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 acceptability Factors 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 Microstructure Properties of Materials Mechanical properties The behavior of materials deformed by a set of 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 resistance Classification of materials based on atomic structures and the nature of bonds Metals and their alloys Organic polymers Ceramics Mechanical 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 materials 1 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 separately Solids exist in the nature in two principal forms crystalline and amorphous An elementary cell of crystal lattice is described Three sections a b and c Three angles made by each 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 Reflective Iron 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 steel One third of the weight of steel Good thermal and electrical conductivity High strength to weight ratio Can be given a hard surface by anodizing and hard coating Most alloys are weldable Copper and its alloys copper brass and bronze Magnesium The lightest of all structural metals Specific gravity 1 75 Magnesium weighs 1 5 times less than an equal volume of aluminum and 4 times less than zinc High strength stiffness dimensional stability High strength to weight ratio Alloys have Relatively high thermal and electrical conductivities Good energy absorption characteristics Nonmagnetic properties Mechanical properties For basic types of stresses tensile compressive shear torsion 拉力 压力 剪切力 扭转力拉力 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 positive ion Crystalline structure High thermal and electrical conductivity Ability to be deformed plastically Metallic luster 光泽 or reflectivity Body centered cubic columbium barium vanadium 钶 钡 钒 Face centered cubic calcium aluminum copper lead nickel gold Hexagonal close packed zinc titanium magnesium There are several ways to protect against corrosion Corrosion can be prevented or lessened by Coatings Design considerations Environmental control Alloying among others Ceramic 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 7 Traditional ceramics are derived and processed from clay or nonclay minerals Most advanced ceramics are produced from fine relatively poor powers using new technology The 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 glass Glass is an inorganic product of fusion which has cooled to a rigid condition without crystallization Glass formation Glass 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 which forms 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 Al2O3 Two model of glass 1 continuous random network model 2 random close packing model Physical properties Density glass cooled at various rates from above the annealing point will differ in density with the more rapidly cooled glasses having a lower density Strength The measured mechanical strength of glass is much lowe