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The effect of solid solution and aging treatment on microstructure evaluation and resulting mechanical properties of as-cast Mg-9wt.%Li-5wt.%Al-3wt.%Zn-1wt.%Sn (LATZ9531) light-weight alloys were investigated for the application in automobile, aerospace, and bio-medical field. The hardness of the Mg-rich (α-phase, hardness: 2.13 GPa) and the Li-rich (β-phase, hardness: 1.49 GPa) of the solutionized alloy derived from nanoindentation was increased to ~ 35 and ~ 21%, respectively, as compared to the as-cast condition. The hardness of both α- and β-phase was found to be decreased after aging treatment due to the age softening effect. Also, the resulting microstructures were analyzed using finite element modeling (FEM) to understand the effect of the distribution of precipitates on the mechanical properties. Further, the effective elastic modulus for the different heat-treated LATZ9531 alloy was quantified using stress-strain contour obtained from OOF2 (Object Oriented Finite Element Modeling). Also, the role of precipitates, α- and β-phase that possesses different elastic modulus was shown a different stress-strain contour at the interfaces. [ABSTRACT FROM AUTHOR]

The engineered role of coarse‐SiC (D50 ≈72 μm) and fine‐SiC (D50 ≈3 μm) particles on the wear damage of zirconium boride (ZrB2) is assessed at different length scales. Monolithic ZrB2 and 20 vol% SiC reinforced ZrB2 with SiC of two different particle sizes are consolidated via spark plasma sintering. Wear tests conducted on sintered samples for examining multi‐length scale performance include fretting (micro‐wear), micro‐scratching (meso‐wear) and ball‐on‐disk (macro‐wear), under dry and unlubricated conditions. The damage assessment and wear mechanism, characterised via scanning electron microscopy and optical profilometry, show Hertzian tensile cracking in all the samples at loads ≥5 N during micro‐scratching. Wear volume, wear rate and coefficient of friction (cof) decreased with SiC reinforcement during macro‐wear. Fine‐SiC reinforced ZrB2 (ZSF) composite showed least cracking at loads ≥5 N owing to its highest fracture toughness (4.6 MPa m1/2) as compared to coarse‐SiC reinforced composite (ZSC, 2.1 MPa m1/2) and monolithic ZrB2 (3.9 MPa m1/2). Hardness of composites increases as compared to ZrB2, and ZSF shows enhanced elastic modulus and fracture toughness. In summary, superiority of ZSF in terms of improved mechanical performance and wear resistance makes it a potential high‐end material for aerospace applications, where particles with high surface impact may cause material deformation and removal. [ABSTRACT FROM AUTHOR]

Fully dense (ZrC-TaC-WC-TiC)-SiC (named as ZTaWT-S) based high entropy carbide (HEC) composites were fabricated using spark plasma sintering (SPS) at 1750 °C. Herein, effect of carbonaceous reinforcements (multi-walled carbon nanotube (CNT), graphite (G) and graphene (GNP) on microstructure and mechanical properties of the composites is assessed. The formation of a cubic rock salt high entropy carbide (HEC) phase is indicated via phase and microstructural characterization. Further, local elemental distribution using energy dispersive spectroscopy, and interplanar spacing calculation using transmission electron microscopy (TEM) confirmed the HEC phase formation in the sintered samples. Refined grains (∼3.9 μm), and high densification (>99%), has elicited an increasing hardness from 23.1 GPa to 30.2 GPa (by 30.7%) and elastic modulus from 372 GPa to 419 GPa (by 12.6%), which is attributed to an effective load transfer between matrix/reinforcement in ZTaWT-SGNP composite. An attempt is made to delineate the strengthening contributions from the porosity, high entropy phase, and other complex oxy-carbide and/or unreacted phases in multiphasic (ZTaWT-S) based HEC. Instrumented indentations (micro-indentation and nanoindentation) have facilitated delineation of contribution from various phases (i.e. HEC, TaC, SiC, and oxide phases). A remarkable enhancement is observed in the flexural strength from 390 MPa for ZTaWT-S composite to 487 MPa (by 24.9%), 519 MPa (by 33.1%) and 576 MPa (by 47.7%) for CNT, graphite, and graphene reinforced ZTaWT-S composites, respectively. The graphene reinforced composite exhibited highest flexural strength due to wrapping of GNP along grain boundaries, enhanced matrix/reinforcement adhesion, grain shearing and crack deflection. In summary, ZTaWT-SGNP composite exhibit superior mechanical properties and, thus, have potential structural applications in extreme environments. • Spark Plasma Sintering of Zr-Ta-W-Ti based High Entropy Carbides (HEC). • Effect of carbonaceous reinforcement (i.e. CNT, Graphite and Graphene) in HECs. • Delineated contribution of hardness, elastic modulus and flexural strength in HEC. • Damage tolerance mechanism in carbonaceous reinforced Zr-Ta-W-Ti-Si based HECs. [ABSTRACT FROM AUTHOR]

