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High-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics, with different carbon contents (x=0.55−1), were prepared by spark plasma sintering using powders synthesized via a carbothermal reduction approach. Single-phase, high-entropy (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)Cx ceramics could be obtained when using a carbon content of x=0.70−0.85. Combined ZrO2 and Mo-rich carbide phases, or residual graphite, existed in the ceramics due to either a carbon deficiency or excess at x=0.55 and 1, respectively. With the carbon content increased from x=0.70 to x=0.85, the grain size decreased from 4.36 ± 1.55 μm to 2.00 ± 0.91 μm, while the hardness and toughness increased from 23.72 ± 0.26 GPa and 1.69 ± 0.21 MPa·m1/2 to 25.45 ± 0.59 GPa and 2.37 ± 0.17 MPa·m1/2, respectively. This study showed that the microstructure and mechanical properties of high-entropy carbide ceramics could be adjusted by the carbon content. High carbon content is conducive to improving hardness and toughness, as well as reducing grain size.

High-entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C ceramics, with different contents (0, 5, 10, and 20 vol.%) of SiC whiskers (SiCw), were fabricated by spark plasma sintering using raw powders synthesized via carbothermal reduction. The application of a uniaxial compaction force led to texture development of the SiCw within the (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C matrix. Fracture toughness increased with the increase in SiCw content, while Vickers hardness remains almost unchanged. The toughness of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C-20 vol.% SiCw ceramics reached 4.3 ± 0.3 MPa∙m1/2, which was approximately 43% higher than that of the monolithic (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C ceramic (3.0 ± 0.2 MPa∙m1/2). The main toughening mechanisms were attributed to crack deflection, whisker debonding, and whisker pullout.

This research focuses on specimen geometry and the associated surface roughness of H13 hot-work tool steel, processed using laser-directed energy deposition additive manufacturing, and varying both the powder feed rate and the laser scanning speed. Under the examined conditions, the test sample measurements of length and width did not vary, but the sample heights were significantly affected by the scanning speed. An increase in scan speed resulted in ‘underbuilding’, while a decrease resulted in ‘overbuilding’, as might be anticipated. The top surface roughness of the samples was found to be greater than the side surface roughness, due to the capture of extra powder particles. For the single-track and multitrack clad samples, the surface roughness was increased when decreasing the scan speed. The addition of a draft angle, when producing 3-D components, was shown to reduce the side surface roughness. Using a finer layer thickness results in overbuilding the target height, while a coarser layer thickness results in underbuilding. Finally, the surface roughness exhibited no clear trend when the layer thickness was changed.

In the current work, fine-grained dual-phase, high-entropy ceramics (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2-(Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C with different phase ratios were prepared from powders synthesized via a boro/carbothermal reduction approach, by adjusting the content of B4C and C in the precursor powders. Phase compositions, densification, microstructure, and mechanical properties were investigated and correlated. Due to the combination of pinning effect and the boro/carbothermal reduction approach, the average grain size (∼0.5−1.5 μm) of the dual-phase high-entropy ceramics was roughly one order of magnitude smaller than previously reported literature. The dual-phase high-entropy ceramics had residual porosity ranging from 0.3 to 3.2 % upon sintering by SPS and the material with about 18 vol% boride phase exhibited the highest Vickers hardness (24.2±0.3 GPa) and fracture toughness (3.19±0.24 MPam 1/2).

High toughness and high hardness Si3N4 ceramics with fine and bimodal microstructure was prepared by combination of HfB2 additive and spark plasma sintering (SPS). HfB2-free SPSed Si3N4 ceramics at 1600 °C exhibited major α-Si3N4 phase, a fine and equiaxed grain microstructure, high Vickers hardness (21.3 ± 0.2 GPa), and low fracture toughness (3.7 ± 0.3 MPa m1/2). The introduction of 2.5 vol% HfB2 into Si3N4 ceramics at 1600 °C promoted α-to β-Si3N4 phase transformation, produced a fine and bimodal microstructure, significantly improved the toughness (7.7 ± 0.6 MPa m1/2) but slightly decreased the hardness (20.4 ± 0.6 GPa) which was higher than that of traditionally hot-pressed or pressurless sintered Si3N4 ceramics (~14–18 GPa).

Dense pressure-sintered reaction-bonded Si3N4 (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu2O3–MgO–Y2O3 sintering additive. The addition of Eu2O3–MgO–Y2O3 was shown to promote full nitridation of the Si powder. The nitrided Si3N4 particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu2O3–MgO–Y2O3 were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu2O3 doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m−1 K−1, significantly higher than the counterpart without Eu2O3 doping, or with ZrO2 doping by conventional methods.

The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.

