Ni Si Research Articles

Effects of Si/B ratio on the isothermal crystallization behavior of FeNiSiBCuNb amorphous alloys

In the present work, (Fe40Ni40SixByCu1)0.97Nb0.03 (Si/B = 1:1, 1:2, and 1:3) alloys were prepared by the as-melt spun method. The effect of different Si/B ratios on the isothermal crystallization behavior of FeNiSiBCuNb glass alloys were investigated. The activation energies of the Si/B = 1:1, 1:2, and 1:3 alloys for nucleation and grain growth were calculated by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model as 123.6 kJ/mol and 207.3 kJ/mol, 151.0 kJ/mol and 251.3 kJ/mol, and 88.6 kJ/mol and 170.0 kJ/mol respectively; hence, crystal nuclei needed to cross a higher energy barrier in the growth process. The variation of local Avrami exponent n(α) with crystallization fraction α demonstrates that the crystallization mechanism was divided into three stages: i: initial crystallization stage with n＞2, indicating that α-Fe(Si) phase or γ-(Fe, Ni)Si phase with a high nucleation rate stage, ii: middle crystallization stage with n≈2, indicating that FeNiB phase with a stable nucleation stage, and iii: the end of crystallization stage with n＜2, indicating that γ-(Fe, Ni)Si and FeNiB phases with a growth stage; The crystallization process was transformed from diffusion-controlled one-dimensional growth to diffusion-controlled three-dimensional growth.

Metallogeny of a base metal sulfide-bearing magnetitite body from the Eretria mine, East Othris massif, Greece: Insights into an ancient seafloor hydrothermal system

Magnetite deposits comprise a very small volume of a serpentinized peridotite body that constitutes the Eretria chrome mine of the East Othris ophiolite in central Greece. Magnetite deposits have been examined to aid determination of their mode of occurrence, mineralogy and origin. Research attention has been focused on an ore body that consists of a ~30 cm-thick pod of semi-massive to massive magnetite (~75%–85% modal) hosted in a serpentinite shear zone. The silicate matrix of magnetitite (~10%–15% modal) is composed of unstrained serpentine, chlorite and subordinate amounts of andradite and actinolite. Base metal sulfides (BMS; ~5%–10% modal) and phosphates are dispersed between the magnetite grains. Variably altered Cr-spinel crystals are poikilitically enclosed within magnetite. The investigated ore samples show great variations in the Cu (890–9530 ppm), Ni (190–3260 ppm), Co (120–2180 ppm) and Zn (20–1240 ppm) contents. The δ18ΟSMOW value for magnetite from a magnetitite sample is −2.2‰.The undeformed nature of the silicate minerals in magnetitite points toward crystal growth from a post-magmatic fluid. The low Ni, Mn, Mg and high Si contents in magnetite suggest that it was not derived from fluids produced concurrent to serpentinization. The presence of phosphates, BMS and hydrosilicates suggest that the ore forming fluids were acidic and halogen-bearing. Our preferred hypothesis for the formation of magnetitite is that mixing of upwelling, metal-rich brines along the dilational segments of the host shear zone caused saturation of the ensuing fluids with Fe, which eventually prompted magnetite precipitation. The T estimates deduced from mineralogy, with an uppermost limit of ~460 °C required, and cessation of mineralization at ~150–100 °C, are consistent with the ambient T present within a cooling oceanic lithospheric slab. In analogy with some modern serpentinite-hosted BMS deposits at rifted settings, the BMS-bearing magnetitite of Eretria may represent part of an ancient seafloor hydrothermal system. Our study provides important insights into the initiation and episodicity of hydrothermal activity in oceanic settings.

