Mechanical Behavior Monitored by Acoustic Emission of Nanostructured Alumina-Titania Coatings

[EN] This study aims to evaluate the mechanical behavior of nanostructured and conventional alumina-titania coatings by means of combining four-point bend tests monitored with acoustic emission. Determination of bending strength, along with information received from acoustic emission signal, such as quantity, amplitude, energy and length of events gives a better understanding of failure mechanisms in coatings. This information has been complemented with optical analysis of fracture surfaces. Failure of coatings has been observed to follow four stages that are clearly defined in the acoustic emission data. This fracture behavior has been observed for all three types of coating tested, but the nanostructured coating presented the best combination of hardness and strength, due to its duplex microstructure.Klyatskina, E.; Segovia-López, F.; Salvador Moya, MD.; Sanchez, E.; Stolyarov, V. (2022). Mechanical Behavior Monitored by Acoustic Emission of Nanostructured Alumina-Titania Coatings. Journal of Machinery Manufacture and Reliability. 51(5):441-446. https://doi.org/10.3103/S105261882205006544144651

A study of the influence of TiO2 addition in Al2O3 coatings sprayed by suspension plasma spray

In this work, five different concentrations of a mixture of TiO2/Al2O3 nanopowders in an alcoholic suspension at 10wt.% solid content were sprayed by Suspension Plasma Spraying on steel discs. The influence of the presence of TiO2 at 0, 13, 40 and 75wt.% in Al2O3 was analysed by studying the properties of the sprayed coatings. Microscopy analysis of the projected coatings revealed a homogeneously distributed microstructure, where the densification of the coating increases with TiO2 content, while the original nanostructure is maintained. A nanoindentation study revealed an increment of nanohardness and elastic modulus due to the densifying effect of TiO2. The addition of significant amounts of TiO2 has been revealed as necessary in order to favour the fusion of Al2O3 in the SPS process

Structure Features and Properties of Graphene/Al2O3 Composite

[EN] Since its discovery, graphene has attracted worldwide attention in the scientific community owing to its unique combination of properties. Thus, graphene is an ideal second phase to improve the structure and properties of metal, ceramic and polymer composite materials. This work presents a comparative study of two types of alumina-graphene composites fabricated with two sizes of delta-Al2O3 powders, nanometer and submicrometer, reinforced by graphene nanoplatelets (GNPs) and consolidated with the spark plasma sintering technique. The microstructure, mechanical and tribological properties of Al2O3-GNPs composites are influenced by the grain size of the ceramic matrix. Hardness values improve notably. The maximum value reached was 27.4 GPa for a composite fabricated with nanometric alumina powders, which is about 27 % higher than that of the Al2O3 monolithic material. Also, the methodology of powder mixing has a fundamental importance in obtaining materials with high-level properties.This work has been supported by the Competitiveness Program National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Russian Ministry of Education and Science No. 02. A 03.21.0005; the Russian Science Foundation No16 - 19 - 10213; the Spanish Ministry of Economy and Competitiveness project MAT2015 - 67586-C3-R. E. Klyatskina acknowledges the Valencian Government for her Post-Doc. Contract APOSTD/2014/046 and A. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her contract RYC2016 - 20915.Klyatskina, E.; Borrell Tomás, MA.; Grigoriev, E.; Zholnin, A.; Salvador Moya, MD.; Stolyarov, V. (2018). Structure Features and Properties of Graphene/Al2O3 Composite. Journal of Ceramic Science and Technology. 9(3):215-223. https://doi.org/10.4416/JCST2018-00006S2152239

The Effect of Ti/Ta Ratio and Processing Routes on the Hardness and Elastic Modulus of Porous TiNbZrTa Alloys

TiNbZrTa alloys are promising for multidisciplinary applications, such as refractory and biomedical purposes, due to their high thermal stability and non-toxicity. Hardness and elastic modulus are among the key features for their adequate industrial applications. The influence of porosity and Ti/Ta ratio were investigated on TiNbZrTa alloys produced by three different processing routes, i.e., (i) blend element and posterior press and sintering (BE + P&S); (ii) mechanical alloying with press and sintering (MA + P&S); and (iii) arc melting and casting. Porosity decreased in the following order: casting < MA + P&S < BE + P&S. The total porosity of alloys increased with increasing Ta contents, i.e., by lowering the Ti/Ta ratio. However, the Ti/Ta ratio did not considerably affect the bonding energy or the elastic modulus. Hardness was increased significantly in dense alloys compared to porous ones. However, porosity and Ti/Ta ratio did not show a clear trend in hardness among the porous alloys

Sliding Wear Behavior of Al2O3-TiO2 Coatings Fabricated by the Suspension Plasma Spraying Technique

[EN] The friction and dry sliding wear behavior of alumina and alumina-titania near-nanometric coatings were examined. Coatings were obtained by the suspension plasma spraying technique. Dry sliding wear tests were performed on a ball-on-disk tribometer, with an Al2O3 ball as counterpart material, a normal load of 2 N, a sliding distance of 1200 m and a sliding speed of 0.1 m/s. The effect of including TiO2 in the fabricated coatings on friction coefficient behavior, wear rates and wear damage patterns was determined. The addition of TiO2 to the coatings was found to greatly increase wear resistance by, for example, 2.6-fold for 40 wt% of TiO2. The analysis of the wear surface was correlated with microstructural parameters, mechanical properties and wear rates.The authors wish to thank for the Spanish Ministry of Economy and Competitiveness (MAT2012-38364-C03) and the Autonomous Government of Valencia for funding for the stay in SPCTS-UMR CNRS (France), and the French FCENANOSURF consortium funded by the French Ministry and Industry and local governments of Region Centre and Region Limousin.Klyatskina, E.; Espinosa Fernández, L.; Darut, G.; Segovia López, EF.; Salvador Moya, MD.; Montavon, G.; Agorges, H. (2015). Sliding Wear Behavior of Al2O3-TiO2 Coatings Fabricated by the Suspension Plasma Spraying Technique. Tribology Letters. 59(1):1-9. https://doi.org/10.1007/s11249-015-0530-5S19591Pawlowski, L.: The Science and Engineering of Thermal Spray Coatings. Wiley: Hoboken (2008)Lampe, Th, Eisenberg, S., Cabeo, E.R.: Plasma surface engineering in the automotive industry—trends and future prospective. Surf. Coat. 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Phase stability and stress evolution of nano-multilayered coatings upon thermal treatment

This contribution addresses recent advances in the experimental investigation of the phase stability, microstructural integrity and stress evolution of metal/metal (Cu/W) [1] and metal/ceramic (Ag/AlN, Ag60wt.%Cu40at.%/AlN, AgGe10at% /AlN) NML coatings during heating by advanced in-situ diffraction methods in combination with XPS, SEM and TEM analysis