The densification behavior, microstructural development, toughening and strengthening mechanisms of Al2O3 whisker-reinforced 3Y-TZP and 12Ce-TZP composites were systematically and comparatively investigated with varying whisker lengths. Compared with 3Y-TZP/Aw composites, the presence of a Ce-Al-Si-O amorphous phase, caused by the addition of Al2O3 whiskers, promoted the densification and grain growth of 12Ce-TZP/Aw composites. Crack deflection and bridging are proposed as the primary toughening mechanisms for 3Y-TZP/Aw composites, while the t-m martensitic transformation would dominate the toughening and strengthening processes of 12Ce-TZP/Aw composites. Changes in Al2O3 whisker length would vary the distributions of internal stress and amorphous phase within the ceria-stabilized ZrO2 matrix, and hence affect the toughening and strengthening results. It indicates that effective toughening and strengthening of the Al2O3 whisker-reinforced TZP composites can be achieved by taking advantage of collaborative engineering control on the reinforcement morphology and the interface chemistry/structure.

Starting from metal oxides, B4C and graphite, a suite of high-entropy boride ceramics, formulated (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2, (Hf0.2Zr0.2Mo0.2Nb0.2Ti0.2)B2 and (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 derived from boro/carbothermal reduction at 1600 °C were fabricated by spark plasma sintering at 2000 °C. It was found that the synthetic high-entropy boride crystalized in hexagonal structure and the yield of the targeting phase was calculated to be over 93.0 wt% in the sintered ceramics. Benefitting from the nearly full densification (96.3% ˜ 98.5% in relative density) and the refined microstructure, the products exhibited the relatively high Vickers hardness. The indentation fracture toughness was determined to be comparable with the single transition metal-diboride ceramics. It should be noted that the formation of high-entropy boride ceramics were featured with the relatively high hardness at no expense of the fracture toughness.

First-principles and experimental studies of fundamental mechanical (elastic moduli, Poisson ratio and hardness) and thermal (expansion coefficient) properties were compared to assess the responses in titanium carbide (TiC) based ceramic-metal (cermet) composite systems, and evaluate the potential for predictive modelling of cermet behaviour. The TiC cermets were prepared with 30 vol-% of stoichiometric nickel aluminide (Ni3Al) binder using a liquid phase sintering process, performed at 1500 °C for 60 min. Densities greater than 99% of theoretical were achieved under these conditions. The experimental elastic moduli were determined using a pulse-echo method, while hardness was assessed using the Vickers indentation test. The volumetric thermal expansion of the sample was studied using dilatometry.

Cermets based on titanium carbide with a nickel aluminide binder (TiC-Ni3Al) offer potential as substitutes for tungsten carbide (WC) based hardmetals due to their high wear and corrosion resistance at ambient and elevated temperatures. In the current work, the effects of post-sinter heat treatments (between 600 and 1340 °C) on atomic ordering of the Ni3Al have been assessed through Vickers indentation, scratch testing and computational modelling. Changes in the atomic structure are evidenced from X-ray diffraction by abrupt increases in the (111) and (200) peak intensities. An increase in Vickers hardness, from 1400 to 1530 HV, is observed as a result of heat treatment at 1200 °C. Furthermore, the scratch hardness value was improved from 11.89 to 18.12 GPa, with the main wear mechanisms being identified as TiC grain pull out and brittle fracture. Ordering transitions were subsequently related to the structural changes predicted through ab-initio modelling approaches.

Highly dense high-entropy boride ceramics with ultra-high hardness were prepared by spark plasma sintering of the self-synthesized high-entropy boride powders. High-entropy boride compounds of (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2, (Hf0.2Mo0.2Zr0.2Nb0.2Ti0.2)B2 and (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 with some oxide impurities were obtained by borothermal reduction at 1600 °C. The yield of the samples after sintering was improved to be 97.2 wt%, 92.8 wt% and 97.6 wt%. The densification and hardness of the high-entropy boride ceramics were remarkably enhanced after sintering the as-obtained powders at 2000 °C. The relative density of Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2 ceramics was 99.2% and the hardness achieved a value up to 28.3 ± 1.6 GPa, which was significantly higher than reported values.

TiC-Ni3Al cermets are potential replacement materials for WC-based hardmetals in several applications. Potential improvements to selected mechanical and tribological properties of these cermets are investigated, through addition of graphene nano-platelets (GNPs) to a baseline TiC-30 vol.% Ni3Al cermet system. GNP contents up to 2.5 vol.% were assessed, replacing Ni3Al in the overall composition, with samples vacuum sintered at 1550 °C for 2 h. GNP additions up to 2.5 vol.% increase the Vickers hardness (from ∼1060 to ∼1220 HV1) and indentation fracture resistance (from ∼14.2 to ∼16.7 MPa m0.5). GNP additions significantly lower the coefficient of friction, from ∼0.53 to ∼0.15, and the specific wear rate, from ∼15.5 to ∼1.7 × 10−6 mm3/Nm, when assessed with a pin-on-ring wear test geometry.