Effect of pre-deformation before aging on discontinuous precipitation behaviour in Cu-Ni-Si alloys

ABSTRACT The effect of deformation before aging on discontinuous precipitation in Cu–4.75wt%Ni–1.13wt%Si and Cu–6wt%Ni–1.42wt%Si alloys after solution treatment was investigated. Two kinds of deformation, one under and the other over the uniform deformation limit were implemented after solution treatment. With increasing deformation strain in both alloys, the discontinuous precipitation is accelerated and the aging time for a fully covered region by discontinuous precipitation is shortened. However, the Cu–6wt%Ni–1.42wt%Si alloy deformed under the uniform deformation limits showed an enhanced discontinuous precipitation compared to that for the alloy deformed over the uniform deformation limit. The deformation defects including dislocations and shear bands play the role of encouraging discontinuous precipitation. The shear bands formed during prior deformation beyond the necking point could provide sites for discontinuous precipitation initiation in the early stages of annealing However, shear bands tend to hinder the advance of discontinuous precipitation with further aging in the Cu–Ni–Si alloy with a high content of Ni and Si.

Effect of Si/B ratio on glass-forming ability, phase transitions and magnetic properties in (Fe40Ni40SixByCu1)0.97Nb0.03 alloys

The (Fe40Ni40SixByCu1)0.97Nb0.03 (Si/B = 3:1, 2:1, 1:1, 1:2 and 1:3) alloys were fabricated through the melt-spun technique. The effects of Si/B ratio on the glass-forming ability (GFA), phase transitions and soft magnetic properties were investigated. Results showed that when Si/B = 1:1, 1:2 and 1:3, the GFA of the FeNiSiBCuNb alloy is good, and the amorphous structure is homogeneous. We found a phase transition from the amorphous phase to α-Fe (Si) phase and then to γ-(Fe,Ni)Si phase in Si/B = 1:1 alloy by employing a simple heat treatment process. The alloys with Si/B = 1:1 and 1:2 containing a low coercivity of 0.30 A/m and 0.25 A/m domain structures were characterized with magneto-optical Kerr microscope (MOKE) to unveil that the internal stress relief is beneficial to the magnetization process. The three alloys exhibit different crystallization behaviors, and moderate Si can effectively inhibit γ-(FeNi) grains overgrowth.

Cu–Ni–Si合金板の強度と導電率に及ぼす極低温高速圧延の影響

Cu–Ni–Si合金板の強度と導電率に及ぼす極低温高速圧延の影響

Effect of two-step cryorolling and aging on mechanical and electrical properties of a Cu–Cr–Ni–Si alloy for lead frames applications

Abstract High strength and high electrical conductivity Cu–Cr-based alloys are important candidate materials for preparing lead frames, railway contact wires and connects. However, high strength and high electrical conductivity are mutually exclusive in nature. To optimize the mechanical and electrical properties of a Cu–Cr–Ni–Si alloy, the two-step cryorolling and aging (CRA) was carried out in this study. Here, by the analysis of microstructure evolution, precipitation behavior, and corresponding strengthening mechanisms of the alloy at different rolling and aging conditions, we find that the yield strength and electrical conductivity for the two-step CRA sample are improved by 91.3 MPa and 4.9 %IACS (International Annealed Copper Standard) than those of the sample subjected to single-step room temperature rolling and aging (RTRA). The higher yield strength for the two-step CRA sample is mainly determined by the precipitation strengthening contributed from Ni2Si and Cr precipitates, rather than the twin boundary strengthening and dislocation strengthening. In fact, the dislocation density of the two-step CRA sample is lower than that of the single-step RTRA sample because of the faster drop rate of recovery, which weakens the effect of dislocation strengthening. The combination of the first-step aging and second-step CR process for the two-step CRA sample contributes to the formation of more precipitates from the matrix, thereby significantly increasing the precipitation strengthening and decreasing the impurity scattering in the final aging. The results provide a new preparation process and a reliable theoretical approach for optimizing the mechanical and electrical properties of the Cu–Cr alloys.