In this study, nanoindentation measurements within the hcp a-phase and the bcc ß-phase were carried out on two thermomechanically (TM) processed Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys to reveal the individual mechanical strength of the phases. Commercially pure Mg and AZ31 Mg alloys were also analysed to study the contribution of alloying addition on the mechanical strength on nano-length scale, such as hardness and elastic modulus of the constituent phases, in Mg-Li alloys. The average hardness and reduced elastic modulus values of TM processed Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn measured by nanoindentation were observed to be higher (80% and 30%, respectively) than that of pure Mg. The elastic modulus values of both alloys are about 58 GPa, which is much larger than that of other Mg-based alloys (~45 GPa). Pop-in events (serrated yielding due to the Portevin-Le Chatelier effect) were also observed in TM processed Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys and were quantified using models developed by Taylor and Morris. [ABSTRACT FROM AUTHOR]

Electrophoretically deposited Ni-BN composite coating was strengthened with graphene (Ni-BN-Gr), carbon nanotubes (Ni-BN-CNT) and diamond (Ni-BN-D) carbonaceous reinforcements. Highest hardness (2.0 GPa) and elastic modulus (133.5 GPa) of Ni-BN-D coating than Ni-BN-CNT (1.96 GPa and 102.1 GPa, respectively), Ni-BN-Gr (1.94 GPa and 92.0 GPa respectively) and also from Ni-BN (1.89 GPa and 91.5 GPa, respectively) coatings was linked through high compressive stress (−601 MPa), dislocation density (8.9 × 10 15 m −2 ) and yield strength (4.4 GPa). The micro-scratching damage was contributed by ploughing and adhesion components, which were compared with that of experimental frictional values. Addition of graphene, CNT and diamond in Ni-BN composite showed a decrease in wear volume (from 1.66 × 10 −8 m 3 to 0.45 × 10 −8 m 3 ) due to the synergetic lubricating effect of BN and carbonaceous reinforcements. Thus, Ni-BN-D restrict inception of multiscale wear and can be a potential three phase metal-ceramic coating for engineering and industrial applications. [ABSTRACT FROM AUTHOR]

Role of carbon nanotubes (CNTs) on solid solutioning in SiC reinforced equi-volume (40:40) composition of HfB 2 + ZrB 2 is investigated. Incomplete solid solutioning occurred under given sintering conditions in presence of 20 vol% SiC. However, CNTs addition resulted in heterogeneous solid solution formation which is evident from SEM and TEM micrographs and confirmed through EDS analysis and peak de-convolution in XRD. TEM investigation revealed the retention of CNTs and presence of defect structures like stacking faults in the SiC phase is ascribed to the compressive stresses generated during cooling after the sintering process. With CNTs reinforcement, micro-hardness and elastic modulus increased from 10.2 GPa to 11.7 GPa and 129 GPa to 141 GPa, respectively. The reduction in peak oxidation temperature (from 751‐773 °C to 725‐746 °C) and weight gain starting temperature (from 731‐750 °C to 684‐707 °C) with CNTs reinforcement elicits a concurrent reduction in the oxidation resistance. [Display omitted] • CNTs addition increase solid solutioning inhomogeneity in HfB 2 - ZrB 2 -SiC composite. • CNTs (and their effect on solid solutioning) improve micro-mechanical properties. • Inhomogeneous solid solutioning decrease peak oxidation temperature. • Compressive stresses generated in SiC phase produce defects like stacking faults. • Compressive stresses in SiC phase remain un-altered with CNTs incorporation. [ABSTRACT FROM AUTHOR]

