Zirconium diboride (ZrB₂)–silicon carbide (SiC) composites are promising candidates for ultra-high temperature applications, yet optimizing their densification and mechanical performance without sintering additives remains a challenge. This study systematically investigates the independent and combined effects of three critical spark plasma sintering (SPS) parameters, that is, temperature, applied pressure, and dwell time, on the densification behavior, microstructure, and mechanical properties of ZrB₂–20 vol% SiC composites. Building upon prior work on powder preparation effects (e.g., Tungsten Carbide (WC) vs. ZrO₂ milling), this research uniquely focuses on how precise control of sintering conditions alone can tailor final material characteristics. The results demonstrate that optimizing sintering parameters yields significant property enhancement, achieving a maximum relative density of 99.2% (at 2100°C, 65 MPa, 15 min) and peak flexural strength of 516 MPa (at 2000°C, 65 MPa, 60 min). Hardness and fracture toughness reached 17.08 GPa and 3.85 MPa m^1/2, respectively, under optimized conditions. Through detailed microstructural and performance analysis, this work explains the fundamental role of individual sintering parameters in governing densification kinetics and mechanical outcomes. The findings offer practical guidance for additive-free, energy-efficient processing of ZrB₂–SiC ceramics for advanced aerospace and thermal protection systems.

ZrC Ultra-High Temperature Ceramic is a promising material for future extreme environment applications. However, its susceptibility to oxidation at elevated temperatures poses a significant challenge. There remains unresolved controversy in literature regarding its oxidation kinetics and activation energies. The temperature, oxygen pressure and time effects on the oxidation and passivation of ZrC are still not fully understood. To address these questions, we fabricated near-stoichiometric ZrC ceramic via spark plasma sintering (SPS) and for the first time investigated the temperature-oxygen pressure-time (T-P-t) dependent oxidation kinetics of SPS-sintered ZrC. A three-stage oxidation mechanism including a passivation stage was reported. The study also revealed the complexity of activation energy dependence on temperature and pressure within the 3D T-P-t space. Additionally, it uncovered the conditions necessary to maintain the passivation of ZrC. These findings provide valuable insights for future design of oxidation-resistant ZrC and carbides, paving the way for advancements in materials for extremes.

An optimization-driven approach is presented to create a “double-tough” ceramic. The material features two main toughening mechanisms – crack deflection in a brick-and-mortar microstructure, and transformation toughening in the mortar – and it is engineered to achieve high strength and fracture toughness levels simultaneously. The material design involves high-strength alumina bricks interconnected via a ceria-stabilized zirconia mortar. Given that the design of the optimal material, featuring multiscale toughening mechanisms, typically requires a laborious trial-and-error approach, a Bayesian optimization framework is proposed to streamline and accelerate the experimental campaign. A Gaussian process is used to emulate the material’s mechanical response, and a cost-aware batch Bayesian optimization is implemented to efficiently identify optimal design process parameters, accounting for the cost of experimentally varying them. This approach expedites the optimization of the material’s mechanical properties. As a result, a bio-inspired all-ceramic composite is developed, exhibiting an exceptional balance between bending strength (704MPa) and fracture toughness (13.6MPam^0.5), along with a stress intensity factor at crack initiation of 6.7MPam^0.5. The material exhibits significantly higher strength than both nacre-like ceramic composites and transformation-toughened zirconia at comparable toughness levels.

Superelastic metamaterials have attracted significant attention recently, but achieving such functionality remains challenging due to partial superelasticity and premature fracture in additively manufactured components. To address these issues, this study investigates the premature fracture in Ni-rich NiTi metamaterials fabricated by laser powder bed fusion. A comparative analysis of two structures (Gyroid network and Diamond shell) reveals that the structural stability of bending- and stretching-dominated structures is reversed compared to typical elastic-plastic response, due to the tension-compression asymmetry of base NiTi. The premature fracture and partial superelasticity of these as-fabricated samples are attributed to low deformation ability for accommodating tensile stress. Based on these findings, a heat treatment introducing Ni₄Ti₃ precipitates was employed, successfully achieving macroscopic superelasticity in the NiTi metamaterials, with consistency between model prediction and experiments.

