Influence Of Aging Temperature Research Articles

On the microstructural evolution and mechanical property development of additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy with aging temperature

In this study, the microstructure and mechanical properties of a laser powder bed fusion processed eutectic high-entropy alloy, AlCoCrFeNi2.1, and the influence of aging temperature have been investigated. The as-printed material consists of a hierarchical cellular eutectic microstructure with γ cells and a B2 network along the cell boundaries. The γ matrix contains homogeneously distributed Al2O3 nanoparticles and sporadically distributed L12 long-range ordered (LRO) domains. Some B2 grains contain ultrafine body-centred cubic Cr-rich precipitates. Aging at 500–700 °C leads to disruption of the B2 network and coarsening of the B2 grains at the intersections of several cells and thinning of the rest of the regions. At 800 °C, the B2 cellular network completely disappears and turns into large isolated spherical or near-spherical B2 particles with the original γ cells being fully integrated. At 600 °C, numerous ultrafine γ′ nanoparticles form from the γ matrix and turn into elongated γ′ at 700 °C but completely disappear at 800 °C due to the formation of thermally more stable B2 precipitates. The as-printed samples show a high yield strength (YS∼ 1050 MPa) and good ductility (elongation ∼ 20 %) due to the strengthening effects from the LRO domains and the less deformable B2 and Al2O3 particles. Aging at 600–700 °C leads to significant strength improvement mainly owing to the γ′ particles. Aging at 800 °C results in a considerable decrease in YS but improves the ductility due to the disappearance of γ′ precipitates and the B2 cellular network.

The Influence of Aging Temperatures on the Microstructure and Stress Relaxation Resistance of Cu-Cr-Ag-Si Alloy

Copper alloys used in connectors rely significantly on stress relaxation resistance as a key property. In this study, a heavily deformed Cu-Cr-Ag-Si alloy underwent aging at varying temperatures, with a subsequent analysis of its mechanical properties and microstructure, with a particular emphasis on understanding the mechanism of improving stress relaxation resistance. As the aging temperature rose, the Cr precipitated into a Cr-Si composite element precipitated phase. Both work hardening and precipitation strengthening played vital roles in enhancing the stress relaxation resistance of the Cu-Cr-Ag-Si alloy, with the latter exerting a more pronounced impact. The notable performance enhancement observed after aging at 450 °C can be attributed to the synergistic effects of work hardening and precipitation strengthening. Following aging at 450 °C, the alloy demonstrated optimal performance, boasting a tensile strength of 495.25 MPa, an electrical conductivity of 84.2% IACS, and a level of 91.12%. These exceptional properties position the alloy as a highly suitable material for connector contacts.

Evolution of the Microstructure and Mechanical Properties of a Biomedical Ti-20Zr-40Ta Alloy during Aging Treatment

The research focus in the field of medical titanium alloys has recently shifted towards the development of low-modulus and high-strength titanium alloys. In this study, the influence of aging temperature on the microstructure and mechanical properties of a β-type Ti-20Zr-40Ta alloy (TZT) was investigated. It was found that the recovery and the recrystallization occurred in the as-rolled alloy depended on the aging temperature. The periodically distributed Ta-lean phase (β1) and Ta-rich phase (β2) were produced by the spinodal decomposition in all the samples aged at different temperatures. The spinodal decomposition significantly influenced the mechanical properties and deformation mechanisms of the TZT alloy. Upon aging at 650 °C and 750 °C, the as-rolled alloy exhibited a double-yield phenomenon during tensile testing, indicating a stress-induced martensitic transformation; however, its ductility was limited due to the presence of ω phases. Conversely, aging at 850 °C resulted in an alloy with high strength and good ductility, which was potentially attributed to the enhanced strength resulting from modulated structures introduced with spinodal decomposition.

