Effect Of High-temperature Aging Research Articles

The effect of high temperature aging on fluorescence properties of Eu3+-doped La2(Zr0.7Ce0.3)2O7

Introduction of luminescent rare earth ions into thermal barrier coatings (TBCs) for the study of TBCs failure mechanism is a very effective non-destructive method. In this paper, Eu3+ ions were doped into La2(Zr0.7Ce0.3)2O7 (LZ7C3) to form LZ7C3:Eu fluorescent material using a high-temperature solid-phase synthesis method. By analyzing the physical structure, fluorescence properties and thermophysical properties of LZ7C3:Eu powders synthesized with different Eu3+ dopant concentrations at different temperatures, we determined that a synthesis temperature of 1400 °C, a dopant concentration of 1 mol% are the optimal synthesis conditions for LZ7C3:Eu. Independent LZ7C3:Eu coating was prepared by atmospheric plasma spraying technology, and high temperature aging test was carried out at 1400 °C. The influence of high temperature aging on the 5D0→7F2 energy level transition peak of Eu3+ in LZ7C3 powder and its coating was examined by microscopic emission spectroscopy. The results show that the peak of the 5D0→7F2 energy level transition is red-shifted, and the peak intensity and the full width at half maxima (FWHM) of the powder decrease gradually with the increase of high temperature aging time. The peak of the 5D0→7F2 energy level transition of the coating exhibits a constantly fluctuating tendency of red-shifting and then blue-shifting, and the peak intensity and the FWHM also continue to decrease. High temperature aging has a negative effect on the fluorescence properties of LZ7C3:Eu materials.

Significant hardening effect of high-temperature aging of alloy Ti-6Al-4V composite reinforced with TiC

Titanium alloy composites, reinforced with a light second phase and made using inexpensive powder metallurgy, attract considerable attention due to the directness of their intentional hardness increase without compromising low weight of materials. In this study the metal-matrix composites (MMC) of Ti-6Al-4V alloy reinforced with light and hard particles of TiC (up to 80%, vol.) were made using blended elemental powder metallurgy of hydrogenated titanium. Post-sintering solution treatment for 45 min. at 880 °C and 1000 °C and water quenching followed by the 5 hrs. aging at 550 °C was used to additionally refine the microstructure and properties of MMC. For the duration of thermal exposure throughout solution treatment and additional aging the matrix and reinforcement phase underwent distinct structural changes that modified the mechanical properties of materials. It has been shown that the used reinforcement presents an exceptional opportunity for hardening of Ti-based composites without compromising their low specific weigh. It can increase the hardness of material by more than 40% due to the ability of TiC to chemically react with the matrix to form a strong interfacial bond and its ability to form hard compounds of Ti2C and Ti3AlC in the expense of the relatively soft matrix alloy.

Effect of high-temperature aging on microstructure properties of Sn96.5%Ag3-Cu0.5% (SAC305) lead-free solder joints

The use of Sn96.5%Ag3%Cu0.5% (SAC305) as lead-free solder is increasing rapidly as an interconnection for electronic devices. Electronic devices face harsh environmental applications during the operation which can reach temperatures of 200 °C and expose soldiers. The microstructure properties of lead-free solders are highly dependent on the process and operating parameters such as salty water, moisture, and high temperature. In this study, the effects of aging (storing) the samples at high temperatures on SAC305 alloy were investigated as a function of microstructure characterization. Microstructure morphologies are evaluated regarding the growth of inter-metallic compounds IMCs (Ag3Sn and Cu6Sn5) and grain size. The scanning electron microscope (SEM) and optical microscope were used to analyze the microstructure of Sn grain morphology. Also, to investigate the elemental distribution, energy dispersive spectroscopy (EDS) was used. The results show distinct changes in the microstructure of SAC305 solder alloy due to the aging effect; the quantitative analysis of grain size and intermetallic particle support this result.

Long-Term Conductivity Stability of Electrolytic Membranes of Scandia Stabilized Zirconia Co-Doped with Ytterbia.

