Low Temperature Aging Research Articles

Optimization of combined properties of aluminum matrix and interface in an aluminum/steel bimetal via low temperature aging

Optimization of combined properties of aluminum matrix and interface in an aluminum/steel bimetal via low temperature aging

The influence of secondary aging on the microstructure and corrosion resistance of Al-Zn-Mg-Cu alloy

In this study, through process optimization, we successfully identified a 7-day T6I4 secondary low-temperature aging treatment that significantly enhances the corrosion resistance of Al-Zn-Mg-Cu alloys. Microstructural analysis revealed that the Guinier-Preston (GP) zones and η' phases, are uniformly dispersed within the aluminum matrix after this treatment, effectively reducing the width of the precipitate-free zone (PFZ), thereby significantly lowering the risk of intergranular corrosion. Electrochemical testing results indicate that the alloy treated with this process exhibits superior electrochemical corrosion resistance, characterized by the highest charge transfer resistance (Rct) and the lowest corrosion current density (Icorr). Furthermore, long-term corrosion experiments have provided an in-depth understanding of the alloy's corrosion durability mechanisms under optimal process conditions. Density Functional Theory (DFT) calculations have further elucidated the work function and surface energy of the precipitates, providing a theoretical foundation for the enhancement of alloy performance.

Insights into the effect of emulsifiers on the quality of aerated emulsions: Fat-emulsifier-protein interactions and re-equilibration of the interfacial layer during low-temperature ageing

Insights into the effect of emulsifiers on the quality of aerated emulsions: Fat-emulsifier-protein interactions and re-equilibration of the interfacial layer during low-temperature ageing

EFFECT OF ORIGINAL STRUCTURE ON AGING-INDUCED MICROSTRUCTURE AND TRANSFORMATION BEHAVIOR OF Ni-RICH NITI ALLOY USING VARIOUS AGING MODEs

In the present study we discuss the evolution of aging-induced microstructure, critical temperatures of martensitic transformations (MTs) and their specific temperature ranges, latent heat and thermal hysteresis in Ni50.8Ti alloy with various original structures (OS) obtained using three different processing (including cold rolling/drawing, hot shear rolling and subsequent various solution treatment): fine-grained recrystallized structure (OS_1); hot deformation-induced structure (OS_2); coarse-grained recrystallized structure (OS_3). Subsequent aging was performed in a temperature range of 300−500 °C for 1−20h. After aging, OS_1 ensures two-stage MTs A→R and R→M upon cooling regardless of aging mode; OS_2 provides evolution from one-stage MT A→R to triple-stage MT at latest stage of aging; the quadruple-stage MT is revealed in OS_3 after aging at 430°C. Low-temperature aging at 300 °C ensures the most effective stabilization of R-martensite regardless of an original structure; high-temperature aging at 500 °C provides the least effective stabilization of R-martensite. Specific features of evolution of the latent heat and the width of hysteresis vs aging modes was explained by microstructural evolution. The correlation between values in the latent heats upon cooling/heating and hysteresis vs the aging duration were revealed. Hysteresis of an original structure is inherited after subsequent aging. The combined effect of an original structure and aging mode on the above characteristics is very complex and depends on a lot of competing factors; they are analyzed in detail. The revealed regularities permit precise tuning of the studied characteristics in a wide range to ensure the most favorable their combination for practical use.

Effect of heat treatment on the microstructure and mechanical properties of AZ91D magnesium alloy fabricated via GTA wire arc additive manufacturing

This study aims to address elemental segregation and poor mechanical properties in as-deposited AZ91D magnesium alloy fabricated via wire arc additive manufacturing through heat treatment. Three distinct heat treatments are investigated: solution treatment (T4), artificial aging treatment (T5), and a combination of solution and aging treatment (T6). Microstructural analysis reveals equiaxed grains in all samples. In the T4 state, the eutectic phase along grain boundaries dissolvs into the matrix, reducing elemental segregation but increasing grain size. In the T5 state, elemental segregation is further reduced; however, due to the relatively low aging temperature, the microstructural features of the as-deposited state are largely retained. In the T6 state, solution treatment increases grain sizes, and the uneven distribution of the reprecipitated β phase leads variations in mechanical properties between vertical and horizontal directions. Compared to the as-deposited state, the T6 treatment achieves a synergistic improvement in both strength and ductility. The ultimate tensile strength increases to 262.3 MPa, and the elongation rises to 13.8%, representing improvements of 12.5% and 32.7%, respectively, compared to the as-deposited values of 233.2 MPa and 10.4%.

