arXiv subjects

Reinhard Pippan

Publications and source records attributed to Reinhard Pippan.

26 records · Page 2Linked to original sources

arXiv2020

Magnetic Binary Supersaturated Solid Solutions Processed by Severe Plastic Deformation

Samples consisting of one ferromagnetic and one diamagnetic component which are immiscible at the thermodynamic equilibrium (Co-Cu, Fe-Cu, Fe-Ag) are processed by high-pressure torsion at various compositions. The received microstructures are investigated by electron microscopy and synchrotron X-ray diffraction, showing a microstructural saturation. Results gained from microstructural investigations are correlated to magnetometry data. The Co-Cu samples show mainly ferromagnetic behavior and a decrease in coercivity with increasing Co-content. The saturation microstructure of Fe-Cu samples is found to be dual phase. Results of magnetic measurements also revealed the occurrence of two different magnetic phases in this system. For Fe-Ag, the microstructural and magnetic results indicate that no intermixing between the elemental phases takes place.

cond-mat.mtrl-sci↗

arXiv2020

Microstructure and Failure Characteristics of Nanostructured Molybdenum Copper Composites

Liquid-metal infiltrated Cu30Mo70 (weigth percentage) is subjected to severe plastic deformation using high pressure torsion. The initially equiaxed dual phase structure is gradually transformed into a lamellar structure composed of individual Cu and Mo layers. The thickness of the lamellae varies between the micrometer and nanometer ranges depending on the amount of applied strain. Consistent with the refinement of the microstructural features, strength and hardness substantially increase. In addition, an acceptable ductility is found in the intermediate deformation range. An assessment of the damage tolerance of the produced composites is performed by measuring the fracture toughness in different crack propagation directions. The results indicate the development of a pronounced anisotropy with increasing degree of deformation which is an effect of the concurrent alignment of the nanostructured lamellar composite into the shear plane.

cond-mat.mtrl-sci↗

arXiv2020

Fracture mechanics of micro samples: Fundamental considerations

In this review article we consider the crack growth resistance ofmicrometer and submicrometer sized samples from the fracture mechanics point of view. Standard fracture mechanics test procedures were developed for macroscale samples, and reduction of the specimen dimensions by three to five orders of magnitude has severe consequences. This concerns the interpretation of results obtained by micro and nanomechanics, as well as the life time and failure prediction of micro and nano devices. We discuss the relevant fracture mechanics length scales and their relation to the material specific structural lengths in order to conduct rigorous fracture mechanics experiments. To ensure general validity and applicability of evaluation concepts, these scaling considerations are detailed for ideally brittle, semi brittle and micro ductile crack propagation, subject to both monotonic and cyclic loading. Special attention is devoted to the requirements for determining specimen size for various loading types to measure material characteristic crack propagation resistance at small scales. Finally, we discuss novel possibilities of micron and submicron fracture mechanics tests to improve the basic understanding of specific crack propagation processes.

cond-mat.mtrl-sci↗

arXiv2018

Mechanical properties of electrodeposited amorphous/crystalline multilayer structures in the Fe-P system

Amorphous/crystalline multilayer structures of Fe-P alloys were deposited electrochemically using the single bath technique. Hall-Petch behavior of microhardness with respect to sublayer thickness was observed down to a sublayer thickness of 15 nm. For thinner sublayers, a hardness plateau was obtained. The transition at a sublayer thickness of 15 nm coincides with the loss of the multilayer structure as observed in transmission electron microscopy. The transition is a possible result of a change in the amorphous to crystalline sublayer thickness ratio and the interface roughness development during the deposition process. Additionally, crack deflection at the interfaces was observed for the layered structures with small sublayer thickness in microbending experiments.

cond-mat.mtrl-sci↗

arXiv2017

On nanostructured molybdenum-copper composites produced by high pressure torsion

Nano-structured molybdenum-copper composites have been produced through severe plastic deformation of liquid-metal infiltrated Cu30Mo70 and Cu50Mo50 (wt.%) starting materials. Processing was carried out using high pressure torsion at room temperature with no subsequent sintering treatment, producing a porosity-free, ultrafine grained composite. Extensive deformation of the Cu50Mo50 composite via two-step high-pressure torsion produced equiaxed nanoscale grains of Mo and Cu with a grain size of 10-15 nm. Identical treatment of Cu30Mo70 produced a ultrafine, lamellar structure, comprised of Cu and Mo layers with thicknesses of ~5 nm and ~10-20 nm, respectively and an interlamellar spacing of 9 nm. This microstructure differs substantially from that of HPT-deformed Cu-Cr and Cu-W composites, in which the lamellar microstructure breaks down at high strains. The ultrafine-grained structure and absence of porosity resulted in composites with Vickers hardness values of 600 for Cu30Mo70 and 475 for Cu50Mo50. The ability to produce Cu30Mo70 nanocomposites with a combination of high strength, and a fine, oriented microstructure should be of interest for thermoelectric applications.

physics.app-ph↗

arXiv2016

New insights on the formation of supersaturated solid solutions in the Cu Cr system deformed by high pressure torsion

In the Cu Cr system, the formation of supersaturated solid solutions can be obtained by severe plastic deformation. Energy dispersive synchrotron diffraction measurements on as deformed Cu Cr samples as a function of the applied strain during deformation confirm the formation of supersaturated solid solutions in this usually immiscible system. Due to evaluation of the diffraction data by a newly developed energy dispersive Rietveld program, lattice parameter and microstructural parameters such as domain size and microstrain are determined for as deformed as well as annealed samples. The obtained information is used to deepen the understanding of the microstructural evolution and the formation of supersaturated solid solutions during severe plastic deformation. Complimentary transmission electron microscopy investigations are furthermore performed to characterize the evolving microstructure in detail. After annealing at elevated temperatures, the formed solid solutions decompose. Compared to the as deformed state, an enhanced hardness combined with a high thermal stability is observed. Possible mechanisms for the enhanced hardness are discussed.

cond-mat.mtrl-sci↗

arXiv2010

Homogeneous Cu-Fe super saturated solid solutions prepared by severe plastic deformation

A Cu-Fe nanocomposite containing 50 nm thick iron filaments dispersed in a copper matrix was processed by torsion under high pressure at various strain rates and temperatures. The resulting nanostructures were characterized by transmission electron microscopy, atom probe tomography and Mössbauer spectrometry. It is shown that alpha-Fe filaments are dissolved during severe plastic deformation leading to the formation of a homogeneous supersaturated solid solution of about 12 at.% Fe in fcc Cu. The dissolution rate is proportional to the total plastic strain but is not very sensitive to the strain rate. Similar results were found for samples processed at liquid nitrogen temperature. APT data revealed asymmetric composition gradients resulting from the deformation induced intermixing. On the basis of these experimental data, the formation of the supersaturated solid solutions is discussed

cond-mat.mtrl-sci↗

arXiv2008

Nanostructure and properties of a Cu-Cr composite processed by severe plastic deformation

A Cu-Cr composite was processed by severe plastic deformation to investigate the role of interphase boundaries on the grain size reduction mechanisms. The as-deformed material exhibits a grain size of only 20nm. This gives rise to a dramatic increase of the hardness. Some deformation induced Cu super saturated solid solutions were clearly exhibited and it is shown that they decrease the hardness. The formation of such supersaturated solid solution and their influence on the mechanical properties are discussed.

cond-mat.mtrl-sci↗