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The use of composite materials for structures subjected to impacts requires a deep understanding about the dynamic behaviour of the material. To this end, a physically-based computational micromechanics simulation tool has been developed to predict failure initiation in a composite ply over a wide range of strain rates. The computational micromechanics framework incorporates constitutive models for the fibre, matrix and fibre-matrix interface, which are partly calibrated with novel micromechanical testing techniques. The simulation tool was applied to two matrix-dominated deformation modes of the ply: transverse compression and in-plane shear. The comparison of simulation and experimental results at coupon level have revealed a change in failure initiation mechanism of the composite ply with strain rate, which was then corroborated through observation of the fracture surfaces on the samples.

In advanced ceramics, improving toughness usually relies on the introduction of a soft metallic or polymeric ductile phase, which decreases the mechanical properties. Some natural materials are strong, stiff and tough due to a combination of mechanisms operating at different length scales. However, such structures have been extremely difficult to replicate into synthetic materials. Here we investigate the microstructure and the micromechanical properties of a bioinspired ceramic-ceramic composite. The micromechanical properties at room temperature show slight differences as a function of the platelet orientation. The hardness strongly decreases with increasing temperatures (up to 550 °C) for all the investigated orientations. The elastic strain to failure, defined as the H/E ratio, was used to estimate the wear resistance of materials, which is higher at room temperature because the dislocation mobility is lower than that at high temperature.

This work describes the fabrication process of moth eye antireflective poly (methyl methacrylate) transparent films via roll to roll thermal nanoimprint lithography. The process parameters are investigated and adjusted in order to obtain from a single moth-eye structured mold, a range of antireflective topographies that gradually vary their geometry from protruding to intruding nanocones. A correlation between the process parameters with the optical and mechanical properties of the films is established to illustrate the influence of the processing parameters and serve as guideline to produce antireflective flexible films with balanced properties and optimized performance adequate to the application environment. A finite element model is described predicting the mechanical behavior of the moth-eye PMMA imprinted nanostructures.

Optimization of the intermetallic layer thickness and the suppression of interfacial defects are key elements to improve the load bearing capacity of dissimilar joints. However, till date we do not have a systematic tool to investigate the dissimilar joints and the intermetallic properties produced by a welding condition. Friction Melt Bonding (FMB) is a recently developed technique for joining dissimilar metals that also does not exempt to these challenges. The FMB of DP980 and Al6061-T6 was investigated using a new physical simulation tool, based on Gleeble thermo-mechanical simulator, to understand the effect of individual parameter on the intermetallic formation. The proposed method demonstrates its capability in reproducing the intermetallic characteristics, including the thickness of intermetallic bonding layer, the morphology and texture of its constituents (Fe2Al5 and Fe4Al13), as well as their nanohardness and reduced modulus. The advantages of physical simulation tool can enable novel developing routes for the development of dissimilar metal joining processes and facilitate to reach the requiring load bearing capacity of the joints.

The microstructure, mechanical properties and thermal stability of AlxTi1􀀀 xN and Al1Ti1-xBN coatings grown by reactive high-power impulse magnetron sputtering (HiPIMS) have been analyzed as a function of Al/(Al + Ti) ratio (x) between 0.5 and 0.8. The coatings were predominantly formed by a face-centered cubic Ti(Al)N crystalline phase, both with and without B, even for x ratios as high as 0.6, which is higher than the ratio typically encountered for AlxTi1􀀀 xN coatings deposited by reactive magnetron sputtering. B doping, in combination with the highly energetic deposition conditions offered by HiPIMS, results in the suppression of the columnar grain morphology typically encountered in AlxTi1􀀀 xN coatings. On the contrary, the AlxTi1􀀀 xBN coatings grown by HiPIMS present a dense nanocomposite type microstructure, formed by nanocrystalline Ti(Al) N domains and amorphous regions composed of Ti(Al)B2 and BN. As a result, high-Al content (x ≈ 0.6) AlxTi1 􀀀 xBN coatings grown by HiPIMS offer higher hardness, elasticity and fracture toughness than AlxTi1􀀀 xN coatings. Moreover, the thermal stability and the hot hardness are substantially enhanced, delaying the onset of formation of the detrimental hexagonal AlN phase from 850 ◦C in the case of Al0.6Ti0.4N, to 1000 ◦C in the case of Al0.6Ti0.4BN.

