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25 Cards in this Set
- Front
- Back
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imperfections
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Many of the important properties of materials are due to the presence of ______.
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What is a vacancy?
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This defect is a result of an unoccupied atom site. It has a specific equilibrium number at which energy is reduced.
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What is an interstitial?
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This defect is a result of an atom occupying a small space between other atoms.
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What is a substitutional solid solution?
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The impurity of this solid solution sits on a lattice site requiring less than a 15% difference in atomic radius, similar electronegativity, similar crystal structure and similar valence.
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What are the Hume-Rothery rules?
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These rules are required in a substitutional solid solution.
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What is an interstitial solid solution?
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In this solution impurity atoms with radii smaller than that of the solvent sit in interstitial sites.
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What is a tetrahedral interstitial?
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This interstitial has a hole between four atoms. An FCC structure has eight of these sites per unit.
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What is an octahedral interstitial?
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This interstitial has a hole between six atoms. An FCC structure has four per unit cell (center + cube edges.)
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size
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Which interstitial site an atom sits in depends on _______. Octahedral sites are larger than tetrahedral.
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What is an edge dislocation?
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In this linear defect atoms above the dislocation line are in compression and those below in tension. It is denoted by the perpendicular symbol.
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What is a screw dislocation?
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This linear defect is like cutting a crystal. The crystal is sheared from the top and the bottom in opposite directions.
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What is a mixed dislocation?
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This dislocation has both edge and screw components.
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What is Burger's vector?
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This vector is used to express magnitude and direction of lattice distortion around *perpendicular symbol.* In an edge dislocation it is perpendicular to the dislocation line. In screw dislocation it is parallel.
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What is a grain boundary?
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This boundary is formed during solidification and separates crystals with different orientations.
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What is a twin boundary?
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This special type of grain boundary occurs on specific planes along specific directions, depending on crystal structure. Atoms on one side of a boundary are mirror images of atoms on the other side.
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What is an external surface defect?
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This defect has higher energy because atoms are not bonded to the maximum of nearest neighbors.
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What is a stacking fault?
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This defect occurs when in FCC metals when a stacking sequence is locally disrupted.
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pores, cracks and other phases (AuAl2 in Au-Al alloy)
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What are examples of bulk defects?
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What is diffusion?
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This process transports mass by atomic motion. It is very difficult in solids and aided by point defects. It is dependent on temperature and the size of the species.
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What is vacancy diffusion?
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The extent of this diffusion depends on the number of vacancies.
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What is interstitial diffusion?
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This interdiffusion of impurities like H, C, N or O (small atoms) occurs more rapidly than vacancy diffusion because small atoms are more mobile and there are more interstitial sites.
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What is steady-state diffusion?
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The rate of this diffusion is not time dependent. The concentration gradient is the driving force; atoms move from areas of high concentration to areas of low concentration.
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What is 'short circuit' diffusion path?
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This diffusion occurs along dislocations, grain boundaries and external surfaces. Its rate is faster than that of bulk diffusion.
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What is case hardening?
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This application of diffusion diffuses carbon atoms into the host iron atoms at the surface. An example of interstitial diffusion is a case hardened gear. The presence of carbon atoms makes iron (steel) harder.
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What is doping?
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This application using diffusion deposits phosphorous rich layers onto a silicon surface. It is then heated creating semiconductor regions.
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