9 - Metal-ceramic functionally graded materials (FGMs)

Four-component barium titanate stannate (BaTi1−x Sn x O3, BTS) functionally graded materials (FGMs) were designed, processed and examined. BTS powders with different tin content (x = 0.025, 0.05, 0.07 and 0.10, abbreviated as BTS2.5, BTS5, BTS7 and BTS10, respectively) were used as ingredient materials. Four-layered samples, produced by powder-stacking method and uniaxial pressing, were consolidated in BTS2.5/BTS5/BTS7/BTS10 FGMs by sintering at 1420 °C with dwell time of 2 h. To achieve high-quality FGMs, without structural or microstructural damages, the master sintering curve (MSC) approach were used. In this study, the MSC was constructed for four-layered FGMs using shrinkage data obtained by a heating microscope during non-isothermal part of the sintering up to 1420 °C with heating rates of 2, 5, 10 and 30°/min. To prepare FGMs with desired final density the corresponding Θ value was estimated from the abscissa of the master sintering curve. Estimated Θ value was used in Φ(ρ) = logΘ(t,T(t)) equation, which correlate density (ρ) and the time and temperature dependent parameter Θ(t,T(t)). This calculation allowed us to determine experimental parameters which should be applied in sintering procedure to obtain FGMs with projected density. According to constructed MSC, four different sintering schedules were designed and applied where four BTS2.5/BTS5/BTS7/BTS10 FGMs were prepared. To validate the constructed MSC, the microstructure and chemical (Ti/Sn) gradient in the prepared FGMs were examined by SEM–EDS methods.

Functionally Graded Material (FGM) is a material with engineered gradients of composition, structure and/or specific properties aiming to become superior over homogeneous material composed of same or similar constituents. In the recent years, research has been undertaken on manufacturing of functionally graded materials (FGM) using numerous techniques like powder metallurgy, melt processes, centrifugal casting, electrophoretic deposition, spark plasma sintering, physical vapor deposition, chemical vapor deposition etc. Most of these techniques may be well suited for a specific application yet they suffer from one or more limitations like lower graded thickness, low deposition rate, complexity in process requirement, or high processing cost. To circumvent these limitations innovative technique called laser assisted manufacturing technique is applied for manufacturing functionally graded materials. Three methods that employ Laser for synthesis of FGM is elaborated in this work (i) 3-D Laser Cladding, (ii) LENS and (iii) Selective laser sintering. Laser Cladding is used for obtaining coatings of FGM by direct powder injection into the laser beam. 3-D Laser-engineered net shaping (LENS) is used to fabricate FGM directly from CAD solid models and thus further reduce the lead times for metal art fabrication. Selective laser sintering (SLS) is a layered manufacturing based freeform fabrication approach for constructing three dimensional structures in functionally graded composites. All these methods are used to manufacture FGMs in a short interval of time and the process can be controlled digitally, thus all these methods come in the heading of rapid manufacturing (RM). These methods have a huge industrial potential and can be commercialized for manufacturing bulk FGM.

Capability of multiwalled carbon nanotubes (CNTs) to create in-depth gradients in properties and functionalities of conventional materials has been investigated for the first time. Functionally graded material (FGM) concept has also been employed for the first time to bridge conventional materials to their advanced nanocomposites containing a high concentration of CNTs, which is promising for unexplored yet novel structural, electronic and biomaterial applications. In this study, α-alumina ceramics considered as the most challenging case has been used as the matrix. Bulk, layered, nanostructure-controlled, CNT-based, functionally graded α-alumina ceramics have been fabricated employing a recently established powder processing technology. In-depth gradients in microstructure, grain size and hardness have been successfully achieved in alumina ceramic without cracking, delamination or warping, after homogeneous and gradual incorporation of the CNTs within the alumina ceramic matrix. The FGM approach showed promise to successfully bridge conventional ceramics to their nanocomposites containing a high concentration of CNTs.

Functionally Graded Materials (FGMs) can outperform their homogeneous counterparts. Advances in digitalization technologies, mainly additive manufacturing, have enabled the synthesis of materials with tailored properties and functionalities. Joining dissimilar metals to attain compositional grading is a relatively unexplored research area and holds great promise for engineering applications. Metallurgical challenges may arise; thus, a theoretical critical analysis is presented in this paper. A multidisciplinary methodology is proposed here to unify optimal design, multi-feed Wire-Arc Additive Manufacturing (WAAM), and image-based characterization methods to create structure-specific oriented FGM parts. Topology optimization is used to design FGMs. A beam under pure bending is used to explore the layer-wise FGM concept, which is also analytically validated. The challenges, limitations, and role of WAAM in creating FGM parts are discussed, along with the importance of numerical validation using full-field deformation data. As a result, a conceptual FGM engineering workflow is proposed at this stage, enabling digital data conversion regarding geometry and compositional grading. This is a step forward in processing in silico data, with a view to experimentally producing parts in future. An optimized FGM beam, revealing an optimal layout and a property gradient from iron to copper along the build direction (bottom-up) that significantly reduces the normal pure bending stresses (by 26%), is used as a case study to validate the proposed digital workflow.