A combinatorial thin-film synthesis approach together with a high throughput analysis methodology was successfully applied to synthetize TiN/Ni coatings with optimum mechanical properties. The synthesis approach consists of the deposition of TiN/Ni coatings with the Ni content ranging from around 0 to 20 at.% by reactive magnetron sputtering with a well-defined composition gradient, so that almost all possible compositions are produced in one single coating under identical conditions, removing uncertainties from processing conditions. The analysis methodology continuously screened the microstructure, residual stresses, hardness and fracture toughness of TiN/Ni coatings. The results show that a nanocomposite microstructure of equiaxed nanograins of crystalline δ-TiN embedded in a Ni rich amorphous phase is formed in the composition window between 8 and 12 Ni at.%. This microstructure offers a superior combination of hardness and toughness and a simultaneous reduction of residual stresses with respect to TiN coatings grown in the same conditions. Higher Ni contents are however detrimental because they compromise the integrity of the coatings.

This work presents two new compositions of high entropy alloys (HEAs) that were designed with the aim of obtaining a body-centered cubic (BCC) phase with high hardness values and a moderate density. Sintering was performed using Spark Plasma Sintering (SPS) with different heating rates to determine the influence of the processing parameters on the phase formation. The microstructural study revealed that the presence of Ni in the composition promoted phase separation, and the mechanical study confirmed a clear influence on the mechanical properties of both the composition and heating rate. The combination of microscopy with compression and nanoindentation tests at room and high temperature made it possible to advance our understanding of the relationships between the composition, processing, and properties of this emerging group of alloys.

A dedicated in situ heating setup in a scanning electron microscope (SEM) followed by an ex situ atomic force microscopy (AFM) and electron backscatter diffraction (EBSD) is used to characterize the nucleation and early growth stages of Fe-Al intermetallics (IMs) at 596 {\deg}C. A location tracking is used to interpret further characterization. Ex situ AFM observations reveal a slight shrinkage and out of plane protrusion of the IM at the onset of IM nucleation followed by directional growth. The formed interfacial IM compounds were identified by ex situ EBSD. It is now clearly demonstrated that the {\theta}-phase nucleates first prior to the diffusion-controlled growth of the {\eta}-phase. The {\theta}-phase prevails the intermetallic layer.

Open-porous scaffolds of WE43 Mg alloy with a body-center cubic cell pattern were manufactured by laser powder bed fusion with different strut diameters. The geometry of the unit cells was adequately reproduced during additive manufacturing and the porosity within the struts was minimized. The microstructure of the scaffolds was modified by means of thermal solution and ageing heat treatments and was analysed in detail by means of X-ray microtomography, optical, scanning and transmission electron microscopy. Moreover, the corrosion rates and the mechanical properties of the scaffolds were measured as a function of the strut diameter and metallurgical condition. The microstructure of the as-printed scaffolds contained a mixture of Y-rich oxide particles and Rare Earth-rich intermetallic precipitates. The latter could be modified by heat treatments. The lowest corrosion rates of 2–3 mm/year were found in the as-printed and solution treated scaffolds and they could be reduced to ~0.1 mm/year by surface treatments using plasma electrolytic oxidation. The mechanical properties of the scaffolds improved with the strut diameter: the yield strength increased from 8 to 40 MPa and the elastic modulus improved from 0.2 to 0.8 GPa when the strut diameter increased from 275 μm to 800 μm. Nevertheless, the strength of the scaffolds without plasma electrolytic oxidation treatment decreased rapidly when immersed in simulated body fluid. In vitro bicompatibility tests showed surface treatments by plasma electrolytic oxidation were necessary to ensure cell proliferation in scaffolds with high surface-to-volume ratio.

A high-throughput correlative study of the local mechanical properties, chemical composition and crystallographic orientation has been carried out in selected areas of cast Inconel 718 specimens subjected to three different tempers. The specimens showed a strong Nb segregation at the scale of the dendrite arms, with local Nb contents that varied between 2 wt.% in the core of the dendrite arms to 8 wt.% in the interdendritic regions and 25 wt.% within the second phase particles (MC carbides, Laves phases and {\delta} phase needles). The nanohardness was found to correlate strongly with the local Nb content and the temper condition. On the contrary, the indentation elastic moduli were not influenced by the local chemical composition or temper condition, but directly correlated with the crystallographic grain orientation, due to the high elastic anisotropy of nickel alloys.

The nano-impact test is a technique for high strain rate mechanical characterization of materials at the nano/microscale. However, its use has been limited so far due to the lack of appropriate methods to determine the dynamic hardness under impact conditions. The main limitation up to date has been the determination of the true applied force due to considerable inertia effects. For this reason, dynamic hardness from nano-impact tests has traditionally been computed using an energy-based approach. This work overcomes this limitation by instrumenting the test device with force-sensing capability by means of a piezoelectric load cell. The methodology was evaluated on six materials covering a wide spectrum of mechanical behaviour. The work shows that the energy-based approach used so far yields significant errors on the determination of dynamic hardness, explaining contradictory results existing in literature, and identifies the main sources of error with the aid of finite element simulations. As a result, a new energy-based approach to determine dynamic hardness that overcomes the current limitations is proposed.

