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The wear resistance of boron-modified supermartensitic stainless steel coatings produced by high-velocity oxygen fuel (HVOF) was investigated through pin-on-disk measurements. It was shown that addition of boron leads to the formation of an interconnected and rigid boride network delimiting the grain boundaries of the martensitic matrix. A very refined structure was formed as result of the high cooling rates imposed to the molten alloy during the HVOF process. The specific wear rates of the HVOF coatings were about tenfold lower than the boron-free supermartensitic stainless steel, lying in the order of 10−5 mm3/N m. The refined boride skeleton along the HVOF coating was found to be effective to reduce the materials’ removal from the exposed softer martensitic matrix. While the supermartensitic stainless steel master alloy and the mild steel substrate displayed severe adhesive wear, the HVOF coatings exhibited mild delamination wear at low sliding velocities (10 and 20 cm/s) and abrasive wear at the highest tested velocity (40 cm/s). The studied boron-modified supermartensitic HVOF coatings are an interesting approach to protect the surface of inexpensive steel substrates against wear.

An in-depth analysis of the effect of boron addition on the microstructure of the equiatomic AlCoCrFeNi High Entropy Alloy (HEA) was performed. Alloys with nominal compositions AlCoCrFeNiB0.1 and AlCoCrFeNi were produced and analyzed by multi-scale characterization techniques, including X-ray diffraction, scanning and transmission electron microscopy coupled with TEM-based orientation mapping technique. CALPHAD simulation was carried out to understand the solidification sequence and the phase stability of the studied alloys. The equiatomic AlCoCrFeNi alloy forms a mixture of an Al-Ni rich B2 phase with a Fe-Cr rich body centered cubic (BCC) phase; small face centered cubic (FCC) islands were also observed. The boron addition leads to the formation of needle-like Cr-rich borides with an orthorhombic structure. Moreover, this addition changes considerably the solidification sequence in later stages of the solidification process, resulting in a more complex microstructure.

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.

Typically, aluminum alloys are contaminated by iron during recycling cycles. Such a procedure leads to the formation of intermetallic phases with detrimental morphology, which acts as stress risers, impairing mechanical properties and consequently hindering further mechanical processing and restricting recycling. This paper aimed at studying the solidification of an AA6061 alloy highly contaminated with iron (1.4 wt%). Spray forming processing allowed altering the solidification path of the Fe-modified AA 6061 alloy, resulting in the formation of primary α-Al15(Fe, Mn)3Si2 phase with polyhedral morphology, which traps Fe and Si at elevated temperature. Furthermore, spray forming prevented the formation of intermetallic AlFeSi phases with platelet-like morphology, such as β-AlFeSi as well as the typical Chinese script morphology, resulting in a final ductile microstructure, allowing further processing by hot extrusion.

TiFe is a very interesting material for hydrogen storage in the solid state, due to its hydrogen capacity of 1.9 wt % and to the fact it can be absorb/desorb hydrogen at room temperature. However, the TiFe produced by casting does not absorb hydrogen, unless a procedure called activation is applied, which is based on a repetition of several thermal cycles. This study evaluates the effects of a mechanical activation route for the TiFe intermetallic compound, namely, cold rolling (CR) under inert atmosphere. Stoichiometric TiFe was prepared from elementary powders by arc melting. Ingot was grinded and then cold rolled for 20 and 40 passes under argon inside a glove box, with moisture and oxygen contents below 0.1 ppm. Cold rolled samples consisted of two parts: powder particles and thin cracked flakes. The results showed that mechanically activated samples by CR exhibited rapid absorption of hydrogen at room temperature, without using a thermal activation process. In general, the average storage capacity of hydrogen was 1.4 wt% H2 for the first absorption, regardless of the number of passes for both flake and powder samples.

The behaviour of the martensitic phase transformation of a Cu-Al-Ni-Mn shape memory alloy was studied for as-atomized and heat-treated powders. X-ray diffraction, microscopy techniques and thermodynamic calculations were used to understand the different transformation behaviour observed during differential scanning calorimetry (DSC) analysis. Two overlapped transformation peaks were observed in the DSC curves for the as-atomized powder. After annealing, the peaks progressively became only single peak when the annealing temperature and time were increased. No difference in phase formation and microstructure was observed by X-ray diffraction and scanning electron microscopy when compared as-atomized and annealed powders, although transmission electron microscopy analyses showed that the as-cast powders had more dislocations trapped in the microstructure than the annealed samples. Considering the experimental results and thermodynamic considerations, it was concluded that the smooth double peak effect in the as-atomized powders occurred due to a different state of internal stresses and elastic energy accumulation during forward transformation. The absence of this effect after heat treatment shows that the internal stresses and defects were annihilated after annealing, changing the elastic energy accumulation and the transformation behaviour. Understanding the martensitic transformation on Cu-Al-Ni-Mn powders is important considering the potential use of powder metallurgy processing route.

Wear and corrosion resistant amorphous/nanocrystalline Fe-Cr-Nb-B coatings have been successfully synthesized by high velocity oxygen fuel in previous works. These coatings show excellent wear resistance and superior corrosion resistance. However, the phase evolution during cooling of the new alloys in the Fe-Cr-Nb-B system is not well understood. In addition, commercial thermodynamic databases for Fe-based alloys do not fully describe the system at the composition ranges of interest. In the present work, the phase evolution of as-melted Fe 51 Cr 10 Nb 20 B 19 alloy was investigated by combining detailed microstructural characterization with thermodynamic evaluation using a database developed for the Fe-Nb-B system. The solidification path starts with the formation of (Fe,Cr,Nb) 3 B 2 diboride phase, followed by the formation of austenite at lower temperature. On further cooling, the remaining liquid transforms eutectically to (Fe,Cr)NbB boride and austenite. In the solid-state region, the austenite transform allotropically to ferrite. At even lower temperature, there exists a peritectoid-like transformation, where the (Fe,Cr)NbB boride nucleates both at ferrite grain boundaries and around the existing (Fe,Cr,Nb) 3 B 2 diboride. Thermodynamic calculations showed good agreement with experimental observations, opening new possibilities to guide future alloy development in the Fe-Cr-Nb-B quaternary system.