This study investigates the impact of different powder milling methods on the densification and mechanical properties of ZrB₂-SiC ceramic composites processed via spark plasma sintering (SPS). Powders were prepared using two ball milling techniques: tungsten carbide (WC) and conventional ZrO₂. The densification behavior during SPS was monitored, and the sintered samples were evaluated for their relative density, hardness, fracture toughness, and flexural strength. Results show that WC milling significantly enhances densification, achieving 99.2 % relative density at 2100 °C/65 MPa/15 min, compared to 96.5 % for ZrO₂-milled samples. This improvement is due to WC's sintering aid effect, which promotes grain boundary diffusion and particle packing. However, ZrO₂-milled composites exhibit superior hardness (17.38 GPa) and fracture toughness (3.97 MPa m¹/²), attributed to their refined grain structure and the absence of softer ZrO₂ phases. Conversely, WC-milled samples show slightly higher flexural strength (384–516 MPa), likely due to the transformation toughening effect of the secondary ZrO₂ phase. Overall, WC milling improves densification and flexural strength, while ZrO₂ milling yields finer-grained composites with higher hardness and toughness, making it better suited for wear-resistant and mechanically demanding applications.

Boron doped MoSi₂ particles have been envisioned as sacrificial particles for self-healing thermal barrier coatings (TBCs) but their oxidation behaviour is yet not well understood. In this work, oxidation of MoSi₂ based particle is studied in the temperature range of 1050–1200 °C. The oxidation proceeds from a transient to a steady-state oxidation stage. The kinetics during steady-state oxidation is captured with a thermal diffusion-based model. As compared to the oxidation of pure MoSi₂ particles, the addition of boron strongly enhances the silica formation. Also, a finer dispersion of MoB_x in the MoSi₂ matrix accelerates the formation of silica. The oxide growth rate constant increases proportional with the boron content of the MoSi₂ particles. This enhanced oxidation is related to the microstructure of the oxide scale. Upon oxidation, boron yields B₂O₃, which promptly merge with SiO₂ to form amorphous borosilicate, hindering the formation of crystalline SiO₂. Consequently, the migration of oxygen in the borosilicate oxide scale is faster than in the silica oxide scale on pure MoSi₂ particles.

In this study, we experimentally screen a promising class of intermetallic alloys for the electrochemical reduction of CO₂ toward hydrocarbon products. Based on previous DFT-based screening papers, combinations of strongly CO-binding metals such as iron, cobalt, and nickel with weakly CO-binding metals such as gallium, aluminium or zinc were selected as potentially promising catalytic materials. Despite the challenging production of these alloys, we report a general two-step synthesis method for intermetallic alloys and discuss the specific synthesis conditions that must be taken into account when synthesising these materials. After their synthesis, we use a recently developed differential electrochemical mass spectrometry (DEMS) setup to rapidly quantify the CO₂ reduction products over a range of potentials. Almost all newly developed intermetallic catalysts are shown to produce methane and ethylene, while the CoSn catalyst showed higher selectivity towards formate production. However, all tested catalysts mostly produced hydrogen and only reduce CO₂ to a small extent, despite the favourable computational screening results. We discuss possible reasons for this discrepancy and outline a more holistic approach for linking future DFT studies with experiments.

Boron containing MoSi₂ is a promising material for applications at high temperature, but the oxidation mechanism is still unclear. In this work, the high temperature (1100 °C) oxidation of B doped MoSi₂ in synthetic air has been investigated. A (boro)silicate layer is formed on the surface of the alloy, which features a mixture of amorphous SiO₂ and cristobalite. After an initial transient period, the oxidation kinetics follows a parabolic growth rate law. The growth rate constant of the oxide layer is enhanced by the boron in the alloy by 90 % per at.% B. The increase in growth rate is associated with boron mitigating the formation of cristobalite thereby promoting the formation of amorphous SiO₂.

The pursuit of enhancing NiTi superelasticity through laser powder bed fusion (L-PBF) and [001] texture creation poses a challenge due to increased susceptibility to hot cracking in the resulting microstructure with columnar grains. This limitation restricts NiTi's application and contributes to material waste. To overcome this, we introduce a pioneering approach: utilising spark plasma sintering (SPS) to heal directional cracks in [001] textured L-PBF NiTi shape memory alloy. Diffusion bonding and oxygen utilisation for Ti₂NiO_x formation was found to successfully heal the cracks. SPS enhances mechanical properties, superelasticity at higher temperatures, and two-way shape memory strain during thermomechanical cycling. This work provides an alternative solution for healing cracks in L-PBF parts, enabling the sustainable reuse of cracked materials. By implementing SPS, this approach effectively addresses hot cracking limitations, expanding the application potential of L-PBF NiTi parts while improving their functional and mechanical properties.

