M. Lungu SCTHPB - PN-III-P1-1.1-PD-2019-0745

Project Proposed Milestones

Phase I 2020 (4 months): Synthesis of hydrogen permeation barriers

Synthesis of metallic layers: Different types of coatings as single and multilayer configuration from pure W and Be metals will be synthesized by means of TVA and CMSII methods;

Synthesis of oxides: Different type of oxides as: Al2O3, Cr2O3, Er2O3, SiO2 will be synthesized by means of TVA, AP-Plasma jet and CMSII methods;

Synthesis of reinforced metal matrix composites: Metallic (W, Be) reinforced configurations with oxides (Al2O3, Cr2O3, Er2O3, SiO2) will be manufactured by means of TVA, AP-Plasma jet and CMSII methods;

Surface preparation of substrates: Different type of substrates such as austenitic steels, vanadium alloys, zirconium alloys, aluminium alloys will be prepared for better adherence in order to succeed the deposition of film coatings;

Phase II 2021 (12 months): Microstructural, morphological, chemical and mechanical investigations

Morphological studies: The potential to develop state of the art HPB materials at different thicknesses and having high purity will impose different studies on the synthesized samples.

Structural, volumetric studies: This will impose the use of non-destructive and destructive methods for conducting multi-scale structural investigations. This objective is to ensure a high purity and dense, artefact free coatings in order to conduct physical testing on proper samples and to remove the artefact impact on the permeability properties.

Phase III 2022 (8 months) – Permeability, thermal conductivity, hardness testing on HPB deposited layers

Thermal cycling exposures: The adhesion to the substrate of the synthetized oxides, metallic reinforced matrix composites and metallic layers will be analysed after thermal cycling stress exposure.

Permeability properties testing: The permeability of the synthetized oxides, metallic reinforced matrix composites and metallic layers will be measured and expressed regarding the layer configuration, structure results and thermal stress testing.

Summary of main findings

Synthesis of hydrogen permeation barriers:

Metallic layers (W, Be) reinforced with oxides (Al2O3, Cr2O3, Er2O3 and SiO2) were deposited applying different techniques as follows: TVA for W / (Al, SS), Be (Al, SS), W:Be / (Al, SS); CMSII for W(Al, SS, V, Zr); AP-plasma for W/(Al, SS), Cr2O3 / (Al, SS), Er2O3 / (Al, SS), Al2O3 / (Al, SS), Al2O3+TiO2 / (Al, SS); HiPIMS: (W,Be) – (SiO2, Cr2O3, Al2O3, Er2O3)/(Al, SS); Additionally, due to high delamination of samples deposited by HiPIMS method, and as a complementary method, the deposited configurations were repeated using DC and RF magnetron sputtering technique that produced stabilized, and more adherent to substrate samples.

Morphological and compositional characterization by SEM, EDX, GDOES, XPS and XRF methods:

AFM, here applied as complementary method to SEM, determined that roughness measurements in Al2O3 metallic-oxides is increased to an extent that could favor gaseous trapping, while co-depositions with Be seem to promote an increased roughness and defects formation probability compared to W co-depositions. Also, distinctive topology variations were observed for film configurations including Be while the other configurations presented a smoothness (below 30 nm) that could be an indication of film imitating the substrate roughness during the deposition process;

SEM pointed out the morphology differences such as deposition defects expressed as thin flakes detached layers or grains with random orientation, randomized nucleation with the growth of cones and grains, smooth surfaces without any definite shape or sizes, formation of isolated grains, high roughness with visible defects illustrated as cavities;

For EDX measurements applicable on proposed samples, we mention that no elemental conglomeration could be observed during mapping measurements;

XPS characterized the co-deposited films as a mixture of oxidized and metallic states of the constituent elements. Forth mentioning is that for the Al-based configurations, the Be presence determined the occurrence of metallic aluminum. Erbium oxide in both stable cubic phase and metastable monoclinic phase, respectively, were observed in pure and with W addition configurations; for pure Al2O3, a metastable κ-Al2O3 crystalline phase was observed, while the addition of W breaks the stability of κ-Al2O3, without significant influence on the structure;

XRF method was applied as a quick overview alternative method to EDX measurements, thus validating the deposition procedures, while some Fe contamination could be observed on studied samples, (i.e., magnetron sputtering facility), which imposed the repetition of several configuration;

GDOES method was applied for layer thickness validation and was generally applicable for CMSII deposited samples, while thickness validation of other samples was assured via SEM cross-section and XRF (Fundamental parameter assisted) methods. All thickness validation methods were highly important to further understand the layer behavior during mechanical, thermal and permeation test.

