Lattice structure of metals

This article provides answers to the following questions, among others:

  • Why do metals have a regular structure?
  • What is meant by a crystal?
  • How does the atomic structure of an amorphous solid look like?
  • Which statement does the lattice constant provide?
  • What is the order of magnitude of the lattice constant of metals?
  • How many atoms are contained in an iron cube of 25 mm edge length?
  • What is a unit cell?
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Important types of lattice structures

This article provides answers to the following questions, among others:

  • How is a body-centered cubic lattice structured?
  • What is meant by the coordination number?
  • Which statement provides the packing density?
  • How does the hexagonal closest packed grid build up?
  • What is meant by a stacking sequence?
  • How does the face-centered cubic unit cell come about?
  • Why does the hcp-lattice and the fcc-lattice have a maximum packing density?
  • Why can one write with a pencil?
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Derivation of the packing density

This article provides answers to the following questions, among others:

  • What is meant by the packing density (or packing factor)?
  • How is the packing density calculated for the body-centered cubic lattice (bcc)?
  • How is the packing density calculated in the face-centered cubic lattice (fcc)?
  • Why is the packing density for the hexagonal closest packed lattice identical to the fcc-lattice?
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Crystallographic defects

This article provides answers to the following questions, among others:

  • Which types of crystallographic defects can be distinguished?
  • What are vacancy defects?
  • What are the differences between substitutional atoms and interstitial atoms with regard to their inclusion in the metal?
  • What are dislocations?
  • What distinguishes a grain in a metal?
  • What is the difference between a high angle and a low angle grain boundary?
  • What is the difference between a coherent, partially coherent and incoherent phase boundary?
  • What is a stacking fault?
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Fundamentals of deformation

This article provides answers to the following questions, among others:

  • What is the difference between elastic and plastic deformation?
  • What is the atomic process of deformation?
  • In which cases must springback be considered during the deformation process?
  • What is meant by a slip system?
  • What is the relationship between slip plane, slip direction and slip system?
  • What is the difference between a normal stress and a shear stress?
  • Why are only shear stresses responsible for the deformation process at the atomic level?
  • What is meant by critical resolved shear stress?
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Influence of the lattice structure on the ductility

This article provides answers to the following questions, among others:

  • What is a lattice plane?
  • What is meant by a slip system?
  • Why should well-deformable lattice structures have as many slip systems as possible?
  • In what capacity do wrought metals differ from cast metals?
  • How many slip systems does the body-centered cubic lattice have?
  • Why is the face-centered cubic lattice more malleable than the body-centered cubic lattice, even though they both have the same number of slip systems?
  • How many slip planes does the hexagonal closest packed lattice have?
  • What is meant by polymorphism or allotropy?
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Deformation process in real crystal structures

This article provides answers to the following questions, among others:

  • What influence do dislocations have on the ductility of metals?
  • What does the Peierls stress describe?
  • What is meant by strengthening?
  • How is an increase in strength achieved in solid solution strengthening?
  • How do you achieve an increase in strength during precipitation strengthening?
  • Why do you achieve an increase in strength through grain-boundary strengthening?
  • What happens at an atomic level in case of strain hardening?
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Schmid’s law

This article provides answers to the following questions, among others:

  • What is the mathematical relation between an external applied normal stress and the resulting shear stress in the slip system?
  • What statement makes the Schmid factor?
  • What is meant by a critical resolved shear stress (CRSS)?
  • At which angle is the shear stress in a slip system maximum?
  • Why do single crystals have slip steps at an angle of 45°?
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Deformation process in single crystals

This article provides answers to the following questions, among others:

  • How to explain the stress-strain curve for single crystals?
  • What is meant by Hooke’s law?
  • What characterizes easy gliding?
  • Which atomic processes occur in the case of multiple gliding?
  • What is a forest dislocation?
  • What is meant by climbing and cross-slipping of dislocations?
  • What is crystal recovery?
  • What ist the atomic principle of strain hardening?
  • How to explain the stress-strain curve for polycrystals?
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Microstructure formation

