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Nowadays high entropy carbides (HECs) are an important group of advanced ceramics. They are composed by at least by five transition metals (TMs) in nearly equiatomic proportion and disordered distributed in the cationic sublattice of face centered cubic structures, with carbon atoms in the octahedral interstitial voids, with general formula (TM1,TM2,TM3,TM4,TM5)C. These HECs belong to the recent novel group of ultra-high temperature ceramics (UHTCs), with superior properties in comparison with the constituent binary carbides. However, the synthesis of those HECs can be modified to develop high entropy carbonitrides, HECNs, where the C are partially substituted by N, to form a solid solution in the anionic sublattice, with expected improved properties as UHTCs, but they are in an incipient state of development. Here, we report the synthesis and deep characterization of a non-previously obtained Hf0.2Nb0.2Ta0.2V0.2Zr0.2C0.5N0.5 HECN, via a facile, single step and reproducible solid- gas reaction mechanosynthesis route. The synthesis was successfully completed in a planetary ball mill device, after 2h of milling time, at 400 rpm and using a ball-to- powder ratio of 60:1 in a pure N2 atmosphere at room temperature. The as-synthesized HECNs powdered showed nanostructured morphology and outstanding high- temperature oxidation resistance up to 1500ºC.

Water pollution by toxic dyes is an environmental problem that threatens human health. A green technology to solve this problem is the use of highly efficient photocatalysts under visible/solar light to degrade these organic molecules. However, develop affordable photocatalytic particles with high luminescence performance, enhanced stability, and low degradation is still a challenge. Here, it is reported the hydrothermal synthesis of an advanced and cost-effective nanocomposite based on a ceramic, cadmium sulphide, covered by silver nanoparticles (CdS/Ag), with outstanding photocatalytic efficiency for toxic dyes degradation under ultraviolet and direct solar light. The CdS/Ag nanocomposite completely degrade the Reactive Red 120 (RR 120), Acid Black 1 (AB 1) and Direct Blue 15 (DB 15) dyes in both light irradiations. Without scavenger, about 93% of degradation was observed at 75 min, remaining a high stability (more than 90%) after fourth degradation cycles.

Photocatalysis embraces prodigious ability as an efficient and sustainable oxidation technology for application in wastewater treatment. In general, a good photocatalytic material should have chemical stability, low production cost, and especially environment-friendliness characteristics. The present study involves the development of visible light active semiconductors by surface-grafted Fe(III) ions and bulk metal oxide. Fe-grafted ZnO nanocomposites were synthesized at two different temperatures. Initially, the precipitation-decomposition method was adopted for the ZnO preparation; later, surface of ZnO was grafted with Fe3+ ions at two different temperatures under basic condition. The prepared materials have been characterized by various characterization techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), High-resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectra (XPS), diffuse reflectance spectra (DRS) and Photoluminescence (PL) study. The degree of electron-hole recombination decreased in Fe-modified ZnOs as evidenced by PL measurements. The prepared materials used for naphthol blue black (NBB) dye destruction under visible light, and found that Fe modification slightly enhances the degradation ability of the ZnO. DRS measurements confirm the higher absorbance at the visible region in Fe/ZnOs materials. The catalyst was found to be reusable. A suitable degradation mechanism is proposed for the destruction of Naphthol Blue Black (NBB) dye by Fe-grafted ZnO nanocomposites under visible light.

Photocatalysis process has emerged as a prompt method for wastewater treatment and microbial disinfection. The development of visible light active (VLA) photocatalysts, especially Blue LED active (BLA) is a challenge task for the current research scenario towards pollutants degradation and real wastewater treatment. Here, we have developed a material which is highly active under Blue LED. BiOX (X = I or Cl) modified Na-K2Ti6O13 with two concentrations of BiOX was fabricated and effectively utilized for Acid Black 1 (AB 1) dye and tetracycline (TCN) degradations under Blue LED. The TCN degradation was also performed under white LED and direct solar light for comparison, and found that Na-K2Ti6O13/BiOX composite was very efficient in Blue LED and white LED than direct solar irradiation. The higher activity of Na-K2Ti6O13/BiOX in Blue LED confirmed by Blue light absorption of Na-K2Ti6O13/BiOX via DRS measurements. The bare Na-K2Ti6O13 is almost no active (≈10 %) under Blue LED, while Na-K2Ti6O13/BiOX showed 99 % degradation under the same condition for AB 1 degradation. The stability of the Na-K2Ti6O13/BiOX was tested against AB 1 dye degradation with multiple runs. The degradation intermediates of AB 1 and TCN were analysed by GC–MS, and suitable degradation pathways were proposed. The Na-K2Ti6O13/BiOX was tested real wastewater treatment via microbial disinfection under Blue LED. The prepared composite could be effectivity used for piolet or industrial scale level effluent treatment.

