Important Questions and Answers: Advanced Engineering Materials Metallic Glasses

MODERN ENGINEERING MATERIALS

1. What are metallic glasses?

Metallic  glasses  are  the  newly  developed  engineering  materials  which  shares  the properties of both metals and glasses. They are glasses having metallic properties.

2. What are the types of metallic glasses and mention few metallic glasses.

There are two types of metallic glasses, they are

i.           Metal –Metalloid metallic glasses

ii.           Metal –Metal metallic glasses

Metal –Metalloid metallic glasses

(Fe, Co, Ni) Metal –(B, Si, C, P)

Metalloid Metal –Metal metallic glasses

Nickel –niobium (Ni –Nb)

3. State the structural properties of metallic glasses.

i.                    They do not have any crystal defects such as grain boundaries dislocation etc

ii.          Metallic glasses have tetrahedral close packing (TCP) in contrast to hexagonal close packing (HCP) of the crystalline solid.

4. What are the mechanical properties of metallic glasses?

i.           Extremely high strength due the absence of point defects, dislocation and slip plane.

ii.          They have high elasticity.

iii.         They are highly ductile

5. What are the electrical properties of metallic glasses?

i.           Electrical resistively of metallic glasses is high (> 100µcm)Ωand it does not vary

much with temperature.

ii.          Due to high resistivity, the eddy current loss is very small.

6. What are the magnetic properties of metallic glasses?

i.           Metallic glasses have both soft magnetic and hard magnetic properties.

ii.          They exhibit high saturation magnetization.

iii.         The core losses of metallic glasses are very less.

7. What are the chemical properties of metallic glasses?

i.           They are highly resistant to corrosion due to the formation of protective

oxide film in chromium containing glasses.

ii.          They are highly reactive and stable.

8. What are the applications of metallic glasses?

i.           Metallic glasses possess high tensile strength. They are superior than common steels. This makes them useful as reinforcing elements in concrete, plastic or rubber.

ii.          Due to their high strength, high ductility, rollability and good corrosion resistance, they are used to make razor blades. This fact is also utilized to make different kinds of springs.

9. What are the advantages of using metallic glasses as transformer core material?

Metallic glasses are ferromagnetic. They possess low magnetic losses, high permeability and saturation magnetization with low coactivity. They also have extreme mechanical hardness and excellent initial permeability.

These properties make them useful as transformer core materials. Moreover power transformers made of metallic glasses are smaller in size and efficient in their performance.

10. What are shape memory alloys?

The group of metallic alloys which demonstrate the ability to return to their original shape or size (i.e., the alloy appears to have memory) when subjected to the appropriate thermal procedure (heating/cooling) is called Shape Memory Alloys (SMAs).

11. What is shape memory effect?

Certain metallic alloys like alloy of gold (Au) and Cadmium (Cd) exhibit a plastic nature, when cooled to a lower temperature. The return to their original dimensional configuration (metallic) during heating at high temperature. This effect is called Shape Memory Effect (SME).

12.            What are the properties of shape memory alloys?

i.           They can exist in two different solid phases with distinct crystal structures in SMA.

ii.          If temperature is increased, material goes to austenite phase which has cubic crystal structure and on cooling; the material comes back to its original shape in the martensite phase.

iii.         SMAs exhibit changes in electrical resistance, volume and length during the transformation with temperature.

iv.          They are extremely elastic or exhibit pseudo elasticity, i.e., strain can be very large for a given stress in the martensite phase.

v.          SMAs exhibit self-healing effect.

13.            What are the applications of shape memory alloys?

i.           Shape memory alloys can act as actuators and sensors.

ii.          Fiber composite shape memory alloys are used to produce twist on the helicopter

blades.

iii.         They are used in orthopaedic devices for pulling fractures together, artificial hearts and shrink-wrap.

14.            What is glass transition temperature?

The temperature at which the transition from liquid (metallic liquid) to solid (glass) occurs is known as the glass transition temperature.

15. What are nano phase materials?

Nanophase materials or nanaomaterials are newly developed materials with grain size at the nanometer range (10^-9), i.e., in the order of 1 –100 nm. The particle size in a nano materials is 1 nm.

16. Mention different forms of nanomaterials.

Nanodots, nanorods, Carbon nanotubes and Fullerenes.

17.            What are two routes through which nano particles can be synthesized?

(i) Top down approach: involving breaking down bulk materials to nanosizes. Example: Mechanical alloying

(ii) Bottom up approach: where the nano particles are made by building atom by atom.

Example: Inert gas condensation

18. Mention few techniques for synthesis of nano phase materials.

i)       Mechanical

ii) Inert gas condensation        alloying      

iii) Sol-gel technique     

iv) Electro-depostion

v) Laser synthesis

vi) Spraying

19.            What are physical properties of nanomaterials?

Melting point reduces with decrease in cluster size.

Interparticle spacing decreases with decreases in grain size for metal clusters. Ionization potential changes with cluster size of the nano grains.

Greater luminescence efficiency in nano semiconductor materials.

20.     What are mechanical properties of nanomaterials?

Higher hardness and mechanical strength (2-7 times) when grain size reduces from 1 μm to 10 nm.

Higher moduli of elasticity (30%-40%)

Very high ductility and super plastic behavior at low temperatures.

21. What are magnetic properties of nanomaterials?

Non-magnetic materials become magnetic when the cluster size reduces to 80 atoms. Bulk magnetic moment increases with decreases in coordination number Ferro magnetic materials exhibit superparamagnetism at nanograin sizes. Paramagnetic materials exhibit ferromagnetism at nano grain size.

22. What is non-linear optics?

The field of optics dealing with the non-linear behavior of optical materials.

23. Name few non-linear optical phenomena.

The few of the nonlinear phenomena observed are

1.     Second harmonic generation

2.     Optical mixing

3.     Optical phase conjugation

4.     Soliton