C. Martini

Compatibility tests on steels in molten lead and lead-bismuth

Abstract The compatibility of steels with liquid lead and liquid lead–bismuth is a critical issue for the development of accelerator-driven system (ADS). In this work the results of a set of preliminary tests carried out in stagnant molten lead at 737 K and in lead–bismuth at 573, 673 and 749 K are summarised. The tests were conducted for 700, 1200, 1500 and 5000 h. Three steels were tested: two martensitic steels (mod. F82H and MANET II) and one austenitic steel (AISI 316L). The martensitic steels underwent oxidation phenomena at the higher testing temperature, due to oxygen dissolved in the melts. At a lower test temperature (573 K) and higher exposure time (5000 h) the oxidation rate of the martensitic steel seems to be lower and the developed oxide layer protective against liquid metal corrosion. The austenitic steel, in turn, exhibited an acceptable resistance to corrosion–oxidation under the test conditions.

“Tribological behaviour of multi-layered PVD nitride coatings”

Abstract Multi-layers resulting from the combination of layers of different PVD nitrides (TiN, Ti 2 N, Ti(C,N), (Ti,Al)N) were deposited by arc evaporation on AISI M2 tool steel and their tribological behaviour has been investigated. The effect of a MoS 2 layer deposited on top of the PVD nitride multi-layers was also studied. Dry sliding and abrasive wear behaviour have been studied by a slider-on-cylinder tribometer and a micro-scale abrasion tester, respectively. The main sliding wear mechanism was abrasion from hard particles formed at the contact interface as a consequence of extensive oxidation of the counter-material (hard chromium). The prevalence of abrasion damage in the sliding tests explains the good correlation between the results given by sliding tests at low applied loads and the micro-abrasion tests, and shows that hardness plays a key role in influencing the behaviour of the multi-layers. Milling tests, carried out in order to evaluate the cutting performance of coated tools, showed that end mills coated with the TiN-based multi-layers live longer than the others. The difference of performance was much less marked at the highest cutting speed.

Relationships among crystallographic structure, mechanical properties and tribological behaviour of electroless Ni–P(9%)/B4C films

Abstract The tribological behaviour of electroless Ni–P composite coatings was investigated by dry sliding tests with a slider-on-cylinder tribometer. The tests were carried out in laboratory air at room temperature against a PVD-TiN coated HSS cylinder. Friction and wear data are discussed on the basis of the mechanical properties (microhardness, plasticity parameter, fracture toughness) of the coatings, that were derived by indentation measurements at low loads. The wear depths measured on unreinforced Ni–P were about one order of magnitude larger than those obtained on the corresponding composite coatings. Furthermore, wear depth proved to increase with increasing annealing time, for both pure matrix and composite layers. The wear volume Q was correlated to the mechanical properties using Archard-type equations. For composite coatings the plasticity parameter δ H was inserted into the equation for the estimation of Q , in order to take into the account the action of a B 4 C-rich layer observed on the surface of the worn coatings.

Behaviour of materials for accelerator driven systems in stagnant molten lead

The behaviour of a modified F82H martensitic steel (both uncoated and aluminised) and tungsten was evaluated by immersion tests in stagnant, oxygen-saturated liquid lead at 793 K under an argon atmosphere, for exposure times up to 3700 h. The F82H steel is a candidate structural material for Accelerator Driven Systems (ADS), while tungsten is potentially suitable for a beam window working immersed in liquid lead. Layers of Me3O4 consisting of an inner sublayer with Me=Fe and Cr and an outer chromium-free sublayer of Fe3O4, formed on the surface of the uncoated steel while the aluminised steel showed no significant alteration. On tungsten, a compact and adherent layer of WO3 formed and reacted with liquid lead leading to the formation of friable Pb–W–O ternary compounds. A two-step mechanism is proposed for interactions of metals and alloys exposed to oxygen-saturated molten lead: the first step is the solid phase oxidation of the base metal; the second is the interaction between liquid lead and the oxide layer formed on the metal surface.

