Influence of titanium addition on the microstructure of the novel ferrous-based stainless steel

The microstructural characteristics of the Fe-9Al-30Mn-1C-5Ti (wt.%) alloy were determined by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectrometry. The microstructure of the alloy was essentially a mixture of (γ + TiC_x + (α + B2 + DO₃)) phases during solution treatment between 950 °C and 1150 °C. The TiC_x carbide had a face-center-cubic structure with a lattice parameter a of 0.432 nm. When the as-quenched alloy was subjected to aging treatment at temperatures of 450-850 °C, the following microstructural transformation occurred: (γ + TiC_x + κ + (α + DO₃)) → (γ + TiC_x + κ + (α + B2 + DO₃ + TiC_x)) → (γ + TiC_x + κ + κ′ + (α + B2 + DO₃)) → (γ + TiC_x + (α + B2 + DO₃)). Addition of Ti promotes the formation of the α phase at high temperatures.     

铋对SAC305−xBi/Cu焊接接头显微组织、热性能、力学性能和界面行为的影响

通过添加1％ 和2％(质量分数)的Bi提高SAC305焊接接头的性能,并研究Bi掺杂对SAC305?xBi/Cu焊接接头显微组织、热性能和力学性能的影响.Bi掺杂通过细化初始β-Sn和共晶相改善焊接接头的显微组织.当Bi含量低于2％ 时,Bi溶解到β-Sn基体中形成固溶体;而当Bi含量等于或高于2％时,β-Sn基体中形...     

On surface temperatures during high power pulsed magnetron sputtering using a hot target

A study of temperature of a magnetron target was performed for the case of high power pulsed magnetron sputtering (HPPMS) of titanium thin films, using a water-cooled target and a hot target. Temporal evolution and spatial distribution of surface temperature were investigated. Temperature measurements were made by an infrared camera for target diameter of 100 mm, pulse repetition frequencies of 1 and 10 kHz, and discharge average pulse currents of from 2.5 to 35 A. For the case of hot target, surface temperature of the erosion zone increased up to 1750 °C and melting occurred. Temporal evolution of temperature after the end of deposition revealed phase change in solid-state from β-Ti to α-Ti at 882 °C and, for the case of high average pulse currents, also solidification at 1670 °C. The solid state phase transformation plateau was used to determine an emissivity of Ti target for the present case, and therefore precisely calibrate infrared camera measurements. The target melting was analysed in detail. The dependencies of maximum temperature on average pulse current and on average target power density for the case of hot target revealed the existence of heat losses other than radiation (i.e. enhanced sputtering, sublimation, electron emission and evaporation) at temperatures above 1500 °C, which correlates with higher erosion and deposition rates shown in another work.     

Characterization of the hot deformation behavior of a Ti-22Al-25Nb alloy using processing maps based on the Murty criterion

Isothermal compression testing of Ti-22Al-25Nb alloy was carried out at deformation temperatures between 940 and 1060 °C with strain rate between 0.001 and 10 s⁻¹, and a height reduction of 50%. The hot deformation behavior of Ti-22Al-25Nb alloy was characterized based on an analysis of the stress-strain behavior, kinetics and the processing map, for obtaining optimum processing windows and achieving desired microstructures during hot working. The constitutive equation was established, which described the flow stress as a function of the strain rate and deformation temperature. The apparent activation energies were calculated to be 788.77 kJ/mol in the α₂ + β/B2 + O phase region and 436.23 kJ/mol in the α₂ + B2 phase region, respectively. Based on Dynamic Material Model and the Murty instability criterion, the processing map for the Ti-22Al-25Nb alloy was constructed for strain of 0.6. The map exhibits a stable domain for the temperature range of 940-1060 °C and strain rate range of 0.001-0.1 s⁻¹ with two peaks in power dissipation of 51 and 56%, occurring at 940 °C/0.001 s⁻¹ and 1060 °C/0.001 s⁻¹, respectively. One is associated with lamellar globularization, and the other displays a phenomenon of recrystallization. Therefore, the desired processing condition of the Ti-22Al-25Nb alloy is 940 °C/0.001 s⁻¹ in the α₂ + β/B2 + O phase field. Moreover, the material also undergoes flow instabilities at strain rates higher than 1 s⁻¹. This instability domain exhibits flow localization and adiabatic shear bands which should be avoided during hot processing in order to obtain satisfactory properties.     

