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In this study, we propose a method to produce nanocrystalline TiFe powder by high-energy ball milling, in order to avoid the common sticking problem of the material to the milling tools, assuring a material prompt to absorb hydrogen as well. The method consists of making a preliminary milling operation with the elemental powders (50:50 stoichiometric ratio) to form a strong adhered layer of the milled material on the surfaces of the vial and balls. The main milling operation is then performed with a new powder charge (same composition as before), but now adding a process control agent (stearic acid). Various processing times - 2, 6, 10 and 20 h - were used in the milling experiments. Nanocrystalline TiFe was synthesized in this way with low oxygen contamination, full yields for milling times of 6 h or over, requiring no heat treatments for the first hydrogen absorption. Hydrogen storage capacity of 1.0 wt% at room temperature under 20 bar was attained by the sample milled for 6 h. Kinetic data from samples milled for 2 h and 6 h agreed with Jander model for the rate limiting step of the hydriding reaction, which is based on diffusion with constant interface area.

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.

Heating-induced crystallization of high-entropy (HE) (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)86‒89B11‒14 amorphous (am) alloys is examined to develop new structural materials with low B contents. The crystallization of 11B alloy occurs in three stages: first nanoscale bcc precipitates form in the amorphous matrix, second nanoscale fcc precipitates form, and the residual amorphous phase disappears in the third stage which yields borides in addition to the bcc and fcc phases. Crystallization of 14B alloy is the same, except that the order of appearance of bcc and fcc is reversed. The bcc and fcc particle diameters are 5–15 nm and remain almost unchanged up to ∼960 K. On annealing, ultrahigh hardness of 1500–1550 (unprecedented for boride-free structures) is attained just before the third crystallization stage. This hardening and the thermal stability of the novel [am + bcc + fcc] structures are remarkable at such low boron content and encouraging for development as ultrahigh-strength alloys. The results are interpreted in terms of the nature and extent of partitioning of elemental components between the bcc/fcc phases and the amorphous matrix, and the size and defect structures of the bcc and fcc precipitates. The magnetic flux density at room temperature increases by precipitation of bcc and decreases by appearance of fcc. Slower quenching of the 11B alloy shows a pseudo-polymorphic crystallization that may be characteristic of multicomponent HE systems.

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.

The body-centered cubic (BCC or β) titanium alloys are attractive materials for hydrogen storage applications, due to their relatively high absorption capacities that can be attained in some cases, even at room or moderate temperatures. It is known that the ball milling techniques improve the H-absorption/desorption kinetics. Thus, different compositions with Ti/Nb atomic ratios of 1.0, 1.5 and 2.3 were prepared by mechanical alloying (MA) and reactive milling (RM), and the composition effects on the microstructure and the hydrogenation properties were characterized. Both procedures, MA and RM, were able to produce TixNb1-x BCC alloys. It was observed a significant influence of Ti/Nb atomic ratios on lattice parameters, crystallite and particle sizes, effective kinetic parameter, Avrami exponent, hydrogen storage capacities, reversibility, and desorption temperature ranges. The RM synthesized hydrides acquired better H-absorption/desorption properties than the Ti Nb hydrides produced by mechanical alloying hydrogenated at 250–300 °C. The results demonstrated changes in the hydride nucleation manner and improvement of the hydrogenation rates when the Nb addition is increased.

Mg - 40 wt % TiFe nanocomposite was prepared by high-energy ball milling, HEBM, aiming improved hydrogen absorption at room temperature (RT). Four processing routes were chosen to separately investigate the effects of TiFe addition, HEBM processing and dispersion of TiFe particles, being: Route 1 – mechanical mixture of Mg and TiFe powders; Route 2 – HEBM of Mg + TiFe at 400 rpm for 12 h; Route 3 – HEBM of pure Mg at 400 rpm for 12 h to be used as reference; and Route 4 – HEBM of Mg + TiFe at 600 rpm for 36 h. In this case, TiFe was previously milled with ethanol to improve its refinement level. It is shown that the synergetic effects of TiFe addition, HEBM processing and thermal activation – involving the creation of Mg TiFe interfaces, the refinement and distribution of TiFe and also the presence of free Fe – lead to good hydrogenation kinetics at RT in Mg TiFe nanocomposite. It is also shown for the first time that the milled pure Mg can absorb hydrogen at RT.

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.

