Accurate determination of the number density of G-phase precipitates in thermally aged duplex stainless steel

G-phase precipitation in the ferrite phase in thermally aged duplex stainless steel (DSS) was investigated. A needle-shaped sample of DSS aged at 673?K for 5000?h was observed by transmission electron microscopy (TEM), and subsequently by atom probe tomography (APT). The precipitates of the G-phase observed by TEM corresponded well to clustering atoms observed by APT. On the other hand, regarding the precipitates of the G-phase that formed in an earlier stage of aging, the present study suggests that not all the precipitates can be detected by TEM. A large area of DSS aged at 673?K for 5000?h containing both the ferrite and austenite phases was observed. The number density of precipitates of the G-phase in the ferrite phase was small in the vicinity of the phase boundary and increased with the distance between the phase boundary and each field of view. The number density reached an almost constant value at a distance of approximately 4?µm from the phase boundary. The suppression of G-phase precipitation in the vicinity of the phase boundary is discussed in terms of the depletion of alloying elements that comprise the G-phase.     

Effects of aging temperature on G-phase precipitation and ferrite-phase decomposition in duplex stainless steel

G-phase precipitation and ferrite-phase decomposition in a cast duplex stainless steel (DSS) aged at 623–723?K for up to 8000?h were investigated using atom probe tomography (APT). Large sample volume was observed in every APT experiment, which yielded significantly statistical results. The number density of G-phase precipitates tended to be high and their sizes were small at lower aging temperatures. G-phase precipitates grew during prolonged isothermal aging. The concentrations of nickel, silicon, manganese and molybdenum in G-phase precipitates tended to increase as the precipitates grew. Heterogeneous distributions of alloying elements within G-phase precipitates were observed. An interesting positional relationship of G-phase precipitates with dislocations was revealed. Regarding the ferrite-phase decomposition, local chromium concentrations in the ferrite phase varied fast at higher aging temperatures. Good correlation between the variation of local chromium concentrations and aging conditions was revealed, which indicates that the variation can be estimated for arbitrary aging conditions. Representative distances between chromium-enriched and chromium-diluted regions were long at higher aging temperatures. Time exponent of the representative distances of ferrite-phase decomposition as well as the size of G-phase precipitates increased with aging temperatures.     

Study on Ultra-fast Cooling Behaviors of Water Spray Cooled Stainless Steel Plates

Spray cooling is an effective tool to dissipate high heat fluxes from hot surfaces. This article thoroughly investigates the effect of thickness of a hot stainless steel plate on the cooling time, cooling rate, heat flux, and heat transfer coefficient under constant mass flow rate maintained at 1 MPa using water as the coolant. Cylindrical samples of stainless steel with constant diameter (D = 25 mm) and thickness (δ = 7.5, 12, 16.5, and 21 mm) were used in the present study. Critical droplet diameter to achieve an ultra-fast cooling rate of 300°C/s was estimated by using an analytical model for samples of varying thicknesses. The analytical model (one side spray cooling) showed good agreement with experimental results with a relative error of 3.2% in the plate thickness range of 1–12 mm. An increasing trend in maximum heat flux was found with increasing thickness of the plate. Maximum heat flux as high as 1,800 kW/m² was achieved for a 21-mm-thick sample. Heat transfer coefficients in the range 0.092–96.24 kW/m²K, 0.111–98.9 kW/m²K, 0.074–63.4 kW/m²K, and 0.127–55.63 kW/m²K were reported for sample of varying thicknesses in the present study. Limited published work is available with reference to water spray cooling dynamics and thickness of stainless steel plate. Therefore, the present study focuses on the correlation between the thickness of the plate and spray dynamics of water spray cooling.     

Five-parameter crystallographic characteristics of the interfaces formed during ferrite to austenite transformation in a duplex stainless steel

The crystallography of interfaces in a duplex stainless steel having an equiaxed microstructure produced through the ferrite to austenite diffusive phase transformation has been studied. The five-parameter interface character distribution revealed a high anisotropy in habit planes for the austenite–ferrite and austenite–austenite interfaces for different lattice misorientations. The austenite and ferrite habit planes largely terminated on (1 1 1) and (1 1 0) planes, respectively, for the austenite–ferrite interfaces associated with Kurdjumov–Sachs (K–S) and Nishiyama–Wasserman (N–W) orientation relationships. This was mostly attributed to the crystallographic preference associated with the phase transformation. For the austenite–ferrite interfaces with orientation relationships which are neither K–S nor N–W, both austenite and ferrite habit planes had (1 1 1) orientations. Σ3 twin boundaries comprised the majority of austenite–austenite interfaces, mostly showing a pure twist character and terminating on (1 1 1) planes due to the minimum energy configuration. The second highest populated austenite–austenite boundary was Σ9, which tended to have grain boundary planes in the tilt zone due to the geometrical constraints. Furthermore, the intervariant crystallographic plane distribution associated with the K–S orientation relationship displayed a general tendency for the austenite habit planes to terminate with the (1 1 1) orientation, mainly due to the crystallographic preference associated with the phase transformation.     