Transmission electron microscopy observations on the phase composition and microstructure of the oxidation scale grown on as-polished and yttrium-implanted β-NiAl

Phase transformations and microstructural evolution of thermally grown oxide scale on polycrystalline β-NiAl at 1100 °C up to 6 h, with and without (e.g., as-polished) yttrium implantation, were examined by glancing angle X-ray diffraction, photostimulated luminescence, scanning and transmission electron microscopy. Site-specific TEM specimens were prepared by using focused ion beam in-situ lift-out technique. The oxide scale developed on as-polished β-NiAl consisted of the islands of 390 nm-thick flat regions (e.g., patches) in 916 nm-thick scales. Regardless of microstructure, the oxide scale consisted of α-Al₂O₃ with very little trace of θ-Al₂O₃, and had uniform compressive residual stress. The oxide scale on Y-implanted β-NiAl had a two-layer microstructure: the outer layer was mainly α-Al₂O₃ and the inner layer was made up of α-, δ-, and θ-Al₂O₃ phases. Clearly, the Y addition retarded the θ-to-α Al₂O₃ phase transformation. The oxide scale on Y-implanted β-NiAl, in general, consisted of a 722 nm-thick layer with islands of 470 nm-thick patched regions, some of which contained Y-rich nodules that protruded with thickness up to 1200 nm. Except for islands of patch-regions, the oxide scale developed on Y-implanted β-NiAl was thinner (722 nm) than that on as-polished β-NiAl (916 nm).     

A new temperature stable microwave dielectric ceramics: ZnTiNb2O8 sintered at low temperatures

The phases, microstructure and microwave dielectric properties of ZnTiNb₂O₈-xTiO₂ composite ceramics with different weight percentages of BaCu(B₂O₅) additive prepared by solid-state reaction method have been investigated using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that the microwave dielectric properties were strongly dependent on densification, grain sizes and crystalline phases. The sintering temperature of ZnTiNb₂O₈ ceramics was reduced from 1250 °C to 950 °C by doping BaCu(B₂O₅) additive and the temperature coefficient of resonant frequency (τ_f) was adjusted from negative value of −52 ppm/°C to 0 ppm/°C by incorporating TiO₂. Addition of 2 wt% BaCu(B₂O₅) in ZnTiNb₂O₈-xTiO₂ (x = 0.8) ceramics sintered at 950 °C showed excellent dielectric properties of ?_r = 38.89, Q × f = 14,500 GHz (f = 4.715 GHz) and τ_f = 0 ppm/°C, which represented very promising candidates as LTCC dielectrics for LTCC applications.     

Microstructure and mechanical performance of new Al0.5CrFe1.5MnNi0.5 high-entropy alloys improved by plasma nitriding

Effects of plasma nitriding at 525 °C on microstructure and mechanical performance of a brand-new Al_0.5CrFe_1.5MnNi_0.5 high-entropy alloy (HEA) were investigated. This alloy exhibits a large age hardening effect at temperatures from 600 to 800 °C and can be well-nitrided in the as-cast condition or the homogenized and furnace-cooled state. The nitrided layer has a thickness around 75 μm and a peak hardness level of Hv 1250 near the surface. The nitrided Al_0.5CrFe_1.5MnNi_0.5 alloys exhibit superior adhesive wear resistance to conventional nitrided steels by 25-54 times due to their much thicker highly-hardened layer and higher peak hardness than that of conventional steels.     

Microstructure, kinetic analysis and hardness of Sn-Ag-Cu-1 wt% nano-ZrO2 composite solder on OSP-Cu pads

