Silicon Nitride-based Ceramics Research Articles

Densification modeling for gas pressure sintered silicon nitride-based ceramics with Thermo-Optical dilatometry

The complexity of gas pressure liquid phase sintering (GPS-LPS) of silicon nitride induces a certain savoir-faire. This highly challenging strong bond ceramic uses sintering additives of a liquid phase sintering under high temperatures close to the silicon nitride phase decomposition which requires a gas pressure. The sintering behavior encompasses various phenomena such as Ostwald ripening grain growth, phase transition, and swelling when the pore elimination approach close porosity. The aim of this study was to model such sintering behavior. In this aim, master sintering curves (MSC) were used to study the temperature and porosity dependence of the sintering model. Then, the grain growth sensitivity of the sintering model was incorporated. Finally, the swelling phenomenon responsible for transient de-densification and sintering rate limiting mechanism at final stage sintering was extracted by an inverse method. A comprehensive sintering model reproducing all the silicon nitride sintering complexity result this study.

Influence of ink rheology and post processing in the structural performance of silicon nitride-based ceramics fabricated by robocasting

The fabrication of complex shaped Si3N4 parts by conventional methods is challenging due to its high hardness and mechanical strength. Additive manufacturing (AM) appeared as a competitive way to attain three-dimensional complexity at lower costs. However, most of AM technologies still present limitations in producing high dense ceramics, mainly due to several difficulties in developing proper feedstock. This work presents the fabrication of dense silicon nitride-based ceramics by using an extrusion based additive manufacturing technique (direct ink writing, also known as robocasting) and cold isostatic pressing (CIP) as a post processing step. Silicon-nitride aqueous based inks containing different amounts of solids loading (36, 38 and 39 vol%) and proper rheological characteristics for the printing process were studied. The use of CIP (200 MPa) is suggested to reduce or even eliminate defects and porosity and consequently, to improve mechanical performance of the final parts. Relative density, microhardness and flexural strength increased as solids loading in the inks increased and were further improved when CIP pressing was used. Parts produced by robocasting with an ink containing 39 vol% and cold isostatic pressed at 200 MPa exhibited an average relative density around 99%, 1475 HV2 microhardness value and 650 MPa flexural strength, values similar to those of silicon nitride ceramics fabricated by conventional processing.

Design of Reliable Remobilisation Finger Implants with Geometry Elements of a Triple Periodic Minimal Surface Structure via Additive Manufacturing of Silicon Nitride

When finger joints become immobile due to an accident during sports or a widespread disease such as rheumatoid arthritis, customised finger joint implants are to be created. In an automated process chain, implants will be produced from ceramic or metallic materials. Artificial intelligence-supported software is used to calculate three-dimensional models of the finger bones from two-dimensional X-ray images. Then, the individual implant design is derived from the finger model and 3D printed. The 3D printing process and the structures used are evaluated via model tests and the final implant design via a reliability calculation in a way to ensure that this is also possible via an AI process in the future. Using additive manufacturing with silicon nitride-based ceramics, model specimens and implants are produced via the lithography-based ceramic vat photopolymerisation process with full geometry or elements of triple periodic minimal surfaces structure. The model specimens are tested experimentally, and the loads are matched with a characteristic strength assuming a Weibull distribution of defects in the volume to generate and match failure probabilities. Calculated fracture forces of the silicon nitride-based ceramic structure was validated by comparison of simulation and tests, and the calculation can be used as a quality index for training of artificial intelligence in the future. The proposed method for individualized finger implant design and manufacturing may allow for correction of potential malpositions of the fingers in the future.

