1、About this course(contd)4.Course evaluation How to assess the learning quality?Final exam 70%weight(multiple choice,analysis and calculation,English/Chinese alternatively)In-class quiz 30%weight(1 quiz/Per 2 weeks,totally 6 quizzes)Homework By your choice,not a must 5.Textbook:D.R.Askeland and P.P.P
2、hule,Essentials of Materials Science and Engineering(材料科学与工程基础材料科学与工程基础),Tsinghua University Press,2005(影印本影印本).Evolution of materialsOur tasks,challenges and goalsCompositionStructures Processing Properties/performance Stronger Tougher Lighter Cheaper Safer Smarter Friendly Our tasks 4 components i
3、n materials research&the linear interrelationship Our challenges&goals:To make materialsMaterials scienceMaterials engineeringWhat is Materials Science&Engineering?Materials Science:Investigate the material structures Understand how the material behaves/works in a scientific way Underlie relationshi
4、ps among composition,processing,structures and properties/performance of materials.Materials engineering:Based on materials science How to translate or transform materials into useful devices or structures Making products using materials with a good cost-to-performance ratio (性价比性价比)and environment
5、friendly.Materials Science and Engineering:This subject is an interdisciplinary field concerned with inventing new materials and improving previously known materials by developing deeper understanding of the composition-processing-structure-property relationships.Materials family classification(by b
6、ond)X.P.Zhang(张新平张新平)X.Ma(马骁马骁)Z.M.Yang(杨中民杨中民)Hui He(何慧何慧)PE,PP,PCPA(Nylon)PolymersButyl rubberNeopreneGFRPCFRPCompositesKFRPPlywoodAluminaSi-CarbideInorganic mat./CeramicsSoda-glassPyrexFe,Cu,Al,Ni,Au,Metals&AlloysSteels,cast ironMaterials family classification(by use)MaterialsStructural materials
7、Functional materialsMagnetic materials Optical materials Electronic materials Superconductive materials:Metallic materials Plastic materials Wood structural materials Other structural materials :What is a metal?What is a ceramic?Natural&synthetic rock:hard,brittle&heat-resistantWhat is a polymer?The
8、 word polymer literally means many parts Better know as“plastics”by general public The great majority of elements in the periodic table are metals.A metal has a particular type of bonding known as metallic bonding(as distinct from ionic bonding and covalent bonding).Metals tend to be ductile strong
9、shiny materials that corrode easilyWhat is a composite material?An engineering material which consists of more than one material type1.Macrostructure(宏观结构宏观结构)We can see it by our eyes:100 m.2.Microstructure(微观结构微观结构)We can only see it by a microscope:0.01 1 m.3.Nano-structure(纳米结构纳米结构)Only see it b
10、y special tools (AFM&HRTEM):1000 nm.4.Short-&long range atomic arrangement(短程和长程有短程和长程有 序原子排列序原子排列)We can only see it by special tools:100 nm5.Atomic structure Nearly can not see it:2 N.Microhardness Hardness of materials typically measured using loads less than 2 N using such test as Knoop(HK).Nano
11、-hardness Hardness of materials measured at 110 nm length scale using extremely small(100 N)forces.Indenters for the Brinell&Rockwell hardness tests(a)Charpy&Izod tests;(b)dimensions of typical specimensImpact tests Fracture mechanics(断裂力学断裂力学)Fracture mechanics The study of a materials ability to w
12、ithstand stress in the presence of a flaw or a crack（裂纹）（裂纹）.Fracture toughness（断裂韧性断裂韧性）The resistance of a material to failure in the presence of a flaw or a crack.It is totally different from conventional tensile test or impact test,and gives much more accurate evaluation of a materials propertie
13、s.Charpy specimen:V-notch Less to see in practice A crack with the sharp tip More often to see in practiceSchematic of fracture toughness specimensEdge flaws（边裂纹）（边裂纹）Internal flaws（内部裂纹）（内部裂纹）afKStress intensity factor:（应力强度因子）（应力强度因子）Kc:Fracture toughness（断裂韧性断裂韧性）It is a materials property growth