A structural, mechanical and thermal characterization of an Al-Co-Fe-Cr coating alloy was performed. An atomized powder with atomic composition of Al 71 Co 13 Fe 8 Cr 8 was thermally sprayed by high velocity oxygen fuel (HVOF) on a steel substrate. X-ray diffraction, scanning and transmission electron microscopy and differential scanning calorimetry were used to characterize the atomized powder and the sprayed coating. Vickers microhardness and pin-on- plate wear test were carried out for mechanical and tribological characterization and an infrared camera was used to evaluate the insulation capacity of the coating material. The results show that both the atomized powder and the coating material were composed predominantly by a quaternary extension of the hexagonal Al 5 Co 2 phase and by the monoclinic Al 13 Co 4 . Both phases are quasicrystalline approximants of a decagonal Al-Co quasicrystal. The coating samples presented high values of micro-hardness, close to 500 HV and substantially low friction coefficient values, around 0.05. The coatings were good thermal insulators, decreasing by 30% the surface temperature of a sample exposed to a hot plate in comparison with the carbon steel substrate.

Recently a Fe 60 Cr 8 Nb 8 B 24 quaternary amorphous/nanocrystalline composite coating has been successfully synthesized by high velocity oxygen fuel in our group. The composite coating shows excellent wear and corrosion resistance. In order to understand the phase evolution of the quaternary alloy during cooling and interpret its good glass forming ability, the stable phases in the as-melted ingot of the same composition were studied by X-Ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. Thermodynamic calculation was performed based on a database compiled from literature. The calculated results show good agreement with the microstructural observation. It was found that Fe 60 Cr 8 Nb 8 B 24 alloy lies very close to the eutectic point of the system, which is related to its high glass forming ability. The thermodynamic calculation could provide insightful understanding and guidance for the future amorphous composition designing in Fe-Cr-Nb-B quaternary system.

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.

The conflicting role of crystalline phase on the corrosion and wear resistance of the glass former Fe66Cr10Nb5B19 alloy was investigated. Amorphous to crystalline structures were produced by amorphous ribbons annealing and solidification of the liquid into a wedge-shaped copper mold. Amorphous and amorphous/nanocrystalline microstructures displayed good balance of properties. Their corrosion resistance remained elevated since α-(Fe,Cr) and (Fe,Cr)2B crystals were non-percolated within the corrosion-resistant amorphous matrix. Wear resistance was still high because (Fe,Cr)2B is even harder than the amorphous matrix. Crystalline microstructures were resistant against wear thanks to the large fraction of (Fe,Cr)2B and (Fe,Cr)NbB, both effective to protect the softer α-(Fe,Cr) matrix. Their corrosion resistance, however, was severely compromised, given the elemental partitioning to form crystals, with the interfaces more prone to corrode. While amorphous and amorphous/nanocrystalline microstructures presented the best-combined resistance to corrosion and wear, the crystalline microstructures are interesting for load-bearing applications where high corrosion resistance is not required.

In this paper, two Mg-Zn-Ca amorphous alloys were processed and their mechanical and corrosion properties were evaluated and compared. The first alloy was a new composition, Zn-rich, Mg60Zn34Ca6, designed thanks to a multifold approach involving two different criteria, topological instability, and electronic criteria. The second alloy, with less Zn content, was a well-known Mg73Zn23Ca4, used for the sake of comparison. Three kinds of rapidly solidified samples were processed for each composition: ribbons, wedge, and cylindrical samples. The new composition showed much better glass-forming ability and superior corrosion and mechanical properties than the Zn-poorer composition. The effect of Fe content, a typical contaminant in Mg-based alloys, was also evaluated. Electrochemical results in amorphous and in crystalline samples showed that increasing iron to certain amounts has no influence on the corrosion resistance of the investigated alloys. Keywords: Mg-Zn-Ca amorphous alloys, Design of amorphous alloys, Contaminant effect, Mechanical and corrosion properties, Biomaterial

A series of Al-rich Al-Mn-Ce alloys have been chill cast in copper molds and some were subjected to subsequent heat treatments. For all compositions studied, the ternary Al20Mn2Ce phase is formed as the primary phase surrounded by different constituents. The mechanical properties as a function of composition and heat treatment are presented and illustrate that this system is very versatile and that it is possible to tailor the compositions to produce alloys with high yield strengths, alloys with high hardnesses (for wear applications), and alloys with reasonably high ductilities. Alloys with high yield strengths and some ductility are obtained when the microstructure contains the ternary phase surrounded by the Al-Al11Ce3 eutectic constituent. Alloys with high hardnesses, can be obtained at higher Mn levels where the ternary phase and other intermetallics constitute most of the structure. Alloys with relatively high ductilities are possible at lower Ce and Mn levels where a metastable FCC solid solution of Mn in Al forms surrounding the ternary phase. Although the finely-distributed ternary phase is metastable, it appears to be relatively resistant to coarsening or decomposition. Finally, it is shown that Ce can be substituted by Mischmetal with no significant changes in either microstructure or properties. Keywords: Aluminum alloys, Al-Mn-Ce, Chill mold casting, High specific strength, Dispersion hardening, Electron microscopy

In this work, the effect of Si additions on the glass-forming ability (GFA) and the mechanical behaviour of a Ti42.5Cu42.5Ni7.5Zr7.5 alloy is investigated. An optimum GFA occurs for addition of 0.5 at% Si and it is explained based on a balance between two factors: an increased thermal stability of the supercooled liquid and the detrimental effect of Ti5Si3 on vitrification. On rapid cooling, composites consisting mainly of the cubic B2 phase and glass can form. Their plasticity increases with increasing Si additions without sacrificing their high yield strength. A characteristic core–shell microstructure is formed in the rod with 2 at% Si, for which the combination of an amorphous outer surface and a refined dendritic structure in the centre gives rise to a composite with enhanced mechanical properties.

