain boundary?
a) Precipitate can have incoherent interfaces with both grains
b) Precipitate can have coherent or semi coherent interface with one grain and an incoherent interface with the other
c) Precipitate can have a coherent or semi coherent interface with both grains.
d) Nothing is predictable
Answer: c
Clarification: The first two options are commonly encountered but the third possibility is unlikely since the very restrictive crystallographic conditions imposed by coherency with one grain are unlikely to yield a favourable orientation relationship towards the other grain.
5. 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
Answer: c
Clarification: 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.
6. If the precipitate and inclusion have different elastic moduli the elastic strain energy is no longer shape independent.
a) False
b) True
Answer: b
Clarification: 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.
7. 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