This work identifies the mechanisms governing dislocation transmission across lamellar interfaces in a Ti-45Al-2Nb-2Mn (at.%) + 0.8(vol%) TiB2 (Ti4522XD) alloy. With this aim, a microgrip and a microtensile specimen were designed and fabricated using a focused ion beam (FIB), to test micrometer-sized specimens in tension. The deformation mechanisms acting in a microtensile specimen of a Ti4522XD alloy were investigated through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results revealed that domain boundaries (order variant) and lamellar interfaces (order variant, true twin and pseudo-twin) are relatively transparent to dislocation propagation, but they present significant differences in the geometrical alignment between the incoming and outgoing slip systems. While for order variant interfaces, the incoming and outgoing slip systems are perfectly aligned, true twin and pseudo twin interfaces require a change in slip plane and direction, which leaves residual dislocations with Burgers vectors lying on the interface plane. The analysis of the slip transfer mechanisms revealed that the outgoing slip system is governed more by the maximum geometrical alignment, than the applied resolved shear stress. Keywords: Fully lamellar TiAl alloys, Slip transfer, Microtensile testing

The Zr62Cu22Al10Fe5Dy1 bulk metallic glass (BMG) was subjected to high pressure torsion (HPT) at room temperature. The state after HPT processing demonstrates presence of large number of heterogeneities in amorphous structure – shear bands. Nanoindentation was used to study the effect of HPT processing on deformation behavior and strain rate sensitivity (m). It was found that HPT significantly affects mechanical behavior of BMG during nanoindentation. Decrease in hardness and Young's modulus was observed after HPT. At the same time HPT processing led to an increase in m from 0.014 for the as-cast material to 0.036. The lack of serration flow and shear bands around imprints was observed in addition to above mentioned changes. A much less localized deformation mode under nanoindentation along with an increase in values of strain rate sensitivity of HPT-processed state in comparison with the initial state imply homogeneous deformation behavior after processing. The observed drastic changes in deformation behavior and structure can be explained as the formation of a highly-heterogeneous amorphous structure resembling nanoglasses in result of HPT processing.

The article focuses on the effect of alloying and microstructure on formability of advanced high strength steels (AHSSs) processed via quenching and partitioning (Q&P). Three different Q&P steels with different combination of alloying elements and volume fraction of retained austenite are subjected to uniaxial tensile and Nakajima testing. Tensile mechanical properties are determined, and the forming limit diagrams (FLDs) are plotted. Microstructure of the tested samples is analyzed, and dramatic reduction of retained austenite fraction is detected. It is demonstrated that all steels are able to accumulate much higher amount of plastic strain when tested using Nakajima method. The observed phenomenon is related to the multiaxial stress state and strain gradients through the sheet thickness resulting in a fast transformation of retained austenite, as well as the ability of the tempered martensitic matrix to accumulate plastic strain. Surprisingly, a Q&P steel with the highest volume fraction of retained austenite and highest tensile ductility shows the lowest formability among studied grades. The latter observation is related to the highest sum of fractions of initial fresh martensite and stress/strain induced martensite promoting formation of microcracks. Their role and ability of tempered martensitic matrix to accumulate plastic deformation during forming of Q&P steels is discussed., 12 figures, 6 tables

A high-throughput methodology is proposed, based on the combination of diffusion couples and advanced nanomechanical testing methods, to directly measure alloying effects on the critical resolved shear stress (CRSS) of individual deformation modes in Mg alloys. The methodology is tested in Mg-Zn alloys by assessing the alloying effects, up to Zn contents of 2 at.%, on basal slip, extension twining and pyramidal slip in two metallurgical conditions: as-quenched, for which the Zn solute atoms remain homogenously dispersed in solid solution; and peak-aged, for which the Zn atoms form rod-shape β1′ (MgZn2) precipitates. A combined approach including micromechanical testing, transmission Kikuchi diffraction, and high-resolution transmission electron microscopy was performed to reveal the corresponding deformation mechanisms. It was found that the CRSS enhancement for basal slip and extension twinning by MgZn2 precipitates is considerably larger than the effect of Zn in solid solution, while the strengthening of pyramidal slip is similar in both cases. As a result, the anisotropy ratios remain high and similar to pure Mg in the solid solution strengthened Mg-Zn alloys. However, they are substantially reduced in precipitation strengthened Mg-Zn alloys.

