For each of the following observations, identify what is the likely strengthenin

Question

For each of the following observations, identify what is the likely strengthening mechanism and describe briefly how the mechanism increases strength, making reference to dislocation movement.

a) Plastic deformation of an aluminium alloy at room temperature increases its hardness.

b) An alloy of 80wt% copper with 20wt% zinc has higher tensile strength than pure copper.

c) The tensile strength of nickel is increased by the addition of fine particles of thorium oxide.

d) A sample of commercially pure titanium with an average grain size of 20um shows higher tensile strength than a sample of the same alloy with an average grain size of 500um.

Explanation / Answer

Aluminium hardens due to the phenomenon of STRAIN HARDENING on being plasticaly deformed.

Zinc forms PRECIPITATES in Copper when alloyed with it hence resulting into PRECIPITAION HARDENING

Nickel RECRYSTALIZES on addition of THORIUM OXIDE and hardens due to RECRYSTALISATION

Remember FINER the grain size more hard will be the material, hence the on of 20 microns is more harder than 500 microns (Titanium hard due to GRAIN FINENESS).

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