Advanced Ceramic Materials Sintered by Microwave Technology

Processing of ceramic materials has also a strong impact in the quality of the consolidated body, as it plays a key role in the resulting microstructure and, as a consequence, in its final properties. Advanced ceramic materials are commonly processed as powders and densified via a high-temperature process. Traditional processing techniques include hot isostatic pressing, mold casting, and sintering in conventional ovens. As ceramics require very high processing temperatures compared to metals and polymers, these processes tend to be very energy intensive and result in higher production costs to the manufacturers. Therefore, new technologies known as nonconventional sintering techniques, such as microwave technology, are being developed in order to reduce energy consumption, while maintaining or even improving the characteristics of the resulting ceramic material. This novel and innovative technology aims at helping industrial sectors lower their production costs and, at the same time, lessen their environmental impact. On the other hand, it is interesting and necessary to know and explore the basic principles of microwaves to advance in the development of materials that demand, every day more, the different industrial sectors. This chapter presents the most recent advances of two materials with a great industrial future: zirconia and lithium aluminosilicate

Wear behavior of conventional and spark plasma sintered Al2O3-NbC nanocomposites

[EN] This study aims to investigate the dry sliding wear behavior of Al2O3-5vol.% NbC nanocomposites sintered by two different consolidation techniques: conventional sintering (CS) and spark plasma sintering (SPS) at temperatures ranging from 1450 to 1600 degrees C. The dry sliding wear tests were performed on a tribometer with a ball-on-disc configuration using an Al2O3 ball as a counterpart material, with a normal contact load of 15 and 30 N, a sliding distance of 2000m and a sliding speed of 0.1m/s at room temperature and ambient environment. The sintering methods, mechanical properties and applied load acted directly on the wear mechanism of the nanocomposites. The samples sintered by SPS exhibited higher densification and hardness, in addition to a lower friction coefficient and wear rate. Based on the wear rate, these nanocomposites exhibited a moderate regime with 15N of load, and several regimes when 30 N of applied load was used. The main wear mechanisms observed were plastic deformation, abrasion and grain pull-out. The excellent results show that Al2O3-NbC nanocomposites are ideal for the manufacture of new products such as cutting tools.Brazilian institution CAPES for the project CAPES-PVE A086/2013, Grant/Award Number: 23038.009604/2013-12Alecrim, L.; Ferreira, J.; Salvador Moya, MD.; Borrell Tomás, MA.; Pallone, E. (2018). Wear behavior of conventional and spark plasma sintered Al2O3-NbC nanocomposites. International Journal of Applied Ceramic Technology. 15(2):418-425. https://doi.org/10.1111/ijac.12800S418425152Wahi, R. P., & Ilschner, B. (1980). Fracture behaviour of composites based on Al2O3-TiC. Journal of Materials Science, 15(4), 875-885. doi:10.1007/bf00552097Tedesco, N. R., Pallone, E. M. J. A., & Tomasi, R. (2010). Effects of the Pin-on-Disc Parameters on the Wear of Alumina. Advances in Science and Technology, 65, 39-44. doi:10.4028/www.scientific.net/ast.65.39Rodriguez-Suarez, T., Bartolomé, J. F., Smirnov, A., Lopez-Esteban, S., Torrecillas, R., & Moya, J. S. (2011). Sliding wear behaviour of alumina/nickel nanocomposites processed by a conventional sintering route. Journal of the European Ceramic Society, 31(8), 1389-1395. doi:10.1016/j.jeurceramsoc.2011.02.011Gustafsson, S., Falk, L. K. L., Lidén, E., & Carlström, E. (2008). Pressureless sintered Al2O3–SiC nanocomposites. Ceramics International, 34(7), 1609-1615. doi:10.1016/j.ceramint.2007.05.005Qu, H., & Zhu, S. (2013). Two step hot pressing sintering of dense fine grained WC–Al2O3 composites. Ceramics International, 39(5), 5415-5425. doi:10.1016/j.ceramint.2012.12.049Alecrim, L. R. R., Ferreira, J. A., Gutiérrez-González, C. F., Salvador, M. D., Borrell, A., & Pallone, E. M. J. A. (2017). Sliding wear behavior of Al2O3-NbC composites obtained by conventional and nonconventional techniques. Tribology