Atom probe characterisation of segregation driven Cu and Mn–Ni–Si co-precipitation in neutron irradiated T91 tempered-martensitic steel

The T91 grade and similar 9Cr tempered-martensitic steels (also known as ferritic-martensitic) are leading candidate structural alloys for fast fission nuclear and fusion power reactors. At low temperatures (300–400 °C) neutron irradiation hardens and embrittles these steels, therefore it is important to investigate the origin of this mode of life limiting property degradation. T91 steel specimens were separately neutron irradiated to 2.14 dpa at 327 °C and 8.82 dpa at 377 °C in the Idaho National Laboratory Advanced Test Reactor. Atom probe tomography was used to investigate the segregation driven formation of Mn–Ni–Si-rich (MNSPs) and Cu-rich (CRP) co-precipitates. The precipitates increase in size and, slightly, in volume fraction at the higher irradiation temperature and dose, while their corresponding compositions were very similar, falling near the Si(Mn,Ni) phase field in the Mn–Ni–Si projection of the Fe-based quaternary phase diagram. While the structure of the precipitates has not been characterised, this composition range is distinctly different than that of the typically cited G-phase. The precipitates are composed of CRP with MNSP appendages. Such features are often observed in neutron irradiated reactor pressure vessel (RPV) steels. However, the Si, Ni, Mn, P and Cu solutes concentrations are lower in the T91 than in typical RPV steels. Thus, in T91 precipitation primarily takes place in solute segregated regions of line and loop dislocations. These results are consistent with the model for radiation induced segregation driven precipitation of MNSPs proposed by Ke et al. Cr-rich alpha prime (α’) phase formation was not observed.

Intertube Aggregation-Dependent Convective Heat Transfer in Vertically Aligned Carbon Nanotube Channels

The heat transfer of carbon nanotube fin geometry has received considerable attention. However, the flow typically occurred over or around the pillars of nanotubes due to the greater flow resistance between the tubes. Here, we investigated the forced convective heat transfer of water through the interstitial space of vertically aligned multiwalled carbon nanotubes (VAMWNTs, intertube distance = 69 nm). The water flow provided significantly a greater Reynolds number (Re) and Nusselt number (Nu) than air flow due to the greater density, heat capacity, and thermal conductivity. However, it resulted in surface tension-induced nanotube aggregation after the flow and drying process, generating random voids in the nanotube channel. This increased permeability (1.27 × 10-11 m2) and Re (2.83 × 10-1) but decreased the heat transfer coefficient (h, 9900 W m-2 K-1) and Nu (53.77), demonstrating a trade-off relationship. The h (25,927 W m-2 K-1) and Nu (153.49) could be further increased, at an equivalent permeability or Re, by increasing nanotube areal density from 2.08 × 1010 to 1.04 × 1011 cm-2. The area-normalized thermal resistance of the densified and aggregated VAMWNTs was smaller than those of the Ni foam, Si microchannel, and carbon nanotube fin array, demonstrating excellent heat transfer characteristics.

Primary dendrite arm spacing and preferential orientations of the Ni–Si hypereutectic composites at different solidification rates

A hypereutectic alloy is a metallic alloy which has a composition beyond the eutectic point. As the temperature of a non-eutectic composition is lowered, the liquid mixture will precipitate one component of the mixture before the other. In the present paper, Ni–Si hypereutectic composites at the different solidification rates were prepared by a modified Bridgman directional solidification technique. Primary dendrite arm spacings of the Ni–Si hypereutectic composites were calculated at the different solidification rates according to Kurz–Fisher model, Hunt–Lu model and Trivedi model, respectively. Relation between micro-hardness and primary dendrite arm spacing was obtained. The selected area electron diffraction was adopted to confirm the preferential orientation of Ni–Si hypereutectic composites. It is found that primary dendrite arm spacing of the experimental results are very close to Kurz–Fisher model, while deviating from that predicted from Hunt–Lu model and Trivedi model. Therefore, Kurz–Fisher model is much more suitable to describe primary dendrite arm spacing of Ni–Si hypereutectic.