Nano-sized, nonreacting, noncoarsening ZrO₂ particle-reinforced Sn-Ag-Cu composite solders were prepared by mechanically dispersing ZrO₂ nano-particles into Sn-Ag-Cu solder and the interfacial morphology between the solder and organic solderability preservative (OSP)-Cu pads were characterized metallographically. At their interfaces, island-shaped Cu₆Sn₅ and Cu₃Sn intermetallic compound (IMC) layers were found in solder joints with and without the ZrO₂ particles and the IMC layer thickness was substantially increased with reaction time and temperature. In the solder ball region, needle-shaped Ag₃Sn and spherically-shaped Cu₆Sn₅ IMC particles were found to be uniformly distributed in the β-Sn matrix. However, after the addition of ZrO₂ nano-particles, Ag₃Sn and Cu₆Sn₅ IMC particles appeared with a fine microstructure and retarded the growth rate of the IMC layers at their interfaces. From a kinetic analysis, the calculated activation energies for the total (Cu₆Sn₅ + Cu₃Sn) IMC layers for Sn-Ag-Cu and Sn-Ag-Cu-1 wt% ZrO₂ composite solder joints on OSP-Cu pads were about 53.2 and 59.5 kJ/mol, respectively. In addition, solder joints containing ZrO₂ nano-particles displayed higher hardness due to the uniform distribution of ZrO₂ nano-particles as well as the refined IMC particles. The hardness values of the plain Sn-Ag-Cu solder joint and solder joints containing 1 wt% of ZrO₂ nano-particles after 5 min reaction at 250 °C were about 15.0 Hv and 17.1 Hv, respectively. On the other hand, their hardness values after 30 min reaction were about 13.7 Hv and 15.5 Hv, respectively.     

Microstructure evolution of TA15 titanium alloy subjected to equal channel angular pressing and subsequent annealing at various temperatures

TA15 titanium alloy was successfully processed for the first time by equal channel angular pressing (ECAP) in the temperature range of 900-1000 °C and annealed in a wide temperature interval from 650 to 800 °C. The investigation was achieved by light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) on the microstructure evolution of TA15 alloy subjected to ECAP and subsequent annealing after ECAP. In the present work, equal channel angular pressing (ECAP) was taken as the effective method to acquire severe plastic deformation (SPD). The studies we have performed show that grains have been obviously refined and well globularized after ECAP. When TA15 alloy was pressed at the temperatures of α + β phase region equiaxed microstructure was created. There was an increase in the equilibrium grain size with increasing pressing temperature, while a decrease in the volume fraction of equiaxed α phase. TEM microstructural images illustrate that an amount of deformation twins emerged while pressing TA15 below α-β transformation temperature (T_β), which led to the continued plastic deformation through the restarting of many slip bands. Severe coarsening took place in β grains during ECAP at the temperature above T_β. A larger number of well globularized and more homogeneous equiaxed α phase of TA15 alloy annealed after ECAP has been attained. Furthermore, with annealing at the optimum temperature, grains have not grown significantly.     

Self-propagating high-temperature synthesis of La(Sr)Ga(Mg,Fe)O3−δ with planetary ball-mill treatment for solid oxide fuel cell electrolytes

This study investigated the combined effects of self-propagating high-temperature synthesis (SHS), planetary ball-mill (PBM) treatment, and sintering temperature on La_0.7Sr_0.3Ga_0.7Mg_0.1Fe_0.2O_3−δ (LSGMF73712) as an electrolyte material for solid oxide fuel cells (SOFC). The SHS products (SHS-LSGMF73712) were compared with that prepared via solid-state reaction (SSR) in terms of sinterability and power generation performance. The SHS products were treated with PBM for 10, 30, 50, and 70 h. The SHS products contained the by-product LaSrGaO₄; however, in the SHS products treated with PBM for longer than 50 h, the by-product disappeared after sintering at 1350 °C for 3 h in air. Among the samples, SHS products treated with PBM for 70 h displayed superior sintering (1350 °C), whereas the SSR product (SSR-LSGMF73712) was successfully sintered at 1450 °C for 3 h in air. Under the cell configuration of Ni-Fe/SHS-LSGMF73712-PBM70 h (0.3 mm thick)/Sm_0.5Sr_0.5CoO₃, the maximum power density was 0.673 W/cm² at 800 °C using humidified hydrogen gas (3 mol% H₂O) as a fuel and air as an oxidizing agent at a flow rate of 100 mL/min, which was almost equivalent to that using SSR-LSGMF73712 (0.629 W/cm² at 800 °C) under the same conditions.     

