applications precipitation hardening Flashcards
What does a system at equilibrium mean in a macroscopic sense?
A system is at equilibrium if its free energy is at minimum. In macroscopic sense, it means that the phase characteristics of the system do not change with time but persist indefinitely, i.e., the system is stable.
What happens when you know T and Co in binary phase diagrams? (3)
If we know T and Co,
- then we know: which phase(s) is (are) present.
- the composition of each phase.
- we can determine the fraction of each phase using the Lever Rule

What does limited solid solubility result from?
Limited solid solubility results from elements of differing atomic radii. When this limit is exceeded, the excess solute element is rejected into a second phase.
What is a eutectic reaction?
Eutectic reaction is a process that transform a liquid phase into two solid phases upon cooling of a component with a eutectic composition .
A lamellar structure of alternating layers of the two phases will usually result.
What is a eutectoid transformation?
In some systems, particularly the iron carbon system, a solid solution stable at a higher temperature decomposes into a two‐phase structure on cooling below a critical temperature.
What happens if a small amount of element B is added to a?
If a small amount of element B is added to A, the freezing point of the alloy is lowered. This will continue as the amount of B is increased.
Where is the eutectic point in phase diagrams?
The intersection of the two falling liquidus lines is known as the eutectic point as previously explained, and the temperature at which this occurs is the eutectic temperature.
What are the alloys to the left of the eutectic composition known as?
The alloys to the left of the eutectic composition are known as hypoeutectic alloys and those to the right are known as hypereutectic alloys.
What is the age hardening or precipitation hardening?
A heat treatment process known as age hardening or precipitation hardening can be applicable which will provide a strengthening effect.
How are PPTs formed?
The PPTs are formed as extremely small & uniformly dispersed particles through phase transformations induced by appropriate heat treatments
What are the essential conditions of precipitation hardening? **__ (3)
– an appreciable maximum solubility of one component in the other, on the order of several percent, at point*
– a solubility limit that rapidly decreases in the major component with temp reduction, on the boundary of**
– the composition of a precipitate‐hardening alloy MUST be less than the maximum solubility.
What is the difference between solution heat treatment and precipitation heat treatment?
Solution heat treatment is done at a higher temperature and allows total dissolution of B then diffusion and formation of B is prevented (Quench)
Precipitation occurs after solution heat treatment is complete. The temperature is lower and it allows total diffusion and PPT of B.
