High Temperature Aging Research Articles

A new method for preventing stress cracking in repairable ceramic packages by changing the sealing ring shape

High-reliable ceramic packages are impressionable to the parallel seam welding (PSW) parameters leading to low yield and reliability. In this study, the structure of the ceramic package was modified by changing the sealing ring to improve weldability and high-temperature reliability. Three types of ceramic packages with different-shaped sealing rings, which are conventional rectangular rings, notch inward rings, and notch outward rings, were fabricated by Au-Sn soldering and a follow-up PSW process. The packages with the rectangular ring failed in the subsequent high-temperature aging test. The packages with the notch inward ring exhibited an early failure after PSW. Cracks were generated in the Au-Sn solder and propagated into the ceramic substrate. The packages with the notch outward ring exhibited remarkable weldability and reliability. Sequential thermo-structural coupling was used to simulate the temperature and stress distribution in the packages. The maximum principal stress in the aforementioned ceramic substrates rapidly increased to approximately 170.0 MPa, 168.5 MPa and 101.4 MPa in the PSW process. Stress concentration existed at the outside corner around the rectangular and notch inward-shaped sealing rings. The maximum temperature at the local position in the ceramic was raised to 250.3 °C, 238.6 °C and 157.2 °C depending on the shape of the sealing ring. The extra transmission path in the notch outward ring relieved thermal mismatch and deformation at the Au-Sn/ceramic interface during PSW. The packages with notch outward rings were recommended especially in the repairable ceramic packaging.

Ageing evolution process of the [formula omitted]-phase in Al-Si-Cu-Mg alloys: Atomic-scale observations and first-principles calculations

This work characterizes the high temperature (above 200 °C) ageing process of the θ′ phase in Al-Si-Cu-Mg alloys by using atomic-resolution HAADF-STEM and first-principles calculations. By characterizing the morphology and coarsening growth process of the θP′ and θP1′ precursor, experimental observations suggest that the θP′ phase is based on GPI (Guinier-Preston I) growth expansion. With the ageing time increases and the atomic concentration changes, the Cu atoms on the outside of the θP′ phase rearrange to form the θP1′ phase. Subsequently, the θP2′ precursor phase is formed locally in the θP1′ phase as the Cu atoms gradually enter the θP1′ phase. Besides, it has been observed experimentally that the θP2′ precursor phase can be directly transformed into the θ′ phase without changing the morphology, structure and orientation relationships of the phase. Based on the experimental characterization and theoretical calculations of this work, we have proposed a novel ageing precipitation sequence: SSSS (Super Saturated Solid Solution)→GPI→θP′→θP1′→θP2′→θ′.

Microstructure and mechanical properties evolutions of 9Cr heat resistant steel deposited metals with different Si contents during 550 °C aging process

The stability of microstructure and mechanical properties of 9Cr heat resistant steel under high temperature and long term service conditions has been a hot issue of great interest. In the present study, the relationships between microstructure and mechanical properties evolutions of 9Cr heat resistant deposited metals with different Si contents (0.25 wt.% and 1.07 wt.%) at 550 °C aging for different times were investigated systematically. The results indicate that the degradation of mechanical properties during aging is mainly attributed to the coarsening of precipitates, transformation of precipitate types, decreasing of dislocation density and coarsening of martensite laths, and these factors are related to the Si content in the deposited metals and the aging time. It is worth mentioned that the sub-grain boundaries pinned by M23C6 forming after post weld heat treatment (750 °C/2.5 h) stabilize the tensile strength during aging. The recrystallization occurring after post weld heat treatment and high temperature aging is beneficial for the impact toughness but not for the strength. During aging process, the precipitate transformation follows the following sequence: M23C6→M6X→Laves phase. Moreover, the increase of Si content promotes the nucleation and coarsening of M6X, and then deteriorates the mechanical properties of the deposited metals.