Al/SiC nanolaminates with equal nominal thicknesses of the Al and SiC layers (10, 25, 50 and 100 nm) were manufactured by magnetron sputtering. The mechanical properties were measured at 25 °C and 100 °C by means of nanoindentation and micropillar compression tests and the deformation mechanisms were analyzed by in situ micropillar compression tests in the transmission electron microscope. In addition, finite element simulations of both tests were carried out to ascertain the role played by the strength of the Al layers and by the elastic constraint of the ceramic layers on the plastic flow of Al in the mechanical response. It was found that the mechanical response was mainly controlled by the constraint during nanoindentation or micropillar compression tests of very thin layered (≈10 nm) laminates, while the influence of the strength of Al layers was not as critical. This behavior was reversed, however, for thick layered laminates (100 nm). These mechanisms point to the different effects of layer thickness during nanoindentation and micropillar compression, at both temperatures, and showed the critical role played by constraint on the mechanical response of nanolaminates made of materials with a very large difference in the elasto-plastic properties.

The bimodal microstructure of a metastable β Ti–7Mo–3Nb–3Cr–3Al (Ti-7333) alloy was successfully tuned through various thermomechanical processing steps, to achieve strength and ductility combinations, in the range between 903 and 1443 MPa and 2.9 % and 17 %, respectively. The influence of the microstructural variables on the deformation micro-mechanisms and fracture mechanisms were further elucidated by the assistance of TEM and fractographic analysis. The results indicate that the strength of bimodal Ti-7333 is mainly governed by secondary αS precipitation through the introduction of a high density of α/β interfaces that effectively block dislocation transmission, whereas ductility is tuned through the control of the primary αP, rod-like αr and retained β phases. Moreover, ductility can be extremely deteriorated if the formation of a continuous grain boundary αCGB phase is not prevented. Plastic deformation of bimodal Ti-7333 is dominated by dislocation slip and tangling, whereas the microstructural sensitivity that accelerated at high strength level is originated from the deformation incompatibility between the fine acicular αS and parent β. In addition, the {10–11} α micro-twinning of equiaxed αP phases also contributes to improved ductility and coordinates deformation to an extent. The fractographic analysis revealed either fracture by microvoid coalescence or a mixture of intergranular fracture and microvoid coalescence, depending on thermomechanical condition. The mixed fracture mode results in a relatively flat crack propagation path and reduced ductility; whereas a tortuous crack propagation is obtained when the alloy solely undergoes fracture by microvoid coalescence.

This study aims at determining the strength of a fully lamellar Ti-45Al-2Nb-2Mn (at.%) + 0.8 (vol.%)TiB2 alloy, with nanoscale lamellar thicknesses. With this aim, the average lamellar thickness of a centrifugally cast alloy was refined one order of magnitude, down to just a few nanometers, by water quenching, followed by a low temperature ageing treatment. The strengthening induced by the lamellar thickness reduction down to just a few nanometers, determined as a function of lamellar orientation by micropillar compression, was found to be very significant, even higher than what can be achieved by high Nb alloying.

Weak fiber/matrix interface dominates the toughening properties of ceramic matrix composites. This paper reports a novel sol-gel fabricated carbon fiber reinforced mullite matrix composite, in which the fiber/matrix interface was inherently weak in shear properties (∼25 MPa), measured in-situ by fiber push-in tests. The interface microstructure was chemically sharp, characterized by transmission electron microscopy. The outcome of the weak interface was the full trigger of the toughening mechanisms like crack deflection, etc., leading to significant enhancement of the fracture toughness of the composite (∼12 MPa√m), measured by single edged notch beam method. Finally, due to the weak fiber/matrix interface and large thermal expansion mismatch of the fiber and matrix, the high temperature fracture strength was enhanced in the temperature range from 25 to 1200 °C, which is attributed to the enhancement of the interfacial property at elevated temperatures that favors better load transfers between composite constituents.

Novel Nextel™ 440 aluminosilicate fiber reinforced SiC matrix composites, with/without chemical vapor deposited carbon interphase were fabricated by polymer derived ceramic process, and they were studied by a combination of micro- and macro- mechanical techniques such as nanoindentation, micropillar splitting, fiber push-in, digital image correction and high temperature three point bend tests. Specifically, micropillar splitting test was firstly employed to measure in-situ the localized fracture toughness. The results revealed that the carbon interphase can effectively hinder the interfacial reactions between Nextel™ 440 fiber and SiC matrix, thus remarkably weakening the composite interfacial shear strength from ∼293 MPa to ∼42 MPa, and enhance the composite fracture toughness from ∼1.8 MPa√m to ∼6.3 MPa√m, respectively. This is mainly a consequence of weak interface that triggers crack deflection at the fiber/interphase interface. Finally, this novel composite showed stable mechanical properties in vacuum at temperature range from 25 °C to 1000 °C.

