同济大学：《工程材料》课程电子教案（课件讲稿）Chapter 3 Defect in Crystals

190 TONGU UNIVER Chapter 3.Defect in Crystals 大举横城三置州

SINO-ITALIAN CAMPUS Chapter 3. Defect in Crystals

1907 3.1 Defects in crystal Defects influence: I Physical properties II Mechanical properties I"Technological"properties (Formability, corrosion,…) By controlling the lattice defects,materials with properties different from the original ones can be obtained

SINO-ITALIAN CAMPUS 3.1 Defects in crystal Defects influence: Ⅰ、Physical properties Ⅱ、Mechanical properties Ⅲ、“Technological” properties (Formability, corrosion,…) By controlling the lattice defects, materials with properties different from the original ones can be obtained

190> Why studying defects G "Perfect"solids DO NOT exit!!! All contain large numbers of various defects or imperfections.As a matter of fact,many of the properties of materials are profoundly sensitive to deviations from crystalline perfection By "crystalline defect"is meant a lattice irregularity having one or more of its dimensions on the order of an atomic diameter. Classification of crystalline imperfections is frequently made according to geometry or dimensionality of the defect

Why studying defects “Perfect” solids DO NOT exit!!! All contain large numbers of various defects or imperfections. As a matter of fact, many of the properties of materials are profoundly sensitive to deviations from crystalline perfection. By “crystalline defect” is meant a lattice irregularity having one or more of its dimensions on the order of an atomic diameter. Classification of crystalline imperfections is frequently made according to geometry or dimensionality of the defect

190 ONGJI UNIVER、内 Different imperfection are possible ●Impurities in solids Point defects Linear defects Surface defects (interfacial defects, or boundaries,which are two- dimensional) ● Three dimensional defects

SINO-ITALIAN CAMPUS Different imperfection are possible  Impurities in solids  Point defects  Linear defects  Surface defects (interfacial defects, or boundaries, which are two￾dimensional)  Three dimensional defects

190 3.1.1 Impurities in solids UNIV All the“real"solids are“impure": It is difficult to refine metals to a purity in excess of 99.9999%>1022-1023 impurity atoms per m3 -The presence of impurity may be undesired,or it could be intentional: Example:C in Fe→steel B in Si ->transistor semi-conductor Alloys:intentional admixing of metals Ex:sterling silver 92.5%-Ag 7.5%Cu Improvement of mechanical properties of Ag

3.1.1 Impurities in solids All the “real” solids are “impure”: It is difficult to refine metals to a purity in excess of 99.9999%→1022 -1023 impurity atoms per m3 -The presence of impurity may be undesired, or it could be intentional: Example: C in Fe →steel B in Si →transistor semi-conductor Alloys: intentional admixing of metals Ex: sterling silver 92.5%-Ag 7.5%Cu Improvement of mechanical properties of Ag

1907 Solid solutions UNIVE A solid solution is a solid made up of two or more elements,dispersed in a mono-phase structure. A solid solution is defined when,adding atoms of the solute in the host material,the crystal structure is maintained and no new structure is formed. Two types of solid solution: -substitutional -interstitial

Solid solutions A solid solution is a solid made up of two or more elements, dispersed in a mono-phase structure. A solid solution is defined when, adding atoms of the solute in the host material, the crystal structure is maintained and no new structure is formed. Two types of solid solution: -substitutional -interstitial

190 (1)Substitutional solid solutions The fraction of atoms of an element that can solute between 0,00x%to 100%, according to the cases

(1)Substitutional solid solutions The fraction of atoms of an element that can solute between 0,00x% to 100%, according to the cases

190> Conditions to improve solubility: 1.Atomic size factor Appreciable quantities of a solute may be accommodated in this type of solid solution only when the difference in atomic radii between the two atom types is less than about 15% 2.Crystal structure For appreciable solid solubility the crystal structures for metals of both atom types must be the same

SINO-ITALIAN CAMPUS Conditions to improve solubility: 1. Atomic size factor Appreciable quantities of a solute may be accommodated in this type of solid solution only when the difference in atomic radii between the two atom types is less than about 15% 2. Crystal structure For appreciable solid solubility the crystal structures for metals of both atom types must be the same

190> 3.Electronegativity The more electropositive one element and the more electronegative the other,the greater is the likehood that they will form an intermetallic compound instead of a substitutional solid solution. 4.Valences Other factors being equal,a metal will have more of a tendency to dissolve another metal of higher valency than one of a lower valency

SINO-ITALIAN CAMPUS 3. Electronegativity The more electropositive one element and the more electronegative the other, the greater is the likehood that they will form an intermetallic compound instead of a substitutional solid solution. 4. Valences Other factors being equal, a metal will have more of a tendency to dissolve another metal of higher valency than one of a lower valency

490>2 TONGJI UNIVERSY Substitutional solid solutions

Substitutional solid solutions