A gelatin-based hydrogel was infiltrated and degraded-released in two different titanium foams with porosities of 30 and 60 vol.% (Ti30 and Ti60 foams) and fabricated by the space holder technique to evaluate its potential to act as an innovative, alternative, and localised method to introduce both active pharmaceutical ingredients, such as antibiotics and non-steroidal anti-inflammatory drugs, and growth factors, such as morphogens, required after bone-tissue replacement surgeries. In addition, the kinetic behaviour was studied for both infiltration and degradation-release processes. A higher infiltration rate was observed in the Ti60 foam. The maximum infiltration hydrogel was achieved for the Ti30 and Ti60 foams after 120 min and 75 min, respectively. Further, both processes followed a Lucas-Washburn theoretical behaviour, typical for the infiltration of a fluid by capillarity in porous channels. Regarding the subsequent degradation-release process, both systems showed similar exponential degradation performance, with the full release from Ti60 foam (80 min), versus 45 min for Ti30, due to the greater interconnected porosity open to the surface of the Ti60 foam in comparison with the Ti30 foam. In addition, the optimal biocompatibility of the hydrogel was confirmed, with the total absence of cytotoxicity and the promotion of cell growth in the fibroblast cells evaluated.

Compositional and structural elucidation of the materials is important to know their properties, chemical stability, and electro-photoactivity. The heterojunction electrocatalyst and photocatalyst activity could open a new window for solving the most urgent environmental and energy problems. Here, for the first time, we have designed and fabricated Bi2O3/bismuth titanates modified with MOF-In2S3/CdIn2S4 materials by a stepwise process. The detailed structural elucidation and formation of mixed composite phases were studied in detail. It has been found that the formed composite was efficiently utilized for the electrocatalytic H2 production reaction and the photocatalytic degradation of tetracycline. XRD patterns for the metal-organic framework-In2S3 showed a main compound of MOF, and it was assigned to a MIL-53 MOF phase, with a monoclinic structure. The addition of CdCl2 onto the MOF-In2S3 phase effectively produced a CdIn2S4 flower platform on the MOF rods. The uniform dispersion of the bismuth titanates in MOF-In2S3/CdIn2S4 materials is detected by mapping of elements obtained by dark-field HAADF-STEM. Finally, the predictions of how to integrate experiments and obtain structural results more effectively and their common development in new heterojunctions for electro-/photocatalytic applications are presented. © 2023 The Authors. Published by American Chemical Society.

Hydrogen is the ideal energy vector to reduce our fossil-fuels dependency and diminish the climate change consequence. However, current production is still methane based. It is possible to produce hydrogen using bioethanol from the alcoholic fermentation of organic waste by chemical looping processes, but unfortunately current redox systems generate hydrogen with significant traces of CO. In the case of proton exchange membrane fuel cells (PEMFC), hydrogen must be highly purified to produce electricity. Here, high porosity interconnected Fe2O3 foams doped with 2 wt% Al2O3 were manufactured by the freeze-casting method, obtaining around 5.1 mmol H2 g1 sample of highly pure hydrogen (<10 ppm of CO) consuming only 3.42 mmol of ethanol on each redox cycles, with no deactivation. This result shows the possibility of using an abundant and inexpensive raw material as the iron oxide to scale-up the direct pure H2 production and facilitates its use in the automotive sector

Hydrogen is the next energy vector for a decarbonization society but industrial production is still methane-based. The Steam Iron Process (SIP) could provide a carbon-free production and safety storage option. Here, we show that a Fe2O3-3 wt% of Al2O3 foams created by freeze-casting withstand 10 redox cycles at different temperatures with no reduction in performance or pore shrinking. The use of stearic acid as a dispersant agent/binder produces the porous structure enhancement of the foam and promotes the early reduction of the hematite phase during foam sintering. The Al2O3 incorporation was detected as a solid solution in the Fe2O3 phase at the particle surface. This result is relevant as correlated the positive values of the zeta potential observed. Freeze-casted foams could improve long-term redox performances combining a unique tailored interconnected pore structure with a specific chemical composition.

In this work, a blend of Ti, Nb, and Mn powders, with a nominal composition of 15 wt.% of Mn, and balanced Ti and Nb wt.%, was selected to be mechanically alloyed by the following two alternative high-energy milling devices: a vibratory 8000D mixer/mill® and a PM400 Retsch® planetary ball mill. Two ball-to-powder ratio (BPR) conditions (10:1 and 20:1) were applied, to study the evolution of the synthesized phases under each of the two mechanical alloying conditions. The main findings observed include the following: (1) the sequence conversion evolved from raw elements to a transitory bcc-TiNbMn alloy, and subsequently to an fcc-TiNb15Mn alloy, independent of the milling conditions; (2) the total full conversion to the fcc-TiNb15Mn alloy was only reached by the planetary mill at a minimum of 12 h of milling time, for either of the BPR employed; (3) the planetary mill produced a non-negligible Fe contamination from the milling media, when the highest BPR and milling time were applied; and (4) the final fcc-TiNb15Mn alloy synthesized presents a nano-crystalline nature and a partial degree of amorphization.