Cu–45Zr–8Al and Cu–44.1Zr–7.8Al–2Y metallic glass ribbons were prepared by melt spinning and heat treated at two different temperatures followed by microstructural characterization by SEM and TEM. The compositions were selected to better understand the effect that oxygen has in the sequence and morphology of the phases formed during devitrification. A novel microstructure consisting of the Heusler Cu 2 ZrAl phase precipitated inside a B2–CuZr matrix that has shape memory properties was produced. It is proposed that this novel microstructure may be used to prepare samples with improved shape memory responses. The known cube–cube relationship between the Heusler and B2 phases also provides direct evidence about the orientation relationship between the martensite and the parent B2 austenite and the results are in contrast to what is reported in the literature. The results also confirm that oxygen dissolved in these alloys leads to the formation of the B2–CuZr phase at lower temperatures than comparable low oxygen alloys.

In this paper the chemical composition of the supermartensitic stainless (SM) was modified with the addition of small boron contents (0.3, 0.5 and 0.7 wt.%) and processed by spray forming aiming the development of functionalized stainless steel with higher wear resistance. The addition of boron to the SM leads to the formation of continuous network of M2B type borides uniformly distributed in the refined microstructure promoted by the spray forming process. The wear resistance was evaluated by two different methodologies: (1) the standardized dry sand/rubber wheel test (ASTM G65); and (2) a plate-on-cylinder (POC) wear test which was designed to simulate in laboratorial scale the tribosystems found in wear of risers and casings. It was shown that the wear mechanisms that take place in both tests are quite different, but in all cases increasing the boron content is always accompanied by an increase in the wear resistance. Electrochemical analyses were performed to evaluate the corrosion resistance of the designed alloys. It could be seen that corrosion properties similar to the commercial SM can be achieved in the SM modified with 0.7 wt.% of boron if an over content of chromium is added to the chemical composition. Keywords: Spray forming, Supermartensitic stainless steel, Borides, Wear resistance, Corrosion resistance

In this study the Fe43.2Co28.8B19.2Si4.8Nb4 (at.%) alloy was processed by spray forming in an industrial facility with the aim of investigating the formation of amorphous phases. The thicker layers (5–15 mm) presented partial/fully crystalline microstructure with onset of crystallization of the amorphous phase at T x = 595 °C. On the other hand, thinner layers (below 2.5 mm) presented fully amorphous structure, and glassy behaviour with glass transition (T g ) at 555 °C. The thermal stability and the crystallization kinetics of the alloy were studied using the isothermal DSC curves, measured at different heating rates and temperatures. Despite its good glass-forming ability (GFA) and high stability against crystallizations, its incubation time for crystallization is almost zero. In order to rule-out the complete crystallization mechanism, in situ temperature resolved studies using TEM were done. In addition, the amorphous part of the deposit was heat treated at various temperatures/times and the results were compared with the in situ crystallization behavior observed by TEM.

Bulk consolidated samples of 2 Mg–Fe were produced by hot extrusion and by hot extrusion followed by cold rolling. The starting 2 Mg–Fe mixture was obtained by high-energy ball milling. The cold-rolled samples, which presented a favorable (0 0 2) texture in Mg, absorbed 5.23 wt.% H2, almost the full capacity of Mg2FeH6, without any incubation time. This level of hydrogen absorption capacity was higher than the ones observed for the milled powders or the extruded samples. The hydrogen desorption temperatures were very close for all types of samples. The good results observed in the hot-extruded plus cold-rolled sample were explained by the smaller grain sizes, along with a favorable texture and the catalytic effect of residual Fe.

Commercial Mg was processed by two combined processes: ECAP and cold rolling. Samples were first processed by ECAP for four passes using route Bc, at 300 °C and ram speeds of 3 and 25 mm/min. The ECAPed samples were cold-rolled in several passes. The cold rolled samples, which presented a favorable (0 0 2) texture, presented faster hydrogen absorption kinetic than the just ECAPed samples. No significant changes of desorption temperatures were found. The good results observed in the ECAPed plus cold rolled samples were explained by the acquired preferred orientation and by the increase of defects after cold rolling.

Hot extrusion processing was employed to produce 2Mg–Fe bulk mixtures for hydrogen storage. 2Mg–Fe powder mixtures were prepared by high-energy ball milling. These mixtures were cold pressed into cylindrical pre-forms, which were then processed by hot extrusion (at 300 °C) to produce bulks. In this work, we analyzed the influence of the extrusion ratio (3/1, 5/1 and 7/1) on the sorption properties of the bulks. The nanometric grain size remained unaltered after all hot extrusion conditions. More porous bulks were produced at an extrusion ratio of 3/1. In the first cycle of hydrogenation, the sample processed at 3/1 absorbed more hydrogen (4 wt% of H) than the precursor powders (3 wt% of H). The results showed that the desorption temperature of bulks were very similar to that of 2Mg–Fe powders, which is good considering the lower surface area of bulks, and that samples with Fe in excess presented lower desorption temperatures.