Superior Pseudocapacitive Storage of a Novel Ni3Si2/NiOOH/Graphene Nanostructure for an All-Solid-State Supercapacitor

HighlightsThree types of Ni3Si2 were successfully fabricated by low-pressure all-solid melting-reconstruction chemical vapor deposition, and the growth pattern changed with the carbon source content.In a carbon-rich atmosphere, high-energy atoms bombard the Ni and Si surface, and reduce the free energy in the solid Ni–Si particles’ thermodynamic equilibrium, considerably catalyzing the growth of Ni–Si nanocrystals.Ni3Si2/NiOOH/graphene provides a large specific area and NiOOH inhibits insulation on the electrode surface in an alkaline solution and accelerates the electron exchange rate.

Effects of heat treatment and Nd: YAG laser repair welding parameters on the microstructure and properties of a Cu–Ni–Si–Cr mold alloy

The novel Cu–Ni–Si–Cr alloy (Cu-6.7Ni-1.6Si-0.3Cr) has good prospects for substitution with toxic Be–Cu alloy. This study used a Nd: YAG laser process with a variety of heat treatment processes and repair welding parameters to investigate the effects of heat treatment and repair welding parameters on the microstructure and properties of the Cu–Ni–Si–Cr mold alloy. To eliminate the disadvantages of the laser welding process for the Cu–Ni–Si–Cr mold alloy, such as high thermal conductivity and high thermal expansion coefficients, many improved approaches have been used, including pre-weld heat treatments (expected to reduce thermal conductivity), control of the laser shape, and preheating (to slow down the cooling rate and avoid excessive expansion and contraction). The results showed that after the pre-weld heat treatment and preheating, deeper penetration and defect-free welds were obtained. However, continuous Ni/Si phase precipitates were observed along the grain boundaries in the welding fusion zone (WFZ), which may have harmful effects on the mechanical properties of the welds. This problem was improved by post-weld heat treatment (PWHT). The repair welds (including WFZ and HAZ) after PWHT showed a good combination of hardness, tensile strength, and thermal properties. The high hardness or tensile strength in the weld was attributed to the formation of a nano-sized Ni/Si phase, which was identified via a transmission electron microscope.

The Nature and Compositional Peculiarities of Volcanogenic Diamonds

Abstract —We have studied volcanogenic diamonds in the context of a discussion of their genesis, including some assumption on their artificial origin. The carbon isotope composition of diamonds collected from the eruption products of Tolbachik volcano (δ13CVPDB from –22 to –29‰) is within the range of the δ13CVPDB values of natural diamonds, including those from kimberlites. The δ15NAir values of the Tolbachik diamonds, measured for the first time (–2.58 and –2.32‰), correspond to δ15NAir of volcanic gases and differ from that of atmospheric nitrogen (δ15NAir = 0‰), which may be expected in synthetic diamonds. In the studied volcanogenic diamonds, as in synthetic ones, the nitrogen impurity is unaggregated. However, such an unaggregated form of nitrogen is specific to many natural diamonds (e.g., variety II diamonds, according to Orlov’s classification). Impurity elements (Cl, F, O, S, Si, Al, Ca, and Na) are locally concentrated in volcanogenic diamonds; they are a constituent of micro- and nanoinclusions in them. The high contents of F and Cl in the studied diamonds are correlated with the composition of volcanic gases; there is no reason to expect a similar correlation in synthetic diamonds. Moreover, the studied cube-octahedral Tolbachik diamonds have a number of accessory forms, some of which are not observed in synthetic diamonds. Their surfaces are frequently covered with films composed of Mg–Fe and Ca–Mg silicates, aluminosilicates, sulfates, metal alloys, and native Al. Mineral inclusions in the studied diamonds are Mn–Ni–Si alloys and silicides varying in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2, Mn5Si2, and pure Mn silicide MnSi. Summing up the obtained data, we conclude that volcanogenic diamonds form in a strongly reducing environment, in which silicides and native metals and their alloys are stable. The predominant cube-octahedral morphology of these diamonds and the unaggregated nitrogen impurity point to their short-term residence under high-temperature conditions. This makes them similar, to some extent, to synthetic diamonds. There are, however, clear differences as well. Volcanogenic diamonds are similar in compositional peculiarities, including isotope compositions, to natural diamonds that form under most unfavorable conditions, such as cuboids, balases, carbonado, and some diamonds of the eclogite paragenesis. They also resemble diamonds found in situ in harzburgite and chromitite of ophiolites. This suggests a specific mechanism of formation of both volcanogenic and ophiolitic diamonds in the oceanic lithosphere.