Microstructure, mechanical properties, and damping capacity of high-Zn-content Al–Zn–Mg alloys with Sc and Zr additions

In this study, Al–15Zn–0.5 Mg–Sc–Zr alloys with different Sc and Zr contents were fabricated by casting, rolling, solution treatment, and aging at low and high temperatures. Primary and precipitated Al3(Sc,Zr) and Al3Zr phases could promote grain refinement in the high-Zn-content Al alloys more effectively than the Al3Sc phase, and the composition characteristics of high Zn and low Mg contents led to the Al–15Zn–0.5 Mg–Sc–Zr alloys exhibiting high thermal stability of η′ phases during aging at high temperature and long time. The Al3Sc and Al3(Sc,Zr) phases could promote the formation of fine η phases in the Al–15Zn–0.5 Mg–Sc–Zr alloys, but the Al3Zr phase could not. Finer grains and second phases led to the Al–15Zn–0.5 Mg–Sc–Zr alloys with Zr single addition and Sc, Zr collaborative additions exhibiting better mechanical properties than the alloy with Sc single addition. Meanwhile, the damping capacities of the Al–15Zn–0.5 Mg–Sc–Zr alloys with high-temperature aging were higher than those of the same alloys with aging at a low temperature due to their less numbers of dislocation pinning points and higher interface slipping ability.

Accelerating the precipitation kinetics of nano-sized T1 and S’ phases in Al-Cu-Li alloys by hot-deformation and creep-aging

ABSTRACT It is well known that a Cu/Li ratio over 4.0 leads to significant precipitation hardening in the third generation of Al–Li alloys, which have been widely used in aerospace and aeronautic industries. However, increasing Cu levels not only cancels some gains in weight reduction but also results in reductions in ductility when the traditional age-hardening process is adopted. In this study, we show that higher strength and ductility can be achieved simultaneously by replacing traditional artificial aging with new creep aging and tailoring the entire process from casting to age hardening without changing any nominal chemical compositions. Surprisingly, the precipitation kinetics of AA2060 alloy is significantly enhanced through the combination of hot extrusion, creep aging, and pre-strain compared to traditional artificial aging. For example, at 160°C, it follows the transformation path of supersaturated solid solution (SSSS)→GP zones + δ′+T1 precursors which will further transform into T1 +S’; at 200°C, SSS→ GP zones, and they transform into T1 + S’ immediately. The precipitation of θ′ and δ′ phases is significantly inhibited at elevated temperatures due to the competing relationship with T1 and S’ phases at a peak-aged state. Contrary to traditional knowledge in Al–Li alloys, we have found that the greater extrusion ratio at 33.0 and higher aging temperature at 200°C can give a much higher peak aging strength with average ultimate tensile strength 659 MPa.

Comparison on the performance of solid coumarone-indene resin and liquid coumarone-indene resin modified asphalt

Coumarone-indene resin (CIR) has great potential for use as an asphalt modifier because of the cost-effective, high viscosity, and excellent mechanical properties. CIR is classified into two types based on polymerization degree: solid coumarone-indene resin (S-CIR) and liquid coumarone-indene resin (L-CIR). In this study, solid coumarone-indene resin modified asphalt (S-CMA) and liquid coumarone-indene resin modified asphalt (L-CMA) were prepared, and the comparison of the high-temperature performance, compatibility, aging performance, low-temperature performance, microstructure and modification mechanism of S-CMA and L-CMA was researched following the SuperPave standard. The results reveal that S-CIR is a solid resin with a high molecular weight that improves the high-temperature performance, permanent deformation resistance, and viscosity of asphalt, but impact on low-temperature performance negatively. In contrast, L-CIR is a liquid resin with low molecular weight that enhances the low-temperature properties and plasticity of asphalt, but decreases high-temperature properties. Additionally, solid resins with large molecular weight are prone to agglomeration in asphalt, while liquid resins with small molecular weight have better dispersibility, especially in high-content situations. Meanwhile, CIR exhibits good compatibility with asphalt. Based on the FTIR test results, chemical compositions and structures of S-CIR and L-CIR are similar, and physical miscibility was demonstrated between CIR and asphalt. In summary, modifier with different molecular polymerization degrees have a greater impact on modified asphalt, S-CMA has better high-temperature performance and viscosity than L-CMA, L-CMA has better low-temperature performance and plasticity than S-CMA, and S-CMA and L-CMA can be used for pavement construction in hot and cold areas respectively.

