Eutectic Composites Research Articles

An Al2O3/Y3Al5O12 eutectic nanocomposite rapidly solidified by a new method: Liquid–metal quenching

A liquid–metal quenching method is designed for studying the rapid solidification behavior of oxide eutectic composites. The lamellar spacing of an Al2O3/Y3Al5O12 eutectic nanocomposite processed using this method is only 50 nm, which is an order of magnitude smaller than that reported previously. Results from the microstructural characterization of the resulting materials are described. Using the classical eutectic growth model, the relative solidification rate in this method is calculated to be 1.88 × 10−2 m s−1.

Estimation of rod-like phase spacing in melt-grown eutectic composites

Directional solidification of rod-like eutectic is an important route to produce in situ composites. The rod-like phase spacing of composites is a crucial parameter in determining the properties of the materials. In this study, the rod-like phase spacing of melt-grown in situ eutectic composites is estimated by the method that is established based on the classical Jackson-Hunt theory and completed by considering the minimum undercooling principle in eutectic solidification at steady state. The density difference between the solid phases is also considered when calculating the diffusion field in the liquid. It is found that the rod-like phase spacing of in situ eutectic composites is generally a not unique value but displays a finite range under fixed growth conditions. Also, the range width, which decreases with increasing growth rate and vice versa, is only dependent on the intrinsic properties of an alloy at a given growth rate. By comparing with the experimental observations, the results show that the predicted spacings are in reasonable agreement with experimental data for nonfaceted-nonfaceted Succinonitrile-(D)camphor, MnSb-Sb, and Al-Al3Ni alloys and faceted-nonfaceted MnBi-Bi system when growing in a coupled manner.

In Situ Fabrication of B4C–NbB2 Eutectic Composites by Spark–Plasma Sintering

This contribution reports, for the first time, the sintering, microstructure and properties of in situ synthesized/consolidated eutectic composites by spark–plasma sintering (SPS). SPS involves a number of processing parameters that may be used to tailor the composition of eutectic composites. It was shown that pressure may be used as a means of controlling the eutectic formation. By changing the pressure, temperature and composition, we propose a processing route that results in the in situ formation of strengthened eutectic composites, consisting of a matrix (B4C, and B4C–NbB2 composite) and also containing regularly distributed whiskers of NbB2. The composites with the eutectic composition of 35 mol.% NbB2 obtained by SPS exhibit a high Vickers hardness (26–27 GPa) and indentation fracture toughness (~6 MPa·m1/2).

Long‐Range Ordered Structure of Ti–B–C–N in a TiB2–TiCxN1−x Eutectic Composite

A TiB2–TiCxN1−x quasi‐binary eutectic composite, with a rod‐like faceted texture and a long‐range ordered structure of Ti–B–C–N, was prepared by the arc‐melting of TiB2, TiC, and TiN powders. Hexagonal single‐crystalline TiCxN1−x rods were grown in a single‐crystalline TiB2 matrix with a crystal orientation relationship of TiB2 //TiCxN1−x and TiB2 [0001]//TiCxN1−x [111]. A long‐range ordered structure of Ti–B–C–N was formed by the intermixing of the coherent interplanar spacings of seven TiB2 (0001) and nine TiCxN1−x (111) planes.

Mechanical Properties and Fracture Behavior of Directionally Solidified NiAl-V Eutectic Composites

Directional solidification of eutectic alloys has been recognized as promising technique for producing in situ composite materials exhibiting balance of properties. Therefore, an in situ NiAl-V eutectic composite has been successfully directionally solidified using Bridgman technique. The mechanical behavior of the composite including fracture resistance, microhardness, and compressive properties at room and elevated temperatures was investigated. Damage evolution and fracture characteristics were also discussed. The obtained results indicate that the NiAl-V eutectic retains high yield strength up to 1073 K (800 °C), above which there is a rapid decrease in strength. Its yield strength is higher than that of binary NiAl and most of the NiAl-based eutectics. The exhibited fracture toughness of 28.5 MPa√m is the highest of all other NiAl-based systems investigated so far. The material exhibited brittle fracture behavior of transgranular type and all observations pointed out that the main fracture micromechanism was cleavage.

Effect of the method of producing Ni3Al-based alloy single crystals on the macro- and microhomogeneity of component distribution, structure, and properties

The mechanisms of hardening heterophase Ni3Al-based cast alloys, which are thermally stable natural eutectic composites, are studied in the operating temperature range. The distribution of basic and alloying elements and impurities in macrovolumes along the height of a charge billet prepared in a vacuum induction furnace is analyzed. The effect of the deviation of the axis of intermetallic alloy single crystals from the 〈111〉 orientation on their mechanical properties is considered. It is shown that the deviation from this orientation within 2.5°–5.4° does not affect the short-term strength characteristics and substantially affects the ductility characteristics of the single crystals. The effect of the method of introducing basic components and refractory reaction- and surface-active alloying elements in the alloys on the structure-phase state of Ni3Al-based alloys and their service life is investigated.

