From the following numbered list of characteristics, decide which pertain to (a) precipitation hardening, and which are displayed by (b) dispersion strengthening. 1. The strengthening mechanism involves the hindering of dislocation motion by precipitates/particles.
2. The hardening/strengthening effect is not retained at elevated temperatures for this process.
3. The hardening/strengthening effect is retained at elevated temperatures for this process.
4. The strength is developed by a heat treatment.
5. The strength is developed without a heat treatment

(a) Precipitation hardening - 1, 2, 4

(b) Dispersion strengthening - 1, 3, 5

Explanation:

The correct options for each are shown as follows:

Precipitation hardening

From the first statement; Dislocation movement is limited by precipitated particles. This resulted in an expansion in hardness and rigidity. Precipitates particles are separated out from the framework after heat treatment.

The aging process occurs in the second statement; because it speaks volumes on how heated solutions are treated with alloys above raised elevated temperature. As such when aging increases, there exists a decrease in the hardness of the alloy.

Also, for the third option for precipitation hardening; This cycle includes the application of heat the alloy (amalgam) to a raised temperature, maintaining such temperature for an extended period of time. This temperature relies upon alloying components. e.g. Heating of steel underneath eutectic temperature. Subsequent to heating, the alloy is extinguished and immersed in water.

Dispersion strengthening

Here: The effect of hearting is not significant to the hardness of alloys hardening by the method in statement 3.

In statement 5: The process only involves the dispersion of particles and not the application of heat.