B4C-TiB2 composites with a 75/25 volume ratio were fabricated through pressureless sintering with and without gas pressure in the final stage of densification, using a new prototypal furnace. The densification was improved by high-energy milling, which introduced WC impurities that served as a sintering aid and resulted in the size reduction of the starting ceramic powders. For comparison, a B4C-TiB2 composite of the same composition and powder treatment was sintered using hot pressing. The gas pressure sintered ceramic showed better strength, stiffness, and toughness than the hot-pressed composite when densified at 2050 °C, but lower hardness. Depth of Penetration tests on discs with thicknesses of 3, 4 and 5 mm and 50 mm of diameter showed that the gas pressure sintered material outperformed the hot-pressed material, and the results were confirmed through statistical analysis. The study also showed that hardness does not determine the best ballistic performance.

A contract has been stipulated for technical/scientific consultancy and technology transfer activities (ISSMC Contract N. CO-2022-01 protocol 117/2022 of 31/01/2022) between the National Research Council - Institute of Science, Technology and Sustainability for Ceramics (CNR-ISSMC former ISTEC) and Industrie Bitossi S.p.A. for the industrialization of a series of ceramic materials based on B4C-TiB2 developed by ISSMC researchers. The ISSMC know-how on materials and on the process developed, is the subject of a patent application for industrial invention in the filing phase.

TiB2 is a promising material for several fields including impact-resistant armor, wearresistant coatings, cutting tools and crucibles given its physical, mechanical and chemical properties, especially due to the combination of high hardness and exceptional wear resistance. It is however very difficult to sinter below 2000 C, even under mechanical pressure; moreover, the low fracture toughness limits the applicability of the ceramic material. By using sintering additives, it is possible to improve the sintering process and increase the mechanical properties since the additives react with oxidized layers and form secondary phases. In this study, different preparation methods and various combinations of additives (B4C, Si3N4 and MoSi2) via hot pressing sintering have been explored. Through the synergy between optimized process and tailored composition, an almost fully dense material was obtained at 1700 C with hardness of 24.4 0.2 GPa and fracture toughness of 5.4 0.2 MPam1/2. However, the highest hardness (24.5 0.2 GPa) and density values were obtained for only the high-energy-milled sample with WC-Co media, featuring a core-shell grain structure. Finally, optical properties for selected samples were measured, identifying the high-energy-milled TiB2 as the sample with the highest spectral selectivity /" and solar absorptance.

Spark plasma sintering (SPS) is an advanced sintering technique using electric current, mechanical pressure in an atmosphere/vacuum apparatus for densification of traditional or advanced materials in one step. Raw powders or mixtures, regard-less of whether they are electrical insulating or conducting, are placed in a predesigned die before sintering. The SPS system applies uniaxial pressure and electric current to consolidate loose powders or a cold-formed compact with the desired shape. This special machine allows a homogeneous volume heating by means of the Joule effect, with high heating rates, 10-100 times higher than conventional systems, minimizing the grain growth. A wide range of material types can be consolidated, including metals, alloys and intermetallics and ceramics such as borides, carbides, nitrides, silicides and oxides, plus all imaginable composites and special material systems. SPS is the best densification technique for nanocomposites or composites containing nanoparticles and nanophases (graphene, CNT, etc.) due to lower temperature and shorter sintering times. Amongst the others, functionally graded materials and high entropy alloys are successfully fabricated with a minimum heat waste compared to other sintering techniques.

This work explores the fine microstructural features of BC-TiB composites and suggests an overall microstructure evolution from powder processing to sintering. In addition, small-scale grain structures are correlated to local properties measured by nanoindentation, thus providing trends in mechanical behavior. Dense ceramics were typified by development of a core/shell structure of the boride grains, with the shell comprising a (Ti,W)B solid solution with different assemblage and variable amount of W guest cation depending on the processing route. TEM analyses revealed chemical and morphological differences that were associated to the presumed densification mechanisms. Nanoindentation was used to extract the overall and single phase properties of TiB core, shell and BC phase highlighting for the first time hardness and modulus variation as a function of the lattice perturbation, i.e. of nominally pure core boride and shells region. This work provides new experimental findings fundamental for the development and synthesis of high-performance structural materials starting from a small-length scale perspective.