(Invited) Nickel and Nickel-Platinum Silicide for BiCMOS Devices

Recently, the world’s fastest SiGe-HBT was presented by IHP researchers [1], which applies low ohmic nickel silicide (NiSi). Among other measures, this feature contributed to speed improvements. On the other hand, the integration of low-ohmic NiSi creates the risk for NiSi defects which could result in increased MOSFET leakage currents. The goal of this contribution is to find out from several two-step silicidations of Ni or NiPt layers a suitable process for a BiCMOS technology which enables low silicide RS for high cutoff frequencies of bipolar and MOS transistors without degradation of leakage currents. In result, a 300°C/450°C silicidation is proposed providing RS values of 3 to 4 Ω for both NiSi and NiPtSi. However, only the NiPtSi shows acceptable low leakage currents compared to NiSi. Therefore, NiPt extends the silicide process window for HBTs and MOSFETs.The phase transitions of Ni and NiPt silicides as a function of temperature are shown in Fig. 1, where the temperature range of the targeted NiSi phase is enlarged for NiPt compared to Ni. The investigated two-step NiSi formations are listed in Table 1. The NiPt layers were deposited in an Applied Materials laboratory. First, Ni2Si was formed by furnace anneal, low pressure anneals, or by a NiPt sputtering at 400°C. The Ni rich silicide was converted into NiSi by a second anneal at 450°C.The final Ni(Pt)Si sheet resistance (RS Ni(Pt)Si:1.+2.Ann) was tunable from 1.5 Ω to 10.5 Ω by the temperature and time of the first anneal (Fig. 2). At 300°C, the RS saturates at 3.3 Ω for 20 nm Ni and 1.6 Ω for 40 nm Ni, respectively. This indicates full Ni consumption. The furnace anneals at 200°C and 230°C do not show any RS saturation since Ni is consumed only partially. An RS increase for NiSi and NiPtSi on PSD (p source-drain) compared to NiSi on substrate is observed.One figure of merit of SiGe-HBTs is the maximum oscillation frequency fmax, which depends by the following equation fmax=sqrt(fT/(8πrBcBC)) on the transit frequency fT, the base resistance rB, and the collector-base capacitance cBC. A silicide resistance variation could mainly influence rB. In Fig. 3a, the sheet resistance of the silicided base polysilicon (RS BasePolySilicide) together with fmax of two HBT layouts are plotted for several silicide formations. It exists a correlation between fmax and RS BasePolySilicide, which is shown in Fig. 3b. In general, fmax could be enlarged by a silicide resistance reduction for special HBT layouts.For these low-ohmic and thick Ni(Pt)Si layers, special attention has to be paid to the MOSFET leakage currents, which can be enlarged by lateral silicide pipes towards the conducting channel or by defects along the SD – STI (shallow trench isolation) interface [2]. Another leakage current source are silicide spikes shortening in a perpendicular direction the SD and the well. Three types of P+Nwell and N+Pwell diodes are suitable to determine and distinguish these silicide based yield killers: area diodes to detect spikes, STI separated island diodes to recognize SD-STI defects, and diodes with long poly-gates on SD-well areas to determine pipes at gate edges. In result, the area and island diodes showed no leakage current increase for the studied silicidations, i.e. defects along the SD-STI edge and spikes are not critical here. The leakage currents of gate-edged diodes on N+Pwell and P+Nwell are presented in Fig.4. Both diode types show low leakage currents for the 200°C and 230°C anneals, because the low lateral silicidation at these temperatures reduces the probability for piping. At 300° the N+Pwell leakage current increases slightly up to 2x10-9A, but significantly up to 1x10-7A for the P+Nwell diode. This is a clear indication for pipes at the gate edges [3]. In contrast, almost no enhanced leakage current was observed for the NiPt silicidations with 200° to 300°C anneals. The pipe suppression of the NiPt silicide system might be caused by the Pt agglomeration at the silicide-SD interface [4]. The limits of the NiPt pipe suppression are shown for N+Pwell diodes silicidated with a NiPt deposition at 400°C. Leakage currents of 1x10-8A could indicate NMOS-typical pipes, as described by Yamaguchi [5].In summary, silicide layers with low RS values of 3Ω to 4Ω were formed by two-step annealing of Ni and NiPt at 300°C and 450°C. These silicides support high fmax values of SiGe HBTs. However, only the NiPt silicide process provided acceptable low leakage currents of MOSFET test structures indicating an extended process capability of NiPtSi compared to NiSi. Figure 1