Titanium carbide (TiC) based cermets are commonly used in a variety industries because of their high hardness, strength and wear resistance. In many applications, such as bearings, cermets are exposed to ‘Hertzian-type’ loading scenarios. The present work is focused on the Hertzian indentation contact damage of a new family of TiC-316L stainless steel cermets. Samples were fabricated using a vacuum melt-infiltration procedure, at 1550 °C for between 60 and 240 min, with the steel binder contents ranging from 10 to 30 vol%. Various diameter WC-6Co spheres (nominally 10 vol% Co), from 1.19 mm to 3.97 mm, were used for indentation. The applied indentation loads were varied from 250 N to 2000 N. Indentation stress-strain curves were plotted to study the effects of differences in the cermet microstructure and the loading condition. ‘Ideal’ Hertzian elastic responses were also calculated, to demonstrate the deviation of the curves. It is shown that the materials deform in a ‘quasi-plastic’ manner, with evidence of ‘strain-hardening’ phenomena.

The objectives of this work were to assess the effects of incorporating Mo 2 C additions into TiN-Ni 3 Al cermets, in terms of their densification response and microstructural development. The individual powder components, together with the milled/compacted powder blends were characterised using differential scanning calorimetry and thermogravimetric analysis. Dilatometry was used to determine the densification and sintering response. It is demonstrated that an increase in the Mo 2 C content reduces both the melting and solidification temperature of the Ni 3 Al-based component of the system, which is initially formed via reaction sintering. Crystalline phases were identified using X-ray diffraction, which demonstrated that TiN and Mo 2 C are retained following sintering, and confirmed the formation of Ni 3 Al. The wettability of the Ni 3 Al binder was improved through additions of Mo 2 C, enhancing the densification process. A simple microstructural development model has been outlined, proposing that the Mo 2 C dissolves during liquid phase sintering, and re-precipitates as a shell on TiN grains either during sintering or solidification, which improves the wetting response between the nitride phase and intermetallic binder.

Peening is used across a wide range of materials to improve fatigue response. Recently, a new approach to peening has been developed using an ultrasonic-pulsed waterjet (UPWJ). In the present work, UPWJ peening has been conducted on a powder metallurgy derived aluminum-based metal matrix composite (Al-MMC), containing 5 wt% aluminum nitride (AlN) additions. Traverse speed is one of the most important parameters in UPWJ peening, which primarily modulates the mechanistic interaction between the waterjet and the target surface. In the current study, a focus was placed on assessing the effects of traverse speed (which was varied from 150 to 1000 mm/s), while the other primary process parameters, including the pressure, frequency and standoff distance were kept constant. Confocal laser scanning microscopy and scanning electron microscopy were used to evaluate the surface roughness and microstructure of the Al-MMC samples, in both un-peened and UPWJ peened states. The induced residual stress generated by UPWJ was also determined, with profiles obtained by electropolishing to remove micro-layers of material until an attenuation of the residual stresses was realized. It is shown that the Al-MMC was generally responsive to UPWJ peening. The surface roughness increased due to UPWJ processing, though the extent of increase was lower for increasing traverse speed. Mass losses were recorded at UPWJ traverse speeds lower than 500 mm/s due to material removal. Generally, the UPWJ peening process produced significant increases in compressive stresses, with the best combination of low surface roughness and high compressive stress obtained at a traverse speed of 700 mm/s.

High-density titanium carbide (TiC) based cermets were prepared using 10 to 30 vol% 304L grade stainless steel binder. A range of electrochemical techniques was applied to study the corrosion response in an aqueous solution (with 3.5 wt% NaCl), including potentiodynamic, cyclic and potentiostatic polarisation. Corroded samples were characterized using SEM and associated EDS, while the post-corrosion aqueous solutions were analysed by ICP-OES, to determine the dissolved solute ions and the composition of any particulate material released during corrosion. It is shown that by increasing the steel binder content the corrosion resistance of the cermets decreases slightly, which appears to be related to the preferential dissolution of the steel binder at higher rate when lower metallic content is selected. A general corrosion mechanism is seen, whereby the composites exhibit similar electrochemical characteristics. Single-phase analysis has confirmed that the 304L steel and TiC exhibit broadly similar oxidation properties, which eliminates the formation of galvanic couple at a controlled ratio between the metallic and ceramic phases.

The aqueous corrosion resistance of TiC–Ni3Al based cermets was examined with the specific aims of assessing the influence of both the raw materials and the test methods, using a 3.5 wt% NaCl containing solution. The effects of W contamination in the ceramic phase was investigated using a single-phase ceramic, with and without W, and with a stoichiometric intermetallic Ni3Al binder. The influence of the electrolyte O2 content was examined for TiC cermets with 30 vol% binder, for both the stoichiometric composition and sub-stoichiometric variants, containing either Zr and B (alloy IC50) or Zr, B and Cr (alloy IC221) additions. Electrochemical measurements were matched with chemical and microstructural analyses at various stages of oxidation, and the rate of material loss in combination with the corrosion mechanisms were identified. The effects of O2 concentration were most significant for the TiC based cermets with Ni3Al due to the diffusion controlled nature of the reaction.