Experimental and first-principles novel insights of atomic collapsed structure and composition-driven ω-precipitates

A complex ω phase transition is often observed in titanium alloys; nevertheless, the underlying knowledge of ω-embrittlement are not yet fully understood and require deeper insight. In this study, the ωT and ωH phases, as well as their interfacial structures, have been systematically investigated to examine compositional partitioning and to estimate Z values. A combination of aberration-corrected HAADF-S/TEM advanced characterization techniques, together with first-principles density functional theory calculations were performed under various heat treatment conditions. The results revealed that the low-temperature ageing process suppresses ω-assisted secondary α precipitations at ωT/β interfaces, whereas high-temperature ageing process promotes ω-assisted secondary α precipitations at ωH/β interface, due to relatively higher concentrations of Mo and Al contents. The interfacial energies (γ{ωβ}) between β and ω phases increase with decreasing local compositions of Mo and Al, suggesting increased stability of the ω phase and decreased stability of the β phase. Furthermore, the formation energies of β and ω phases were computed with Mo content at different Al composition, results indicate that the ω phase transition process is affected by the reduced Al content. The observations of this work provide deeper understanding of the ω phase transition mechanism in titanium alloys.

Achieving superior strength-ductility balance by tailoring dislocation density and shearable GP zone of extruded Al-Cu-Li alloy

Pre-stretching is commonly employed to accelerate ageing precipitation kinetics in wrought Al-Cu-Li alloys, but uneven precipitation resulting from dislocation pile-ups often degrades ductility. Herein, the strength and ductility of extruded Al-Cu-Li alloy are significantly improved through a novel thermomechanical treatment, involving pre-ageing and pre-stretching, followed by low-temperature interrupted ageing. A superior balance between high yield strength (∼ 657 MPa) and good ductility (elongation to fracture of ∼ 13.5 %) is obtained, with elongation increased by 105 % compared to the conventional T8 temper, while maintaining a respectable yield strength. Microstructure analysis reveals that dense Guinier–Preston (GP) zones induced by pre-ageing effectively dissipate energy from dislocation sliding, resulting in a uniform dislocation configuration even at 8 % pre-stretching. However, the GP zone density is greatly reduced due to their dissolution following pre-stretching. Upon interrupted ageing, the reprecipitation of GP zones forms a homogeneous mixture of δ′, GP zones, and T1 phases. This combination alleviates local stress concentrations and lengthens the dislocation mean free path during tensile testing by shearing the GP zones at multiple sites, thereby improving ductility. Simultaneously, T1 precipitates strengthen the alloy by pinning dislocations and promoting dislocation cross-slip, improving work hardening capacity. The dissolution of GP zones also redistributes the Cu atoms within the matrix, further enhancing the intrinsic ductility of the Al matrix. These findings offer valuable insights for developing high-performance wrought Al-Cu-Li alloys.

Rheological and Aging Properties of Nano-Clay/SBS Composite-Modified Asphalt.

Nano-organic montmorillonite (OMMT) not only inhibits the harmful asphalt fume generation during the production and construction processes of asphalt mixtures but also effectively improves the performance of asphalt pavements. In order to prepare asphalt materials with smoke suppression effects and good road performance, this study selects nano-OMMT and SBS-modified asphalt for composite modification of asphalt mixtures and systematically investigates its road performance. Through the temperature sweep test, the frequency sweep test, the multiple stress creep recovery (MSCR) test, the bending beam rheometer (BBR) test, and the atomic force microscope (AFM) test, the high-temperature rheological properties, low-temperature rheological properties, high-temperature properties and aging resistance of the modified asphalt are studied. The research findings indicate that OMMT can effectively reduce the sensitivity of modified asphalt to load stress and improve its high-temperature rheological properties. SBS-modified asphalt shows increased creep stiffness and a decreased creep rate after OMMT modification, resulting in reduced flexibility and decreased low-temperature crack resistance. After short-term and long-term aging, the complex modulus aging index of OMMT/SBS composite-modified asphalt is lower than that of SBS-modified asphalt, and the phase angle aging index is higher than that of SBS-modified asphalt, demonstrating that OMMT enhances the aging resistance of SBS-modified asphalt. OMMT inhibits oxidation reactions in the asphalt matrix, reducing the formation of C=O and S=O bonds, thereby slowing down the aging process of modified asphalt and improving its aging resistance.