Oxyacetylene torch testing was performed at a range of angles of attack on C/ZrB-SiC-YO composites, from 10° to 90°. The ablation behaviour was studied in-situ with thermography, and the post-ablation morphologies investigated optically and with elemental analysis. Significantly lower surface temperatures were observed at oblique angles of attack leading to less damage in terms of both oxidation extent and material removal. Rudimentary modelling of a gas stream impinging on a perfect surface showed that the angular variation also led to a significant drop in pressure at more oblique angles of attack, with a commensurate increase in shear stress. The surface oxide formed during testing seemed mainly to correspond to the temperature distribution and was apparently more susceptible to damage from higher impinging pressure than shear stress. This study elucidated some interesting aspects of a modified ablation test and showed some new parameter ranges which may be useful in targeted material screening.

Il documento contiene l'attività relativa alla prima produzione dei materiali e prime caratterizzazioni, ovvero "Attività 3.2": requisiti, sintesi/densificazione/prime caratterizzazioni dei materiali individuati. Sono stati scelti tre diversi materiali UHTC come candidati per plasma-facing materials (PFM) nel divertore, in accordo con CNR-ISTP (partner di progetto della Linea 2), e ottimizzato i parametri di processo al fine di ottenere una piena densificazione per ognuna delle tre composizioni scelte. L'attività sperimentale, sviluppo del processo e caratterizzazione microstrutturale, è stata condotta interamente al CNR-ISTEC ed era prevista come task 1.2 della linea 3 (Milestone 3.2) del Joint Research Agreement Eni-CNR.

Il CNR-ISTEC assiste le Industrie Bitossi nell'attività del contratto di consulenza tecnico/scientifica N. CO-2019/06. In questo rapporto tecnico viene descritta l'attività di sinterizzazione senza pressione (PLS) con riscaldamento veloce ad induzione e con riscaldamento lento a resistore di grafite di campioni di allumina-carburo di boro (Al2O3-B4C) sinterizzati presso il CNR-ISTEC.

Obiettivo del secondo anno di attività è quella di produrre piastrine di piccole dimensioni (WP5) per effettuare i test balistici preliminari (WP6) a cui farà seguito la selezione delle composizioni migliori per produrre in fine il materiale finale con dimensioni maggiori per i test balistici finali presso il poligono di tiro, WP7 e WP8. Alla luce dei risultati ottenuti nel WP4, i materiali prodotti mediante la tecnica della sinterizzazione in pressione di gas (materiali indicati come materiali ottenuti eseguendo una pressatura isostatica a 4000 bar, RT-2019/05) hanno ottimi valori di proprietà meccaniche paragonabili ai materiali ottenuti mediante pressatura a caldo. Le attività della seconda fase del secondo anno del progetto sono state articolate in 4 parti (detti anche work packages) di seguito elencati: WP5: Produzione piastrine WP6: Test balistici preliminari WP7: Produzioni di piastrelle per test balistici finali WP8: Test balistici presso poligono di tiro AD

B4C is a lightweight ceramic with a unique combination of physical and mechanical properties but is very difficult to densify, also under pressure, below 2000 °C. We used TiB2 as secondary phase to achieve a conductivity that enables the electro-discharge machining and to improve the fracture toughness and strength, maintaining high hardness and low weight. In this work we explored the densification of bulk B4C/TiB2 ceramics with different sintering techniques: hot pressing and pressureless sintering. Detailed SEM and TEM studies evidenced microstructure and properties differences. Mechanical properties such as Vickers hardness, elastic modulus, flexural strength and fracture toughness are here compared. For the first time, we will show a fibre-reinforced B4C material, designed to improve the damage tolerance of this brittle ceramic. The combination of high hardness and high toughness could give boost a new technological sector in the armour ballistic field.