Precipitation behavior of γ′ phase with a multi-model morphology in the Ni-based superalloy GH4720Li during water quenching and subsequent artificial aging and related mechanisms

The microstructure evolution of the γ′ precipitates in GH4720Li superalloy during the heat treatment processes of water quenching and subsequent aging at temperatures of 760 °C, 800 °C, and 850 °C was investigated with particular emphasis on the variation in the morphology, size, and size distribution of the precipitates and related mechanisms. Influence of aging temperature and time on the nucleation, growth, and coarsening behavior of the bimodal dispersion of secondary and tertiary γ′ precipitates were discussed. Results showed that only spherical-shaped secondary γ′ precipitates with sizes ranging from 10 to 50 nm formed during the cooling process of quenching. During aging, the nucleation of tertiary γ′ precipitate, growth of both secondary and tertiary γ′ precipitates follow the typical solid-diffusion-assisted precipitation mechanism, while the abnormal coarsening of the secondary precipitates occurs through coalescing adjacent particles. Aging temperature has a less effect on the precipitation of the tertiary γ′ precipitate but substantially influences the coarsening of the secondary γ′ precipitates. At higher aging temperatures such as 850 °C, the abnormal coarsening of the secondary γ′ precipitates, which always takes place at 760 °C and 800 °C, are significantly suppressed. The aging time mainly influences the growth rate of the secondary γ′ but shows little effect on the evolution of the tertiary γ′ phase. Precipitates strengthen the alloy through strong coupling interaction mechanism. An optimal aging strategy heating at 850 °C for 8 h is proposed for the GH4720Li superalloy, yielding the best uniform dispersion of the precipitates, maximum hardness of the sample, and being considered time and energy-saving.

Influence of ageing temperature on the tribological characteristics of LM25/Al2O3/SiC hybrid metal matrix composite for lightweight applications

The demand for hybrid composites has lately increased due to their extraordinary qualities, which include unique mechanical, tribological, and physical capabilities not found in other materials. These composites improve performance and utility by mixing different reinforcing components, making them highly sought after. However, there is a study gap on the effects of long-term ageing on the tribological characteristics of LM25 (Al–6.6Si–0.2Mg)/Al2O3/SiC metal matrix composites (MMCs). As a result, extensive studies on the influence of ageing temperature on the tribological properties of LM25/Al2O3/SiC MMCs via long-term ageing effects still need to be included. Therefore, this study investigated the metallurgical and hardness properties of stir-cast LM25 alloy reinforced with Al2O3 and SiC particulates with varying ageing temperatures. Furthermore, dry sliding wear behaviour is also examined. The investigation concluded that adding micron-sized Al2O3 and SiC particles to LM25 improves hardness and tribological properties. As the ageing temperature increased, the eutectic particles became coarser. Furthermore, the result illustrates that the coefficient of friction (COF) values also enhanced with wear rates. Higher loads increased the wear rate and COF, whereas higher sliding speeds decreased the COF and wear rate.

Influence of Aging Temperature and Duration on Flavor and Tenderness Development of Vacuum-Packaged Beef Longissimus

The objective of this study was to investigate the influence of beef wet-aging temperature and duration on beef palatability. Paired beef strip loins were obtained from USDA Choice carcasses (n=60) at a commercial processing facility. Paired strip loins were assigned to a storage temperature (−2°C, 0°C, or 4°C). Strip loins were portioned into half loins and further assigned to an aging duration (14, 28, 42, or 56 d). Loins were aged in commercial upright refrigerators.After aging, loins were fabricated into 2.54-cm steaks and assigned to either volatile compound analysis, descriptive sensory analysis, or consumer sensory analysis. Data were analyzed as a split-plot in which carcass served as the whole plot and loin portion served as the subplot. An alpha of  P<0.05 was used. For descriptive sensory analysis, an interaction was observed for beef identity, bloody/serumy, fat-like, liver-like, bitter, sour, and musty/earthy (P<0.05). Loins aged for 56 d at 4°C were the most intense for liver-like, sour, and musty/earthy notes compared with all other treatments (P<0.05). An interaction was observed for consumer juiciness, tenderness, and overall liking (P<0.05). Steaks from loins aged for 14 d at −2°C were rated the least for juiciness, tenderness, and overall liking (P<0.05). Ethanol, acetic acid,1-penten-3-ol, and 2-methylbutanal were each greatest in loins aged for 56 d (P<0.05). Aging at 4°C yielded the greatest concentrations of ethanol and heptanoic acid (P<0.05). Off-flavor development increased during extended aging but was dependent on storage temperature. Extended aging (>28 d) conducted at colder temperatures did not negatively influence palatability. Aging for 14 d at −2°C was detrimental to consumer liking. It may be concluded that both aging temperature and duration should be considered when seeking to optimize beef palatability.