In the current work the corrosion mechanisms of Ti(C,N) based cermets are analysed in a 3.5 wt.% NaCl aqueous solution. The effects of varying the Ni 3 Al intermetallic binder content are assessed, with either 20 or 30 vol.% binder used. The assessment of corrosion involved a variety of electrochemical measurements, including open circuit potential, along with anodic and cathodic potentiodynamic polarisation. Both the corrosion potential and current density were determined from Tafel extrapolation, which allowed an estimation of the cermet corrosion rates. It is demonstrated that the primary corrosion mechanism for these cermets involves dissolution of the intermetallic phase during oxidation attack, and thus this response increases with the amount of binder in the cermet. It was also observed that addition of N to the Ti(C,N) ceramic phase is beneficial to the corrosion characteristic the cermets, due to significant refinement of the grain size of the hard phase.

The structural and/or functional design of multiphase ceramics, along with their processing, are timely research topics in the area of field-assisted sintering techniques, such as spark plasma sintering, especially for systems containing both electrically insulating and conductive phases. In the present study, spark plasma sintering of Si3N4&ndash, TiN composites was investigated by changing the TiN particle size and electrical current waveform. Their combined effects on both the densification behavior and &alpha, to-&beta, phase conversion of the Si3N4 matrix was studied and compared by means of a thermodynamic approach and dilatometric measurements. Through the control of TiN phase characteristics and heating mode, double-layered Si3N4-based components were also prepared using a one-step spark plasma sintering process, which was compared with conventional hot-pressing. It was shown that the size of the conductive TiN phase has a significant influence on the particle rearrangement, with the formation of a liquid phase, and the solution&ndash, diffusion&ndash, precipitation process, through the field-induced local heating and electrowetting mechanisms. Moreover, the contribution of current pulsing to the densification and &alpha, conversion of the layered Si3N4-based components was mostly dependent upon the particle size distribution and content of the TiN phase, indicating that the electric-field effect is dependent upon current path.

A wide variety of commercial cylindrical lithium-ion batteries are available for use in nanosatellites (CubeSats) that cycle in low Earth orbit (LEO). This space application differs greatly from the conditions used to create the manufacturer datasheets that CubeSat teams rely on to screen cell types and estimate performance lifetimes. To address this, we experimentally test three LIB cell types using a representative LEO CubeSat power profile in three progressively complex test representations of LEO. The first is “standardized” condition (101 kPa-abs, 20 °C), which uses only a power cycler, the second adds a thermal chamber for “low temperature” condition (101 kPa-abs, 10 °C), and the third adds a vacuum chamber for “LEO” condition (0.2 kPa-abs, 10 °C). Results indicate that general “standardized” and “low temperature” conditions do not yield representative results to what would occur in LEO. Coincidentally, the “LEO” condition gives similar capacity degradation results as manufacturer datasheets. This was an unexpected finding, but suggests that CubeSat teams use full experimental thermal-vacuum testing or default to the manufacturer datasheet performance estimates during the lithium-ion cell screening and selection process. The use of a partial representation of the LEO condition is not recommended.

Titanium aluminide based alloys have shown significant potential in high temperature applications, but the high production cost of TiAl considerably limits its utilisation. Although the use of powder metallurgy processes can reduce the cost by minimising post-machining, an economical powder production route is still required. Therefore, in the present study a pre-alloyed Ti-48Al powder is developed using an elemental Ti and Al powder blend prepared using a simple vacuum heat treatment. A formation model of the intermetallic phases (i.e. TiAl, Ti3Al, TiAl2, TiAl3) during powder synthesis is proposed. In order to improve the sinterability, various milling methods (i.e. ball, attrition and shatterbox milling) are examined to reduce the particle size. The sintered microstructures, particularly the two-phased (α2-Ti3Al γ-TiAl) lamellar structures are also investigated. Improved densification is achieved at 1300 °C, held for 2 h, using the manufactured powder, compared to the elemental powder blend (∼55%). With higher sintering temperatures or longer hold periods, increased density TiAl components are possible.

High density TiC-based cermets were fabricated using a simple melt-infiltration/sintering method, with three different grades of stainless steel binder. Reciprocating wear tests were conducted using a ball-on-flat geometry, with the test material sliding against a WC-Co counter face. The morphology of the worn surface and wear debris were investigated using SEM and EDS chemical analysis. FIB microscopy was applied to study sub-surface damage within the wear tracks, to aid explanation of the operative wear mechanism(s). The wear behaviour is moderately complex, transitioning from two- to three-body abrasive wear, with both steel binder extrusion and TiC fragmentation observed to contribute towards third-body formation. A further transition to adhesive wear is also observed, with tribolayer generation on both tribo pair surfaces.

TiC based cermets have been prepared with three different grades of stainless steel binder (304L, 316L and 410L). The cermets were densified by vacuum melt infiltration, at 1500 °C, which allows the steel binder content to be readily varied from 5 to 30 vol%. The cermets were assessed for their hardness and indentation fracture resistance using Vickers testing. The reciprocating wear response was evaluated using a ball on flat geometry, with a WC-Co counter face sphere. It was shown that the coefficient of friction increases with increasing steel binder content, and also with increasing load and wear time. Similarly, the specific wear rate increases with both steel binder content and applied load, but was largely independent of the steel grade used.

