Isothermal Aging Conditions Research Articles

Investigation of isothermal aged Sn-3Ag-0.5Cu/Sn58Bi-Co hybrid solder joints on ENIG and ENEPIG substrate with various mechanical performances

The stability of solder joints is of utmost critical in electronic equipment. The integration of packaged devices in these systems often leads to the generation of heat, which might have a significant impact on how long the equipment lasts when exposed to high temperatures. It is imperative to perform an isothermal aging test on the solder joints in order to replicate the extended use of these joints. This research looked into how the mechanical characteristics and IMC growth of hybrid solder joints were affected by isothermal aging over 240 h, 480 h and 720 h. The reliability of solder joint under isothermal aging condition was improved by adding Pd coating and Co element. The results revealed that Pd coating over ENIG (Electroless Nickel Immersion Gold) pad reduced the growth rate of IMC in SAC305/SnBi hybrid solder joints during isothermal aging. ENIG solder joint strength dropped by 57.66% after 720 h of isothermal aging, and practically all fractures were IMC fractures. ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) shear strength lowered 31.01%, IMC fracture mode 20%, strong reliability at high temperature. IMC development was suppressed in SAC305/SnBi-Co hybrid solder joints by higher Co content. After 720 h isothermal aging, SAC305/SnBi-Co solder joints had better shear strength than non-Co joints. According to fracture morphology, SAC305/SnBi-Co hybrid solder joints reliability improves owing to the change of IMC morphology and grain refining.

Growth kinetics and IMCs layer analysis of SAC305 solder with the reinforcement of SiC during the isothermal aging condition

The Sn–3.0wt.%Ag–0.5wt.%Cu(SAC305) - xSiC composite solder was prepared by powder metallurgy method with the addition of SiC ceramic reinforcement with various compositions (0, 0.5, 1, and 1.5wt.%). The IMC layer thickness of Cu3Sn and Cu6Sn5 was suppressed during 100 h aging and the minimum thickness was found for 1.0wt.% SiC addition. The SAC305-1.0wt.%SiC/Cu was then subjected to different aging conditions (413, 423, 433, and 443 K). The IMCs thickness at the Cu-solder interface was investigated by using FIB-SEM and image analysis software (ImageJ). The SiC and Ag3Sn particles were identified in the matrix's bulk area, and the growth kinetics were examined in a detailed manner in aging conditions. Diffusion coefficients and activation energies for the two mentioned IMCs were plotted as a temperature function, and the values were calculated by the Arrhenius equation.

Effect of multi-walled carbon nanotubes on DC electrical conductivity and acetone vapour sensing properties of polypyrrole

• First time utilization of PPy/MWCNTs nanocomposite for acetone vapour sensing. • Effect of MWCNTs on thermal stability, electrical conductivity and acetone sensing performance of PPy. • Conductivity of PPy increased from 0.16 Scm −1 to 2.27 Scm −1 by incorporating MWCNTs. • Sensing performance in terms of sensing response, reversibility and long term stability. • PTh/MWCNTs sensor showed 7.44 times greater response than PPy sensor at 0.01 vol% acetone concentration. Polypyrrole (PPy) and polypyrrole/multi-walled carbon nanotubes nanocomposite (PPy/MWCNTs) were synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmittance electron microscopy (TEM) and thermogravimetric analysis (TGA). PPy and PPy/MWCNTs were converted into pellets which were used in conductivity and acetone sensing experiments. The initial electrical conductivity of PPy increased from 0.16 Scm −1 to 2.27 Scm −1 by loading of MWCNTs into PPy matrix. At the same time, PPy/MWCNTs showed excellent conductivity retention properties as compared to PPy under both the isothermal and cyclic ageing conditions. A comparative acetone vapour sensing studies were carried out on PPy and PPy/MWCNTs sensors at different acetone concentration, i.e., 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.04, 0.03, 0.02 and 0.01 vol%. The PPy/MWCNTs sensor offered much-improved acetone vapour sensing performance as compared to PPy in terms of sensing response, reversibility and long term stability. PPy/MWCNTs sensor exhibited 2.44, 2.82, 3.06, 3.28, 3.88, 5.0, 5.42, 6.02, 6.08 and 7.44 times greater% sensing response than PPy sensor at 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.04, 0.03, 0.02 and 0.01 vol% acetone concentration, respectively.

