Question

31. Why grain boundary sliding/rotation become more important in Nona-sized grains (<50 nm)? 32. Compare the mechanical properties of pure metals and their solid solutions. 33. State the conditions which are needed for age hardening. 34. State the difference between 2nd phase particles and precipitates

Answer 1

31) Grain boundary sliding is a process in which grains slide along each other. Grain boundary sliding sufficiently decreases grain interaction in the intracrystalline plastic deformation regime and it can be a mechanism for accommodating strain incompatibility between neighboring grains.

32) Pure metals have higher melting and boiling point, lustrous, ductility, malleability, have good electrical and heat conductivity and have a high density whereas solid solutions have higher hardness and lower electrical conductivity than the metals. Solid solutions are more valuable than pure components.

33) Conditions for age hardening is as follows

Presence of sloping solvus line in the phase diagram

A system which contains two equilibrium phases at room temperature, which can be heated to a temperature that dissolves the second phase

An appreciable maximum solubility of one component in the others

Alloy system must show a decrease in solubility with a decrease in temperature

Alloy must be quenchable

Coherent precipitate must form

Matrix should be soft and ductile whereas precipitate should be hard and brittle

34) Difference between 2nd phase particles and precipitates

Primary species of precipitation strengthening are second phase particles which cause movement of dislocations throughout the lattice. Second phase particles forms due to rejection of additional alloying element, when more solute element is added than solid solubility.

In any dispersion-strengthened alloy, the continuous phase is known as matrix and the second phase present in smaller amount is called precipitate.