Fe–Si alloys have excellent soft magnetic properties, especially around 12 at.% Si. However, their industrial applications are limited because they lack the ductility required in rolling operations for the fabrication of thin sheets, thus leading to cracking. The brittleness of high silicon alloys is caused by order–disorder reactions at low temperatures. This work involved an analysis of the effect of heat treatment on the crystalline structure of thin sheets of Fe–5 wt%Si alloy obtained in a two-step fabrication route: (1) spray forming of Fe–3.5%Si + 2.0%Sip composite and (2) rolling and heat treatment of the composite to dissolve the silicon and homogenize its content across the thickness of sheet samples. Structural and microstructural analyses indicated the success in fabricating thin sheets of Fe–5 wt%Si alloys with such strategy. The presence of the ordered B2 phase had an important effect on the texture development and therefore on the magnetic properties of these alloys.

Fe–Si alloys are widely used for magnetic applications. However, it is very difficult to process Fe–Si with a silicon content exceeding 3.5 wt.%Si (upper limit for products commercially available by the I/M route) due to the alloy's low ductility, which is attributed mainly to the formation of B2 and DO3 ordered phases that embrittle the material. To overcome this obstacle, the main focus of this work was to produce thin sheets of Fe–5 wt.%Si alloy in two steps: (1) as a Fe–3.5%Si + 3%Sip (Si particles) composite, using spray forming, and (2) rolling and heat treating (HT) the composite to dissolve the silicon and homogenize its content throughout the thickness of the sheet. To this end, 3 wt.%Sip were co-injected into the main stream of the Fe–3.5 wt.%Si spray, followed by hot-rolling of the billet at 850 °C to obtain 0.45 mm gauge thin sheets. The final material was heat-treated at 780/510 °C for 8 h or at 1250 °C for 1 h and then air cooled. The grain orientation was analyzed by EBSD and the distribution of iron, silicon and impurities was identified by X-ray dot mapping. The heat treatment caused diffusion and dissolution of the silicon particles and grain growth. However, the final silicon content was strongly dependent on the atmosphere of the heat treatment furnace. In the absence of oxygen, the silicon content reached 4.9 wt.% distributed homogeneously throughout the thickness of the composite. In the presence of oxygen, the silicon diffused to the surface and only 3.5 wt.% remained in the matrix.

The present paper evaluates the corrosion resistance of four new amorphous Fe-Cr-based alloys containing Mo or Nb, as well as their thermal stability and the effect of their partial crystallization. Ribbons of Fe 68 B 20 Cr 12 , Fe 67.7 B 20 Cr 12 Mo 0,3 , Fe 67.7 B 20 Cr 12 Nb 0,3 and Fe 67.7 B 20 Cr 12 Nb 0,15 Mo 0,15 alloys were processed by the melt-spinning technique. The crystallization process of the four compositions occurs in a single-stage step with the simultaneous precipitation of fcc-Fe and Fe 3.5 B phases . The addition of Nb and/or Mo leads to an increase in the crystallization temperature, indicating that these elements stabilize the amorphous phase. The results also indicate that the alloy containing both Nb and Mo presented greater uniform corrosion resistance than the alloy containing either one or the other of these elements in NaCl and H 2 SO 4 solution.

article i nfo Article history: Received 8 December 2009 An investigation was made into the thermal stability and mechanical behavior under nanoindentation of a new glassy alloy with composition Ni50Nb28Zr22, produced in the form of melt-spun ribbons and copper mold-cast wedges. The alloy composition was designed based on the lambda criterion combined with the electronegativity difference among the elements. X-ray diffraction and scanning electron microscopy confirmed that the ribbons and wedges (up to 200 μm in thickness) are amorphous. The thermal properties of these samples were evaluated by differential scanning calorimetry (DSC). Nanoindentation revealed that the hardness of this alloy, around 10 GPa, is among the highest reported for metallic glasses. Remarkably, the cast wedge exhibits greater hardness and higher elastic modulus than the ribbon. This correlates with the larger amount of frozen-in free volume in the ribbons than in the cast wedges, as evidenced by DSC. In addition, finite element simulations of nanoindentation curves were performed. The Mohr-Coulomb yield criterion allows for better adjustment of the experimental data than the pressure-independent Tresca yield criterion. The simulations also reveal that the cohesive stress in the ribbons is lower than in the wedges, which explains the difference in hardness and Young's modulus between the two samples.

Spray forming (SF) can be classified as a two-stage manufacturing process in which solidification begins during particle flight, a relatively rapid solidification step that ends as the deposit builds up, with the remaining liquid droplets solidifying at considerably slower rates. Due to the high cooling rate of the atomization step and the special conditions of deposit buildup, with incoming materials dynamically refining the solidifying material, as-sprayed deposits typically display a fine-scale microstructure which may also exhibit some extended solid solubility and metastable phases. Our group has studied several alloys in order to investigate the potential formation of novel microstructures by this process. This paper describes some of the results obtained by spray forming of aluminum- and iron-based alloys, whose compositions derive from rapid solidification studies aimed at obtaining amorphous structures. Al85Y8Ni5Co2, Fe83Zr3.5Nb3.5B9Cu1, [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4, and Fe63Nb10Al4Si3B20 glass-forming alloys were processed. Formation of amorphous phase was observed throughout the deposit of the Al-based alloy processed at a high G/M ratio, which was not observed in the Fe-based alloys. In addition, the [(Fe0.6Co0.4)0.75B0.2Si0.05]96Nb4 alloy, which displayed the highest glass-forming ability among the Fe-based alloys, showed a high volume percent of amorphous phase formation up to 4mm thickness of the deposit, a similar value obtained for this alloy when processed by copper mold casting.