Antibacterial behavior of oxynitride glasses as a glassy grain boundary phase for silicon nitride‐based ceramics

International Journal of Applied Glass ScienceVolume 13, Issue 1 p. 152-152 CORRIGENDUMFree Access Antibacterial behavior of oxynitride glasses as a glassy grain boundary phase for silicon nitride-based ceramics This article corrects the following: Antibacterial behavior of oxynitride glasses as a glassy grain boundary phase for silicon nitride-based ceramics Seniz R. Kushan Akin, Emrah Dolekcekic, Thomas J. Webster, Volume 12Issue 3International Journal of Applied Glass Science pages: 328-336 First Published online: March 3, 2021 First published: 03 December 2021 https://doi.org/10.1111/ijag.16542AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Seniz R. Kushan Akin1,2 | Emrah Dolekcekic3 | Thomas J. Webster1 1Department of Chemical Engineering, Northeastern University, Boston, MA, USA 2Department of Materials Science and Engineering, Cankaya University, Ankara, Turkey 3Department of Materials Science and Engineering, Eskisehir Technical University, Eskisehir, Turkey Correspondence Seniz R. Kushan Akin, Department of Materials Science and Engineering, Cankaya University, Ankara, Turkey. Emails: senizakin@cankaya.edu.tr ; kushanakin@gmail.com The manuscript titled “Antibacterial behavior of oxynitride glasses as a glassy grain boundary phase for silicon nitride-based ceramics” contains one mistake. This Corrigendum acknowledges and corrects the error. “Department of Materials Science and Engineering, Cankaya University, Ankara, Turkey” was added in the affiliation list post publication of the article. REFERENCE Kushan Akin SR, Dolekcekic E, Webster TJ. Antibacterial behavior of oxynitride glasses as a glassy grain boundary phase for silicon nitride-based ceramics. Int J Appl Glass Sci. 2021; 12: 328– 336. https://doi.org/10.1111/ijag.15902Wiley Online LibraryCASWeb of Science®Google Scholar Volume13, Issue1January 2022Pages 152-152 ReferencesRelatedInformation

Automation of the technology of connecting parts in the manufacture of aerospace products

The paper describes the improvement of the technology of manufacturing parts and components of aerospace production using computer-aided design and technological process control. The theoretical foundations and algorithms for constructing the technological process of manufacturing parts and components of the aerospace industry using various methods of joining heat-resistant materials, for example, by diffusion welding, are designed on the basis of theoretical and experimental studies proposed by the author of the patented connection method «Method for joining a heat-resistant cobalt-based alloy with silicon nitride-based ceramics» and technological equipment «Installation for obtaining metal-ceramic products», as well as «Attribute database for creating technological processes for obtaining parts of aerospace production by diffusion welding» and «Attribute database of technological equipment, tools and devices for mechanical processing of aerospace production parts», registered in the register of databases of the Russian Federation. The research is conducted at the Department of Mechanical Engineering Technology of the Institute of Mechanical Engineering and Mechatronics of the Siberian State University of Science and Technology named after academician M.F. Reshetnev.

A műszaki kerámiák kopási viselkedését befolyásoló vizsgálati tényezők

Due to the excellent mechanical properties of technical ceramics, they can be widely used as mechanical components exposed to wear. In many fields, they are suitable not only for replacing metals but also for providing superior properties. During their application, many environmental (temperature, humidity) and loading factors (number of cycles, loading force) play a role in the appearance of the evolving wear formats. The present article deals with the study of the effect of loading factors, for which the measurements were performed by the fretting method at room temperature, in air with 50% relative humidity with a loading force of 2 and 5 N, and with 30.000 and 50.000 cycles. The effect of loading force and test length on the wear of silicon nitride-based ceramics was clearly demonstrated during the tests.

Effects of pore structures on the dielectric properties of silicon nitride-based ceramics

The pore structures are invariably ignored when evaluating the dielectric properties of silicon nitride (Si3N4) ceramics. In this work, the effects of pore structures on the dielectric properties were revealed using both theoretical models and experimental evaluation. Theoretical models illustrate that the pore geometry and average pore radius are the determinants of dielectric properties when porosity remains constant. Experimentally, Si3N4-based ceramics with different pore structures were achieved via adding different amounts of β-Si3N4 whiskers. Then the correlations between dielectric properties and pore structures were investigated. The marked variation between experimental dielectric constants and three homogeneous isometrical sphere models reveals that the pore structures have conspicuous effects on the dielectric properties, as well as the consistent loss tangents.

