Phase Formation Sequence Research Articles

Selection of the first Ni silicide phase by controlling the Pt incorporation in the intermixed layer

During the deposition of a Ni film on a Si substrate, an intermixed layer usually forms at the Ni/Si interface. In this work, the influence of Pt incorporation in this intermixed layer on the phase formation sequence and especially on the first phase formation is studied by in situ-XRD measurements and atom probe tomography (APT). Four different samples were elaborated where the intermixed layer was modified by deposition of a 3 nm of Ni or Ni(10 at% Pt) on the Si substrate prior to the deposition of Ni(10 at%Pt) or Ni film respectively. These results show that the formation of the first phase changes between δ-Ni2Si and θ-Ni2Si depending on the Pt concentration integrated in the intermixed layer. Using this selection method to control the formation of the first phase, can impact the self-aligned silicide process used by the industry.

Investigation of the Aluminum Nitride Formation During the Aluminum Nanopowder Combustion in Air

The phase formation sequences, intermediate and final products of aluminum nanopowder combustion are studied. The experiments were performed in the Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, at the “Precision Diffractometry II” station (SR beamline No. 6 of the VEPP-3 electron storage ring). The main combustion product was found to be aluminum nitride. In the combustion of aluminum nanopowder aluminum γ-oxide is the first to form, and aluminum nitride arises next. The formation of aluminum nitride probably occurs by successive replacement of oxygen by nitrogen from the aluminum oxide. The use of synchrotron radiation with high photon flux made it possible to determine with moderate time resolution the sequence of stages of formation of crystalline products during combustion of the aluminum nanopowder.

Phase Formation of the Yttrium Aluminates in the Y2O3-Al2O3-SiC System

Phase formation sequence of the yttrium aluminates in the Y2O3-Al2O3-SiC ternary system as temperature increases were investigated via x-ray diffraction (XRD). Results showed that YAM (monoclinic), YAP (perovskite) and YAG (garnet) were the yttrium aluminates presented in the solid-state reacted samples at a fixed Al2O3:SiC ratio of 1:1. Formation of the yttrium aluminates depended on the temperature. The YAM, YAP and YAG started to form below 1150 °C, at 1300 °C, and at 1450 °C, respectively. Accordingly, two behavior phase diagrams of the Y2O3-Al2O3-SiC ternary system were recognized, one is in the temperature range of 1150-1300 °C and the other is in 1300-1450 °C, respectively. Thereafter, the phase equilibrium was reached in the temperature range of 1450-1700 °C. Effects of SiC on the phase formation processes in the ternary system were discussed.

Solidification Sequence of Spray-Formed Steels

Solidification in spray-forming is still an open discussion in the atomization and deposition area. This paper proposes a solidification model based on the equilibrium solidification path of alloys. The main assumptions of the model are that the deposition zone temperature must be above the alloy’s solidus temperature and that the equilibrium liquid fraction at this temperature is reached, which involves partial remelting and/or redissolution of completely solidified droplets. When the deposition zone is cooled, solidification of the remaining liquid takes place under near equilibrium conditions. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to analyze the microstructures of two different spray-formed steel grades: (1) boron modified supermartensitic stainless steel (SMSS) and (2) D2 tool steel. The microstructures were analyzed to determine the sequence of phase formation during solidification. In both cases, the solidification model proposed was validated.

Atomic structure and formation of CuZrAl bulk metallic glasses and composites

Cu47.5Zr47.5Al5 metallic glass is studied experimentally by high-energy X-ray diffraction, neutron diffraction with isotopic substitution, electron diffraction and X-ray absorption spectroscopy. The atomic structure of the glass is modeled by reverse Monte-Carlo and molecular dynamics simulations. RMC modeling of seven experimental datasets enabled reliable separation of all partial pair distribution functions for Cu47.5Zr47.5Al5 metallic glass. A peculiar structural feature of the ternary alloy is formation of the strong Al–Zr bonds, which are supposed to determine its high viscosity and enhanced bulk glass formation. Analysis of the local atomic order in Cu47.5Zr47.5Al5 glass and Cu10Zr7, CuZr2 and CuZr B2 crystalline structures elucidates their similarities and differences explaining the phase formation sequence by devitrification of the glass.

