Metals and Engineering Alloys I

Question 1

Alloy

Answer 1

Mixture of a metal with one or more other metals or non-metals (binary, ternary etc.)

Question 2

Component

Answer 2

An element included in an alloy

Question 3

Phase

Answer 3

A region of material having uniform physical and chemical characteristics

Question 4

Composition

Answer 4

The mass of each component present in an alloy or phase

Question 5

Constitution

Answer 5

The sum of the phases, the mass of each phase and the composition

Question 6

Phase diagram

Answer 6

The equilibrium constitution of all combinations of temperature and composition

Question 7

Complete Solid Solution

Answer 7

The term, complete solid solubility means that the solute atoms are completely soluble in the solvent atoms for any composition of solute and solvent. Thus, a second phase does not form if complete solid solubility exists.

Question 8

What rule can be used to determine the composition of different phases in an alloy at a given temperature

Answer 8

The lever rule

Question 9

What is the lever rule

Answer 9

1. The tie line is constructed across the two-phase region at the temperature of the alloy
2. The overall alloy composition is located on the tie line
3. The fraction of one phase is computed by taking the length of tie line from the overall alloy composition to the phase boundary for the other phase, and dividing by the total tie line length
4. The fraction of the other phase is determined in the same manner
5. If phase percentages are desired, each phase fraction is multiplied by 100. When the composition axis is scaled in weight percent, the phase fractions computed using the lever rule are mass fractions—the mass (or weight) of a specific phase divided by the total alloy mass (or weight). The mass of each phase is computed from the product of each phase fraction and the total alloy mass

Question 10

Why are single crystal materials preferred over polycrystalline materials for some applications?

Answer 10

Single crystals have no grain boundaries. Grain boundaries have more free volume so give easy diffusion paths for atoms leading to creep and oxidation. Therefore, single crystals are typically more chemically and thermally resistant.

Question 11

Describe what is meant by a eutectoid composition

Answer 11

Eutectoid composition is the composition associated with the point where a solid is in equilibrium with two other solid phases. This is not to be confused with the eutectic point where a liquid is in equilibrium with 2 solid phases.

Question 12

What is the invariant point on a phase diagram

Answer 12

Point where the liquidus lines meet

Question 13

What temperature does pearlite form at?

Answer 13

723’c

Question 14

When austenite cools slowly at eutectoid composition what does it form?

Answer 14

At the eutectoid composition it forms pearlite.

Question 15

What does bainite transform from?

Answer 15

Rapid cooling of austenite, ( air cooling)

Question 16

What is the micro structure of martensite?

Answer 16

Needle like structure surrounded by γ that failed to transform

Question 17

What are the mechanical properties of martensite?

Answer 17

Martensite is very hard and brittle.