International, 110, 216-221. doi:10.1016/j.triboint.2017.02.028Pasotti, R. M. R., Bressiani, A. H. A., & Bressiani, J. (1998). Sintering of alumina-niobium carbide composite. International Journal of Refractory Metals and Hard Materials, 16(4-6), 423-427. doi:10.1016/s0263-4368(98)00053-5Acchar, W., & Segadães, A. M. (2009). Properties of sintered alumina reinforced with niobium carbide. International Journal of Refractory Metals and Hard Materials, 27(2), 427-430. doi:10.1016/j.ijrmhm.2008.05.004Huang, S. G., Liu, R. L., Li, L., Van der Biest, O., & Vleugels, J. (2008). NbC as grain growth inhibitor and carbide in WC–Co hardmetals. International Journal of Refractory Metals and Hard Materials, 26(5), 389-395. doi:10.1016/j.ijrmhm.2007.09.003Santos, C., Maeda, L. D., Cairo, C. A. A., & Acchar, W. (2008). Mechanical properties of hot-pressed ZrO2–NbC ceramic composites. International Journal of Refractory Metals and Hard Materials, 26(1), 14-18. doi:10.1016/j.ijrmhm.2007.01.008Meng, F., Liu, C., Zhang, F., Tian, Z., & Huang, W. (2012). Densification and mechanical properties of fine-grained Al2O3–ZrO2 composites consolidated by spark plasma sintering. Journal of Alloys and Compounds, 512(1), 63-67. doi:10.1016/j.jallcom.2011.09.015Sun, L., Yang, T., Jia, C., & Xiong, J. (2011). VC, Cr3C2 doped ultrafine WC–Co cemented carbides prepared by spark plasma sintering. International Journal of Refractory Metals and Hard Materials, 29(2), 147-152. doi:10.1016/j.ijrmhm.2010.09.004Bonache, V., Salvador, M. D., Fernández, A., & Borrell, A. (2011). Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr3C2 addition and consolidation by SPS and HIP technologies. International Journal of Refractory Metals and Hard Materials, 29(2), 202-208. doi:10.1016/j.ijrmhm.2010.10.007Sun, X., Wang, Y., & Li, D. Y. (2013). Mechanical properties and erosion resistance of ceria nano-particle-doped ultrafine WC–12Co composite prepared by spark plasma sintering. Wear, 301(1-2), 406-414. doi:10.1016/j.wear.2013.01.113Pallone, E. M. J. ., Trombini, V., Botta F, W. ., & Tomasi, R. (2003). Synthesis of Al2O3–NbC by reactive milling and production of nanocomposites. Journal of Materials Processing Technology, 143-144, 185-190. doi:10.1016/s0924-0136(03)00411-4Botta F, W. ., Tomasi, R., Pallone, E. M. J. ., & Yavari, A. . (2001). Nanostructured composites obtained by reactive milling. Scripta Materialia, 44(8-9), 1735-1740. doi:10.1016/s1359-6462(01)00789-8ISO 3078-1983 Hardmetals, vickers hardness test 1983Chen, W.-H., Lin, H.-T., Chen, J., Nayak, P. K., Lee, A. C., Lu, H.-H., & Huang, J.-L. (2016). Microstructure and wear behavior of spark plasma sintering sintered Al2O3/WC-based composite. International Journal of Refractory Metals and Hard Materials, 54, 279-283. doi:10.1016/j.ijrmhm.2015.07.030Espinosa-Fernández, L., Borrell, A., Salvador, M. D., & Gutierrez-Gonzalez, C. F. (2013). Sliding wear behavior of WC–Co–Cr3C2–VC composites fabricated by conventional and non-conventional techniques. Wear, 307(1-2), 60-67. doi:10.1016/j.wear.2013.08.003Alecrim, L. R. R., Ferreira, J. A., Gutiérrez-González, C. F., Salvador, M. D., Borrell, A., & Pallone, E. M. J. A. (2017). Effect of reinforcement NbC phase on the mechanical properties of Al2O3-NbC nanocomposites obtained by spark plasma sintering. International Journal of Refractory Metals and Hard Materials, 64, 255-260. doi:10.1016/j.ijrmhm.2016.10.021Bonny, K., De Baets, P., Vleugels, J., Huang, S., & Lauwers, B. (2009). Tribological Characteristics of WC-Ni and WC-Co Cemented Carbide in Dry Reciprocating Sliding Contact. Tribology Transactions, 52(4), 481-491. doi:10.1080/10402000802716921Kato, K., & Adachi, K. (2002). Wear of advanced ceramics. Wear, 253(11-12), 1097-1104. doi:10.1016/s0043-1648(02)00240-5Pasaribu, H. R., Sloetjes, J. W., & Schipper, D. J. (2004). The transition of mild to severe wear of ceramics. Wear, 256(6), 585-591. doi:10.1016/j.wear.2003.10.025Tucci, A., & Esposito, L. (2000). Second phases and material transfer in alumina ceramics sliding systems. Wear, 245(1-2), 76-83. doi:10.1016/s0043-1648(00)00467-1Borrell, A., Torrecillas, R., Rocha, V. G., Fernández, A., Bonache, V., & Salvador, M. D. (2012). Effect of CNFs content on the tribological behaviour of spark plasma sintering ceramic–CNFs composites. Wear, 274-275, 94-99. doi:10.1016/j.wear.2011.08.01