Temperature effects on ribbon characteristics in soft gelatin capsule manufacture

In the manufacture of soft gelatin capsules using a rotary-die encapsulation machine, the formation of ribbons at the cooling drums and their subsequent mechanical performance are key attributes for a smooth machinability. In this paper we present the results of a comprehensive investigation of the intricate impact of the cooling drum temperature in the range between 5 and 25 °C on the mechanical and the microstructural properties of a highly concentrated gelatin formulation (40% w/w) typically used in soft capsule manufacture.The study demonstrates that the temperature at the cooling drums strongly affects the gelation kinetics, the gel elasticity and the tensile strength of the ribbons. The temperature correlates linearly with the storage modulus G′ under low shear deformation, i.e. the lower the temperature of the gel, the higher the gel elasticity. A reverse linear relationship was found for the temperature-dependent ultimate tensile strength (UTS) of the gelatin ribbons, i.e. a higher drum temperature leads to a higher UTS. This inverse effect of the ageing temperature on G′ and UTS can be explained by temperature-induced microstructural differences within the gel network, as indicated by FTIR spectroscopy and Differential Scanning Calorimetry (DSC) measurements. Lower ageing temperatures result in a higher number of triple helical junction zones with fewer and/or weaker hydrogen bonds, which translate into a higher gel elasticity under low shear deformation, but a lower resilience of the ribbons against rupture in tensile testing. At higher temperatures, fewer but longer and/or more thermostable triple helical links in the gel network enhance the stability of the ribbons against tensile stress.In summary, the results clearly reveal that a detailed understanding of the complex relationship between the drum temperature, the gel network structure and the mechanical properties of gelatin ribbons is essential for process optimization.

Atomistic Modelling of [formula omitted]-Fe2C Formation During Low-Temperature Tempering of Martensitic Carbon Steel

The control of carbide formation is crucial for the development of advanced steels. One of the more stable carbides occurring at room temperature ageing of martensite is η-Fe2C. In this work, we study structural transformations which occur during low-temperature ageing in Fe-C martensite using computer modelling based on the atomic density field method. It is shown that homogeneous bct solid solution with 2at.% of C undergoes bct →η-Fe2C transformation. An important result is that the ordering Fe2C structure may be considered a deformed rutile structure. In addition, the link between η-carbide and other meta-stable carbides is discussed based on the Fe2n+1Cn (n=1,2,3,…) Magnéli phases. The Magnéli phases comprise a sequence of carbon-rich 110α′ layers with different periods to accommodate the loss in stoichiometry. The simulated microstructure is compared to experimental data found in the literature.

State-of-the-Art Review on the Behavior of Bio-Asphalt Binders and Mixtures.

Asphalt binder is the most common material used in road construction. However, the need for more durable and safer pavements requires a better understanding of asphalt's aging mechanisms and how its characteristics can be improved. The current challenge for the road industry is to use renewable materials (i.e., biomaterials not subjected to depletion) as a partial replacement for petroleum-based asphalt, which leads to reducing the carbon footprint. The most promising is to utilize biomaterials following the principles of sustainability in the modification of the asphalt binder. However, to understand whether the application of renewable materials represents a reliable and viable solution or just a research idea, this review covers various techniques for extracting bio-oil and preparing bio-modified asphalt binders, technical aspects including physical properties of different bio-oils, the impact of bio-oil addition on asphalt binder performance, and the compatibility of bio-oils with conventional binders. Key findings indicate that bio-oil can enhance modified asphalt binders' low-temperature performance and aging resistance. However, the effect on high-temperature performance varies based on the bio-oil source and preparation method. The paper concludes that while bio-oils show promise as renewable modifiers for asphalt binders, further research is needed to optimize their use and fully understand their long-term performance implications.

Role of the aging procedure on the ω + β microstructure in the metastable β Ti-30Nb-3Fe alloy

This report investigated the effect of low-temperature aging on the ω + β microstructure in the Ti-30Nb-3Fe alloy (wt%). Samples were subjected to several aging procedures. The ω + β microstructure remained quite stable under conventional transmission electron microscopy across most temperature/time regimes. Only the double aging treatment led to the growth of ω particles and an increased in Vickers hardness, indicating that the pre-aging treatment was necessary to promote rapid ω growth in the subsequent treatment. Furthermore, the early stages of solute partitioning that accompanies ω growth did not drastically increase hardness, suggesting that no embrittlement occurred.