In this study, the effect of the microstructural characteristics on the mechanical properties of rapidly solidified A359-type alloy was analyzed. As a result of the rapid solidification processing by melt-spinning, fine equiaxed cells grains with sizes in the range of 0.4–0.7 μm were observed in the ribbon. Heat treatment of the as melt-spun ribbon showed a growth of the nanosized Si particles from 19 nm to 80 nm (200 °C/12 h) and to 1.72 μm (450 °C/12 h). The improvement in hardness and tensile properties are related to supersaturated α-Al solid solution and to the structural refinement. The decrease in hardness and in the tensile properties after thermal ageing is attributed to Si precipitation and subsequent growth of Si particles. The as melt-spun and after heat treated at 200 °C ribbons exhibited a brittle fracture different of the after heat treated at 450 °C ribbon which showed a ductile fracture surface.

In the present work, an Al–Fe–Cr–Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted using laser processing techniques. The surface of spray formed Al91Fe4Cr3Ti2 bulk samples was remelted using a 2 kW CW Nd:YAG laser. Two different laser beam powers were applied with the goal of studying its influence in the quasicrystalline phase formation in the remelted coating. After laser treatment, the samples were characterized by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (FEG-SEM). The formation of quasicrystalline phases was observed in the X-ray diffractograms and their transformations were verified in DSC analyses. A greater formation of quasicrystalline phase was verified in the coating produced with smaller laser beam power, i.e. higher cooling rate, and its morphology was more close to the sphere. The results indicate the possibility of producing low density coatings containing quasicrystalline phases by laser remelting of spray formed materials.

Three nanostructured aluminium-powder alloys were utilized as follows: a) supersaturated Al-4.5%Cu prepared by rapid solidification and mechanical-alloying; b) non-supersaturated Al-3.0%Fe, rich in precipitates, prepared by rapid solidification via gas atomization; and c) non-supersaturated 6061 Al alloy, rich in precipitates, prepared by rapid solidification via gas atomization and reinforced with Si3N4 particles). The three different alloys were consolidated into bulk material under various processing conditions via hot extrusion. The microstructure modifications of the consolidated alloys as a function of the extrusion conditions were discussed and investigated. The effect of the pre-existent precipitates from non-supersaturated alloys is shown to be more effective to grain growth controlling. The increase in the extrusionload with the increase of extrusion-rate and decrease of temperature are discussed in association with the modification in the microstructures

Nanostructured Al-3.0Fe-0.42Cu-0.37Mn powder alloy was deformed by extrusion over a temperature range of 375 °C to 425 °C, a ram speed range of 1 to 30 mm/s, and an extrusion rate of 10:1. Flow stresses and strain rates were calculated from the experimental ram pressures and speeds. The stress–strain-rate–temperature relationship in the extrusion of the nanostructured alloy was found to be similar to that in hot-worked conventional materials. The extrusion, torsion, compression, and creep data of nanostructured and conventional materials, extending over ten orders of magnitude of strain rate and over two orders of magnitude of stress, were correlated by a hyperbolic-sine constitutive equation, because the power and exponential laws lose linearity at high and low stresses, respectively. The hyperbolic-sine equation is widely used to correlate the hot-working behavior of conventional materials. It was concluded that the hot working of nanostructured powders is a thermally activated process in which the rate-controlling mechanism is the climb of edge dislocations. Microstructural changes in the consolidated alloys as a function of the extrusion conditions were investigated. An analysis was made of the dislocation behavior in very small grains of nanostructured metal by transmission electron microscopy (TEM) and we identified a dislocation structure and the different ways it appears in 40- to 100-nm Al-alloy grains. We also discuss the thermally activated propagation of dislocations and their interactions with shear bands/grain boundaries (SBs/GBs), and dislocation loops. Microstructural features including low-angle GBs, high-angle GBs, and equilibrium GBs and subgrain boundaries were observed. Dislocation structures under a deformation condition were studied to investigate the microstructural evolutions, which revealed some unique microstructural features such as dislocation tangle zones (DTZs) and dense-dislocation walls (DDWs), and the recovery process is discussed herein.

A bulk sample of Al–Fe–Cr–Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted, using laser processing techniques, to produce a quasicrystalline surface coating. After the laser treatment, the samples were characterized by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and scanning/transmission electron microscopy. The results indicate the feasibility of producing low-density coatings containing quasicrystalline phases by laser remelting on a bulk sample of an aluminum-based alloy.

Two nanostructured aluminum powder alloys (supersaturated Al4.5Cu prepared by mechanical alloying, and Al3.0Fe0.42Cu0.37Mn rich in precipitates and prepared by rapid solidification via gas atomization) were consolidated into bulk material under various processing conditions via hot extrusion. The microstructural modifications and mechanical properties of the consolidated alloys as a function of the extrusion conditions were investigated and are discussed here. The effect of pre-existing precipitates from nonsupersaturated alloy is shown to be more effective for controlling grain growth during consolidation. The increase in the extrusion load, with a concomitant increase in the extrusion rate and decrease in temperature, is shown to lead to microstructural modifications. The differences in mechanical properties measured by compressive tests are also discussed in association with the extrusion parameters. Furthermore, suggestions are given for rationalizing the extrusion rate and temperature for the consolidation of nanostructured aluminum powder alloys via hot extrusion.

