An as-cast Mg–1Zn–1Ca alloy has been soundly characterized to be used as a biodegradable material in biomedical applications. Ca and Zn additions have a great influence in the microstructure, ...mechanical properties and corrosion behaviour of Mg alloys. SEM examinations revealed that most of the Ca and Zn atoms form Mg2Ca and Ca2Mg6Zn3 precipitates, which distribute preferentially along the grain boundaries forming a continuous network of secondary phases. The results of nanoindentation tests show differences in hardness and elastic modulus between the α-Mg matrix and the secondary phases. The results of three-point bending tests shows that cracks propagate following the network formed by the intermetallic compounds at the grain boundaries (GBs). The evolved hydrogen after immersion in Hank’s solution of the alloy has been also estimated, showing a change in the corrosion mechanism after 160 h. The intermetallic compounds act as a barrier against corrosion, so that it progresses through the α-Mg matrix phase.
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•Mg–1Zn–1Ca alloy is formed by α-Mg matrix and Mg2Ca and Ca2Mg6Zn3 secondary phases.•Fracture mechanism occurs along the continuous secondary phases in a brittle way.•Mg–1Zn–1Ca alloy shows proper mechanical properties for biomedical applications.•Mg2Ca and Ca2Mg6Zn3 secondary phases act as barriers for corrosion progress.•Immersion in Hank’s solution produces Mg(OH)2 and HA as corrosion products.
Disulfide containing vitrimers are being widely studied to get renewable, reprocessable and self-healable resins. The most of them are based on thermally cured epoxy resin. Herein, new thermoset ...systems based on typical acrylate monomers with photo-curing were synthesized with self-healing capabilities by introducing monomers with disulfide bonds. These disulfide groups are able to exchange upon heating, leading to a renewal of the crosslinks across the damaged surfaces. Different ratios of associative reversible exchange covalent bonds have been studied. The samples were evaluated in terms of thermal and mechanical properties. It was found that the glass transition temperature (Tg) is lower than that corresponding to typical acrylate thermosets, but mechanical properties are better. Increases in hardness of 2.4 times and in elastic modulus of 1.7 times with respect to the reference networks were achieved.
Finally, the self-healing properties of the disulfide acrylates were demonstrated by monitoring the repair of a scratch upon heating. A new experimental test for quantifying the self-healing efficiency has been optimized, following the recovery of the surface crack by perfilometry. The composition optimization allows us to achieve repair percentages of 95% in shorter times.
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•Disulfide Exchange reaction was employed to prepared self-healing acrylate networks.•The obtained disulfide networks presented a high increase of mechanical properties with respect to typical acrylate networks.•The materials obtained exhibited a self-healing performance of 95%.
Nowadays, research on additive manufacturing of Ti6Al4V alloy is growing exponentially but there are just a few studies about additive manufacturing of metal matrix composite components. In this ...work, highly reinforced Ti6Al4V matrix composites with SiC particles have been additively manufactured by direct laser deposition (DLD). Ti6Al4V powder and SiC particles have been deposited layer by layer to form an additive thin wall structure. The geometry, microstructure, and microhardness of the samples are strongly influenced by the laser scanning speed used during de fabrication process. In addition, the effect of the SiC increment in reinforcement concentrations and the influence of SiC particle sizes in the microstructure have been evaluated, and the reaction mechanisms have been established. The percentage of reinforcement measured is lower than expected due to the reinforcement-matrix reactivity that results in partially dissolved SiC particles and the formation of a TiC and Si
5
Ti
3
ring around them. The size and number of particles and reaction products depend on the initial size and percentage of reinforcement and the DLD scanning speed. The higher the size and percentage of SiC particles and reaction products in the matrix, the higher the hardening effect of the composite matrix.
Graphic Abstract
The aim of present work is to study the effect of VC and/or Cr3C2 in densification, microstructural development and mechanical behavior of nanocrystalline WC-12wt.%Co powders when they are sintered ...by spark plasma sintering (SPS) and hot isostatic pressing (HIP). The results were compared to those corresponding to conventional sintering in vacuum. The density, microstructure, X-ray diffraction, hardness and fracture toughness of the sintered materials were evaluated. Materials prepared by SPS exhibits full densification at lower temperature (1100A degree C) and a shorter stay time (5min), allowing the grain growth control. However, the effect of the inhibitors during SPS process is considerably lower than in conventional sintering. Materials prepared by HIP at 1100A degree C and 30min present full densification and a better control of microstructure in the presence of VC. The added amount of VC allows obtaining homogeneous microstructures with an average grain size of 120nm. The hardness and fracture toughness values obtained were about 2100 HV30 and close to 10MPam1/2, respectively. a-ordm WC-12Co-VC/Cr3C2 cemented carbides near fully dense were obtained by SPS and HIP at 1100A degree C. a-ordm The addition of inhibitors, especially VC, has been demonstrated to be an efficient method for controlling the grain growth in the solid state. a-ordm The VC addition and HIP sintering allowed manufacturing near-nanostructured cemented carbides. a-ordm Materials with hardness values about 2100 HV30 and fracture toughness values close to 10MPam1/2 were obtained.
•The resultant microstructure is characterized by forming a diffusion layer in contact with tungsten base material constituted by W, Fe and Cr.•The TEM/STEM examination showed that the copper phase ...and the Fe-rich band generated are highly distorted and dislocated.•The examination of the EUROFER material close to the copper band revealed the presence of precipitates possibly formed by carbides of carbide forming elements but the region, however, as introduced in EUROFER material, a more martensitic like microstructure is observed typical of this steel.•The mechanical characterization showed an increase of hardness associated with a high dislocation density and, therefore, a decrease in the toughness is expected.