Since the oxidation reactions in the process of steel production occur in harsh conditions (i.e., high temperatures and gas atmospheres), it is practically impossible to observe in situ the compositional changes in the steel and the formed oxide scale. Hence, a coupled thermodynamic-kinetic numerical model is developed that predicts the formation of oxide phases and the composition profile of the steel alloy’s constituents in a short time due to external oxidation. The model is applied to high-temperature oxidation of Fe–Mn alloys under different conditions. Oxidizing experiments executed with a thermogravimetric analyzer (TGA) on Fe–Mn alloys with different Mn contents (below 10 wt %) are used to determine kinetic parameters that serve as an input for the model. The mass gain data as a function of time show both linear and parabolic regimes. The results of the numerical simulations are presented. The effect of different parameters, such as temperature, Mn content of the alloy, oxygen partial pressure, and oxidizing gas flow rate on the alloy composition and oxide phases formed, is determined. It is shown that increasing the temperature and decreasing the oxygen partial pressure both lead to a thicker depleted area.

To prevent premature triggering of the healing reaction in Mo-Si containing self-healing thermal barrier coating system, an oxygen impenetrable shell (α-Al₂O₃) around the sacrificial healing particles (MoSi₂) is desired. Here an encapsulation method is presented through selective oxidation of Al in Mo(Al_xSi_1-x)₂ particles. Healing particles of Mo(Al_xSi_1-x)₂ is designed in terms of alumina shell thickness, particle size and fraction Al dissolved. By replacing Si by Al in MoSi₂ up to the maximum solubility (x = 0.65) a strong crack healing ability is maintained (relative volume expansion ≥ 40 %). The formed exclusive α-Al₂O₃, featuring a two-layered structure, results from a counter-diffusion process along the grain boundaries, and its oxidation kinetics fits well with the 3D diffusion-Jander model. After 16 h exposure in gaseous ambient with a pO₂ of 5 × 10^-10 atm. at 1100 °C, a closed and dense shell of α-Al₂O₃ is formed with a thickness of about 1.3 µm. The oxide shell produced under this condition provided healing particles with significantly improved stability upon exposure to high pO₂ of 0.2 atm. at 1100 °C for 50 h. The particles after exposure feature an inner core of MoSi₂ with Al completely consumed and an oxide shell of α-Al₂O₃.

Mo(Al_xSi_1-x)₂ alloy with x in the range of 0.35–0.65 were prepared by a one-step spark plasma sintering. To study the exclusive formation of an α-Al₂O₃ scale, oxidation experiments were conducted in low and high oxygen partial pressure ambient at 1373 K; viz.: 10⁻¹⁴ and 0.21 atm. The oxidation kinetics follows a parabolic rate law after a transient period. A counter-diffusion process of O and Al along grain boundaries of Al₂O₃ scale is responsible for the equiaxed and columnar grain growth based on a two-layered microstructure. The formation of a dense equiaxed α-Al₂O₃ layer contributes to excellent oxidation resistance.

The surface oxidation and wettability of Mn and Si-alloyed steel after annealing at different conditions are studied with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and a so-called de-wetting method. After exposure at 950 °C for 1 hour in an Ar + 5 vol pct H₂ gas atmosphere with dew points (DP) ranging from – 40 °C to 10 °C, oxides were observed along the grain boundaries or dispersed on the surface for the Fe–1.8 Mn steels while a continuous oxides layer was formed on Fe–1.9 Mn–0.94 Si steels (composition in weight fractions). The oxides formed at different DPs were predicted based on thermodynamic calculations. (Fe,Mn)O was formed on Fe–1.8 Mn steel at the whole range of DPs, while the oxide phase on Fe–1.9 Mn–0.94 Si steel depends on the DP. At low-DP SiO₂ were formed and with increasing the DP (Fe,Mn)SiO₃ or (Fe,Mn)SiO₃ + (Fe,Mn)₂SiO₄ were formed and finally (Fe,Mn)₂SiO₄ were formed. An increase of the fraction of Fe in the oxide with increasing DP for both steels was observed with XPS analysis. As a measure for the surface wettability, the contact angle of Pb droplets on the annealed steels surfaces was determined with SEM and image analysis software. Also, the contact angle of Pb on pure Fe and on the Mn and Si alloyed steels free of surface oxides was measured for comparison. The results show that the contact angle of Pb on the steel surfaces after annealing decreases with increasing DP. This improved wettability with increasing dew point is related to the Fe fraction of the oxides formed on the surface.

