Purdue University School of Materials Engineering MSE 230 Fall 2003 Exam II November 13 2003 Show All Work and Put Units on Answers Name Key Recitation Day and Time Recitation Instructor s Name 1 17 2 15 3 18 4 16 5 12 6 12 7 10 Total 100 General Concepts 5 pts 1 a Complete the following matching section by placing the appropriate letter in the blank C 1010 Steel A Cr F 2024 T6 B Graphite Flakes B Gray Cast Iron C 0 1 wt carbon A Stainless Steel D Incoherent Precipitates E 1080 Steel E Eutectoid Composition F Coherent Precipitates 5 pts b Schematically illustrate the hardness profile for a 1040 and a 4340 steel as a function of distance from the quenched end of a Jominy bar Label each curve 4340 HRC 1040 Distance from Quenched End water Jominy Bar 7 pts c Draw a schematic of a binary eutectic phase diagram in the box provided I ve provided the eutectic line Label the areas of the phase diagram with the phases present or L or some combination Indicate on the diagram for what compositions would you not expect any eutectic microstructure upon equilibrium cooling to just below the eutectic temperature Note no numbers are required for this problem Temperature L L L A Increasing B B The compositions indicated by the dotted lines and arrows would not form a eutectic microstructure because there would be no liquid phase with the eutectic composition transforming through the eutectic temperature Fe Fe3C Iron Carbon Phase Diagram 15 pts 2 The following question deals with a 10100 steel that has been cooled to 720oC a What is the pro eutectoid phase for this alloy Fe3C b What weight fraction of proeutectoid phase would you expect to have WP F3 C 1 76 04 6 7 76 c What is the total weight fraction of cementite in the microstructure W 1 0 022 0 15 6 7 0 022 d What is the composition of cementite in terms of carbon CFe3C 6 7 wt C e What is the weight fraction of eutectoid Fe3C would you observe WFeTotal WP Fe3C WE Fe3C 3C 0 15 0 04 WE Fe3C WE Fe3C 0 11 f What is the weight fraction of pearlite would you expect to observe in the microstructure W W pearlite 1 WP Fe3C 96 Carburizing Diffusion 18 pts 3 Your goal is to determine the time it takes to carburize a gear such that it has a carbon concentration of 0 80 wt 1 mm below the surface You are beginning with a steel with 0 1 wt carbon at a temperature of 1100oC The carbon concentration on the outer surface of the gear is maintained at 1 2 wt Use the tables provided and the Fe Fe3C phase diagram to determine the time required for this process z 0 100 0 200 0 300 0 330 0 350 0 364 0 400 0 500 erf z 0 113 0 223 0 329 0 364 0 379 0 389 0 428 0 521 C x Co x 1 erf C s Co 2 Dt 0 8 0 1 1 erf z erf z 36 1 2 0 1 From table z 33 x 2 Dt 1x10 3 m 33 or 2 5 3x10 11 m2 t s 33 t 43000 sec onds Note D is given in the table for carbon diffusion in Fe or you can calculated it using the equation given in class D Doexp Q RT Polymer Basics 16 pts 2 A polymer contains three molecular fractions as follows A 150 chains or 200 grams of molecular weight 2 x 103 g mol B 100 chains or 200 grams of molecular weight 2 x 104 g mol C 20 chains or 100 grams of molecular weight of 1 x 105 g mol a What is the value of the weight average molecular weight M w M W wi M i 200 200 g 3 g 4 g 2 x10 2 x10 mol mol 500 500 g g 100 g 1x10 5 g mol 28 800 mol 500 g b If its weight average degree of polymerization is 685 which type of polymer is this most likely C 12 g mol H 1 g mol You must show your work for credit Polyproplyene or Polystyrene circle one MW m 28 800 685 m 42g mol m PP m 3 12g mol 6 1g mol 42g mol PS m 8 12g mol 7 1g mol 103g mol So PP nW c Label the polymer structures below in the blanks provided 1 3 2 4 1 Linear 2 Cross Linked 3 Branched 4 Network d Which would be the most thermally stable structure No explanation required 1 2 3 4 circle one Network because all the molecules linked by covalent bonding Non Equilibrium Microstructures 5 12 pts 6 The following questions deal with precipitation hardening of an Al Cu wheel cover Your goal is to produce a material with a very high strength For whatever alloy you choose assume it begins with large coarse precipitates a Begin by choosing a composition that you could age harden Indicate your choice by drawing a compositional line on the adjacent phase diagram 2 pts Need to choose a composition where you can heat the wheel cover into a single phase region and quench There must be some Cu in alloy otherwise there will be nothing to precipitate out Can t choose compositions great than the indicated line because would have to heat into liquid region to dissolve precips which would destroy your part b b Next using the Temperature Time plot below draw in the processing steps Make sure you choose temperatures that would accomplish your goals for the microstructure USE a straight edge to draw your lines Name and label the three key steps 7 pts This is directly from the class notes 800 o Temperature C 700 Solution Treat 600 500 Quench 400 300 Age Precipation Treat 200 100 0 Time c With your goal in mind to produce a high strength alloy show a schematic plot of yield strength versus aging time and identify on the plot where you want to stop aging 3 pts Stop here refers to T6 heat treat Yield Strength As we age we precipitate out a very fine strengthening phase With time though we can coarsen this phase and begin to lose strength We want to stop before that 0 0 Aging Time Ceramics and Crystals 6 a Match the crystal structure number to the name There are 2 extra crystal structures given 2 CsCl 3 NaCl 1 2 3 4 6 Martensite 5 Perovskite c a 5 6 b What general type of additive do you add to fused silica to make it a soda lime glass Glass modifier c At the same temperature would you expect a soda lime glass to have a higher or lower viscosity than fused silica Higher or Lower circle one General Knowledge 10 pts 7 Answer the following True False questions by placing and F or T in the blank F Pearlite is a phase that …
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