In this article, a preliminary microscale study of a brazed joint of two materials that will conform the future fusion reactors is carried out. Tungsten will act as plasma-facing material attached to a structure made of some reduced activation ferritic-martensitic steel (Eurofer-like steel). The proposed brazing process introduces copper as filler material and develops the thermal process in a high vacuum atmosphere at 1135 °C for 10 min. The resultant microstructure is characterised by forming a diffusion layer in contact with tungsten base material constituted by W, Fe and Cr. In addition, an iron-rich phase is formed between the diffusion layer and Cu braze region. This steel band presented two different structures: a typical martensite lath structure and another without it. At the centre of the steel band, the laths are replaced by a more homogeneous matrix where copper precipitates nucleated due to its enrichment in this element during the brazing process. It is worth highlighting the presence of dislocations and residual stresses in all the different phases that appear associated with the brazing process. This presence of dislocation stresses shows how the nanomechanical analysis increases the modulus and hardness values of the steel band concerning the Eurofer base material. The diffusion layer presents the highest values in the mechanical characterisation due to its morphology and the components that constite the phase.
The aim of this present work is to study the effect of VC and/or Cr3C2 in densification, microstructural control and mechanical behaviour of WC–12Co ultrafine and nanocrystalline mixtures, ...consolidated by spark plasma sintering at 1100°C, applying a pressure of 80MPa in combination with a heating rate of 100°Cmin−1. Nanocrystalline and ultrafine mixtures with an average size of 30nm and 100–250nm, respectively, with the addition of 1 and 0.5wt.% of VC/Cr3C2 grain growth inhibitors, respectively, were investigated. The density, microstructure, hardness and fracture toughness of the consolidated samples were measured and observed. The addition of VC inhibitor allows an excellent grain growth control keeping microstructures with an average grain size of 154nm. The hardness values and fracture toughness obtained were about 2000HV30 and above 10MPam1/2, respectively.
A statistical indentation analysis of WC–Co coatings obtained by atmospheric plasma spray (APS) with two secondary plasma gases, H
2 and He, was investigated using an instrumented indentation ...technique with the aim of correlating the influence of the nanomechanical behaviour of each constituent phase with the micromechanical characteristics of these coatings.
X-ray diffraction (XRD) and backscattered electron (BSE) analysis showed that H
2 gas produced a greater decarburisation of the WC phase. The dissolution and decomposition of the WC phase during the process produced a Co
+
W+C solid solution as binder phase and the formation of W
2C and W as secondary phases. The nanohardness (
H) and Young's modulus (
E) resulting from a grid of 300 indentations performed at 50
nm in depth identified the characteristics of each phase in the heterogeneous structure produced by decarburisation. Statistical study by a CDF fit and Gaussian simulated distributions showed that the mechanical properties of the coatings were governed by the binder phase content, which decreased the possible hardening effect of the arising hardest phases (W
2C and Co+W
+
C solid solution).
► The mechanical properties of WC–12Co coatings were analyzed by nanoindentation. ► The nanohardness and Young's modulus were identified for each phase. ► Statistical analysis correlated macroscopic with nanomechanical behavior. ► The binder phase reduces the hardening effect due to decarburisation process.
► CNFs/ceramic nanocomposites were densified by spark plasma sintering. ► The tribological properties have been investigated as a function of CNFs content. ► Low wear resistance of CNFs material and ...CNFs/ceramic nanocomposites have been found. ► The friction coefficient of the nanocomposites with high CNFs content was very low.
Alumina-carbon nanofibres (CNFs) and silicon carbide–CNFs nanocomposites with different volume fraction of CNFs (0–100vol.%) were obtained by spark plasma sintering. The effect of CNFs content on the tribological behaviour in dry sliding conditions on the ceramic–carbon nanocomposites has been investigated using the ball-on-disk technique against alumina balls. The wear rate of ceramic–CNFs nanocomposites decreases with CNFs increasing content. The friction coefficient of the Al2O3/CNFs and SiC/CNFs nanocomposites with high CNFs content was found to be significantly lower compared to monolithic Al2O3 and SiC due to the effect of CNFs and unexpectedly slightly lower than CNFs material. The main wear mechanism in the nanocomposite was abrasion of the ceramic and carbon components which act in the interface as a sort of lubricating media. The experimental results demonstrate that the addition of CNFs to the ceramic composites significantly reduces friction coefficient and wear rate, resulting in suitable materials for unlubricated tribological applications.
Al2O3-TiO2 coatings were deposited on austenitic stainless steel coupons from nanostructured powders by atmospheric plasma spraying (APS). Commercial suspensions of nanosized Al2O3 and TiO2 particles ...were used as starting materials. Mixtures of these suspensions and of more concentrated suspensions of Al2O3 and TiO2 were then agglomerated into plasma sprayable feedstock. Agglomeration was performed by spray drying, followed by consolidation thermal treatment. These powders were successfully deposited, yielding coatings that were well bonded to the substrates. The coating microstructure thus consisted of semi-molten feedstock agglomerates surrounded by fully molten particles that acted as binders. Agglomerates from suspensions with higher solids contents yielded coatings with lower porosity and fewer semi-molten areas.
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