a$)$ In the modification of Al$-$Si eutectics: What are the common modificators? Draw the modified

and unmodified microstructures simply. $(10$p$)$

b$)$ Explain required conditions and formation differences of lamellar and spheroidal graphite growth

in cast irons. $(10$p$)$

a$)$ In binary metallic eutectic systems: What is the volumetric requirement for formation of lamellar

eutectic structure? Define the relation between inter lamellar spacing, growth rate and strength. $(10$p$)$

b$)$ Specify sources of insoluble particles in melts and their distribution types in solidified micro

structures. $(10$p$)$

a$)$ What is the source of solute hydrogen during metal melting? Give its solution reaction for

aluminium. $(8p)$

b$)$ Define schematically the effect of growth rate on the interaction between a gas bubble and the

solid$-$liquid interface. $(12$p$)$

a$)$ In the structure of castings, explain the variation of the length of the columnar zone with pouring

temperature and alloy content. $(10$p$)$

b$)$ What are the main differences between macrostructures of ingot castings and fusion welds? $(10$p$)$

a$)$ Explain formations of grain boundary segregation. $(8$p$)$

b$)$ Specify the formation of normal and inverse segregation and their main difference. $(12$p$)$