Julian Rosalie

Bundesanstalt für Materialforschung und -prüfung | BAM · Department of Materials Engineering (Dpt.5)

In this letter, we demonstrate the robust presence of an elastic microstructure in a Zr-based metallic glass (MG) with a characteristic length-scale of the order of 100 nm. This length scale increases systematically towards the MG surface in differently sized casts, whereas thermal relaxation homogenizes both the internal length-scale gradient and...

Functional fatigue of shape-memory alloys is a considerable threat to the reliable service of actuation devices. Here, we demonstrate the essentially degradation-free cyclic phase-transformation behavior of Ni-Mn-Ga mi-crocrystals up to one million stress-driven superelastic cycles. Cyclic dissipation amounts to about 1/5 of the bulk counterpart an...

Iron aluminides, already reported in the late 19th century, did not cease to attract the interest of scientists and engineers ever since. Besides good oxidation resistance, low density and resource availability, potentials for high-temperature strengths that compete with high-alloy steels were unlocked by low alloy contents. Still, research on allo...

A round-robin study has been carried out to estimate the impact of the human element in small-angle scattering data analysis. Four corrected datasets were provided to participants ready for analysis. All datasets were measured on samples containing spherical scatterers, with two datasets in dilute dispersions and two from powders. Most of the 46 pa...

Ni-Mn-Ga shape-memory alloys are promising candidates for large strain actuation and magnetocaloric cooling devices. In view of potential small-scale applications, we probe here nanomechanically the stress-induced austenite–martensite transition in single crystalline austenitic thin films as a function of temperature. In 0.5 µm thin films, a marked...

A Round Robin study has been carried out to estimate the impact of the human element in small-angle scattering data analysis. Four corrected datasets were provided to participants ready for analysis. All datasets were measured on samples containing spherical scatterers, with two datasets in dilute dispersions, and two from powders. Most of the 46 p...

Filigree structures can be manufactured via two‐photon‐polymerization (2PP) operating in the regime of non‐linear light absorption. For the first time it is possible to apply this technique to the powder processing of ceramic structures with a feature size in the range of the critical defect size responsible for brittle fracture and, thus, affectin...

A combination of high strength and reasonable ductility has been achieved in a copper-1.7 at.%titanium alloy deformed by high-pressure torsion. Grain refinement and a spinodal microstructure provided a hardness of 254 +/- 2 HV , yield strength of 800 MPa and elongation of 10%. The spinodal structure persisted during isothermal ageing, further incre...

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 dependi...

Nanodiamond reinforced silver matrix nanocomposites with different nanodiamond content are produced from pure silver and nanodiamond powders by a combination of two severe plastic deformation methods, ball-milling and high-pressure torsion (HPT). The ball milling parameters are varied to improve the distribution of the nanodiamonds in the powder bl...

Nanodiamond reinforced silver matrix nanocomposites with different nanodiamond content are produced from pure silver and nanodiamond powders by a combination of two severe plastic deformation methods, ball-milling and high-pressure torsion (HPT). The ball milling parameters are varied to improve the distribution of the nanodiamonds in the powder bl...

Precipitation is accompanied by the formation and migration of heterophase interfaces. Using the combined approach of advanced imaging and atomistic simulations, we studied the precipitate-matrix interfaces in various aluminium alloy systems, aiming to resolve their detailed atomic structures and illuminate their role in phase transformations.

Liquid‐metal infiltrated Cu30Mo70 (wt%) 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 micro‐ and nanometer ranges depending on the amount o...

The gamma prime (Ag2Al) phase in the Al–Ag alloy system has served as a textbook example for understanding phase transformations, precipitating hexagonal close-packed (HCP) crystals in the face-centred cubic (FCC) aluminium matrix. The gamma prime precipitates display fully coherent interfaces at their broad facets and semicoherent interfaces at th...

Mg 4 Zn 7 phase, with a monoclinic unit cell, a layered structure and a unique axis showing pseudo-tenfold symmetry, grows over icosahedral quasicrystalline phase in a manner similar to a decagonal quasicrystal. In this study, the relationship of this phase to icosahedral quasicrystal is brought out by a transmission electron microscopy study of Mg...

Oxygen contamination is a problem which inevitably occurs during severe plastic deformation of metallic powders by exposure to air. Although this contamination can change the morphology and properties of the consolidated materials, there is a lack of detailed information about the behavior of oxygen in nanocrystalline alloys. In this study, aberrat...

Cu-refractory composites containing Cr, Mo or W were subjected to severe plastic deformation using room temperature high-pressure torsion (HPT). A lamellar microstructure developed in each of the composites at equivalent strains of ~75. The refractory metals developed {hkl}<111> fibre textures with a slight tilt to the tangential direction, as expe...