Extrinsic contributions to the dielectric and pyroelectric properties of Pb0.99[(Zr0.52Ti0.48)0.98Nb0.02]O3 thin films on Si and Ni substrates

The character of extrinsic contributions to the dielectric and pyroelectric properties of Pb0.99[(Zr0.52Ti0.48)0.98Nb0.02]O3 (PZT) films on Ni foil and Si wafers was explored using Rayleigh analysis, third harmonic phase angle, and Preisach analysis from 15 K to 296 K. The temperature dependence of the domain structure, domain wall mobility, and domain switching influenced the intrinsic, extrinsic, and secondary contributions to the pyroelectric coefficients. This, in turn, produced markedly different room temperature pyroelectric coefficients of ∼250 μC/m2 K and ∼100 μC/m2 K, respectively, for films on Ni and Si. At room temperature, the dielectric irreversible Rayleigh parameter αray was 15.5 ± 0.1 and 28.4 ± 1.6 cm/kV for PZT on Si and Ni, respectively. The higher αray value for the Ni sample suggests more domain wall motion at room temperature, which was attributed to the lower stiffness on the Ni foil compared to the ∼500 μm thick Si substrate. Below 200 K, αray for the PZT Si sample exceeds that of the Ni/PZT sample. This is believed to arise from differences in the energy landscape of pinning centers for the domain wall motion. It is proposed that the residual stresses not only set the preferred domain structures but also the barrier heights for domain wall motion and domain switching.

Relationship and mechanism between double cold rolling-aging process, microstructure and properties of Cu–Ni–Si alloy prepared by two-phase zone continuous casting

Developing Cu–Ni–Si alloy with high strength and high electrical conductivity is a key issue in the electrical conductor industries. The C70250 copper alloy was prepared by two-phase zone continuous casting (TZCC) technology first, and then carried out by double cold rolling-aging process. The relationship between different double cold rolling-aging processes, microstructure, mechanical properties and electrical conductivity of the alloy was studied in detail, the mechanism was revealed. The results show that the C70250 copper alloy strip fabricated by TZCC technology can be subjected to large deformation double cold rolling-aging treatment. When the alloy is primary cold rolled by 97.5% reduction rate, primary aged at 400 °C for 30 min, second cold rolled by 60% reduction rate, second aged at 400 °C for 45 min, the tensile strength and electrical conductivity of the alloy can reach 879 MPa and 48.9% IACS respectively, owning excellent comprehensive properties. The Ni2Si phases inside C70250 copper alloy after primary aging effectively pin dislocations during the secondary cold rolling process, which forms high density dislocation entanglement, promotes the further precipitation of Ni2Si phase during the process of secondary aging, and finally produces a large number of fine, dispersed, multi-scale mixed and evenly distributed Ni2Si phases, the increase of alloy strength is mainly ascribed to dislocation and Orowan strengthening effect. Solute atoms inside the C70250 copper alloy get adequately precipitated after large deformation double cold rolling-aging treatment, the recrystallization is delayed, and the fibrous microstructure along the rolling direction is produced, the scattering effect of transverse grain boundaries and solute atoms on electrons is significantly reduced, which is helpful to improve the electrical conductivity of the C70250 copper alloy.

