### Material Science: Short answer questions from AMIE exams

Shear modulus, G (GPa), obeys proportionality with elastic modulus, E (GPa). If G = 45 GPa for a metal and Poisson's ratio,    = 0.31, calculate the value of E for the metal.

117.9 GPa

Stainless steels (an alloy of iron, a = 0.2867 nm) always can contain a huge amount of chromium. (a = 0.2885 nm). Explain.

From the given lattice parameters (a) the corresponding radii for iron and chromium are 0.124 nm. and 0.125 nm which are nearly the same so can easily form the crystal bonding. Stainless steel contains about up to 11% chromium.

Define isomorphous system with examples.

The term isomorphous system is related to the phase diagram, isomorphicity means having the same crystal structure or complete solubility for all compositions. The copper-nickel system is an example of an isomorphous system.

A pure copper wire has been drawn at a temperature of 750 °C. Is it hot or cold working by relevant parameter?

The melting point of copper is 1085°C. While the temperature at which it is drawn is 750°C which is 305°C less than the melting point. As for hot working the working temperature should be about 50°C less than the melting point, so the working temperature (750°C) much less (about 250°C) as required for hot working, so the copper wire has been drawn by cold working.

Define (a) remanence, and (b) coercivity.

• Remanence: (remnant induction Br) For a ferromagnetic or ferrimagnetic material, the magnitude of residual flux density that remains when the magnetic field is removed is called remanence.
• Coercivity: In materials science, the coercivity. also called the coercive field or coercive force, of a ferromagnetic material, is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has been driven to saturation. Thus coercivity measures the resistance of a ferromagnetic material to becoming demagnetized.

What is TD nickel?

TD nickel: TD Nickel is a recently developed alloy containing 2 volume per cent thoria and the balance nickel (Ni-2ThO₂).
The Thoria-dispersed nickel alloys (TD Nickel) contain thorium oxide additions (~2wt%) for increased elevated temperature strength up to 1200°C
The high-temperature strength of nickel alloys may be enhanced significantly by the addition of 3 volume % of Thoria (THO2) as finely dispersed particles. This material is known as thoria-dispersed (or TD) nickel.

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