Pseudo-high entropy (PHE) amorphous alloys have emerged as novel metallic materials. Some Fe-containing PHE amorphous alloys display the unique characteristic of maintaining a clustered glassy structure in a wide temperature range, and eventually crystallize multi-principal element (MPE) phases whose composition is close to the parental alloy composition. Therefore, these PHE amorphous alloys promise to surpass the trade-off between crystallization and corrosion resistance typical of most bulk metallic glasses. This work investigates the corrosion resistance in chloride media of (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)100−xBx (x = 8, 10, 12) alloys produced by melt-spinning. The B-richest composition, (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)88B12, ensured fully amorphous ribbons, while MPE nanocrystals were formed within the amorphous (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)90B10 and (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)92B8 ribbons. All alloys were corrosion-resistant in acidic (pH 3) and alkaline (pH 10) chloride-rich electrolyte (35 g L−1 NaCl) and in a hypersaline medium (250 g L−1 NaCl, pH 3), as verified from potentiodynamic polarization and electrochemical impedance spectroscopy measurements. From x-ray photoelectron spectroscopy, the formation of a nanometric-thick film composed of Fe-, Co-, Ni-, Cr-, and Mo- compounds on the alloys' surface was observed, responsible for granting the corrosion resistance of all alloys. Although containing crystals, the B-poorest alloy, (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)92B8, presented comparable and even superior corrosion resistance than the fully amorphous B-richest alloy, (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)88B12. The maintenance of the corrosion resistance of the (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)90B10 and (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)92B8 alloys in the presence of crystals were ascribed to the reduced elemental partition upon crystallization of MPE phases. The excellent corrosion resistance nevertheless vanished if excessive crystallization occurs, forming borides. These findings open new prospects for overcoming the corrosion-wear resistance paradigm of amorphous/crystalline alloys, essential to design materials and coatings to endure harsh environments.

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.

The influence of Cr addition in a rapidly solidified Al-Ni-Co alloy was investigated. Melt spun samples of atomic composition Al71Ni20Co9, Al72Ni19Co7Cr2 and Al72Ni20Co5Cr3 were studied by X-ray diffraction and transmission electron microscopy. Aiming to develop quasicrystalline compositions enriched in corrosion resistant elements such as Cr and Ni this work presents, for the first time, the effect of Cr addition on the quasicrystalline phase formation of a high-Ni Al-Ni-Co rapidly solidified alloy chosen to be within the range of formation of the decagonal quasicrystalline phase observed in this ternary system. The composition of the quaternary alloys was chosen by reducing the Co content in favor of Cr on the ternary alloy and keeping the average valence electron per atom (e/a) around 1.86. The phase constitution of the ternary alloy consisted of the decagonal phase along with two intermetallic phases, Al3Ni and Al3Ni2. The addition of Cr resulted in the formation of a second quasicrystalline decagonal phase, rich in Cr. This was due to the low Cr solubility on the ternary Al-Ni-Co decagonal and intermetallic phases, which rejected Cr and resulted on the formation of the Cr-rich quasicrystal.

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.

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 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.

In this work, the corrosion behavior of amorphous and partially crystallized Fe68Cr8Mo4Nb4B16 alloys has been studied. Fully amorphous ribbons were prepared by melt spinning and then partially and fully crystallized at different heat treatment temperatures. The corrosion behavior was evaluated in chloride-rich media at different pHs, ranging from acidic to alkaline. An exceptionally high corrosion resistance was observed for the new Fe68Cr8Mo4Nb4B16 amorphous alloy in the proposed media and pHs. The amorphous phase containing corrosion-resistant alloying elements such as chromium and molybdenum led to the formation of a highly stable passivating film, which coated and protected the active exposed metal surface. Partially crystallized samples heated up to 700 °C still grant the formation of a corrosion-resistant passivating layer. The presence of such a layer was correlated to the non-percolation of crystals embedded into the corrosion-resistant amorphous matrix. The corrosion resistance of fully crystalline annealed ribbons and as-cast ingots did not present the similar superior corrosion performance. This behavior was assigned to element partitioning throughout the crystallization, particularly chromium, which led to a non-homogeneous structure that preferentially triggered and held pitting corrosion along with the percolated crystalline material. These results indicate that the Fe68Cr8Mo4Nb4B16 alloy is a candidate for corrosion resistant coating where the suppression of crystallization is unavoidable.