Eutectic morphology evolution and Sr-modification in Al-Si based alloys studied by 3D phase-field simulation coupled to Calphad data

The mechanical properties of Al-Si cast alloys are mainly controlled by the morphology of the eutectic silicon. Phase-field simulations were carried out to study the evolution of the multidimensional branched eutectic structures in 3D. Coupling to a Calphad database provided thermodynamic data for the multicomponent multiphase Al-Si-Sr-P system. A major challenge was to model the effect of the trace element Sr. Minor amounts of Sr are known to modify the silicon morphology from coarse flakes to fine coral-like fibers. However, the underlying mechanisms are still not fully understood. Two different in literature most discussed mechanisms were modelled: a) an effect of Sr on the growth kinetics of eutectic silicon and b) the formation of Al2Si2Sr on AlP particles, which consumes most potent nucleation sites and forces eutectic silicon to form with lower frequency and higher undercooling. The phase-field simulations only revealed a successful modification of the eutectic morphology when both effects acted in combination. Only in this case a clear depression of the eutectic temperature was observed. The required phase formation sequence L → fcc-(Al) → AlP → Al2Si2Sr → (Si) determines critical values for the Sr and P content.

Microstructural Evolution of Mg-4Al-2.5Ca Alloy during Solidification

In the present work, the microstructure evolution of Mg-4Al-2.5Ca alloy during solidification was investigated by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and differential scanning calorimetry (DSC). The results showed that the as-cast microstructure was typical dendritic structure, consisting of α-Mg and the Al2Ca with a C15 structure formed at inter-dendritic regions. But during slow solidification, the sequence of phase formation of this alloy consisted of following stages: L→ L + α-Mg → L + α-Mg + (Mg, Al)2Ca → α-Mg + (Mg, Al)2Ca + Al2Ca → α-Mg + Al2Ca. Thermal analysis showed that the (Mg, Al)2Ca and Al2Ca phase separation temperature was about 520°C and 510°C respectively, which is different from thermodynamic calculation. With the temperature decreasing, the liquid (Mg, Al)2Ca phase with thick and continuous morphology transformed into lamellar-shaped eutectic phase, and parts of (Mg, Al)2Ca phase translated into Al2Ca phase with bone-shaped and needle-like.

Effect of Si additions on thermal stability and the phase transition sequence of sputtered amorphous alumina thin films

Si-alloyed amorphous alumina coatings having a silicon concentration of 0 to 2.7 at. % were deposited by combinatorial reactive pulsed DC magnetron sputtering of Al and Al-Si (90-10 at. %) split segments in Ar/O2 atmosphere. The effect of Si alloying on thermal stability of the as-deposited amorphous alumina thin films and the phase formation sequence was evaluated by using differential scanning calorimetry and X-ray diffraction. The thermal stability window of the amorphous phase containing 2.7 at. % of Si was increased by more than 100 °C compared to that of the unalloyed phase. A similar retarding effect of Si alloying was also observed for the α-Al2O3 formation temperature, which increased by more than 120 °C. While for the latter retardation, the evidence for the presence of SiO2 at the grain boundaries was presented previously, this obviously cannot explain the stability enhancement reported here for the amorphous phase. Based on density functional theory molecular dynamics simulations and synchrotron X-ray diffraction experiments for amorphous Al2O3 with and without Si incorporation, we suggest that the experimentally identified enhanced thermal stability of amorphous alumina with addition of Si is due to the formation of shorter and stronger Si–O bonds as compared to Al–O bonds.

