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Here we report for the first time that the anodization of the biphasic (α'+β) Ti13Nb13Zr alloy form arrays of TiO2 nanotubes with well-defined circular geometry in the α′ phase, while nanopores of TiO2 are formed in the β phase. Samples of the Ti13Nb13Zr alloy were severely plastic deformed using High-Pressure Torsion (HPT) to refine the microstructure and to redistribute α′ and β phases. The anodization was performed using an organic electrolyte (glycerol) containing fluoride ions and a few percentages of water. All the specimens coated with nanotubes were annealed at 550 °C to crystallize the modified surface of the as-anodized samples. XRD analyses confirmed that the as-anodized amorphous nanostructures crystallize in a mixture of anatase and rutile after heat treatment, and SEM observations showed no significant morphological changes in the surface phases. The evaluation of corrosion resistance showed that anodized samples have much better corrosion properties than polished ones without any evidence of pitting corrosion. Quantitative comparison between anodized coarse-grained (α'+β)-Ti alloy and ultra-fine grained (α'+β)-Ti one showed that the nanostructuring of the (α'+β)-Ti alloy by HPT helped to improve the bioactivity when compared with the coarse-grained sample.

Microstructural and mechanical characterization of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys were performed. The alloys were processed by a method that uses centrifugal force to cast the samples into a rotating copper mold. Microstructural characterization was carried out by means of x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. Compressive tests at room and at 300 °C were performed in selected samples to evaluate their mechanical properties. Microstructural characterization showed the formation of quasicrystalline phases as well as other intermetallic phases embedded within an Al-FCC matrix. The Ce-containing alloy exhibited promising results regarding quasicrystalline phase formation and stability as well as with respect to its mechanical properties at high temperatures. The quasicrystalline phase of this alloy appears to be stable up to 545 °C when the DSC reveals an exothermic transformation. In addition, the presence of a eutectic structure surrounding the Al-FCC grains enhanced the mechanical strength of this alloy. At 300 °C, the Ce-containing alloy showed yield strength and ultimate tensile strength of 180 MPa and 360 MPa, respectively. If compared to a commercial aluminum alloy 2024 at the T6 condition, close to 300 °C, the alloy studied here showed an increase of more than 4 times in the yield strength, and almost 7 times in the ultimate tensile strength. The high thermal stability and mechanical properties at high temperatures of this alloy open interesting possibilities for further studies and future applications of this Al-Fe-Cr-Ce alloy. Keywords: Al-alloys, Centrifugal force casting, Quasicrystal, Mechanical properties

FeCrMnCoSi coating (so-called CaviTec alloy) is recognized as an efficient protective measure to extend the service-life of steel components subjected to severe cavitation erosion. Besides this requirement, many applications also demand coatings with proper corrosion and wear resistances. The aim of this study is to evaluate the pitting corrosion and the sliding wear resistances of CaviTec coatings produced by high-velocity oxygen fuel (HVOF) and deposited onto a 304 stainless steel (SS). The corrosion performances in simulated seawater indicated that these coatings exhibit satisfactory corrosion resistance with regions around the inter-splats representing the preferential weak links sites for pitting corrosion initiation. CaviTec coating wear is characterized by mild delamination followed by severe abrasive wear once the hard-martensitic debris are added in the tribosystem due to the transformation induced plasticity (TRIP) effect. Corrosion and wear results point out that the CaviTec coatings, originally developed to possess high cavitation erosion resistance, also present satisfactory corrosion resistance in seawater-like medium and interesting dry sliding wear performance, which can extend their application domain.

2Mg-Fe mixtures produced by high-energy ball milling were consolidated into bulk form by hot extrusion at different processing temperatures (573 K (300 °C), 623 K (350 °C) and 673 K (400 °C)), aiming to evaluate their influence on the structure and microstructure of bulk materials and their consequent influence on the hydrogen sorption properties. In spite being in the nanosize range, the highest the processing temperature, the larger the grain sizes. However, the nanometric grain size remained after any hot extrusion condition, as estimated by Rietveld refinement. The pinning effect of Fe on Mg grain boundaries explained this effect. In the first absorption (activation), powders showed a hydrogen storage capacity of ∼4.53 wt%, while the extruded samples (bulk materials) reached almost the same capacity during the period of hydrogenation (∼94% of the maximum hydrogen storage capacity for Mg 2 FeH 6 - 5.5 wt%). The smallest crystallite sizes and highest surface area for hydrogenation explain the good performance of powders. However, when comparing only extruded samples, it was observed that the highest capacity and the lowest incubation times were mainly related to grain sizes and to the favorable texture along (002) plane of αMg. The desorption temperature of bulk materials was very similar to that of powders, which is good considering the lower surface area of bulk materials.