In the present work, the glass forming ability (GFA) and its compositional dependence on Al-Ni-Ce system alloys were investigated as a function of several thermal parameters. Rapidly quenched Al 85 Ni 15-x Cex (X=4,5,6,7,10), Al 90 Ni 5 Ce 5 , Al 89 Ni 2.4 Ce 8.6 , Al 80 Ni 15.6 Ce 4.4 and Al 78 Ni 18.5 Ce 3.5 amorphous ribbons were produced by melt-spinning and the structural transformation during heating was studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that the GFA and the thermal stability in the Al-rich corner of Al-Ni-Ce system alloys were enhanced by increasing the solute content and specifically the Ce content. © 2008 Elsevier B.V. All rights reserved.

Amorphous alloys present exceptional values of mechanical strength but lack any significant plasticity at room temperature. Deformation of amorphous alloys occurs in shear transformation zones that connect to form shear bands, which are easier to deform than the surrounding matrix, thus facilitating further deformation in the same location of the specimen. However, the presence of particles dispersed in the amorphous matrix can modify such strain softening behavior, resulting in real plastic deformation before fracture. Also, depending on the type of particles and how they are introduced, they can modify the crystallization behavior of the amorphous matrix by acting as heterogeneous nucleation sites. In this context, this paper reports on the effects of the addition of SiC particles on the crystallization of Al 84 Ni 8 Co 4 Y 3 Zr 1 amorphous ribbons. Pre-alloyed ingots with and without added SiC particles were melt-quenched into amorphous ribbons by the single-roller melt-spinning technique and then selectively and partially crystallized at the first and second crystallization temperatures, as determined by differential scanning calorimetry. Primary crystallization of nanometric-sized fcc-Al crystals was found to occur in both ribbons (with and without added SiC), confirming that crystallization reactions were not altered by the ceramic particles. Aluminum carbide (Al 4 C 3 ) crystals resulting from high-temperature liquid metal/SiC reactions were observed as coatings on the SiC particles and as isolated particles dispersed in the amorphous solid matrix. In both cases, the Al 4 C 3 particles also did not change the crystallization behavior of the amorphous Al 84 Ni 8 Co 4 Y 3 Zr 1 matrix, since no heterogeneous nucleation of fcc-Al crystals was observed.

Despite, the homogeneous and refined microstructure, spray-formed deposits of binary Fe–Si alloys with high silicon content are still difficult to hot/cold roll due to A2-disordered/B2-ordered reactions. The addition of aluminum to Fe–Si alloys may be able to keep the A2-disordered phase metastable at temperatures below 973 K, allowing the deposits to be rolled without cracking while adequately maintaining their magnetic properties. This study is a first attempt to investigate the microstructure and the magnetic properties of spray-formed Fe–3 wt.%Si–3.5 wt.%Al alloy. Argon and nitrogen were used as atomization gases. The addition of aluminum to Fe–Si alloys led to the successful production of thin sheets (0.5 mm thickness) from spray-formed deposits when using argon as atomizing gas. In contrast, the use of nitrogen led to the formation of AlN particles, resulting in excessive brittleness of the spray-formed deposit, which fractured during cooling to room temperature. Otherwise, the magnetic properties of the Fe–3.0 wt.%Si–3.5 wt.%Al alloy performed very well when compared with binary Fe–6.5 wt.%Si, especially when spray formed with argon.

The microstructure and the tensile properties of an spray co-deposited Al-8.9 wt.% Si-3.2 wt.% Cu-0.9 wt.% Fe + (Al-3 wt.% Mn-4 wt.% Si)p composite was investigated after extrusion and heat treatment. The composition of the AlMnSi p alloy was selected aiming to improve the formation of α-Al(Fe,Mn)Si instead of β-Al(Fe,Mn)Si intermetallic. The spray formed deposits were extruded at 623 K and heat treated to peak aged (T6) condition. Room temperature tensile tests of the spray formed and extruded/heat treated alloy showed significant increase of elongation to fracture when compared with the values observed for the as-spray formed deposits, >10% and

In this study the Fe63Nb10Al4Si3B20 (at.%) alloy was processed by spray forming with the aim of investigate the formation of amorphous phases and novel microstructures by the high cooling rate involved in this process. The gas/metal mass flow rate used was 0.25, and nitrogen was used as the atomization gas. The resulting deposit of a mass of about 1.2 kg, as well as the overspray powder, with a median particle diameter about 120 μm, were characterized by using X-ray diffractometry, differential scanning calorimetry and scanning and transmission electron microscopy with energy of dispersive spectroscopy. Magnetic properties were measured through hysteresis loop tracer equipment. The overspray powder presented a mass median diameter of d50 ≅ 120 μm and an increasing of amorphous phase volume fraction with decreasing of particle size. The microstructure of the deposit was heterogeneous varying with the thickness, presenting at center region 20 mm and at border 1 mm with different porosities 5 and 10%, respectively. The thicker region presented fully crystalline microstructure whereas the thinner presented about 75% amorphous phase. The phases identified in both deposit and overspray powder were: amorphous, α-Fe, Fe23B6, FeB and FeNbB. Amorphous phase formation in the thinner region of the deposit and the absence in the thicker region indicates that the resulting amorphous phase depend on the maintenance of amorphous phase formed during atomization that might be controlled by process parameters. Spray forming of Fe-based amorphous alloys followed by hot consolidation in T

The microstructure and the tensile properties of an Al–8.9 wt.% Si–3.2 wt.% Cu–0.9 wt.% Fe–0.8% Zn alloy processed by spray forming was investigated. The porosity level, the conditions of the heat treatment applied and the presence/addition of certain alloying elements to this alloy is known to greatly affect its mechanical properties. In this work, the alloy was gas atomized with argon and deposited onto a copper substrate, extruded at 623 K and heat treated to the T6 temperature Mg was added to some heats. Room temperature tensile tests of the spray formed and extruded alloy showed significant increase of elongation when compared with the values observed for the as-spray formed deposits. This result can be ascribed to the decrease of porosity promoted by the extrusion process. The spray formed and extruded, T6 heat-treated samples showed significant increase of strength without lowering the elongation results. The addition of 0.3 wt.% Mg increased the response to the heat treatment process.