This article provides answers to the following questions, among others:

  • What is meant by a microstructure?
  • What are grains and grain boundaries?
  • What is a single crystal and a polycrystal?
  • Why is a fine-grained microstructure in metals often desirable?
  • What ist meant by crystallization?
  • Why are monocrystalline materials used for high-temperature applications?
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Conditions of solidification

This article provides answers to the following questions, among others:

  • Which atomic processes take place during solidification?
  • What conditions must be fullfiled for crystallization?
  • What is supercooling?
  • What are nuclei used for in a melt?
  • How is the solidification temperature defined?
  • What conditions must be met for supercooled water?
  • What is freezing rain?
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Types of nuclei

This article provides answers to the following questions, among others:

  • What is homogeneous and heterogeneous nucleation?
  • How can homogeneous nucleation occur in the melt?
  • Which type of nucleation is more likely during solidification?
  • What measures can influence the solidification process so that the structure is as fine-grained as possible?
  • What is meant by seeding of a melt?
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Heat of solidification

This article provides answers to the following questions, among others:

  • Why does the temperature remain constant when pure substances solidify?
  • How can it be explained on a microscopic level that the temperature is kept constant during crystalisation?
  • What is a “thermal arrest”?
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Amorphous metals

This article provides answers to the following questions, among others:

  • What are amorphous metals (metallic glasses)?
  • Why is glass a thermodynamic liquid?
  • What is meant by the term glass transition temperature?
  • What are the technological properties of amorphous metals?
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Homogeneous nucleation

This article provides answers to the following questions, among others:

  • How can the Gibbs energy be used to assess whether a process is voluntary or not?
  • How can the different states of matter be explained?
  • What influence does surface energy have on nucleation?
  • Why are only nuclei above a critical radius stable and can initiate the solidification process?
  • What is the free energy barrier for nucleation?
  • What effect does undercooling have on the rate of nucleation?
  • Why do one suppress crystallization when undercooling is too high?
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Heterogeneous nucleation

This article provides answers to the following questions, among others:

  • How can foreign particles promote nucleation?
  • What is the contact angle?
  • What influences the contact angle?
  • What is the connection between heterogeneous and homogeneous nucleation?
  • What property should a foreign particle have in order to promote nucleation?
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Crystal growth

This article provides answers to the following questions, among others:

  • What is polygonal crystal growth?
  • What distinguishes a microstructure with polygonal crystal growth?
  • What is dendritic crystal growth?
  • What distinguishes a microstructure with dendritic crystal growth?
  • How is the 3-zone casting structure of a casting block formed?
  • What ist microshrinkage?
  • Why does a snowflake have a branched hexagonal shape?
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Typs of alloys

This article provides answers to the following questions, among others:

  • What are alloys and why are they needed?
  • What are binary alloy systems?
  • What characterizes a solid solution alloy?
  • What types of solid solutions can be distinguished?
  • What is a complete solid solution series?
  • What characterizes a mixture of pure crystals?
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Complete solubility of components in solid state (solid solution)

This article provides answers to the following questions, among others:

  • What is a solid solution?
  • What do the cooling curves of solid solution look like?
  • What is a phase?
  • What is a phase diagram?
  • How to create a phase diagram?
  • How to read a phase diagram?
  • What characterizes the liquidus line or solidus line?
  • How can the chemical composition of the phases be determined from the phase diagram?
  • How can the phase fractions be determined from the phase diagram?
  • How do crystal segregation occur?
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Complete insolubility of components in solid state

This article provides answers to the following questions, among others:

  • What is a crystal mixture?
  • How do the cooling curves of an alloy with insoluble components look like?
  • How do you create the phase diagram of such an alloy?
  • What is a eutectic point?
  • What is a eutectic, hypoeutectic and hypereutectic alloy?
  • How does the microstructure of the above mentioned alloys form?
  • How can the chemical composition of the phases be determined from the phase diagram?
  • How can the phase fractions and microstructure fractions be determined from the phase diagram?
  • What is a microstructure diagram?
Continue reading Complete insolubility of components in solid state