Investigation of the mechanical properties of Ti-Fe-Sn ultrafine eutectic composites by dendrite phase selection

Microstructural investigation of Ti-Fe-Sn ultrafine eutectic composites reveals that β-Ti primary dendrite in eutectic matrix consists of TiFe and β-Ti for Ti72Fe22Sn6 alloy. Similarly, the Ti64Fe32Sn4 alloy and Ti68Fe23Sn9 alloy consists of TiFe and Ti3Sn micron-scale primary dendrites uniformly embedded in the TiFe and β-Ti eutectic structure. The β-Ti dendrite was formed in Ti72Fe22Sn6 alloy, the large number of shear bands propagation and makes multiple steps on the fracture surface. The Ti3Sn dendrite in Ti68Fe23Sn9 ultrafine eutectic alloy leads slip bands which induce the work hardening that have important role in plasticity during deformation. On the other hand, TiFe dendrite in Ti64Fe32Sn4 alloy was presented shear bands bypass and extinction while the propagation of shear bands. These microstructural changes lead to different deformation behavior in primary dendrite. Therefore, it is believed that the mechanical properties of Ti-Fe-Sn alloys could improve due to a different deformation behavior through the minute compositional tuning of Ti-Fe-Sn alloys.

Effects of ternary additions on the microstructure and thermal stability of directionally-solidified MoSi2/Mo5Si3 eutectic composites

Effects of ternary additions on the microstructure and thermal stability of directionally-solidified MoSi2/Mo5Si3 eutectic composites have been studied for twelve different elements (Ti, V, Cr, Fe, Co, Ni, Nb, Ta, W, Ir, B and C) paying special attention to the variation of lattice misfits and interface segregation behavior with ternary additions. Among six elements (type-1: Ti, V, Cr, Nb, Ta and W) with a relatively high solubility in MoSi2 and Mo5Si3, Ta and W are found to be beneficial to microstructure refinement. All other six ternary elements (type-2: Fe, Co, Ni, Ir, B and C) with a negligibly low solubility in MoSi2 and Mo5Si3 exhibit a strong tendency to segregate on MoSi2/Mo5Si3 interfaces, resulting in both microstructure refinement and the modification of the interface morphology.

Low Temperature Processing of Reaction‐Bonded Boron Carbide Composites

ABSTRACTThe present paper is concerned with the fabrication of fully dense B4C‐Mg, B4C‐AZ91 alloy, and B4C‐Mg,Si (eutectic) composites at a significantly lower (750–1000 °C) temperature range. The key feature of the novel approach is based on the Mg‐vapor atmosphere, under which the infiltration process is carried out. This approach has also been used to fabricate B4C‐Al composites at a low temperature. The microstructure and the mechanical properties of the composites are described and discussed. It was concluded that the formation of the deleterious aluminum carbide (Al4C3) depends on the presence of free carbon in the boron carbide powders. The suggested approach for low temperature fabrication of reaction bonded composites under Mg vapor can be further expanded to other boride and carbide phases.

The influence of Ti addition on fracture toughness and failure of directionally solidified LaB6–ZrB2 eutectic composite with monocrystalline matrix

Abstract Fracture toughness and failure mechanism of directionally solidified eutectic composites LaB 6 –ZrB 2 and LaB 6 –(Zr 0,9 Ti 0,1 )B 2 were investigated. The addition of Ti increases the cohesion strength of the matrix–fiber interface, causes redistribution of stresses in the whole composite, and thus influences the mechanism of crack propagation. Fracture toughness of composites was determined by Brazilian test. The central crack was introduced in the plane, parallel to the axis of the eutectic rod, in direction, perpendicular to the axis. Such experimental setup enables to investigate the interaction of crack with fiber–matrix interface and eliminates the effect of other factors on K 1 C . The present investigation shows that Ti additions to LaB 6 –ZrB 2 result in up to 25% increase of fracture toughness of the composites.