Wicks are the main component of Loop Heat Pipe systems, whereby coolant liquid flow through their porous structure. They are usually formed by a primary wick to produce liquid transportation by capillary force, and a secondary wick that is continuously wetted by the liquid coolant. Traditionally, the two wicks are manufactured separately and subsequently joined, thereby creating an interface that reduces the liquid transfer efficiency. In order to overcome this situation, a gradient porous wick is proposed and successfully manufactured through the freeze-casting method in a single operation. The influence of two different dispersant agents, KD4® and stearic acid was studied on the processing parameters, final pore size and morphology, and capillarity performances. A variate of gradient porosity was obtained by applying a diverse thermal gradient and solidification front velocity during directional solidification. The rheological characterisation of the camphene-based NiO suspensions was performed using a rotational viscometer. The final pore size and morphology were characterised by Optical Microscopy, Field Emission Scanning Electron Microscopy, and X-ray computed tomography. The use of stearic acid improves the particle stabilisation and generates pore enlargement with an equiaxed pore structure, while commercial dispersant KD4® shows a dendritic pore morphology at lower thermal gradient.

The influence of the mechanical activation process and sintering atmosphere on the microstructure and mechanical properties of bulk Ti2AlN has been investigated. The mixture of Ti and AlN powders was prepared in a 1:2 molar ratio, and a part of this powder mixture was subjected to a mechanical activation process under an argon atmosphere for 10 h using agate jars and balls as milling media. Then, the sintering and production of the Ti2AlN MAX phase were carried out by Spark Plasma Sintering under 30 MPa with vacuum or nitrogen atmospheres and at 1200 °C for 10 min. The crystal structure and microstructure of consolidated samples were characterized by X-ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy. The X-ray diffraction patterns were fitted using the Rietveld refinement for phase quantification and determined their most critical microstructural parameters. It was determined that by using nitrogen as a sintering atmosphere, Ti4AlN3 MAX phase and TiN were increased at the expense of the Ti2AlN. In the samples prepared from the activated powders, secondary phases like Ti5Si3 and Al2O3 were formed. However, the higher densification level presented in the sample produced by using both nitrogen atmosphere and MAP powder mixture is remarkable. Moreover, the high-purity Ti2AlN zone of the MAX-1200 presented a hardness of 4.3 GPa, and the rest of the samples exhibited slightly smaller hardness values (4.1, 4.0, and 4.2 GPa, respectively) which are matched with the higher porosity observed on the SEM images.

Chemical looping water splitting systems operate at relatively high temperatures (450–800 °C) to produce, purify, or store hydrogen by the cyclic reduction and oxidation (redox) of a solid oxygen carrier. Therefore, to improve long-term operation, it is necessary to develop highly stable oxygen carriers with large specific surface areas. In this work, highly interconnected doped Fe2O3 foams are fabricated through the freeze-casting technique of a submicrometric camphene-based suspension to prevent Fe sintering and pore clogging during redox operation. The influence of the dopant elements (Al and Ce) over the pore morphology evolution, and redox performances are examined. The use of an Fe2O3 porous structure with initial pore size above 100 microns shows a significant reduction of the sample densification, and the addition of Al2O3 by the citrate method prevent the rapid formation of an Fe3O4 layer at the foams struts that diminish the reoxidation rate step in the redox processing.

In this work, the mechanical and bio-functional behavior of a TiNbTa alloy is evaluated as a potential prosthetic biomaterial used for cortical bone replacement. The results are compared with the reference Ti c.p. used as biomaterials for bone-replacement implants. The estimated mechanical behavior for TiNbTa foams was also compared with the experimental Ti c.p. foams fabricated by the authors in previous studies. A TiNbTa alloy with a 20–30% porosity could be a candidate for the replacement of cortical bone, while levels of 80% would allow the manufacture of implants for the replacement of trabecular bone tissue. Regarding biocompatibility, in vitro TiNbTa, cellular responses (osteoblast adhesion and proliferation) were compared with cell growth in Ti c.p. samples. Cell adhesion (presence of filopodia) and propagation were promoted. The TiNbTa samples had a bioactive response similar to that of Ti c.p. However, TiNbTa samples show a better balance of bio-functional behavior (promoting osseointegration) and biomechanical behavior (solving the stress-shielding phenomenon and guaranteeing mechanical resistance).