The effect of high-temperature aging for 4800 h at a temperature of 1123 K on the crystal structure and the conductivity of (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 and (ZrO2)0.90(Sc2O3)0.08(Yb2O3)0.02 single-crystal membranes were studied. Such membrane lifetime testing is critical to the operation of solid oxide fuel cells (SOFCs). The crystals were obtained by the method of directional crystallization of the melt in a cold crucible. The phase composition and structure of the membranes before and after aging were studied using X-ray diffraction and Raman spectroscopy. The conductivities of the samples were measured using the impedance spectroscopy technique. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition showed long-term conductivity stability (conductivity degradation not more than 4%). Long-term high-temperature aging of the (ZrO2)0.90(Sc2O3)0.08(Yb2O3)0.02 composition initiates the t″ → t' phase transformation. In this case, a sharp decrease in conductivity of up to 55% was observed. The data obtained demonstrate a clear correlation between the specific conductivity and the change in the phase composition. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition can be considered a promising material for practical use as a solid electrolyte in SOFCs.

A Study on Aging Fracture Behavior of Sintered Joint by Bi-Modal Cu Paste

Power semiconductors for automobiles were joined by high Pb soldering to joint properties at high temperatures during operations. However, this process is being replaced by low-temperature sintering. In the low-temperature sintering bonding method, Cu powder is low-cost and exhibits high-performance material and excellent bonding properties. In this study, the effect of high-temperature aging on Cu paste sintered joints and the failure mechanism of the shear test were investigated. Cu monomodal and bimodal pastes were manufactured, and electroless nickel immersion gold (ENIG) surface treatment was applied on the Cu chip side. In the ENIG-treated joints, a significant number of Kirkendall voids were observed at the interface under Au after 2,000 h at 200 °C, and Cu2O was also formed. This is attributed to the difference between the interdiffusion coefficients of Au and Cu, which decreases the shear strength of the junction and rapidly increases the electrical resistance. After the shear strength tests, the crack propagation pattern at the interface of the ENIG-treated joint was confirmed via cross-section scanning electron microscopy. Future studies on surface treatment are required to clarify the long-term stability of the joints.

Reliability of SnPbSb/Cu Solder Joint in the High-Temperature Application

With the continuous miniaturization and increase in functionality of the electronic devices used in the aerospace and national defense industries, the requirements for reliability of the solder joints in these devices keep increasing. In this study, a SnPbSb solder with excellent wettability was used as the research object, and the effects of high-temperature aging at 150 °C on the microstructure and mechanical properties of SnPbSb/Cu solder joints were investigated according to the relevant industry standards. It was found that high-temperature aging does not change the eutectic structure of the SnPbSb solder, but it does significantly coarsen the Sn-rich phase and the Pb-rich phase in the solder. In addition, the interfacial intermetallic compound (IMC) layer in the SnPbSb/Cu solder joint changes from a Cu6Sn5 single layer to a Cu6Sn5/Cu3Sn double layer after the aging, and the thickness of the IMC layer increases greatly. High-temperature aging significantly deteriorates the mechanical properties of the solder joints. After aging at 150 °C for 1000 h, the shear strength of the SnPbSb/Cu solder joints decreased by 45.39%, while the ductile fracture mode did not change.

Microstructure evolution and mechanical properties of 16Cr–25Ni superaustenitic stainless steel weld metal during 600 °C aging

The effect of high temperature aging on the microstructure evolution and mechanical properties of 16Cr–25Ni superaustenitic stainless steel weld metal was investigated at 600 °C for up to 5000 h. Interdendritic micro-size M6C carbide, nano-size M6C and M23C6 carbides were identified in the 200 h aged weld metal, which appeared in clusters and distributed dispersedly. With the aging time increased to 1000 h, the interdendritic region was filled with newly formed precipitates, which were identified as nano-size M12C and M23C6 carbides. Compared with M6C carbide, M12C carbide was preferred to precipitate for lower Gibbs free energy, and the pre-existed M6C carbide had transformed to M12C carbide through the release of C atoms to the matrix. As the aging time further increased to 5000 h, the M12C carbide kept stable with the M23C6 carbide. Due to the precipitation and coarsen of M12C and M23C6 carbides that consumed massive solute atoms from matrix, which weakened the precipitation strengthening effect and suppressed the dynamic strain aging, the tensile properties kept superior stability during aging. The evolution of impact toughness was also closely related to the interdendritic precipitates. As the interdendritic region was occupied by precipitates since the aging time increased from 200 h to 1000 h, the impact toughness rapidly decreased from 76 J to 39 J, and then slightly decreased to 33 J with the aging time increased to 5000 h.

