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Commercial solid freeform fabrication (SFF) systems, which have been developed for fabrication of wax and polymer parts for form and fit and secondary applications, such as moulds for casting, etc., require further improvements for use in direct processing of structural ceramic and metal parts. Defects, both surface as well as internal, are undesirable in SFF processed ceramic and metal parts for structural and functional applications. Process improvements are needed before any SFF technique can successfully be commercialized for structural ceramic and metal processing. Describes process improvements made in new SFF techniques, called fused deposition of ceramics (FDC) and metals (FDMet), for fabrication of structural and functional ceramic and metal parts. They are based on an existing SFF technique, fused deposition modelling (FDM) and use commercial FDM systems. The current state of SFF technology and commercial FDM systems results in parts with several surface and internal defects which, if not eliminated, severely limit the structural properties of ceramic and metal parts thus produced. Describes systematically, in detail, the nature of these defects and their origins. Discusses several novel strategies for elimination of most of these defects. Shows how some of these strategies have successfully been implemented to result in ceramic parts with structural properties comparable to those obtained in conventionally processed ceramics.

We study the temperature dependence of dielectric constant (K) and spontaneous polarization (Ps) in the range of −95–200°C. Cubic (C)-tetragonal (T) and T-orthorhombic (O) transitions are observed at 264 and 25°C, respectively. The Curie–Weiss temperature of C-T transition is 249°C, indicating it is first order. X-ray data indicate T-O phase coexistence at 25°C. A singularity in Ps at 25°C and a T-O phase coexistence spanning 25–31°C was observed, wherein Ps increases from 17×10−2C∕m2 at 31°Cto23×10−2C∕m2 25°C. The transition at 25°C appears diffusionless and polymorphic with martensite start and finish temperatures of 31 and 25°C, respectively. The maximum in d33 is 345pC∕N and is attributed to the instability at 25°C, where Ps and K show singularity.

Bismuth sodium titanate (Bi 0.5 Na 0.5 TiO 3 , BNT) with 0-6 at.% lanthanum was prepared by the conventional mixed oxide method. Each composition was calcined at 800-900°C for 2-5 h to form a pure perovskite phase. Green pellets were sintered at 1050-1150°C for 1-4 h to obtain dense ceramics with at least 95% of theoretical density. X-ray diffraction (XRD) showed phase distortion as lanthanum was added to this system. Meanwhile, a small amount of La was found to affect the grain size and had an influence on the poling conditions and electrical properties. The BNTbased composition with 1 at.% La doping provided a dielectric constant (K) of 560, a piezoelectric charge constant (d 33 ) of 92 pC/N, and a hydrostatic piezoelectric coefficient (d h ) of 72 pC/N.

Ceramic lead magnesium niobate–lead titanate ((1‐x)PMN‐xPT) of different compositions has been prepared by the columbite precursor method. This study discusses compositions ranging from 0.94PMN–0.06PT to 0.60PM–N0.40PT, focusing on two areas of the (1‐x)PMNxPT system: compositions that exhibit electrostrictive behavior, and those that show piezoelectric behavior. In electrostrictive compositions where x is in the range of 0.06–0.20, the dielectric constant and electromechanical coupling factor dependencies on the bias field are evaluated. The optimal electromechanical properties are obtained with the composition 0.82PMN–0.18PT, measured at temperature T=Tm (the temperature of maximum dielectric constant) = 80°C and with a dc bias of 5 kV/cm. X–ray diffractometry is used to show that the (1‐x)PMN‐xPT system has a compositionally wide two–phase region and that 0.655PMN–0.345PT is the morphotropic phase boundary (MPB) composition. Electromechanical property evaluation shows that the optimal piezoelectric properties (piezoelectric charge coefficient (d33) value of 720 pC/N, dielectric constant (K) value of 5400, and electromechanical planar and thickness coupling coefficient (kp and kt, respectively) values of 62% and 46%, respectively) are obtained at the MPB composition.

Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on extrusion of highly loaded polymer systems. The process utilizes particle loaded thermoplastic binder feedstock in the form of a filament. The filament acts as both the piston driving the extrusion and also the feedstock being deposited. Filaments can fail during FDC via buckling, when the extrusion pressure needed is higher than the critical buckling load that the filament can support. Compressive elastic modulus determines the load carrying ability of the filament and the viscosity determines the resistance to extrusion (or extrusion pressure). A methodology for characterizing the compressive mechanical properties of FDC filament feedstocks has been developed. It was found that feedstock materials with a ratio (E/Z a ) greater than a critical value (3610 5 to 5610 5 s -1 ) do not buckle during FDC while those with a ratio less than this range buckle.

In the past two decades, piezoelectric ceramic/polymer composites with different connectivities have been developed for transducer applications such as hydrophones, biomedical imaging, nondestructive testing, and air imaging. Recently, much attention has been given to fine‐scale piezoelectric ceramic/polymer composites. These composites allow higher operating frequencies, and thus increased resolution, in medical imaging transducers. In this review, methods for processing fine‐scale piezoelectric ceramic/polymer composites are discussed. The current capabilities, strengths, and weaknesses of each method are compared. The importance of spatial scale in composite performance is also reviewed. Several of the processing methods have demonstrated composites with fine‐scale ceramic phases (<50 μm), and others have potential to form composites with a ceramic scale of under 20 μm.

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