Corrosion inhibition in magnesium-aluminium-based alloys induced by rapid solidification processing

The effect of rapid solidification on the corrosion behaviour in aerated 0.001 M NaCl solution of Mg-Al alloys containing 9.6 to 23.4wt% AI has been investigated in comparison with chill-cast material. Polarization studies show that rapid solidification decreases corrosion current by up to two orders of magnitude corresponding to a corrosion rate of 6 to 11 mil y^–1. Increasing the aluminium content in solid solution by rapid solidification gave rise to a steep increase in pitting potential between 10 and 23 wt% Al and resulted in development of an anodic plateau at 30Acm^–2 attributable to magnesium depletion for the alloy surface and formation of a protective film. Chemical analysis of the electrolyte as a function of dissolution time for the rapidly solidified material indicated that initially only magnesium dissolved and that this dissolution of magnesium ceased within 2 to 5 min. The results indicate the formation of an aluminium-enriched interdiffusion zone at the surface underlying a more stable surface oxide than for ingot-processed Mg-Al-based alloys.     

Corrosion resistance enhancement of marine alloys by rapid solidification

Copper-nickel alloys used in marine applications, are known for their anti-fouling properties. However, they are generally of low strength and are moderately susceptible to corrosion when used in a marine environment. Attempts at adding iron to Copper-nickel alloys by conventional ingot metallurgy, to improve their mechanical and corrosion resistant properties, have met with limited success. In this work, rapid solidification technology was employed to produce rapidly solidified (RS) Cu-10Ni and Cu-10Ni-8Fe. It was found that both the RS Cu-10Ni and Cu-10Ni-8Fe exhibited superior mechanical and corrosion resistant properties, compared with their sand-cast counterparts. Furthermore, the addition of iron to Cu-10Ni alloy, produced by RS, increased the corrosion resistance of the alloy, whereas the addition of iron to Cu-10Ni alloy produced by conventional means, had an adverse effect.     

Al-based nanocrystalline composites by rapid solidification of Al-Ni-Sm alloys

Nanophase composites (Al-based materials with α-Al particles dispersed in an amorphous matrix) can be produced by melt spinning and annealing Al₈₈Ni_{12 − x}Sm_x (x = 2 to 10 at%) master alloys. The structures and the thermal stability of the ribbons obtained, asquenched and after annealing, are characterised by X-ray diffraction and differential scanning calorimetry. The mechanical properties of these composites, including hardness and abrasive wear resistance, are measured as a function of the volume fraction of α-Al nanocrystals in the amorphous matrix. The properties of these nanophase composites are compared with other industrial alloys in the aluminium family and show an exceptional hardness and wear resistance.     

The solidification characteristics of near rapid and supercooling directional solidification

In the comparison of the solidification characteristics of supercooling directional solidification (SDS) with constrained directional solidification (DS) and with the consideration of the inheritance of supercooled melt, the SDS technique established with the combination of melt supercooling and traditional DS was proposed. An exploring study on SDS techniques was also conducted using appropriate facilities, designed and manufactured by the authors’ laboratory and the deep supercooling of Cu–5.0%Ni alloy, and its DSs were implemented.     

The solidification characteristics of near rapid and supercooling directional solidification

In the comparison of the solidification characteristics of supercooling directional solidification (SDS) with constrained directional solidification (DS) and with the consideration of the inheritance of supercooled melt, the SDS technique established with the combination of melt supercooling and traditional DS was proposed. An exploring study on SDS techniques was also conducted using appropriate facilities, designed and manufactured by the authors’ laboratory and the deep supercooling of Cu–5.0%Ni alloy, and its DSs were implemented.     

Development and application of ferromagnetic alloys made by rapid solidification

Abstract

Amorphous alloys, made by rapid solidification, were first introduced in 1960 and precipitated a major new field of research in metallurgy. A part of this new field, dating from around 1975, involves magnetic alloys made by rapid solidification. These new magnetic alloys are critically assessed against the background of existing Si–Fe alloys and the new developments in high induction Si–Fe. It is concluded that these new alloys, of potentially very low cost, may be important in the highly automated manufacture of small transformers and small electricals machines.

MST/726     

Comparison of Fe-Ni based alloys prepared by ball milling and rapid solidification

Mechanical alloying (MA) and rapid solidification (RS) are two important routes to obtain amorphous alloys. An Fe-Ni based metal-metalloid alloy (Fe₅₀Ni₃₀P₁₄Si₆) prepared by these two different processing routes was studied by differential scanning calorimetry, scanning electron microscopy with microanalysis, inductive coupled plasma, X-ray diffraction (XRD) and transmission Mössbauer spectroscopy (TMS). The results were compared with that obtained from other Fe-Ni based alloys of similar compositions. The structural analyses show that the materials obtained by mechanical alloying are not completely disordered after 40 h of milling whereas fully amorphous alloys were obtained by rapid solidification. TMS analyses show that, independent of the composition, after milling for 40 h, about 7% of the Fe remains unreacted. Furthermore, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. In the MA alloys, a broad exothermic process associated to structural relaxation begins at low temperature. XRD patterns of crystallized alloys indicate that the crystallization products are bcc(Fe,Ni), fcc(Ni,Fe), and (Fe,Ni)-phosphides and -silicides.     

Synthesis of an icosahedral quasicrystalline phase in the Al-Cu-Fe system via mechanical activation

A quasicrystalline compound of composition Al₆₄Cu₂₄Fe₁₂ has been prepared through mechanical activation. We have studied the morphology of powder particles after heat treatment under various conditions, identified the sequence of phase transformations in Al-Cu-Fe alloys in the stability region of the ico-phase, and optimized conditions for the preparation of powders containing the maximum possible percentage of the quasicrystalline phase.     

Thermal analysis of copper-tin alloys during rapid solidification

A series of solidification experiments using a mirror furnace and a levitation technique were performed on different Cu-Sn alloys. Cooling curves during solidification were registered using a thermocouple of type K connected to a data acquisition system. The undercooling, cooling rates of the liquid and of the solid state, solidification times and temperatures were evaluated from the curves. The samples were found to solidify far below the liquidus temperature. The cooling curves for different samples and alloys were simulated using a FEM solidification program. The heat transfer coefficient, heat of fusion and specific heat were evaluated. It was found that the calculated values of the heat of fusion were much lower than the tabulated ones. The calculated values of the specific heat in the solid state were also found to be much higher than those quoted in the literature, especially for the mirror furnace experiments. The effect of rapid cooling on the thermodynamic state and the solidification process of the alloys has been evaluated. The effect of cooling rate on the formation and condensation of vacancies is discussed. It is proposed that a large number of vacancies form during rapid solidification and that they condense during and after the solidification. The influence of these defects on the thermodynamics and solidification of the alloys has been evaluated.     

In situ nanoparticulate-reinforced lead-free Sn–Ag composite prepared by rapid solidification

Rapid solidification technology has been successfully adopted for the preparation of in-situ nanoparticulate-reinforced Sn–Ag composite solder. The applied rapid solidification process promotes nucleation and suppresses the growth of intermetallic compounds (IMCs) of Ag₃Sn during the eutectic solidification, yielding fine Ag₃Sn nanoparticulates with spherical morphology in the solidified solder structures. Those spherical, homogeneously-distributed nanoparticulates IMCs are benefit to improve the surface area per unit volume and obstruct the dislocation lines passing through the solder. Hence, this in-situ nanoparticulate-reinforced Sn–Ag composite exhibits higher microhardness.