Nanomechanical and tribological properties of nickel–chromium multilayer coating on Inconel 617

Multilayer coatings of Ni and Cr were deposited onto Inconel 617, and multi-scale physical properties were characterized using high temperature tribological experiments, nanoindentation, and microscratch. The effect of high temperature aging (950 °C under helium environment) on two different Ni/Cr multilayer coatings with individual layer thicknesses of 50 and 200 nm denoted by Ni/Cr(50) and Ni/Cr(200) was investigated. Nanoindentation of original coatings showed a hardness of 6 GPa that increases to 14 GPa for both samples once aged. Microscratch results support the macro-tribology results where Ni/Cr(50) (without aging) was the only delaminated coating with significant wear. Additionally, aging in both cases reduced the in situ coefficient of friction and wear. Cross-section energy dispersive spectrometry confirmed that the aged oxide layer was two to three times thicker than the original coating. An abundance of chromium oxide was found in the main body of the coatings, which led to higher hardness and better wear resistance.

High-temperature strength properties of epoxy-based adhesive joints and the effects of hightemperature aging

Lap joints were prepared using epoxy adhesive and aluminum plates, and the properties of high-temperature strength were studied. Tensile test and aging test were performed at high temperature. The effects of test temperature were systematically investigated. The obtained conclusions were following. When the specimen was exposed at temperature of 135℃, the strength decreased significantly. The adhesive changed its chemical structure by oxidation. The relationship between test temperature and tensile strength could be expressed using the Arrhenius equation.

The effect of high temperature aging on the corrosion resistance, mechanical property and antibacterial activity of Cu-2205 DSS

The effects of high temperature aging on the corrosion resistance, mechanical property and antibacterial activity of a copper–bearing 2205 duplex stainless steel (Cu-2205 DSS) were investigated. The results from scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and EDS analysis showed that after aging the proportion of γ phase in microstructure was increased and new σ phase and copper-rich precipitates were formed. The mechanical properties including hardness and tensile and yield strengths of the aged Cu-2205 DSS were significantly enhanced compared to the solution-treated Cu-2205 DSS as well as the 2205 DSS. Electrochemical measurements including electrochemical impedance spectroscopy, potentiodynamic polarization curves and potentiostatic polarization scan were performed to evaluate the corrosion behavior of the Cu-2205 DSS. It was found that aging increased the uniform corrosion resistance but had slightly adverse effect on the pitting corrosion resistance. Additionally, the antibacterial performance of aged Cu-2205 DSS was significantly improved compared to the solution treated Cu-2205 DSS, which was attributed to the more release of copper ions from the matrix that killed the bacteria cells and inhibited the biofilm formation on the surface. The above results suggest that Cu-2205 DSS after high temperature aging revealed good mechanical property, antibacterial performance, and corrosion resistance, which will further expand the application of duplex stainless steel in marine engineering fields.

Thermal Analysis and Selected Properties of CuNi2Si Alloy Used for Railway Traction.

This paper investigates the effect of high-temperature aging (600 °C and 650 °C) on the microstructure and functional properties of copper CuNi2Si alloy. The paper also presents the results of elastomeric tests performed by means of the Gleeble 3800 heat and plastic treatment simulator, as well as DTA (Differential Thermal Analysis) analysis carried out for the investigated alloy aged for 1, 2, 4 and 7 h. Corrosion resistance tests were performed by means of the potentiodynamic method with Atlas Sollich Atlas 0531 potentiostat/galvanostat in a 3% sodium chloride solution. Based on the tribological tests, it was confirmed that the CuNi2Si alloy was solution heat treated from the temperature of 1000 °C and gradually aged at the temperature of 600 °C and 650 °C for 1–7 h, characterized by a stable wear resistance. The alloy aged at the temperature of 600 °C was characterized by a lower mass loss compared to the one aged at 650 °C. Based on the DTA analysis, it was found that for the alloy aged for 2, 4 and 7 h, at the temperatures of 401 °C, 411 °C and 412 °C, respectively, the decomposition of a supersaturated solid solution took place by spinodal transformation accompanied by a sequence of phase transitions DO22 [(Cu, Ni)3Si],→ δ-Ni2Si → (Cu, Ni)3Si. The results of these investigations have proved that the CuNi2Si alloy can be widely used for electric traction. The use of alloys that replace elements made entirely of copper and, in this way influencing its lower demand, is in line with the global policy of economical management of natural resources.