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (dWC) and cobalt volume fractions (VCo), implying different binder mean free paths ( Co), was studied. The mechanical strength was measured at 600º C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of theWeibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600ºC due to oxidation phenomena, but higherWeibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (Nf) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher KIc. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.

Porous titanium is a metallic biomaterial with good properties for the clinical repair of cortical bone tissue, although the presence of pores can compromise its mechanical behavior and clinical use. It is therefore necessary to characterize the implant pore size and distribution in a suitable way. In this work, we explore the new use of electrical impedance spectroscopy for the characterization and monitoring of titanium bone implants. Electrical impedance spectroscopy has been used as a non-invasive route to characterize the volumetric porosity percentage (30%, 40%, 50% and 60%) and the range of pore size (100–200 and 355–500 mm) of porous titanium samples obtained with the space-holder technique. Impedance spectroscopy is proved to be an appropriate technique to characterize the level of porosity of the titanium samples and pore size, in an affordable and non-invasive way. The technique could also be used in smart implants to detect changes in the service life of the material, such as the appearance of fractures, the adhesion of osteoblasts and bacteria, or the formation of bone tissue.

In this work, an equiatomic TiNbTaMoZr-based high-entropy alloy (HEA) has been developed by a powder metallurgy route, which consists of a process of combined one-step low-temperature mechanical milling starting from the transition metals as raw materials and a subsequent pressureless sintering. In this way, the optimized synthesized specimen, after 10 h of milling time, showed two di erent body-centered cubic (bcc) TiNbTaMoZr alloys, which, after sintering at 1450 C, 1 h of dwell time and a heating and cooling rate of 5 C min-1, it remained formed as two bcc TiNbTaMoZr-based HEAs. This material, with micrometric and equiaxed particles, and with homogeneously distributed phases, presented a Young’s modulus that was significantly higher (5.8 GPa) and lower (62.1 GPa) than that of the usual commercially pure (cp) Ti and Ti6Al4V alloy used for bone-replacement implants. It also presented similar values to those of the HEAs developed for the same purpose. These interesting properties would enable this TiNbTaMoZr-based HEA to be used as a potential biomaterial for bulk or porous bone implants with high hardness and low Young´s modulus, thereby preventing the appearance of stress-shielding phenomena

Titanium (Ti) and its alloys are used for biomedical applications because of their high resistance to corrosion, good strength-to-weight ratio, and high fatigue resistance. However, a problem that compromises the performance of the material is the mismatch between Young’s modulus of Ti and the bone, which brings about stress shielding. One strategy that has been investigated to reduce this di erence is the manufacture of Ti-based foams, using powder metallurgy (PM) methods, such as the space-holder technique. However, in the uniaxial compaction, both non-uniform density distribution and mechanical properties remain because of the compaction method. This work studies the influence of compaction by adopting a floating-action die related to a single-action die (SAD), on the density of green and sintered Ti foams with porosities around 50 vol.% characterized by optical microscopy, ultrasound analysis, compression tests, and microhardness. The compaction process employing a floating-action die generates Ti foams with a higher density up to 10% with more control of the spacer particle added compared to the single-action die. Furthermore, compaction method has no relevant e ect on microhardness and Young’s modulus, which allows getting better consolidated samples with elastic modules similar to those of human bone.

Objetivos Los implantes óseos son utilizados cada vez con mayor frecuencia en la práctica clínica y, entre los materiales, el Ti o sus aleaciones son los de mejor rendimiento por sus propiedades fisicoquímicas. Aleaciones como TiNbTa han demostrado mejorar las características biomecánicas del Ti puro comercial (c.p.), sin embargo, su capacidad osteointegradora necesita ser evaluada. El objetivo del presente estudio fue valorar la citotoxicidad y la capacidad de adhesión, proliferación y diferenciación de células osteoblásticas en cultivo, influida por discos de material TiNbTa frente a Ti c.p. Material y métodos Analizamos a los 4 y 7 días del cultivo la línea celular MC3T3, la viabilidad celular (AlamarBlue Cell Viability Reagent. Invitrogen, España), así como la proliferación y diferenciación celular (actividad de fosfatasa alcalina (ALP) y microscopía electrónica de barrido (Fijación para SEM). Se realizó la prueba t de Student para determinar diferencias estadísticamente significativas entre los dos grupos de discos de estudio. Resultados Los resultados obtenidos demuestran muy buena viabilidad celular durante el periodo de estudio, sin diferencias significativas para ambos materiales. Así mismo, detectamos una caída en los niveles de ALP que fue significativa para ambos componentes entre los días 4 y 7 del estudio (p<0,05). Las imágenes de microscopía electrónica revelaron buena capacidad de adhesión al material, así como diferenciación celular frente a ambos tipos de discos. Conclusiones La aleación de TiNbTa como material para implantes óseos cuenta con una buena capacidad osteointegradora, además de resolver problemas de biomecánica que presenta el titanio puro como componente., Objetive Bone implants are increasingly used in clinical practice and, among the materials, Ti or its alloys are offer the best performance given their physicochemical properties. Alloys such as TiNbTa have been shown to improve the biomechanical characteristics of commercial pure Ti (c.p.), however, its osseointegration capacity needs to be evaluated. The objective of the present study was to assess the cytotoxicity and the adhesion, proliferation and differentiation capacity of osteoblastic cells in culture, influenced by discs of TiNbTa material versus Ti c.p. Material and methods At 4 and 7 days after culture, we analyzed the MC3T3 cell line, cell viability (AlamarBlue Cell Viability Reagent. Invitrogen, Spain), as well as cell proliferation and differentiation (alkaline phosphatase activity (ALP) and scanning electron microscopy (Fixation for SEM) Student's t test was performed to determine statistically significant differences between the two groups of study discs. Results The results obtained show very good cell viability during the study period, with no significant differences for both materials. Likewise, we detected a drop in ALP levels that was significant for both components between days 4 and 7 of the study (p <0.05). Electron microscopy images revealed good adhesion capacity to the material, as well as cell differentiation against both types of discs. Conclusions The TiNbTa alloy as a material for bone implants offers good osseointegrative capacity, in addition to solving biomechanical problems that pure titanium presents as a component.

