Please explain the meaning of this statement with close reference to Precipitation hardening,"The relative rates of nucleation and growth are controlled by temperature. The size and dispersion of the secondary phase is controlled by time, with coarsening occurring as time proceeds."What I do not understand is the difference between the usage of "growth" and "size" as different parameters. They say they are dependent on temperature and time respectively.Arent they basically the two sides of the same coin.Please explain me with close reference the the precipitation hardening in Al-4.5wt%Cu alloy.
The difference and relationship between growth and size is analogous to the relationship between velocity and displacement. Do you think of velocity and displacement as being two sides of the same coin? I do not! The different things that are related. You can only determine displacement from velocity if you know the initial displacement and the velocity at all times. Likewise you can determine size from growth rate if and only if you know the time at which growth started and the growth rate as a function of time for all times.
The difference and relationship between growth and size is analogous to the relationship between velocity and displacement. Do you think of velocity and displacement as being two sides of the same coin? I do not! The different things that are related. You can only determine displacement from velocity if you know the initial displacement and the velocity at all times. Likewise you can determine size from growth rate if and only if you know the time at which growth started and the growth rate as a function of time for all times.
The extent of growth of the precipitate particles will decide the size, shape and morphology of the particles. During precipitation hardening the growth and in turn size of grains of microconstituents (phases) in the microstructure developed under the governing conditions such as temperature, rate of cooling, medium of cooling etc decides the material properties.
Dear Dr. Rajorshi Koyal,
I find myself in perfect harmony with what was said by Dr. w.s.l. Boyer. To continue further on this similarity, in addition to what is clearly stated, the importance of the time factor (acceleration, if we want to consider the hypothesis of displacement and velocity) is to be emphasized, as it has a great influence, as is widely known, in the results obtained in the different thermal treatments performed on the materials.
Best regards, Pierluigi traverso
Dear Rajorshi,
The formation of the Second phase particles over the primary phase is both
temperature and time dependent. While growth is a vector quantity size is a scalar
one. Both cannot be thetwo sides of a coin. The clarifications given by both
Mr. Boyer and Mr. Traverso are very interesting. Hope we have answered your query.
A.V.Sethuraman
4.5% Cu in aluminium is a super saturated solid solution. We are adding more copper than the solubility limit. The heat treatment is done in two stages- Quenching and Aging. During aging, based on the temperature of bath, nucleation and growth of take place as a result excess copper gets precipitated. For a certain temperature of bath, based on the aging time the precipitate size can be controlled.
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