Microstructural control of ultrafine and nanocrystalline WC-12Co-VC/Cr3C2 mixture by spark plasma sintering

The aim of this present work is to study the effect of VC and/or Cr 3C 2 in densification, microstructural control and mechanical behaviour of WC-12Co ultrafine and nanocrystalline mixtures, consolidated by spark plasma sintering at 1100 °C, applying a pressure of 80 MPa in combination with a heating rate of 100 °C min -1. Nanocrystalline and ultrafine mixtures with an average size of 30 nm and 100-250 nm, respectively, with the addition of 1 and 0.5 wt.% of VC/Cr 3C 2 grain growth inhibitors, respectively, were investigated. The density, microstructure, hardness and fracture toughness of the consolidated samples were measured and observed. The addition of VC inhibitor allows an excellent grain growth control keeping microstructures with an average grain size of 154 nm. The hardness values and fracture toughness obtained were about 2000 HV 30 and above 10 MPa m 1/2, respectively. © 2010 Elsevier Ltd and Techna Group S.r.l.The work is supported financially by the Spanish Ministry of Science and Innovation by means of the project MAT 2006-12945-C02. A. Borrell, is grateful to this Ministry for the mobility grant to the Institute of Materials Technology (ITM) of the Polytechnical University of Valencia, Spain.Bonache Bezares, V.; Salvador Moya, MD.; García-Rocha, V.; Borrell Tomás, MA. (2011). Microstructural control of ultrafine and nanocrystalline WC-12Co-VC/Cr3C2 mixture by spark plasma sintering. Ceramics International. 37(3):1139-1142. https://doi.org/10.1016/j.ceramint.2010.11.026S1139114237

Sliding wear behavior of WC-Co-Cr3C2-VC composites fabricated by conventional and non-conventional techniques

