Structural and mechanical properties of ?-irradiated Zr/Nb multilayer nanocomposites

Zr/Nb multilayers with periodicities of 10, 30 and 60 nm were prepared by magnetron sputtering and irradiated for prolonged time (1311 h) by ?-rays with energy of 1.25 MeV and a dose of 510 kGy. A qualitative comparison between XRD patterns acquired before and after irradiation revealed a progressive increase of compressive stress, especially in Nb layers, for smaller periodicities with a consequent increase in hardness measured by nanoindentation. The combination of smaller grain size and radiation-induced defect density distribution, primarily in Nb layers, was found to be responsible for the observed radiation hardening effect

Evolution of structural, mechanical and tribological properties of Ni-P/MWCNT coatings as a function of annealing temperature

Collaborative research project Hardalt (Grant No. 606110) funded by the EU's seventh framework programme

The role of Ni–Ti–(Cu) interlayers on the mechanical properties and nano-scratch behaviour of solid lubricant W–S–C coatings

A self-lubricant W–S–C coating with different Ni–Ti–(Cu) interlayers was fabricated by magnetron sputtering following a three-step process. It consisted of deposition and annealing of Ni–Ti–(Cu) layers with different Cu contents and subsequent deposition of the transition metal dichalcogenide W–S–C coating bonded to the Ni–Ti–(Cu) layer through a gradient Cr-based thin layer. Doping the Ni–Ti interlayer with Cu led to significant microstructural changes which influenced mechanical properties, such as the H/Er ratio and the resistance against plastic deformation. The response of the bilayers, i.e. W–S–C/Ni–Ti–(Cu) coatings, to indentation was affected by the interlayer material. The resistance to adhesion damage of the W–S–C coating was improved by using Ni–Ti–(Cu) interlayers. It was found that interlayers with lower H/Er ratio showed an improved capability to increase the adhesion of the functional top laye

Structural, mechanical and functional properties of irradiated multilayer nanocomposites

A common goal for materials employed in nuclear environments is to exhibit the highest radiation tolerance. The lifetimes of current and even more of future reactors are largely determined by materials issues such as embrittlement and swelling. In the process of energy production via fission and fusion, structural materials are subject to substantial radiation damage, which appears in the form of point defects and their agglomeration to form dislocation loops and vacancy clusters. Combination of vacancy clusters with transmutation products such as helium (He) promotes the formation of He bubbles. These bubbles cause swelling, embrittlement and dimensional instabilities in structural metals, which represent a real challenge for application of metals in nuclear industry. It is well known that surfaces, grain boundaries and heterointerfaces are good sinks for radiation-induced point defects and traps for implanted He. Composite materials with a high interface density distribution showed enhanced radiation tolerance compared to conventional single phase metals. In spite of this beneficial effect, the role of He bubbles on the mechanical properties and structural integrity of nanostructured materials is still to be understood. This study is aimed at evaluating and correlating the effects of He bubbles formation with structural and mechanical properties of nanomaterials with high interface density distributions such as nanoscale metallic multilayers. With this aim, Cu/W multilayers were deposited by magnetron sputtering and subjected to He ion implantation (1 MeV) with two different fluences (1.1 and 3.2 ×1016 cm-2) and incident angles. Structure of pristine and irradiated multilayers was investigated by XRD and FIB/TEM analyses, while mechanical properties changes were evaluated by nanoindentation, through which possible deformation mechanisms in multilayers with He bubble-decorated interfaces were also investigated. By combining calculated He concentration profiles, throughout the multilayer thickness and TEM images, it is found that in low He concentrations regions, bubbles formed mostly along interfaces, while more homogeneously distributed bubbles were found in Cu layers and along columnar grain boundaries in higher He concentrations regions. It is suggested that the capability of interfaces to annihilate point defects is weakened by the He bubbles shielding effect. Nanoindentation tests revealed a hardness decrease amounting to ~ 0.5 and ~ 1 GPa for low and high fluences, respectively. The observed softening effect is mostly attributed to He storage induced changes in residual stresses, and columnar grain boundary sliding facilitated by He bubbles. <br/

Structural characterisation of Zr/Nb nanoscale metallic multilayers

Structural characterisation of Zr/Nb nanoscale metallic multilayers through X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). Dataset to support: Monclus, Miguel A. et al (2016) Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers. Acta Materialia Funding: Multiscale Modelling and Materials by Design of interface-controlled Radiation Damage in Crystalline Materials (RADINTERFACES, 263273), 2011 to 2014. Virtual Design, Virtual Processing and Virtual Testing of Metallic Materials (VIRMETAL, 669141), 2015 to 2020. South of England Analytical Electron Microscope (EPSRC; EP/K040375/1), 2013 to 2017.</span

Combined size and texture-dependent deformation and strengthening mechanisms in Zr/Nb nano-multilayers