Titanium carbide (TiC) based cermets are commonly used as wear resistance and corrosion resistance components. In the present work, the effects of microstructure of TiC-316L stainless steel cermets are assessed in terms of Vickers indentation damage, with both the steel binder content and TiC grain size varied. Binder contents from 5 to 30 vol.% were examined, with samples fabricated using a simple vacuum melt-infiltration procedure at temperatures between 1475 °C and 1550 °C (held for up to 240 minutes). Two primary Vickers indentation-cracking patterns arise in these materials, namely median or Palmqvist cracks, and this response relates to both the volume fraction of ductile metal binder present and the binder ligament dimension. Focused ion beam microscopy has been utilised for sub-surface evaluation of the cracks, to confirm the anticipated crack patterns.

The aqueous corrosion behaviour of TiC and Ti(C,N) based cermets, sintered with 30 vol.% Ni3Al binder, has been investigated. For comparison purposes, the single-phase constituents were prepared using spark plasma sintering (SPS). The potentiodynamic and cyclic polarisation responses of the cermets and single-phase materials have been determined. Post-test corrosion solutions were analysed using inductively coupled plasma optical emission spectrometry, while samples were evaluated using scanning electron microscopy and associated energy dispersive X-ray analysis. Selective attack of the binder occurs, while the extent of corrosion and primary operative mechanism depends on the C:N ratio in the Ti(C,N).

This work explores the incorporation of Mo2C additions into TiC0.3N0.7–Ni3Al cermets from a thermal analysis perspective. The individual powder components were first characterised through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was observed that increasing concentrations of Mo2C decreased the onset temperature of both melting and solidification of the Ni3Al. Higher concentrations of Mo2C showed this decrease to be the result of peak convolution and that a secondary peak developed in both the melting and solidification peaks. This second peak is likely associated with the formation of a Mo-rich alloy phase, present in all microstructures containing both TiC0.3N0.7 and Mo2C. Additionally, weight loss observed in pure Mo2C powder, and attributed to the sublimation of MoO3, is not observed in the cermets prepared within this paper. It is thus suggested that Mo is incorporated into the Ni3Al through the reduction of MoO3, which explains the enhanced dissolution of Mo2C observed in previous studies.

Spark plasma sintering (SPS) is a fairly novel powder metallurgy (PM)-based process. Compared with more traditional PM processes, SPS technology provides greater sintering efficiency for the Ti-48Al alloy, due to its fast heating and cooling rates, combined with an applied pressure and electric field during the process. In this study, three fundamental processing parameters (i.e. sintering temperature, time and particle size) are investigated, and their effects on densification, hardness and phase transformations are studied. Three grain morphologies were found in the microstructures, present in different ratios in the samples, depending on the sintering parameters. A model is proposed to explain the (α2) grain-phase growth and the transformation of two types (fine and coarse) of lamellar structural development. The pore configurations (i.e. size and quantity) are examined, and their interactions with the phases, which suggest the phase-formation sequence and sintering state, are also discussed.

Titanium carbide (TiC) based cermets are commonly used in wear and corrosion resistance applications. The microstructural evolution, and related compositional instability, of TiC-based cermets prepared with a 316-L stainless steel binder is described in the present work. Samples were fabricated using a simple vacuum melt-infiltration procedure, with 5 to 30 vol.% binder. Infiltration temperatures ranged from 1475 °C to 1550 °C, held for up to 240 min, typically resulting in sintered samples with densities in excess of 99% of theoretical. It is demonstrated that irregularly shaped grains (concave/hollow) can arise after sintering, especially at 1475 °C, which is discussed in terms of the ‘instability of the solid-liquid interface’ theory. It is demonstrated that a complex, multi-layer core-rim structure arose for the cermets, with accommodation of selected steel constituents into the rim of the TiC grains. In particular, it is shown that the Mo in the original 316-L stainless steel is essentially fully depleted from the metallic binder phase, forming a Mo-rich inner-rim layer on the TiC grain cores.

TiC-based cermets are heavily utilised in applications demanding good resistance to both wear and corrosion. In the current work, TiC-stainless steel (grade 316L) cermets have been developed, with the TiC grain size varied through heat-treatment, for steel binder contents between 10 and 30 vol%. Microstructural analysis showed mean TiC grain sizes of ~4 and 10 μm, respectively, for fine- and coarse-grained cermets, with the grain size nominally consistent as a function of binder content. Sliding wear resistance was assessed in a reciprocating motion, using a WC–Co counter face sphere paired against the TiC cermets. Overall, the fine-grained cermets exhibit better wear resistance and hardness. The specific wear rate was seen to increase with applied load and/or binder content, for both fine- and coarse-grained materials. SEM and FIB microscopy were used to assess the microstructural changes occurring during wear. A two- to three-body abrasive wear transition was apparent, together with the formation of a surface tribolayer, which highlights a further evolution to an adhesive wear mechanism. The tribolayer showed incorporation of a high concentration of O, which increased with the applied load, together with a predominance of the binder constituents.