Microstructure and Properties of Ni70.2Si29.8 Eutectic Alloy Produced by Directional Solidification

The directional solidification of Ni70.2Si29.8 eutectic alloy was carried out, and the solidification microstructure and compression properties of Ni2Si – Ni31Si12 eutectic composite were systematically studied. Directional solidification samples were obtained by induction heating and down – draw process. During directional solidification, well-aligned lamellar structure with a micron scale was obtained in directional solidified Ni70.2Si29.8 eutectic alloy. Despite it is a kind of faceted – faceted eutectic alloys, highly regular and homogeneous structure was obtained through directional solidification. Compared with other methods, the compress test results showed that fracture strength of Ni70.2Si29.8 eutectic alloy obtained through directional solidification was improved obviously, reaching 2100 MPa.

Analysis of the Strength Property for TiC-Mo Composites at High Temperature

TiC-21 mol% Mo solid solution (<TEX>${\delta}$</TEX>-phase) and TiC-99 mol% Mo solid solution (<TEX>${\beta}$</TEX>-phase), and TiC-(80~90) mol% Mo hypo-eutectic composite were deformed by compression in a temperature range from room to 2300 K and in a strain rate range from <TEX>$4.9{\times}10^{-5}$</TEX> to <TEX>$6.9{\times}10^{-3}/s$</TEX>. The deformation behaviors of the composites were analyzed from the strengths of the <TEX>${\delta}$</TEX>- and <TEX>${\beta}$</TEX>-phases. It was found that the high strength of the eutectic composite is due primarily to solution hardening of TiC by Mo, and that the <TEX>${\delta}$</TEX>-phase undergoes an appreciable plastic deformation at and above 1420 K even at 0.2% plastic strain of the composite. The yield strength of the three kinds of phase up to 1420 K is quantitatively explained by the rule of mixture, where internal stresses introduced by plastic deformation are taken into account. Above 1420 K, however, the calculated yield strength was considerably larger than the measured strength. The yield stress of <TEX>${\beta}$</TEX>-phase was much larger than that of pure TiC. A good linear relationship was held between the yield stress and the plastic strain rate in a double-logarithmic plot. The deformation behavior in <TEX>${\delta}$</TEX>-phase was different among the three temperature ranges tested, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurred, and from the beginning the work hardening level was high. At the tested temperature, a good linear relationship was held in the double logarithmic plot of the yield stress against the plastic strain rate. The strain rate dependence of the yield stress was very weak up to 1273 K in the hypo-eutectic composite, but it became stronger as the temperature rose.

High yield strength bulk Ti based bimodal ultrafine eutectic composites with enhanced plasticity

Ti-based bulk metallic glass (BMGs) and their bimodal composites are linked with the pronounced strain hardening after yielding but with much low value of strength. Therefore, developing Ti-based alloys with high yield strength and high plasticity is the current challenge. Here, we report the synthesis of ultra-fine grained bulk (UFG) (Ti0.705Fe0.295)100−xGax (0⩽x⩽2) bimodal eutectic composites with not only high strength and larger plasticity but also with high yield strength which is one of the important mechanical property for structural application. Reasonably high strength, high yield strength, strain to failure ratio, and enhanced plasticity of ∼7±0.8% was observed in (Ti70.5Fe29.5)98Ga2 composite which is superior than Ti-based BMGs and bimodal composites. Modification of degree of eutectic structure refinement and volume fraction of constituent phases with the addition of Ga are the crucial factors in enhancing the mechanical properties of Ti–Fi–(Ga) composites.

Rod-like eutectic structure of arc-melted TiB2–TiC N1− composite

Abstract TiB 2 –TiC x N 1− x composites were synthesized by arc-melting mixtures of TiB 2 , TiC and TiN powders in a N 2 atmosphere at 60 kPa. TiB 2 –TiC x N 1− x composites were obtained at TiN contents below 20 mol%, whereas TiB formed in the composites at higher TiN contents. TiB 2 –TiC x N 1− x composites with a nominal composition of 36TiB 2 –44TiC–20TiN (mol%) had a rod-like eutectic structure, where the TiC x N 1− x single-crystal rods dispersed in the TiB 2 single-crystal matrix. The crystal orientation relationship between the TiB 2 matrix and the TiC x N 1− x rods was TiB 2 (0 0 0 1)//TiC x N 1− x (1 1 1). Vickers hardness ( H v ) of the rod-like eutectic composite was 22.5 GPa.