Black garlic production: The influence of ageing temperature and duration on some physicochemical and antioxidant properties, and sugar content

SummaryHerein, some quality characteristics (water content, pH, antioxidant activity and sugar contents) of fresh garlic (Taşköprü, Türkiye) and black garlic, which were produced under various ageing temperatures (60 °C, 70 °C and 80 °C) and durations (30, 45 and 60 days), and the effect of ageing processes on these quality characteristics were determined. The ageing process caused a reduction (P < 0.01) in the water content and pH value of the samples, while enhanced (P < 0.01) antioxidant activity and increased (P < 0.01) the content of glucose, fructose, sucrose and reducing sugar. Both the water content and pH value of the black garlic declined significantly with increasing ageing temperature, while only pH value of the black garlic declined significantly with increasing ageing duration. Ageing samples at 60 °C and 70 °C exhibited higher antioxidant activity than those aged at 80 °C, which had similar activity to the fresh samples. A similar status was observed when the ageing temperature was prolonged to 60 days. Sucrose concentration of the black garlic samples raised with elevating the ageing temperature and declined with prolonging the duration. While a remarkable decline in the reducing sugars of the black garlic samples was observed with elevating the ageing temperature, the maximum concentration was recorded on the 45th day of the ageing process. However, the black garlic samples produced at 60 °C for 60 days or 70 °C for 30 days could be recommended to get a final product with good antioxidant capacity, adequate amount of free sugars, pH value and water content.

Unified theory of nucleation and coarsening in the solid state

ABSTRACT Despite numerous contributions made to the modelling of precipitation kinetics, no theory seems to have unified all the concepts required to simulate the nucleation, growth, and ripening processes as one continuous process. In the present work, a novel approach was used to reshape the master equation calculating the evolution of the size distribution, so that the zero-flux condition can represent a steady-state evolution. This modification was made by introducing explicitly the probability for clusters to grow or to dissolve in each size class. The expression found to calculate this probability allowed the calculation of the entire evolution of the size distribution from the first step of nucleation to the final stages of the ripening process. The winners-losers concept also allowed for a better definition of the average condensation and evaporation rates, which were found by applying the thermodynamic extremum principle and assuming that a population of clusters of a given size behaves on the average as one cluster of the same size and submitted to the same driving forces. Furthermore, the thermodynamic extremum principle allowed us to show that the subcritical growth regime must be interface controlled to maximise the dissipation rate of energy. The computational scheme based on the new theory was applied to calculate the size evolution of precipitates in the Al-Cu system. The influence of aging temperature on the evolution of the number density of precipitates during homogeneous nucleation was found to agree with experimental estimations of number densities made on uniformly distributed θ′-Al2Cu precipitates.

Influence of Aging Temperature on Mechanical Properties and Structure of M300 Maraging Steel Produced by Selective Laser Melting.

This paper deals with the study of high-strength M300 maraging steel produced using the selective laser melting method. Heat treatment consists of solution annealing and subsequent aging; the influence of the selected aging temperatures on the final mechanical properties-microhardness and compressive yield strength-and the structure of the maraging steel are described in detail. The microstructure of the samples is examined using optical and electron microscopy. The compressive test results show that the compressive yield strength increased after heat treatment up to a treatment temperature of 480 °C and then gradually decreased. The sample aged at 480 °C also exhibited the highest observed microhardness of 562 HV. The structure of this sample changed from the original melt pools to a relatively fine-grained structure with a high fraction of high-angle grain boundaries (72%).