[EN] The present work aims are to study the dry sliding wear behavior of WC-12 wt.%Co materials, with or without addition of Cr3C2/VC grain growth inhibitors, and to sinter them by two different consolidation techniques: conventional sintering and spark plasma sintering (SPS). The dry sliding wear tests were performed on a tribometer with a ball-on-disc configuration using a WC-Co ball as a counterpart material with a normal contact load of 60 N, a sliding distance of 10000 m and a sliding speed of 0.1 m/s. The influence of the grain growth inhibitors and the consolidation techniques in sintered samples were related to the friction coefficient, wear rates and wear pattern damage. Samples sintered by non-conventional technique (SPS) show the best wear resistance and lower friction coefficient. The addition of inhibitors reduces the wear rates in materials consolidated by both techniques. The differences in the wear damage are related to microstructural parameters, mechanical properties and wear ratesThe work is supported financially by the Spanish Ministry of Science and Innovation by the project MAT2009-14144-C03-C02. L. Espinosa-Fernández, acknowledges the AECI program for the realization of the Ph.D in the ITM-UPV. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva contract (JCI-2011-10498)Espinosa-Fernández, L.; Borrell Tomás, MA.; Salvador Moya, MD.; Gutierrez-González, C. (2013). Sliding wear behavior of WC-Co-Cr3C2-VC composites fabricated by conventional and non-conventional techniques. Wear. 307:60-67. https://doi.org/10.1016/j.wear.2013.08.00S606730

From freeze-dried precursors to microwave sintered Al2O3-ZrO2 composites

[EN] Homogeneous Al2O3-Zr0.91Y0.09O1.955 (65-35 mol%) nanopowders have been prepared in a wide temperature range (from 1073 to 1573 K) by thermal decomposition of amorphous precursors, made previously by freeze-drying of appropriate solutions in air Electron microscopy images show that, whereas at low temperatures (973 K) pseudo-spherical particles constituted of Al2O3 and Zr0.91Y0.09O1.955 grains are observed (similar to 38nm), at high temperatures (1573 K) a homogeneous dispersion of nanocrystalline ZrO2-based grains (similar to 186 nm) is dispersed in the sintered Al2O3 matrix. The comparison between phase and microstructure evolution in these samples clearly indicates that the disorder at the atomic scale in the precursor makes the attainment of higher temperatures necessary for nucleation and growth of both phases. Finally, a selected material was sintered in a mono-mode microwave device at 2.45 GHz in air at 1573 and 1673 K. This fast-microwave technology allows fabrication of composites with high densities (similar to 99% TD) and excellent mechanical properties, such as hardness and Young's modulus reaching 25.6 GPa and 358 GPa, respectively.The authors would like to thank to the Generalitat Valenciana for financial support received for the project PROMETEO/2016/040 and Santiago Grisolia program scholarship (GRISOLIAP/2018/168). A. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her RyC contract (RYC-2016-20915).Borrell Tomás, MA.; Gil-Flores, L.; Guillén-Pineda, RM.; Salvador Moya, MD. (2019). From freeze-dried precursors to microwave sintered Al2O3-ZrO2 composites. Processing and Application of Ceramics. 13(2):157-163. https://doi.org/10.2298/PAC1902157BS15716313

Improvement of microstructural properties of 3Y-TZP materials by conventional and non-conventional sintering techniques

3 mol% Y2O3-stabilized zirconia nanopowders were fabricated using various sintering techniques; conventional sintering (CS) and non-conventional sintering such as microwave (MW) and pulsed electric current-assisted-sintering (PECS) at 1300 °C and 1400 °C. A considerable difference in the densification behaviour between conventional and non-conventional sintered specimens was observed. The MW materials attain a bulk density 99.4% theoretical density (t.d.) at 1300 °C, while the CS materials attain only 92.5% t.d. and PECS 98.7% t.d. Detailed microstructural evaluation indicated that a low temperature densification leading to finer grain sizes (135 nm) could be achieved by PECS followed by MW with an average sintered grain size of 188 nm and CS 225 nm. It is believed that the high heating rate and effective particle packing are responsible for the improvements in these properties. © 2011 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved.This work has been carried out with programme to support research and development of the Polytechnic University of Valencia (U.P.V) under multidisciplinary projects PAID-05-09 and PAID-05-10. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her FPI Ph.D. grant and the people from Institute Technological of Materials (ITM) of the U.P.V for helping us with the microwave experiments during a stay in 2010-2011. Felipe L. Pefiaranda-Foix wants to thank the Generalitat Valenciana for the grant obtained in the frame of the Program BEST/2010, because some results of this paper have been possible with this help.Borrell Tomás, MA.; Salvador Moya, MD.; Rayón Encinas, E.; Penaranda-Foix, FL. (2012). Improvement of microstructural properties of 3Y-TZP materials by conventional and non-conventional sintering techniques. Ceramics International. 38(1):39-43. https://doi.org/10.1016/j.ceramint.2011.06.035S394338