BiFeO ₃ is a multiferroic material with a perovskite structure that has a lot of potential for use in sensors and transducers. However, obtaining pure single-phase BiFeO ₃ ceramic with a low electrical conductivity via solid-state reactions remains a problem that limits its application. In this work, the suppression of secondary phases in BiFeO ₃ was studied by varying the compositional parameters and the sintering temperature. The addition of 1% Bi ₂O ₃ to the stoichiometric precursor mixture prevented the formation of secondary phases observed when sintering stoichiometric precursors. The pure phase ceramic had a p-type conductivity and a three-decade lower electrical conductivity as measured by impedance spectroscopy. Annealing of optimally synthesized material at different partial pressures of oxygen in an oxygen–nitrogen gas atmosphere showed that the reason for this type of conductivity lies in the high concentration of defects associated with oxygen. By annealing in various mixtures of nitrogen and oxygen, it is possible to control the concentration of these defects and hence the conductivity, which can go down another two decades. At a pO ₂  (Formula presented.) the conductivity is determined by intrinsic charge carriers in the material itself.

The present work deals with oxide dispersion strengthened (ODS) Eurofer steel fabricated by powder metallurgy involving mechanical alloying and spark plasma sintering. A heat treatment route including normalising and tempering was applied to the as-produced steel, based on differential scanning calorimetry (DSC) measurement. The microstructure was characterised by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), electrolytic extraction, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermodynamic calculations conducted using Thermo-Calc software were used to determine the precipitation conditions. The results show that the Vickers microhardness of the sample after the designed heat treatment is more uniform compared to the as-produced condition. A dual phase and bimodal microstructure is formed in the as-produced and tempered steels. M₂₃C₆ and M₆C carbides were found in the as-produced sample while only M₂₃C₆ carbides were observed in the tempered sample. The carbides dissolve and reprecipitate during the heat treatment, preferably at the grain boundaries. Nanosized Y₂O₃ particles were found to be homogenously distributed in the steel matrix, which is crucial for the mechanical properties. The dislocation density in the material is decreased significantly after the normalising and tempering treatment. A yield strength model was developed that includes the strengthening contributions of solid solutes, grain size, dislocation density and nanoparticles. Good agreement is obtained between the experimentally measured and theoretically calculated strength of the as-produced and tempered steels.

Bones of humans and animals combine two unique features, namely: they are brittle yet have a very high fracture toughness linked to the tortuosity of the crack path and they have the ability to repeatedly heal local fissures such that full recovery of overall mechanical properties is obtained even if the local bone structure is irreversibly changed by the healing process. Here it is demonstrated that Ti₂AlC MAX phase metallo-ceramics also having a bone-like hierarchical microstructure and also failing along zig-zag fracture surfaces similarly demonstrate repeated full strength and toughness recovery at room temperature, even though the (high temperature) healing reaction involves the local formation of dense and brittle alumina within the crack. Full recovery of the fracture toughness depends on the healed zone thickness and process zone size formed in the alumina reaction product. A 3-dimensional finite element method (FEM) analysis of the data obtained from a newly designed wedge splitting test allowed full extraction of the local fracture properties of the healed cracks.

Pulsed laser beam welding was used successfully to join the oxide dispersion-strengthened (ODS) Eurofer steel. The joining was conducted with a laser power of 2500 W and a pulsed duration of 4 ms. With the filler material being used, a minor material loss and microvoids were observed in the joint. The microstructure of the fusion zone consists of dual phase elongated structures. The heat-affected zone has a width of around 0.06 mm with finer grains. The transmission electron microscopy observation reveals that nanoprecipitates are finely distributed in the fusion zone. The tensile strength, yield strength and elongation of the joint are slightly inferior to the base material. The fractography results reveal a typical ductile fracture. The experimental results indicate a reasonable joint from the perspective of both the microstructure and mechanical behaviour.