Artificial intelligence inspired design of non-isothermal aging for γ–γ′ two-phase, Ni–Al alloys

In this paper, a state-of-the-art Artificial Intelligence (AI) technique is used for a precipitation hardening of Ni-based alloy to predict more flexible non-isothermal aging (NIA) and to examine the possible routes for the enhancement in strength that may be practically achieved. Additionally, AI is used to integrate with Materials Integration by Network Technology, which is a computational workflow utilized to model the microstructure evolution and evaluate the 0.2% proof stress for isothermal aging and NIA. As a result, it is possible to find enhanced 0.2% proof stress for NIA for a fixed time of 10 min compared to the isothermal aging benchmark. The entire search space for aging scheduling was ~ 3 billion. Out of 1620 NIA schedules, we succeeded in designing the 110 NIA schedules that outperformed the isothermal aging benchmark. Interestingly, it is found that early-stage high-temperature aging for a shorter time increases the γ′ precipitate size up to the critical size and later aging at lower temperature increases the γ′ fraction with no anomalous change in γ′ size. Therefore, employing this essence from AI, we designed an optimum aging route in which we attained an outperformed 0.2% proof stress to AI-designed NIA routes.

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.

Formation of Pt-Pd 'Janus' Biphasic Particles During High-Temperature Aging of Diesel Oxidation Catalysts.

Formation of Pt-Pd 'Janus' Biphasic Particles During High-Temperature Aging of Diesel Oxidation Catalysts.

Achieving high strength-ductility properties of wire-arc additive manufactured Al-Mg-Sc aluminum alloy via friction stir processing post-treatment and high temperature aging treatment

In this study, the high strength-ductility properties of wire-arc additive manufactured (WAAM) Al-Mg-Sc aluminum alloy were achieved by friction stir processing post-treatment (FSPPT) and high temperature aging treatment (HTAT). The FSPPT significantly refined the microstructure and eliminated porosity defects, which the average grain size was about 2.4 ± 0.2 μm in stirring zone (SZ). There was no obvious growth in grain size after HTAT and the average grain size was about 2.7 ± 0.4 μm in SZ. Many fine secondary Al3(Sc,Zr) phases were precipitated. Compared to WAAM sample, the average ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of FSPPT + HTAT sample increased by 57.9%, 54.7% and 205.9%, respectively.

Precipitates evolution during isothermal aging and its effect on tensile properties for an AFA alloy containing W and B elements

A 20Cr-25Ni-2.5Al alumina-forming austenitic alloy containing W and B elements was aged at 923 K for 5000 h, and the microstructure and tensile properties with different aging time were investigated. NiAl, σ and Laves were observed at grain boundaries (GBs) successively. The matrix was covered by NiAl and Laves with the extension of aging. The evolution of precipitates during aging contributed to the variation of tensile properties. Precipitation of nanosized NbC carbides within grains and σ phase at GBs led to a rapid increase in strength and a decrease in elongation for 500 h aging sample. In the later stage of aging, the coarsening of NiAl and Laves phases, as well as the reduction in dislocation density caused a decline in strength. The coarsening of precipitates upon aging time follows the Ostwald ripening theory. Due to its lower diffusion rate in austenite compared to Mo, W may accelerate the growth of Laves at GBs. Boron was mainly enriched in Laves instead of NiAl, NbC and σ phases after high temperature aging. The addition of W and B improved the precipitation strengthening of Laves, increasing the high temperature tensile strength after long term thermal aging. The difference in tensile properties between room temperature and 923 K is due to the ductile–brittle transition of NiAl. No σ phase was observed within grains even after 5000 h aging and elemental chromium particles occurred around Laves due to boron hindering the growth of σ.

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.

Study of Heat Treatment Effect on Mechanical Properties of Epoxy Resin Reinforced with Fiber Glass.

In this paper, mechanical properties of the diglycidyl ether of bisphenol A epoxy resin (EP) reinforced with a 20% fiber glass (GF) with layered structure after high temperature aging are studied. Tensile and flexural stress-strain curves of the GF/EP composite after aging tests in the temperature range of 85-145 °C in air were measured. Tensile and flexural strength demonstrate gradual decrease with the increase in the aging temperature. The failure mechanism at the micro scale is studied by the scanning electron microscopy. A separation of the GFs and EP matrix and evident pullout of the GFs are observed. Degradation of the mechanical properties is explained by a cross-linking and chain scission of the initial molecular structure of the composite and decrease in the interfacial adhesion force between GFs and EP matrix caused by oxidation of the EP matrix and difference of the GF and EP coefficients of thermal expansion.