In this work, a titanium–tantalum carbonitride based cermet, with cobalt as the binder phase and boron as a sintering additive, was developed by a mechanically induced self-sustaining reaction process using two different methodologies. The boron additive was added to prevent the formation of brittle intermetallic compounds generally formed during the liquid phase sintering step due to the excessive ceramic dissolution into the molten binder phase. A systematic study was carried out to understand the effects of boron addition on the nature of the phases, microstructure, and mechanical properties of cermets. With the boron addition, the formation of two different boride solid solutions, i.e., (Ti,Ta)B2 and (Ti,Ta)3B4, was observed. Moreover, the nature of the binder was also modified, from the (Ti,Ta)Co2 brittle intermetallic compound (for cermets without boron addition) to ductile and tough (Ti,Ta)Co3 and -Co phases (for cermets with boron addition). These modifications caused, as a general trend, the increase of hardness and toughness in cermets.

An original (beta + gamma)-TiNbTa material was manufactured by an optimised powder metallurgy treatment, based on a mechanical alloying (MA) synthesis, carried out at low energy, and a subsequently field assisted consolidation technique, the pulsed electric current sintering (PECS). The successful development of this (beta + gamma)-TiNbTa material was possible by the optimisation of the milling time (60 h) for the MA synthesis and the load and sintering temperature for the PECS (30 MPa and 1500 °C), as key parameters. Furthermore, the selected heating and cooling rates were 500 °C min−1 and free cooling, respectively, to help maintain the lowest particle size and to avoid the formation of a detrimental high stiffness, hexagonal (alpha)-Ti alloy. All these optimised experimental conditions enabled the production of a full densified (beta + gamma)-TiNbTa material, with partially nanostructured areas and two TiNbTa alloys, with a body centred cubic (beta) and a novel face-centred cubic (gamma) structures. The interesting microstructural characteristics gives the material high hardness and mechanical strength that, together with the known low elastic modulus for the beta-Ti alloys, makes them suitable for their use as potential biomaterials for bone replacement implants.

In this work, a titanium boron carbonitride advanced ceramic was successfully synthesised by a solid-gas mechanochemical reaction in a planetary ball mill from a mixture of elemental Ti, B, and C under nitrogen atmosphere. This material, with a general formula of Ti(BCN), exhibits a face-centred cubic structure (NaCl type) that is analogous to Ti(CN). This phase was gradually formed with sufficient milling time as a result of diffusional processes, which were permitted by the reduction of the energy in the system caused by the decrease in the spinning rate of the planetary ball mill. In contrast, under more energetic milling conditions, a mechanically induced self-sustaining reaction (MSR) took place, leading to the formation of a TiB2-Ti(CN) ceramic composite. The microstructural characterisation revealed that Ti(BCN) was composed of ceramic particles constituted of misoriented nanocrystalline domains. B, C and N were optimally distributed in the Ti(BCN) phase. The TiB2-Ti(CN) ceramic composite was composed of micrometric and nanometric particles homogeneously distributed. Additionally, the nitrogen content obtained for Ti(BCN) was higher than for the Ti(CN) phase in the composite material.

