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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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

Aluminum matrix composites reinforced with Al–Ni intermetallic compounds and Al 2 O 3 were obtained by hot pressing of high-energy milled powders. Using the reaction between Al and NiO and aiming to preserve part of the Al content after completing the reaction by increasing the relative amount of Al, composites containing Al 2 O 3 and Al–Ni intermetallic compounds were produced. These composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Depending on the Al/NiO molar ratio, the reaction can be activated either during milling or during subsequent hot pressing. Hence, two different processing routes can be used to produce such composites. Starting from powder mixtures with an Al/NiO molar ratio of 15/3, the reaction took place during milling, forming Al 3 Ni and Al 3 Ni 2 plus Al 2 O 3 reinforced Al composite powder, which was consolidated by hot pressing. An Al/NiO molar ratio of 20/3 prevented the reaction from occurring during milling, but enabled it to occur during subsequent hot pressing, forming the same reinforcement phases. The reactive-milled composite is harder and presents higher porosity than the reactive-sintered ones, after consolidation by hot pressing under the same parameters. In the latter route, the longer the milling time prior to hot pressing, the smaller the size of the reinforcement phases.

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.

A thermodynamic approach to predict bulk glass-forming compositions in binary metallic systems was recently proposed. In this approach, the parameter γ * = Δ H amor /(Δ H inter − Δ H amor ) indicates the glass-forming ability (GFA) from the standpoint of the driving force to form different competing phases, and Δ H amor and Δ H inter are the enthalpies for glass and intermetallic formation, respectively. Good glass-forming compositions should have a large negative enthalpy for glass formation and a very small difference for intermetallic formation, thus making the glassy phase easily reachable even under low cooling rates. The γ * parameter showed a good correlation with GFA experimental data in the Ni–Nb binary system. In this work, a simple extension of the γ * parameter is applied in the ternary Al–Ni–Y system. The calculated γ * isocontours in the ternary diagram are compared with experimental results of glass formation in that system. Despite some misfitting, the best glass formers are found quite close to the highest γ * values, leading to the conclusion that this thermodynamic approach can be extended to ternary systems, serving as a useful tool for the development of new glass-forming compositions. Finally the thermodynamic approach is compared with the topological instability criteria used to predict the thermal behavior of glassy Al alloys.

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 present work Fe 73− x Nb x Al 4 Si 3 B 20 ( x = 5, 10) alloys have been processed by melt-spinning with the aim of studying the crystallization sequence through annealing in suitable temperatures. Melt-spun ribbons were characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) through Cu-Kα ( λ = 1.54 A) and synchrotron radiation ( λ = 1.77 A) and transmission electron microscopy (TEM). Soft magnetic properties were measured through the hysteresis loop tracer. In-situ XRD through synchrotron radiation was very accurate in phase identification. Fe 73− x Nb x Al 4 Si 3 B 20 ( x = 5, 10) alloys showed the possibility of forming ferromagnetic amorphous alloys composed of commercial Fe-based master alloys with fine nanocrystalline structure and good soft magnetic properties.

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.