A Study on the Thermal Degradation of an Acrylamide and 2-Acrylamido-2-Methylpropanesulfonic Acid Copolymer at High Temperatures.

As a temperature-resistant and salt-resistant polymer, acrylamide and 2-acrylamide-2-methylpropane sulfonic acid (abbreviated as AM-AMPS) copolymer is currently widely used in drilling, water control and oil production stabilization, enhanced oil recovery and other fields, but its stability under high temperature has been less studied. The degradation process of the AM-AMPS copolymer solution was studied by measuring viscosity, the degree of hydrolysis, and weight-average molecular weight at different temperatures and aging time. During the high-temperature aging process, the viscosity of the AM-AMPS copolymer saline solution first increases and then decreases. The combined action of the hydrolysis reaction and the oxidative thermal degradation leads to the change of the viscosity of the AM-AMPS copolymer saline solution. The hydrolysis reaction of the AM-AMPS copolymer mainly affects the structural viscosity of its saline solution through intramolecular and intermolecular electrostatic interactions, while the oxidative thermal degradation mainly reduces its molecular weight by breaking the main chain of the copolymer molecules, reducing the viscosity of the AM-AMPS copolymer saline solution. The content of AM and AMPS groups in the AM-AMPS copolymer solution at various temperatures and aging time was analyzed using liquid nuclear magnetic resonance carbon spectroscopy, demonstrating that the hydrolysis reaction rate constant of AM groups was significantly higher than that of AMPS groups. The contribution values of hydrolysis reaction and oxidative thermal degradation of the AM-AMPS copolymer at different aging time to viscosity were quantitatively calculated at temperatures ranging from 104.5 °C to 140 °C. It was determined that the higher the heat treatment temperature, the smaller the contribution of hydrolysis reaction to viscosity, while the bigger the contribution of oxidative thermal degradation to the viscosity of the AM-AMPS copolymer solution.

Artificial intelligence optimization and controllable slow-release iron sulfide realizes efficient separation of copper and arsenic in strongly acidic wastewater

Iron sulfide (FeS) is a promising material for separating copper and arsenic from strongly acidic wastewater due to its S2− slow-release effect. However, uncertainties arise because of the constant changes in wastewater composition, affecting the selection of operating parameters and FeS types. In this study, the aging method was first used to prepare various controllable FeS nanoparticles to weaken the arsenic removal ability without affecting the copper removal. Orthogonal experiments were conducted, and the results identified the Cu/As ratio, H2SO4 concentration, and FeS dosage as the three main factors influencing the separation efficiency. The backpropagation artificial neural network (BP-ANN) model was established to determine the relationship between the influencing factors and the separation efficiency. The correlation coefficient (R) of overall model was 0.9923 after optimizing using genetic algorithm (GA). The BP-GA model was also solved using GA under specific constraints, predicting the best solution for the separation process in real-time. The predicted results show that the high temperature and long aging time of FeS were necessary to gain high separation efficiency, and the maximum separation factor can reached 1,400. This study provides a suitable sulfurizing material and a set of methods and models with robust flexibility that can successfully predict the separation efficiency of copper and arsenic from highly acidic environments.

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.

Ageing precipitation sequence and effect of ω and secondary α phases on tensile properties of metastable β Ti-6Cr-5Mo-5V-4Al alloy

The ageing precipitation sequence and the relationship between microstructure and tensile properties of metastable β titanium alloy Ti-6Cr-5Mo-5V-4Al during solution and ageing were investigated. Ageing from 400 to 450 °C, isothermal ω phase (ωiso) precipitated in the alloy, resulting in high hardening and brittle fracture. After ageing at 450–500 °C, ωiso phase was gradually replaced by secondary α phase (αs) with the ageing time increasing. At higher ageing temperature (580–600 °C), ωiso precipitation was suppressed, and αs phase precipitated directly from β phase. The yield strength of sample aged at 450 °C for 12 h was 1368 MPa and the elongation was 5.5% due to ωiso precipitation. The yield strength of sample aged at 600 °C for 12 h was 1108 MPa and the elongation was improved to 15.4% due to the precipitation and coarsening of αs phase.