Cu-refractory metal composites containing Cr, Mo or W were subjected to severe plastic deformation using room temperature high-pressure torsion (HPT). A lamellar microstructure developed in each of the composites at equivalent strains of ~75. The refractory metals developed {hkl}<111> fibre textures with a slight tilt to the tangential direction. T...

Nanostructured 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. Exten...

The Al-Ag system is thought to be a well-understood model system used to study diffusional phase transformations in alloys. Here we report the existence of a new precipitate phase, ζ, in this classical system using scanning transmission electron microscopy (STEM). The ζ phase has a modulated structure composed of alternating bilayers enriched in Al...

The Al-Ag system is thought to be a well-understood model system used to study diffusional phase transformations in alloys. Here we report the existence of a new precipitate phase, ζ, in this classical system using scanning transmission electron microscopy (STEM). The ζ phase has a modulated structure composed of alternating bilayers enriched in Al...

Usually immiscible Cu-Cr compounds in equilibrium condition were mechanically processed via high pressure torsion with large and controlled strains. A systematical investigation on 57 wt%Cu−43 wt%Cr was carried out to get insights into the microstructural evolution of Cu-Cr nanocomposites and their dissolution process, as well as to determine the s...

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. Ext...

Normally immiscible 57wt% Cu–43wt% Cr compoundsweremechanically alloyed bymeans of high pressure torsion with large and controllable strains. A strain-saturated state in 57 wt% Cu–43 wt% Cr bulkwas achieved after 100 rotations deformation (effective strain 1360), with a stable grain size of 13.7 nm and largest solubility of 32 wt% Cu in Cr matrix....

Precipitation hardening in aluminium alloys provides well‐known examples of how identical materials can develop very different microstructures through different processing conditions or the addition of trace alloying elements. Desirable microstructures for useful materials properties such as high mechanical strength often involve the precipitation...

For the first time, we report here segregation of Zn atoms to twin boundaries formed under 9% compression at room temperature (RT) in a Mg-3Zn-0.5Y (in at%) alloy. The wrought processed (textured) alloy was severely plastically deformed (SPD) through high pressure torsion (HPT) at RT. Zn segregation (2 to 4 at%) was observed on newly formed boundar...

Precipitation strengthening in Mg-Zn-Y alloys occurs via the formation of a fine dispersion of β'1 (Mg4Zn7) rods aligned parallel to the hexagonal axis. In this study, texture and controlled deformation have been used to control the directionality and morphology of the precipitates and their effect on the ageing response. The resulting precipitates...

Precipitation strengthening in Mg-Zn-Y alloys occurs via the formation of a fine dispersion of β’1 (Mg4Zn7) rods aligned parallel to the hexagonal axis. In this study, texture and controlled deformation have been used to control the directionality and morphology of the precipitates and their effect on the ageing response. The resulting precipitates...

Microstructural investigation of extremely strained samples, such as severely plastically deformed (SPD) materials, by using conventional transmission electron microscopy techniques is very challenging due to strong image contrast resulting from the high defect density. In this study, low angle annular dark field (LAADF) imaging mode of scanning tr...

The interfacial structure and composition of θ′ (Al2Cu) precipitates in Al-0.9at.%Cu-0.9at.%Ag alloys were examined using high resolution electron microscopy. High angle annular dark field scanning transmission electron microscope (HAADF-STEM) images showed the presence of a silver(Ag)-rich bi-layer on the coherent (100) θ′-Al interfaces of the pre...

Microstructural investigation of extremely strained samples, such as severely plastically deformed (SPD) materials, by using the conventional transmission electron microscopy (CTEM) techniques is very challenging due to strong image contrast resulting from the high defect density. In this study, the low angle annular dark field (LAADF) imaging mode...

Precipitation behavior in severely plastically deformed Mg–3.4 at%Zn was studied by ageing treatment at 348 and 423 K. Microstructural observations reveal two kinds of precipitates: one from the dynamic precipitation during high-pressure torsion processing and the other from the ageing treatment. Precipitates formed from annealing treatment are obs...

Microstructural analysis of a Mg-Zn alloy deformed at room temperature by high-pressure torsion indicates that fine-scale precipitation occurs even without post-deformation heat treatment. Small-angle X-ray scattering detects precipitates with radii between 2.5-20 nm after 1 rotation, with little increase in particle size or volume fraction after 2...