A páratartalom hatása a Si3N4 alapú kerámiák kopására

A Si3N4 alapú kerámiákhoz kapcsolódó tribológiai kutatások célja a különböző környezeti tényezők kopási folyamatra gyakorolt hatásának vizsgálata volt. A műszaki kerámiák alkalmazásánál gyakran előfordul, hogy nedves közegben alakul ki a súrlódó párok kölcsönhatása, kenőanyag hozzáadása nélkül. A vizsgálatok fretting-módszerrel történtek szobahőmérsékleten, 10 N terhelőerővel, 3, 50 és 99,5% relatív páratartalmú levegőn. A vizsgálatok során egyértelműen kimutatható volt a páratartalom hatása a szilícium-nitrid alapú kerámiák kopására, ami a tribokémiai kopás sajátosságaival magyarázható.

Dense, Strong, and Precise Silicon Nitride-Based Ceramic Parts by Lithography-Based Ceramic Manufacturing

Due to the high level of light absorption and light scattering of dark colored powders connected with the high refractive indices of ceramic particles, the majority of ceramics studied via stereolithography (SLA) have been light in color, including ceramics such as alumina, zirconia and tricalcium phosphate. This article focuses on a lithography-based ceramic manufacturing (LCM) method for β-SiAlON ceramics that are derived from silicon nitride and have excellent material properties for high temperature applications. This study demonstrates the general feasibility of manufacturing of silicon nitride-based ceramic parts by LCM for the first time and combines the advantages of SLA, such as the achievable complexity and low surface roughness (Ra = 0.50 µm), with the typical properties of conventionally manufactured silicon nitride-based ceramics, such as high relative density (99.8%), biaxial strength (σf = 764 MPa), and hardness (HV10 = 1500).

Bioactive silicon nitride by surface thermal treatment

Silicon nitride-based ceramics with SiO2, CaO and Ca3(PO4)2 as sintering additives, have been prepared in order to study the bioactivity. Dense ceramic bodies were oxidized by an oxy-acetylene flame at approx. 1475 °C for 60 s, in order to modify the surface in terms of bioactivity enhancement and the formation of optimal porosity for cell viability. During oxidation two concurrent processes occurred on the ceramic body surface: (i) formation of thin glassy layer with a composition close to that of grain boundary phase in ceramic body, and (ii) partial decomposition of silicon nitride matrix. The latter one resulted in the formation of gases (N2 and SiO), which formed bubbles in the viscous surface glassy phase, resulting in porosity required for cell adhesion (small pores) and tissue ingrowth (large pores). The best bioactivity was obtained for oxy-acetylene flame treated Si3N4 ceramics with Ca3(PO4)2 sintering additive.

Study on the Effect of Bonding Process of Silicon Nitride-Based Ceramics with Yb-β/Glass Composite Solders on the Structure and Properties of Joints

Dense Si3N4 ceramics, porous/dense ceramics, SiC reinforced Si3N4 ceramics and other materials have been successfully bonded with Yb-β/glass composite solders. The effect of bonding process on the structure and properties of joints was studied.

High graphene fillers content for improving the tribological performance of silicon nitride-based ceramics

The effect of large graphene nanoplatelets (GNPs) additions on the friction and wear of silicon nitride (Si3N4) ceramics is evaluated under isooctane lubrication. All Si3N4/GNPs composites, with up to 20.6 vol% of graphene fillers, exhibit better tribological response than Si3N4, in particular, a 50% reduction in the friction that continuously decreases with the GNPs content is attained, jointly with an improvement in the wear resistance of up to 63%. The survival of a self-lubricant carbon-rich tribolayer formed on the worn surfaces controls the tribological properties of the materials. Si3N4/GNPs composites are promising materials to enhance the performance of gasoline direct injection systems.

In vitro bioactivity of silicon nitride–hydroxyapatite composites

Silicon nitride-based ceramics are characterised especially by high chemical resistance, superior combination of fracture toughness, hardness and bioinertness. However, the biological applications often require additional properties, e.g. bioactivity enabling stronger bonding to the host tissue. Hydroxyapatite coating prepared by sol–gel route, which provides pure, stable and nano-crystalline product is one of the ways to achieve bioactivity of bioinert ceramics. Therefore silicon nitride–hydroxyapatite composites were prepared by infiltration of hydroxyapatite precursor sol into the silicon nitride based porous ceramics. The conditions of sol preparation were optimised to be appropriate for pure HA synthesis: ageing at elevated temperature (85°C) and calcinations at 500°C for 1h. Cytotoxicity and in vitro bioactivity of Si3N4–HA composites were tested in order to verify the effect of hydroxyapatite addition on the biological properties of composite. After immersion of porous composite into simulated body fluid (SBF) for 21 days, calcium phosphate layer was formed on the surface of silicon nitride–hydroxyapatite composites, indicating their bioactivity.