The Phase-Formation Behavior of Composite Ceramic Powders Synthesized by Utilizing Rice Husk Ash from the Biomass Cogeneration Plant

The development and utilization of biomass as a vital source of renewable energy were stimulated in order to reduce the global dependency on fossil fuels. A lot of rice husk ashes (RHA) were generated as the waste after the rice husk as the main fuel was burnt in the biomass cogeneration plant. The phase-formation behavior of composite ceramic powders synthesized by using rice husk ash from the biomass cogeneration plant at the different carbon ratios and temperatures was investigated. The sequence of phase formation with the calcining temperatures ranging from 1773 K to 1853 K was followed by O′-Sialon→SiC + Si3N4→SiC in samples with C/SiO2 = 1 : 1–4 : 1. Ca-α-Sialon formed in samples with C/SiO2 = 5 : 1 and 6 : 1. The results highlighted that series of reactions happening sensitively depended on C/SiO2and the temperature and demonstrated that the carbothermal nitridation provided an alternative for converting RHA waste into composite ceramic powders.

Obtaning of nanodispersed ferriferous pigments using contact nonequilibrium plasma

The paper shows the efficiency of using a contact nonequilibrium low-temperature plasma for producing nanodispersed pigments of different colours. The influence of the initial pH, treatment time and electrical parameters of the plasma-chemical synthesis on the main technological properties of the pigments was determined. Colour characteristics of the obtained products were studied. Their phase composition was analyzed. According to the data on the dependence of the phase composition of the products formed by the oxidation of iron hydroxide (II) on the synthesis parameters, the system diagram was created to display predominant areas of each phase formation in the pH plasma treatment time coordinates. The main trends in changing the phase composition of the solid phase from the synthesis conditions were determined during the studies. It was found that the final product of iron hydroxide (II) oxidizing depending on the synthesis parameters can be oxyhydroxide of iron (III -a) − modification, magnetite or iron hydroxide (II). A phase composition of the obtained product depends largely on the solution’s pH. With increasing the pH from 6 to 10 under the same synthesis parameters, such sequence of phase formation is indicated: Fe(OH) 2 − a − FeOOH − Fe 3 O 4 . With the further increase of the solution’s pH, Fe 3 O 4 is formed.

Effect of annealing on phase sequence and their composition in the Pt-coated Mo system

The phase formation sequence and the composition of phases induced by thermal annealing in a platinum (Pt) coated molybdenum (Mo) system were investigated by X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The X-ray diffraction study of a 0.2μm thick platinum layer deposited on a Mo substrate and annealed at temperatures between 800°C and 900°C for different periods of time shows the formation of MoPt2 and MoPt phases. It was also found that these phases nucleate sequentially and the MoPt2 phase becomes unstable at 900°C after a longer annealing time of 8h. Rutherford backscattering spectroscopy and transmission electron microscopy showed that the coating thickness approximately doubled after thermal annealing, from 0.22μm to 0.46μm, due to the formation of the Pt–Mo phases.

Effects of Zr and Si on the Glass Forming Ability and Compressive Properties of Ti-Cu-Co-Sn Alloys

To succeed in finding novel Ti-based bulk metallic glasses, which are free from Be, Ni, and noble metallic elements, a comprehensive study was performed on the effects of Zr and Si on the microstructural evolution, glass-forming ability (GFA), and mechanical properties of Ti46Cu44−xZrxCo7Sn3 (x = 0, 5, 10, 12.5, and 16 at. pct) and Ti46Cu31.5Zr12.5−xCo7Sn3Six (x = 0.5, 1, and 1.5 at. pct) alloys. It is shown that with the increase of Zr, the sequence of phase formation is β-Ti + α-Ti + (Ti, Zr)3Cu4 ⇒ β-Ti + α-Ti + TiCu ⇒ β-Ti + Ti2Cu + glass ⇒ glass ⇒ β-Ti + Ti2Cu + TiCuSn. The quinary Ti-Zr-Cu-Co-Sn alloy with 12.5 pct Zr exhibits the best GFA. The addition of 1 pct Si results in the improvement of the critical size of glassy rods up to 3 mm in diameter. The yield stress and Young’s modulus of Z-series alloys increases, and the plastic strain decreases with the addition of Zr. The yield stress and ultimate compression stress of Ti46Zr11.5Cu31.5Co7Sn3Si1 glassy alloy reach 2477.9 and 2623.3 MPa, respectively. It was found that the addition of Si promotes the generation and multiplication of shear bands, resulting in certain plasticity in these kinds of glassy alloys.

