MSE 230 Assignment 11 Fall 2013 due 11 14 11 15 Problems with an by them will not be graded but solutions will be provided In this assignment set problems 3 5 7 and 10 will be graded 1 Callister 11 6 On the basis of microstructure briefly explain why gray iron is brittle and weak in tension 2 You are given a sample of an aluminum alloy and asked to determine if it is either alloy 5052 or alloy 6061 Describe two methods by which you may decide which alloy you have 3 If it is assumed that for steel alloys the average cooling rate in the heat affected zone HAZ in the vicinity of a weld is 10 C s compare the microstructures and associated properties that will result for 1080 eutectoid and 4340 alloys in their HAZs Hint refer to the CCT diagrams in Chapter 10 4 Callister 11 D14 Copper rich copper beryllium alloys are precipitation hardenable After consulting the portion of the phase diagram Fig 11 30 on page 450 do the following a Specify the range of composition over which these alloys may be precipitation hardened b Briefly describe the heat treatment procedures in terms of temperatures that would be used to precipitation harden an alloy having a composition of your choosing yet lying within the range given for part a 5 A pyrex beaker is scrubbed clean by a particularly enthusiastic glass washer Subsequent use shows that the T for thermal shock has decreased to 100 C from the original 270 C Calculate the strength of the beaker associated with a T of 270 C and 100 C Also calculate the critical flaw size associated with each strength value assume K1c 0 7 MPa m0 5 for pyrex What may have caused the decrease in strength and can we do anything to fix it Assume that the Young s modulus of pyrex is 70 GPa and that Poisson s ratio is 0 20 pyrex 3 10 6 C 6 The diagram below shows the temperature distribution in a plate of glass during the tempering process On the same graph sketch quantitative plots estimating the corresponding residual stress distribution after the entire plate has cooled to room temperature 20 C for the following situations a The plate is made of pyrex pyrex 3 10 6 C E 70 GPa 0 20 b The plate is made of soda lime glass soda lime 10 10 6 C E 70 GPa 0 20 Assume that the plate has a thickness of 10 mm There are a couple of ways to estimate the residual stresses in the plate 1 Temperature Distribution A ir Ai r Temperature C 700 C 20 C 2 8 10 Position mm 7 For this problem it will help to read Chapter 12 11 pgs 489 490 of Callister in addition to Chapter 13 A powder compact of Al2O3 aluminum oxide is prepared by dry pressing Al2O3 powder to 60 of its theoretical density a Calculate the modulus of elasticity of the powder compact if Young s modulus for Al2O3 is 393 GPa b The powder compact is placed into a furnace and heated to 0 95Tm of Al2O3 Sketch a qualitative plot of the modulus of elasticity of the powder compact versus time time 0 is when the powder compact is placed in the furnace 8 The presence of a small amount of liquid phase is helpful in increasing the rate of sintering densification in a powder compact more than 10 wt and you just have a mess Consider the sintering behavior of mullite a ceramic that is a solid solution alloy of Al2O3 and SiO2 The phase diagram may be found in Fig 12 27 on page 480 of Callister For the two alloy compositions below determine the minimum temperature needed to form a liquid phase the weight fraction of liquid present at that temperature and state whether or not you believe that the alloy composition would be suitable for liquid phase sintering a 70 wt Al2O3 and 30 wt SiO2 b 80 wt Al2O3 and 20 wt SiO2 2 9 a Make a plot of the specific surface area m2 g against particle diameter from 10 nm to 10 3 m for zirconium oxide powders Assume the particles are spherical ZrO2 6 0 g cm b You have three powder compacts of zirconium oxide all made up of spherical particles One compact is made up of particles 10 nm in diameter the second of particles 100 nm in diameter and the third of particles 1 m in diameter Assuming that each powder compact starts at a packing density 65 of theoretical density and is heated to 80 of its melting temperature make a qualitatively correct plot for each compact of density versus time Assume that each powder compact eventually reaches 100 of theoretical density 10 Aluminium oxide Al2O3 has a theoretical density of 3 97 g cm3 10 grams of a powder of spherical Al2O3 particles is pressed uniaxially in a die 25 mm diameter such that the particles take on a FCC packing arrangement a What is the packing density e g of theoretical of the FCC packing arrangement b What was the height of the cylindrical powder compact c If the powder compact is heated such that it sinters to full density can you determine the height and diameter of the fully dense Al2O3 cylinder If so perform the calculation and state any assumptions that you made if not explain why not 3
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