Difficulties associated with the manufacturing of diboride based large and complex shapes mandate them to be joined for extreme applications. In the present work, spark plasma sintering is utilized to join HfB 2 -ZrB 2 -SiC-B 4 C-CNT (HZSBC) based composites with Ni-interlayer at 1100 °C and without interlayer at 1800 °C. Microstructural analysis has elicited the formation of Ni diffused reaction zone (150–200 μm), and unaffected HZSBC composite for HZSBC-Ni-HZSBC joined composite (at 1100 °C), which gets merged into a homogeneous microstructure (without any distinguishable interface) in the HZSBC-HZSBC joint (without Ni-interlayer). An overall reduction of 18% and 14% is elicited in hardness and elastic modulus, respectively, in the HZSBC-Ni-HZSBC joint, whereas in HZSBC-HZSBC joined composite, uniform hardness and elastic modulus of ∼22 GPa and ~398 GPa, respectively, is observed. Further, the bending and shear strength of the joined composites was obtained to be ∼209 MPa and ∼41 MPa, respectively, for HZSBC-Ni-HZSBC, which increased to ~342 MPa and ∼81 MPa, respectively, for HZSBC-HZSBC. In conjunction, though superior high-temperature (1500 °C) oxidation protection is witnessed in HZSBC-HZSBC joint, with a thinner oxide layer, both display SiO 2 -rich protective glassy layer, making these composites potential candidates for use in atmospheric re-entry conditions. [ABSTRACT FROM AUTHOR]

Abstract: Multiwalled carbon nanotube (CNT) reinforced aluminum nanocomposite coatings were prepared using cold gas kinetic spraying. Spray drying was used to obtain a good dispersion of the nanotubes in micron-sized gas atomized Al–Si eutectic powders. Spray dried powders containing 5 wt.% CNT were blended with pure aluminum powder to give overall nominal CNT compositions of 0.5 wt.% and 1 wt.% respectively. Cold spraying resulted in coatings of the order of 500 μm in thickness. Fracture surfaces of deposits show that the nanotubes were uniformly distributed in the matrix. Nanotubes were shorter in length as they fractured due to impact and shearing between Al–Si particles and the Al matrix during the deposition process. Nanoindentation shows a distribution in the elastic modulus values from 40–229 GPa which is attributed to microstructural heterogeneity of the coatings that comprise the following: pure Al, Al–Si eutectic, porosity and CNTs. [Copyright &y& Elsevier]

Effect of B 4 C addition on the lower damage tolerance of spark plasma sintered (Hf, Zr)B 2 based ceramics has been elucidated. Increased densification (from 89% to 95%) with B 4 C addition has elicited hardness and elastic modulus increase from 25 GPa to 38 GPa (52%) and 439 GPa–635 GPa (45%), respectively. Systematic 3–9 vol% B 4 C addition resulted in an increased fracture toughness (from 2.2 MPa m0.5– 4.4 MPa m0.5) and flexural strength (from 320 MPa to 357 MPa) compared to that of (Hf, Zr)B 2 due to synergistic effect of solid solutioning and compressive residual stresses generated around reinforcement. The decreased wear rate (from 0.163 mm3/N.m to 0.061 mm3/N.m) with optimal B 4 C addition, affirms enhanced damage tolerance of (Hf, Zr)B 2 composite. Enhanced cracking and fracture in (Hf, Zr)B 2 shifts to abrasion induced restricted micro-cracking as micro-scratch wear mechanism with B 4 C addition. Estimated elastic-modulus and extracted scratch-hardness are correlated with microstructural attributes of porosity, phase content and residual stress in (Hf, Zr)B 2 composites. • Spark plasma sintering of dense (up to 95%) HfB2-ZrB2-B4C composites. • Fracture toughness doubled to 4.4. MPa.m0.5 in HfB2-ZrB2-9 vol% B4C. • Modelling the effect of solid solutioning on estimated elastic modulus. • Estimating scratch toughness/hardness and correlating to damage mechanics. • 60% increased damage tolerance with B4C addition in HfB2-ZrB2 composites. [ABSTRACT FROM AUTHOR]