New Cu3TeO6 Ceramics: Phase Formation and Dielectric Properties

Targeting low temperature cofired ceramics (LTCC) applications and base-metal electrode multilayer ceramic capacitors (BME-MLCCs), ceramics of a new composition, tricopper tellurate (Cu3TeO6), are reported here. The crystal structure of Cu3TeO6 was determined to be cubic, Ia3, with the unit cell parameter a = 9.538 Å. The sequence of phase formation is proposed with the oxidation of tetravalent tellurium (Te(4+)) into hexavalent tellurium (Te(6+)) as a key step for the formation of Cu3TeO6. Ceramics sintered at 865 °C with densities of 94% exhibit two dielectric anomalies in the temperature dependence of the dielectric response, around -150 °C and +50 °C, respectively, accompanied by obvious frequency dispersion of the relative permittivity (ε(r)) and dielectric losses (tan δ), with an Arrhenius like behavior. A temperature stable dielectric region (near room temperature) formed between the two anomalies with ε(r) ∼ 12 and tan δ ∼ 0.01, and a very low positive temperature coefficient of the relative permittivity (TCε(r)), 2.07 × 10(-4) °C(-1), was obtained in the same region. The low temperature dielectric anomaly is associated with the possible mixed Cu(+)/Cu(2+) valence in Cu3TeO6 ceramics, while the high temperature anomaly is attributed to point defect ordering, including VO, CuCu2+(+)', which might be formed during sintering. Therefore, Cu3TeO6 ceramics are of interest in view of not only the possible applications in BME-MLCCs, LTCC, and related technologies, but also for their possible compatibility with low cost abundant Cu electrodes.

In Situ Phase Evolution of Ni/Ti Reactive Multilayers

Joining shape-memory alloys (SMA) to other materials is strongly required in order to enlarge their fields of application. Fusion welding induces strong compositional and microstructural changes that significantly affect the shape-memory effect and the superelastic behavior of these alloys. The exothermic and in some cases self-propagating character of some nano-multilayer reactions is explored in this study as an alternative for joining SMA. To follow these very fast reactions, high brilliance sources, such as synchrotron radiation, are required. In situ high-resolution x-ray diffraction data, giving the phase evolution sequence with temperature of the Ni/Ti multilayer thin films under study, are presented. A correlation between the multilayer design and the tendency for the sequence of phase formation is established.

Thermal and electron microprobe analyses of an Ni-0.5C-15Cr-3.2Si-2B alloy

The melting and solidification of a powder alloy Ni-0.5 wt % C-15 wt % Cr-3.2 wt % Si-2 wt % B is studied. The microstructure and chemical composition of the phases present in the compact alloy prepared by melting of the powder are investigated. The sequence of phase formation during solidification of the alloy is suggested.

Investigation of phase evolution of CaCu3Ti4O12 (CCTO) by in situ synchrotron high-temperature powder diffraction

In situ synchrotron X-ray powder diffraction was used to study the high-temperature phase evolution of CaCu3Ti4O12 (CCTO) precursors prepared via solid-state and sol–gel methods. After the precursors are heated to 1225°C, the CCTO phase is the main phase observed in the calcined powder, with the presence of some minor impurities. Comparing the two precursors, we found that the onset temperature for the CCTO phase formation is 800°C in the sol–gel precursor, lower than that in the solid-state precursor (875°C). Intermediate phases were only observed in the sol–gel precursor. Both precursors are able to be calcined to sub-micrometric sized powders. Based on the synchrotron data along with differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), the phase formation sequence and mechanism during calcination are proposed in this study.

