Electro Conductive Alumina Nanocomposites From Different Alumina-Carbides Mixtures

This work presents the results of an electro-discharge machined ceramic composites consisting of a base non-conductive ceramic component such Al2O3, to which is added sufficient amounts of an electro-conductive ceramic nanoparticles such as TiC, TiNC, NbNC, TaNC, and SiC (whiskers) to achieve an electrical resistance of less than about 100W.cm. With these compositions intricate geometries and features as holes, chamfers, slots, angles, changing radii and complex curves can be electro-discharge machined (EDM) into the ceramic body after Pulsed Electrical Current Sintering (PECS) to achieve maximum density and mechanical properties. In EDM, the electrically conductive workpiece or ceramic blank is eroded by electric discharges or sparks which on a small scale generate localized shock waves and intense heat. The four compositions studied were in the same proportion for all raw materials: alumina 42 (vol %) + conductive material (TiC, TiNC, NbNC, and TaNC) 22 (vol %) + SiCw 36 (vol %). Processing was carried out mixing raw materials in the suitable proportions in a polypropylene container with zirconia balls and isopropanol media for 72 hours in order to guarantee the homogeneity of the final compositions. The powders were dried and introduced into a PECS furnace for sintering to 1650°C (100 MPa/2 min). The diameters of the pieces obtained were 20 and about 40 mm and 7 mm thickness. SiC whiskers reinforced electrically conductive ceramic compositions provide a fully dense material with optimal mechanical properties. The capability of electro-discharge machining obtains good surface quality, chip-free edges, dimensional accuracy and complex shapes. The fracture toughness is improved two to three fold over individual ceramic components. Strength and hardness is also increased. Some composites were tested as a cutting tool to machine IN-718 nickel-base superalloy industrial laminating cylinders. The composites were formed and electro-discharge machined to a standard size cutting inser

Effect of drying methods of Al

Well-dispersed alumina ceramic-graphene oxide (GO) powder mixtures were fabricated using a colloidal processing route and three drying techniques were applied: in vacuum, spray and freeze dryers. Dense composites were obtained via spark plasma sintering, the technique reducing GO to graphene in situ during the sintering process. The mechanical properties of the sintered composites were investigated. The composites obtained by spray drying have shown the fracture toughness of 4.5 ± 0.4 MPa·m1/2, and hardness of 18.4 ± 0.8 GPa with an extremely high dispersion of graphene within the ceramic matrix

Effect of drying methods of Al2O3-GO powder mixture on the properties and microstructure of sintered composites obtained by spark plasma sintering

Well-dispersed alumina ceramic-graphene oxide (GO) powder mixtures were fabricated using a colloidal processing route and three drying techniques were applied: in vacuum, spray and freeze dryers. Dense composites were obtained via spark plasma sintering, the technique reducing GO to graphene in situ during the sintering process. The mechanical properties of the sintered composites were investigated. The composites obtained by spray drying have shown the fracture toughness of 4.5 ± 0.4 MPa·m1/2, and hardness of 18.4 ± 0.8 GPa with an extremely high dispersion of graphene within the ceramic matrix

Direct Ink Writing Technology (3D Printing) of Graphene-Based Ceramic Nanocomposites: A Review

In the present work, the state of the art of the most common additive manufacturing (AM) technologies used for the manufacturing of complex shape structures of graphene-based ceramic nanocomposites, ceramic and graphene-based parts is explained. A brief overview of the AM processes for ceramic, which are grouped by the type of feedstock used in each technology, is presented. The main technical factors that affect the quality of the final product were reviewed. The AM processes used for 3D printing of graphene-based materials are described in more detail; moreover, some studies in a wide range of applications related to these AM techniques are cited. Furthermore, different feedstock formulations and their corresponding rheological behavior were explained. Additionally, the most important works about the fabrication of composites using graphene-based ceramic pastes by Direct Ink Writing (DIW) are disclosed in detail and illustrated with representative examples. Various examples of the most relevant approaches for the manufacturing of graphene-based ceramic nanocomposites by DIW are provided

Assessment Effect of Nanometer-Sized Al₂O₃ Fillers in Polylactide on Fracture Probability of Filament and 3D Printed Samples by FDM