Effects of molybdenum on precipitation behaviours in aged cast stainless steels

The effects of Mo on precipitation behaviours in aged cast stainless steels have been investigated. Mo-free CF3 steel and Mo-bearing CF3M steel, both of which consisted of a duplex structure of ferrite and austenite phases, were prepared. Microstructural evolution in the ferrite phase during ageing at 723 K has been observed by transmission electron microscopy (TEM). Precipitates in CF3 steel were identified to belong to the G-phase and possess lattice coherency with the ferrite phase at interphase boundaries. On the other hand, precipitates in CF3M steel were found to be nanodomains of not only to the G-phase but also to another phase enriched in Mo. Some of the nanodomains containing Mo exhibited diffraction patterns having pseudo five-fold symmetry, but others exhibited regular periodicity in high-resolution TEM images. The atomic structure of the Mo-related nanodomains is proposed to be a distorted χ-phase that retains coherency with the matrix.     

A Mössbauer spectrometry study on the phase decomposition of cast duplex stainless steel

Cast CF3M duplex stainless steel having 25% of ferrite in volume fraction was aged at 723 K for time periods up to 10000 h. Phase decomposition of ferrite was investigated by Mössbauer spectroscopy. Ferrite decomposed initially via a spinodal process to finally yield the Fe-rich and the Cr-rich phase. The hyperfine magnetic field distribution obtained from the experimental Mössbauer spectrum was analyzed by assuming trinomial distribution of main constituent atoms Fe, Cr, Ni to determine Cr and Ni content of the Fe-rich phase. Main compositions of the phase were 84 at.% Fe, 11 at.% Cr, 5 at.% Ni.     

Helium irradiation-induced defects in deformed 316L stainless steel

Well-annealed 316L stainless steel was first cold rolled to 10% and 20% reductions in thickness and then irradiated by 50 keV He⁺ to a dose of 1 × 10²⁰ He⁺/m² at room temperature. Thermal desorption spectroscopy was used to investigate the helium desorption behaviour at different helium trapping states. The results showed that high-density dislocations had stronger inhibitory effect for helium desorption at temperatures from 800 to 1200 K. Positron annihilation Doppler broadening spectroscopy measurements were used to investigate the distribution of helium irradiation-induced defects. The S–E and ΔS–E plots clearly demonstrated that the helium irradiation-induced defects were trapped and restricted in motion by dislocations. The interaction between dislocations and helium irradiation-induced defects in deformed 316L stainless steel was investigated.     

Surface modification of stainless steels by carbon/nitrogen implantation

Plasma immersion ion implantation has been used for simultaneous implantation of carbon and nitrogen into austenitic, ferritic, and duplex stainless steels at 400°C for 3 h. The surface phase composition, studied by means of Conversion Electron Mössbauer Spectroscopy and X-Ray difraction, is correlated with the mechanical properties represented by hardness (Vickers) measurements. The results extend information about the expanded austenite phase formed during the low temperature modification of stainless steel surface by nitrogen.     

Magnetic and Mössbauer spectroscopic studies of NiZn ferrite nanoparticles synthesized by a combustion method

The properties of nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ synthesized by an auto-combustion method have been investigated by magnetic measurements and Mössbauer spectroscopy. The as-synthesized single phase nanosized ferrite powder is annealed at different temperatures in the range 673–1,273 K to obtain nanoparticles of different sizes. The powders are characterized by powder X-ray diffraction, vibrating sample magnetometer, transmission electron microscopy and Mössbauer spectroscopy. The as-synthesized powder with average particle size of ~9 nm is superparamagnetic. Magnetic transition temperature increases up to 665 K for the nanosized powder as compared to the transition temperature of 548 K for the bulk ferrite. This has been confirmed as due to the abnormal cation distribution, as evidenced from room temperature Mössbauer spectroscopic studies.     

Thermal Induced Processes in Laminar System of Stainless Steel – Beryllium

The paper reports on investigation of the laminar system ‘stainless steel 12Cr18Ni10Ti – Be’ at thermal treatment. There have been determined sequences of phase transformations along with relative amount of iron-containing phases in the samples subjected to thermal beryllization. It has been revealed that thermal beryllization of stainless steel thin foils results in γ→α transformation and formation of the beryllides NiBe and FeBe₂. It has also been revealed that direct γ→α- and reverse α→γ-transformations are accompanied by, correspondingly, formation and decomposition of the beryllide NiBe. It is shown that distribution of the formed phases within sample bulk is defined by local concentration of beryllium. Based on obtained experimental data there is proposed a physical model of phase transformations in stainless steel at thermal beryllization.     

