MIL Composites Research Articles

Fabrication and microstructure evolution of B2 structure-based metal-intermetallic-laminate composites

The B2 structure based MIL composites was fabricated by a two-step processing: the stacked Al and Fe foils were firstly hot pressed under eutectic reaction to form the Al-rich intermetallic phase(Fe2Al5) layer by consuming all the Al foils. And then, for forming the Fe-rich intermetallic phase (FeAl with B2 structure), three kinds of experiments were carried out to transfer the Al-rich phase layer to B2 structure: annealing at eutectic temperature for a long time; hot pressing or Spark plasma sintering (SPS) at higher temperature (1000 °C). The EDS, EBSD, XRD, micro-hardness tests and quasi-static compression are applied to study microstructure evolution, phase transformation and identification during fabricating the B2 structure based MIL composites. Mechanical properties of the B2 structure based MIL composites has proved the reduction of the stress concentration on the interface.

Fabrication and characterization of NiTif-SiCf synergistically reinforced (Al3Ti+Al3Ni)-based metallic-intermetallic laminated composite

In this work, a novel NiTif-SiCf synergistically reinforced (Al3Ti+Al3Ni)-based metallic-intermetallic laminated (NiTif-SiCf/(Al3Ti+Al3Ni)-MIL) composite was designed and synthesized using NiTi and SiC fibers, Ti and Al foils with the “Ti (TC4)-NiTif-Al-Ti (TA1)-Al-SiCf-Ti (TC4)” stacked unit by hot pressing sintering process in vacuum. The TA1 foils as barrier (Tib) are favorable to promote the consumption of Al, meanwhile, allow NiTif and SiCf to co-exist in one intermetallic layer. SEM, EDS, XRD and EBSD techniques were employed to investigate microstructure features, phase constituents and growth kinetics of the NiTif-SiCf/(Al3Ti+Al3Ni)-MIL composite. Besides, the mechanical performances of the composite were detected through compressive tests. The results showed that the newly formed phases in the composite consisted of Al3Ti, Al3Ti0.8V0.2 and Al3Ni, which were obtained from the reactions of Ti/Al and NiTif/Al, resulting in the generation of inhomogeneous intermetallic layer. In addition, NiTif and SiCf, lined up respectively, were distributed uniformly in one intermetallic layer along parallel orientation and the oval shaped eutectic areas were in-suit formed around NiTif by reaction of NiTif/Al. While Tib layers were disappeared between NiTif and SiCf due to the complete reaction of Tib/Al, and were replaced by Al3Ti and Al3Ni phases. However, the Al3Ti grains at this area grew abnormally by devouring the surrounding grains after recrystallization, which were harmful to the strength of the composite. Furthermore, the kinetic calculation results showed that the growth of NiTif/Al and Tib/Al interfacial layers are governed solely by chemical reaction mechanism at 630 °C. Moreover, the NiTif-SiCf/(Al3Ti+Al3Ni)-MIL composite acquired superior specific strength and ductility in both perpendicular and parallel directions, which were attributed to the pull-out and breakage of SiCf and NiTif, as well as crack deflection at interfaces.

Continuous carbon fiber reinforced Ti/Al3Ti metal-intermetallic laminate (MIL) composites fabricated using ultrasonic consolidation assisted hot pressing sintering

A continuous carbon fiber reinforced Ti/Al3Ti metal-intermetallic laminate (Cf–Ti/Al3Ti MIL) composite was fabricated using an ultrasonic consolidation (UC) assisted hot pressing (HP) sintering technique. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were employed to characterize the microstructure of the UC-prepared laminate tapes (LT) and as-sintered Cf–Ti/Al3Ti MIL composite. The tensile and compressive mechanical properties of the Cf–Ti/Al3Ti MIL composites were measured. The results show that under a large normal force exerted by the sonotrode and severe transverse shear force transformed by the ultrasonic vibration, the Cf bundles could be separated into individual fibers and uniformly embedded into the Al foils surface layer without macroscopic defects. Using subsequent HP sintering, the Cf were successfully implanted into the Al3Ti matrix, and the mutual diffusion of the elements occurred between the fibers and the Al3Ti matrix, which indicated that the metallurgical bonding formed at the interface of the fiber/matrix during HP sintering. Furthermore, Cf–Ti/Al3Ti MIL composites exhibited better combinations of tensile and compressive properties than the MIL composite without the fiber reinforcement. The reinforcing mechanisms of the fibers are also discussed in detail.