Effect of high temperature ageing on TiO2 nanoparticles enhanced drilling fluids: A rheological and filtration study

Design of drilling fluids is critical to the techno-economic success of drilling a petroleum well bore and the present study is a forward step in that direction. Effect of TiO2 nanoparticles on the thermal stability of drilling fluid properties is evaluated using two different mud systems based on polyanionic cellulose (PAC) and hydroxyethyl cellulose (HEC). Drilling fluids were subjected to high temperature rolling conditions at 110 °C and 30 rpm for 16 hours in order to simulate the wellbore environment using a roller oven. Due to 16 h long hot rolling, the API FL values for DFB (base mud), DFP3 (1.0 w/v% PAC) and DFH3 (1.0 w/v% HEC) increased by ~56%, ~18% and ~46% respectively; whereas in presence of 0.5 w/v% nanoparticles respective figures were ~28%, ~16% and ~25%. In case of DFP3, AV at 25 °C was reduced due to hot rolling by ~34% without nanoparticles and by only ~15% in presence of nanoparticles. For DFH3, the percentage reduction in AV at 25 °C due to ageing was ~24% which decreased to ~16% for DFHN (1.0 w/v% HEC and 0.5 w/v% TiO2). It was found that nanoparticles imparted resistance to thermal degradation in rheological and filtration characteristics of drilling fluids. Filter cakes were studied using scanning electron microscopy and showed nanoparticles scattered over the surface of filter cakes which were filling the micro and nano sized gaps in the porous structure of mud cake and reducing the filtration rate. This study shows that using TiO2 nanoparticles along with a conventional fluid loss reducer additive not only enhances the efficacy of that additive but also improves the thermal stability and rheological properties of mud systems.

Effects of High-Temperature Aging on Precipitation and Corrosion Behavior of a Ni-Cr-Mo-Based Hastelloy C276 Superalloy

The effects of short-term aging on the precipitation and corrosion behavior of a Ni-Cr-Mo-based superalloy Hastelloy C276 were studied in this work. Aging treatments were performed at 800 °C for 1 h, 2 h, 4 h, 8 h, 12 h and 15 h. It is found that M6C carbide, which is rich in Mo and W, is prone to precipitate at grain boundary when the aging time exceeds 4 h, associated with the formation of a Mo and W depletion zone adjacent to the grain boundary. The potentiodynamic polarization curves in 3 wt.% NaCl solution show no obvious differences among the aged samples. But the surface morphologies of samples after double-loop electrochemical potentiodynamic reactivation method (DL-EPR) tests in HCl solution present typical intergranular corrosion attack. The calculated degrees of sensitization based on the DL-EPR curves increase dramatically with the increase in aging time, which is consistent with the precipitation trends. It is recommended that hot working of Hastelloy C276 superalloy should avoid high temperature exposure (e.g., at 800 °C more than 4 h) or do heat treatment again after high-temperature processing.

Effect of High Temperature Aging on Wear Resistance of a High-Nitrogen Stainless Steel

The wear resistance of a Cr19Mn19Mo2N0.7 stainless steel treated by solution treatment 1160°C for 6h then aging at 900°C for different times is investigated in this paper. Microstructures are analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). A fingerprint nitride (Cr2N) structure is formed during aging, which first nucleates within ferrite laths and along the austenite grain boundaries, and then grows into austenite with increasing aging time. It is shown from the laboratory wear test that the optimum wear resistance is obtained through a solution treatment at 1160°C for 6h and aging at 900°C for 3h, which is mainly attributed to a moderate amount of fingerprint nitrides formed within ferrite laths.

Effect of high-temperature ageing on (La,Sr)(Co,Fe)O3-δ cathodes in microtubular solid oxide fuel cells

Microtubular solid oxide fuel cells with La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathodes were aged in ambient air at temperatures ranging from 700 to 1000 °C for up to 700 h. Distribution of relaxation time analysis of electrochemical impedance spectroscopy (EIS) measurements indicated an increase in the cathode resistance with increasing ageing temperature up to 900 °C. The cells aged at 1000 °C were not measurable. The degradation did not result from microstructural changes, as shown by focused ion beam-scanning electron microscopy (FIB-SEM) 3D tomography that showed no significant changes at ageing temperatures ≤900 °C. On the other hand, the amount of segregated Sr, present both on LSCF surfaces and in Sr-rich particles, increased with increasing ageing temperature and correlated well with the increase in cathode resistance. Analysis of the EIS and microstructural data using the Alder-Lane-Steele model indicates that the Sr surface segregation increases cathode resistance via a decreased oxygen surface exchange rate.