Theoretical assessment on mixing properties of liquid Tl–Na alloys

Thermodynamic and structural properties of mixing of molten Tl–Na alloys at 673 K have been investigated using quasi-chemical model. To understand the mixing behaviour in more detail, emphasis is placed on the role of interaction energy term, and viscosity and surface tension of the alloys have also been analysed under statistical considerations. Our study shows negative deviation from the Raoultian behaviour in the properties of Tl–Na alloy thereby indicating hetero-coordination in the Tl–Na melt at 673 K in the full range of concentration. Theoretically, computed thermodynamic data at 673 K agree very well with the corresponding experimental data. The viscosities of the alloys computed from Kaptay equation show small negative deviation and those computed from Singh and Sommer’s formulation show small positive deviation from ideal values while the Budai-Benko-Kaptay equation predicts noticeable negative deviation in Na-rich end and positive deviation in Tl-rich end of the composition. The calculations of surface tension reveal that results obtained from layered structure approach and compound formation model are in good agreement in the Na-rich side and in reasonable agreement in Tl-rich side of the composition, while those computed from Butler equation show noticeable deviations in the intermediate compositions. Both the viscosity and surface tension of liquid Tl–Na alloys increase with addition of Tl-component, viscosity having approximately linear variation with concentration. The study shows that there is non-linear variation in surface composition with bulk concentration and for most of the compositions the surface of the alloy is enriched with Na-atoms which segregate to the surface.     

Electrochemical recycling of cell phone Li-ion batteries: application as corrosion protector of AISI 430 stainless steel in artificial seawater

This article aims to present a new alternative to waste management of spent Li-ion batteries from cell phones. In this sense, the proposed is recycling the cobalt from Li-ion cathode by electrodeposition and apply it as corrosion protector of AISI 430 stainless steel. Thus, two greatest environmental problems can be solved, producing a low-cost and high-corrosion-resistant stainless steel. The cobalt electrodeposition bath came from acid dissolution of spent Li-ion cathode with chemical formula LiCoO₂. The charge efficiency for cobalt electrodeposition in ?1.0 V and pH = 3 reaches 95 %. A protective layer of Co₃O₄ was successfully obtained by treatment of AISI 430 stainless steel with cobalt electrodeposited at 800 °C for 200 h in air atmosphere. The corrosion current of AISI 430 stainless steel in artificial seawater was reduced from 30 to 0.76 μA cm^?2. The treatment proposed produces a AISI 430 stainless steel with double of corrosion resistance and half of cost if compared with AISI 304 stainless steel.     

Phase transitions and electrical conduction in thermal energy storage compound (n-C12H25NH3)2CdCl4

Differential scanning calorimetry (DSC) and differential thermal analysis (DTA) are performed for the compound (n-C₁₂H₂₅NH₃)₂CdCl₄. The ac conductivity σ_(ω,T), and the complex dielectric permittivity ?*_(ω,T) are measured as a function of temperature (100 K < T < 375 K) and at some selected frequencies (3 → 100 kHz). Two structural phase transitions are detected at T = (330 ± 1) K and T = (343 ± 1) K as minor and major transitions, respectively. The analysis of the measured electrical parameters reveals that the frequency-dependent conductivity obeys the power law, and the quantum mechanical tunneling (QMT) model is the main conduction mechanism in the low-temperature phase (LTP; phase III). The role of hydrogen bond N–H…Cl as a trigger force for phase transitions has been discussed. While the LTP is of the order–disorder type, the high-temperature phase (HTP) or phase I seems to be conformational and represents the main transition.     

Martensitic transformation and physical properties of ‘steel–TiNi’ bimetal composite,produced by explosion welding

The aim of this work is an investigation of structure and martensitic transformation in bimetal composite ‘TiNi–stainless steel’ produced by explosion welding. The results have shown that the mixture of chemical elements is observed in very narrow intervals of 6 µm close to the joint – 2 µm from the TiNi side and 4 µm from the steel one. Micro-hardness distribution in the vicinity of the joint is non-monotonic in the interval of 60 µm. Connection of stainless steel and TiNi plates by explosion welding leads to a dramatic change of martensitic transformation kinetics. Temperatures and the temperature interval of phase transformation increase strongly and heat transformation decreases. Annealing at 500°C for 2 h of bimetal composite decreases the interval of micro-hardness variation and partially recovers kinetics of phase transitions.     