Synthesis of MIL composites by various methods

Four methods such as thermal explosion, reactive sintering, reactive pressing, and explosive welding + sintering are considered for the obtaining of the Ti-TiAl3 metal-intermetallic laminate composite. The microstructure and phase composition of the samples are studied by the X-ray diffraction, local X-ray spectrum and optical microscopy methods. The study shows that multi-laminate composites can be obtained by all four methods.

Microstructure and Fracture Toughness of a TiAl/Ti Laminated Composite

In this paper, the TiAl/Ti laminated (MIL) composite was fabricated via hot-pack rolling of the as-forged Ti-43Al-9V-0.3Y (at.%) plates and commercial Ti6Al4V (wt.%) sheet at 1250°C and then annealed at 90°C for 6 hours. The composite was analyzed by XRD and SEM techniques, respectively. Results showed that the interface between Ti and TiAl in the composite was consisted of four different microstructure areas and the phase constitutions for each area were: area 1: acicular β-Ti and α2 phase; area 2: acicular α2 phase; area 3: acicular α2 phase and B2 matrix; and area 4: acicular γ, α2 phase and B2 matrix. The fracture toughness of the TiAl/Ti MIL composite was tested, showing that the KIC value was about 38.35MPa·m1/2 at room temperature and higher than that of the pure Ti-43Al-9V-0.3Y alloy, which had a value of about 24.72 MPa·m1/2. The possible toughening mechanism for the TiAl/Ti MIL composite was discussed.

Deposition of CdS nanoparticles on MIL-53(Fe) metal-organic framework with enhanced photocatalytic degradation of RhB under visible light irradiation

A novel composite, CdS/MIL-53(Fe), was successfully fabricated via a facile solvothermal method and characterized with XRD, SEM, TEM, XPS, FT-IR and UV–vis DRS. The results showed that the fabrication was able to result in a good dispersion of CdS nanoparticles onto MIL-53(Fe). The photocatalytic activities of the as-synthesized composite were investigated through the degradation of Rhodamine B (RhB) in water under visible light irradiation. It was found that the composite prepared at the mass ratio of CdS to MIL-53(Fe) of 1.5:1 displayed the highest photocatalytic activity. An approximately 92.5% of photocatalytic degradation of RhB was achieved at 0.5g/L of 1.5-CdS/MIL dosage, 10mg/L of initial RhB concentration and 23°C of reaction temperature under visible light irradiation. The RhB photocatalytic degradation followed well the first-order kinetics equation and the increased catalyst dosage and optimal initial RhB concentration were responsible for the enhanced photocatalytic degradation. Quenching tests revealed that the predominant free radicals in the CdS/MIL-(53)-RhBaq-visible light system was O2−; nevertheless, h+ and OH also contributed to a certain degree. The enhanced photocatalytic performance was ascribed to the formation of heterojunction structure between CdS and MIL-53(Fe) which significantly suppressed the recombination of photogenerated electron-hole pairs. Moreover, the reusability of 1.5-CdS/MIL composite was also studied.

Fabrication, interfacial characterization and mechanical properties of continuous Al2O3 ceramic fiber reinforced Ti/Al3Ti metal-intermetallic laminated (CCFR-MIL) composite

Continuous Al2O3 ceramic fiber reinforced Ti/Al3Ti metal-intermetallic laminated (CCFR-MIL) composite was fabricated using a vacuum hot pressing (VHP) sintering method and followed by hot isostatic pressing (HIP). The microstructure characteristics of the interfaces between Ti and Al3Ti, as well as Al2O3 fiber and Al3Ti intermetallic were analyzed by scanning electron microscopy (SEM). Elemental distribution in the interfacial reaction zones were quantitatively examined by energy-dispersive spectroscopy (EDS). The phases in the composite were identified by X-ray diffractometer (XRD). The mechanical properties of the CCFR-MIL composite were measured using compression and tensile tests under quasi-static strain rate. The experimental results indicated that the residual Al was found in Al3Ti intermetallic layer of CCFR-MIL composite. The interfacial reactions occurred during HIP and the reaction products were determined to be Al2Ti, TiSi2, TiO2 and Al2SiO5 phases. Compared to Ti/Al3Ti MIL composite without fiber reinforcement, both the strength and failure strain of CCFR-MIL composite under both compressive and tensile stress states increased due to the contribution of the continuous ceramic Al2O3 fiber.