Aluminum additions to brittle Fe–6.5 wt.% Si alloys made possible the mechanical processing of these alloys at lower temperatures and thus being determinant in the development of the texture. The aim of this work was to analyse the evolution of the crystallographic texture of a spray-formed (SF) Fe–6.5 wt.% Si–1.0 wt.% Al during rolling operation for thin sheets production. The SF deposit was warm-rolled and then air cooled to obtain partial recrystallisation. The initial texture (0 1 1) [ 0 1 ¯ 1 ] [1 0 0] (// to normal direction-ND) of the deposit was changed to approximately (0 1 3) [ 1 1 ¯ 0 ] [1 1 0] (8° from ND) after the last reduction step. The maxima intensities of texture was found at 700 °C (89% of reduction) showing the influence of rolling temperature; after warm-rolling the entire texture changes to a partial ND fibre running from {0 0 1} to {1 1 0}, with negligible Goss intensities. The transition away from an ND fibre texture in the lattermost case (99.5% reduction) was in turn associated with the near-absence of shear bands.

In the Ni–Si system, the eutectic structure composed of Ni–Ni3Si presents inherent thermal stability, allowing composite materials to be obtained with well-aligned and finely dispersed microstructures. The work reported here consisted of an investigation into the microstructure and morphology of such a eutectic alloy from the standpoint of its growth conditions. A Ni–Si eutectic alloy was processed by applying the directional solidification method at low growth rates and the rapid solidification technique using a melt-spinning process. The results indicate that samples processed under conditions close to equilibrium show a regular and aligned microstructure, while rapid solidification leads to an anomalous microstructure and the formation of a metastable phase.

The glass former Fe 83 Zr 3.5 Nb 3.5 B 9 Cu 1 (at.%) alloy was processed by spray forming. The aim was to investigate the possibility of forming novel microstructures using this process. The ratio between the gas mass flow rate and the metal mass flow rate used was 0.23, and nitrogen was used as atomization gas. The resulting deposit, weighting about 0.8 kg, as well as the overspray powder with a median particle diameter about 150 μm, were characterized by using X-ray diffratometry, differential scanning calorimetry and scanning electron microscopy with energy dispersive spectroscopy. Saturation induction ( B s ), maximum permeability ( μ max ) and coercive field ( H c ) were measured. The overspray powder showed a microstructure consisting of amorphous and α-Fe phases. The volume fraction of the amorphous phase decreased as the granulometric size range increased. The deposit presented fully crystalline structure with α-Fe, Fe 3 Nb, Fe 2 Zr and Fe 2 B phases. The formation of amorphous phase in the overspray and its absence in the deposit indicates that the deposit was formed by the impacting of a high volume fraction of fully liquid droplets, providing temperature and time enough for complete crystallization of the deposit.

The microstructure and the tensile properties of an Al–8.9 wt.% Si–3.2 wt.% Cu–0.9 wt.% Fe–0.8% Zn alloy processed by spray forming was investigated. The alloy was gas atomized with argon and deposited onto a copper substrate. The microstructure was evaluated by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Small faceted dispersoids observed surrounding equiaxial α-Al matrix were identified by SEM–EDS as silicon particles. Sand cast samples with the same composition showed a columnar dendritic α-Al matrix, Al–Si eutectic, polyhedric α-AlFeSi and needle-like β-AlFeSi intermetallics. In the spray formed material the formation of the Al–Si eutetic was suppressed, and the formation of the α-AlFeSi and β-AlFeSi intermetallics was strongly reduced. The fine and homogeneous microstructure showed an aluminium matrix with grain size ranging from 30 to 40 μm, and particle size of the silicon dispersoids having a mean size of 12 μm. Room temperature tensile tests of the spray formed alloy showed relative increasing of strength and elongation when compared with the values observed for the conventionally cast counterparts. These results can be ascribed to the refined microstructure and the scarce presence of intermetallics of the spray formed material.

In the present work the fluxing technique was applied to the Sn–51 wt.% Se hypoeutectic alloy. The aim was to study the influence of the undercooling on the microstructure of this alloy, particularly concerning the formation of oriented microstructure and even some metastability occurrence. High undercooling (63 °C) was achieved for the primary SnSe phase leading to an oriented microstructure in the firstly solidified region. Although the undercooling for the eutectic was not so high (19 °C) morphological changes were observed. The rapid movement of the interface interfered with cooperative eutectic growth producing an irregular eutectic in the first region to solidify followed by a fine lamellar and directional eutectic. In order to detect some supersaturated solid solution in the SnSe phase a precise lattice parameter measurement was done from the accurate performed X-ray diffraction (XRD) on the firstly solidified region of the sample.