In this paper, a mathematical model for the description of the failure probability of filament and fused deposition modeling (FDM)-printed products is considered. The model is based on the results of tensile tests of filament samples made of polyacrylonitrile butadiene styrene (ABS), polylactide (PLA), and composite PLA filled with alumina (Al2O3) as well after FDM-printed products of “spatula” type. The application of probabilistic methods of fracture analysis revealed that the main contribution to the reduction of fracture probability is made by the elastic and plastic stages of the fracture curve under static loading. Particle distribution analysis of Al2O3 combined with fracture probability analysis shows that particle size distributions on the order of 10−5 and 10−6 mm decrease the fracture probability of the sample, whereas uniform particle size distributions on the order of 10−1 and 10−2 mm do not change the distribution probability. The paper shows that uneven distribution of Al2O3 fillers in composite samples made using FDM printing technology leads to brittle fracture of the samples

The influence of hydrojet surface processing on the adhesive strength of wear-resistant coatings deposited on a metal-cutting tool of oxynitride ceramics

The work represents a new approach of preliminary surface treatment of replaceable polyhedral cutting ceramics inserts for significant increase of adhesion strength with deposited wear-resistant nitride ceramics. By this method the hydrojet treatment was used to repair surface defects occurring during manufacturing process of any required geometry of cutting inserts

Developing processes for manufacturing metal aviation technology components using powder bed fusion methods

Favorable parameters for selective melting methods using electron and laser radiation have been established to obtain the required geometric, physical and mechanical characteristics of thin-walled parts for aviation purposes from H18N9T (analogue AISI 321) and Ti6Al4V alloys. Parts were manufactured and field tests were carried out on the stand. It has been shown that the technological processes developed using the SLM and SEBM methods can be recommended for the manufacture of thin-walled parts working in conditions of rapidly changing deformations

The influence of hydrojet surface processing on the adhesive strength of wear-resistant coatings deposited on a metal-cutting tool of oxynitride ceramics

The work represents a new approach of preliminary surface treatment of replaceable polyhedral cutting ceramics inserts for significant increase of adhesion strength with deposited wear-resistant nitride ceramics. By this method the hydrojet treatment was used to repair surface defects occurring during manufacturing process of any required geometry of cutting inserts

Mechanisms Involved in the Formation of Secondary Structures on the Friction Surface of Experimental Aluminum Alloys for Monometallic Journal Bearings

The processes taking place on the friction surface of high-alloyed aluminum alloys working with steel whilst replacing bronze journal bearings with aluminum are investigated. In this regard, eight experimental aluminum alloys with an Sn content from 5.4% to 11.0%, which also included Pb, Zn, Si, Mg, and Cu, were cast. The surface and subsurface layer of experimental aluminum bearings were studied before and after tribological tests with a 38HN3MA steel counterbody by scanning electron microscopy including energy-dispersive analysis. The best aluminum alloy, which had an Sn content of 5.8% after the friction tests, showed 6.5-times better wear resistance and steel counterbody wear rate than the bronze reference. Both structural and compositional changes in the surface layer were observed. It was revealed that secondary structures formed on the surface during the friction process and included all of the chemical elements in the tribosystem, which is a consequence of its self-organization. Generally, the secondary structures are thin metal-polymer films generated as a result of the high carbon and oxygen content. The interaction behavior of some of the chemical elements in the tribosystem is shown and discussed. In addition, the influence that Sn, Pb, Cu, and C content in the secondary structures has on the tribological properties of low-tin and medium-tin alloys is shown

The Effect of Elements of Secondary Structures on the Wear Resistance of Steel in Friction against Experimental Aluminum Alloys for Monometallic Journal Bearings

This article describes the elemental composition of secondary structures formed on the steel contact surface during wear test against experimental Al alloys. Wear tests were carried out according to the rotating steel roller-fixed shoe of an antifriction alloy scheme under boundary lubrication conditions. The duration of the test was 40 h, and motor oil M14V2 was used as a lubricant. The microstructure and elemental characterization of the steel surface before and after the tribological test was obtained by scanning electron microscopy equipped with EDX. The simultaneous presence of various constituents of oil, steel, and Al alloys can produce both positive and negative effects on the friction characteristic of the tribosystem. It was shown that presence of Mo, F, S, Si, Ni, and Cr have a favorable effect on the wear resistance of steel and the friction coefficient of the rubbing surfaces due to the formation of secondary structures with optimal composition