The effect of Al atoms in solid solution on the critical resolved shear stress for twin nucleation and growth was analyzed by means of the combination of diffusion couples with compression tests in micropillars oriented for twinning. The critical resolved shear stress for twin nucleation was higher than that for twin growth and both increased by the same amount with the Al content. Nevertheless, the increase was small ( approx. 10 MPa) for 4 at.%Al but large (up to 60-70 MPa) for 9 at.%Al. These results were in agreement with Labusch-models based on first principles calculations in the dilute regime (< 5 at.%Al) [51]. Comparison with recent data in the literature showed that Al atoms are more effective in increasing the critical resolved shear stresses for twin nucleation and growth than for basal slip [21]. Finally, compression tests in micropillars oriented along [0001] showed the critical shear stress for pyramidal slip increased rapidly with the Al content from 98 MPa in pure Mg to 250 MPa in Mg-9 at.%Al. Thus, the addition of Al increased the plastic anisotropy of Mg alloys.

Room and high temperature mechanical properties of reactive magnetron sputtered TaSiN coatings were measured using nanoindentation (between 25 °C and 500 °C). Fracture toughness was also evaluated at a similar temperature range using the micropillar splitting method. The influence of the nitrogen concentration on the evolving phases and microstructure of the TaSiN coatings, before and after the high temperature testing, were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. XRD spectra showed broad peaks with hexagonal γ-Ta2N as the main phase, with the cubic δ-TaN phase emerging for higher N contents. Phase composition remained unchanged before and after the 500 °C tests. However, after the high temperature tests, TEM analysis showed the presence of an oxide surface layer, with a thickness that decreased (from 42 to 15 nm) with N content, due to residual oxygen diffusion, which replaces nitrogen to form amorphous SiOx. Beneath the oxide-rich surface layer, coatings exhibited a stable nanocrystalline columnar microstructure. Hardness and fracture toughness increased with N content, initially due to the formation of an amorphous Si–N tissue at grain boundaries, and for even higher N contents, due to the appearance of the hard cubic δ-TaN phase. Hardness at 500 °C decreased only by 15%, while fracture toughness followed the opposite trend, due to increased plasticity with temperature. The optimum composition turned out to be Ta55Si10N35, which retained a hardness of 30 GPa at 500 °C, being also the toughest. These observations make this system very interesting for high temperature applications.

Intermetallics (θ and η phases) with high aluminum content (>50 at.% Al) formed at the interface of Fe/Al welded joints significantly reduce the mechanical strength of those joints. Seeking to modify the intermetallics (IM) thus constitutes an opportunity to minimize the risk of brittle failure of the bimetallic joints. In this work, we proposed a method to modify the IM layers by a second diffusion of segregated elements. Firstly, thermomechanical simulation performed using DICTRA® allows estimating the segregation of alloying elements near the interface during friction melt bonding (FMB) of Al/Fe joints. For the experimental part, FMB welded joints composed of DP600 steel and AA6061 were used in this study. FMBed samples with the existing thin θ and η phases were reheated to verify the proposed method via second diffusion. The study revealed that the segregated Si at the interface contributes in a forward diffusion, while other elements (e.g. Mg and Cu) lead to backward diffusion. The experimental observations support that, the joint forms relatively thick θ phase compared to η phase due to the forward diffusion of Si. Moreover, the second heating facilitates the formation of a ternary IM (τ3 - FeAl2Si) at the interface. Using a second diffusion heat treatment may provide an alternate route to change the nature of the intermetallics or the compositions of the IM layer.

Cr-doped diamond-like carbon (Cr-DLC) films with Cr contents ranging from 3 up to 20 at. % were synthesised in a codeposition process with HiPIMS (Cr deposition) and DC-pulsed technology (C deposition). The application of HiPIMS at low frequencies was observed to significantly enhance the energy density during the Cr plasma discharge due to the interaction of Cr–C species. The higher energy bombardment at low HiPIMS frequencies allowed doping with Cr the DLC structure avoiding the graphitization of the carbon structure. EELS spectroscopy was used to evaluate sp3 content and Raman was used for sp2 structural characterization of the films. Enhanced mechanical properties (hardness up to 30 GPa) were observed with nanoindentation for Cr-doped DLC at low frequencies. High temperature nanoindentation tests were also performed from room temperature to 425 °C in order to evaluate the evolution of hardness and Young Modulus with temperature. The results showed that the mechanical properties at high temperature mainly depend on the initial sp3-sp2 structure. Tribological tests were carried out in air from room temperature to 250 °C. Cr-doped DLC coatings deposited by low-frequency HiPIMS showed lower friction and wear compared to undoped DLC.

