Functionally graded materials (FGMs) are a broad research area and attract considerable tremendous attention today in the materials science and engineering society. In recent years, FGMs have experienced remarkable developments in manufacturing methods. FGMs can be produced using several well-known processing techniques from conventional to advanced. This research provides an overview of manufacturing methods for FGMs, thus describing the fundamental difficulties and strengths of these methods based on the available literature over 30 years. Besides, this critical review gives a comprehensive summary of the various applications and the future trends for research required for the design and production of these materials properly with a smooth graded. The anticipated findings of the current paper can be considered as a milestone for future production and analysis investigations for FGMs and are beneficial for researchers, designers, and manufacturers in this scope.

30 Years of functionally graded materials: An overview of manufacturing methods, Applications and Future Challenges

The pH dependent surface charging and points of zero charge. VII. Update.

Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. Some methods have been developed to achieve directional grain arrangement and preferred orientation growth during ceramic preparation, and then textured ceramics with anisotropic properties are obtained. Texture microstructures give particular properties to ceramics along specific directions, which can effectively expand their application fields. In this review, typical texturing techniques suitable for ceramic materials, such as hot working, magnetic alignment, and templated grain growth (TGG), are discussed. Several typical textured structural ceramics including α-Al2O3 and related nacre bioinspired ceramics, Si3N4 and SiAlON, h-BN, MB2 matrix ultra-high temperature ceramics, MAX phases and their anisotropic properties are presented.

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Preparation and anisotropic properties of textured structural ceramics: A review

Dual-functional crosslinked polymer-inorganic materials for robust electrochemical performance and antibacterial activity

Mechanical characteristics of functionally graded materials (FGMs) can be optimized for specific application depending on the demands of different engineering sectors using appropriate combinations of material amounts and processing parameters. In recent years, many approaches to the production of functionally graded metal matrix composites (FGMMCs) using the centrifugal casting method have been proposed. This paper presents an overview of different available materials and process parameters for FGMs based on their mechanical and wear characteristics. The major conclusions in this paper are drawn from the previous studies on experimental investigations on mechanical properties and wear characteristics of FGMMCs. The findings in current work are classified according to material parameters such as the type of matrix material, reinforcing material (type, weight, and size), in addition to process parameters such as mould rotational speed and pouring temperature.

Effect of Main Parameters on the Mechanical and Wear Behaviour of Functionally Graded Materials by Centrifugal Casting: A Review

This paper focused on the characterization of the composites containing nickel aluminate spinel from Al2O3/NiO and Al2O3/Ni systems. The composites were prepared by die pressing of powders and subsequent sintering of green bodies in air atmosphere. Composites were characterized by XRD, SEM, EDS and DTA/TG/MS analyses. The physical properties of the composites were measured by Archimedes method. Quantitative description of the composites microstructure was made on the basis of SEM images using computer image analysis. The XRD studies and SEM observations of composites confirmed the presence of two phases Al2O3 and NiAl2O4 in the whole volume of samples from both systems. Spinel phase was evenly distributed throughout the volume of the material. Morphology of NiAl2O4 obtained from both systems was characterized by the presence of voids. The DTA/TG/MS measurements showed the characteristics of organic binder decomposition and type of gases released to the atmosphere during thermal treatment. Moreover, the DTA/TG analysis showed the temperature of spinel-phase formation for both systems. It was found that the spinel-phase NiAl2O4 formation retards the process of densification. Therefore, it can be concluded that densification of samples with spinel phase depends mainly on the volume of spinel phase in composite material and does not depend on the substrates used to prepare spinel phase. The values of the selected properties of Al2O3–Ni- and Al2O3–NiO-based materials confirmed that the physical properties depend on the type of substrates used in the fabrication of composites. The type of powder influences the open porosity of samples. For composites produced using NiO powder, open porosity is lower than for samples formed with nickel powder.