Shape memory effect enhancement via aging treatment of the Cu-Al-Mn-Si alloy manufactured using laser powder bed fusion

This study investigated the effects of aging treatments (200–500℃, 1 h) on the Cu-11.1Al-8.15Mn-0.37Si shape memory alloy manufactured using laser powder bed fusion (LPBF). As the aging temperature increased, the residual stress of the alloy decreased, and the microstructure transitioned from an austenite-martensite dual-phase structure to an austenite single-phase structure. A phenomenon of martensite stabilization induced by low-temperature aging at 200–300℃ was observed, leading to increased phase transformation temperatures and decreased mechanical properties. After aging at 400℃, the plasticity was improved and the shape memory effect (SME) recovery strain experienced a significant 48 % enhancement and reached a maximum value of 3.10 %. This enhancement was due to the improved ordering and texture homogenization of the austenite phase, confirmed by EBSD results. Meanwhile, EPMA analyses revealed the pinning effect of Mn5Si3 precipitations migrated from the grain interior to the grain boundaries which no longer obstructed the movement of martensitic habit planes during the recovery process. Thus, the SME improved. Additionally, after aging at 500℃, a large amount of α phase precipitated along grain boundaries leading to a decrease in mechanical properties. These findings underscore the importance of tailored aging treatments for optimizing shape memory properties in LPBF-manufactured Cu-based shape memory alloys.

Effect of {10–12} Twins on Precipitation Behavior of Extruded Mg–8Al–0.5Zn Alloy During Low-temperature Aging

Effect of {10–12} Twins on Precipitation Behavior of Extruded Mg–8Al–0.5Zn Alloy During Low-temperature Aging

Unraveling the potential of Cu addition and cluster hardening in Al-Mg-Si alloys

With the aim of further exploiting the trade-off between formability and strength in Al alloys, this study addresses the influence of Cu in Al-Mg-Si alloys that achieve simultaneously high strength and high ductility via cluster hardening. The study carefully examines the mechanical properties and strain hardening behavior of various Mg/Si ratios with and without Cu and compares the effects of pre-aging and atypical long-term low-temperature aging treatments at 100°C to conventional heat treatments. Interestingly, in all cases adding Cu improved ductility. In the extremal case cluster hardening plus the addition of Cu quadruples elongation, while keeping yield strength similar to the classical T6 state. The results of the study are discussed with a focus on the dense distribution of clusters and partial hardening phases based on atom probe tomography data. Most importantly, the cluster-hardened alloys exhibit pronounced strain-hardening properties, which we evaluate using a Kocks-Mecking approach in combination with a microstructural analysis in the pre-aging and long-term aging condition. The key finding of the study involves the role of Cu in refining clusters/precipitates, where it causes a substantial increase in number density and volume fraction. This refinement, in combination with strain-induced clustering, contributes significantly to improving the alloys’ overall mechanical performance and underlines the central role of Cu in tailoring microstructural features, especially in alloys primarily strengthened by clusters.

Property improvement of epoxy emulsified asphalt modified by waterborne polyurethane in consideration of environmental benefits

Waterborne epoxy modified emulsified asphalt (EMEA) has the shortcomings of insufficient toughness and poor aging resistance, which limits its application of low-carbon cold-paving technology in plateau zones. To obtain a cold-mix asphalt binder with excellent performance, waterborne polyurethane (WPU) was utilized to modify EMEA in this work. Properties, modification mechanism, action process, environmental benefits, and cost-benefit of composite-modified emulsified asphalt (CMEA) were analyzed. Results show that CMEA had good rutting resistance, low-temperature rheological, tensile toughness, adhesion with aggregate and moisture damage resistance, and aging resistance properties. These were closely related in that WPU was cross-linked with the waterborne epoxy resin (WER) to form an interpenetrating polymer network (IPN) structure, when the space network structure of WER and the soft and hard segments of WPU worked together. Based on the above results, it was recommended that EA containing 4.0 wt% WER was modified by 7.5 wt% WPU to achieve the best pavement properties. Furthermore, it was discovered that a physical process by which WER and WPU modified EA, served as a skeleton connection and toughening agent. CMEA has excellent performance and is especially suitable for use in low-temperature and strong aging areas, while can bring good environmental benefits.