Taper-free InP twinning superlattice (TSL) nanowires with an average twin spacing of ∼13 nm were grown along the zinc-blende close-packed [111] direction using metalorganic vapor phase epitaxy. The mechanical properties and fracture mechanisms of individual InP TSL nanowires in tension were ascertained by means of in situ uniaxial tensile tests in a transmission electron microscope. The elastic modulus, failure strain, and tensile strength along the [111] direction were determined. No evidence of inelastic deformation mechanisms was found before fracture, which took place in a brittle manner along the twin boundary. The experimental results were supported by molecular dynamics simulations of the tensile deformation of the nanowires that also showed that the fracture of twinned nanowires occurred in the absence of inelastic deformation mechanisms by the propagation of a crack from the nanowire surface along the twin boundary.

This paper analyzes the evolution of the internal damage in two types of steel that show different fracture behaviors, with one of them being the initial material used for manufacturing prestressing steel wires, and the other one being a standard steel used in reinforced concrete structures. The first of them shows a flat fracture surface perpendicular to the loading direction while the second one shows the typical cup-cone surface. 3 mm-diameter cylindrical specimens are tested with a tensile test carried out in several loading steps and, after each of them, unloaded and analyzed with X-ray tomography, which allows detection of internal damage throughout the tensile test. In the steel used for reinforcement, damage is developed progressively in the whole specimen, as predicted by Gurson-type models, while in the steel used for manufacturing prestressing steel-wire, damage is developed only in the very last part of the test. In addition to the experimental study, a numerical analysis is carried out by means of the finite element method by using a Gurson model to reproduce the material behavior.

Micropillar compression technique was employed to study the microscale deformation mechanisms of basal slip, twinning and non-basal slips at selected grains in a Mg-2 wt.% Y alloy. The results suggest a critical resolved shear stress (τCRSS) for basal slip 12.5 ± 1.7 MPa, and for twin nucleation and twin growth 38.5 ± 1.2 MPa and 33.8 ± 0.7 MPa, respectively. The higher values compared to those in pure Mg suggests a more balanced deformation in Mg alloy with Y addition. The activation of dislocations in the twinned orientation is highlighted, which leads to strong work hardening in twinned favorable orientation [ 10 1 ‾ 0 ] . In addition, at prismatic-slip favorable orientation [ 11 2 ‾ 0 ] , a twinning-to-prismatic slip transition was observed when elevating temperature from 25 °C to 100 °C and 250 °C. Specially at 250 °C, twinning was completely prohibited, and pure prismatic slip was triggered. The measured τCRSS for prismatic slip at 250 °C was 39.7 ± 0.3 MPa, much higher than that for pure Mg at the same temperature. Finally, at pyramidal-slip favorable orientation [ 0001 ] , an abnormal strengthening was observed at 100 °C and 250 °C due to activation of pyramidal slips. Decompositions of dislocations and Y segregation at stacking faults are the main mechanisms leading to the high-temperature strengthening in Mg–Y alloy.

Recycled carbon fibres have been employed as a reinforcement material for the synthesis of polypropylene-based thermoplastic matrix composites with different fibre/resin ratios (10, 20 and 30%) by means of injection moulding. A thorough study of their mechanical properties including tensile, impact and bending tests, as well as fibre distribution and orientation and chemical behaviour was conducted. The stiffness and strength of the composites increased linearly with the fibre fraction in a ratio of 180 and 0.9 MPa/% Vf respectively. The distribution and alignment of the fibres in the injection flow contributed to the improvement of the mechanical behaviour of the composite. In addition, changes in the fibre orientation were found along the injected sample, which emphasised the importance of temperature control during injection on the alignment of the fibres. However, even though the addition of a coupling agent improved the fibre/matrix adhesion, the unremarkable impact results reveal that future efforts in long recycled-carbon-fibre reinforced thermoplastic composites should be directed to enhance interface performance.

The aim of this study is to determine the influence of lamellar orientation on the strength and operative deformation mechanisms of a fully lamellar Ti-45Al-2Nb-2Mn (at.%) + 0.8(vol.%) TiB2 (Ti4522XD) alloy. With this aim, micropillars with lamellae oriented at 0°, 45° and 90° with respect to the loading direction were compressed at room temperature. The results revealed a large plastic anisotropy, that was rationalized, based on slip/twin trace analysis, according to the relative orientation of the main operative deformation modes with respect to the lamellar interfaces. Loading at 45° resulted in the activation of soft longitudinal deformation modes, where both the slip plane and the slip direction were parallel to the interfaces, and therefore, little interaction of dislocations with lamellar interfaces is expected. At 0° loading, deformation was mainly accommodated by harder mixed deformation modes (with an oblique slip plane but a slip direction parallel to the lamellar interfaces), although the lamellar interfaces seemed to be relatively transparent to slip transfer. On the contrary, 90° loading represented the hardest direction and deformation was accommodated by the activation of transverse deformation modes, confined to individual lamellae, together with longitudinal modes that were activated due to their softer nature, despite their very small Schmid factors. Finally, a thorough study of pillar size effects revealed that the results were insensitive to pillar size for dimensions above 5 μm. The results can therefore be successfully applied for developing mesoscale plasticity models that capture the micromechanics of fully lamellar TiAl microstructures at larger length scales.