Influence of aging temperature on the properties of Cu/(SAC0307 powder +Zn-particles)/Al joints ultrasonic-assisted soldered at low temperature

Purpose This study aims to evaluate the effect of thermal aging temperature on the properties of Cu/Al joints. Design/methodology/approach A new method in which 1 µm Zn-particles and SAC0307 with a particle size of 25–38 µm were mixed to fill the joint and successfully achieved the micro-joining of Cu/Al under ultrasonic-assisted at 200°C, and then, the effect of aging temperature on the properties of Cu/Al joints at different aging times was researched. Findings The results showed that the Cu interface intermetallic compounds (IMCs) had the same composition and had two layers with Cu5Zn8 near the Cu substrate and CuZn5 near the solder. As the aging time increased, CuZn5 gradually transformed to Cu5Zn8, and the thickness of the CuZn5 layer gradually decreased until CuZn5 disappeared completely. There was a Sn–Zn solid solution at the Al interface, and the composition of the Al interface of the Cu/Al joints did not change with changing temperature. The IMC thickness at the Cu interface of the joints continued to increase, and the shear strength of the Cu/Al joints decreased with increasing aging temperature and time. Compared with the as-received samples, the IMC thickness of the Cu interface of joints increased by 371.8% and the shear strength of the Cu/Al joints was reduced by 83.2% when the joints were aged at 150°C for 24 h. With an increase in aging temperature, the fracture mode of the Cu/Al joints changed from being between solder balls and Zn particles to between Zn particles. Originality/value With increasing aging temperature, the shear strengths of the Cu/SACZ/Al joints decreased at the same aging time, the shear strength of Cu/SACZ/Al joints at 150°C for 24h decreased by 83.2% compared with that of the as-received joints.

Influence of Aging Temperature and Duration on Spoilage Organism Growth, Proteolytic Activity, and Related Chemical Changes in Vacuum-Packaged Beef Longissimus

The objective was to evaluate the influence of vacuum-packaged aging temperature, duration, and their inter-action on spoilage organism growth, proteolytic activity, and resulting beef tenderness. Paired strip loins were collected from 60 USDA Low Choice beef carcasses (n=60), then assigned a storage temperature (−2°C, 0°C, or 4°C). Loins were portioned into half loins and assigned to an aging duration (14, 28, 42, or 56 d) and vacuum packaged. Loins were aged in commercial upright refrigerators. Half-loin packages, at their respective aging duration, were aseptically opened and cut surface swabbed for microbial analysis before fabrication into 2.54 cm strip steaks (n=5). Steaks assigned to slice shear force (SSF) were cooked to 71°C. A raw steak was used for microbial, proteolytic, and volatile analyses. Two-way interactions were observed for all spoilage organisms (P < 0.001). Aging for 42 and 56 d at−2°C produced lower microbial counts compared to individual aging durations at 4°C (P < 0.05). Loins aged for 14 d at 4°C had increased desmin and troponin-T degradation compared to aging for 14 at−2°C and 0°C (P < 0.05). Loins aged at 4°C produced more tender steaks compared to−2°C and 0°C (P = 0.001). Steaks aged for 42 and 56 d possessed the lowest SSF values (P < 0.05). Aging for 56 d at 4°C produced the greatest amount of total free amino acids (P < 0.001). Two-way interactions were observed for 7 compounds (alcohols, aldehydes, carboxylic acids, ketones, and sulfur-containing compounds; P < 0.05). Aging for 56 d at 4°C had the greatest ethanol concentration (P < 0.05). These data indicate aging at 4°C increases the rate of proteolysis and subsequent tenderness development and flavor precursor accumulation. However,extended aging at 4°C resulted in increased microbial counts. Many traits peaked at 42 d of aging.