Toward a Standardized Approach for Characterizing β‐Fleck Defects in Titanium Alloys

β‐flecks are a type of segregation defect commonly encountered during the solidification of titanium alloys enriched with β‐stabilizing elements. These defects are associated with a detrimental impact on mechanical properties, which potentially limit the service life of parts containing them. Despite their significance, a standardized method for identifying these defects is lacking. In this study, a systematic approach is provided to detecting and characterizing β‐flecks in a representative metastable β‐Ti alloy and β‐C (ASTM Grade 19/Ti–3Al–8V–6Cr–4Mo–4Zr). By combining low temperature but prolonged aging, time‐dependent etching, and Fiji‐assisted image analysis, the presence and characteristics of β‐flecks are determined with precision and impartiality. This straightforward technique offers a reliable means for visualizing and quantifying β‐flecks in titanium alloys. It establishes a foundational framework that can be broadly applied to various β‐Ti alloys prone to β‐fleck formation.

Laboratory investigations on influence of thermoplastic polyurethane and its hard segment content on pavement performance of asphalt mixture

ABSTRACT Thermoplastic polyurethane (TPU) is an excellent asphalt modifier, which is consisted of hard and soft segments in the TPU molecular chain. In this paper, The conventional road performances (high and low temperature performance, water stability, fatigue performance and aging resistance) of TPU modified asphalt mixture (TPU-AM) with different hard segment content were evaluated. The results proved that the hard segment of TPU can effectively improve the high temperature performance of asphalt. Compared with TPU-AM with high hard segment content, using TPU with low hard segment content as modifier, the low temperature flexibility and fatigue resistance of TPU-AM are significantly improved. TPU-AM with hard segment content of 40% has excellent high temperature performance, while the TPU-AM with hard segment content of 10% has the best fatigue ability and low temperature performance. The water stability of TPU-AM is obviously stronger than that of base asphalt mixture, although the content of TPU hard segment has little influence on the water stability of TPU-AM. The aging results show that TPU-AM has the best aging resistance when the hard segment content is 30%. Based on the above analysis, the high performance of TPU-AM can be designed by changing the hard segment content.

Low temperature aging induced conjugated polymers aggregation by UV–Vis spectroscopy

AbstractMultiscale structural evolution of conjugated polymer (CP) solutions from disorder to aggregation via environmental perturbations is a universal phenomenon in condensed matter physics. Here, we take poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) as a model material and use Ultraviolet–Visible (UV–Vis) spectroscopy to study the hierarchical structure evolution during prolonged aging at relatively low temperature. Using in‐situ UV–Vis spectroscopy and the Franck‐Condon (FC) method, the dynamics of multiscale structural transitions in P3HT were elucidated. Hierarchical structural details can be extracted from the UV–Vis spectra, including the overall percentage of aggregates, conjugation length, degree of H‐/J‐type molecular packing, and site energetic disorder. Through covariance analysis of conformational disorder to aggregation transitions of conjugated polymers obtained under multiple conditions, we find that the trends of the above four key parameters are not consistent, which informs the unique evolution of the degree of ordering at different length scales within the aggregates. This work facilitates the scrutiny of the hierarchical structural transition from multi‐length scale perspective.

Structure and Properties of Metastable β Ti-25Nb-8Sn Alloy following Cold Rolling and Aging Treatments.

Metal implants require an elastic modulus close to cortical bone (<30 GPa) to avoid stress shielding and ensure adequate load-bearing strength. The metastable β-type Ti-25Nb-8Sn alloy has a low elastic modulus (52 GPa), but its yield strength (<500 MPa) needs enhancement. This study enhances Ti-25Nb-8Sn's elastic admissible strain through cold rolling and aging heat treatments, investigating the microstructure's impact on mechanical and corrosion properties. The results show that lower-temperature aging (<450 °C) leads to ω-phase precipitation, yielding a 300% increase in yield strength (>1900 MPa). However, this also increases the elastic modulus (~80 GPa), limiting the deformation ability. Higher-temperature aging (>500 °C) eliminates the ω phase, transforming it into α precipitates, resulting in a lower elastic modulus (~65 GPa) and improved deformation ability, with substantial yield strength (>1000 MPa). In summary, the optimal process conditions are determined as 90% cold rolling followed by aging treatment at 550 °C. Under these conditions, Ti-25Nb-8Sn achieves the most suitable yield strength (1207 MPa) and high corrosion resistance, retaining a relatively low elastic modulus (64.7 GPa) and high elastic admissible strain (1.93%). This positions it as an ideal material for biomedical implants.