Microstructural characterization of cold-worked 316 stainless steel flux thimble tubes irradiated up to 100 dpa in a commercial Pressurized Water Reactor

Two flux thimble tubes (FTTs) made of 15% cold-worked 316 stainless steel (SS) were harvested from Ringhals Pressurized Water Reactor (PWR) Unit 2, with peak damages of 76 and 100 displacements per atom (dpa) after 29 and 34 years’ service, respectively. Specimens sectioned from parent tubes were comprehensively characterized with nominal damage levels of ∼0, ∼41, ∼74, 76, and 100 dpa at a nominal temperature range of 285–323 °C. Both FTTs contained helium and hydrogen gases as transmutation products. The helium follows a production rate of ∼9.8 appm/dpa, while environmental factors complicate hydrogen production obscuring an exact H/dpa ratio. Irradiation-induced dislocation loops, nano-cavities, solute clusters, and microsegregation were all observed. The dislocation loops and nano-cavities indicated saturation at 41 dpa. The solute clusters continued to evolve with Ni–Si clusters formed at 41 dpa, and Ni–Si–Mn–P clusters formed at 74 and 100 dpa, but neither clusters exhibited distinct diffraction patterns at any damage levels. Solute clusters were observed to frequently be co-located with dislocation loops, but fully decorated loops were rarely detected. Significant radiation-induced segregation (RIS) was observed around grain boundaries at all damage levels. The modified inverse Kirkendall (MIK) model captured the RIS behavior of major elements. Large cavities within or around an Mn–S rich region were observed for the first time. Through all the damage levels, void swelling is always below 0.05%, making significant dimensional change unlikely in core internals when used at similar conditions. Meanwhile, the role of overwhelming nanocavities, presumably helium bubbles, should be considered in other potential degradation mechanisms, including irradiation-assisted stress corrosion cracking, embrittlement, and loss of fracture toughness, which remain the concerns for extended operation of nuclear power plants.

Mineralogy and geochemistry of the Berong Ni-Co laterite deposit, Palawan, Philippines

Intense weathering of the serpentinized peridotite resulted in the formation of the Berong Ni-Co laterite deposit in Palawan (Philippines). The studied laterite profiles are divided from base to top into: (i) serpentinized bedrock, (ii) saprolite horizon, and (iii) limonite horizon. Olivine in the peridotite contains a significant amount of Ni (average 0.38 wt% NiO), thus representing the main source of the ore in the laterite horizons. Six types of Ni-bearing serpentines (up to 6.65 wt% NiO) in the saprock are discriminated based on their textures and Raman signatures. Garnierite (a mixture of serpentine-, kerolite- and sepiolite-like clays) typically occurs as coatings or fracture fillings in the saprock and is characterized by strikingly high NiO content up to 34.86 wt%. Goethite and Mn-oxy-hydroxides (i.e. lithiophorite-asbolane intermediates) are the principal hosts of Ni in the limonite (up to 2.15 wt% NiO and 23.89 wt% NiO, respectively) with the latter also being the main Co carriers (up to 12.59 wt% CoO). The whole-rock XRF data show typical trends observed in other Ni laterite deposits, where Mg and Si are depleted toward the surface, and the transition metals (i.e. Fe, Al, Ni, Co, and Mn) are retained in the weathered horizons. The saprolite horizon is particularly enriched in Ni, while the lower section of the limonite horizon is enriched in Co. The mildly acidic environmental condition (pH ≤ 6.57) in the limonite horizon was found to enhance the mobilization and re-distribution of Ni from the limonite towards the lower section of the profiles. Geological observations, coupled with mineralogical and geochemical data, show that the Berong Ni-Co laterite deposit formed in two weathering processes: (i) development of the saprolite and the limonite horizons, and (ii) late precipitation of secondary phyllosilicates (i.e. garnierite), Mn-oxy-hydroxides and silica.