Volumetric (XCT), structural (XRD) and desorption (TDS); Mechanical studies by micro-indentation technique (Vickers method):

Volumetric XCT measurements were addressed in XCL measuring configuration and applied as non-destructive structural analysis technique, here as an alternative to the limited to surface SEM technique. With a resolution near to micron range, this method preliminary pointed out defective and high porous single and co-deposition layers observed mainly for the AP-plasma and CMSII deposition methods;

XRD: Most importantly, erbium oxide in both stable cubic phase and metastable monoclinic phase, respectively, were observed in pure and with W addition configurations; for pure Al2O3, a metastable κ-Al2O3 crystalline phase was observed, while the addition of W breaks the stability of κ-Al2O3, without significant influence on the structure;

TDS: here the desorption spectra of H2O (18), N2 (28), O2 (32), and CO2 (44) were investigated. Modifications regarding the desorption mechanism were visible between oxide standards and oxide-metal configurations, while the desorption of O2 is mitigated and the bound of N2 peak is increased in the presence of W in the configuration.

Permeability, thermal conductivity, hardness testing on HPB deposited layers:

Permeation measurements were conducted on the most compact, dense samples and without visible defects. For reference, the SS substrates were studied. From the experimental point of view, the samples acted as a membrane between two cavities at different pressure conditions, 1uBar up to 1 Bar, respectively. Therefore, the permeation measurement of H2 were held at the Jožef Stefan – JSI, under the supervision of Dr. V. Nemanic on W, Be and Al2O3 samples deposited by TVA and DF/RF magnetron sputtering, respectively. The applied laborious method was the “pressure-rise” or “static permeation” method. The W and Al2O3 depositions were found to be most promising having a higher permeation reduction factor in comparison to Be sample;

Some of the hardness testing results were observed as fallows: Lower elastic modulus on metal-oxide co-depositions was observed, while the indentation hardness increased for Be and decreased for W matrix configurations. Significantly better adhesion behavior was observed for pure configurations of oxides, while co-depositions were highly sensitive to premature delamination;

Thermal conductivity was studied using the thermal diffusivity method, conducted at Politehnica University – Faculity of Material Science. Thus, the rate of heat transfer for metallic oxides co-depositions and comparing them to reference sample (non-deposited sample) was done. Measurements produces no notable variations between samples and references, while a partially explanation relies on the fact that the deposited layer thicknesses were within two orders of magnitude thinner in comparation to the substrate, thus failing to influence the heat transfer rate and thermal conductivity, respectively.

Conferences

M. Lungu et. al., “Synthesis and morphology characterization of Hydrogen Permeation Barriers (HPBs) candidates applicable as a safety measure for future fusion reactors”, 18th International Conference on Plasma-Facing Materials and Components for Fusion Applications (17th - 21st ) May 2021, virtual conference, poster;

M. Lungu et. al., “RF Magnetron Sputtering Co-deposition and Characterization of Hydrogen Permeation Barrier Oxides in Tungsten & Beryllium Metallic Reinforced Matrix Composites”, 19th International Conference on Plasma Physics and Applications, August 31 – September 3, Magurele, Romania, poster;

M. Lungu et. al., “Microstructural and Microchemical Evaluation of Hydrogen Permeation Barriers-like Candidates Deposited with Thermionic Vacuum Arc and RF Magnetron Sputtering”, European Materials Research Society (EMRS), Fall Meeting 20th-23rd September 2021, virtual conference, poster.

M. Lungu et. al., “Surface, structural and mechanical property changes of Oxides in Tungsten & Beryllium Metallic Reinforced Matrix Composites”, 20th International Balkan Workshop on Applied Physics and Materials Science, Constanta, Romania 12-15 July 2022, poster.

Funded published papers

M. Lungu, C. Staicu, F. Baiasu, A. Marin, B. Butoi, D. Cristea, O. G. Pompilian, C. Locovei and C. Porosnicu, „Deposition, morphological and mechanical evaluation of W and Be - Al2O3 and Er2O3 as mixed films in comparison with pure oxides”, Coatings 2021, 11, 1430, https://doi.org/10.3390/coatings11111430, IF = 2.881;

V. Malinovschi, A. Marin, C. Ducu, V. Andrei, E. Coaca, V. Craciun, M. Lungu, „Influence of sodium aluminate concentration and process duration on microstructure, mechanical and electrochemical behavior of PEO coatings formed on CP-Ti”, Surface and Coatings Technology, Vol. 418, 25 July 2021, 127240, https://doi.org/10.1016/j.surfcoat.2021.127240, IF = 4.158.

V. Malinovschi, A.H. Marin, C. Ducu, S. Moga, V. Andrei, E. Coaca, V. Craciun, M. Lungu, P.C. Lungu, Improvement of Mechanical and Corrosion Properties of Commercially Pure Titanium Using Alumina PEO Coatings, COATINGS, Volume12, Issue1, Article Number29, DOI10.3390/coatings12010029, IF = 2.881;

M. Lungu, D. Cristea, F. Baiasu, C. Staicu, A. Marin, O.G. Pompilian, B. Butoi, C. Locovei, C. Porosnicu, Surface, Structural, and Mechanical Properties Enhancement of Cr2O3 and SiO2 Co-Deposited Coatings with W or Be. Nanomaterials 2022, 12, 2870. https://doi.org/10.3390/nano12162870;