Microstructure of low-dose neutron-irradiated Si3N4 and SiAlON ceramics after thermal annealing

Four kinds of silicon nitride-related ceramics were neutron irradiated up to 8.5 × 1024 n/m2 (E > 0.1 MeV) at 563 K. Induced swelling were almost recovered by thermal annealing up to 1473 K. Microstructure of the as-irradiated silicon nitride-based ceramics and those of after thermal annealing up to 1123, 1223 and 1473 K were observed with a high-resolution transmission electron microscope (HREM) in order to clarify their feature and thermal stability. HREM microstructures of the as-irradiated specimens revealed that the atomic configuration projected onto the basal plane was similar as a perfect crystalline arrangement without lattice distortion. It was confirmed that only point defects or point-like defects were generated during the neutron irradiation of the present condition. In addition, microstructure analysis of thermally annealed specimens did not reveal any voids along grain boundaries and triple junctions. Furthermore, formations of dislocation loops were not confirmed after thermal annealing up to 1473 K, in all Si3N4 and SiAlON polymorphs.

Analysis of recovery process of low-dose neutron irradiation-induced defects in silicon nitride-based ceramics by thermal annealing

Two kinds of silicon nitride ceramics consisting of different polymorphs were neutron-irradiated up to 8.5×1024n/m2 (E>0.1MeV) at 563K, and their annealing behaviors were compared to those of previously reported SiAlON polymorphs subjected to the same irradiation condition. The macroscopic length change of α- and β-Si3N4 and α- and β-SiAlON were 0.11%, 0.06%, 0.12% and 0.14%, respectively. Based on swelling data and microstructural observations, the low dose neutron irradiation-induced defects in silicon nitride-based ceramics were considered to be primarily point defects. In order to investigate the kinetics of defect recovery, these irradiated specimens were isothermally and isochronally annealed continuously up to 1473K. Macroscopic length change decreased gradually with increasing annealing temperature. Recovery curves of isochronal annealing of α-Si3N4 and α-SiAlON were similar, and those of β-Si3N4 and β-SiAlON were also similar. The recombination rate constant as a first-order reaction increased with the increasing of the isothermal annealing temperature. A two-stage recovery process was considered between the irradiation temperature and 1473K. The activation energies at higher temperatures were almost double those at lower temperatures in both Si3N4 and SiAlON. At lower temperatures range the recovery should occur by annihilation of close-spaced Frenkel pairs. On the other hand, at higher temperatures, the recovery process may be governed by the annihilation of separated Frenkel pairs. In addition, the activation energies for defect recovery in Si3N4 were larger than defects in SiAlON. Recovery characteristics of α- and β-phases were different in both crystals that are suggested to be due to differences in crystal structures.

Porous silicon nitride ceramics designed for bone substitute applications

Abstract Porous silicon nitride ceramics having properties similar to the human trabecular bone have been sintered and characterized in order to develop a material applicable as bone substitute. At first, human trabecular bone was characterized especially in terms of pore structure which is, besides the non-toxicity, the most critical for acceptation of the substitute. The pore network of highly porous trabecular bone is formed by interconnected large pores of approximately 300–1000 μm. Similar pore structure of silicon nitride-based ceramics was attained by the replica method with polyurethane sponge as pore forming agent. Porous ceramics were prepared in two ways, namely as air-sintered silicon nitride and sintered reaction-bonded silicon nitride. The materials were characterized using the same methods as for the human bone samples. Both types of ceramic materials fulfilled the microstructural requirements for bioapplications. Moreover, their non-cytotoxicity was proved by measuring the yellow tetrazolium MTT proliferation assay using human fibroblast cell line.