14、crackNoKKC:Importance of fracture mechanics Selection of a material Design of a component Design of a manufacturing or testing method Brittle fracture（脆断脆断）&Griffith flaw（格里菲思微格里菲思微裂纹裂纹）A crack or flaw in a material that concentrates（集中）（集中）&magnifies（放大）（放大）the applied stress.Schematic diagram of a
15、 Griffith flaw in a ceramicraactual/2The actual stress at the crack tip:Micro-structural features of fracture in metallic materials Ductile fracture(韧韧/塑塑/延性断裂延性断裂)A metal fractures with good ductility and toughness.It normally occurs in a transgranular（穿晶断裂）（穿晶断裂）manner(through the grains),i.e.,the
16、 cracks would go thru the grains.Microvoids(微孔微孔)form in fracture process.Brittle fracture(脆性断裂脆性断裂)A metal or alloy fractures with poor ductility and toughness.It occurs without plastic deformation and takes an intergranular path（沿晶断裂）（沿晶断裂）(along the grain boundaries).Cleavage fracture（解理断裂）（解理断裂）
17、is often observed.Chevron pattern fracture(人字纹形断裂人字纹形断裂)A common fracture feature produced by separate crack fronts propagating（扩展）（扩展）at different levels in the material.Fatigue（疲劳）（疲劳）of materials oFatigue It means that the material is tired from the applied cyclic load（循环载荷）（循环载荷）.It is the lower
18、ing of strength or failure of a material due to repetitive stress（反复应力）（反复应力）which may be above or below the yield strength.80%of failures of engineering parts&structures are related to fatigue,more or less!oCreep（蠕变）（蠕变）A time dependent,permanent deformation at high temperatures,occurring at consta
19、nt load（恒载荷）（恒载荷）or constant stress（恒应力）（恒应力）.oBeach（海滩纹）（海滩纹）or clamshell（蛤壳纹）（蛤壳纹）marks Patterns often seen on a component subjected to fatigue.oRotating cantilever beam（悬臂梁）（悬臂梁）test An older test for fatigue testing（P.197）.oS-N curve(also known as the Whler curve)A graph showing stress as a func
20、tion of number of cycles in fatigue.Creep（蠕变）（蠕变）,stress rupture（应力断裂）（应力断裂）&stress corrosion（应力腐蚀）（应力腐蚀）oStress-rupture curve（应力断裂曲线应力断裂曲线）A method of reporting the results of a series of creep tests（蠕变（蠕变试验）试验）by plotting the applied stress versus the rupture time.oStress-corrosion A phenomenon in
21、 which materials react with corrosive（腐蚀性）（腐蚀性）chemicals in the environment leading to the formation of cracks and lowering of strength.o Creep（蠕变）（蠕变）A time dependent,permanent deformation at high temperatures,occurring at constant load（恒载荷）（恒载荷）or constant stress（恒应力）（恒应力）.Strain Hardening and Ann
22、ealing（应变（应变/加工硬化与退火）加工硬化与退火）Strain hardening and annealing relationship of cold working（冷加工）（冷加工）to the stress-strain curve:Manufacturing processes that make use of cold working as well as hot working.Common metalworking methods轧制轧制 rolling挤出挤出 extrusion拉拔拉拔 wire drawing冲压冲压 stamp/punch锻造锻造 forging
23、Three stages of annealingoRecovery（回复）（回复）A low-temperature annealing heat treatment designed to eliminate residual stresses（残余应力）（残余应力）introduced during deformation without reducing the strength of the cold-worked material.oRecrystallization（再结晶）（再结晶）A medium-temperature annealing heat treatment de
24、signed to eliminate all of the effects of the strain hardening produced during cold working.oGrain growth（晶粒长大）（晶粒长大）Movement of grain boundaries by diffusion in order to reduce the amount of grain boundary area.An Introduction to Materials Science&Engineering Lecture 5(Chapters 9+10)Todays objectiv
25、es:What is solidification凝固?why solidification can occur?Solidification mechanism and theory;Solidification defects&how to prevent the defects;Some application(glass-making,joining metals etc);What is a phase相 and what is a phase diagram相图(PD)?Solid-solution strengthening 固溶强化and other;Typical solid