Understanding the crystallization of metallic glasses is essential for the consolidation of amorphous ribbons and powders into larger bodies. In this paper, we describe the evolution of crystalline phases formed during thermal induced crystallization of amorphous Al 84 Ni 8 Co 4 Y 3 Zr melt-spun ribbons. Partially and fully crystallized samples were prepared either by heating in a differential scanning calorimeter to temperatures corresponding to each crystallization stage or by isothermal annealing in a heated oil bath at 473 and 628 K (±1 K). Isothermal annealing time ranged from 1 to 120 min. Thermal analysis. X-ray diffraction and transmission electron microscopy were used to determine both the reactions involved and the phases formed upon crystallization. Crystallization occurred in multiple stages, with nanometer-sized crystals of fcc-Al and Al 9 Co 2 phases formed in the first and second initial stages, respectively, and formation of Al 16 Ni 3 Y-like. Al 3 Y and Al 3 Zr phases upon the final reactions. Both fcc-Al and Al 9 Co 2 were found to primarily crystallize from the amorphous material. An Al 16 Ni 3 Y-like phase was formed by polymorphous crystallization of the amorphous phase remaining after the second stage.

Amorphous Fe‐M‐B (M‚Zr, Nb) based alloys with nanometer-sized crystallites have attracted attention due to their magnetic properties. Although corrosion resistance is a desirable property in such alloys, no study concerning this aspect has been reported. The eAect of metalloid content and partial crystallization on corrosion resistance of Fe‐M‐B (M‚Zr, Nb) amorphous alloys, Fe84Nb7B9 ,F e 84Zr7B9 and Fe83Zr3:5Nb3:5B9Cu1, was investigated. Corrosion resistance measurements were carried out by mass loss, potentiodynamic polarization, and thermogravimetric mass gain measurements. The partial crystallization of the amorphous alloy results in a decrease of the corrosion resistance for all the compositions analyzed. We also observed a greater corrosion resistance when Nb was present in comparison to the case when Zr was present. These results are an eAect of the superficial passive film protector formed. ” 2000 Published by Elsevier Science B.V. All rights reserved.

Process parameters optimization for the spray forming of a Cu–6% Zn alloy was developed by a combination of mathematical simulation and the factorial design method (FDM). The finite difference method was used for the mathematical simulation of the atomization stage and two levels FDM was applied considering the initial gas velocity, the axial distance between the atomizer and the substrate, the superheating of the melt and the melt flow rate. The validation of the optimized process parameters was done by processing the Cu–Zn alloy, a high-density deposit, as high as 98.5% of the theoretical density with a very homogeneous microstructure being produced.

Mechanical alloying, MA, is a high-energy ball milling technique, in which elemental blends are milled to achieve alloying at atomic level. This communication describes the results of an investigation on the phase transformation of a mixture of Fe and Si powders with 6wt%Si during MA processing. Besides the verification of the effect of milling time on the structure and on the compositional homogeneity, this study was undertaken in order to confirm, by using TEM technique, the possibility of amorphous phase formation for Si content lower than 17.7wt%.

Nano-quasicrystalline Al-Fe-Cr based alloys produced by rapid solidification processes exhibit high strength at elevated temperatures. Nevertheless, the quasicrystalline particles in these systems become unstable at high temperature limiting the industrial applications. In early works, it was observed that the use of Nb or Ta increases the stability of the Al-Fe-Cr quasicrystalline phase delaying the microstructural transformation to higher temperatures. Thus, these nano-quasicrystalline Al-based alloys have become promising new high strength material to be used at elevated temperatures in the automotive and aeronautical industries. In previous works, nano-quasicrystalline Al-Fe-Cr-Nb based alloys were obtained by rapid solidification using the melt-spinning technique. In order to obtain bulk alloys for industrial applications other fabrication routes such as powder production by gas atomization followed by compaction and extrusion are required. In the present work, the production of Al-Fe-Cr-Nb based alloys by powder atomization at laboratory scale was investigated. The powders obtained were sieved in different ranges of sizes and the microstructures were characterised by means of X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive of X-ray analysis. Mechanical properties have been measured by compression tests at room temperature and at 250C. It was observed that a very high temperature is required to produce these alloys by gas atomization; the icosahedral quasicrystalline phase can be retained after the atomization in powder sizes typically under 75um, and also after the extrusion at 375C. The extruded bars were able to retain a very high strength at elevated temperature, around 60% of the yield stress at room temperature, in contrast with the 10-30% typically obtained for many commercial Al alloys. Fil: Audebert, Fernando Enrique. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Galano, Marina Lorena. University Of Oxford; Reino Unido Fil: Triveño Rios, C.. Universidade Federal Do Sao Carlos; Brasil Fil: Kasama, H.. Universidade Federal Do Sao Carlos; Brasil Fil: Peres, M.. Universidade Federal Do Sao Carlos; Brasil Fil: Kiminami, C.. Universidade Federal Do Sao Carlos; Brasil Fil: Botta, W. J.. Universidade Federal Do Sao Carlos; Brasil Fil: Bolfarini, C.. Universidade Federal Do Sao Carlos; Brasil

The microstructure and the tensile properties of a spray-formed and extruded Al-9Si-4Cu-1Fe alloy were investigated. Manganese (0.3, 1, 2 in wt%) was added to the alloy to avoid the formation of the needle-like β-AlFeSi intermetallic phases that are highly detrimental to the alloy's ductility. The deposits were extruded at 623K with a n area reduction of 5 to 1. Small faceted dispersoids surrounding the equiaxial α-Al matrix, mainly in the form of silicon particles, were identified by SEM-EDS, as well as the Mn-containing α-Al15(Fe,Mn)3Si2 phase. The presence of the needle-like β-Al(Fe,Mn)Si was scanty, even with the lowest Mn content. The room temperature tensile tests of all the extruded alloys showed a significant increase in elongation to fracture when compared with the values observed fo r the as-spray formed deposits.This result can be ascribed to the elimination of porosity promoted by the extrusion process and to the smaller grain size of the extruded samples.