材料概论复习资料

影响材料使用的因素 Materials behavior Availability Cost Synthesis and production method（材料的合成与生产方法） Processing techniques Environmental acceptabilityFactors on the properties of materials 组成材料的各元素的原子结构， Atomic structure 原子间的相互作用、相互结合， Nature of chemical bonds 原子或分子在空间的排列分布和运动规律, Atomic ordering 原子集合体的形貌特征。 MicrostructureProperties of Materials Mechanical properties: The behavior of materials deformed by a setof forces. 弹性Elasticity 塑性Plasticity 强度Strength 硬度Hardness 韧性Toughness 疲劳特性Fatigue behaviour 耐磨性Abrasion resistanceClassification of materials: based on atomic structures and the nature of bonds Metals and their alloysOrganic polymers CeramicsMechanical properties : which reflect the behavior of materials ,deformed by a set of forces Physical properties : which describe the behavior of materials subjected to the action of temperature ,electric or magnetic fields ,or light .Chemical properties : which characterize the behavior of material in a reactive environment .Types of materials1 metal it is strong and can be readily formed into practical shapes .its extensive , permanent ductility is an important asset in permitting small amounts of yielding to sudden and severe loads .2 ceramics and glasses Chemical stable , siginificantly higher melting point , brittleness 3 polymers polymers are frequently lightweight ,lowcost ,lower strength ,lower melting point and higher chemical reactivity 4 composites it carries along the superior properties of each component , producing a product that is superior to either of the components separatelySolids exist in the nature in two principal forms : crystalline and amorphousAn elementary cell of crystal lattice is described Three sections a, b, and c, Three angles made byeach two of these sections, , and . 晶格常数lattice constant /lattice spacing: a、b、c.crystal structure : body-centered cubic structure , face-centered cubic structure , hexagonal close-packed structure the properties of crystals are different in various crystallographic directions ,which are associated with an ordered arrangement of atoms in space. Advantages of Metals Strong Soft: Cutting, Machining, Shaping Melting and casting Heat conductive Electric conductive Light-ReflectiveIron consist of slag and carbon ,but steel consist of many element such as carbon ,silicon ,manganese ,nickel and so on.The types of cast iron ； white cast iron , gray cast iron , alloy cast iron , nodular or ductile cast iron , malleable cast iron Aluminum Rust resistant High reflectivity Can be die cast Easily machined Good formability Nonmagnetic Nontoxic One-third the stiffness of steelOne third of the weight of steelGood thermal and electrical conductivityHigh strength-to-weight ratio Can be given a hard surface by anodizing and hard coatingMost alloys are weldableCopper and its alloys : copper , brass and bronzeMagnesium The lightest of all structural metals Specific gravity:1.75 Magnesium weighs 1.5 times less thanan equal volume of aluminum and 4 timesless than zinc. High strength, stiffness, dimensionalstability, High strength-to-weight ratio Alloys have Relatively high thermal and electricalconductivities; Good energy absorption characteristics; Nonmagnetic propertiesMechanical propertiesFor basic types of stresses : tensile, compressive, shear ,torsion (拉力，压力，剪切力，扭转力)Strength : the strength of a metal is its ability to resist changing its shape or size when external forces are applied.Elasticity : the ability of a material to strain under load and then return to its original shape and size when unloaded.Yield point : yielding or plastic flow occurs in materials when the elastic limit has been exceeded.Plasticity : metals undergo plastic flow when stressed at or beyond their elastic limits .Brittleness : a material that will not deform plastically is said to be brittle .Stiffness : stiffness is expressed by the modulus of elasticity.Ductility : the property that allows a metal to deform permanently when loaded in tension .As temperature decreases ,the strength ,hardness ,and the modulus of elasticity increase for almost all the metals .Metals and nonmetals Ability to donate electrons and form a positiveion Crystalline structure High thermal and electrical conductivity Ability to be deformed plastically Metallic luster (光泽) or reflectivityBody-centered cubic : columbium, barium, vanadium, (钶，钡，钒)Face-centered cubic : calcium,aluminum,copper, lead ,nickel, goldHexagonal close-packed : zinc,titanium,magnesiumThere are several ways to protectagainst corrosion. Corrosion can beprevented or lessened by Coatings, Design considerations, Environmental control, Alloying, among othersCeramic compounds:Can be defined as inorganic compounds made by heating clay or other mineral matter to a high temperature at which they partially melt and bond together.7Traditional ceramics are derived and processed from clay or nonclay minerals.Most advanced ceramics are produced from fine ,relatively poor powers using new technologyThe property of ceramics Extreme hardness Heat resistance Corrosion resistance Low electrical and thermal conductivity Low ductility (brittleness)Pores affect the strength of ceramics in two ways：they produce stress concentrations. Once the stress reaches a critical level, a crack will form and propagate.pores reduce the cross-sectional areas over which a load can be applied and, consequently, lower the stress that these materials can support.Definition of glassGlass is an inorganic product of fusion which has cooled to a rigid condition without crystallization.Glass formationGlass formation occurs in materials of all chemical types : covalent, ionic , molecular, metallic and hydrogen bonded materials. Glass have been made from element, simple chemical compounds, complex organic molecules , salt mixtures and alloys . there is no particularly advantageous way of grouping glass forming materials.Composition of oxide glass Main oxides in glass Glass formers: an oxide whichforms a glass easily （形成体）B2O3, SiO2, P2O5. Glass modifiers: （修改体）Li2O, Na2O, K2O, MgO, CaO . Intermediates: （中间体）TiO2, ZnO, PbO, Al2O3Two model of glass1 continuous random network model2 random close packing modelPhysical propertiesDensity : glass cooled at various rates from above the annealing point will differ in density with the more rapidly cooled glasses having a lower densityStrength : The measured mechanical strength of glass is much low