26、ification of solid-solution alloy by PD Solidification of materials&Phase equilibrium(材料材料的凝固及相的凝固及相平衡平衡)Development of the ingot（铸锭）（铸锭）structure of a casting during solidification:(a)Nucleation begins,(b)The chill zone（激冷区）（激冷区）forms,(c)Preferred growth produces the columnar Zone（柱状区）（柱状区）,and(d)A
27、dditional nucleation creates the equiaxed zone（等轴（等轴区）区）How is a solidification process going?Two steps:nucleation&growth（形核与长大）Phases Equilibrium and Phase Diagram（相平衡及相图）（相平衡及相图）Phase Any portion including the whole of a system,which is physically homogeneous within it and bounded by a surface so
28、that it is mechanically separable from any other portions.Gibbs phase rule Describes the number of degrees of freedom（自由度）（自由度）,or the number of variables that must be fixed to specify the temperature and composition of a phase(2+C=F+P,where pressure and temperature can change,1+C=F+P,where pressure
29、 or temperature is constant).P-T diagram 压力温度相图压力温度相图 A diagram describing thermodynamic stability of phases under different temperature and pressure conditions(same as a unary phase diagram一元相图一元相图).oSolubility The amount of one material that will completely dissolve（溶解）（溶解）in a second material wit
30、hout creating a second phase（不产生第二相）（不产生第二相）.oUnlimited solubility（无限互溶）（无限互溶）When the amount of one material that will dissolve in a second material without creating a second phase is unlimited.oLimited solubility（有限互溶）（有限互溶）When only a maximum amount of a solute material can be dissolved in a solv
31、ent material.Solubility and Solid Solutions（固溶体）（固溶体）oSolid-solution/alloying strengthening（合金强化）（合金强化）Increasing the strength of a metallic material via the formation of a solid solution（固溶体）（固溶体）.oDispersion strengthening（弥散强化）（弥散强化）Strengthening,typically used in metallic materials,by the formati
32、on of ultra-fine dispersions of a second phase（第二相）（第二相）,including nano-sized particle(dispersion).oReinforcement strengthening（复合强化）（复合强化）Material is enhanced by adding strong reinforcements,such as ceramic particles or fibers/whispers(metal matrix composites)oTwinning strengthening（孪晶强化）（孪晶强化）Twin
33、s are introduced into materials(metals or alloys)to increase the strength.Solid-Solution Strengthening（固溶强化）（固溶强化）The effects of several alloying elements on the yield strength of copper.Ni镍镍 and Zn锌锌 atoms are about the same size as copper atoms,but beryllium铍铍 and tin锡锡 atoms are much different fr
34、om copper atoms.Increasing both atomic size difference and amount of alloying element increases solid-solution strengthening.Strengthening by solid-solution deformationThe cooling curve for an isomorphous alloy during solidification.We assume that cooling rates are small so as to allow thermal equil
35、ibrium(热平衡热平衡)to take place.The changes in slope of the cooling curve indicate the liquidus（液相线（液相线）and solidus（固相线）（固相线）temperatures,in this case for a Cu-40%Ni alloy.Solidification of a binary alloy in Phas.Diag.liquidusAn Introduction to Materials Science&Engineering Lecture 7(Chapters 11+12)Toda
36、ys objectives:Fundamentals of dispersion（弥散）strengthening to determine the microstructure.Types of reactions that produce multiple-phase alloys（多相合金）.Methods to achieve dispersion strengthening by controlling the solidification process.Dispersion strengthening by studying a variety of solid-state tr
37、ansformation（固态转变）processes.Nonequilibrium（非平衡）phase transformations martensitic reaction（马氏体转变）strengthening.Materials strengthening by multiphase,Phase transformation&heat treatment(材料的多相弥散强化材料的多相弥散强化、相变和热处理相变和热处理强化强化)nDispersion strengthening-Increasing the strength of a material by forming more