Interface reaction and mechanical properties of Sn58Bi-XCr/Cu30Zn (Cu7Sn) solder joints under isothermal aging conditions

The interfacial reaction and mechanical properties of Sn58Bi-XCr/Cu30Zn and Sn58Bi-XCr/Cu7Sn (X = 0, 0.1, 0.2, 0.3 wt%) composite solder joints were investigated under 100 °C isothermal aging. The results show that the growth rate of intermetallic compound layer (IMCs) of Sn58Bi-XCr/Cu30Zn composite solder joint is faster than that of Sn58Bi-XCr/Cu7Sn composite solder joint, and the rapid growth of IMCs decreases the mechanical properties of the solder joint. As the aging time increases, the thickness of IMCs layer becomes thicker and the mechanical properties decrease. The addition of Cr inhibits the interdiffusion of atoms at the interface. The addition of Zn/Sn reduces the consumption of Sn and thus reduces the segregation of Bi phase. The Bi segregation at the interface of Sn58Bi-0.2Cr/Cu30Zn and Sn58Bi-0.2Cr/Cu7Sn composite solder joints is improved obviously. In addition, the comprehensive mechanical properties of Sn58Bi-XCr/Cu30Zn composite solder joint are higher than those of Sn58Bi-XCr/Cu7Sn composite solder joint. With the extension of aging time, mechanical strength increases first and then decreases. Among them, the mechanical strength of Sn58Bi-0.2Cr/Cu30Zn and Sn58Bi-0.2Cr/Cu7Sn composites is superior to other alloys. The fracture morphology of solder joints changes from brittle fracture mechanism to ductile-brittle fracture mechanism.

Electrical conductivity based ammonia, methanol and acetone vapour sensing studies on newly synthesized polythiophene/molybdenum oxide nanocomposite

Polythiophene (PTh) and polythiophene/molybdenum oxide nanocomposites (PTh/MoO 3 ) were synthesized by an in-situ chemical oxidative method. The successful synthesis of both the materials was confirmed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The thermal stability of the materials was examined in terms of conductivity retention under isothermal and cyclic aging conditions. PTh/MoO 3 showed much greater conductivity retention (i.e., thermal stability) than pristine PTh under both conditions. PTh/MoO 3 showed 18.22 times greater electrical conductivity than pristine PTh at room temperature. The sensing properties of PTh and PTh/MoO 3 were tested against ammonia, methanol, and acetone vapour at room temperature. The percent sensing response (%) of the PTh/MoO 3 sensor was found to be about 1.64, 1.44, and 1.48 times greater than the PTh sensor towards ammonia, methanol, and acetone at 1 M, respectively. The PTh/MoO 3 sensor showed 1.48, 1.60, and 1.72 times greater reproducibility than the PTh-based sensor towards ammonia, methanol, and acetone, respectively. Thus, at a 1 M concentration of ammonia, methanol, and acetone, the PTh/MoO 3 sensor performed much better than the PTh sensor in terms of the sensing response and reproducibility. Furthermore, the PTh/MoO 3 sensor showed a maximum and minimum sensing response towards ammonia and acetone, respectively.