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Characterization of composites containing NiAl2O4 spinel phase from Al2O3/NiO and Al2O3/Ni systems

The centrifugal-slip casting method was used for producing the Al2O3-Ni composites with a gradient distribution of the Ni phase. The final products had the shape of hollow cylinders. The casting slurries were water-based and contained alumina and nickel powders with two different particle sizes. The cast samples were then subjected to sintering at a temperature of 1400 °C in an N2/H2 reducing atmosphere with heating and cooling rates of 1 °C/min, and the dwell time - 4 h. The rheological properties of the water-based slurries were examined. It appeared that the presence of the Ni particles strongly affected the slurry properties which was probably associated with the strong interactions between the Ni and α-Al2O3 particles. The Al2O3-Ni composites with a gradient distribution of the Ni particles were examined using the X-ray diffraction method. No new phases such as the nickel aluminate spinel were identified in the sintered composites. The microstructure of the samples was analyzed using Scanning Electron Microscopy (SEM). The observations revealed that the samples were composed of three zones with different distributions of the Ni particles on their cross-section. Finally, the Ni particle distribution in the functionally graded materials was described quantitatively.

Combined centrifugal-slip casting method used for preparation the Al2O3-Ni functionally graded composites

The paper presents the analysis of thermal decomposition of selected organic additives, which are commonly used in shaping of ceramic materials by colloidal methods. Shaping of ceramics requires using different additives which then are burned out during sintering process. For this reason, the knowledge about thermal degradation of organics used, as well as decomposition products, seems to be very important from the application point of view. The analyzed substances were as follows: diammonium hydrocitrate, citric acid, ammonium salt of acrylic polymer, l-ascorbic acid, N,N,N′,N′-tetramethylethylenediamine, and ammonium persulfate. The thermal analysis has been done on the apparatus coupled with mass spectrometer what allowed to observe what types of gasses are released to the atmosphere during heating. The obtained results showed important differences in thermal degradation of organic additives. It was possible to determine at what temperature regions harmful gases like N2O, NO2, or SO2 are released from the organics and which additives can be treated as environmentally friendly.

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Thermal degradation of organic additives used in colloidal shaping of ceramics investigated by the coupled DTA/TG/MS analysis

Polymerization reactions are frequently used in fabrication of a wide range of ceramic components, from 3D elements (gelcasting, UV-curing), through thin tapes (gel-tape casting) to porous samples (mechanical foaming coupled with gelcasting). The analysis of the properties of organic additives used in these techniques as well as factors which influence the polymerization reaction in ceramic suspension are seldom described in the scientific literature. For this reason this paper presents the properties of selected monomers and polymers with influence on the elasticity of zirconia tapes obtained by gel-tape casting. The measured parameters were as follows: glass transition temperature of polymers with and without external plasticizers, wetting angle of ceramic substrates by monomers, and viscoelastic properties of zirconia slurries. The issues of oxygen inhibition, polymerization rate and polymerization shrinkage with influence on unwanted cracking of thin tapes are also discussed. The location of polymeric binder in green bodies was analyzed by SEM.

Organic additives in gel-tape casting of ceramic powders – A novel approach to the problem of elasticity and cracking of thin tapes

The paper reports the synthesis of a new compound named diglyceryl acrylate (DGA) and its application in manufacturing of ZTA composites by gelcasting method. The compound can be used as a monomer able to polymerize in suspensions and also as a dispersing agent for fine-crystalline powders. The paper describes the synthesis of DGA, the properties of the monomer, the resulting polymer, ceramic suspensions and sintered bodies. The distribution of zirconia grains in alumina matrix was observed on SEM. Vickers hardness and fracture toughness of ZTA composites have been measured. The research revealed that with the use of DGA it is possible to obtain highly concentrated ceramic suspension (60 vol%) of low viscosity. The positive influence of the new monomer on the properties of ceramic suspensions and sintered bodies is explained on the basis of the analysis of spatial structures of all 8 regioisomers of DGA molecule.

Diglyceryl acrylate as alternative additive dedicated to colloidal shaping of oxide materials – Synthesis, characterization and application in manufacturing of ZTA composites by gelcasting

Paulina Wiecinska

Papers

Characterization of composites containing NiAl2O4 spinel phase from Al2O3/NiO and Al2O3/Ni systems

Combined centrifugal-slip casting method used for preparation the Al2O3-Ni functionally graded composites

Thermal degradation of organic additives used in colloidal shaping of ceramics investigated by the coupled DTA/TG/MS analysis

Organic additives in gel-tape casting of ceramic powders – A novel approach to the problem of elasticity and cracking of thin tapes

Diglyceryl acrylate as alternative additive dedicated to colloidal shaping of oxide materials – Synthesis, characterization and application in manufacturing of ZTA composites by gelcasting