Tutorial 2 : Crystalline Solid, Solidification, Crystal Defect and Diffusion

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1 Tutorial 1 : Introduction and Atomic Bonding 1. Explain the difference between ionic and metallic bonding between atoms in engineering materials. 2. Show that the atomic packing factor for Face Centred Cubic (FCC) structure is Gold has an FCC crystal structure, an atomic radius of nm and an atomic weight of g/mol. Calculate the density of gold. (Given: Avogardo s Number is 6.02 x atoms/mol) 4. Determine the directions and Miller indices for planes drawn in the following cubic unit cells; (i) (ii) (iii) (iv) 5. Draw the following direction and planes in a separate cubic unit cells. (i) [3 3 1] (ii) [1 2 0] (iii) (1 1 2 ) (iv) (1 0 1) Tutorial 2 : Crystalline Solid, Solidification, Crystal Defect and Diffusion 1. Describe and illustrate with relevant sketches solidification process of pure aluminium. 2. Distinguish between homogenous and heterogeneous nucleation for the solidification of a pure metal. 3. What are the conditions that are favorable for extensive solid solubility of one element in another for a substitutional solid solution? 4. Give two reasons why substitutional solute atoms diffuse more slowly than interstitial solute atoms in a given solvent metal lattice at the same temperature. 5. Briefly explain the concept of steady state as it applies to diffusion. 1

2 6. A plate of iron is exposed to a carburizing (carbon-rich) atmosphere on one side and a decarburising (carbon-deficient) atmosphere on the other side at 700 o C. If a condition of steady state is achieved, calculate the diffusion flux of carbon through the plate if the concentrations of carbon at positions 5 and 10 mm beneath the carburising surface are 1.2 and 0.8 kg/m 3, respectively. Assume a diffusion coefficient of 3 x m 2 /s at this temperature Tutorial 3 : Dislocations and Strengthening Mechanisms 1. Consider two edge dislocations of opposite sign and having slip planes that are separated by several atomic distances as indicated in the diagram. Briefly describe the defect that results when these two dislocations become aligned with each other. 2. Is it possible for two screw dislocations of opposite sign to annihilate each other? Explain your answer. 3. (a) Define a slip system. (b) Do all metals have the same slip system? Why or why not? 4. (a) List four major differences between deformation by twinning and deformation by slip relative to mechanism, conditions of occurrence and final result. 5. Briefly explain why small angle grain boundaries are not as effective in interfering with the slip process as are high angle grain boundaries. 6. Briefly explain why HCP metals are typically more brittle than FCC and BCC metals. 7. Briefly cite the differences between recovery and recrystallisation processes. 8. Explain the differences in grain structure for a metal that has been cold worked and one hat has been cold worked and then recrystallised. 9. Briefly explain why some metals (e.g lead and tin) do not strain harden when deformed at room temperature. 10. A cylindrical specimen of cold worked copper has a ductility (%EL) of 15%. If its cold worked radius is 6.4mm. What was its radius before deformation? Figure 1 : Effect of percentage of cold work on ductility 2

3 Tutorial 4 : Mechanical Properties and Materials Testing 1. A specimen of aluminium having a rectangular cross section 10mm X 12.7mm is pulled din tension with 5.5kN force producing only elastic deformation. Calculate the resulting strain. 2. A steel bar 100mm long and giving a square cross section 20mm on an edge is pulled in tension with a load of 89kN, and experiences an elongation of 0.10mm. Assuming that the deformation is entirely elastic, calculate the elastic modulus of the steel A cylindrical rod of copper (E=110GPa) having a yield strength of 140MPa is to be subjected ro a load of 6660N. If the length of the rod is 380mm, what must be the diameter to allow an elongation of 0.5mm? 4. Consider a cylindrical specimen of some hypothetical metal alloy that has a diameter of 10mm, A tensile force if 1500N produces an elastic reduction in diameter of 6.7 X 10-4 mm. Compute the elastic modulus of this alloy, given that Poisson s ratio is Cite the primary differences between elastic, anelastic and plastic deformation behaviours. 6. A cylindrical specimen of aluminium having a diameter of 12.8mm and a gauge length of 50.8mm is pulled in tension. Use the load-elongation characteristics tabulated below to complete parts (a) through (f). Table 1: load-elongation Load (N) Length (mm) Load (N) Length (mm) Fracture (a) Plot the data as engineering stress versus engineering strain. (b) Compute the modulus of elasticity (c) Determine the yield strength at a strain offset of (d) Determine the tensile strength of this alloy. (e) What is the approximate ductility in percent elongation. 7. Upon what criteria are factors of safety based? 8. Cite five factors that lead to scatter in measured material properties. 3

4 Tutorial 5 : Phase Diagram 1. Cite three variables that determine the microstructure of an alloy. 2. What thermodynamic condition must be met for a state of equilibrium to exist? 3. Table 1 below shows the solidus and liquidus temperatures for the copper-gold system. Construct the phase diagram for this system and label each region. 4. By using the phase diagram for copper nickel system, or otherwise, derive the lever rule. 5. By using the phase diagram of Pb-Sn system (Figure 2) answer the following questions: (a) For a 40wt% Sn 60wt% Pb alloy at 150 O C, what phases are present, and what are the compositions of the phases. (b) Calculate the relative amount of each phase present in terms of mass fraction and volume fraction. (Density of Pb = 11.23g/cm 3, density of Sn = 7.24g/cm 3 ). Table 2 : Solidus-Liquidus temperatures for Cu-Ag system. Composition (wt% Au) Solidus temperature ( O C) Liquidus temperature ( O C) Figure 2 : Pb-Sn System. 4

