《清华材料科学基础课件(英文)skja_04》由会员分享，可在线阅读，更多相关《清华材料科学基础课件(英文)skja_04（28页珍藏版）》请在金锄头文库上搜索。
1、材料科学基础Fundamental of MaterialsLesson four*材料科学基础u.Crystal structure is the real arrangement of atom in crystalsCrystal structure Space lattice + Basisor structure unit2.3 Crystal Structure and Complex LatticeDateDate材料科学基础材料科学基础+ += =DateDate材料科学基础材料科学基础Fe : Al = 1 : 1FeFeAl AlThe difference between
2、 space lattice and crystal structure DateDate材料科学基础材料科学基础23 atoms / cellDateDate材料科学基础材料科学基础1. BCC Example: -Fe , V, Nb, Ta, Cr, Mo, W,alkali metals n = 2 atoms/cell CN=8 The number of nearest neighbours around each atom is called Coordination Number.uu.Typical crystal structures of metals.Typical c
3、rystal structures of metalsDateDate材料科学基础材料科学基础 Packing fraction To determine, The atom is looked as a hard sphere, and the nearest neighbours touch each other. For BCC, Volume of atoms / cellVolume of atoms / cellVolume of unit cell Volume of unit cellDateDate材料科学基础材料科学基础2. FCC Example: -Fe , Al ,
4、Ni , Pb , Cu ,Ag , Au , stainless steal n= 81/8+61/2=4 atoms/cell CN=12 DateDate材料科学基础材料科学基础3. HCP Example: Be, Mg, Zn, Cd, Zr, HfTi( low temperature) n CN12 0.74DateDate材料科学基础材料科学基础Structurea0 vs. rAtoms per cellCoordination NumberPacking factorExamplesSC160.52Polonium (Po),-MnBCC280.68Fe,Ti,W,Mo,
5、Nb,Ta,K,Na, V,Zr,CrFCC4120.74Fe,Cu,Au,Pt, Ag,Pb,NiHCP2120.74Ti,Mg,Zn,Be, Co,Zr,Cd4. Summary4. SummaryDateDate材料科学基础材料科学基础2.4 Interstices in typical crystals of metalsu.Two types of Interstitials in typical crystalsOctahedral interstitialTetrahedral interstitialDefinition:In any of the crystal struct
6、ures, there are small holes between the usual atoms into which smaller atoms may be placed. These locations are called interstitial sites.DateDate材料科学基础材料科学基础1. Octahedral interstitialBCCDateDate材料科学基础材料科学基础FCCDateDate材料科学基础材料科学基础HCPDateDate材料科学基础材料科学基础2. Tetrahedral interstitialBCCDateDate材料科学基础材料科
7、学基础FCCDateDate材料科学基础材料科学基础HCPDateDate材料科学基础材料科学基础u.Determination of the sizes of interstitials Definition: By size of an interstitial we mean diameter of the maximum hard sphere which can be accommodated in the interstitial without distorting the lattice.di dadiameter of interstitial atom diameter o
8、f atom in lattice pointDateDate材料科学基础材料科学基础uOctahedral interstitialcondition for touching DateDate材料科学基础材料科学基础For BCCFor FCCDateDate材料科学基础材料科学基础uTetrahedral interstitialH HL LA AD DC CB Binterstitialinterstitialhost atomhost atomDateDate材料科学基础材料科学基础For BCCFor FCCDateDate材料科学基础材料科学基础uSummaryn CNinter
9、sticesdi/daoct.tete.oct.tete.BCC280.6866/2=3 1212/2=60.150.29FCC4120.7444/4=188/4=20.410.22HCP6120.7466/6=1 1212/6=20.410.22DateDate材料科学基础材料科学基础Examples and Discussionsl Both FCC and BCC are close-packed structures while BCC is more open? l The interstitial atoms most likely occupy the oct. intersti
10、tial position in FCC and HCP, while in BCC two types of interstitial can be occupied equally.DateDate材料科学基础材料科学基础3. The solid solubility in BCC is much lower than in FCC. 4. Diffusion of interstitial atoms in BCC diffusion is much faster than in FCC or HCP at same temperature. 5. Determine the relat
11、ionship between the atomic radius and the lattice parameter in SC, BCC, and FCC structures when one atom is located at each lattice point.DateDate材料科学基础材料科学基础6.6. Determine the density of BCC iron, which has Determine the density of BCC iron, which has a lattice parameter of 0.2866nm.a lattice param
12、eter of 0.2866nm.Solution:Solution:For a BCC cell, Atoms/cell = 2a0 = 0.2866nm = 2.866108cmAtomic mass = 55.847g/molVolume of unit cell = a03 = 23.5410 24cm3/cellDensityDateDate材料科学基础材料科学基础ExerciseuDetermine the coordinates of centers of both the octahedral and the tetrahedral interstitials in HCP referred to a, b and c.a ab bc c120120o oDateDate材料科学基础材料科学基础Thank you !4 4 DateDate材料科学基础材料科学基础