Nano-sized AlN powders were successfully synthesized using a wet chemical route, with dicyandiamide as the nitrogen source reagent. The influence of dicyandiamide/metal precursor molar ratio on the purity, crystallization, microstructure, and optical properties of the calcined powders were studied. The underlying reaction mechanisms, along with the intermediates formed during the reactions, were also investigated. The compositions and morphologies of the as-received and prepared powders were subsequently characterized using XPS, FTIR, XRD, SEM, and TEM. The optical properties of the prepared powders were measured by ultraviolet–visible spectroscopy (UV–Vis). The precursor components decompose, and follow a complex reaction sequence as a function of temperature, finally leading to AlN formation at 800 °C. Increasing AlN content is achieved between 800 and 890 °C. Essentially only AlN arises following calcination at 900 °C. The AlN crystallite size and degree of crystallization further increase when calcining at 1000 °C. This work demonstrates a promising route to produce nano-sized AlN powders with favorable microstructures and optical properties.

Three types of 18-65 cylindrical lithium-ion cells with different positive active materials (NCA – nickel cobalt aluminium, NMC – nickel manganese cobalt, LFP – lithium iron phosphate), negative active material graphite average particle sizes (2 – 30 µm) and electrode designs (high power, high energy) were tested using an accelerated low earth orbit (LEO) CubeSat power profile cycle. Each design yields a unique energy density, power capability and cycle life. Each cell type was tested in a 3P group configuration at 10°C in atmospheric pressure (101 kPa-abs) and under vacuum (0.2 kPa-abs). Cell groups were operated in their respective pressure condition until they failed to successfully execute the accelerated LEO cycle. In atmospheric pressure and vacuum, both NMC groups failed due to internal resistance (IR) growth. The atmospheric pressure NCA group failed due to excessive internal gas build-up triggering the current interrupt device (CID) to electrically disconnect. The NCA group in vacuum failed from both IR growth and capacity degradation. The LFP groups both in atmospheric pressure and vacuum have completed approximately 5078 LEO cycles or 2800 equivalent cycles of initial measured coulombic capacity and are still operational with 19% and 21% capacity degradation from their initial measured coulombic capacity, respectively.

TiC–Ni3Al samples were successfully fabricated with varying amounts of the Ni3Al intermetallic binder (alloy IC-50), ranging from 10 to 40 wt-%, through a simple melt-infiltration method. Each sample was then tested to determine the degree of resistance of that composition to electrochemical corrosion in an aqueous solution containing 3.5 wt-% NaCl, using a range of testing procedures including open-circuit potential, potentiodynamic polarisation and cyclic polarisation. Results indicate that the lowest binder content results in greater potential to resist corrosion. It is demonstrated that the Ni3Al binder undergoes dissolution for the examined conditions, which was confirmed through the high amount of Al and Ni in the electrolyte solutions following testing. It was also confirmed from the electrochemical experiments and the SEM that localised corrosion was visible.

Core–shell structure positive electrode materials, based on layered Li–Ni–Mn–Co oxides, could be the next generation of positive electrode materials for high energy density lithium-ion batteries. Diffusion of the transition metal cations between the core and shell phases occurs during sintering, which can significantly affect the final core–shell (CS) properties. However, the interdiffusion constants have never been measured. Laminar pellets of the pure core phase and pure shell phase were pressed in contact and then heated to measure the interdiffusivity of the transition metals at various temperatures. The diffusion couples Ni3+/Co3+, Co3+/Mn4+, and Ni3+/Mn4+ were measured by analyzing composition versus position, with respect to the initial interface between the core and shell phase pellets. The transition metal composition profiles were measured with energy dispersive spectroscopy (EDS) line scans. This is the first time interdiffusion constants have been reported in the layered cathode materials to o...

The simple press-and-sinter powder metallurgical technique has provided an economical route for the manufacture of components from lightweight alloys, including titanium. However, the issue of residual porosity is limiting Ti alloy use in demanding applications. The presence of a liquid phase during sintering can potentially facilitate diffusion, leading to improved densification. In the present work a comparison of liquid phase sintering mechanisms is undertaken, with either persistent or transient liquid formation, for Ti–Ni and Ti–Sn alloys, respectively. Samples are produced using blended elemental powders, with up to 10 wt% alloying addition. Compacts were uniaxially pressed, and sintered at 1200–1400 °C. The benefit of Ni addition is significant in terms of sintering, with close to full density (~99.5% of theoretical) achieved for optimised conditions. Sn additions also exhibit a beneficial sintering response, particularly at lower temperatures (

Combining hard but brittle Ti(C,N) ceramic particles with the ductile Ni 3 Al intermetallic produces a ceramic–metal composite, or cermet, with high wear resistance. However, for high N content Ti(C,N) cermets, the wettability of molten Ni 3 Al is relatively poor, which leads to materials with residual porosity when a low binder volume fraction is used. Through a reaction sintering process, various amounts of Mo 2 C (from 1.25 to 10 vol.%) were incorporated into TiC 0.3 N 0.7 –Ni 3 Al cermets, with the aim of improving the densification behaviour. Materials were prepared with Ni 3 Al binder contents from 20 to 40 vol.%, and were densified by vacuum sintering. Mo 2 C was found to improve upon the wettability during sintering, thus enhancing the densification, especially for the lowest binder contents. The sliding wear and Vickers indentation behaviour of these cermets were assessed. It was found that Mo 2 C additions had a positive effect on both the hardness and indentation fracture resistance of the samples, but had a detrimental effect on the sliding wear response of the cermets. This behaviour was attributed to increased microstructural inhomogeneity with Mo 2 C additions.