Effect of Si–Ni–P on the emergence of dislocations loops in Fe–9Cr matrix under neutron irradiation: TEM study and OKMC modelling

The expected degradation of mechanical properties of structural materials under irradiation (i.e. “in operation”) in nuclear components represents a significant challenge for the design to account the impact of long-term irradiation effects. Therefore, a development of scientific and engineering expertise to understand and possibly control the severe impact of harsh neutron irradiation on materials is one of the tasks in the current material’s research agenda. As it is well known from long-standing experience with fission systems, radiation embrittlement is caused by nano-scale features that obstruct plasticity mediated by dislocations. The present contribution highlights recent research and development efforts addressed towards the assessment of the interrelation between nano-structural features and hardening induced by neutron irradiation in fusion structural high-Cr ferritic/martensitic steels.In this work, the impact of doping by three chemical elements (nickel, silicon and phosphorus) on the microstructural evolution under neutron irradiation at 300 °C and 450 °C is studied experimentally as well as by computer simulations. The evolution of microstructure is assessed by transmission electron microscopy and object kinetic Monte Carlo simulations. The latter method utilizes a new approach enabling to follow both nano-scale irradiation defects and micro-segregation zones causing the formation of solute rich clusters, detectable by atom probe tomography. The results of the present work clearly point out that Ni–Si segregation alters the spatial and size distribution of dislocations loops already at as low dose as 0.1 dpa. The physical mechanisms behind the impact of minor alloying elements are discussed.

Thermodynamic Assessment of the Mg–Ni–Si System

The thermodynamic assessment of the Mg–Ni–Si system has been developed in the framework of the CALPHAD method. The critical review of the literature data has been provided. A set of selfconsistent thermodynamic parameters for the phases in this ternary system is obtained using the phase diagram data available in the literature. The excess Gibbs energy term of solution phases is described using the Redlich–Kister polynomial. The sublattice model is used to describe the MgNi2 intermetallic phase having homogeneity range in the ternary system. Ternary intermetallic compounds are modelled as line compounds. Isothermal sections and liquidus surface, as well as the coordinates of the invariant reactions, are calculated. The calculated results are in satisfactory agreement with the experimental data. The calculated liquidus surface is extremely complex and contains 38 invariant reactions including 8 degenerated reactions and 10 invariant maxima. Most of the presented invariant reactions must be considered as approximate. The τ3 and τ5 phases melt congruently at 1544 and 1487 K, respectively. The τ4 forms via the peritectoid τ5 + NiSi + βNi2Si ↔ τ4 reaction at a temperature of 1193 K. According to our calculations, τ1 and τ8 melt at 1359 K (the L + τ5 ↔ τ1 reaction) and 1267 K (the L + τ1 ↔ τ8 reaction). The τ2 and τ6 are formed via the peritectic reactions at 1317 K (the L + τ3 + MgNi2 ↔ τ2 reaction) and at 1229 K (the L + τ5 + Mg2Si ↔ τ6 reaction), and the τ7 is formed via peritectoid Mg2Si + τ1 + τ5 ↔ τ7 reaction at 1279 K.

Grain refinement and mechanical properties improvements in a high strength Cu–Ni–Si alloy during multidirectional forging

Abstract Microstructure evolutions and properties variations of a high-strength Cu–Ni–Si alloy during multidirectional forging have been systematically investigated using microstructure characterizations and properties measurements. Experiment results indicated that nano-scale grains formed in the block samples having been multidirectional forged (MDF) at room/cryogenic temperatures. With the increase of the MDF cycle, the sub-grain structure was further refined to nano-grains with tens of nanometers in diameter. The ultimate tensile strength of the cryogenic temperature multidirectional forged sample was 1057 MPa, the yield strength was 923 MPa, and the fracture elongation was 7.2%. Rather than the solid solution strengthening from solutes impeding the glide of dislocation motion and the second phase particle precipitation strengthening from the Orowan looping, the grain boundary strengthening from the Hall–Petch effects plays crucial roles in strengthening the samples having been cryogenic multidirectional forged. These findings indicated that multidirectional forging is a passport to an ultrafine-grained structure and high yield strength material for the nuclear industry.