Microstructure and thermoelectric properties of InSb compound with nonsoluble NiSb in situ precipitates

Abstract

Microstructure and size effect in ultrafine (Ti0.705Fe0.295)100−xSnx (0⩽x⩽4at.%) composites

Abstract The effect of Sn addition on the microstructure evolution in ultrafine lamellar (Ti0.705Fe0.295)100−xSnx (0 ⩽ x ⩽ 4 at.%) eutectic composites and size effect during Vickers microhardness measurements at load in the range of 0.049 N and 19.61 N have been studied. The hardness of all the lamellar composites with varying Sn content decreases with increase of applied load pointing the existence of normal indentation size effect (ISE). The load dependence microhardness values have been analysed using existing models such as, Meyer’s law, depth dependence hardness model, proportional specimen resistance model (PSR), modified PSR model, Hays-Kendall approach, and elastic–plastic deformation model. Furthermore, the load dependent microhardness has been correlated with the dislocation density, microstructure length-scale, and ISE. The microscopic mechanisms of ISE and strain hardening behaviour in lamellar eutectic composite have been explored.

Deformation Properties of TiC-Mo Eutectic Composite at High Temperature

Abstract The deformation properties of a TiC-Mo eutectic composite were investigated in a compression test at temperaturesranging from room temperature to 2053 K and at strain rates ranging from 3.9×10 −5 s −1 to 4.9×10 −3 s −1 . It was found that thismaterial shows excellent high-temperature strength as well as appreciable room-temperature toughness, suggesting that thematerial is a good candidate for high-temperature application as a structure material. At a low-temperature, high strength isobserved. The deformation behavior is different among the three temperature ranges tested here, i.e., low, intermediate and high.At an intermediate temperature, no yield drop occurs, and from the beginning the work hardening level is high. At a hightemperature, a yield drop occurs again, after which deformation proceeds with nearly constant stress. The temperature- andyield-stress-dependence of the strain is the strongest in this case among the three temperature ranges. The observed high-temperature deformation behavior suggests that the excellent high-temperature strength is due to the constraining of thedeformation in the Mo phase by the thin TiC components, which is considerably stronger than bulk TiC. It is also concludedthat the appreciable room-temperature toughness is ascribed to the frequent branching of crack paths as well as to the plasticdeformation of the Mo phase.Key wordsplastic deformation, TiC-Mo, eutectic composite, compression test, high temperature strength.

Mechanical properties and deformation mechanisms of B4C–TiB2 eutectic composites

Abstract Samples of B 4 C–TiB 2 eutectic are laser processed to produce composites with varying microstructural scales. The eutectic materials exhibit both load dependent and load independent hardness regimes with a transition occurring between 4 and 5 N indentation load. The load-independent hardness of eutectics with a microstructural scale smaller than 1 μm is about 31 GPa, and the indentation fracture toughness (5–10 N indenter load) of the eutectics is 2.47–4.76 MPa m 1/2 . Indentation-induced cracks are deflected by TiB 2 lamellae, and indentation-induced spallation is reduced in the B 4 C–TiB 2 eutectic compared to monolithic B 4 C. Indentation-induced amorphization in monolithic B 4 C and the B 4 C phase of the eutectic is detected using Raman spectroscopy. Sub-surface damage is observed using TEM, including microcracking and amorphization damage in B 4 C and B 4 C–TiB 2 eutectics. Dislocations are observed in the TiB 2 phase of eutectics with an interlamellar spacing of 1.9 μm.

Preparation, microstructure characterisation and corrosion behaviour of directionally grown TaSi2 fibre arrays with sharp tip fabricated by selective wet etching

Abstract Directionally solidified Si–TaSi2 eutectic composite is selectively etched to fabricate well aligned TaSi2 tip array for field emission application. The effect of etching parameters on TaSi2 tip structure, and its corrosion behaviour in HNO3/HF solution are investigated. At the optimised condition (HNO3/HF = 5 for 50 min), sharp TaSi2 tips with curvature radius of 18 nm and homogenous distribution are obtained, which greatly improves the figure of merit associated with field emission current. The TaSi2 fibre presents smaller dissolution rate in the HNO3/HF solution than Si matrix. The formation mechanism of etching pit on the Si matrix surface is also discussed.

Room and high temperature toughening in directionally solidified B4C–TiB2 eutectic composites by Si doping

Directionally solidified В4С–TiB2 eutectics doped with different Si contents were prepared by floating zone method. Silicon doping (up to 3vol.%) promotes a more coherent interface between B4C matrix and TiB2 inclusions, a decrease of the spacing between TiB2 (when solidification rate is constant), and formation of a more uniform morphology with thinner inclusions. These features lead to simultaneous enhancement of Vickers hardness (HV), fracture toughness (K1c) and bending strength (σ) when compared with Si-free В4С–TiB2 eutectics. For our materials, the average HV, K1c and σ were 45.2GPa, 7.04MPam1/2, and 460MPa at room temperature or 487MPa at 1600°C, respectively. The values of σ at indicated temperatures are approximately twice higher than for the Si-free В4С–TiB2 eutectic composites.