A combination of transmission electron microscopy analyses and nanomechanical measurements was performed in this study to reveal deformation and strengthening mechanisms occurring in sputtered Zr/Nb nanoscale metallic multilayers (NMMs) with a periodicity (L) in the range 6–167 nm. Electron diffraction analyses revealed a change in the crystallographic orientation of a-Zr when L = 27 nm, while Nb structure retained the same orientations regardless of L. For L &gt; 60 nm, the strengthening mechanism is well described by the Hall-Petch model, while for 27 &lt; L &lt; 60 nm the refined CLS model comes into picture. A decrease in strength is found for L &lt; 27 nm, which could not be simply explained by considering only misfit and Koehler stresses. For L = 27 nm, plastic strain measured across compressed NMMs revealed a change in the plastic behaviour of a-Zr, which experienced a hard-to-soft transition. At these length scales, the combination of two structural factors was found to affect the strength. These relate to the formation of weaker interfaces which extend the effective distance between strong barriers against dislocation transmission, thus producing a softening effect. The second effect relates to the crystallographic orientation change exhibited by a-Zr for L &lt; 27 nm with a consequent change of the dominant slip system. The actual strength at these smaller length scales was effectively quantified by taking these structural aspects into account in the interface barrier strength model

Deformation behaviour of Zr/Nb nano-multilayers: XRD and FIB/SEM data

Structure and deformation behaviour of as-deposited Zr/Nb NMMs investigated by XRD, Nanoindentation and FIB/SEM. Dataset to support: Callisti, Mauro and Polcar, Tomas (2017) Combined size and texture-dependent deformation and strengthening mechanisms in Zr/Nb nano-multilayers. Acta Materialia Funded by EPSRC (South of England Analytical Electron Microscope , EP/K040375/1, 2013 to 2017).</span

Stress-induced martensitic transformation in Ni–Ti(–Cu) interlayers controlling stress distribution in functional coatings during sliding

The stress-induced martensitic transformation occurring in sputter-deposited Ni48.1Ti51.9 and Ni43.4Ti49.6Cu7 interlayers, integrated in a W-S-C/Ni–Ti(–Cu) bilayer design, was investigated by transmission electron microscopy, after these bilayers were subjected to different sliding conditions. Martensitic bands across the interlayers were formed depending on the sliding direction with their shape and distribution a function primarily of both applied normal load and grain size.The Ni48.1Ti51.9 interlayer (lateral grain size of ?3 ?m) showed well oriented and ordered martensitic bands extended through the interlayer thickness under low load (5 N). At a higher load (18 N) the growth of these bands was limited by the stabilised martensite formed as a consequence of the high compressive stress, at the interface with the substrate.The Ni43.4Ti49.6Cu7 interlayer (lateral grain size of ?650 nm) exhibited no significant evidence of stabilised martensite under different loading conditions. The martensitic transformation was limited by the smaller grain size and most of the stress was relaxed by elastic and, to some extent, pseudo-elastic deformation of the austenitic phase. Grain boundaries were found to stop the growth of martensitic bands, thus limiting the activation of the martensitic transformation into the neighbouring grains during sliding.The grain refinement caused a change in the capability of the interlayer to relax shear and compressive stresses. Such a change was found to affect the formation of the WS2-rich tribolayer on the W-S-C sliding surface, and consequently the shear stress transmitted down throughout the bilayers thickness. Accordingly, different levels of deformation were observed on the top layer.<br/

Microstructural investigation on the grain refinement occurring in Cu-doped Ni-Ti thin films

The mechanism of grain refinement in Cu-doped Ni-Ti thin films have been investigated by transmission electron microscopy (TEM). Sputter deposited (Ni,Cu)-rich Ni-Ti-Cu thin films exhibited a columnar structure consisting of grains with a decreasing lateral size with increasing Cu content. Cu-rich grain boundary segregations were found to become prominent in films containing higher Cu contents. These segregations were attributed to a non-polymorphic crystallisation process which lowered the grain growth rate in relation to the Cu content in the films

Bubbles formation in helium ion irradiated Cu/W multilayer nanocomposites: effects on structure and mechanical properties

This study investigates the effects of He bubbles on structural and mechanical properties of sputter-deposited Cu/W multilayers. A multilayer with a periodicity of 10 nm was deposited and subjected to helium ion irradiation with two different fluences. He bubbles formed mostly in Cu layers and their distribution was affected by He concentration and radiation damage. According to SRIM calculations, in low He concentration regions bubbles formed mostly along interfaces, while more homogeneously distributed bubbles were found in Cu layers and along columnar grain boundaries in higher He concentration regions. We suggest that the capability of interfaces to annihilate point defects is weakened by the He bubbles shielding effect. Nanoindentation tests revealed a hardness decrease amounting to ?0.5 and ?1 GPa for low and high fluences, respectively. The observed softening effect is attributed to He storage-induced changes in residual stresses and columnar grain boundary/interfacial sliding facilitated by He bubbles