Strong and tough bioinspired nacre-like B4C/Al functionally graded materials with eliminated abrupt interfaces

Actuators and materials play a key role in developing advanced precision engineering. The breakthroughs in this field are closely related to the development of various types of actuators and related materials. The successes of piezoelectric ceramics and ceramic actuators have. For instance, the propagating‐wave type ultrasonic motor that produces precise rotational displacements has been used in autofocusing movie cameras and VCRs. Multimorph ceramic actuators prepared from electrostricitive Pb(Mg1/3Nb2/3)O3(PMN) ceramics are used as deformable mirrors to correct image distortions from atmospheric effects. The likelihood that the range of applications and demand for actuators will grow actively and has stimulated intensive research on piezoelectric ceramics. Functionally graded materials (FGMs) are a new class of composites that contain a continuous, or discontinuous, gradient in composition and microstructure. Such gradients can be tailored to meet specific needs while providing the best use of composite components. Furthermore, FGM technology is also a novel interfacial technology for solving the problems of the sharp interface between two dissimilar materials. In recent years, significant advances in developing FGMs have been achieved. In this article, we introduce and summarize the recent progress in piezoelectric ceramic actuators and review recent applications of FGMs in piezoelectric ceramic devices.

In this paper, a rotating beam made of metal/ceramic-based functionally graded materials (FGMs) is examined under free vibration. In the research reported in this paper, the states of both tapered and uniform beams with a constant angular velocity are taken into consideration, in which the FGM properties could change across the thickness. In the research reported in this paper, the fraction of changes in metal and ceramic components is modeled by a power function with symmetric structure. The discretized equations of motion of the system are obtained based on two theories of Euler–Bernoulli and Timoshenko beams, using finite elements with two different types of elements [(1) four-degree-of-freedom (DOF) model, and (2) eight-DOF model] for in-plane (lead-lag), out-of-plane (flapping), and flap-lag, to obtain the vibration properties and therefore the eigenfrequencies. In the sequel, the effect of various parameters on the eigenfrequencies, such as the volume fraction of two constituent phases, the ...

The microscale vibration characteristics of microbeams made of functionally graded materials (FGMs) are investigated based on the strain gradient Reddy beam theory capable of capturing the size effect. The non-classical governing differential equations, together with the corresponding boundary conditions, are obtained using Hamilton's principle. Then, the free vibration problem of simply supported FGM microbeams is solved using the Navier solution. The natural frequencies of FGM microbeams are calculated corresponding to a wide range of dimensionless length scale parameters, material property gradient indices, and aspect ratios to illustrate the influences of size effect on the vibrational response of FGM microbeams.

This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Functionally graded material is an enabling technology for lightweight body armor improvements. The objective was to demonstrate the ability to produce functionally graded ceramic-polymer and ceramic-metal lightweight armor materials. This objective involved two aspects. The first and key aspect was the development of graded-porosity boron-carbide ceramic microstructures. The second aspect was the development of techniques for liquid infiltration of lightweight metals and polymers into the graded-porosity ceramic. The authors were successful in synthesizing boron-carbide ceramic microstructures with graded porosity. These graded-porosity boron-carbide hot-pressed pieces were then successfully liquid-infiltrated in vacuum with molten aluminum at 1,300 C, and with liquid polymers at room temperature. Thus, they were able to demonstrate the feasibility of producing boron carbide-aluminum and boron carbide-polymer functionally graded materials.

Estimation of C(t) and the creep crack tip stress field of functionally graded materials and verification via finite element analysis

Microstructural design of connective base cells for functionally graded materials

The concept of functionally graded materials (FGMs) was originated in the research field of thermal barrier coatings. Continuous changes in the composition, grain size, porosity, etc., of these materials result in gradients in such properties as mechanical strength and thermal conductivity. In recent years, functionally graded structural composite materials have received increased attention as promising candidate materials to exhibit better mechanical and functional properties than homogeneous materials or simple composite materials. Therefore the research area of FGMs has been expending in the development of various structural and functional materials, such as cutting tools, photonic crystals, dielectric and piezoelectric ceramics, thermoelectric semiconductors, and biomaterials. We have developed functionally graded structural ceramic/metal composite materials for relaxation of thermal stress, functionally graded anti-oxidation coatings for carbon/carbon composites, and functionally graded dielectric ceramic composites to develop advanced dielectric ceramics with flat characteristics of dielectric constant in a wide temperature range. This paper introduces functionally graded coatings for C/C composites with superior oxidation resistance at high temperatures.

In this study, a curved sandwich beam with Functionally Graded Materials (FGM) face sheets and a homogeneous core under thermomechanical loads is investigated. The problem is studied numerically by the finite element method (FEM). Plane, eight nodes isoparametric elements are used, where the gradient of the material properties is incorporated into the formulation of the element. The effect of the thickness and volume fraction index (VFI) of the FGM face sheets on the stress and the temperature fields are studied. The results are valuable in the design of hydrogen mechanical applications, since the FGM sandwich curved beam could be a part of hydrogen storage tanks.

This paper presents the convergence behavior of Discrete Kirchhoff Mindlin Triangular (DKMT) element in buckling analysis under uniaxial compression of square plate problems. The DKMT element has a good result for a thin plate and a thick plate. For the Functionally Graded Material (FGM) problem, the DKMT element is reformulated. FGM is a graded composite material that has high-temperature and structural flexibility resistance. The numerical results of mechanical buckling of square FGM plate under uniaxial compression using the DKMT element are reported. The critical buckling of the square FGM plate is compared to the reference existing solutions. The effects of parametric variation, such as the type of meshing, boundary conditions, power-law index, and ratio L/h are presented. The results show that the DKMT element gives good results on the buckling analysis of square FGM plate problems.

We propose the use of a quartz crystal plate thickness-shear (TSh) mode resonator to measure material property variations in a functionally graded material (FGM). A theoretical analysis is performed on TSh vibrations of an AT-cut quartz plate carrying a layer of an FGM whose density and stiffness vary along its thickness. The effect of the material property gradient on the resonant frequencies of the two-layer plate as a compound resonator is examined. It is shown that this effect may be used to measure the material property gradient of the FGM.