High-nickel, cobalt-free, single-crystal positive electrode materials could provide the ultimate intersection of high-specific capacity, low cost, and long-lifetime in lithium-ion batteries. In this work, the synthesis of LiNiO2, LiNi0.975Mg0.025O2, and LiNi0.95Al0.05O2 is studied by dynamic XRD during heating, in order to guide improvements in synthesis procedures. A comparison of Li2CO3 and LiOH·H2O lithium sources shows that either can be used to prepare these materials, but Li2CO3 requires a higher temperature. Mg doping is shown to be beneficial in lowering the temperature required to get fully lithiated, crystalline material. Additional experiments show that synthesis with a 480 °C preheat step, or synthesis directly from individual metal hydroxides (without a precursor), could be used as potentially viable alternative synthesis methods.

TiC and Ti(C,N) based cermets offer several improved characteristics relative to conventional WC-based “hardmetals”, such as lower mass and improved oxidation resistance, which are combined with high toughness, hardness and wear resistance. In the present work the tribological behaviour of TiC and Ti(C,N) cermets has been evaluated under reciprocating sliding conditions. The cermets were produced using an in-situ, reaction sintering procedure to form the stoichiometric Ni3Al binder, with the binder contents varied from 20 to 40 vol%. Wear tests were conducted using a ball-on-flat geometry, with a WC–6 wt% Co sphere as the counter-face material, for loads from 20 to 60 N. The wear response was characterised using a combination of optical profilometry, scanning electron microscopy, energy dispersive X-ray spectroscopy, and focused ion beam microscopy. Initially, two-body abrasive wear was observed to occur, which transitions to three-body abrasion through generation of debris from the cermet and counter-face materials. Ultimately, this wear debris is incorporated into a thin tribolayer within the wear track, which indicates a further transition to an adhesive wear mechanism. It was found that specific wear rates of the cermets increased with both applied load. The highest wear resistance was found for intermediate Ni3Al contents.

The room temperature electrochemical response of TiC-based cermets, with 10 to 30 vol.% 316L stainless steel binder and either fine- or coarse-grained TiC, has been investigated in an aqueous 3.5 wt.% NaCl solution. The assessment methods included Tafel extrapolation, in combination with potentiodynamic and potentiostatic polarisation. Corroded samples were characterised using SEM, with post-corrosion solutions analysed using ICP-OES. The highest corrosion resistance was achieved at the lowest binder contents, while those with a more coarse-grained structure generally showed superior resistance, due to a reduced TiC–316L interfacial area. Preferential dissolution of the steel binder was observed, leaving the TiC essentially unaffected.

Ferroelectric ceramics have a wide range of industrial applications. While components can be formed through simple ‘press and sinter’ approaches, there is an increasing need for more flexible processing methods. Suspension based forming promotes greater homogeneity, through elimination of processing defects, and allows the formation of more complex shaped components. In the present work, the application of aqueous gel casting technologies is reviewed, and in particular the use of natural biopolymers as gelation aids for such approaches. Recent studies of the application of such technology to complex shape forming of BaTiO3 ferroelectric ceramics are examined. Emphasis is placed upon a simple subtractive rapid prototyping method, utilizing aqueous gel casting in combination with green machining.

Herein, we demonstrate the fabrication of tungsten boride from high-purity tungsten (W) and boron (B) powders through mechanical alloying (MA), followed by spark plasma sintering (SPS) for the first time. First, WB2 powders are synthesized by mechanical alloying, which is achieved by high energy ball milling for 50 h. The phase composition and microstructure of the as-milled powders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-milled WB2 powders possess an AlB2-type structure, with a crystallite size of 5–10 nm. The as-synthesized powders are sintered by SPS at 1600 °C, under the pressure of 30 MPa, for 10 min and 5 wt % of MgO is added as a sintering aid. Furthermore, the as-sintered WB2 and MgO-added WB2 ceramics are characterized by XRD, SEM and microindentation. The results reveal that the metastable AlB2-type WB2 phase has been transformed into a stable WB2-type WB2 phase after sintering. Moreover, a slight increase in the Vickers hardness is observed due to the addition of MgO, which can be ascribed to the grain refinement effect in the presence of sintering aid.