5 Tutorial 6 : Carbon Steel and Heat Treatment 1. Draw and label the phase diagram for steel from o C. 2. Name and explain the four microstructure of steel. 3. Draw and describe the change in microstructure for the following steels when slowly cooled from the austenitic region to room temperature. (a) hypoeutectic (0.4%C steel) (b) Eutectoid (0.8%C steel) (c) hypereutectoid (1.2%C steel) 4. For the following heat treatment, explain in terms of procedure, microstructure and properties expected. (a) normalizing (b) full annealing (c) quenching (d) sub-critical annealing (e) quenching followed by tempering (f) spheroidising 5. (i) How can these processes can be carried-out? (a) martempering (b) austempering (c) conventional quenching and tempering (ii) What are the advantages of martempering compared to conventional quenching and tempering? 6. Sketch a time-temperature-transformation diagram (TTT) for a plain carbon eutectoid steel. Show the cooling path form austenite phase to form the following microstructure and explain the heat treatment process. (a) 100% martensite (b) 100 % coarse pearlite (c) 50% bainite and 50% martensite (d) 100% lower bainite 7. Small thin pieces of 0.25mm thickness hot-rolled eutectoid steel are heated for one hour at 900 o C and followed by the heat treatment listed below. Using the TTT diagram (provided), draw the cooling curve and determine the microstructure of the samples after each treatment. (a) water quenched to room temperature 5

6 (b) hot quenched in molten salt at 690 o C, hold for 2 hours and water quench. (c) hot quenched to 610 o C, hold for 2 seconds and water quenched. (d) hot quenched to 580 o C, hold for 3 minutes and water quenched. (e) hot quenched to 450 o C, hold for 1 hour and water quenched (f) hot quenched to 300 o C, hold for 5 hours ad water quenched. 8. What is meant by hardenibility of steel?. How this property is determine and what are the factors affecting this properties. Tutorial 7 : Cast Iron 1. List four main types of cast iron and give examples of typical application for each type of cast iron. 2. How the solidification rate, percentage of silicon and heat treatment effecting the formation of cast iron? 3. How nodular and ductile cast iron being produced and sketch their microstructure. 4. Why does the fracture surface of white cast iron appear white 5. What casting condition favour the formation of grey cast iron? 6. Explain the properties of grey and white cast iron. How both cast iron can be improved 7. Differentiate between malleable cast iron and nodular cast iron. Tutorial 8 : Alloy Steel 1. List four common elements that form alloy steel 2. Describe the effect of alloying elements to improve the properties of carbon steel. 3. List five alloy steels and their main alloying elements. 4. State three types of stainless steel in terms of chemical composition, properties and give example of application. 5. Why ferritic and austenic stainless steels are considered non-heat-treatable? 6. Explain briefly how maraging steel being produced. Tutorial 9 : Surface Hardening 1. What is surface hardening and describe its differences with through/full hardening process. 2. Give some examples of components that are normally surface hardened and give reasons why they are not through/fully hardened. 6

7 3. (a) Name the surface hardening processes that altered the composition of the component after the treatment. (b) Explain briefly the carburizing methods and give their advantages and disadvantages. (c) What are the main elements added to the component surface when carbonitriding and cyaniding process are used? Explain each process. 4. (a) What kind of steels are normally surface hardened using flame and induction hardening process? (b) Give the process differences between flame and induction process. 5. What is decarbu (a) How does decarburizing will affect the hardenability of the steel surfaces (b) How can decarburizing be avoided? Tutorial 10 : Non Ferrous Metal 1. (a) What are the advantages of using non-ferrous metals as an engineering components compare to ferrous metals? (b) Name the most common non-ferrous metals used in engineering applications. 2. (a) Give the main characteristics of copper that make it desirable for various applications. (b) What is brass and give the differences between α-brass and α+β brass? Give some application examples of brass. (c) What is bronze and give its main advantages over brass. 3. (a) What are some of the properties which make aluminium an extremely useful engineering material? (b) Which series of aluminium alloys are non-heat treatable and heat treatable? (c) Explain how the strength and hardness of non-heat treatable and heat treatable aluminium alloys can be increased. (d) Give some applications of,(i) non-heat treatable, and (ii) heat treatable aluminium alloys. 4. What make nickel alloys superior than other common non-ferrous alloys? Give examples of application. 7

8 Tutorial 11 : Non Metallic Materials 1. (a) List the main characteristics of polymeric materials and its importance in engineering applications. (b) Distinguish between thermoplastic and thermosetting polymers. Give the examples of the application. (c) Explain how the strength of natural rubber can be increased. 2. (a) What is ceramic and list some properties common to most ceramic materials. (b) Distinguish between traditional and engineering ceramic. Give the examples of the application. (c) Briefly explain the basic steps in processing of ceramic products. 3. (a) Define a composite materials. (b) What are the differences between fiber reinforced composite and particulate reinforced composite? (c) What is the function of matrix and reinforcement in the continuous fiber reinforced composite? (d) Give the applications of MMC, PMC and CMC. 8