A ultrafine-grained structure was produced in a Mg–3.4Zn (at.%) alloy subjected to high-pressure torsion (HPT) at ambient temperature. Hardness and X-ray diffraction measurements indicated the microstructure reached a steady state after three revolutions. Transmission electron microscopy observations showed equiaxed, dynamically recrystallized grai...

This work describes a multidisciplinary research methodology for quantifying the size distribution of nanoscale precipitates in polycrystalline alloys. Complementary transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS) are employed in a study of precipitate growth in an isothermally aged Mg-Zn alloy. TEM is used to identif...

The effectiveness of precipitation strengthening against slip and twinning was quantified for a Mg-Zn containing different distributions of rod-shaped ß1′ precipitates. Tensile and compressive testing was carried out on identically heat-treated samples to determine the effect of a well-characterised particle distribution on each deformation mode. P...

The effectiveness of precipitation strengthening against slip and twinning was quantified for a Mg-Zn containing different distributions of rod-shaped ß1′ precipitates. Tensile and compressive testing was carried out on identically heat-treated samples to determine the effect of a well-characterised particle distribution on each deformation mode. P...

A detailed study has been carried out on gamma' (AlAg2) precipitates in Al-Ag and Al-Ag-Cu alloys to reconcile the conflicting reports on chemical ordering and stacking faults in this phase. High angle annular dark field scanning transmission electron microscopy and convergent beam electron diffraction show no indication of chemical ordering on alt...

The interfacial structure and composition of theta' (Al2Cu) precipitates in Al-0.9at.%Cu-0.9at.%Ag alloys were examined using high resolution electron microscopy. High angle annular dark field scanning transmission electron microscope (HAADF-STEM) images showed the presence of a silver(Ag)-rich bilayer on the coherent (100) theta'-Al interfaces of...

Pre-ageing deformation was applied to a Mg-Zn-Y alloy to refine the size of ß′1 precipitates. Reductions in the precipitate length and diameter were accompanied by a substantial increase in the volume fraction of the ß′1 precipitates from 0.5% (no prestrain) to 2.3% (5% pre-strain). This contrasted with Mg-Zn alloys, in which the precipitate volume...

Pre-ageing deformation was applied to a Mg-Zn-Y alloy to refine the size of ß′1 precipitates. Reductions in the precipitate length and diameter were accompanied by a substantial increase in the volume fraction of the ß′1 precipitates from 0.5% (no prestrain) to 2.3% (5% pre-strain). This contrasted with Mg-Zn alloys, in which the precipitate volume...

The effect of pre-ageing deformation on the size and distribution of beta-prime precipitates and subsequently on the resulting strength and ductility have been measured in a Mg-3.0at.%Zn-0.5at.%Y alloy. The alloy was extruded and then subjected to a T8 heat treatment comprised of a solution-treatment, cold-work and artificial ageing. Extrusion was...

θ′ (Al2Cu) precipitates in Al–Cu–Ag alloys were examined using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The precipitates nucleated on dislocation loops on which assemblies of γ′ (AlAg2) precipitates were present. These dislocation loops were enriched in silver prior to θ′ precipitation. Coherent, planar...

We report on a quantitative investigation into the effect of size and distribution of rod-shaped \beta' precipitates on strength and ductility of a Mg-Zn alloy. Despite precipitation strengthening being crucial for the practical application of magnesium alloys this study represents the first systematic examination of the effect of controlled deform...

Precipitation of the θ′ (Al2Cu) phase was examined in Al-(1.75-x) at.%Cu-x at.%Ag alloys. In alloys containing trace Ag the θ′ precipitates formed T- or cross-shaped arrays of sympathetically-nucleated arrays similar to those reported in binary Al-Cu alloys. However, in alloys with equal atomic levels of copper and silver the θ′ plates formed at sp...

Precipitation of the θ′ (Al2Cu) phase was examined in Al-(1.75-x) at.%Cu-x at.%Ag alloys. In alloys containing trace Ag the θ′ precipitates formed T- or cross-shaped arrays of sympathetically-nucleated arrays similar to those reported in binary Al-Cu alloys. However, in alloys with equal atomic levels of copper and silver the θ′ plates formed at sp...

The effect of pre-ageing deformation on the precipitate diameter and length distribution in Mg-Zn(-Y) alloys was examined. Extrusion and pre-ageing deformation were used to introduce dislocations while precluding twin formation. Dislocations provided nucleation sites for rod-like β′ 1 precipitates, resulting in a refinement of the precipitate size...

Intermetallic precipitates formed in heat-treated and aged Mg-Zn and Mg-Zn-Y alloys have been investigated via electron microscopy. Coarse spheroidal precipitates formed on deformation twin boundaries contained domains belonging to either the MgZn2 hexagonal Laves phase or the monoclinic Mg4Zn7 phase. Both phases are structurally related to the qua...