High-entropy (Fe0.25Co0.25Ni0.25Cr0.125Mo0.0625Nb0.0625)100‒xBx amorphous alloys are formed with low (8–14 at%) boron contents by melt spinning. With increasing boron, the broad halo in X-ray diffraction shifts to indicate a decreasing average spacing of nearest-neighbor atoms. The crystallization onset temperature and the Vickers hardness increase with boron content. The glass transition is observed even for a low-boron (13 at%) alloy. The 8–11 at% B alloys crystallize in stages: [am] → [am’ + bcc] → [am″ + bcc + fcc] → [bcc + fcc + borides]. The bcc precipitates, diameter ∼10 nm enriched in (Fe,Co) and the fcc precipitates, diameter ∼15 nm enriched in (Ni,Fe), are stable on annealing over a wide range (900–1060 K) below the temperature at which borides form. The bcc phase shows no internal defects, while the fcc phase has defects such as twin boundaries. The microhardness (Hv) of the [am″ + bcc + fcc] nanostructure reaches a high maximum of 1460–1560 kgf‧mm−2, before decreasing rapidly when the formation of borides marks the disappearance of the residual amorphous phase. The high thermal stability of the three-phase nanostructure is attributed to the residual amorphous phase enriched in B, Cr, Mo and Nb. These low-boron metastable alloys with novel three-phase nanostructures are attractive as potential amorphous coatings or ultrahard structural alloys with high thermal stability.

Heating-induced crystallization of high-entropy (HE) (Fe0.25Co0.25Ni0.25Cr0.125Mo0.125)86‒89B11-14 amorphous (am) alloys is examined to develop new structural materials with low B contents. The crystallization of 11B alloy occurs in three stages: first nanoscale bcc precipitates form in the amorphous matrix, second nanoscale fcc precipitates form, and the residual amorphous phase disappears in the third stage which yields borides in addition to the bcc and fcc phases. Crystallization of 14B alloy is the same, except that the order of appearance of bcc and fcc is reversed. The bcc and fcc particle diameters are 5-15 nm and remain almost unchanged up to ~960 K. On annealing, ultrahigh hardness of 1500-1550 (unprecedented for boride-free structures) is attained just before the third crystallization stage. This hardening and the thermal stability of the novel [am + bcc + fcc] structures are remarkable at such low boron content, and encouraging for development as ultrahigh-strength alloys. The results are interpreted in terms of the nature and extent of partitioning of elemental components between the bcc/fcc phases and the amorphous matrix, and the size and defect structures of the bcc and fcc precipitates. The magnetic flux density at RT increases by precipitation of bcc and decreases by appearance of fcc. Slower quenching of the 11B alloy shows a pseudo-polymorphic crystallization that may be characteristic of multicomponent HE systems.

In this work, we present a wear-resistant coating fabricated by non-vacuum electron beam cladding of Fe62Cr10Nb12B16 at.% powder on a mild steel substrate. The protective coating was 1.3 mm thick, dense, and exhibited an α-(Fe,Cr) matrix reinforced by a significant fraction of hard borides formed upon solidification. Micrometric and nanometric borides homogeneously dispersed within the matrix were formed due to the homogeneous melting and the relatively fast cooling to suppress the excessive phase growth. An intimate metallurgically bonded interface between the coating and substrate was characterized by low compositional dilution and a fine eutectic-like transition zone microstructure anchoring the dissimilar materials. The coatings displayed a higher wear resistance compared to the mild steel substrate, showing specific wear rates, κ, about one order of magnitude lower (10−5 against 10−4 mm3/N.m, respectively). The abrasive wear mechanism was dominant for the coating sample when tested at low sliding velocity, 10 cm/s, due to the detachment of hard borides from the surface and their incorporation into the tribosystem. The adhesive wear mechanism was found to be dominant at higher sliding velocities of 20 and 40 cm/s. Dry sand/rubber wheel testing revealed the higher resistance of the coating against abrasive wear compared to the mild steel substrate. Regardless of the wear mechanism, the Fe62Cr10Nb12B16 at.% coatings showed a superior sliding and abrasive wear resistance and represented an interesting protective measure to extend the service of inexpensive mild steel components.