Impact of microwave processing on porcelain microstructure

[EN] Microstructural evolution on sintering of porcelain powder compacts using microwave radiation was compared with that in conventionally sintered samples. Using microwaves sintering temperature was reduced by similar to 75 degrees C and dwell time from 15 min to 5 min while retaining comparable physical properties i.e. apparent bulk density, water absorption to conventionally sintered porcelain. Porcelain powder absorbed microwave energy above 600 degrees C due to a rapid increase in its loss tangent. Mullite and glass were used as indicators of the microwave effect: mullite produced using microwaves had a nanofibre morphology with high aspect ratio (similar to 32 +/- 3:1) believed associated with a vapour-liquid-solid (VLS) formation mechanism not previously reported. Microwaves also produced mullite with different chemistry having similar to 63 mol% alumina content compared to similar to 60 mol% alumina in conventional sintered porcelain. This was likely due to accelerated Al+3 diffusion in mullite under microwave radiation. Liquid glass was observed to form at relatively low temperature (similar to 900-1000 degrees C) using microwaves when compared to conventional sintering which promoted the porcelains ability to absorb them.W. Lerdprom acknowledges Imperial College London funding no. MMRE_PG54200. A. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporacion contract (IJCI-2014-49839).Lerdprom, W.; Zapata-Solvas, E.; Jayaseelan, DD.; Borrell Tomás, MA.; Salvador Moya, MD.; Lee, WE. (2017). Impact of microwave processing on porcelain microstructure. Ceramics International. 43(16):13765-13771. https://doi.org/10.1016/j.ceramint.2017.07.090S1376513771431

Alumina-zirconia coatings obtained by suspension plasma spraying from highly concentrated aqueous suspensions

[EN] Suspension plasma spraying (SPS) deposition represents an innovative technique to produce coatings that exhib- it improved properties. However, the key to obtain coatings with superior functional properties relies on the in- vestigation of the suspensions as starting materials. For this reason, the present work deals with the suspension preparation for SPS process and its influence on the resulting coatings. Laboratory-prepared 60/40 wt% alumina-zirconia suspensions were concentrated to avoid energy loss and were then successfully deposited by SPS technique. The liquid used was water instead of ethanol due to economical, environmental and safety reasons. The preparation of the suspension plays an important role in SPS process since stable and well-dispersed water suspensions are difficult to obtain. For this reason, colloidal behaviour characterisation of the starting particles as well as rheological optimisation of the feedstock suspensions was ad- dressed in this research. Suspensions with different solid loadings (up to 30 vol.% or 72 wt%) were deposited using several spraying dis- tances. All coatings displayed a bimodal microstructure consisting in partially melted zones surrounded by a fully melted matrix. α-Al2O3 and t′-ZrO2 constituted the main crystalline phases, but differences in the microstructure and properties of the coatings were observed. From these results, some relations between starting suspension and spraying parameters with coating characteristics were found. Thus the optimal spraying distance becomes shorter when the suspension solid loading increases.This work has been supported by the Spanish Ministry of Economy and Competitiveness, MINECO (project MAT2015-67586-C3-R). M.D. Salvador thanks CAPES – Programa Ciências sem Fronteiras (Brazil) for the concession of a PVE project N° A086/2013. A. Borrell acknowledges the MINECO for her Juan de la Cierva-Incorporación contract (IJCI-2014- 19839) and the Program to Support Research and Development (PAID00-15) of the Universitat Politècnica de València.Carpio-Cobo, P.; Salvador Moya, MD.; Borrell Tomás, MA.; Sanchez Vilches, E.; Moreno, R. (2016). Alumina-zirconia coatings obtained by suspension plasma spraying from highly concentrated aqueous suspensions. Surface and Coatings Technology. 307:713-719. https://doi.org/10.1016/j.surfcoat.2016.09.060S71371930

