In the solidification of a metal, what is the difference between an embryo and a nucleus?

Requirements: normal

Engineering Materials

Assignment 2, Weight: 10% towards the final grade.

Due: 10/04/2023

Topics: Chapter 6 – Mechanical Properties.

Solutions to assignments must be computer generated and printed hard copies.

This is a group assignment. Include names of all the group members on your solution.

Answer all sub questions (if any) of a problem for full credit for that problem.

All questions are worth equal points each.

Present data and information in a tabular or graphical form as appropriate.

Identify your answers clearly for quantitative questions.

Late submissions will not be accepted.

Question 1.

(a) In the solidification of a metal, what is the difference between an embryo and a nucleus?

(b) What is the critical radius of a solidifying particle?

(c) What is the difference between homogeneous and heterogeneous nucleation for the solidification of a pure metal.

Question2. What special techniques must be used to produce single crystals? Discuss as many differences in the properties between a single crystal material and polycrystalline material of the same composition.

Question 3. Distinguish between a substitutional solid solution and an interstitial solid solution. Give examples of each type.

Question 4. What are the conditions that are favorable for extensive solid solubility of one element in another as described in Hume-Rothery rules? Demonstrate with at least one example.

Question 5. If there are 300 grains per square inch on a photomicrograph of a metal at 100x, what is its ASTM grain-size number?

Question 6.

(a) How are metal alloys made by the casting process?

(b) Distinguish between wrought alloy products and cast alloy products.

(c) Describe the forging process.

(d) What is the difference between hammer and press forging?

(e) What is the difference between open-die and closed-die forging? Give an example of a metal product produced by each process.

Question 7. Define the following terms:

(a) Modulus of elasticity

(b) Yield strength

(c) Ultimate tensile strength

(d) Modulus of resilience

(e) Toughness,

(f) Poisson’s ratio

(g) Ductility

Question 8. What are some important mechanisms to increase the strength of metals? Give examples.

Question 9. A cylindrical bar of 10.00 mm diameter of some metal is deformed elastically by an axial tensile load of 15,000 N. The diameter of the bar decreases by 0.007 mm subsequent to the load application.

(a) Compute Poisson’s ratio for this material if its elastic modulus is 100 GPa.

(b) What is your best guess on the material being tested?

Question 10. A tensile test is performed on a metal and it is found that a true plastic strain of 0.2 is produced for a true stress of 575 MPa. The value of the strength coefficient for this metal is 860 MPa.

(a) Determine the value of the strain hardening exponent for this metal.

(b) Calculate the value of true stress for the same metal if the true strain is increased to 0.3.

(Hint: the equation of the plastic portion of the true stress – true strain curve is given as: )