Limited solubility of components in solid state

This article provides answers to the following questions, among others:

  • How does the phase diagram of an alloy with limited solubility of components look like?
  • What is a \(\alpha\) solid solution or \(\beta\) solid solution?
  • Why does the solubility of the components decrease with decreasing temperature?
  • How does precipitation occur in the microstructure?
  • What is meant by aging of a material?
  • What is artificial aging?
Continue reading Limited solubility of components in solid state

Iron ore mining and dressing

This article provides answers to the following questions, among others:

  • What is steel made of?
  • Which two main processes can be distinguished in steel production from iron ore?
  • What is ore smelting?
  • What are iron ores made of?
  • What is gangue?
  • What are iron ore deposits?
  • Why are iron ores processed?
  • What is the purpose of flotation and magnetic separation?
  • What is sintering and pelletizing of iron ores?
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Ironworks

This article provides answers to the following questions, among others:

  • What is charge?
  • What is meant by charging a blast furnace?
  • What is the function of the slag in the blast furnace process?
  • What is the slag used for?
  • What is a coking plant?
  • What is the difference between coal and coke?
  • How is the hot blast generated in Cowpers?
  • What is the function of the charging bells?
  • Why does the material to be loaded have to be pressure-resistant?
  • What is called tapping?
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Blast furnace process

This article provides answers to the following questions, among others:

  • Why is carbon used for the blast furnace process?
  • How important is the “Boudouard reaction” for the blast furnace process?
  • What chemical processes distinguish indirect reduction from direct reduction of iron ores?
  • What is carburization?
  • How much carbon does pig iron contain?
  • What is the difference between metastable and stable solidification?
  • What is “grey pig iron” and “white pig iron”?
  • In which “solidification form” is pig iron mostly tapped?
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From crude steel to steel

This article provides answers to the following questions, among others:

  • What is secondary metallurgy?
  • What is rimmed steel, semi-killed steel and killed steel?
  • For what purpose is vacuum treatment carried out?
  • How does the electro-slag remelting (electro-flux remelting) work?
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Microstructure formation during solidification

This article provides answers to the following questions, among others:

  • What is steel made of?
  • What is the difference between steel and cast iron regarding their composition?
  • Why is carbon used as an alloying element for steel?
  • Why do further phase transformations take place in the already solidified state in steels?
  • In which lattice structure does steel crystallize first?
  • Which lattice structure does steel (usually) have at room temperature?
  • What is the steel part in the phase diagram?
  • How does the carbon content influence the solidification range of steels?
  • What is austenite and ferrite?
  • How does the carbon content affect the transformation of \(\gamma\)-iron into \(\alpha\)-iron?
  • Which microstructural changes occur in the stable or metastable system during the \(\gamma\)-\(\alpha\)-transformation?
  • What promotes the respective systems?
  • Which system is relevant for steel and which for cast iron?
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Phase transformations in solidified state (metastable system)

This article provides answers to the following questions, among others:

  • What is the carbon content of a eutectoid steel?
  • Why is virtually no carbon soluble in ferrite?
  • What phases does pearlite consist of and at what temperature does it form?
  • What is the structure of pearlite under the microscope?
  • What is the difference in the name between eutectic and eutectoid?
  • Why does the solubility of carbon in austenite decrease with decreasing temperature?
  • What is the maximum percentage of carbon that can be dissolved in austenite and at what temperature?
  • What is an undersaturated, supersaturated and saturated state?
  • How is the insoluble carbon precipitated from austenite?
  • What does the microstructure of a hypereutectoid steel look like?
  • How is carbon precipitated in hypoeutectoid steels during \(\gamma\)-\(\alpha\)-transformation?
  • What does the microstructure of a hypoeutectoid steel look like?
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Cast iron