This work reports on the degradation of two (Zn-poor and Zn-rich) Mg-Zn-Ca crystalline alloys produced by mold casting yielding different kinds of microstructures with several scales. The dependence of corrosion properties and hydrogen evolution with alloy compositions, sizes and kinds of microstructure was exhaustively analyzed. The results were compared with amorphous alloys of same compositions. Zn-rich composition with average grain sizes of less than 500 nm presented marginal and an acceptable level of hydrogen, which was lower than for larger grains or Zn-poor composition. This behavior was explained by the reduction of the intrinsic metallic surface reactivity and the higher stability of the oxide film, which reduce the corrosion rate and, consequently, the hydrogen evolution. Mg-Zn-Ca crystalline alloys with Zn-alloying threshold and homogeneous grain size (

The composition of a commercial duplex stainless steel was modified with boron additions (3.5, 4.5, and 5.5 wt.%) and processed by rapid-quenching techniques: Melt-spinning, copper-mold casting, and high-velocity oxygen fuel (HVOF). Spray deposition was also used to produce alloys as the process may induce rapid-solidified-like microstructures. These processing routes led to microstructures with distinguished corrosion resistance. Among the alloys with different boron contents, the 63.5Fe25Cr7Ni4.5B composition enabled the production of fully amorphous ribbons by melt-spinning. The cooling rate experienced during copper-mold casting, high-velocity oxygen fuel, and spray deposition did not ensure complete amorphization. The crystalline phases thereby formed were (Fe,Cr)2B and (Fe,Mo)3B2 borides in an austenitic-matrix with morphology and refinement dependent of the cooling rates. Fully amorphous 63.5Fe25Cr7Ni4.5B ribbons exhibited outstanding corrosion resistance in chloride-rich alkaline and acid media with negligible corrosion current densities of about 10−8 A/cm² and a broad passivation plateau. Although the specimens of the same composition produced by HVOF process and spray deposition exhibited lower corrosion resistance because of intrinsic porosity and crystalline phases, their corrosion behaviors were superior to those of AISI 1045 steel used as substrate with the advantage to be reinforced with hard borides known to be resistant against wear.

Ti13Nb13Zr and Ti35Nb7Zr5Ta alloys containing non-cytotoxic elements for bone tissues can be the right choice for replacing Ti6Al4V for orthopedic implant applications. Formation of ultrafine-grained (UFG) structure in metals and alloys by severe plastic deformation (SPD) techniques allows the achievement of unique mechanical properties. Using high-pressure torsion (HPT), UFG microstructures were formed in both alloys resulting in the average size of grains/subgrains of ∼203 nm and ∼112 nm for the Ti13Nb13Zr and Ti35Nb7Zr5Ta samples, respectively. After processing by HPT, hardness measurements gave the values of about 390 HV and 320 HV, and Young's moduli of about 60 GPa and 44 GPa, respectively for the Ti13Nb13Zr and Ti35Nb7Zr5Ta alloys, being the last very close to the modulus of the bone. Additionally, surface modifications have been carried out by anodization and by chemical methods aimed to induce specific responses on osteoblastic cells after implantation. The results of bioactivity tests indicated that oxide nanostructures produced after anodization could activate the surfaces of both samples. However, chemical treatment was capable of activating only the Ti13Nb13Zr alloy. The bioactivity of the Ti13Nb13Zr alloy was much higher than the one for Ti35Nb7Zr5Ta alloy and was improved after processing by HPT.

International audience; Porous noble metal surfaces were produced by gold-smiths in ancient times by dealloying. These processes lead to the formation of gold or other noble metal rich layers. Such dealloying occurs by corrosion as the most electro-chemically active elements dissolve and the more noble elements aggregate into clusters by phase separation (spinodal decomposition). Here we report results from an alternative path to nanoporosity where the structure patterns and length scales are first fixed in the bulk by high temperature spinodal decomposition followed by chemical dissolution of one of the component products of the phase-separation. The process may be used to form nanoporous titanium for biochemical applications. (C) 2015 Elsevier Inc. All rights reserved.