Microstructural and tribological comparison of HVOF-sprayed and post-treated M-Mo-Cr-Si (M = Co, Ni) alloy coatings

High velocity oxygen-fuel (HVOF)-sprayed wear resistant Co-28%Mo-17%Cr-3%Si and Ni-32%Mo-15%Cr-3%Si coatings, both as-sprayed and after heat treatments at 600 degrees C for 1 h, have been studied. Particularly, their dry sliding wear behaviour has been compared by ball-on-disk tests against different counterbodies (100Cr6 steel and sintered alumina), and differences were discussed based on microstructural characteristics and micromechanical properties (Vickers microindentation and scratch test responses). As-sprayed coatings contain oxide stringers, are mostly amorphous and display rather low Vickers microhardness (about 7.4 GPa for the Co-based and 6.2 GPa for the Ni-based), toughness and elastic modulus. Heat-treated ones display sub-micrometric crystalline intermetallics, improving hardness (9.6 GPa and 7.4 GPa, respectively) and elastic modulus. Scratch tests indicate greater brittleness of the Ni-based alloy (higher tendency to cracking). Due to low hardness and toughness, both as-sprayed coatings undergo wear loss against steel and alumina counterparts. The more plastic Co-based alloy undergoes higher adhesive wear against steel and lower abrasive wear against alumina; the situation is reversed for the Ni-based alloy. After heat treatment, the wear loss against steel is very low for both coatings; abrasive wear still occurs against alumina. (c) 2007 Elsevier B.V. All rights reserved

Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides” Ceramics

Due to their inherently chemical complexity and their refractory nature, the obtainment of highly dense and single-phase High Entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5 and 98.2 %, respectively) are successfully produced by Spark Plasma Sintering (SPS) using powders prepared by Self-propagating High-temperature Synthesis (SHS). Although the latter technique does not lead to the complete conversion of initial precursors into the prescribed HE phases, such goal is fully reached after SPS (1950°C/20min/20 MPa). The three HE products show similar, even better in some cases, mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values are found for the (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2 and (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 systems, i.e. 28.1 GPa/538.5 GPa and 28.08 GPa/498.1 GPa, respectively, in spite of the correspondingly higher residual po-rosities (1.2 and 2.2 vol.%, respectively). In contrast, the third ceramic, not containing Tantalum, displays lower values of these two properties (25.1 GPa/404.5 GPa). However, the corresponding fracture toughness (8.84 MPa m1/2) is relatively higher. This fact can be likely ascribed to the smaller residual porosity (0.3 vol.%) of the sintered material

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certain chemical reactions sequence during synthesis. While the one made up mainly by hydroxyl groups was common to both samples, the two involving mainly organic residues were particle size dependent. Upon crystallization, both samples stabilized in the t'- and t- tetragonal forms and the Xc-cubic form but their amounts and temperatures of appearance were different. On heating, the structure of the smaller particles became gradually monoclinic achieving total degradation upon the subsequent cooling to RT.Instituto de Física La Plat

Synthesis, sintering, mechanical properties, and oxidation behavior of (Zr0.5Me0.5)B2 (Me = Ta, Hf) solid solutions

In this work, (Zr0.5Ta0.5)B2 and (Zr0.5Hf0.5)B2 solid solutions are produced in dense form by coupling the Self-propagating High-temperature (SHS) and Spark Plasma Sintering (SPS) routes. A single boride phase solid solution is formed in both cases by SPS (1850 °C, 20 min) from the multiphasic ceramic powders preliminarily obtained by SHS. The use of small amounts of graphite during SPS is highly beneficial to eliminate oxide contaminants (from 14.5–16.0 wt% to 2.1–2.8 wt%), improve powder consolidation (from 87-90 % to 97.5–98 %), and make the operating conditions milder. Better mechanical properties are exhibited by the binary ceramics with respect to ZrB2 produced by SHS-SPS. The presence of Ta makes the performance of (Zr0.5Ta0.5)B2 superior compared to the Hf-containing system, with hardness, Young's modulus, and fracture toughness equal to 22.1 GPa, 636.9 GPa, and 2.46 MPa m1/2, respectively. On the other hand, (Zr0.5Hf0.5)B2 shows higher oxidation resistance in flowing and stagnant air at elevated temperatures

In-vivo evaluations of bone regenerative potential of two novel bioactive glasses