Il CNR-ISTEC assiste le Industrie Bitossi nell'attività del contratto di consulenza tecnico/scientifica N. CO-2019/06. In questo rapporto tecnico viene descritta l'attività di sinterizzazione, lucidatura, trattamenti termici post sinterizzazione, caratterizzazione microstrutturale e meccanica di campioni di allumina-carburo di boro (Al2O3-B4C) sinterizzati presso il CNR-ISTEC mediante pressatura a caldo (HP). Tale attività, basata in parte sulla precedente esperienza raccolta all'interno dei RT-2020/12, RT-2020/17 e RT-2020/74, è focalizzata sullo studio del ciclo termico da adottare durante la sinterizzazione per materiali a base di Al2O3-B4C con percentuali di B4C che variano dal 5 al 15 v%. In seguito a questo studio è stata condotta un'analisi sull'evoluzione della microstruttura e sulle proprietà di durezza e tenacità dei materiali. Le attività principali richieste dal committente prevedono: o Preparazione di miscele Al2O3-B4C con composizioni 5v%, 10v% e 15v% di B4C. Per questi materiali è stato deciso di utilizzare l'allumina commerciale fornita da Industrie Bitossi (DIPXL0025.19). o Sinterizzazione mediante pressatura a caldo (HP) delle miscele precedentemente descritte in modo da osservare gli effetti del B4C sui parametri della sinterizzazione (temperatura, pressione, tempo di permanenza). o Effettuare l' analisi microstrutturale attraverso il microscopio elettronico a scansione (FE-SEM) per osservare la dimensione dei grani di allumina e osservare la presenza di eventuali fasi secondarie (EDS e analisi XRD) nei campioni sinterizzati. o Effettuare test di durezza e tenacità con il metodo dell'indentazione. Questi test serviranno come linea guida alle Industrie Bitossi per poter mettere a punto un ciclo di sinterizzazione nel loro forno ad induzione per ottenere materiali ceramici per uso balistico più leggeri e più performanti della convenzionale allumina.

Flash Spark Plasma Sintering (FSPS) was used to rapidly sinter pure titanium diboride (TiB2). A pre-sintered sample (Ø= 20 mm with relative density 60%) was discharged under a current of 2-2.5 kA flowing entirely across the sample. The samples were locally densified up to 98% of relative density in a very short time of 20 seconds. The rapid heating (?6000 °C/min) prevented the complete evaporation of B2O3, leading to the formation of rarely seen segregation of boron at the grain boundaries. Compared to SPS or hot press, the rapid FSPS processing promoted the formation boron rich grain boundaries during sintering, thus enhancing consolidation. The FSPS approach might be suitable to consolidate other refractory borides.

This work explores the fine microstructural features of B4C-TiB2 composites and suggests an overall microstructure evolution from powder processing to sintering. In addition, small-scale grain structures are correlated to local properties measured by nanoindentation, thus providing trends in mechanical behavior. Dense ceramics were typified by development of a core/shell structure of the boride grains, with the shell comprising a (Ti,W)B2 solid solution with different assemblage and variable amount of W guest cation depending on the processing route. TEM analyses revealed chemical and morphological differences that were associated to the presumed densification mechanisms. Nanoindentation was used to extract the overall and single phase properties of TiB2 core, shell and B4C phase highlighting for the first time hardness and modulus variation as a function of the lattice perturbation, i.e. of nominally pure core boride and shells region.ì This work provides new experimental findings fundamental for the development and synthesis of high-performance structural materials starting from a small-length scale perspective.

The EU-funded project C3HARME aims at combining the best features of CMCs and UHTCs to design, develop, manufacture and qualify a new class of Ultra-High Temperature Ceramic Matrix Composite (UHTCMCs) with self-healing capabilities. Applications selected to implement the new materials are near-zero erosion nozzles and near-zero ablation thermal protection system (TPS) tiles. This presentation introduces the challenges addressed by C3HARME project including i) the integration between well-established and novel techniques for CMCs and UHTCs production, ii) the need for very high temperature characterization, iii) the meaning of self-healing capability for UHTCMCs, iv) the contribution of modelling to materials development and V) the investigation of the microstructure/thermo-mechanical property correlations. Preliminary results concerning production and testing of prototypes in extreme environments are presented too.