Exam review

ChE 361 Engineering Materials: Topics to Explore for Exam I Introduction 1. What is Materials Science? 2. What is Materials Engineering? 3. What factors affect the performance of a material? 4. What factors affect the properties of a material? 5. What factors affect the structure of a material? 6. Give a specific example of how processing affects the structure/properties of a material. 7. Give a specific example of how structure affects the properties of a material. 8. Understand the nature of the material properties discussed in class: mechanical, thermal,

electrical. 9. How can the type of atomic bonding affect the properties of a material? Give specific

examples: What type of bonding produces good electrical and thermal insulators? What type of bonding produces good electrical and thermal conductors? What type of bonding tends to result in more brittle materials?

10. List the three primary classes of materials. 11. Put it all together: at the beginning of the course, we stated that a material’s properties depend

on its composition, structure, and processing. Cite one specific material and discuss specifically how each aspect of this statement applies to the material. Use only the structures, processes, and compositions discussed in class thus far.

Bonding 12. Given a Periodic Table of the Elements, and specific elements, determine the “Magic

Numbers” (atomic numbers of the noble gases) for bonding. 13. Describe each type of bonding: ionic, covalent, metallic. 14. For each, explain the nature of the bonding (that is, how the electrons adjust to form a stable

configuration). 15. Explain WHY a material of a particular bonding configuration has the properties that it does.

For example, in ionic bonding, the materials tend to be hard and brittle. In terms of atomic bonding, why?

16. Given a specific element, indicate the element with which it is likely to bond ionically. 17. Indicate whether a type of bonding results in directional or non-directional bonding. 18. How does the directionality (or lack thereof) affect material properties? 19. Describe the nature and importance of Van der Waals bonding

Crystal Structures 20. Be able to draw a Face-Centered Cubic or a Body-Centered Cubic crystal structure. 21. Be able to identify and label the cubic and hexagonal crystal structures. The following are for cubes and for Hexagonal basal planes only: 22. Given a figure indicating a crystallographic direction or family of directions, indicate the

indices representing that direction. (Vice versa: given the indices, draw the direction.) 23. Given a figure indicating a crystallographic plane or family of planes, indicate the Miller

Indices representing that plane. (Vice versa: given the indices, draw the plane.) 24. Explain why we should care about crystallographic planes and directions. 25. Determine the closely packed planes in BCC, FCC, and/or HCP crystals. 26. What is the significance of closely packed planes?

27. What is the atomic structure of a non-crystalline material? 28. How do non-crystalline materials form? 29. What can be said about the atomic structure of all crystalline materials? 30. Describe (use diagrams, if desired) the process of formation of polycrystalline materials. 31. What is a nucleation site? Why is it important to crystal growth? 32. Describe/draw each of the types of crystalline defects: point, line, interfacial. 33. Why are interfacial defects highly chemically reactive? How does this reactivity affect

diffusion/corrosion rates at such boundaries? How significant, volumetrically, is interfacial diffusion?

34. How are substitutional defects useful to a Materials Engineer/Scientist? 35. How are interstitial defects useful to a Materials Engineer/Scientist? 36. Give the 4 rules for substitutional atoms to reside in a host crystal lattice. 37. How can you tell from the Periodic Table whether or not two elements have similar

electronegativities. 38. Give the rule for interstitial atoms to reside in a host crystal lattice. 39. Why do vacancies occur in atomic lattices? (A: It’s an imperfect world) 40. Given atomic sizes, crystal structures, and the Periodic table, determine which of a list of

given elements can be substitutional/interstitial. Determine the relative rates of diffusion for different elements.

41. List the 4 most common elements that are interstitials. Why are these the most common? 42. Interstitial carbon strengthens iron. Why (what is happening on the atomic level)?

Diffusion 43. Define diffusion. 44. Describe the general method of performing solid-solid diffusion. 45. What factors have the greatest effect on diffusion rates? 46. On the atomic level, why does increasing temperature increase diffusion rates? 47. Diffusion occurs through atomic motion, what are the two conditions for the atoms to move? 48. Given Fick’s First Law equation, recognize the equation (no, don’t memorize it) describe its

use, the conditions under which it predicts diffusion rates, the terms of the equation. Explain the negative sign, identify the units of each term.

49. Given the table (5.2 in Callister) of Diffusion coefficients, determine relative diffusion rates for different materials.

50. Predict the depth at which a diffusing species will diffuse in a given time. Mechanical Properties of Materials 51. How are metals tested to determine the mechanical properties? How does this differ from the

way that ceramics are tested? What explains the difference in the testing techniques? 52. A nail is less comfortable to sit on than a soft cushion. Why? 53. Understand the concept of stress. 54. Understand the concept of strain. 55. Draw a schematic stress-strain graph for an elastic material. What does the slope of the line

tell us about material properties of elastic materials? 56. Draw two schematic stress-strain curve: one for a material with low stiffness, the other for a

material with high stiffness. What explains the difference in the slopes of the lines?

57. Given various stress-strain curves, identify mechanical properties (determine which curve is the stiffest, strongest, toughest, hardest, most ductile, most brittle, etc.).

58. Know the meaning of material properties: elasticity, plasticity, stiffness, strength, toughness, hardness, ductility

59. Explain both elastic and plastic deformation on the atomic level. How does atomic bonding/breaking of bonds explain the deformation that we see in a specimen?

60. What changes are made to the crystal lattice and the interatomic bonds (on the atomic level) when a material is strained elastically? Plastically? Brittlely?

61. Based on what you know about plastic deformation, why do atomic bonds have to break and re-bond with other atoms?

Dislocations and Strengthening Mechanisms 1. Real metals deform plastically at lower shear stress than predicted theoretically. Why? 2. Why are HCP metals typically more brittle than FCC or BCC metals? (Explain on the atomic

level.) 3. A single-crystal metal with an FCC structure is expected to undergo plastic deformation on

certain planes. For a given crystal structure, what is the family of planes on which we expect plastic deformation? Why would this plane favor plastic deformation, as opposed to other planes? (What is happening on the atomic level?)

4. Given a crystal structure, identify the slip systems, using indices and {}<> notation 5. Polycrystalline metals of a given material tend to be stronger than their single crystal

counterpart. Explain what is happening on the atomic level to account for this. 6. What kind of stress causes plastic strain? Why? 7. Why does introducing impurities into the crystal lattice increase the strength of a metal? 8. Why does decreasing the grain size of a polycrystalline metal strengthen it? 9. Why does plastically straining a metal strengthen it? 10. What is the underlying principle behind all methods for strengthening a material? 11. What is the goal in annealing a metal? 12. What is the process of annealing? 13. What are the three steps involved in annealing? Do all of the steps have to be followed to

change the material properties? What happens if we stop after step 1 (recovery)? Step 2 (recrystallization)? Step 3 (grain growth)?

14. What happens to the strength of a material during annealing? 15. What is happening on the atomic level for each step of the annealing process?