Enhanced particle rearrangement during liquid phase spark plasma sintering of silicon nitride-based ceramics

Densification evolution has been analysed in liquid phase assisted spark plasma sintering (SPS) of silicon nitride (Si 3N 4)-based materials. Monolithic ceramics with variable amounts of Al 2O 3/Y 2O 3 sintering additives, and carbon nanotubes (CNTs) containing Si 3N 4 composites have been considered. The shrinkage behaviour of SPSed monolithic Si 3N 4 showed a noticeable enhancement of the particle rearrangement stage, exhibiting a complete wetting of the grain boundary phase even for the lowest additive content (1.70 vol.%), unlike the corresponding hot pressed (HPed) material. An improvement of the liquid phase wetting by the presence of electromechanical forces is proposed to explain the enhanced densification occurring in the particle rearrangement stage of the SPS process. Furthermore, the addition of CNTs seems to increase the efficiency of this mechanism, decreasing the particle rearrangement temperature.

Mechanical properties of silicon nitride-based ceramics and its use in structural applications at high temperatures

Silicon nitride (Si 3N 4) based ceramics are gaining more and more attention due to their promising high-temperature thermal and mechanical properties. They have been expected to be the main candidates for applications such as turbocharger rotors and gas turbine engine components which can withstand severe conditions of temperature and heavy loads. Although a big number of studies on silicon nitride are published, a continuous progress in monolithic Si 3N 4 as well as Si 3N 4/Si 3N 4 composites (seeded materials) leads to new scientific and technological data providing new insight that should be reviewed taking into account their excellent properties at high temperatures. Silicon nitride possesses a bunch variety of interesting properties that can be specifically designed to produce a given behavior profile. That is why the room temperature and high-temperature properties are discussed and described in more detail.

Influence of additive system (Al2O3-RE2O3 , RE = Y, La, Nd, Dy, Yb) on microstructure and mechanical properties of silicon nitride-based ceramics

Silicon nitride based ceramics have been widely used as structural ceramics, due mainly to their thermo-mechanical properties such as high density, high thermal shock resistance, corrosion resistance and chemical stability. The aim of this study was to determine the influence of rare earth and aluminum oxide additions as sintering aids on densification, microstructure and mechanical properties of silicon nitride. Silicon nitride mixtures with 91 wt. (%) Si3N4 and 9% wt. (%) additives were prepared and sintered. The density, microstructure and mechanical properties of the sintered specimens of these mixtures were determined. In most specimens, scanning electron microscopic examination and X ray diffraction analysis revealed elongated grains of β-Si3N4 with aspect ratio of about 2.0 and dispersed in a glassy phase. The density of the sintered specimens was higher than 94% of the theoretical density (td) and specimens with La2O3 and Al2O3 additions exhibited the highest value. The results of this investigation indicate that the rare earth ion size influences densification of silicon nitride, but this correlation was not observed in specimens containing two different rare earth oxides. The hardness values varied in direct proportion to the density of the specimens and the fracture toughness values were influenced by the composition of the intergranular glassy phase.

Controlled Crystallisation of a Y-Si-Al-O-N Glass Typical of Grain Boundary Glasses Formed in Silicon Nitride-Based Ceramics

This paper provides an overview of the crystallisation of an oxynitride glass likely to remain in a silicon nitride ceramic following firing. The crystallisation process was studied using both differential thermal analysis (DTA) and separate isothermal heat treatments in a tube furnace under nitrogen. The activation energy for the crystallisation process was determined by DTA. The nucleation temperature, Tg + 40°C, which corresponded to the maximum volume fraction of crystalline phases, agreed closely with the optimum nucleation temperature of Tg + 35°C, found from DTA. The optimum crystal growth temperature was observed to be 1210°C and yielded the - and -polymorphs of yttrium disilicate. Heat treatments at other temperatures indicated the development of phase assemblages which contained different polymorphs of yttrium disilicate as well as silicon oxynitride. Not all of the polymorphic transformations of yttrium disilicate were observed by DTA unless some crystallisation exotherms were deconvoluted, indicating that DTA analysis of the crystallisation of complex systems requires careful interpretation. It is, however, possible to simplify the system by substituting some yttrium by lanthanum. This stabilises the -polymorph of yttrium disilicate. The activation energy for crystallisation was observed to be similar to that for viscous flow of Y-Si-Al-O-N glasses.