Metallic-intermetallic Laminate Composites Research Articles

Parametric Examination Anisotropic Thermal Resistance of MIL Composites

Metallic-intermetallic laminate (MIL) composites possess intermediary properties emerging from the different laminates used. They are anisotropic since their properties are direction-dependent. The laminates used in a MIL composite have different thermal conductivities and this results in anisotropic thermal resistance. In a recent study, using the composite dimensions and the electrical conductivity of the laminates used to make the MIL composite, the electrical resistance of rectangular prism-shaped MIL composites for different directions is examined. Since thermal and electrical circuits are analogs, a similar analysis can also be done for thermal conduction quantities. In this study, using the composite dimensions and the thermal conductivity of the laminates used to make the MIL composite, the thermal resistance of rectangular prism-shaped MIL composites for different directions is calculated and its direction-dependent parametric examination is carried out.

Mesoscale hetero-deformation induced (HDI) stress in FeAl-based metallic-intermetallic laminate (MIL) composites

Single-phase intermetallic FeAl layered material is synthesized using a layered foil approach to study the fracture mechanisms of FeAl-based metallic-intermetallic laminate (MIL) composites containing a similarly fabricated structure. The mechanical properties and crack evolution of the single-phase FeAl are investigated via incremental compression testing. Microstructure and composition assessment confirm a similar intermetallic layer laminate microstructure of single-phase FeAl and FeAl-based MIL composites. When compressed perpendicular to the layers, both materials fail by the axial splitting of the FeAl phase along the loading direction. Mesoscale hetero-deformation induced (HDI) stress, which is tensile on the FeAl layers of MIL composites, accelerates crack nucleation and crack propagation, eventually inducing failure. The HDI stress evaluated via finite element analysis (FEA) simulation provides an explanation for the difference between 430SS-FeAl and 304SS-FeAl MIL composites, which posses similar microstructure and composition, but very different strengths. When compressed parallel to the layers, mesoscale HDI stress is expected to be negligible, whereas the geometrically necessary dislocation (GND) pile-up induced HDI stress can enhance the performance of the composites. Fracture toughness is characterized via four-point bend testing, and the results demonstrate improvement of the FeAl-based MIL composites over the single-phase FeAl material.

Design, fabrication and optimization of FeAl–FeAl2 eutectoid metallic-intermetallic laminate (MIL) composites

FeAl/FeAl2 eutectoid metallic-intermetallic laminate (MIL) composites were synthesized using a “multiple-thin-foil” configuration and a “two-stage reaction” strategy. Microstructure analysis via scanning electron microscope (SEM), energy-dispersive X-ray spectrometer (EDS) and electron backscatter diffraction (EBSD) confirms the formation of a two-intermetallic eutectoid structure, which decomposes from the high-temperature Fe5Al8 phase. The metal layers of eutectoid-MIL composites are fabricated with either pure iron or two different stainless steels without altering the intermetallic regions. The volume fraction of eutectoid layers is adjusted for optimizing the performance. The off-eutectoid phase is switched between FeAl and FeAl2 to investigate the effect on strength and ductility. The microstructure of the interfacial regions is fine-tuned, further demonstrating the ability to independently control the constituents of MIL composites. Additionally, a hybrid MIL composite of FeAl and the eutectoid structure is synthesized as a ‘proof-of-concept’. Finite element analysis (FEA) simulation is utilized to study the internal stress in the MIL composites from a macroscopic point of view. Incremental compression tests were conducted to track the fracture evolution from a microscopic point of view.

Deformation and fracture evolution of FeAl-based metallic-intermetallic laminate (MIL) composites

FeAl-based Metallic-Intermetallic Laminate (MIL) composites exhibit enhanced strength and ductility compared to previously studied MIL composites. The deformation and fracture evolution of the FeAl-based MIL composites are investigated here via incremental compression testing. Microstructure assessment via electron backscatter diffraction suggests that deformation proceeds in a fairly homogeneous manner across gradients in the microstructure. Eventual failure is mainly induced by normal stresses, whereas other MIL composites typically fail by shear induced localizations. Geometrically necessary dislocation analysis indicates the FeAl regions deform in similar manners for the three MIL composites (Fe-FeAl-MIL, 430SS-FeAl-MIL, and 304SS-FeAl-MIL), and each fails in a similar mode. While the FeAl phase is the majority constituent of the composites, the mechanical properties are significantly influenced by the softer metal layers. The transition layer formed between the Fe-based metal layers and FeAl regions is the most critical constituent of the composites. Although the volume fraction of the transition layer is only ∼15%, a stronger transition layer can improve the work hardening behavior of the FeAl phase, increasing MIL composite strength by as much as 1 GPa. The findings can guide the design of the MIL composites to achieve even better mechanical properties.