: Due to the aging of population, materials able to repair damaged tissues are needed. Among others, bioactive glasses (BGs) have attracted a lot of interest due to their outstanding properties both for hard and soft tissues. Here, for the first time, two new BGs, which gave very promising results in preliminary in vitro-tests, were implanted in animals in order to evaluate their regenerative potential. The new BGs, named BGMS10 and Bio_MS and containing specific therapeutic ions, were produced in granules and implanted in rabbits' femurs for up to 60 days, to test their biocompatibility and osteoconduction. Additionally, granules of 45S5 Bioglass® were employed and used as a standard reference for comparison. The results showed that, after 30 days, the two novel BGs and 45S5 displayed a similar behavior, in terms of bone amount, thickness of new bone trabeculae and affinity index. On the contrary, after 60 days, 45S5 granules were mainly surrounded by wide and scattered bone trabeculae, separated by large amounts of soft tissue, while in BGMS10 and Bio_MS the trabeculae were thin and uniformly distributed around the BG granules. This latter scenario could be considered as more advantageous, since the features of the two novel BG granules allowed for the neo-formation of a uniformly distributed bony trabeculae, predictive of more favorable mechanical behavior, compared to the less uniform coarse trabeculae, separated by large areas of soft tissue in 45S5 granules. Thus, BGMS10 and Bio_MS could be considered suitable products for tissue regeneration in the orthopedic and dental fields.Due to the aging of population, materials able to repair damaged tissues are needed. Among others, bioactive glasses (BGs) have attracted a lot of interest due to their outstanding properties both for hard and soft tissues. Here, for the first time, two new BGs, which gave very promising results in preliminary in vitro-tests, were implanted in animals in order to evaluate their regenerative potential. The new BGs, named BGMS10 and Bio_MS and containing specific therapeutic ions, were produced in granules and implanted in rabbits' femurs for up to 60 days, to test their biocompatibility and osteoconduction. Additionally, granules of 45S5 Bioglass® were employed and used as a standard reference for comparison. The results showed that, after 30 days, the two novel BGs and 45S5 displayed a similar behavior, in terms of bone amount, thickness of new bone trabeculae and affinity index. On the contrary, after 60 days, 45S5 granules were mainly surrounded by wide and scattered bone trabeculae, separated by large amounts of soft tissue, while in BGMS10 and Bio_MS the trabeculae were thin and uniformly distributed around the BG granules. This latter scenario could be considered as more advantageous, since the features of the two novel BG granules allowed for the neo-formation of a uniformly distributed bony trabeculae, predictive of more favorable mechanical behavior, compared to the less uniform coarse trabeculae, separated by large areas of soft tissue in 45S5 granules. Thus, BGMS10 and Bio_MS could be considered suitable products for tissue regeneration in the orthopedic and dental fields

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certain chemical reactions sequence during synthesis. While the one made up mainly by hydroxyl groups was common to both samples, the two involving mainly organic residues were particle size dependent. Upon crystallization, both samples stabilized in the t'- and t- tetragonal forms and the Xc-cubic form but their amounts and temperatures of appearance were different. On heating, the structure of the smaller particles became gradually monoclinic achieving total degradation upon the subsequent cooling to RT.Instituto de Física La Plat

Human mesenchymal stem cell combined with a new strontium-enriched bioactive glass: An ex-vivo model for Bone Regeneration

A 3D cellular model that mimics the potential clinical application of a biomaterial is here applied for the first time to a bioactive glass, in order to assess its biological potential. A recently developed bioactive glass (BGMS10), whose composition contained strontium and magnesium, was produced in the form of granules and fully investigated in terms of biocompatibility in vitro. Apart from standard biological characterization (Simulated Body Fluid (SBF) testing and biocompatibility as per ISO10993), human bone marrow mesenchymal stromal/stem cells (BM-MSCs) were used to investigate the performance of the bioactive glass granules in an innovative 3D cellular model. The results showed that BGMS10 supported human BM-MSCs adhesion, colonization, and bone differentiation. Thus, bioactive glass granules seem to drive osteogenic differentiation and thus look particularly promising for orthopedic applications, bone tissue engineering and regenerative medicine

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the nanoconfigurations and their thermal behavior in two non-aggregated zirconia nanospheres of unlike sizes obtained by adding different water amounts during preparation. Three residues containing- Zr surroundings were determined for the non-crystalline starting zirconias, the two organics containing- ones being particle size dependent. Upon crystallization, the nanospheres showed the stabilization of both tetragonal (t´- and t- forms) and cubic (Xc- form) phases. Nevertheless, their amounts, temperature of appearance and thermal evolution depended on the residues containing- precursors. It was observed, in addition, that the structure of the smaller nanospheres became gradually monoclinic. The bigger spheres remained stabilized up to the highest temperatures certainly due to their lower specific surface area that favors the permanence of the oxygen defective t´- form

A Multidisciplinary Evaluation of Three-Dimensional Polycaprolactone Bioactive Glass Scaffolds for Bone Tissue Engineering Purposes

: In the development of bone graft substitutes, a fundamental step is the use of scaffolds with adequate composition and architecture capable of providing support in regenerative processes both on the tissue scale, where adequate resistance to mechanical stress is required, as well as at the cellular level where compliant chemical-physical and mechanical properties can promote cellular activity. In this study, based on a previous optimization study of this group, the potential of a three-dimensional construct based on polycaprolactone (PCL) and a novel biocompatible Mg- and Sr-containing glass named BGMS10 was explored. Fourier-transform infrared spectroscopy and scanning electron microscopy showed the inclusion of BGMS10 in the scaffold structure. Mesenchymal stem cells cultured on both PCL and PCL-BGMS10 showed similar tendencies in terms of osteogenic differentiation; however, no significant differences were found between the two scaffold types. This circumstance can be explained via X-ray microtomography and atomic force microscopy analyses, which correlated the spatial distribution of the BGMS10 within the bulk with the elastic properties and topography at the cell scale. In conclusion, our study highlights the importance of multidisciplinary approaches to understand the relationship between design parameters, material properties, and cellular response in polymer composites, which is crucial for the development and design of scaffolds for bone regeneration

Short range investigation of sub-micron zirconia particles

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certain chemical reactions sequence during synthesis. While the one made up mainly by hydroxyl groups was common to both samples, the two involving mainly organic residues were particle size dependent. Upon crystallization, both samples stabilized in the t'- and t- tetragonal forms and the Xc-cubic form but their amounts and temperatures of appearance were different. On heating, the structure of the smaller particles became gradually monoclinic achieving total degradation upon the subsequent cooling to RT.Instituto de Física La Plat