material engineering past paper, Exams of Material Engineering

Download material engineering past paper and more Exams Material Engineering in PDF only on Docsity! MATERIALS SCIENCE AND TECHNOLOGY IKMU 396 Name Instructor: Dr. Selis Önel Midterm Examination, Friday, April 30, 2010 You are allowed to use an A4 size information sheet, which you have to return with the exam paper. Please use English and give brief answers to the following questions: Question 1. (12 pts) Circle the correct word in the following sentence or fill in the blank: a) Materials that have high binding energy have high/low strength and melting temperature. b) Materials with ionic bonding have a particularly large/small binding energy due to the large/small electronegativity difference between the ions. Metals have relatively higher/lower binding energies as the electronegativities of the atoms are similar. c) A steep slope on the force-distance curve or the stress-strain curve in the elastic region correlates with a higher/lower binding energy and higher/lower melting point, which means that a greater/smaller force is required to stretch the bond. d) Smaller grain size higher/lower structural disorder e) Smaller grain size harder/lower to move dislocations across grain boundaries due to more barriers for slip f) More barrier for slip higher/lower material strength g) Adding “impurity” atoms to Cu increases/decreases electrical resistivity and deforming Cu increases/decreases its resistivity. Question 2. (16 pts) Your boss asked you to select a material for the electrical contacts in an electrical switching device which opens and closes frequently and forcefully. a) What are the most important properties that this contact material should have? b) What type of material might you recommend? c) Would Cu be a good choice, why or why not? d) Would Al2O3 be a good choice? Explain briefly. MATERIALS SCIENCE AND TECHNOLOGY IKMU 396 Name Question 3. (12 pts) The strength of a titanium piece is found to be 65,000 psi when the grain size is 17 ×10−6 m and 82,000 psi when the grain size is 0.8 ×10−6 m. What would be the (a) Constants in the Hall-Petch equation (b) Strength of this titanium piece when the grain size is reduced to 0.2 ×10−6 m. Question 4. (10 pts) The number of vacancies in a material is related to temperature by an Arrhenius equation. If the fraction of lattice points containing vacancies is 8 × 10−5 at 600oC, determine the fraction at 1000oC.