A simple method to significantly increase the toughness of carbon fiber reinforced SiC matrix composites is presented. The method is based on the heat treatment of Toray T300 carbon fibers in vacuum, leading to the in-situ formation of carbon coatings on the fiber surface that optimizes the interfacial strength in carbon fiber reinforced SiC matrix composite. The formation mechanism of the in-situ coatings was studied by transmission electron microscopy, and the effects of the in-situ carbon interphase on the interfacial property and fracture resistance of the composites were comprehensively assessed by combining transmission electron microscopy, fiber push-in and macro mechanical testing. The results reveal that the in-situ coating was originated from the pyrolysis of the proprietary sizing of the T300 fibers, that was crystallized during thermal treatment, maintaining a low oxygen content. For this reason, the resulting coating can effectively hinder the interfacial reactions in carbon fiber reinforced SiC composites, and remarkably weaken the composite interfacial shear strength from 105 ± 10 MPa to 30 ± 5 MPa. Due to the introduction of in-situ carbon interphase, the toughness of the carbon fiber reinforced SiC composite increased significantly from 1.7 ± 0.3 MPa m1/2 to 21.3 ± 0.7 MPa m1/2, triggered by toughening mechanisms such as crack deflection and fiber pullout.

Ti-based materials are one of the most important materials used in biomedical engineering. Recently, commercially pure (CP) Ti has attracted significant attention of research community due to its full biocompatibility with human body, and there is an ongoing demand to improve its mechanical properties without sacrificing other beneficial properties. A possible approach to achieving this aim is to use the method of severe plastic deformation (SPD) to obtain an ultra-fine grained (UFG) microstructure. Significant grain refinement by SPD processing leads to an improvement in mechanical and functional properties. This paper gives an overview of a range of the properties that can be achieved in the UFG CP Ti including microstructural features, mechanical properties, corrosion performance and biocompatibility. Attention is paid to the main SPD processing techniques developed for the fabrication of UFG CP Ti. Current and potential applications of UFG CP Ti in biomedical engineering are also considered.

The deformation and damage mechanisms during tensile deformation of [±45] 2s open hole carbon fiber composite materials were quantitatively analyzed by means of image analysis of XCT data. Damage developed progressively in each ply with deformation in two shear bands (parallel and perpendicular to the fiber direction) at ±45° with respect to the loading direction, i.e. cracking started from these shear bands and grew following the fiber direction until encompassing the whole laminate width. Matrix cracking and fiber rotation in both types of shear bands presented different features, which were quantified by means of image processing from XCT data. A small delamination developed around the hole at the intersection from +45° and −45° cracks directions in adjacent plies. However, this delamination does not progress excessively with deformation until the end of the test, when fracture was triggered by the sudden propagation of two main delamination cracks tangent to opposite sides of the hole in the shear band parallel to the fiber direction.

The mechanical properties of Al/SiC nanolaminates with layer thicknesses between 10 and 100 nm were studied by nanoindentation in the temperature range 25 to 100 °C. The strength of the Al layers as a function of the layer thickness and temperature was obtained from the hardness of the nanolaminates by an inverse methodology based on the numerical simulation of the nanoindentation tests by means of the finite element method. The room temperature yield stress of the Al layers showed a large ‘the thinner, the stronger’ effect, which depended not only on the layer thickness but also on the microstructure, which changed with the Al layer thickness. The yield stress of the Al layers at ambient temperature was compatible with a deformation mechanism controlled by the interaction of dislocations with grain boundaries for the thicker layers (>50 nm), while confined layer slip appeared to be dominant for layers below 50 nm. There was a dramatic reduction in the Al yield stress with temperature, which incre...

Metal-ceramic nanolaminate composites show promise as high strength and toughness materials. Micropillar compression was used to characterize the mechanical behavior of Al SiC multilayers in different orientations including loading at 0°, 45° and 90° with respect to the direction of the layers. The 0° orientation showed the highest strength while the 45° orientation showed the lowest strength. Each orientation showed unique deformation behavior. Effects of pillar size and aspect ratio were also studied. Higher compressive strengths were observed in smaller pillars for all orientations. This effect was shown to be due to a lower probability of flaws using Weibull statistics. Additionally, changes in the aspect ratio was shown to have no significant effect on the behavior except an increase in the strain to failure in the 0° orientation. Finite element analysis (FEA) was used to simulate and understand the effect of these parameters on the deformation behavior.

