L9: Copper- Nickel Phase Diagrams

Question 1

What is the at% of the alloy based on?

Answer 1

The percentage of the alloy based on the number of atoms e.g. 40 atoms of nickel with 160 atoms of copper would give a 20 at% Ni

Question 2

What conditions are needed for the solidification processes seen on phase diagrams?

Answer 2

Equilibrium Conditions i.e. slow cooling

Question 3

How does the composition change take place

Answer 3

By diffusion of the atoms enabling the redistribution

Question 4

What happens when solidification processes do you not take place under equilibrium conditions

Answer 4

Rate of cooling is to rapid to enable the complete diffusion of the atoms in the solid-phase this produces polycrystal line materials whether it rains or not homogeneous

Question 5

What is the composition through the grain caused from non-equilibrium cooling

Answer 5

The centre of the grain has the composition of the solid that is first precipitated

The outside of the grain has the composition of the solid that is last to be precipitated

The average composition of the solid that has been precipitated it is given by the diagram

Average composition of the completely solidified alloy is the same as the original average composition however there is not a homogenous distribution of elements the solid alloy is set to be segregated or cored

Question 6

What is the cooling rate affect the phase diagram

Answer 6

The cooling rate determines how far from the original phase diagram the composition of the material varies

Question 7

What property can cored alloys have that cooled alloys do you not

Answer 7

Reduction in tensile strength

Question 8

How can cored alloys be made stronger

Answer 8

Heat treatments of the solid after manufacture can be used to even out the composition (homogenisation)

This provides more time at high-temperature for the atoms to do views and adopt the most thermodynamically stable arrangement