Term
Define a
a) phase in a material
b) phase diagram. |
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Definition
a) Phase is a physically homogeneous and distinct portion of a material system. Phase in a material is a region that differ in its microstructure and/or composition from another region.
b) A graphical representation of phases present in a materials system at various temperatures, pressures and compositions. Phase diagrams are constructed by using equilibrium conditions. Most of the phase diagrams involve temperature versus composition. |
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Term
Refer to figure 8.1 in the textbook (pressure-temperature equilibrium phase diagram for pure water and answer the following:
a)How many degrees of freedom are there at the triple point?
b) How many degrees of freedom are there along the freezing line? |
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Definition
a) P + F = C + 2
3 + F = 1 + 2
F = 0
b) 2 + F = 1 + 2
F = 1 |
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Term
a) What is a cooling curve?
b) What type of information may be extracted from a cooling curve?
c) Draw a schematic of a cooling curve for a pure metal and one for an alloy. Discuss the differences. |
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Definition
a) A cooling curve is the plot temperature vs time aquired during solidification of a metal. It is used to determine phase transition temperature of metal vs time as it cools from a temperature at which it is molten through solidification and finally room temperature.
b) (1) Phase transition temperatures for pure metals and alloys are the latent hears of metal or mixtures for which solidifications are achieved. (2) Solid state phase transformation in the metals.
c) Refer to figure 8.3 and figure 8.6 in the textbook.
The cooling curve for metal alloys in an isomorphous system does not contain the thermal arrest region at a specific temperature and ends at a lower temperature as presented by L & S symbols. As a result, unlike pure metals, alloys solidify over a range of temperatures. |
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Term
| What is a binary isomorphous alloy system? |
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Definition
| A mixture of two metals is called a binary alloy. It is two component system systems since each metallic element is an alloy which is considered a separate component. In a binary metallic system, two elements that are completely soluble into each other in both solid and the liquid state are said to be a binary isomorphous alloy system. |
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Term
| What are the four Hume-Rothery rules for the solid solubility of one element in another? |
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Definition
1) The size of the atom of each of the two elements must not differ by more than 15%
2) The element should not form compound with each other, i.e. there should be no appreciable difference in the electronegativities of the two elements
3) The crystal structure of each element of the solid solution must be the same
4) the elements should have the same valance |
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Term
Write equations for the following invariant reaction:
eutectic
eutectoid
peritectic
pertectoid
How many degrees of freedom exist at invariant reaction points in binary phase diagrams? |
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Definition
eutectic - liquid to a two phase solid
eutectoid - solid to a two phase solid
peritectic - liquid + solid to a different solid phase
pertectoid - two solids to a different solid
P + F = C + 1
3 + F = 2 + 1
F = 0
P = 3 (3 phases in the invariant reactions)
C = 2 (since binary phase diagrams)
1 because pressure is kept constant |
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