This article provides answers to the following questions, among others:

  • What is the difference in microstructure between steels and cast iron?
  • For which manufacturing processes are steels particularly suitable compared to cast iron?
  • What is the difference between the phase diagram of the stable and the metastable system?
  • What is white and grey cast iron?
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Annealing processes

This article provides answers to the following questions, among others:

  • What are the objectives of annealing processes, such as normalizing, soft annealing, coarse grain annealing, recrystallisation annealing, diffusion annealing, solution annealing and stress-relief annealing?
  • In which temperature ranges are the annealing processes carried out?
  • Why is an improvement in machinability also achieved with soft annealing?
  • How can the generally poorer properties of a coarse-grained microstructure be subsequently removed?
  • What is the significance of recrystallisation annealing for transformation-free steels?
  • What is hot forming or cold forming?
  • Why is diffusion annealing relatively cost-intensive?
  • Why does the workpiece have to be cooled slowly after stress relief annealing?
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Quenching and tempering

This article provides answers to the following questions, among others:

  • What is the aim of quenching and tempering compared to hardening?
  • In which three process steps can quenching and tempering be divided?
  • Why is quenching and tempering not counted as an annealing process?
  • Why must the steel be kept at a specific temperature for a certain time during austenitizing?
  • What microstructural changes occur during quenching?
  • What are the characteristics of the martensitic microstructure?
  • What properties must steels have for quenching and tempering?
  • What is bainite?
  • What is a surface-hardening steel?
  • Why should high-alloy steels not be quenched as much as unalloyed steels?
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Surface hardening (case-hardening)

This article provides answers to the following questions, among others:

  • What are the characteristics of surface-hardened workpieces?
  • How is the depth of the hardening layer controlled during flame hardening?
  • What are the advantages of induction hardening compared to flame hardening?
  • Why does laser hardening not require quenching with water?
  • For which steels is case hardening suitable and what are the mechanical properties of case hardened components?
  • What are single-quench hardening, double-quench hardening and direct hardening?
  • For which steels is single or double quench hardening used in comparison to direct hardening?
  • How does nitriding differ from all other surface hardening processes?
  • What is the primary objective of nitriding?
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Tensile test

This article provides answers to the following questions, among others:

  • What kind of tensile specimens are usually used?
  • Why must the tensile specimens not be deformed too quickly?
  • Which quantities are measured during the tensile test?
  • Why does the yield strength play a central role in mechanical engineering?
  • Which material property is described by the elastic modulus?
  • What is the “yield strength effect”?
  • What is “yield point elongation” and what is the role of “Cottrell atmosphere”?
  • What are Lüder bands (stretcher strain marks)?
  • How does the “Portevin-Le Chatelier effect” (dynamic strain aging) occur?
  • Why does “uniform elongation” play an important role in forming technology?
  • Why does the tension curve  drop during necking?
  • Why do shorter tensile specimens show higher elongation at break than longer ones?
  • Which statement can be made on the basis of the area under the stress-strain curve?
  • What is the difference between the strength values and the deformation values with regard to their influence on the design of components?
  • What is an “offset yield strength” and for which materials is it used?
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Compression test

This article provides answers to the following questions, among others:

  • Why are no longish specimens used in the compression test?
  • Why is the true compressive stress lower than the engineering stress?
  • What is the difference between the “compressive yield strength” and the “compressive offset yield strength”?
  • What causes the formation of pressure cones in the material?
  • Why does a crack usually form at an angle of 45°?