The stress shielding and the poor osseointegration in titanium implants are still problems to be resolved. In this context, this work proposes a balanced solution. Titanium samples were fabricated, with a porosity of 100-200 µm of pore size employing space-holder technique (50 vol. % NH4HCO3, 800 MPa at 1250 ºC during 2h under high vacuum conditions), obtaining a good equilibrium between stiffness and mechanical resistance. The porous titanium substrates were coated with hydroxyapatite, obtained by sol-gel technique: immersion, dried at 80ºC and heat treatment at 450ºC during 5h under vacuum conditions. Phases, surface morphology and interfacial microstructure of the transverse section were analyzed by Micro-Computed Tomography, SEM and confocal laser, as well as the infiltration capability of the coating into the metallic substrate pores. The FTIR and XRD showed the crystallinity of the phases and the chemical composition homogeneity of the coating. The size and interconnected pores obtained allow the infiltration of hydroxyapatite (HA), possible bone ingrowth and osseointegration. The scratch resistance of the coating corroborated a good adherence to the porous metallic substrate. The coated titanium samples have a biomechanical and biofunctional equilibrium, as well as a potential use in biomedical applications (partial substitution of bone tissue).

The effect of the temperature on the mechanical strength of WC-Co cemented carbides with different microstructures (grain size and binder content) was evaluated. Biaxial flexural tests were performed on three cemented carbide grades at 600 °C using the ball-on-three-balls (B3B) method. Results were interpreted by Weibull statistics and compared to biaxial strength results at room temperature. A detailed fractographic analysis, supported by Linear Elastic Fracture Mechanics, was performed to differentiate the nature and size of critical defects and the mechanism responsible for the fracture. A significant decrease in the mechanical strength (around 30%) was observed at 600 °C for all grades of cemented carbides. This fact was ascribed to the change in the critical flaw population from sub-surface (at room temperature) to surface defects, associated with the selective oxidation of Co. Additionally, an estimation of the fracture toughness at 600 °C was attempted for the three cemented carbides, based upon the B3B strength results, the corresponding number of the tested specimens fragments and the macroscopic area of the B3B fracture surfaces. The fracture toughness was not affected by the temperature, at least up to 600 °C. In addition, the good agreement with the Single Edge Notch Beam toughness data suggests the possibility of employing this approach for fracture toughness evaluation of brittle materials under different testing conditions.

In this work, a titanium boron carbonitride advanced ceramic was successfully synthesised by a solid-gas mechanochemical reaction in a planetary ball mill from a mixture of elemental Ti, B, and C under nitrogen atmosphere. This material, with a general formula of Ti(BCN), exhibits a face-centred cubic structure (NaCl type) that is analogous to Ti(CN). This phase was gradually formed with sufficient milling time as a result of diffusional processes, which were permitted by the reduction of the energy in the system caused by the decrease in the spinning rate of the planetary ball mill. In contrast, under more energetic milling conditions, a mechanically induced self-sustaining reaction (MSR) took place, leading to the formation of a TiB2-Ti(CN) ceramic composite. The microstructural characterisation revealed that Ti(BCN) was composed of ceramic particles constituted of misoriented nanocrystalline domains. B, C and N were optimally distributed in the Ti(BCN) phase. The TiB2-Ti(CN) ceramic composite was composed of micrometric and nanometric particles homogeneously distributed. Additionally, the nitrogen content obtained for Ti(BCN) was higher than for the Ti(CN) phase in the composite material.

Microstructure and mechanical characterization of (Ti,Ta)(C,N)-Co based solid solution cermets prepared by two mechanochemical synthesis processes (one- and two-step milling) and a pressureless sintering in protective helium atmosphere. Materials with composition of TixTa1- xC0.5N0.5-20%Co with two different Ti/Ta ratios (x = 0.9 and x = 0.95) were developed to prepare four groups of experimental materials. Microstructures were observed using confocal microscopy and grain size was evaluated using image analysis. Mechanical testing was carried out using nanoindentation equipment and nanohardness and indentation Young´s modulus were obtained. Mechanical properties of individual phases were measured using single load/unload method with 20 mN maximum load (40 mN/min loading rate and maximum 10 s holding time for each indent). Mechanical properties of each material as a bulk were obtained also by single load/unload method with 300 mN maximum load (600 mN/min loading rate and maximum 10 s holding time). The resulting mechanical properties were comparable to that of typical industrial hardmetal cermets. Two-step milling resulted in finer microstructure but a wider range of grain size distribution. No significant dependence between mechanical properties and number of milling steps was found. However, the materials with higher amount of Ta showed slightly higher indentation elasticity modulus

Cermets based on titanium–tantalum carbonitride were oxidized in static air between 800 °C and 1100 °C for 48 h. The thermogravimetric and microstructural study showed an outstanding reduction in the oxidation of more than 90% when the Ta content was increased. In cermets with low Ta content, the formation of a thin CoO/Co3O4 outer layer tends to disappear by reacting with the underlying rutile phase, which emerges at the surface. However, in cermets with higher Ta content, the formation of an external titanate layer, observed even at a low temperature, appears to prevent the oxygen diffusion and the oxidation progression