38、than one phase.nMatrix-The continuous solid phase in a complex microstructure.nPrecipitate（沉淀（沉淀/析出物）析出物）-A solid phase that forms from the original matrix phase when the solubility limit is exceeded.nEutectic（共晶）（共晶）-A three-phase invariant（不变、平衡）（不变、平衡）reaction in which one liquid phase solidifies
39、 to produce two solid phases.Principles and examples of dispersion strengthening(弥散强化弥散强化)The five most important three-phase reactions in binary phase diagrams共晶反应共晶反应包晶反应包晶反应偏晶反应偏晶反应共析反应共析反应包析反应包析反应Lead-tin(Pb-Sn)equilibrium phase diagramThe Pb-2%Sn alloy is a single-phase solid solution.Solidific
40、ationµstructure of a solid-solution alloy Solidification 凝固凝固,precipitation 析出析出,and microstructure of a Pb-10%Sn alloy.Some dispersion strengthening 弥散强化弥散强化 occurs as the solid precipitates.Solidificationµstructure of a solid-solution alloy Solidificationµstructure of the eutectic a
41、lloy 共晶合金共晶合金 Pb-61.9%Sn.Example:Phases in Pb-Sn phase diagramThe cooling curve for a eutectic alloy is a simple thermal arrest 热转变热转变,since eutectics freeze or melt at a single temperature,similar to that of a pure metal.The cooling curve for a eutectic alloyoAge hardening（时效强化）（时效强化）A special disp
42、ersion-strengthening heat treatment.By solution treatment,quenching 淬火（快速冷却）淬火（快速冷却）,and aging（时（时效）效）,a coherent precipitate forms that provides a substantial strengthening effect.oAlso known as precipitation hardening（沉淀强化）（沉淀强化）,it is a form of dispersion strengthening.Age or precipitation harden
43、ing时效强化或沉淀强化时效强化或沉淀强化oStep 1:Solution Treatment 固溶处理固溶处理oStep 2:Quench 淬火（快速冷却）淬火（快速冷却）oStep 3:Age 时效时效oGuinier-Preston(GP)zones（GP区）区）Tiny clusters of atoms that precipitate from the matrix in the early stages of the age-hardening process.Microstructural evolution in age or precipitation hardeningT
44、he three steps in the age-hardening heat treatment and the microstructures that are produced.铝合金的时铝合金的时效强化效强化Schematic of three steps in the age-hardening heat treatmentSupersaturatedSolid SolutionAn Introduction to Materials Science&Engineering Lecture 7(Chapter 13)Todays objectives:Designations(牌号
45、)&classifications of steels Why is heat treatment necessary for a steel?What are conventional heat treatments?Discuss how to use the eutectoid reaction(共析反应)to control the structure and properties of steels through heat treatment and alloying.Examine two special classes of ferrous alloys:stainless s
46、teels(不锈钢)and cast irons.Heat treatment of steels&cast irons(钢和铸铁的钢和铸铁的热处理热处理)Designations&classification of steelsoDividing point of Steel&Iron 2.11%C is the dividing point between“Steels”&“Cast irons”:C%below 2.11 is Steel,above 2.11 is Cast iron.oDifferent nations have distinct designations of st
47、eels,USA:AISI+SAE+ASTM,China:GB(国标国标),Germany:DIN,Japan:JIS,UK:BS etc.oDesignations(牌号牌号)The AISI(American Iron and Steel Institute)and SAE(Society of Automotive Engineers)provide designation systems for steels that use a four-or five-digit number.oClassifications Steels can be classified based on t
48、heir composition or the way they have been processed:Carbon steels(碳钢碳钢),alloy steels(合金合金钢钢)and specialty steels(特种钢特种钢)etc.The eutectoid portion of Fe-Fe3C phase diagram An expanded version of the Fe-C diagram.oProcess Annealing(工艺退火工艺退火)Eliminating Cold Work:A low-temperature heat treatment used
49、to eliminate all or part of the effect of cold working in steels.oAnnealing and Normalizing(退火和正火退火和正火)Dispersion Strengthening:Annealing-A heat treatment used to produce a soft,coarse pearlite(珠光珠光体体)in steel by austenitizing(奥氏体化奥氏体化),then furnace cooling(随炉冷却随炉冷却).Normalizing-A simple heat treatm
50、ent obtained by austenitizing and air cooling(空冷空冷)to produce a fine pearlitic structure.oSpheroidizing(球化处理球化处理)Improving machinability(可加工性可加工性):Spheroidite-A microconstituent containing coarse spheroidal cementite particles in a matrix of ferrite(铁素体铁素体),permitting excellent machining characteris