Due to increasing atmospheric carbon dioxide (CO2) concentration, energy sources that release smaller amounts of CO2 to the atmosphere are of considerable interest. Attention is also now being paid to sequestering CO2 from the combustion process and eliminating discharge to the atmosphere from the major source points. Chemical-looping combustion (CLC) is a promising concept that can be used in power generation, which integrates power production and CO2 capture. In the present study, a commercially obtained iron ore was used as an oxygen carrier and the associated reduction reaction kinetics parameters have been estimated based on isothermal thermogravimetric analysis (TGA) in reducing environments. The iron oxide in the ore, which is initially Fe2O3, proceeds through a sequence of reaction steps and can ultimately end up as metallic iron. The reduction mechanism for the first stage reaction (i.e., Fe2O3 to Fe3O4) was evaluated using a number of different gas–solid reaction models. The results indicate tha...

Friction stir processing (FSP) was applied to modify the microstructure of sintered Al–SiC composites with particle concentrations ranging from 4 to 16 vol%. Two SiC particle sizes (490N and 800 grades) were examined. Following FSP, the hardness of the 4 and 8 vol% of 490N grade SiC composites increased from 130 HV and 145 HV to 171 HV and 177 HV respectively. The increase was accounted for by the severe deformation occurring during FSP which uniformly distributed the SiC particles. The composites containing 16 vol% SiC could not be fully consolidated using FSP, and contained residual pores and lack of consolidation which originated from the as-received sintered microstructure. The hardness correlated well with the mean inter-particle spacing for the SiC particles in the case of composites containing 4 and 8 vol% SiC.

TiC-based ceramic–metal composites, or cermets, are widely used in applications requiring wear and corrosion resistance. In the present work, a family of novel TiC–stainless steel (grade 304L) cermets has been developed using vacuum melt infiltration (1500 °C/1 h), with steel binder contents varied from 5 to 30 vol%. Microstructural analysis showed a homogenous distribution of TiC within the steel binder, with mean TiC grain sizes of ∼6 μm. Increasing the steel content resulted in an increase in the indentation fracture resistance and a decrease in the hardness. The reciprocating wear resistance of the cermets was assessed using a ball-on-flat geometry, using a WC–Co sphere dry sliding on the polished cermet surface. It was shown that there is an increase in the specific wear rate with both increasing load and binder content. Similarly, a higher coefficient of friction was observed with higher steel binder contents. The morphology of the worn surface was investigated using scanning electron microscopy, and associated energy dispersive X-ray spectroscopy, to more fully understand the operative wear mechanisms. Evidence of a transition from two- to three-body abrasive wear was observed, together with the formation of a tribolayer, indicating that adhesive wear was also occurring.

Hydride/dehydride titanium powder has been processed using a conventional die compaction powder metallurgical approach. The effects of various processing parameters have been assessed in terms of the microstructure and mechanical behaviour, including lubricant type and amount, compaction pressure, delubrication atmosphere, and sintering conditions. While low lubricant contents can result in high sintered densities, a minimum lubricant content is required to maintain die life. It was also demonstrated that a compaction pressure of 300 MPa is sufficient to provide high sintered densities, while again minimising potential for die damage. Densities close to 99% of theoretical could be achieved when sintering at 1450°C for 4 h. Tensile strengths in excess of 750 MPa were obtained when sintering at 1300 or 1400°C. The mechanical behaviour was strongly influenced by a combination of intrinsic powder impurities (i.e. oxygen), residual carbon contamination from the lubricant, grain growth and retained poro...

Ti(C,N) based cermets have received significant attention due to their enhanced mechanical properties at elevated temperatures, low mass and increased chemical stability, when compared to WC–Co hardmetals. These properties have been found to be superior in many cases to traditional hardmetal replacements, such as TiC–Ni. The current study focuses on Ti(C,N)–Ni3Al cermets formed through melt infiltration (with binder contents ranging from 20 to 40 vol.-%Ni3Al). Comparison is made with TiC–Ni3Al cermets using an identical binder alloy. The reciprocating ball on flat wear properties of the cermets were evaluated as a function of applied load (using a WC–Co counterface), together with the composite hardness and indentation fracture resistance. It is shown that nitrogen content negatively affects infiltration, resulting in non-infiltrated areas within low binder content cermets, which decreases the indentation fracture resistance and hardness. This problem can be largely mitigated by increasing binder ...

TiC-based cermets have become more popular as a replacement to traditional WC–Co ‘hardmetals’ due to their superior mechanical properties at elevated temperatures, improved corrosion resistance and significantly lower density. The current study assesses the reciprocating wear response of TiC–Ni 3 Al cermets fabricated by melt infiltration, with Ni 3 Al binder contents ranging from 20 to 40 vol.%. Wear testing was performed using a ball-on-flat geometry, with a WC–Co sphere used as the counter-face material. It is demonstrated that the cermets are affected by similar wear mechanisms for each of the binder contents, but displayed the lowest wear when prepared with 30 vol.% Ni 3 Al. Additionally, the 40 vol.% samples displayed a clear transitional behaviour, with an improved wear resistance comparable to the 30 vol.% samples at low applied loads, but a degraded wear response comparable to the 20 vol.% samples at high applied loads.