Question

Question 3 View Policies Current Attempt in Progress 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) - 1,2,4 (b) - 3,5 (a) -3,5(b) - 1,2,4 (a) - 1,3,4 (b) - 1,2,5 (a) - 1,3,5(b) - 1,2,4 (a) - 1.24 (b) - 1.3,5

Answer 1

Statment 1 - True Preciptation hardening - In this method, dislocation motion is restricted by precipted particles. This causes increase in hardness and tensile strength. Preciptates are the particles seperated out from matrix after heat treatment.

Statment 2 - True for Preciptation hardening - Heating solution treated alloys above elevated temperature is called aging process. As aging increases hardness of alloy decreases.

Statment 3 - True for Dispersion hardening - Heating does not affect the hardness of alloys hardened by this method.

Statment 4- True for Precipitation hardening - This process involves heating the alloy to a high temperature and holding there for long time.This temperature depends on alloying elements. for eg. Steels are heated below eutectic temperature. After heating, alloys quenched in water.

Statment 5 - True for Dispersion hardening - This process does not involve heat, but involves dispersing hard particles.

Hence, Option A is correct.