Interfacial reaction and mechanical properties of Sn58Bi-XCr solder joints under isothermal aging conditions

Sn–Bi solder is considered a promising lead-free solder which meets the performance requirements with the advantages of low melting point, good wettability and mechanical properties. The interfacial reaction and mechanical properties of Sn58Bi-XCr (X = 0, 0.1, 0.2, 0.3) composite solder joints have been studied. After isothermal aging treatment at 100 °C, the microstructure and reaction mechanism of the interface were analyzed. The results show that the microstructure of Sn58Bi composite solder joint with 0.2wt.% Cr element is obviously refined. At the same time, the average thickness of the interface intermetallic compounds (IMCs) becomes thinner with the addition of Cr content. In addition, the tensile strength of Sn58Bi composite solder joint decreases gradually with the extension of aging time, but the tensile property of Sn58Bi-0.2Cr is better than that of other alloy components. However, with the extension of aging time, the shear strength of Sn58Bi composite solder joints generally decreases at first and then increases, and the fracture morphology of solder joints changes from brittle fracture mechanism to ductile fracture mechanism.

Shear Strength Degradation Modeling of Lead-Free Solder Joints at Different Isothermal Aging Conditions

Abstract SAC-based alloys are one of the most common solder materials that are utilized to provide mechanical support and electrical connection between electronic components and the printed circuit board. Enhancing the mechanical properties of solder joints can improve the life of the components. One of the mechanical properties that define the solder joint structure integrity is the shear strength. The main objective of this study is to assess the shear strength behavior of SAC305 solder joints under different aging conditions. Instron 5948 Micromechanical Tester with a customized fixture is used to perform accelerated shear tests on individual solder joints. The shear strength of SAC305 solder joints with organic solderability preservative (OSP) surface finish is investigated at constant strain rate under different aging times (2, 10, 100, and 1,000 h) and different aging temperatures (50, 100, and 150°C). The nonaged solder joints are examined as well for comparison purposes. Analysis of variance (ANOVA) is accomplished to identify the contribution of each parameter on the shear strength. A general empirical model is developed to estimate the shear strength as a function of aging conditions using the Arrhenius term. Microstructure analysis is performed at different aging conditions using scanning electron microscope (SEM). The results revealed a significant reduction in the shear strength when the aging level is increased. An increase in the precipitates coarsening and intermetallic compound (IMC) layer thickness are observed with increased aging time and temperature.

Fabrication of Reproducible and Selective Ammonia Vapor Sensor-Pellet of Polypyrrole/Cerium Oxide Nanocomposite for Prompt Detection at Room Temperature.

Polypyrrole (PPy) and polypyrrole/cerium oxide nanocomposite (PPy/CeO2) were prepared by the chemical oxidative method in an aqueous medium using anhydrous ferric chloride (FeCl3) as an oxidant. The successful formulation of materials was confirmed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmittance electron microscopy (TEM). A four-in-line probe device was used for studying DC electrical conductivity and ammonia vapor sensing properties of PPy and PPy/CeO2. The significant improvement in both the conductivity and sensing parameters of PPy/CeO2 compared to pristine PPy reveals some synergistic/electronic interaction between PPy and cerium oxide nanoparticles (CeO2 NPs) working at molecular levels. The initial conductivity (i.e., conductivity at room temperature) was found to be 0.152 Scm−1 and 1.295 Scm−1 for PPy and PPy/CeO2, respectively. Also, PPy/CeO2 showed much better conductivity retention than pristine PPy under both the isothermal and cyclic ageing conditions. Ammonia vapor sensing was carried out at different concentration (0.01, 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 vol %). The sensing response of PPy/CeO2 varied with varying concentrations. At 0.5 vol % ammonia concentration, the % sensing response of PPy and PPy/CeO2 sensor was found to be 39.1% and 93.4%, respectively. The sensing efficiency of the PPy/CeO2 sensor was also evaluated at 0.4. 0.3, 0.2, 0.1, 0.05, 0.03, and 0.01 vol % ammonia concentration in terms of % sensing response, response/recovery time, reversibility, selectivity as well as stability at room temperature.