Design, fabrication and characterization of FeAl-based metallic-intermetallic laminate (MIL) composites

FeAl-based MIL composites of various iron alloys were fabricated with an innovative “multiple-thin-foil” configuration and “two-stage reaction” strategy. Alternating stacked metal foils were reactive sintered via SPS at 600 °C and 1000 °C to grow intermetallics. The “multiple-thin-foil” configuration reduces reaction time, enables local chemical composition control and allows metal/intermetallic combinations, which cannot be produced via the conventional methods. Fe–FeAl, 430SS-FeAl, and 304SS-FeAl MIL composites can be synthesized with desired metallic/intermetallic ratios, where FeAl is the single intermetallic phase present in the composites. Microstructure analysis via SEM, EDS, and EBSD confirms phase identification and reveals the formation of transition layers. The transition layer, which incorporates the composition gradient between the metal (Fe, 430SS or 304SS) and the FeAl intermetallic phase, provides a gradual change in mechanical properties from the metal to intermetallic layers, and further functions as a chemical barrier into which other undesired intermetallics dissolve. Driven by diffusion-controlled growth, grains in the transition layers and FeAl regions exhibit ordered arrangement and sintering textures. Hardness profiles from the metal layer to FeAl region reveal the correlation between local mechanical properties and local chemical compositions. In compression testing, the compressive strength can reach 2.3 GPa with considerable plasticity, establishing the best mechanical properties of any MIL composites synthesized to date.

Explosion Welding: Process Evolution and Parameters Optimization

The development of explosion welding (EXW) technology underwent a stop as soon as it was introduced, however, in the recent years an increasing interest was found due to the wide range of materials which can be welded, similar and especially dissimilar ones. In addition to the high quality, such welded joints show a good compromise among the involved materials properties. Literature does not provide a comprehensive understanding of the whole mechanism and occurring phenomena but is mostly limited to analyse just some process parameters, like the investigations on joint properties that can be achieved if process takes place under vacuum or open air. In this work some key points are discussed to describe the evolution step of the process and the innovations introduced like the MIL (metallic-intermetallic laminate) composites for aerospace industry. Process parameters are analyzed to highlight the positive and negative aspects, the experiments in the laboratory will be described to confine the explosion to the joint and in particular to minimize the explosion energy and to improve the efficiency of the technique. At last some significant applications where this technique is widely used are showed.

Microstructure evolution in Ni and Ni-superalloy based metallic-intermetallic laminate (MIL) composites

Pure nickel and Nickel Alloy-X based Metallic-Intermetallic Laminate (MIL) composites were fabricated and investigated for their microstructure evolution, growth kinetics and microhardness distribution across the intermetallic/metal interfaces. Multi-phase layer structure with parabolic growth kinetics is shown in the nickel-based MIL composites. A two-phase eutectic layer along with a uniform layer form in the Alloy-X based MIL composites, which shows a mixed growth kinetic mechanism. The microhardness distribution across the intermetallic/metal interface of the two MIL composites was investigate with respect to the effects of texture and microstructure of the intermetallic phases. A simple intermetallic growth model is developed and validated for predicting the phase formation in binary or ternary reactions for synthesis of these MIL composites.

Annealing effects on the microstructure and properties of an Fe-based Metallic-Intermetallic Laminate (MIL) composite

430SS MIL composites were initially fabricated under semi-solid reaction at 655°C and then annealed at high temperature (1000°C) to obtain the ductile Fe-rich intermetallic phases. The microstructure evolution and micro-hardness distribution across the intermetallic/metal interfaces were investigated, as well as the experimentally and computationally evaluating the growth kinetics of the Fe-rich intermetallic layers. A multilayer structure (namely Al-rich layer, Fe-rich layer and B2 phase layer) with a complex mix of intermetallic phases (FeAl2, Cr5Al8 and FeAl) form in the high temperature annealed 430SS MIL composites. The FeAl phase with a B2 structure formed in the intermetallic layer provides a more gradual transition of mechanical properties across the intermetallic/metal layer. The growth mechanism of the Fe-rich layer is interface controlled, while the growth of the B2 phase layer is diffusion controlled based on both the experimental and numerical analysis. A relationship between the processing-microstructure-properties of the MIL composites has been established and applied to predict and tailor the microhardness distribution across the multi-layered structure of the 430SS MIL composites.

