We study orientation gradients and geometrically necessary dislocations (GNDs) in two ultrafine grained dual-phase steels with different martensite particle size and volume fraction (24 vol.% and 38 vol.%). The steel with higher martensite fraction has a lower elastic limit, a higher yield strength and a higher tensile strength. These effects are attributed to the higher second phase fraction and the inhomogeneous transformation strain accommodation in ferrite. The latter assumption is analyzed using high-resolution electron backscatter diffraction (EBSD). We quantify orientation gradients, pattern quality and GND density variations at ferrite–ferrite and ferrite–martensite interfaces. Using 3D EBSD, additional information is obtained about the effect of grain volume and of martensite distribution on strain accommodation. Two methods are demonstrated to calculate the GND density from the EBSD data based on the kernel average misorientation measure and on the dislocation density tensor, respectively. The overall GND density is shown to increase with increasing total martensite fraction, decreasing grain volume, and increasing martensite fraction in the vicinity of ferrite.

Orientation gradients and geometrically necessary dislocations in ultrafine grained dual-phase steels studied by 2D and 3D EBSD

On discute des mecanismes de renforcement des ceramiques par pontage des fissures a l'aide de trichites et d'autres types de renforcants discontinus. On montre que le renforcement par pontage des fissures peut etre combine avec d'autres mecaniques de renforcement (par exemple par transformation de phase) et que l'on peut obtenir des effets de synergie. La conception des materiaux renforces repose fortement sur le controle des proprietes des materiaux et des constituants microstructuraux

/pdf/microstructural-design-of-toughened-ceramics-1o4ydn67o9.pdf

Microstructural design of toughened ceramics

Indentation fracture of a series of well-characterized WC-Co cermets was studied with a Vickers diamond pyramid indenter. The resulting crack length-indentation load data were analysed in terms of relations characteristic of radial (Palmqvist) and fully developed radial/median (half-penny) crack geometries. The radial crack model gave a better fit to the data on all the alloys studied. Crack shapes determined by repeated surface polishing confirmed the radial nature of the cracks. An indentation fracture mechanics analysis based on the assumption of a wedge-loaded crack is shown to be consistent with the observed linear relation between the radial crack length and the indentation load. The analysis also predicts a simple relation among the fracture toughness (K
lc), the Palmqvist toughness (W) and the hardness (H) of the WC-Co alloys.

Indentation fracture of WC-Co cermets

Semisolid metal (SSM) processingis a relatively new technology for metal forming. Different from the conventional metal forming technologies which use either solid metals (solid state processing) or liquid metals (casting) as starting materials, SSM processing deals with semisolid slurries, in which non-dendritic solid particles are dispersed in a liquid matrix. Semisolid metal slurries exhibit distinctive rheological characteristics: the steady state behaviour is pseudoplastic (or shear thinning), while the transient state behaviour is thixotropic. All the currently available technologies for SSM processing have been developed based on those unique rheological properties, which in turn originate from their non-dendritic microstructures. Year 2001 marks the 30th anniversary of the concept of SSM processing. Today, SSM processing has established itself as a scientifically sound and commercially viable technology for production of metallic components with high integrity, improved mechanical properti...

J. Gurland

Papers

Hardness and deformation of cemented tungsten carbide

The fracture toughness of WCCo alloys measured on single-edge notched beam specimens precracked by electron discharge machining

A structural approach to the yield strength of two-phase alloys with coarse microstructures

Strain partition, uniform elongation and fracture strain in dual-phase steels