DC electrical conductivity retention and acetone/acetaldehyde sensing on polythiophene/molybdenum disulphide composites

In this study, polythiophene (PTh) and a series of polythiophene/molybdenum disulphide (PTh/MoS2) composites were prepared by in-situ chemical oxidative polymerization method using anhydrous ferric chloride (FeCl3) as an oxidant and chloroform (CHCl3) as a solvent. The successful formation of PTh and PTh/MoS2 composites were confirmed by various techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmittance electron microscopy (TEM). DC electrical conductivity and acetone/acetaldehyde sensing studies were carried out by a four-in-line probe device. PTh/MoS2 composites exhibited significantly improved DC electrical conductivity and acetone/acetaldehyde sensing properties as compared to PTh. The electrical properties were investigated in terms of initial conductivity (i.e. conductivity at room temperature) as well as retention of conductivity, i.e. stability under isothermal and cyclic ageing conditions. The maximum initial conductivity, along with the highest conductivity retention, was observed for PTh/MoS2-2 (PTh/MoS2 composite comprising 10% MoS2 with respect to the weight of thiophene monomer). The initial DC electrical conductivity of PTh, PTh/MoS2-1, PTh/MoS2-2 and PTh/MoS2-3 was found to be 5.72 × 10−5 Scm−1, 4.03 × 10−4 Scm−1, 1.09 × 10−3 Scm−1 and 8.96 × 10−4 Scm−1, respectively. The sensing performance at room temperature has been studied in terms of % sensing response, response/recovery time. All the PTh/MoS2 composites based sensors performed much better than PTh. The % sensing response of PTh, PTh/MoS2-1, PTh/MoS2-2 and PTh/MoS2-3 based pellet-shaped sensors towards acetone/acetaldehyde were affirmed as 30.6/22.9, 69.9/47.3, 93.7/70.3, 78.1/65.1, respectively. The purposed sensing mechanism involved the adsorption of acetone/acetaldehyde vapours on the surface of the sensors where electronic interaction between lone pair of electrons on oxygen atoms of the carbonyl group and charge carriers of PTh was responsible for the change in conductivity.

Failure mechanism of plasma-sprayed thermal barrier coatings under high-temperature isothermal aging conditions

The failure of thermal barrier coatings (TBCs) is caused by the stress generated during service owing to the different physical properties and high-temperature behavior of the ceramic top coat made of Y2O3–ZrO2, thermally grown oxide (TGO) primarily composed of β-Al2O3 that forms and grows at high temperature, and metallic bond coat and substrate materials. The operating environment of TBCs varies depending on the objective of use and the operation stage of the gas turbine to which it is applied; therefore, it is important to understand the stress state by considering the operation environment. In this study, we analyzed the failure of TBCs in an operation environment when they were subjected to high-temperature conditions for a long time. For this, the effects of thermal expansion misfit, creep, and TGO growth on the high-temperature stress states were evaluated and analyzed systematically through finite element analysis(FEA.) The failure mechanism under a high-temperature isothermal condition was presented, considering degradation phenomena such as TGO growth rate decrease and creep rate reduction. It reveals that in the early stage of degradation at high temperatures, a valley-to-valley crack propagation was induced; however, at relatively low temperatures, changes in behavior during long-term exposure caused a peak-to-peak crack propagation. Additionally, the proposed mechanism was verified through analysis of the residual top coat area of the surface of the TBC specimen that was delaminated during the isothermal aging tests performed at different temperatures; this is important because the results of the analysis could not be explained by the mechanisms of previous studies in which cooling stresses under thermal cyclic conditions were focused.

Three-dimensional Phase-field simulation of γ″ precipitation kinetics in Inconel 625 during heat treatment

Metastable γ″ (D022-Ni3Nb) particles are strengthening precipitates for commercial Inconel 625 Ni-based superalloy. Understanding their morphological evolution is critical for evaluating its hardening effects and guiding heat treatments to improve its yield strength. Here we present a phase-field model to model and analyze the nucleation and growth kinetics of metastable γ″ in Inconel 625 during isothermal and non-isothermal aging conditions with thermodynamic properties, diffusion coefficients, and misfit strain data from both the literature and calibration to experimental results. We implemented the classical nucleation theory to introduce local nucleation taking into account local supersaturation. The simulated mean particle length and aspect ratio are in agreement with experimental data at 600 °C and 650 °C during isothermal aging. Utilizing the phase-field simulation results as input parameters, the coherency strengthening effect of γ″ as a function of aging temperature and time is predicted. A multistage aging strategy to optimize the γ″ strengthening effect and to reduce aging times using the developed phase-field model and coherency strengthening model is suggested.