Oxidation behaviour of Ti-46.7Al-1.9W-0.5Si in air and Ar-20%O2 between 750 and 950 °C

The oxidation behaviour of an intermetallic alloy, Ti-46.7Al-1.9W-0.5Si, was studied in air and Ar-20%O₂ atmospheres at 750, 850 and 950 °C. Oxidation of the alloy followed a parabolic rate law at low temperature (750 °C) in both environments. The alloy oxidised parabolically in air and at a slower rate in Ar-20%O₂ at 850 °C. Following a parabolic oxidation for a relatively short exposure period (72 h) at 950 °C, the oxidation rate was reduced after prolonged exposure (up to 240 h) in air. The alloy oxidised in a slower manner in the Ar-20%O₂ atmosphere at 950 °C. Higher oxidation rates were observed in air than in Ar-20%O₂ at all three experimental temperatures. Multi-layered scales developed in both environments. The scale formed in air consisted of TiO₂/Al₂O₃/TiO₂/TiN/TiAl₂ layers, ranging from the surface to the substrate—whilst the scale developed in the Ar-20%O₂ atmosphere comprised of the sequence TiO₂/Al₂O₃/TiO₂/Al₂O₃/Ti₃Al/substrate. The two layers of Al₂O₃ in Ar-20%O₂ were more effective in providing protection of the substrate against high temperature corrosion than the single layer of Al₂O₃ formed in air.     

High temperature transformations of the Au7Cu5Al4 shape-memory alloy

The β-phase of Au₇Cu₅Al₄ undergoes a reversible shape-memory phase transformation, however there has been some uncertainty regarding the crystal structure or structures of the parent phase. Here we show that, under equilibrium conditions, the parent phase possesses the L2₁ structure between its A_p (about 79 °C) and ∼630 °C, and the B2 primitive cubic structure between ∼630 °C and its melting point. It melts directly from B2 into the liquid state and hence never achieves the random bcc A2 structure that has been previously mooted. Splat-cast samples of the alloy are martensitic, proving that development of equilibrium order and defect concentration are not pre-requisites for the A → M transformation to occur.     

Investigation on thermal and microstructural characterization of the TeO2-WO3 system

Thermal and microstructural characterization of the TeO₂-WO₃ binary system was accomplished by applying differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Different compositions of the (1 − x)TeO₂-xWO₃ system, where x varies between 0.02 and 0.80 in molar ratio were studied. The samples were prepared by melting high purity powder mixtures of TeO₂ and WO₃ in a platinum crucible with a closed lid at 750 °C for 30 min and quenching in water bath. The glass forming range of the binary system was detected as 0.04 ≤ x ≤ 0.35 in molar ratio. As-cast samples were heat-treated above the crystallization peak temperatures at 550 °C for 24 h to obtain thermal stability and the phase stability of the binary system was investigated by performing systematical thermal, phase and microstructural characterizations with the heat-treated samples. The eutectic reaction of the binary system was detected at 617 ± 3 °C, the endothermic reaction indicating the phase transformation reaction of WO₃ from orthorhombic to tetragonal was determined at 743 ± 1 °C. α-TeO₂ and orthorhombic WO₃ crystalline phases were found to be present in the final structure when the total crystallization was achieved. Microstructural characterization of the TeO₂-WO₃ system was realized for a wide compositional range for the first time in the literature.     

Rapid solidification and phase stability evaluation of Ti-Si-B alloys

Ti-rich Ti-Si-B alloys can be considered for structural applications at high temperatures (max. 700 °C), however, phase equilibria data is reported only for T = 1250 °C. Thus, in this work the phase stability of this system has been evaluated at 700 °C. In order to attain equilibrium conditions in shorter time, rapid solidified samples have been prepared and carefully characterized. The microstructural characterization of the produced materials were based on X-ray diffraction (XRD), scanning electron microscopy (SEM-BSE), high resolution transmission electron microscopy (HRTEM), High Temperature X-ray diffraction with Synchrotron radiation (XRDSR) and Differential Scanning Calorimetry (DSC). Amorphous and amorphous with embedded nanocrystals have been observed after rapid solidification from specific alloy compositions. The values of the crystallization temperature (Tx) of the alloys were in the 509-647 °C temperature range. After Differential Scanning Calorimetry and High Temperature X-ray Diffraction with Synchrotron radiation, the alloys showed crystalline and basically formed by two or three of the following phases: αTi, Ti₆Si₂B; Ti₅Si₃; Ti₃Si and TiB. It has been shown the stability of the Ti₃Si and Ti₆Si₂B phases at 700 °C and the proposition of an isothermal section at this temperature.     

