Chapter4_nonfero09

Chapter4_nonfero09 - Chapter 4 Non-Ferrous Alloys for Aero...

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Chapter 4 Non-Ferrous Alloys for Aero Applications Al, Ti and Mg
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Recall:Typical Use of Al in a Subsonic Aircraft P. Mangonon Principles of Materials Selection for Engineering Design, Prentice Hall, 1999, p. 555
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Other applications of nonferrous metals • Boeing 757 turbofan • 38% Ti • 37% Ni • 12% Cr • 6% Co • Others • Nonferrous metals are essential
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Review • Crystal structure (crystalline, amorphous) – Callister, p. 38-47 • Directionality (single crystal, E 100 E 111 ) and slip systems – Callister, p. 177-183 • Strengthening mechanisms – Callister, p. 188-191 • These are required for understanding the behaviour of nonferrous metals.
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Material Indices – consider the differences Recall PA 1 Al Alloys Mg Alloys Ti Alloys (Steel) E/ ρ min weighht design for stiff ties E 1/2 / ρ min weight design for stiff beams E 1/3 / ρ min weight design for stiff plates σ / ρ min weight design for stiff ties
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Recall Crystal Structures • Crystallographic arrangement dictates behaviour • 3 basic patterns for metals in aerospace are: – bcc (W,Mo,Cr, Fe <912 ° C) – fcc (Al,Ni,Cu,Fe >912 ° C) –hcp ( α -Ti, Mg, Zn) • bcc good strength and moderate ductility - DBTT • fcc moderate strength and good ductility • hcp tend to be brittle
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Manganon op. cit. p. 33
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Recall: Imperfections in Crystal Structure • Point defects p. 81 – missing atom (vacancy) or impurity atom in a regular site or an interstitial atom • Line defects p. 88 – dislocations (edge and screw); the regular structure is dis located • Planar defects p. 93 – grain boundaries are planar defects • Volume defects – typically voids (holes) or inclusions such as sulphides
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Recall - 4 Strengthening Mechanisms Orowan strengthening is a class of strengthening caused by the pinning points blocking mobile dislocations : τ c Gb/l Pinning points include: dislocations, impurity atoms, precipitates and foreign crsystals. 1. Dislocations strain hardening p. 191 (already discussed in class) σ T = K ( ε T ) n Recall that n is a material property, the strain hardening or work hardening coefficient, n= 0 (perfectly plastic, n=1 perfectly elastic)
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Dislocations move in cpd of cpp, these are slip systems. Ductility is a f(# slip systems). More slip systems leads to increased ductility. FCC has 12. BCC has 48 (most text say 12 but 48 comes from less closely packed planes, Dieter p 128). HCP has 3 Crystals have a max. theoretical strength based on breaking all bonds between planes simultaneously. τ t = G/2 π where G = E/(2 (1+ ν )) Actual strengths are lower due to the presence, creation,interaction of dislocations. When dislocations move only a few bonds at a time are broken (recall: carpet analogy)
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Consider a shear stress τ causing a length of dislocation l to move across a crystal. The force F = τ bl (b is burgers vector). The dislocation tries to bypass some pinning points.
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This note was uploaded on 11/13/2011 for the course CIVE 2*** taught by Professor - during the Spring '11 term at Carleton CA.

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Chapter4_nonfero09 - Chapter 4 Non-Ferrous Alloys for Aero...

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