On the effect of SHI irradiation on dielectric properties of Y3+xFe5−xO12 (x=0.0–0.6) system

The present work aims to investigate the pre- and post-effect of 50 MeV Li³⁺ ion irradiation at a fluence of 5×10¹³ ions/cm² on the dielectric properties of Y_3+xFe_5?xO₁₂, x=0.0, 0.2, 0.4 and 0.6, garnet system over broad temperature, 300–673 K, and frequency, 100 Hz–13 MHz, ranges. Thermal variation of ac resistivity measurements suggests that the mechanism responsible for conduction in the system is polaron hopping. The observed modifications in dielectric properties after swift heavy ion irradiation are mainly due to the modifications of the metal–insulator contacts due to radiation damage-induced disorder and irradiation-induced point/cluster of defects in the material and also compressive strain generated in the lattice structure. The electric modulus presentation and the complex impedance spectral analysis have been employed to study the relaxation process. The YFeO₃ phase is found to be irradiation hard phase as compared with the garnet phase.     

Formation and properties of rocksalt-type AlN and implications for high pressure phase relations in the system Si–Al–O–N

Pressure-dependent thermodynamic properties of the ambient and high pressure phases of aluminum nitride (w-AlN and rs-AlN) were calculated from first principles in order to determine their phase boundary in the p? T phase diagram. These predictions were checked by static HP/HT experiments, using a multianvil press and an Al/N/H precursor with low decomposition temperature as educt. The experimental data show that at temperatures between 1000 and 2000 K, the boundary line between the two phases is situated between 11 and 12 GPa, which is ～1.3 GPa lower than the theoretical result and generally lower than previously assumed. The hardness of rs-AlN – measured for the first time – is ～30 GPa (Knoop indenter at loads of 25–50 g), twice as hard as w-AlN. Shock wave recovery experiments on nano w-AlN allowed testing of the chemical and thermal stability of rs-AlN, and determination of its infrared absorption and ²⁷Al NMR data. The shock wave technique will eventually enable the synthesis of larger amounts of rs-AlN, making it available for technological use. Finally, implications on the high pressure stability of phases in the Si–Al–O–N system are discussed in the light of thermoelastic properties of AlN.     

Atomistic study of temperature and strain rate-dependent phase transformation behaviour of NiTi shape memory alloy under uniaxial compression

Molecular dynamics simulation was conducted to investigate the phase transformation behaviour of nickel–titanium (NiTi, 50%-50% at.%) nanopillar under uniaxial compression at loading rates varying from 3.30 × 10⁷ to 3.30 × 10⁹ s^?1 and at temperatures varying from 325 to 600 K. The phase transformation of NiTi was observed to be sensitive to loading rates and temperatures. The phase transformation stress of B2 → B19 increased with increasing temperature while it was insensitive to loading rate. The phase transformation stress of B19 → B19′ → BCO increased with increasing strain rate and decreasing temperature. In addition, reverse phase transformation was observed during compression due to the interaction between the phase transformation of B19 → B19′ → BCO and the deformation twinning/dislocation slide-induced plasticity of the BCO phase, leading to different residual crystal structures after loading. Moreover, a diagram for the phase transformation behaviour of NiTi in the simulated ranges of strain rate and temperature was obtained, from which the contrary experimental observations on the phase transformation behaviour of NiTi from the studies of Nemat-Nasser et al. (Mech. Mater. 37 (2005) p.287) and Liao et al. (J. Appl. Phys. 112 (2012) p.033515) at various strain rates could be well explained.     

The equation of state of triolein up to 1 GPa

In this paper, the compressibility studies of triolein up to 1 GPa at temperature range from 10°C to 50°C have been presented. The discontinuity of V(p) relation, characteristic for the first-order phase transition was observed. At higher temperatures (40°C and above), the time necessary for the phase transition rises considerably. Also the pressure–volume hysteresis due to the phase formation–decomposition cycle was enlarged.     

High–pressure electrical conductivity and Raman spectroscopy of chalcanthite

Abstract

The phase transitions and dehydration of chalcanthite were investigated by electrical conductivity and Raman spectroscopy at 1.0–24.0?GPa and 293–673?K in a diamond anvil cell. At ambient temperature, two secondary phase transitions were observed according to discontinuous changes in the slope of Raman shifts, full width at half maximum and electrical conductivities at ～7.3 and ～10.3?GPa. The dehydration temperatures were determined by the splitting of Raman peaks and changes in electrical conductivity as ～350 and ～500?K at respective ～3.0 and ～6.0?GPa. A positive relationship for chalcanthite between dehydration temperature and pressure is established.