Harvesting biobased epoxy resins with improved thermomechanical properties (e.g., glass transition temperature Tg and storage modulus), mechanical and dielectric similar and even superior to that of bisphenol A epoxy resin (DGEBA) is vital to many applications, yet remains a substantial challenge. Here we develop a novel eugenol-based epoxy monomer (TEU-EP) with a branched topology and a very rich biobased retention (80 wt %). TEU-EP can be well cured by 3,3′-diaminodiphenyl sulfone (33DDS) and the resultant TEU-EP/33DDS system can be considered as a “single” epoxy component, exhibiting adequate reactivity at high processing temperatures. Importantly, compared with DGEBA/33DDS, TEU-EP/33DDS achieves a 33 °C, 39% and 55% increment in the glass transition temperature, Young’s modulus, and hardness, respectively, and shows the improved creep resistance and dimensional stability. TEU-EP/33DDS is also characterized by the considerably reduced permittivity, dielectric loss factor, and flammability with high yie...

Al and SiC nanolaminate films were characterized in the perpendicular, inclined and parallel orientations using nanoindentation. The deformation was dominated by buckling of the layers when the layers were parallel to the indenter and by compression of the ductile Al layers when the layers were perpendicular to the indenter, while indentation in inclined orientations showed an intermediate behavior. Finite element modeling (FEM) of indentation deformation using wavy layers showed much more compliant behavior and prominent layer buckling than the idealized flat structure, highlighting the large effect these microstructural details can have on the deformation behavior.

Quenching and partitioning (Q&P) is receiving increased attention as a novel heat treatment to produce advanced high strength steels (AHSSs) containing martensite/retained austenite mixtures, with desirable combination of strength, ductility and toughness. Despite the significant body of research on microstructure and mechanical properties of Q&P steels, there is still a significant lack of knowledge on the effect of complex microstructure on their mechanical performance. This work addresses the effect of microstructural architecture in multiphase Q&P steels on their fracture behavior at macro- and micro-scales. It is demonstrated that the RA volume fraction does not affect significantly the local fracture initiation toughness, whereas it can greatly improve the total crack growth resistance in Q&P steels. In addition, matrix conditions can play an important role in the fracture behavior of Q&P steels. Based on the analysis of the experimental results, a general recipe to tailor fracture properties of Q&P steels is proposed.

Amorphous carbon (aC), in particular diamond-like carbon (DLC), is one of the most studied and promising coating materials, but many of the atomic-scale mechanisms involved in their plastic deformation process are not fully understood. The mechanical response of non-hydrogenated DLC films with different sp 3 concentrations is investigated using nanoindentation experiments, ab-initio simulations, and classical molecular dynamics simulations. Experimental characterization is carried out with Raman spectroscopy and Electron Energy Loss Spectroscopy (EELS). Ab-initio and classical simulations show good agreement for sp 1 , sp 2 and sp 3 content of in-silico samples. Elastic modulus and hardness of DLC films increase with sp 3 content, for sp 3 between 10% and 55%, and excellent agreement is obtained between experiments and simulations. Simulated strain distributions are shown to be highly anisotropic, unlike continuum-scale predictions for the use of a perfectly spherical indenter in an amorphous solid. MD simulations also reveal two different plasticity modes depending on the sp 3 level of the indented sample. For films with sp 3 concentrations less than 40%, plasticity is mainly mediated by the sp 2 to sp 3 transition. For larger sp 3 concentrations, DLC plastic deformation is attributed to densification due to bond rearrangement. All in all, our work offers a comprehensive study of DLC, revealing unexpected plastic deformation mechanisms that had not been considered before. Our study might help to the fundamental understanding of amorphous carbon coatings for both scientific and technological purposes.

The fracture toughness of Al/SiC nanolaminates with different layer thicknesses (in the range 10 to 100 nm) was measured by means of micropillar splitting and bending of a notched beam. The crack plane was perpendicular to the layers in the former while notched beams with the notch parallel and perpendicular to the layers were milled in the latter. It was found that crack propagation parallel to the layers took place along the metal–ceramic interfaces and the toughness increased with the layer thickness due to the contribution of the plastic deformation of the Al layers. Crack propagation perpendicular to the layers showed evidence of crack deflection/arrest at the interface. The toughness in this orientation increased as the layer thickness decreased due to the higher density of interfaces except for the nanolaminates with 10 nm layer thickness. In this latter case, crack propagation took place along the weak columnar grain boundaries, leading to a marked reduction in toughness.