Impact of Mechanical Property Degradation and Intermetallic Compound Formation on Electromigration-Oriented Failure of a Flip-Chip Solder Joint

Due to the increased complexity and optimization in microprocessor packaging from 2D to 3D packages, the size of solder joints is being reduced significantly. This trend currently leads to an increased amount of current density across flip-chip solder joints as well as microbumps and causes electromigration-oriented void formation and subsequent failure of the solder joints. It has been observed from literature that solder material undergoes microstructure evolution and subsequent degradation of mechanical properties under isothermal aging conditions. The current study is based on the effects of material property degradation due to thermal aging of flip-chip Sn-Ag-Cu (SAC) solder joints on electromigration-oriented failure. Finite element analysis has been used to analyze the diffusion characteristics of a SAC solder joint under isothermal aging conditions of 100°C for a period of 1–20 days, and electromigration simulation has been performed at two different temperatures of 100°C and 125°C for 100 h at an input current range of 0.01–0.05 A. The effect of intermetallic compound (IMC) layer thickness is analyzed to reveal the impact on electromigration-oriented failure in isothermally 60 days long aged solder bumps. Results have revealed that resistance to electromigration-oriented failure is higher in the case of aged components compared to unaged components along with the increment of time to failure with IMC formation in the SAC solder joint.

Synthesis and Antibacterial Aspects of Graphitic C3N4@Polyaniline Composites

In this work, Pani and Pani@g-C3N4 was synthesized by in situ oxidative polymerization methodology of aniline, in the presence of g-C3N4. The as prepared Pani@g-C3N4 was characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction (XRD). The morphological analysis showed well dispersed Pani in g-C3N4, as well as the coating of Pani on g-C3N4. The XRD further revealed this, and peaks of Pani as well as g-C3N4 was observed, thereby suggesting successful synthesis of the composite. The DC electrical conductivity studies under isothermal and cyclic aging conditions showed high stability of composites over 100 °C. Further, the synthesized composite material proved to be an excellent antimicrobial agent against both type i.e., gram positive Streptococcus pneumoniae and negative bacteria Escherichia coli. In the zone inhibition assay 18 ± 0.5, 16 ± 0.75 and 20 ± 0.5, 22 ± 0.5 mm zone diameter were found against E. coli and S. pneumoniae in presence of pure g-C3N4 and Pani@g-C3N4 at 50 µg concentrations, respectively. Further antimicrobial activity in the presence of sunlight in aqueous medium showed that Pani@g-C3N4 is more potent than pure g-C3N4.

Precipitate Characterization in Model Al-Zn-Mg-(Cu) Alloys Using Small-Angle X-ray Scattering

Model 7000 series alloys with and without copper were fabricated into sheets to study precipitation hardening behavior under isothermal aging conditions. Samples of each alloy were subjected to 3 h annealing treatments at various temperatures to produce a range of precipitate size distributions. Hardness, electrical conductivity, and small-angle X-ray scattering (SAXS) were used to characterize the aging behavior of the two alloys. Precipitate size distributions were modeled from the scattering curves for each annealing condition using a maximum entropy method (MEM) and compared to select transmission electron microscopy (TEM) results. The measured average precipitate diameters from TEM were in good agreement with the average precipitate diameters determined from the scattering curves.