Effects of Isothermal Aging on the Thermal Expansion of Several Sn-Based Lead-Free Solder Alloys

In this paper, effects of high-temperature aging on the thermal expansion behavior of several lead-free alloys SAC305, SAC387, Sn-3.5Ag, SnCu, SN100C (SnCu-Ni-Ge) and SnCu-0.01Ge have been explored. The coefficients of thermal expansion (CTEs) of the alloys have been experimentally determined over the temperature range 30-150 °C after isothermal aging at 125 °C for up to 30 days (720 h). The CTE values of SAC305, SAC387 and Sn-3.5Ag increase by 8-16% after 30 days of aging, while the CTE values of SnCu, SnCu-Ge and SN100C solders increase by only 3-6%. The CTE evolution of lead-free solders can be explained by microstructural changes observed during isothermal aging, which causes coarsening of various phases of the solder. As the phases coarsen, dislocation movement proceeds with a consequent increase in the average interparticle distance. The observation of CTE increases during isothermal aging suggests potential reliability problems for lead-free solder joints subjected to long-term aging exposures at high temperatures.

Effect of High Temperature Aging on Microstructure and Mechanical Properties of Environmental Barrier Coatings for CMC.

Effect of High Temperature Aging on Microstructure and Mechanical Properties of Environmental Barrier Coatings for CMC.

Investigating Changes in the Morphological Structure of High-Temperature, Calendar-Aged Li-Ion Cells

A physics-based impedance response model of a graphite|LiNMC cell is developed to investigate the effect of high-temperature calendar aging on electrode microstructure. Experimental data indicate unique contributions to aging from each electrode. The model relaxes the constraints placed by the Bruggeman relation, instead using a free parameter to relate the porosity and tortuosity. The incorporation of a two-layered cathode particle and adjustment of the Bruggeman relation produce mid- and low-frequency responses that quantitatively agree with the experimental data. The significance of the model modifications toward measuring the effects of high-temperature aging is discussed.

Microstructural Evolution and Mechanical Behavior of High Temperature Solders: Effects of High Temperature Aging

This paper explores the effects of aging on the mechanical behavior, microstructure evolution and IMC formation on different surface finishes of two high temperature solders, Sn-5 wt.% Ag and Sn-5 wt.% Sb. High temperature aging showed significant degradation of Sn-5 wt.% Ag solder hardness (34%) while aging has little effect on Sn-5 wt.% Sb solder. Sn-5 wt.% Ag experienced rapid grain growth as well as the coarsening of particles during aging. Sn-5 wt.% Sb showed a stable microstructure due to solid solution strengthening and the stable nature of SnSb precipitates. The increase of intermetallic compound (IMC) thickness during aging follows a parabolic relationship with time. Regression analysis (time exponent, n) indicated that IMC growth kinetics is controlled by a diffusion mechanism. The results have important implications in the selection of high temperature solders used in high temperature applications.

Effects of thermal aging on Cu nanoparticle/Bi-Sn solder hybrid bonding

The effects of high-temperature aging on a novel hybrid bonding layer were investigated. The hybrid layer, which consisted of Cu nanoparticles and a eutectic Bi-Sn solder powder, was formed by a sintering reaction of the solid-phase Cu nanoparticles and a chemical reaction involving the liquid-phase Bi and Sn in combination. The layer was used to bond a SiC chip to a direct bonded aluminum substrate. A conventional Cu nanoparticle-based bonding layer was also prepared as a reference. Samples with these bonding layers were evaluated using the thermal aging test (225 or 250°C, 100h). Bonding strength and synchrotron radiation computed laminography (SRCL) measurements were performed both before and after the thermal aging test. It was observed that thermal aging greatly decreased the bonding strength of the conventional layer. In contrast, the bonding strength of the hybrid layer was reduced only slightly by the thermal aging treatment. SRCL images showed that the conventional layer exhibited numerous cracks, which acted as passages for oxidation. On the other hand, in the hybrid layer, the liquid-phase Bi and Sn densified the Cu sintering phase through the formation of an alloyed Cu-Sn phase. As a result, the hybrid layer contained fewer passages for oxidation as compared to the conventional layer and maintained its bonding strength even against thermal aging. Therefore, the hybrid layer, which is highly stable against thermal aging, will be useful for the high-temperature operation of intelligent power modules.