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Hardness test

This article provides answers to the following questions, among others:

  • How is the hardness of materials defined?
  • On which principles are all hardness testing methods based?
  • Which indenter is used for Brinell hardness testing?
  • What is the load factor and what is it used for?
  • For which materials is Brinell testing particularly suitable?
  • Which indenter is used for the Vickers hardness test?
  • Under what conditions can Vickers hardness values only be compared with each other?
  • For which materials is Vickers testing particularly suitable?
  • Which indenters are used for Rockwell hardness testing and for which materials are they used?
  • What is the purpose of applying the preload?
  • What are the advantages and disadvantages of Rockwell testing?
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Flexural test

This article provides answers to the following questions, among others:

  • How does the flexural stress distribution in the cross-section of a specimen subjected to bend loading look like?
  • Where does the maximum bending stress occur?
  • What characterizes the “neutral axis”?
  • What role does the “axial section modulus” play in a bending load?
  • What is the “flexural yield strength”?
  • Why does the “flexural yield strength” has a higher value than the “tensile yield strength”?
  • For which materials is a “ultimate flexural strength” used instead of a “flexural yield strength”?
  • Why does the flexural test usually offer better results than the tensile test for determining the strength of brittle materials?
  • How can the modulus of elasticity (Youngs modulus) be determined?
  • How do residual stresses occur in the material?
  • Why does the neutral axis shift into the area of compression in grey cast iron?
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Charpy impact test

This article provides answers to the following questions, among others:

  • What are the objectives of the “Charpy impact test”?
  • Why does “notch impact energy” represent a measure of the toughness of a test specimen?
  • What external influences effect the notch impact energy?
  • What are “upper shelf”, “lower shelf” and “transition temperature”?
  • Which lattice structures show a pronounced upper shelf and lower shelf and which do not?
  • What is a ductile fracture, sliding fracture, brittle fracture and cleavage fracture?
  • How does the fracture speed influence the notch impact energy?
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Fatigue test

This article provides answers to the following questions, among others:

  • What are the objectives of the fatigue test and how is it carried out?
  • Why should the test frequencies not be set too high in the fatigue test?
  • What is a stress cycle?
  • How is the stress ratio defined?
  • What is the difference between alternating stress and pulsating stress?
  • What information can be obtained from the Wöhler curve?
  • What are the characteristics of “low cycle fatigue”, “high cycle fatigue” and “fatigue strength”?
  • Why does an increase of the mean stress in the compression range lead to larger bearable stress amplitudes?
  • What is the difference between “fatigue strength” and “fatigue limit”?
  • What are the characteristics of “alternating fatigue limit” and “pulsating fatigue limit”?
  • What are two typical characteristics of the fracture surface of a fatigue fracture?
  • What is the difference between “beach marks” and “fatigue striations”?
  • How can the fatigue strength of components be increased?
  • How to create the Haigh diagram and the Smith diagram and how can they be read?
  • How is the “rotating bending test” and the “reverse bend test” carried out?
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Stress rupture test (creep rupture test)

This article provides answers to the following questions, among others:

  • What is a hot yield strength?
  • What is creep?
  • What factors influence the intensity of creep?
  • At what temperatures is a technically relevant creep to be expected?
  • What is the difference between the “stress-rupture-test” and the “creep rupture test”?
  • What process do creep curves represent?
  • What statement do “creep limits” “and “creep strengths” provide?
  • Why are coarse-grained materials better suited than fine-grained materials for high-temperature applications?
  • What are the characteristics of primary, secondary and tertiary creep?
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Ultrasonic testing (UT)

This article provides answers to the following questions, among others:

  • What is the measurement principle behind ultrasonic testing?
  • What is the coupling agent used for?
  • How are ultrasound waves generated and received?
  • What is the difference between longitudinal waves and transverse waves?
  • What types of ultrasonic probes are used?
  • What is the dead zone?
  • Which probes are used for weld inspection?
  • What are phased array probes and what special advantages do they offer?
  • What is the minimum size of imperfections that can be detected by ultrasonic waves?
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Magnetic particle inspection (MPI)

This article provides answers to the following questions, among others:

  • What is the principle behind magnetic particle inspection?
  • How should flaws be aligned with respect to the magnetic field direction so that they are optimally visible?
  • Why are components tested both in the mode of magnetic field flow and in the mode of current flow?
Continue reading Magnetic particle inspection (MPI)