Abstract The fully dense HfB 2 -ZrB 2 -SiC composites were processed using spark plasma sintering (SPS) at 1850 °C. The effect of reinforcements (B 4 C and CNT) on the densification as well as mechanical properties were investigated and compared (with monolithic) in the present study. The study showed that the addition of B 4 C and CNT were not only beneficial for the densification but also towards enhancing the mechanical properties (hardness, elastic modulus, and fracture toughness) of HfB 2 -ZrB 2 -SiC composites. The augmentation in the mechanical properties establish the synergy between solid solution formation (with the equimolar composition of HfB 2 /ZrB 2) and the reinforcements (SiC, B 4 C, and CNT). The highest increase in the indentation fracture toughness with the reinforcements of B 4 C as well as CNT is >3 times (~13.8 MPam0.5 when it is 3–4 MPam0.5 for monolithic ZrB 2 /HfB 2) on HfB 2 -ZrB 2 -SiC composites, which is attributed to the crack deflection and pull-out mechanisms. An increase in the analytically quantified interfacial compressive residual stresses in the composites during SPS processing with the synergistic addition of reinforcements (SiC, B 4 C, and CNT) and its effect on the indentation fracture toughness has also been addressed. Graphical abstract Unlabelled Image Highlights • Processing of HfB2-ZrB2-SiC-based Ultra High Temperature Ceramics • Densification of HfB2-ZrB2-SiC with reinforcement of B4C and Carbon nanotube • Effect of solid solutioning on mechanical properties of HfB2-ZrB2-SiC composites • Estimating compressive residual stress generation in HfB2-ZrB2 system • Effect of residual stresses on fracture toughness of HfB2-ZrB2-SiC [ABSTRACT FROM AUTHOR]

In the recent years, magnesium–lithium (Mg–Li) alloys have attracted considerable attention/interest due to their high strength-to-density ratio and damping characteristic; and have found potential use in structural and biomedical applications. Here the mechanical behavior of novel Mg–9 wt.% Li–7 wt.% Al–1 wt.% Sn (LAT971) and Mg–9 wt.% Li–5 wt.% Al–3 wt.% Sn–1 wt.% Zn (LATZ9531) alloys is reported. Both, as cast and thermomechanically processed alloys have been studied which possess dual phase microstructure. Nanoindentation data have been utilized to envisage the elastic modulus of alloy via various micromechanics models (such as rule of mixtures, Voigt–Reuss, Cox model, Halpin–Tsai and Guth model) in order to estimate the elastic modulus. Object oriented finite element modeling (FEM) has been performed to predict stress distribution under tensile and compressive strain state. Close match between Halpin–Tsai model and FEM results show the abridgment of nano length scale property to evolution of microscopic stress distribution in novel LAT971 and LATZ9531 Mg–Li–Al based alloys. [ABSTRACT FROM AUTHOR]

Zirconium (Zr) based bulk metallic glasses (BMGs) have emerged as a potential material for various engineering applications due to their unique and tunable mechanical properties. Heat treatment of the BMGs plays a vital role in changing the mechanical as well as tribological properties. In the present work, the effect of the fictive temperature (T f) on the mechanical and tribological behavior of Zr based BMGs with a glass transition temperature (T g) of 352 °C has been studied by nanoindentation and micro-scratch testing at constant (load 10 N) and progressive (0.5–25 N) loading conditions. The BMGs were heat treated at three different fictive temperatures ranging from 0.91 T g (320 °C) to 1.05 T g (370 °C). Hardness and effective elastic modulus were observed to be highest (8.3 GPa and 128 GPa, respectively) for the metallic glass with a fictive temperature of 0.91 T g (320 °C). With an increase in fictive temperature, hardness and effective elastic modulus decrease due to decreased short-range ordering and more free volume (density fluctuations) in the internal structure, which enhances atomic and plastic flow in the material. For constant loading, wear resistance is observed to be similar for as-cast BMG and BMG with T f = 1.05 T g , but increases by 65% and 40% from as-cast to BMGs with T f 's of 0.91 T g and 0.99 T g , respectively. For progressive loading, the wear resistance increases by 10% from as-cast to 0.91 T g , whereas it decreases by 75% and 76% as T f increases to 0.99 T g and 1.05 T g , respectively. BMGs with T f = 0.91 T g are observed to be the most wear resistant in both the loading conditions, making it a viable candidate for biomedical applications, machine tools, and engine parts where wear resistance of the component during service is a dominating factor. [Display omitted] • This research investigates the effect of T f on mechanical and tribological properties of Zr based BMGs. • Increased density and ordering with a decrease in the T f results in improved hardness modulus. • BMG with a T f of 320 °C was observed to have high hardness and better scratch resistance than other samples. [ABSTRACT FROM AUTHOR]