Titanium cylinders with radial graded porosity, which are potentially suitable for biomedical applications (replacement of cortical and trabecular bones involved in different joint and dental restorations), have been developed by a novel uniaxial and sequential compaction device, based on powder metallurgy techniques. The macrostructural, microstructural and mechanical properties of the cylinders were characterized. The microstructure obtained is a new bio-inspired/bio-mimetic approach to solving one of the most important drawbacks of titanium implants, i.e., bone resorption due to the stress-shielding phenomenon. In addition, the developed device has proved to have unique advantages in customizing the structural integrity in conventional powder metallurgy manufacturing in a simple, economic and reproducible manner.

A mechanically induced self-sustaining reaction (MSR) has been successfully employed for manufacturing powdered cermets based on Ti, Ti–Ta and Ti–Nb carbonitrides using Co as the binder phase and Mo2C as the sintering additive. The powders were sintered by hot-pressing, and complete chemical, microstructural and mechanical characterizations were performed on the densified cermets. When elemental Ta, Nb and/or Mo2C were added to the initial raw mixture submitted to the MSR process, smaller ceramic grains were observed after sintering, which suggested that ceramic particle growth was hindered by the presence of Ta, Nb and/or Mo in the host titanium carbonitride structure. Nanoindentation measurements enabled the determination of the hardness of the ceramic and binder phases, and values in the range of 26–29 GPa and 14–16 GPa were found, respectively. The high hardness values of the binder were related to the formation of intermetallic phases.

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.

(TixTa1-x)(C0.5N0.5)-Co-based cermets with various Ta contents (x=0, 0.01, 0.05, 0.1 and 0.2) were oxidized at 900°C for 48h in static air. A parabolic rate law, which is indicative of the formation of a protective oxide layer, was observed for all samples. The multi-layered oxide scale and the internal oxidation region that formed as the oxidation progressed toward the interior of the cermet specimens were characterized using XRD, SEM and EDS. The enhanced oxidation resistance achieved in cermets composed by a hard component with stoichiometry Ti0.95Ta0.05C0.5N0.5 may satisfy the optimal requirements for many applications in the field of cutting tools

Titanium-tantalum carbonitride, (Ti, Ta)(C, N), based cermets with different Ti and Ta contents were prepared using a mechanically induced self-sustaining reaction and then densified using a pressureless sintering process. Complete microstructural and mechanical characterizations were performed on the materials, which revealed that the size of the carbonitride ceramic particle was significantly reduced when the Ta content was increased. The flexural strength and fracture toughness were measured using the ball on three balls test and the indentation microfracture test, respectively. The strength profile was analyzed under the framework of Weibull theory. The change in the mechanical properties as a function of the Ta content was correlated with the normalized microstructural parameters, such as the binder mean free path. The decrease in toughness and flexural strength was attributed to the presence of intermetallic compounds in the binder phase, which was also corroborated by the nanoindentation tests.

Tal como se ha indicado en el capítulo anterior, se ha propuesto que el desarrollo de cermets utilizando como material cerámico de partida (previo al sinterizado) carbonitruros complejos (soluciones sólidas), que contengan en su estructura la totalidad de los metales de transición empleados en su fabricación (exceptuando el empleado como fase cementante), permitiría obtener materiales sin la característica microestructura core-rim, lo que podría mejorar las propiedades mecánicas e, incluso, modularlas mediante la modificación de la composición de dichas soluciones sólidas. Sin embargo, a pesar de estas ventajas, el uso de estos carbonitruros complejos como materia prima no se ha generalizado tanto como hubiera cabido de esperar. La causa principal ha sido la dificultad de encontrar un método de síntesis que permita un control adecuado de la estequiometría de estas soluciones sólidas. Los métodos utilizados han sido la nitruración de mezclas estequiométricas de carburos binarios y metales refractarios, la calcinación de mezclas de carburos y nitruros en atmósfera inerte y la reducción carbotérmica en atmósfera de nitrógeno de mezclas de los correspondientes óxidos [126, 137, 270-273]. Todos estos métodos requieren altas temperaturas y a menudo presión, así como pasos intermedios de molienda, para acelerar el proceso. Como el material así obtenido presenta un elevado tamaño de partícula, es necesario reducirlo incluyendo nuevos procesos de molienda antes de realizar la mezcla final con la fase cementante, añadiendo complejidad al proceso pulvimetalúrgico de fabricación de los cermets. En nuestro grupo de investigación, se ha demostrado que el proceso mecanoquímico MSR permite obtener de forma sencilla, no sólo carbonitruros de metales de transición, sino también soluciones sólidas de estos carbonitruros constituidos por más de un metal, con un elevado control de la estequiometría y una gran reproducibilidad [247, 248]. Además, se demostró que el método MSR podía incor