Hot corrosion and oxidation behavior of a novel Pt + Hf-modified γ′-Ni3Al + γ-Ni-based coating

A new type of Pt + Hf-modified γ′-Ni₃Al + γ-Ni-based coating has been developed in which deposition involves Pt electroplating followed by combined aluminizing and hafnizing using a pack cementation process. Cyclic oxidation testing of both Pt + Hf-modified γ′ + γ and Pt-modified β-NiAl coatings at 1150 °C (2102 °F), in air, resulted in the formation of a continuous and adherent α-Al₂O₃ scale; however, the latter developed unwanted surface undulations after thermal cycling. Type I (i.e. 900 °C/1652 °F) and Type II (i.e. 705 °C/1300 °F) hot corrosion behavior of the Pt + Hf-modified γ′ + γ coating were studied and compared to Pt-modified β and γ + β-CoCrAlY coatings. Both types of hot corrosion conditions were simulated by depositing Na₂SO₄ salt on the coated samples and then exposing the samples to a laboratory-based furnace rig. It was found that the Pt + Hf-modified γ′ + γ and Pt-modified β coatings exhibited superior Type II hot corrosion resistance compared to the γ + β-CoCrAlY coating; while the Pt + Hf-modified γ′ + γ and γ + β-CoCrAlY coatings showed improved Type I hot corrosion performance than the Pt-modified β.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Studies on the development of TZM alloy by aluminothermic coreduction process and formation of protective coating over the alloy by plasma spray technique

TZM alloy is a potential candidate for high temperature structural applications. However, in the preparation of this alloy by conventional melt-casting route, difficulties are encountered in achieving homogenized alloy composition in view of high melting temperature of the alloy and presence of minor alloying components. Therefore, an alternative technique of aluminothermic co-reduction was adopted to prepare TZM alloy of composition, Mo-0.5Ti-0.1Zr-0.02 °C, wt.% by simultaneous reduction of uniformly premixed oxides of MoO₂, TiO₂ and ZrO2 by aluminium in presence of requisite amount of carbon. The as-reduced alloy was further arc melted for consolidation. Since, TZM alloy is by nature highly susceptible to oxidation at elevated temperature in air or oxygen, therefore feasibility of development of silicide type of coating over the synthesized alloy by plasma coating technique was also examined. Silicon powder coated on TZM alloy surface by plasma spray technique was finally converted into MoSi₂ coating by sintering at 1350 ^°C for 2-4 h duration under argon. A double layer coating structure was formed with two distinct phases. The inner thin layer was consisted of Mo₂Si₅ phase (~ 10 μm) followed by thick outer layer of MoSi₂ (~ 150 μm). The coating showed good adhesion strength and stable oxidation with negligible mass gain (10 g/m²) at 1000 ^°C in air.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Onset of thermal degradation in poly(p-phenylene vinylene) films deposited by chemical vapor deposition

We report on the thermal degradation characteristics of heat treated poly(p-phenylene vinylene) (PPV) films deposited using chemical vapor deposition. It was found that no decrease in the thickness of the films (110 nm) occurred after isothermal heat treatment in vacuum at 450 °C for up to 1 h, while films treated at 500 °C for 1 h decreased to 70% of their original thickness. In situ mass spectrometry during heat treatment of the film at 500 °C showed the release of significant amounts of material including toluene and xylene ion fragments. However, Fourier transform infrared spectroscopy shows no significant change in bond structure, indicating that the decrease in film thickness after heat treatment is due to release of material and densification, not crosslinking or bond breaking.     

Phase equilibria of the Cu-Ni-Si system at 700 °C

The phase equilibria at the isothermal section of the Cu-Ni-Si system at 700 °C were experimentally investigated. Thirty Cu-Ni-Si alloys were prepared by arc melting and annealed at 700 °C for 30 or 80 days, and examined with optical microscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and electron probe microanalysis. Twelve three-phase regions were determined. The existence of the ternary compound τ₁-Cu_56.8-63Ni_10.4-16.1Si_26.6-27.3 reported in literature was confirmed and a new compound τ₂-Cu_45.8Ni₂₅Si_29.2 with nearly no homogeneity range was observed. The θ-Ni₂Si compound, which exists above 820 °C in the binary Ni-Si system, was found to be stable at 700 °C and the composition range of Cu is 12.7-20.6 at.% Cu. The ternary solubilities of binary compounds were measured and noticeably the Cu₅₆Si₁₁ compound can dissolve Ni up to 21.9 at.%.