Determination of the Young Modulus of Ti-TiAl3Metallic Intermetallic Laminate Composites by Nano-Indentation

Determination of the Young Modulus of Ti–TiAl3 Metallic Intermetallic Laminate Composites by Nano-Indentation T. Yenera,∗, S. Guler, S. Siddique, F. Walther and S. Zeytin Sakarya University, Engineering Faculty, Department of Metallurgy and Materials Engineering, Esentepe Campus, 54187, Adapazari, Sakarya, Turkey TU Dortmund University, Faculty of Mechanical Engineering, Department of Materials Test Engineering (WPT), Baroper Str. 303, D-44227 Dortmund, Germany

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.

A Study on the Formation of Intermetallics During the Heat Treatment of Explosively Welded Al-Ti Multilayers

Metallic–intermetallic laminate composites are promising materials for many applications, namely, in the aerospace industry. Ti/TiAl3 laminates are one of the interesting laminate composites, which are mostly used in aerospace applications. In this work, commercially pure aluminum and titanium sheets were explosively joined. The multilayer samples were annealed between 1 and 260 hours at 903 K (630 °C) in ambient atmosphere, and the formation and growth of the intermetallic compound at the Ti/Al interface were monitored. Microstructural investigations were carried out using optical and scanning electron microscopes equipped with energy-dispersive spectroscopy and the X-ray diffraction technique. The microhardness profile of the layers was also determined. The thickness and type of Al-Ti intermetallics were determined. It was found that the only intermetallic phase observed in the interfaces was TiAl3. It was also shown that two mechanisms for TiAl3 growth exist: reaction and diffusion controlled. The growth exponent was equal to 0.94 for the reaction-controlled mechanism (first step) and 0.31 for the diffusion-controlled mechanism (second step). These values were in good agreement with theoretical values (1 and 0.5 for the first and second steps, respectively). Based on the results of this research, a kinetic model for the formation and growth of TiAl3 intermetallic phase was proposed.

Structural and mechanical properties of metallic–intermetallic laminate composites produced by explosive welding and annealing

Metallic–intermetallic laminate (MIL) composites are promising materials for the aerospace industry and other applications. In the current work, the results of studies regarding the “Al–Al3Ti–Ti” composite are presented. The composite was fabricated by explosive welding and annealing under an air atmosphere of 630°C. The time was varied from 1 to 100h to study the intricacies of intermetallic layer growth. The structure was investigated by optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The presence of thick oxide films, which may significantly reduce the rate of diffusion, was not found. The kinetics of intermetallic layer growth largely coincides with data from other authors. Nevertheless, some differences were found. In spite of the large annealing time (up to 100h) the complete dissolution of 1-mm thick aluminum plates was not reached. The results of tension tests and impact strength tests are briefly discussed.

Use of Brazilian disk test to determine properties of metallic-intermetallic laminate composites

Metallic-intermetallic laminate (MIL) composites based on Ti-Al3Ti offer a unique combination of structural and ballistic/blast performance capabilities for many defense related platforms. In this study, the Brazilian splitting test was employed, under quasi-static and dynamic loading conditions, using disk specimens cut from the laminate plates in orientations perpendicular (in-plane) and parallel (through-thickness) to the layers. Tests were conducted to evaluate the overall tensile mechanical properties of the Ti-Al3Ti MIL composite, both to determine in-plane tensile properties, as well as the more challenging through-thickness tensile properties. Experimental results indicate that when loaded parallel to the layers, the tensile strength in the through-thickness orientation, determined by Brazilian splitting test, is low, which is not surprising since it is only evaluating the tensile behavior of the brittle intermetallic phase. When loaded perpendicular to the layers, the in-plane tensile strength of the Ti-Al3Ti MIL composites is high due to the contribution of the reinforcement Ti plus the intermetallic component.