Question

Explain precipitate hardening clearly ? Feel free to use a binary phase diagram to illustrate how it is accomplished. Explain how precipitate hardening makes a material stronger and harder ? There are two reasons and only one is pinning of dislocations ?

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Answer 1

In simple words it is the formation of small aggregations of a second phase of a metal alloy within the original matrix. The second phase thus present are unformly distributed over the entire original metal alloy phase.The new phase or the second phase is termed as the precipitate and the entire process is referred to as the precipitate hardening. The precipitate particles are also very fine in size allowing an effecient and easy distribution of them over the original metal phase. This technique is widely applied in the alloy industry. Lets say for example an metal alloy at temperature T has a single phase alpha, as we start cooling the metal alloy, it gives another phase of metal which is present within the alpha phase. By controlling the temperature and the time we can design an alloy with the desired precipitation limit. Metals of alloy are free to dislocate owing to their uniformity. When we have another phase within the system, this dislocation is restricted. So to achieve the same amount of dislocation we have to apply greater amounts of stress on the alloy. Which directly means that the strength of the alloy has increased. This effect increases over time, also known as th age hardening of the precipitate.