Flashcards
metallurgy
Cards in this deck (39)
- 1what is strengtheningincreasing yield strength by preventing motion of dislocations
- 2what is strain hardening or cold workingincreasing strength of material by plastic deformation, and increasing dislocation density. Greater dislocation density improved yield strength but reduced ductility and elongation to failure
- 3what is grain boundary strengtheningGrain boundary strengthening is a mechanism by which the presence of grain boundaries within a material contributes to its overall strength and resistance to deformation.
- 4describe two types of dislocations-edge dislocation: an atomic plane is ‘terminated’ within the crystal; the dislocation line is the edge of this terminated plane. Alternatively: the distortion (Burger’s) vector is orthogonal to the dislocation line.
-Screw dislocation – crystal is sheared or ‘torn’ so that a partial slip occurs in the out-of-plane direction; the end of this partial slip defines the dislocation line. Alternatively: the distortion (Burger’s) vector is parallel to the dislocation line. - 5Briefly explain why dislocations will slip preferentially along planes of greater atomic packing.because these planes offer lower energy paths for dislocation movement
- 6what is dispersion strengtheninga mechanism by which the presence of small ceramic oxide particles dispersed within a metal matrix increases its strength and hardness. Those particles disrupt slip planes and impede dislocation motion
- 7what is solid solution strengthening-when the addition of an alloying element occupy interstitial or substitutional sites causing the lattice to distort and resisting dislocation movement
-when atomic sizes are similar, substitution occurs
-when the sizes are not similar, alloying elements will occupy interstitial sites - 8difference between interstitial and substitutional sites-interstitial and substitutional sites refer to the positions within a crystal lattice where foreign atoms (or ions) can reside when incorporated into a host material
-In interstitial solid solutions, the alloying atoms are smaller than the host atoms and can fit into the spaces between the host atoms in the crystal lattice.
-In substitutional solid solutions, the alloying atoms are of similar size to the host atoms and replace or substitute for host atoms in the crystal lattice. - 9what is precipitation strengthening (ageing)it is the formation of "hard precipitate "particles "made from the same alloying element", which resist dislocation slip.
used in aluminum, titanium, magnesium, nickel and steel alloys.
In precipitation hardening intermetallic compounds or carbides precipitate ‘naturally’ by the combination of alloying elements with the base metal. - 10what are steps for precipitation hardening-step 1: solution treatment: heating the metal until all the alloying elements are dissolved
-step 2: quenching: the alloy is rapidly cooled, or quenched, to room temperature to generate a supersaturated solid solution state.
-step 3: aging: The quenched alloy is then subjected to a lower temperature aging treatment to induce the formation of fine precipitates of the dispersed particles - 11describe the 4 stages of precipitation strengthening for copper alloysA – Solid solution – copper occupy interstitial or substitutional sites distorting the crystal structure.
B – GP zones – copper atoms first start to agglomerate (GP1) and then occupy specific atomic planes (GP2), creating greater crystal distortions.
C – Coherent precipitates – intermetallic precipitates (Al2Cu) forms with same FCC crystal structure as base aluminium, i.e. without clear boundaries.
D – Incoherent precipitates – intermetallic compound changes crystal structure and clear boundaries are formed. - 12what are advantages of aluminum alloys-moderate cost
-high specific strength and stiffness
-ductility, fracture resistance and fatigue resistance - 13disadvantages of aluminum-softens above 150 degrees
-suffer stress corrosion cracking
-suffers galvanic corrosion when in contact with carbon fibers
-low max operating temp than titanium - 14describe the wrought aluminum alloysthey are alloys that can be age hardenable or non-age hardenable, and require a form of plastic forming
- 15what's difference between age hardenable and non age hardenable alloys? (age hardenable is the same as precipitation hardening)-non age hardenable: strengthening via solid solution, grain boundary, and col working
-age hardenable: strengthened using precipitation hardening. Widely used in aerospace - 16which alloying elements and their designation, are age hardenable?-copper: 2xxx
- Mg +Si: 6xxx
-Zinc: 7xxx
(note: Si 4xxx is age hardenable only if Mg present) - 17properties of copper alloys-age hardenable
-high strength and toughness
-excellent fatigue performance
-used for lower wing surfaces - 18properties of zinc alloys-widley used in aerospace
-contains some magnesium
-very high yield strength
-used for high stressed components like upper wing skins, spars, stringers - 19what are GP zones?GP zones are small clusters or nuclei of solute atoms, typically copper atoms, that form within the aluminum matrix during the early stages of aging treatment. They create crystal distortions
- 20disadvantages of precipitation/age hardening-lower ductility and elongation to failure
-lower resistance to stress corrosion cracking
-over aging causes strength to drop - 21what are the two phases of titanium alloys and their properties-alpha titanium: lower strength, ductile, good toughness, excellent creep resistance
-beta titanium: higher strength, less ductile, good creep resistance - 22advantages of titanium alloys-lower galvanic corrosion resistance with carbon fiber compared to aluminum
-high strength
-long fatigue life
-good performance at high temp
-used for landing gear, engine parts - 23disadvantages of titanium alloys-poor "specific" stiffness compared to other aerospace materials
- relatively high density (heavy) compared to aluminum or composites
-expensive - 24describe alpha titanium alloys-entirely of alpha stabilizers
-lower strength and creep resistance than "near alpha" alloys
-non heat treatable
-near alpha alloys: have addition of small amounts of beta stabilizers - 25beta titanium alloys-very high yield strength
-uses solid solution plus precipitation (vIP)hardening
-less ductility - 26describe alpha+beta alloys-most popular in aerospace
-combine pros of both alpha and beta
-applications: wing boxes, spars, skin panels - 27which titanium phase can be used for precipitation hardening?beta titanium as its BCC structures allows for solid solution strengthening which is a pre requisite for participation hardening
- 28describer the most popular titanium alloy and why its popular in aerospace (The Ti-6Al-4V)-it is an alpha+bet alloy. And therefore combines the good qualities of both alpha and beta of good creep resistance, ductility, Hugh strength, and is fully heat treatable
- 29what are steels made ofiron+carbon
- 30describe Maraging steelshigh alloy contents but no carbon, age hardenable, high yield strength, widely used in aerospace
- 31describe stainless steelsbarely any carbon, uses precipitation hardening, widely used in aerospace
- 32describe austenite phase of steel-FCC structure, only stable above eutectoid temperature (temperatures above the critical transformation temperature)
- 33describe ferrite structure-BCC structure, it is the structure of pure iron
-soft and ductile - 34describe cementite structure-iron carbide
-its not a metal, its a ceramic
-hard and brittle ceramic like structure - 35describe the pearlite microstructure phase of steel- its a phase made of two micro constituents
-lamellar/alternating layers of ferrite and cementite
-formed by 'slow cooling' of austenite - 36what forms due to cooling of austenite?-slow cooling=pearlite
-moderate cooling=bainite
-rapid quenching=martensite - 37describe bainitenon lamellar structure of cemintite and dislocations rich ferrite
-difference between it and pearlite is that it is non lamellar and mixed with ferrite rich in dislocations - 38describe martensiteHighly distorted structure supersaturated with carbon, only possible via quenching.
- 39describe eutectoid reaction and peritectic reaction-eutectoid: during cooling, one solid phase goes to two different solid phases
-peritectic: upon heating, one solid phase goes to a different solid plus a liquid phase
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- Flashcards on metallurgy, created by k a on 08/05/2024.
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