A detailed study of the precipitation of the \gamma' (AlAg2) phase in undeformed aluminium-silver alloys has been conducted. Several previously unreported features were observed, including the formation of discrete three-dimensional assemblies comprised of 5-7 precipitates on faulted dislocation loops. The precipitates assemblies adopted a morpholo...

The precipitation microstructure of the \gamma' (AlAg2) intermetallic phase has been examined in aluminium-silver-copper alloys. The microstructure developed in an Al-0.90at.%Ag-0.90at.%Cu alloy was significantly different from that reported for binary Al-Ag alloys. The orientation relationship between the matrix and precipitate was unchanged; howe...

The effect of pre-ageing deformation on the precipitate diameter and length distribution in Mg-Zn(-Y) alloys was examined. Extrusion and pre-ageing deformation were used to introduce dislocations while precluding twin formation. Dislocations provided nucleation sites for rod-like ²′1 precipitates, resulting in a refinement of the precipitate size d...

Precipitation of the γ′ (AlAg2) phase was investigated in Al-Ag(-Cu) alloys using high resolution transmission electron microscopy and scanning transmission electron microscopy. Precipitation commenced with segregation of silver to stacking faults, followed by thickening in steps corresponding to single unit cell ledges. In conjunction with gradual...

The orthorhombic φ-Al5Mg11Zn4 phase is known to be related to quasicrystalline phases, but the exact relationship has not been shown yet. In this study, the relationship of this phase to the icosahedral quasicrystalline phase is explored through analysis of the electron diffraction patterns. It is shown that icosahedral coordinations in three orien...

It is shown here by high-resolution electron microscopy that the structure of rod-like precipitates perpendicular to the basal planes of the magnesium matrix in Mg–Zn–Y alloys consist of complex domains at nanoscale. These domains can be recognized to be those of monoclinic Mg4Zn7 phase and hexagonal Laves phase MgZn2 with axial orientations . Due...

Isothermal ageing of plastically deformed Mg-Zn-Y alloys resulted in precipitation along twin boundaries. The bulky precipitates so formed had structures similar to those recently reported for the rod-like precipitates, but afforded a more detailed study by high-resolution TEM due to their larger size. The core of the precipitates often had the str...

Heat-treated Mg-Zn and Mg-Zn-Y alloys form two binary phase intermediate precipitates; a monoclinic structure based on Mg4Zn7 and a hexagonal Laves phase based on MgZn2. Both phases precipitate along deformation twin boundaries in aged Mg-Zn-Y alloys. High resolution TEM studies determined that the two phases frequently co-exist within individual p...

Although the the rod-like β1 precipitate is among the most important in magnesium alloys, its crystal structure is not yet clear. Its structure has been believed to be based on the Lave's phase MgZn2, but recently reported to be of monoclinic Mg4Zn7 phase. We have studied the structure of these precipitates by high resolution TEM in a Mg-Zn-Y alloy...

Bulk synthesis of hollow carbon stacked-cone-helices of diameter from 10nm to 0.5μm is reported. The fibres’ walls are made up of parallel stacked-cone-like structures with an inter-cone distance from 3.38 to 3.5Å. Apex angles observed are in the range from 30° to 110°, suggesting that the carbon nanofibres are constructed by a single graphene shee...

The nucleation of intermediate phases in aluminium alloys containing silver and copper has been examined. When aged isothermally these alloying elements precipitate as the metastable phases θ′(Al2Cu) and γ(Ag2Al), forming on {100} and {111} habit planes respectively. This study focuses on determining the influence of the θ′ precipitate phase upon t...

The synthesis of block copolyesters by combining transesterification resistant oligoesters with poly(ethylene terephthalate) is described. Critical factors in the synthesis include processing conditions (temperature), end groups and catalysts used in oligoester synthesis. It is necessary to achieve a balance between ease of incorporation/synthesis...

The effect of plasticizer on the ubiquitous ion-pairing observed in polymer electrolytes has been investigated using FTIR as a probe of the local environment of the triflate ion in sodium and lithium triflate based electrolytes. Plasticizers having a range of properties, such as, propylene carbonate, and dimethyl formamide (DMF), have been investig...

Crystalline phase transformations are fundamental to many natural and artificial phenomena, from earthquakes to optical recording. Thus an accurate description of these mechanisms has been a long-standing scientific goal. Yet even some of the structurally simplest phase transformations, such as the nucleation and growth of low-dimensional precipita...