北航考研復(fù)試15專業(yè)英語msei-04

1、Linear defectDislocationEdge dislocationScrew dislocationMixed dislocationextended dislocationPartial dislocationDislocation lineBurgers vectorInterfacial defectsExternal surfacesGrain boundariesSmall-angle boundary (low-Tilt boundaryTwist boundaryLarge-angle boundary (high-Thompson reference tetrah

2、edrona extremely useful tool for fcc lattices to keep the vectors in line The Thompson tetrahedron is simply the tetrahedron formed by the 111 planes with consistently indexed planes and edges. If we look at the 111-planes tetrahedron, we see the following connectionsThe edges are directions, they m

3、ay be used to represent the Burgers vectors of the perfect dislocations and the preferred direction for the line vectors because of the Peierls potential (red lines).The faces are 111 planes, they show the positions of potential stacking faults.The Burgers vector of the Shockley partials that may bo

4、und a stacking fault of the given 111 plane are the vectors running from the center of the triangular faces to the corners (blue lines)The Frank dislocations that also can bound a stacking fault, run from the center of the triangular faces to the center of the tetrahedron (not shown). Stacking fault

5、A defect in a face-centered cubic or hexagonal close-packed crystal in which there is a change from the regular sequence of positions of atomic planes.Braggs law2dSinq = nlDiffractometerDiffraction angleX-ray diffraction patternHume-Rothery RulesThe Hume-Rothery rules, named after William Hume-Rothe

6、ry, are a set of basic rules describing the conditions under which an element could dissolve in a metal, forming a solid solution. There are two sets of rules, one which refers to substitutional solid solutions, and another which refers to interstitial solid solutions.Hume-Rothery RulesFor two solid

7、s to form a substitutional solid solution over a wide range of compositionsI. Size difference between solute and solvent must be 15%II. The electronegativities of the solute and solvent must be comparable. If the electronegativity difference is too great, the metals will tend to form intermetallic c

8、ompounds instead of solid solutions.III. The valences of the solute and solvent must be similarIV. The crystal structures of the pure solute and pure solvent must be the sameInterstitial Solid Solution Rules 1. Solute atoms must be smaller than the pores in the solvent lattice.2. The solute and solv

9、ent should have similar electronegativity. Cu-AgAg-GeAu-Si金屬非晶Diffusion第四講5Diffusion is the movement of atoms to produce a homogenous, uniform compositionApplicationsHeat Treatment of MetalsManufacturing of CeramicsSolidification of MaterialsManufacture of Electronic ComponentsImportant termsDiffusi

10、on coupleInterdiffusionImpurity diffusionSelf-diffusionDiffusion mechanismsVacancy diffusionInterstitial diffusionDiffusion mechanismsExchange, RingDiffusion mechanismsActivation EnergyA diffusing atom must squeeze past the surrounding to reach its new locationImportant conceptDiffusion flux (J )Imp

11、ortant conceptConcentration profileConcentration gradientDriving forceImportant conceptSteady-state diffusionDiffusion coefficient (D )Ficks first lawImportant conceptNonsteady-state diffusionFicks second lawKirkendall EffectThe Kirkendall effect is the migration of markers that occurs when markers

12、are placed at the interface between an alloy and a metal, and the whole is heated to a temperature where diffusion is possible; the markers will move towards the alloy region. For example, using molybdenum as a marker between copper and brass (a copper-zinc alloy), molybdenum atoms will migrate towa

13、rds the brass. This is explained by assuming that the zinc diffuses more rapidly than the copper, and thus diffuses out of the alloy down its concentration gradient. Such a process is impossible if the diffusion is by direct exchange of atoms.The Kirkendall effect was named after Ernest Kirkendall (

14、1914 - 2005-08-22) assistant professor of chemical engineering at Wayne State University from 1941 to 1946. He discovered the effect in 1947.The Kirkendall effect has important practical consequences. One of these is the prevention or suppression of voids formed at the boundary interface in various

15、kinds of alloy to metal bonding. These are referred to as Kirkendall voids.In 1972, C.W. Horsting of the RCA Corporation published a paper which reported test results on the reliability of semiconductor devices in which the connections were made using aluminium wires bonded ultrasonically to gold pl

16、ated posts. His paper demonstrated the importance of the Kirkendall effect in wire bonding technology, but also showed the significant contribution of any impurities present to the rate at which precipitation occurred at the wire bonds. Two of the important contaminants that have this effect are bromine and chlorine. Both Kirkendall voids and Horsting voids are known causes of wire bond fractures, though historically this cause is often confused with the purple colored appearance of one of the five different gold-aluminium interm