Effects of isothermal aging on interfacial microstructure evolution and shear behavior of Au-12Ge/Ni(P)/Kovar Solder Joints

Au-12Ge(wt.%) eutectic solder is widely used in electronic packaging thanks to its good electrical conductivity, solderability, and chemical stability. To investigate the stability of Au-12Ge solder during high-temperature service, the effects of different isothermal aging conditions on the microstructure and performance of Au/Ni(P)/Kovar substrate after soldering were investigated. Solder joints produced at 400 °C for 1 min showed excellent wetting behavior with NiGe/Ni5Ge3/Ni3(P,Ge) intermetallic layers formed at the interface. The thickness of generated interfacial intermetallic compounds was estimated to only 1.56 μm due to the amorphous nature of Ni-P coating that hindered the diffusion of Ni atoms. As aging increased with time and temperature, the interfacial intermetallic compounds grow further, leading to deterioration and failure of solder joints. The growth mechanism of interfacial intermetallic compounds was then examined, and activation energy was estimated to 95.4 kJ/mol. In turn, shear strength of solder joints declined and fracture mode became brittle as aging time and temperature increased. Meanwhile, fracture position evolved from IMC layer to Ni-P layer. At aging temperatures above 290 °C, Ni-P layer showed crystallization transition to porous Ni3P, leading to formation of holes and cracks, and resulting in exfoliation of coating with Kovar substrate.

Polythiophene/graphene/zinc tungstate nanocomposite: Synthesis, characterization, DC electrical conductivity and cigarette smoke sensing application

Herein, we are reporting the synthesis and characterization of polythiophene (PTh) and its novel nanocomposites with zinc tungstate (ZT) and graphene/zinc tungstate (G/ZT) hybrid for Direct current (DC) electrical conductivity based cigarette smoke sensing at room temperature. X-ray diffraction, Fourier-transform infrared, Raman, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible spectroscopy and thermogravimetric analysis techniques were used for the characterization of the as-prepared materials. The results showed that the DC electrical conductivity and sensing performance of PTh significantly improved by incorporation of ZT and G/ZT into it. PTh/G/ZT-3 (i.e. PTh/G/ZT nanocomposite containing 15 wt% G/ZT) was found to be the best sensor in terms of sensing response (81.5%) and reversibility (90.55%) along with the most stable semiconductor under isothermal and cyclic ageing conditions. Sensing response of PTh/G/ZT-3 was also tested in the exposure to various components of cigarette smoke (namely ammonia, carbon dioxide, ethanol, formaldehyde, acetone, benzene, toluene, phenol) and the highest sensing response was observed in the exposure to ammonia. The significant increase in conductivity of PTh/G/ZT nanocomposites was explained by the transfer of polarons from PTh to graphene, that is, creation of a hole in graphene where they achieved rapid mobility along with the extended π-conjugated system. Finally, a sensing mechanism was proposed through adsorption–desorption of cigarette smoke on the surface of PTh/G/ZT where electronic interactions between polarons of PTh and various components of cigarette smoke (mainly ammonia and ethanol) affected the change in DC electrical conductivity.

On the modelling of precipitation kinetics in a turbine disc nickel based superalloy

The precipitation kinetics of gamma prime in the nickel based superalloy RR1000 has been characterised after solid-solution heat treatments and isothermal aging conditions relevant to service conditions. Multi-modal precipitate dispersions are formed within the alloy. Numerical methods are presented for determining the three dimensional size of the particle populations combining information obtained from Scanning Electron microscopy and Transmission Electron microscopy. This information has been used to develop a multi-component mean-field model descriptive of precipitation kinetics. The smallest particle population increases in mean size during isothermal aging at 700 ∘C where classical mean-field models of coarsening kinetics suggest that these particles should dissolve. A phenomenological model has been proposed to capture this behaviour within a statistical formulation that is applicable to both processing and service conditions.