Microstructure evolution in pure Ni and Invar-based Metallic-Intermetallic Laminate (MIL) composites

Metallic-Intermetallic Laminate composites of Ni/Al and Invar/Al were fabricated and investigated for the microstructure evolution, growth kinetics and microhardness distribution across the intermetallic/metal interfaces. A single-phase intermetallic layer, with parabolic growth kinetics, is shown in the pure Ni/Al reaction, while a complex multi-phase layer (eutectic and uniform layer) with mixed growth kinetic mechanisms is identified in the Invar/Al reaction by EDS and EBSD analysis. Primary growth and texture of the intermetallic phase in Invar-based MIL are analyzed with respect to their effects on the microhardness distribution across the metal/intermetallic layer. The intermetallic yield rate of the two different Ni-aluminide reactions are calculated and demonstrated to be reliable for predicting the final intermetallic layer thickness in Ni-based MIL composites.

Microstructure evolution in Fe-based-aluminide metallic–intermetallic laminate (MIL) composites

Metallic–Intermetallic Laminate composites of Fe/Al, 430-SS/Al, 304-SS/Al were fabricated and investigated for the microstructure evolution, growth kinetics and microhardness distribution across the intermetallic/metal interfaces. Fe2Al5 phase was formed as dominant phase in the intermetallic layer of the Fe/Al MIL composites with parabolic growth rate behavior. A multilayer structure (namely a uniform layer and a eutectic layer) with a complex mix of intermetallic phases (Fe2Al5, Fe4Al13, Cr2Al13, Al5.5Cr1.95Fe2.55 and Al9Ni1.9Fe0.1) form in the Fe-alloy/Al MIL composites. The growth of the multilayers in the Fe-alloy/Al reaction can be described as a mixed kinetic growth mechanism that is diffusion controlled growth in the uniform layer, while it is interface controlled growth in the eutectic layer. The growth activation energies of Fe/Al, 430-SS/Al, 304-SS/Al reactions are 150KJmol−1, 200KJmol−1 and 220KJmol−1, respectively. The calculated intermetallic yield rate for pure Fe/Al, 430-SS/Al and 304-SS/Al MIL composites are 1.21, 1.16 and 1.10, respectively, which proved to be reliable for predicting the final intermetallic layer thickness in Fe-based MIL composites.

Fracture toughness of Ceramic-Fiber-Reinforced Metallic-Intermetallic-Laminate (CFR-MIL) composites

Novel Ceramic-Fiber-Reinforced-Metal-Intermetallic-Laminate (CFR-MIL) composites, Ti–Al3Ti–Al2O3–Al, were synthesized by reactive foil sintering in air. Microstructure controlled material architectures were achieved with continuous Al2O3 fibers oriented in 0° and 90° layers to form fully dense composites in which the volume fractions of all four component phases can be tailored. Bend fracture specimens were cut from the laminate plates in divider orientation, and bend tests were performed to study the fracture behavior of CFR-MIL composites under three-point and four-point bending loading conditions. The microstructures and fractured surfaces of the CFR-MIL composites were examined using optical microscopy and scanning electron microscopy to establish a correlation between the fracture toughness, fracture surface morphology and microstructures of CFR-MIL composites. The fracture and toughening mechanisms of the CFR-MIL composites are also addressed. The present experimental results indicate that the fracture toughness of CFR-MIL composites determined by three- and four-point bend loading configurations are quite similar, and increased significantly compared to MIL composites without ceramic fiber reinforcement. The interface cracking behavior is related to the volume fraction of the brittle Al3Ti phase and residual ductile Al, but the fracture toughness values appear to be insensitive to the ratio of these two phases. The toughness appears to be dominated by the ductility/strength of the Ti layers and the strength and crack bridging effect of the ceramic fibers.

