33 6. Mechanical Properties Anwendung in TWIP-Stählen=> Hohe Verformung + FestigkeitDeformation twinningTwinMatrix
34 Hochleistungswerkstoff Stahl – eine faszinierende Vielfalt Streckgrenze [MPa]Verformbarkeit
35 6. Mechanical Properties Deformation: Slip vs. TwinningSlipTwinningAtomic movementLattice orientationAtoms move fractional atomic spacing.Microscopic appearanceThin linesWide bands or broad linesNo change in lattice orientation. The steps are only visible on the surface of the crystal and can be removed by polishing. After polishing there is no evidence of slip.Lattice orientation changes. Surface polishing will not destroy the evidence of twinning.
36 6. Mechanical Properties What is the maximum shear-stress ?
37 6. Mechanical Properties The shear-stress-law of SchmidWinkel zwischen Zug- und Gleitrichtungkristallographische Gleitebenedefiniert AKristallographische Gleitrichtungdefiniert FgSchmid-Faktor
39 6. Mechanical Properties Plastic Deformation of Polycrystalline Materials (Cu)Cu-PolykristallVerschiedene Orientierungen der Gleitsysteme
40 6. Mechanical Properties Plastic Deformation of Polycrystalline MaterialsRequirement of five independent slip systems to realize any plastic deformation in polycrystals (Compatibility of deformation)
41 6. Mechanical Properties Plastic deformation: Single vs. polycrystalIncrease due to:Manifold of grain orientations in polycrystalsGrain Boundaries!!!Why such an increase of strength?
42 6. Mechanical Properties Plastic deformationCharacteristics of Dislocations
43 6. Mechanical Properties Plastic deformationCharacteristics of Dislocations
44 6. Mechanical Properties Plastic Deformation of Polycrystalline MaterialsGrains with the highest Schmid-factor deform first.yield stress (= Streckgrenze) is reached when deformation of all grains occursany plastic deformation of polycrystalline materials needs activation of5 independent slip systems (Compatibility of deformation)The role of Grain size
45 6. Mechanical Properties The Relation of Hall-Petch
46 6. Mechanical Properties Solid solution hardeningAlloying causes hardening effects due to three types of interactions between the dislocations and the alloyed atoms:Parelastic interaction distortion of the lattice; change in the lattice parameter aDielastic interaction different shear modulus G of alloyed atoms compared to that of the matrix atomschemical interaction
47 6. Mechanical Properties Work HardeningPropertyDegree of Deformation
48 6. Mechanical Properties Dispersion and precipitation hardeningThe Fine-Kelly-MechanismThe Orowan-Mechanismshear-modulusparticle diametersurface energyVolume fraction of particlesBurgers-vectorparticle distance
49 6. Mechanical Properties Texture hardeningStrengthening effect due to:bad orientation between applied stress and „slip system“morphological texture (Hall-Petch!!)Loading in direction A shows an enhanced yield stress compared to direction BBA
50 6. Mechanical Properties Mechanisms to enhance strengthPlastic deformation - at lower temperatures (no recyrstallization)grain refinement – Hall Petchsolid solution hardening – solubility and lattice distortiondispersion hardening – input of highly dispers particlesprecipitation hardening – creation of particles (solubility)texture hardening (morphology, orientation and slip systems,
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