Electrical conductivity and alcohol sensing studies on polythiophene/tin oxide nanocomposites

Abstract Conducting polymer-based sensors have short response time at room temperature besides their good electrical conductivity. However, the poor electrical conductivity retention at a higher temperature and the failing reproducibility of sensors which are based on conducting polymers are an area of concern. To this end, we are reporting the preparation of polythiophene (PTh) and polythiophene/Tin oxide (PTh/SnO2) nanocomposites by an in-situ chemical oxidative polymerisation. The as-prepared materials were characterized by FTIR, SEM, UV-vis absorbance spectroscopy, TEM and XRD techniques. PTh/SnO2-3 (i.e. PTh/SnO2 nanocomposite containing 15% SnO2 nanoparticles) showed the highest DC electrical conductivity (9.82 × 10−3 S⋅cm−1) in addition to a maximal stability as a function of DC electrical conductivity retention under accelerated isothermal and cyclic ageing conditions. We utilized PTh/SnO2-3 to fabricate a novel pellet-shaped sensor for the selective detection of some of the higher alcohols, such as butan-1-ol (1° alcohol), butan-2-ol (2° alcohol), and 2-methyl propanol (3° alcohol) at room temperature. PTh/SnO2-3 exhibited the highest response in terms of variation in DC electrical conductivity and maximal reproducibility for butan-1-ol. Finally, the sensing mechanism was explained by the adsorption–desorption process of alcohol vapours on the large surface area of the PTh/SnO2 nanocomposites where electronic interactions between the lone pairs of electrons of alcohol molecules with the polarons of PTh cause the change in the DC electrical conductivity.

The Role of Tungsten on the Phase Transformation Kinetics and its Correlation with the Localized Corrosion Resistance of 25Cr Super Duplex Stainless Steels

Super Duplex Stainless Steels (SDSS) have excellent corrosion resistance due to their high concentration of alloying elements like Cr, Mo, and N. There is still, however, disagreement on the role of tungsten in the corrosion resistance of stainless steels. In this regard, the influence of tungsten on tertiary phase precipitation kinetics remains a chief source of controversy. In this study, three different SDSS with different tungsten contents have been investigated, namely, UNS S32750 (W-free), S32760 (0.6 wt% W), and S39274 (2.1 wt% W). Different isothermal aging conditions were studied, followed by microstructure characterization using scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, and transmission electron microscopy to quantify the type and volume fraction of tertiary phases and intermetallic compounds. Time-Temperature-Transformation-Corrosion maps were constructed by quantifying the changes in pitting corrosion resistance caused by the precipitation of incremental amounts of deleterious phases. Results showed that 2.1 wt% W additions retarded the precipitation kinetics of all tertiary phases—including σ-phase—favoring the formation of χ-phase. Both χ- and σ-phase affected corrosion resistance, reducing the critical pitting temperature by 10 °C–20 °C at concentrations well below 1 vol%.

Precipitation Behavior of Ti15Mo Alloy and Effects on Microstructure and Mechanical Performance

Precipitation behaviors of Ti15Mo alloy subjected to 3, 5, 10 and 20 °C/min cooling from the β phase field were investigated, and the variation trend of the activation energy during the cooling process was analyzed with DSC measurements and the Flynn–Wall–Ozawa method. The texture and microstructure of the phase transformation in different isothermal aging conditions were analyzed with XRD and TEM. The patterns of ω and ω/α in specimens aged at 450 and 500 °C show that β → ω and β → ω/α phase transformations occur, respectively. XRD spectra and SAD patterns illustrate that the precipitates transformed during aging over 525 °C are α phase. The morphology of the precipitation indicates that the size of the α phase formed in the isothermal treatment increases with increasing aging temperature. In contrast, the intensity of the (10-11)α texture decreases with increasing aging temperature. The tensile properties and fractures were investigated to determine the correlation between phase transformation and mechanical performance. The alloy has the highest ultimate tensile strength (UTS) at 1440 MPa because the ω phases transform during aging at 450 °C. A good combination of tensile properties, with a UTS of 970 MPa and an elongation of 14.5%, was obtained in the specimen aged at 550 °C for 8 h.