Friction and wear behavior of C4Al2O3Al composites under dry sliding conditions

Abstract The wear resistance of MMCs can be improved by increasing the volume fraction of the reinforcing ceramic phase (HRC) by as much as 70%. Among the various types of HRC composites, a new Al 2 O 3 Al co-continuous ceramic/metal composite (referred to as C 4 composite) has been recently produced at The Ohio State University. A new method of preparation, based on a displacement reaction between a silica precursor (whose frame is faithfully reproduced in the composite product) and molten aluminum, allows the production of a MMC where both the Al 2 O 3 and Al phases are continuous and interpenetrating. The aim of the present work was to investigate the tribological behavior of C 4 Al 2 O 3 Al composites under dry sliding conditions using a computer-controlled slider-on-cylinder tribometer. The tests were carried out at applied loads in the range 5–30 N and sliding speeds in the range 0.3–1.8 m/s. for sliding distances up to 10 km. Wear scars and debris were characterized by means of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), with an EDS analyzer and X-ray diffraction (XRD) analysis. Under the adopted testing conditions, the C 4 composites underwent only mild wear, mainly as a consequence of the high load-bearing capacity of the ceramic phase which enhances wear resistance. The high wear resistance is also related to the nature of the third-body, mainly constituted by Fe 2 O 3 , which is produced by the abrasive action carried out by the hard ceramic phase on the counterfacing steel. Under the adopted testing conditions, the transition from mild to severe wear, observed at a critical load in conventional MMCs, was never observed in the C 4 materials. Both the continuity between aluminum and alumina, and the increase in interfacial bonding, played an important role in influencing the wear behavior of the C 4 composites. These aspects led to an improvement of wear resistance of the C 4 composites over conventional MMCs, under the same experimental conditions, and probably shifted the transition from mild to severe wear regimes to higher critical loads.

Preliminary study of micro-scale abrasive wear of a NiTi shape memory alloy

Abstract Nitinol (NiTi), a nearly equiatomic nickel–titanium alloy is known for its unique shape memory and superelastic properties, which result from martensitic transformations. It is the material of choice for numerous biomedical applications such as endovascular stents, vena cava filters, dental files and guidewires for non-invasive surgery, etc. Micro-scale abrasion tests (MSATs) have been performed on the NiTi shape memory alloy, so as to evaluate the influence of different commercial abrasives such as silicon carbide, alumina and glass on the wear behaviour. The aim of the work was the selection of the most effective abrasive for cleaning the inner surface of laser-cut cardiovascular stents. Abrasive particles have been characterised by X-ray diffraction, SEM and EDS before and after MSATs. Worn surfaces have been studied by stylus profilometry, SEM and atomic force microscopy. The effect of abrasive particle hardness, size and angularity on the wear behaviour has been evaluated and discussed.

Unalloyed copper inclusions in ancient bronze artefacts

Ancient bronze artifacts, that represent a considerable part of the archeological finds, have been largely studied because of their complex degradation phenomena taking place in the long time span that have not been fully understood. One of the peculiar features of ancient bronzes is the presence of inclusions of copper unalloyed with tin. Unalloyed Copper Inclusions (UCI) have been observed in buried archaeological bronze artefacts by several authors, but each paper reports only on a limited number of cases. In our extensive studies on bronze artefacts, UCI have been observed in many bronze artefacts with very different features and purposes. Both as-cast and wrought artefacts were studied, so that the influence of the manufacturing process and the composition of the artefacts on the formation of UCI might be evaluated. The microstructure and composition of these artefacts were studied and the features of UCI have been related with those of the surrounding phases. The results have been discussed and compared with those obtained by other authors. The presence of UCI in buried archaeological bronze artefacts could indicate some unusual corrosion processes that might need to be accounted for when designing conservation treatments.

Comparison of different porous sol-gel matrices: template synthesis of polythiophene

Abstract Composite using polythiophene as the conducting polymer and different silica sol–gel as the host matrix were prepared by the template method. The electrochemical performance of the composites has been confirmed using cyclic voltammetry and was compared with the results obtained on polythiophene films synthetised under the same condition directly on ITO substrates. UV–Vis–NIR spectroscopy, scanning electron and atomic force microscopic measurements were done on all the different composites.

Cleaning of 19 th century daguerreotypes by means of atmospheric pressure cold plasma jet

Summary form only given. Daguerreotypes represent the first practical form of photographs, particularly in vogue between 1840 and 1860, before becoming outdated due to the development of alternative and faster techniques. In daguerreotypes, the image results from the distribution of silver/mercury microcrystals of varying size and density on a silver-coated copper sheet. Through years, several 19th century daguerreotypes have suffered several corrosion phenomena, which have greatly reduced their historic and artistic value.

Phase Composition of Oxidised Layers Grown on Steel Exposed to Liquid Lead at 749 K

The corrosion resistance of AISI 316 LN stainless steel was studied in contact with stagnant, oxygen-saturated liquid lead at 749 K for times up to 1200 h. The reaction products were analysed by means of optical and scanning electron microscopy, electron probe microanalysis, X-ray diffraction analysis and Mössbauer spectroscopy. Thin layers of largely variable thickness formed on the surface, mainly consisting of Fe3O4, with small amounts of FeO in the inner regions, Fe2O3 and an Fe-Pb-O ternary product in the outermost regions. The alloying elements Cr and Ni diffused to a different extent into Fe3O4. A mechanism is proposed to explain formation and growth of the reaction products.