Growth kinetics and mechanical properties of the Cu20Sn6 phase transited from the full Cu3Sn joint during high temperature aging process

Growth kinetics and mechanical properties of the Cu20Sn6 phase transited from the full Cu3Sn joint during high temperature aging process

Synthesis, Structural Properties, and Resistance to High-Temperature Degradation of Perovskite Ceramics Based on Lanthanum–Strontium Ferrite

This work is dedicated to the study of the properties of perovskite ceramics based on lanthanum–strontium ferrite, and to the evaluation of their resistance to long-term thermal aging. As a method for obtaining perovskite ceramics, the method of solid-phase mechanochemical grinding and consequent thermal annealing of the resulting mixtures was chosen. The novelty of the study consists in the assessment of the phase transformation dynamics in lanthanum–strontium ferrite-based ceramics in relation to the annealing temperature, alongside the study of the effect of the phase composition of ceramics on the resistance to high-temperature aging, which is characteristic of the operating modes of these ceramics as materials for solid oxide fuel cells. To study the properties, the methods of scanning electron microscopy, energy dispersive analysis, and scanning electron microscopy were applied. Pursuant to the outcome of elemental analysis, it was established that no impurity inclusions appear in the ceramic structure during the synthesis, and a growth in the annealing temperature results into a decline in the grain size and a growth in their density. During the analysis of the acquired X-ray diffraction patterns, it was found that a growth in the annealing temperature above 500 °C results in phase transformations of the LaFeO3/SrFe2O4 → La0.3Sr0.7FeO3/LaSr2FeO8/La3FeO6 type, followed by structural ordering and a decline in deformation distortions with a growth in the annealing temperature. An analysis of the conductive properties of ceramics has established that the dominance of the La0.3Sr0.7FeO3 phase in the structure results in a growth in conductivity and a decline in resistance. Life tests for degradation resistance have shown that for three-phase ceramics, the rate of degradation and amorphization is significantly lower than for two-phase ceramics.

Effect of NdCoGa alloy addition to waste wind turbine magnets to enhance the characteristics of recycled sintered NdFeB permanent magnets

Neodymium (NdFeB) permanent magnets play a key role in motors and other devices, and are important to both defense and civilian industrial uses; however, due to the limited rare earth resources, the issue of recycling waste NdFeB magnets to achieve sustainable development has attracted much attention. An innovative and valid method for the recycling of waste NdFeB magnets is demonstrated in this study. Recycled sintered NdFeB permanent magnets were prepared on a large scale up to 100 kg per batch by adding NdCoGa ternary rare earth alloy to waste wind turbine NdFeB magnets, and their magnetic properties, corrosion resistance and high temperature aging characteristics were evaluated. The recycled magnets were manufactured by mixing waste magnets A, B, and NdCoGa alloy according to weight percentage ratio of 90:7:3 respectively. Through BH Curve measurement and FE-EPMA qualitative element analysis, the differences in the magnetic properties and microstructure before and after adding the NdCoGa elements were observed. The results show that the magnetic properties of waste magnet A are Br = 12.60 kG, iHc = 18.92 kOe and (BH)max = 39.19 MGOe; the magnetic properties of waste magnet B are Br = 12.77 kG, iHc = 18.15 kOe and (BH)max = 40.25 MGOe. In contrast, the magnetic properties of the recycled magnets prepared in this study are Br = 12.63 kG, iHc = 18.72 kOe, and (BH)max = 39.95 MGOe, indicating that the proposed process restores the magnetic properties of the recycled magnets to the level of the original waste magnet. Also, a brand new commercial N40H magnet is further used as a control group, where the corrosion resistance and high temperature aging characteristics of bare materials were evaluated by Pressure Cooker Test (PCT), and oven/flux meter respectively. The results show that the average corrosion weights per unit area are 0.89 mg/cm2 and 1.23 mg/cm2, as well as the demagnetization rate of the high temperature aging is less than 0.4%. Compared with the new magnet, the recycled magnet has the same level of high temperature aging resistance, and 28% higher corrosion resistance. As a result, adding only 3% NdCoGa alloy to the waste magnet is beneficial to restore the magnetic properties and high temperature aging resistance, up to the level of new magnets, and also greatly enhances its corrosion resistance and reduces the cost of magnet remanufacturing. This result indicates that the recycled NdFeB permanent magnets developed in this research are more suitable for offshore wind turbine generators and electric vehicle motors operating at high temperatures and high humidity for a long period of time.