Complete solid-solution cermets based on titanium-tantalum carbonitride using a starting nominal composition with 80 wt.% of (Ti0.8Ta 0.2)(C0.5N0.5) and 20 wt.% of Co were performed by pressure-less sintering at 1550 C for different times (from 0 to 180 min) in an inert atmosphere. Chemical and phase analyses were conducted using X-ray diffraction (XRD), elemental analysis and energy dispersive X-ray spectrometry (EDX). The binder mean free path and the contiguity of the carbonitride particles were used to rationalise the microstructural effects of the mechanical behaviour. Mechanical characterisation included determining the Vickers hardness, the fracture toughness (conventional indentation microfractures, IM), the dynamic Young's modulus (ultrasonic technique), the biaxial strength (ball on three ball) and a detailed fractographic examination. Finally, the experimental findings were combined with a theoretical fracture mechanics analysis to estimate the critical processing flaw sizes. Binder-less carbonitride clusters, pores and coarse carbonitride grains were the main defects observed and were responsible for the fractures.

Nanometric powdered TixTa1-xC0.5N0.5-based cermets were fabricated using a mechanically induced self-sustaining reaction and consolidated by spark plasma sintering. Highly dense cermets were obtained, and their chemistry, microstructure and mechanical properties were characterised by X-ray diffraction, scanning electron microscopy, image analysis, microindentation and nanoindentation. The microhardness was found to depend directly on the contiguity and size of the ceramic hard particles. The samples synthesised at the lowest temperature (1150°C) exhibited more homogeneous microstructures and smaller ceramic particles and the best combination of microhardness and fracture toughness.

Different commercial TiC-TiN/Co/Ni mixtures were used as raw materials for Ti(C,N) cermets, and the effects of the sintering parameters (binder content, binder nature, sintering time and additives) on the final hard ceramic phase were studied at the sintering temperature of 1400 °C. When Co is used as the binder medium, it is possible to completely convert the starting commercial TiC-TiN mixture into TiCxN1-x. When Ni is used, which exhibits lower solubilising capacity than Co, the total conversion can never be reached and the metallurgical reactions between TiC and TiN during the liquid-phase sintering are more dependent on the sintering time than on the binder content. However, the use of Co-Ni mixtures, showing a synergic effect between the wettability capacity of Ni and the solubilising capacity of Co, enhances the metallurgical reactions at short sintering times. © 2013 Elsevier B.V. All rights reserved.

A set of powdered cermets based on (Ti,Ta,Nb)C xN 1-x carbonitride solid solutions were synthesized from mixtures of elemental powders by a mechanically induced self-sustaining reaction (MSR) method and subsequently sintered using a pressureless method. Differing nominal compositions of the hard phase were used, and the nature of the metallic-binder phase (Co, Ni, or Co-Ni) was varied. For comparative purposes, the design of the material was performed using two different synthesis pathways. The composition and microstructure of the ceramic and binder phases before and after sintering were analyzed and related to the microhardness of the material, which was found to increase with increasing contiguity of the hard phase and with decreasing particle size.The samples synthesized in one step (SERIES 2) showed higher microhardness and a more homogeneous microstructure with smaller particle size of the hard phase due to the presence of Ti, Ta, and Nb in the molten binder that hindered ceramic growth during liquid phase sintering

(Ti,Ta)(C,N) solid solution-based cermets with cobalt as the binder phase were synthesised by a two-step milling process. The titanium–tantalum carbonitride solid solution (the ceramic phase) was obtained via a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental Ti, Ta, and graphite powder blends in a nitrogen atmosphere. Elemental Co (the binder phase) was added to the ceramic phase, and the mixture was homogenised by mechanical milling (MM). The powdered cermet was then sintered in a tubular furnace at temperatures ranging from 1400 °C to 1600 °C in an inert atmosphere. The chemical composition and microstructure of the sintered cermets were characterised as ceramic particles grown via a coalescence process and embedded in a complex (Ti,Ta)–Co intermetallic matrix. The absence of the typical core–rim microstructure was confirmed.

Cermets with a nominal composition (Ti 0.8Ta 0.2C 0.5N 0.5- 20 wt.% Co) were synthesised by a mechanically induced self-sustaining reaction (MSR) process from stoichiometric elemental powder blends. The MSR allowed the production of a complex (Ti,Ta)(C,N) solid solution, which was the raw material used for the sintering process. The pressureless sintering process was performed at temperatures between 1400 °C and 1600 °C in an inert atmosphere. The microstructural characterisation showed a complex microstructure composed of a ceramic phase with an unusual inverse core-rim structure and a Ti-Ta-Co intermetallic phase that acted as the binde