Phase control in solid state silicide nanowire formation

AbstractPhase manipulation is important for the production of metallic silicide as contacts in Si nanowire based devices. In this proceeding, we present a kinetic competition model that explains the phase formation sequence in 1‐D structures, and the phase control through template modifications. Multiple silicides coexist initially and then the fastest one forms as the first phase in a following growth competition. With kinetic parameters extracted from in‐situ TEM observations, we quantitatively explain the phase formation sequence, which depends on the diameter of Si nanowire. The amount metal supply has been shown to be insignificant in controlling phase formation. Through template structure modifications, we can also selectively enhance or suppress the growth rate of silicides. A thick Al2O3 shell around the nanowire is applied to impede the growth of large volume diffusion limited phases including Ni31Si12, δ‐Ni2Si and θ‐Ni2Si. Moreover, a thin Pt interlayer between Si and Ni is used to suppress the nucleation of NiSi2. Together, all competing silicides were suppressed and the slow growing NiSi emerged as the first phase. Controlled formation of Ni31Si12, δ‐Ni2Si, θ‐Ni2Si, NiSi or NiSi2as the first phase have also been achieved. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spark ignitable ball milled powders of Al and Ni at NiAl composition

Low-energy ball milling of aluminum and nickel particles with an overall composition corresponding to the NiAl intermetallic phase was performed up to milling durations of 13 h. The milled powders and cold-compacted pellets were ignited using a low-energy spark. Interrupted thermal analysis and X-ray diffraction was performed to investigate the effect of milling time on intermetallic phase formation. The results show that microstructural refinement with increasing milling times increases reactivity, where the intermetallic formation temperatures reduce to those of sputtered multilayer foils with a similar phase formation sequence. NiAl intermetallic phase starts forming at 12 h of milling. Loose powders milled for 11 and 12 h and the corresponding pellets ignite locally with uniform thermal wave fronts self-propagating at velocities up to 0.24 m/s.

Thin film Ni-Si solid-state reactions: Phase formation sequence on amorphized Si

The phase formation sequence during the thermally induced solid-state reaction of a 10-nm-thick magnetron-sputtered Ni film with a Si(001) substrate amorphized by ion implantation (a-Si) is investigated using a combination of in situ temperature-resolved x-ray diffraction and ex situ x-ray pole figure analyses, transmission electron microscopy, and Rutherford backscattering spectrometry. Our results reveal (1) that the metastable θ-phase grows from δ-Ni2Si and directly transforms into NiSi and (2) that cleaving the as-prepared, amorphized samples are often subject to a spontaneous reaction possibly resulting from cleaving. In the spontaneously reacted samples, a mixture of θ and NiSi is observed from the beginning of the thermal treatment. The θ phase exhibits a (110) fiber texture with a ±10° misorientation, which is then inherited by NiSi. The rest of the phase sequence is the same as for nonreacted samples, the NiSi2 growing from 390 °C if the amorphized Si is not completely consumed.

Synthesis and reaction pathway investigation of chalcopyrite CuInSe2 nanoparticles for one-pot method

Highly dispersed and near stoichiometric chalcopyrite CuInSe2 nanoparticles were successfully synthesized via a facile and rapid one-pot method. For understanding the reaction pathway, the solid intermediates obtained at different stages of CuInSe2 nanoparticles synthesis process were investigated in detail by powder X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The XRD patterns showed that the phase formation sequence was CuSe→CuInSe2. The XPS results indicated that the valences of Cu and Se in CuSe were +1 and −1, respectively. The chemical composition of the solid intermediates revealed the presence of the solid-state In–Se secondary phases in the synthesis process. However, no XRD signals or Raman signals of the solid-state In–Se secondary phase were observed. Based on the experimental results, the possible reaction pathway was proposed.