Abstract
The microstructure and flow stress of metals are related through many well-known strength-structure relationships based on structural parameters, where grain size and dislocation density are examples. In heterogeneous structures, the local stress and strain are important as they will affect the bulk properties. A microstructural method is presented which allows the local stress in a deformed metal to be estimated based on microstructural parameters determined by an EBSD analysis. These parameters are the average spacing of deformation introduced boundaries and the fraction of high angle boundaries. The method is demonstrated for two heterogeneous structures: (i) a gradient (sub)surface structure in steel deformed by shot peening; (ii) a heterogeneous structure introduced by friction between a tool and a workpiece of aluminum. Flow stress data are calculated based on the microstructural analysis, and validated by hardness measurement and 2D numerical simulations. A good agreement is found over a plastic strain range from ∼1 to 5.
Highlights
Structure-strength relationships for metallic materials provide guidelines for the design and processing of engineering materials and components
The step sizes for electron backscatter diffraction (EBSD) scanning are 1000 nm, 200 nm, 120 nm, 50 nm and 20 nm, chosen according to the fineness of the deformation structure with finer map step sizes used for finer deformation structures
The EBSD microstructure is consistent with the microhardness profile as shown in figure 1e, with the structure divided into three zones: Zone A (0-110 m) has a lamellar structure parallel to the surface, with a sharp hardness increase as the surface is approached; Zone B (110-600 m) has deformed coarse grains with dislocation boundaries and tangles with a slow hardness increase as the surface is approached; and Zone C (600 m-) is the undeformed matrix with an almost constant hardness
Summary
Structure-strength relationships for metallic materials provide guidelines for the design and processing of engineering materials and components An example of such relationships is the Hall-Petch equation [1,2], which relates the yield (or flow) stress to the inverse square root of the grain size, or to the spacing between boundaries in the structure that act as barriers to dislocation glide [1,2,3]. Specimens where such a relationship is tested are typically thermo-mechanically processed, for example, by rolling, drawing and torsion, and they are characterized as bulk materials on the assumption that the structure is homogeneous. By using such techniques it is possible to characterize microstructural parameters that can be the basis for calculation of the strength, for example, by applying the Hall-Petch
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