Microstructure evolution in a martensitic 430 stainless steel–Al metallic–intermetallic laminate (MIL) composite

The formation of intermetallic layers in 430-SS/Al MIL composites was investigated for reaction in solid/solid, solid/semi-solid and solid/liquid states. The Fe2Al5 phase was formed as a major phase in the solid-state reaction and co-existed with the τ phase (Al5.5Cr1.95Fe2.55) as precipitates in a uniform layer in the semi-solid and liquid/solid reaction states. The growth of the uniform layer is mainly governed by lattice diffusion except for the grain boundary diffusion controlled mechanism at the early reaction stage. A porous two-phase layer consisting of Fe4Al13 and δ phase (Cr2Al13) was formed in the semi-solid and liquid/solid reaction states and its growth is controlled by interface reaction growth when the liquid phase is present. The growth activation energies of the uniform layer and two-phase layer were calculated as 200kJmol−1 and 133kJmol−1, respectively. A 430-SS/Al MIL composite with dense intermetallic layers was fabricated in the semi-solid reaction state, which was demonstrated to be the optimized process.

Numerical Investigation of the Ballistic Performance of Metal-Intermetallic Laminate Composites

Metal-intermetallic laminate composites (MIL) based on the Ti-aluminide system are a new class of lightweight structural materials that can be used as either applique or structural armor. The explicit 2D finite element code LS-DYNA was employed to investigate the ballistic performance and failure mechanism of MIL composite plate subjected to impact loading. For comparison’s sake, the penetration simulation was also conducted for a monolithic intermetallic Al3Ti sample under the same conditions. Damage tolerant abilities of the two targets were evaluated based on the analysis of the projectile tail velocity, crack density and absorbed material energy. The simulation results indicated that when cracks initiated in the Al3Ti matrix propagated to the interface between the matrix and reinforcement, their directions changed due to the bridging effect of the reinforcement Ti, which enabled the MIL composite to consume more energy as a result of the increase of the crack path lengths created by the crack deflection and bifurcation. Additionally, some other energy-absorbing mechanisms, such as deflection of cracks, plastic deformation of the ductile Ti also play important roles in enhancing the energy-absorbing capacity of the MIL composites.

Damage evolution in Ti6Al4V–Al 3Ti metal-intermetallic laminate composites

The crack propagation and damage evolution in metal (Ti6Al4V)-intermetallic (Al 3Ti) laminate composites were investigated. The composites (volume fractions of Ti6Al4V: 14%, 20% and 35%) were tested under different loading directions (perpendicular and parallel directions to laminate plane), to different strains (1%, 2%, 3%) and at different strain rates (0.0001 and 800–2000 s −1). Crack densities and distributions were measured. The crack density increases with increasing strain, but decreases (at a constant strain) with increasing volume fraction of Ti6Al4V. Differences in crack propagation and damage evolution in MIL composites under quasi-static (10 −4 s −1) and dynamic (800–2000 s −1) deformation were observed. The fracture stress does not exhibit significant strain-rate sensitivity; this is indicative of the dominance of microcracking processes in determining strength. Generally, the crack density after dynamic deformation is higher than that after quasi-static deformation. This is attributed to the decreased time for crack interaction in high-strain rate deformation. The effect of crack density, as quantified by a damage parameter, on elastic modulus and stress–strain relation were calculated and compared with experimental results.

Processing and mechanical behavior of laminated titanium–titanium tri-aluminide (Ti–Al 3Ti) composites

Ti–Al 3Ti laminated composites have been fabricated through reactive sintering in vacuum using Ti and Al foils with different initial thickness. The aluminum layer was completely consumed resulting in microstructures of well-bonded metal–intermetallic layered composites with Ti residual metal layers alternating with the aluminide intermetallic layers. The MIL composites exhibit a very high degree of microstructural design and control. Microstructure characterization by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectroscopy (EDX) has shown that Al 3Ti is the only titanium aluminide phase due to the thermodynamics and phase selection of the reaction between Ti and Al through mass diffusion in the presence of liquid Al. The mechanical properties and fracture behavior of the fabricated laminated composites were examined through three-point bending test. The results indicated that the composites exhibited anisotropic features. When the load perpendicular to the laminates was applied, they displayed a step-like or saw-tooth load–displacement response and superior flexural strength as well as fracture toughness, which is also dependent on the number and thickness of individual layers. A non-catastropic fracture was observed in the laminated composites due to the deflection of cracks along the Ti/Al 3Ti interface. The Ti layer failed by cleavage mode, showing extensive plastic deformation during the bending process.