Rapidly solidified Al–Mn–Ce alloys have been reported to exhibit desirable properties due to the uniform distribution of quasicrystalline (QC) particles in an Al matrix. In this study, several ternary alloy compositions that encompassed the alloys reported in the previous reports, namely Al–6Mn–2Ce, Al–6Mn–4Ce, Al–8Mn–4Ce, Al–12Mn–2Ce and Al–10Mn–5Ce, were prepared by melt spinning and their microstructures were characterized by electron microscopy and X-ray diffraction. The results are in direct contrast with the previous reports available in the literature in that the formation of QCs was only observed in the Al–12Mn–2Ce alloy; in the others, the dispersed phase was not the QC; rather, the structural and compositional information presented in this paper together with data recently published in the literature enabled a reinterpretation of the effect of Ce on rapidly solidified Al–Mn alloys. The main conclusion is that Ce favors the formation of a ternary metastable phase with approximate stoichiometry Al20Mn2Ce. This phase forms in a wide portion of the Al-rich region of the ternary phase diagram and can even coexist with the QC phase in alloys containing low amounts of Ce; in this case, the QC contains no detectable Ce by TEM/EDS, consistent with the conclusion that Ce does not favor QC formation in contrast to the previous reports.

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

The crystallization behavior of Cu–Zr–Al alloys with different contents of oxygen and yttrium was studied. Three compositions were chosen based on the good glass former Cu–45Zr–8Al with varying Y contents (0, 0.3 and 2%) added to getter the oxygen from the glass. Melt spun ribbons were prepared and their crystallization behavior was analyzed by differential scanning calorimetry (DSC). Heat treatments were performed at selected temperatures based on the DSC data and the phases formed were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results revealed that oxygen has a strong influence on the crystallization behavior, it changes the mode and the phases formed and results in the formation of a metastable crystalline phase prior to the formation of the stable phases. The Y was found to have a more subtle effect: it lowers the incubation time for crystallization and promotes heterogeneous nucleation of Cu10Zr7 and, therefore, adding Y to these alloys has this important drawback that is reported for the first time here. The mechanisms by which each of these elements acts are suggested. Finally the formation of defects in the Cu10Zr7 phase is reported.

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.

The thermal crystallization of Al-based metallic glasses can be described in association with the topological instability λ criterion. In the present work, we report on the crystallization behavior and glass forming ability of Al-rich, Al–Ni–Sm alloys, designed with compositions corresponding to the same topological instability condition of λ ≈ 0.1. Amorphous melt-spun alloys were prepared with the following compositions, varying the ratio of Ni and Sm elements: Al 87.5 Ni 4 Sm 8.5 , Al 83.5 Ni 10 Sm 6.5 , Al 80.5 Ni 14.5 Sm 5 and Al 76.5 Ni 20.5 Sm 3 . The glass forming ability of each alloy composition was evaluated based on the thermal parameters obtained from DSC runs and on X-ray diffraction patterns. Better glass forming ability was observed in compositions whose Sm content was increased and Ni content reduced. Thermal crystallization of the alloys with low Sm content showed only one crystallization peak and no glass transition event. In alloys with higher rare-earth content, a glass transition event was clearly detected before the crystallization event. The results are interpreted considering the different types and proportions of Sm–Al and Ni–Al clusters that can be formed in the alloys along the λ ≈ 0.1 line. They also emphasize the relevance of these different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallization.

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.

In this work, a criterion considering the topological instability ( λ ) and the differences in the electronegativity of the constituent elements (Δ e ) was applied to the Al–La and Al–Ni–La systems in order to predict the best glass-forming compositions. The results were compared with literature data and with our own experimental data for the Al–La–Ni system. The alloy described in the literature as the best glass former in the Al–La system is located near the point with local maximum for the λ ·Δ e criterion. A good agreement was found between the predictions of the λ ·Δ e criterion and literature data in the Al–La–Ni system, with the region of the best glass-forming ability (GFA) and largest supercooled liquid region (Δ T x ) coinciding with the best compositional region for amorphization indicated by the λ ·Δ e criterion. Four new glassy compositions were found in the Al–La–Ni system, with the best predicted composition presenting the best glass-forming ability observed so far for this system. Although the λ ·Δ e criterion needs further refinements for completely describe the glass-forming ability in the Al–La and Al–La–Ni systems, the results demonstrated that this criterion is a good tool to predict new glass-forming compositions.

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.

A combination of an extension of the topological instability “λ criterion” and a thermodynamic criterion were applied to the Al–La system, indicating the best range of compositions for glass formation. Alloy compositions in this range were prepared by melt-spinning and casting in an arc-melting furnace with a wedge-section copper mold. The GFA of these samples was evaluated by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. The results indicated that the γ* parameter of compositions with high GFA is higher, corresponding to a range in which the λ parameter is greater than 0.1, which are compositions far from Al solid solution. A new alloy was identified with the best GFA reported so far for this system, showing a maximum thickness of 286 μm in a wedge-section copper mold.