Molten salt attack on multilayer and funcionally-graded YSZ coating

[EN] Thermal barrier coatings have been extensively studied in the last years in order to increase the operational temperature of the current gas turbines as well as to improve the coating lifetime. Many coating characteristics must be met to achieve these requirements (low thermal conductivity, high thermal fatigue resistance...); therefore, complex systems have been engineered for these purposes. One of the possibilities to optimise the different properties deals with the design of multilayer or functionally-graded coatings where various types of microstructures with different characteristics are combined. One of the most important cause of gas turbines degradation relates to the attack of different type of particles which are suspended in the atmosphere (sand, fly ash...). These solid particles are molten at the operational temperatures and then, the molten salts chemically react with the coating. For this reason, the present research was focused on this type of attack. In the present work, the molten salt attack of various YSZ coatings with multilayer and functionally-graded design was addressed. Two different type of microstructures were specifically combined for this design: the APS coating microstructure obtained from conventional (microstructured) powder and a bimodal structure with nanozones obtained from nanostructured feedstock. Besides, different salts were used to simulate different attack environments (desert sand and volcanic fly ash). Findings show that nanozones act as barrier against the penetration of molten salts toward deeper layer. However, a layer formed by nanozones can detach when the salt attack is too aggressive. Hence, functionally-graded coatings, where two types of microstructures are combined through the whole coating, become ideal to diminish the molten salt attack.This work has been supported by the Spanish Ministry of Economy and Competitiveness (project MAT2015-67586-C3-R) as well as A. Borrell and L. Navarro thanks for their post-doc (RyC-2016-20915) and pre-doc (BES-2016-077792) contracts respectively. P. Carpio acknowledges the Valencia Government for his post-doc contract (APOSTD/2016/040).Carpio-Cobo, P.; Salvador Moya, MD.; Borrell Tomás, MA.; Navarro-López, L.; Sánchez, E. (2018). Molten salt attack on multilayer and funcionally-graded YSZ coating. Ceramics International. 44(11):12634-12641. https://doi.org/10.1016/j.ceramint.2018.04.062S1263412641441

Microwave Sintering of zirconia materials: Mechanical and microstructural properties

Commercially, 3mol% Y2O3-stabilized tetragonal zirconia (7090nm) compacts were fabricated using a conventional and a nonconventional sintering technique; microwave heating in a resonant mono-mode cavity at 2.45GHz, at temperatures in the 11001400 degrees C range. A considerable difference in the densification behavior between conventional (CS) and microwave (MW) sintered materials was observed. The MW materials attain a full density of 99.9% of the theoretical density (t.d.) at 1400 degrees C/10min, whereas the CS reach only 98.0% t.d. at the same temperature and 1h of dwelling time. Therefore, the MW materials exhibit superior Vickers hardness values (16.0GPa) when compared with CS (13.4GPa).This work has been carried out under program to support research and development of the Polytechnic University of Valencia (U.P.V) under multidisciplinary projects, PAID-05-09 and PAID-05-10. A. Borrell acknowledges the Spanish Ministry of Science and Innovation for her FPI Ph.D. grant and the people from Institute Technological of Materials (ITM) of the U.P.V for helping us with the microwave experiments during a stay in 2010-2011. Felipe L. Penaranda-Foix thanks the Generalitat Valenciana for the grant in the frame of the Program BEST/2010 because some results of this paper have been possible with this help.Borrell Tomás, MA.; Salvador Moya, MD.; Penaranda-Foix, FL.; Catalá Civera, JM. (2012). Microwave Sintering of zirconia materials: Mechanical and microstructural properties. International Journal of Applied Ceramic Technology. 10(2):313-320. https://doi.org/10.1111/j.1744-7402.2011.02741.xS313320102Deville, S., Gremillard, L., Chevalier, J., & Fantozzi, G. (2005). A critical comparison of methods for the determination of the aging sensitivity in biomedical grade yttria-stabilized zirconia. 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