Copper-Based Alloys with Optimized Hardness and High Conductivity: Research on Precipitation Hardening of Low-Alloyed Binary CuSc Alloys

Copper alloys, combining optimized strength with high electrical and thermal conductivity, are analyzed in-depth, in order to meet the increasing requirements of today’s and tomorrow’s applications in the electrical and automotive industries. The conducted research analyzes alloys with up to 0.3 wt.% scandium, as an alloying element with limited solubility in copper. For the simultaneous enhancement of mechanical strength and conductivity, precipitation hardening is the conducted process method, accompanied by experimental and simulation-based investigations. Therefore, the influence of aging temperatures, in the range of 350 °C to 500 °C, is analyzed in combination with 25%, 50%, and 75% prior cold deformation. CuSc starts precipitating at 375 °C, without prior cold working, whereas mechanical deformation refines the growing intermetallic precipitates. Higher temperatures improve the formation of precipitates but carry the risk of overaging. The first key achievement is to use a thoroughly examined thermomechanical treatment, investigating the growth of precipitates to reach significantly higher hardness than the benchmark alloy, CuZr0.15. Furthermore, the analyzed CuSc alloys show advantages in the investigated recrystallization behavior, making them, especially, applicable for higher operating temperatures. Future research will assess ternary alloying combinations, to further scoop the latent potential of CuSc alloys.

Aging temperature role on precipitation hardening in a non-equiatomic AlCoCrFeNiTi high-entropy alloy

In the present study, the influence of aging temperature on precipitation hardening in a non-equiatomic Al0.2Co1.5CrFeNi1.5Ti0.3 high-entropy alloy has been evaluated. The aging curves have been deduced for different aging temperatures (650, 750, and 850°C) as a function of time. The aging response was found to be markedly different with varying aging temperatures. A combined FESEM and transmission electron microscope studies have been performed to understand the evolution of precipitates and their characteristics with aging temperature and time. The variation of precipitate morphology, number density and size of precipitates with aging temperature were correlated with the age-hardening response. Additionally, the role of lattice misfit strain on precipitate morphology has been evaluated.

Influence of Aging Temperature on Metallurgy, Impact Toughness and Pitting Behavior of Flux-Cored Arc Welded 2205 Duplex Stainless Steel Joint

Influence of Aging Temperature on Metallurgy, Impact Toughness and Pitting Behavior of Flux-Cored Arc Welded 2205 Duplex Stainless Steel Joint

Microstructure and mechanical properties of 15-5 PH stainless steel under different aging temperature

The influence of aging temperature on microstructure and mechanical properties of Cr15Ni5 precipitation hardening stainless steel (15-5 PH stainless steel) were investigated at aging temperature range of 440–610 °C. The tensile properties at ambient temperature of the 15-5 PH stainless steel processed by different aging temperatures were tested, and the microstructural features were further analyzed utilizing optical microscope (OM), transmission electron microscope (TEM), electron backscatter diffraction (EBSD) as well as X-ray diffraction (XRD), respectively. Results indicated the strength of the 15-5 PH stainless steel was firstly decreased with increment of aging temperature from 440 to 540 °C, and then increased with the increment of aging temperature from 540 to 610 °C. The strength and ductility were well matched at aging temperature 470 °C, and the yield strength, tensile strength as well as elongation were determined to be 1170 MPa, 1240 MPa and 24%, respectively. The microstructures concerning to different aging temperatures were overall confirmed to be lath martensite. The strengthening mechanisms induced by dislocation density and the second phase precipitation of Cu-enriched metallic compound under different aging temperatures were determined to be the predominant strengthening mechanisms controlling the variation trend of mechanical properties corresponding to different aging temperatures with respect to 15-5 PH stainless steel.

Microstructural characterization of aging precipitation behavior of 17Cr-0.86Si-1.2Cu-0.5Nb ferritic stainless steel

Herein, the precipitation behavior of 17Cr-0.86Si-1.2Cu-0.5Nb ferritic stainless steel during isothermal aging is studied by using scanning electron microscopy, energy dispersive spectrometer and high-resolution transmission electron microscopy. Moreover, the influence of aging temperature and time on hardness is systematically investigated. The results reveal that the Cu-rich phase mainly precipitates below 750 °C, whereas the Nb-rich phase precipitates above 750 °C. The Cu-rich phase exhibits an evolution behavior of B2-9R-FCC and the coarsening rate of Cu-rich phase increases by two orders of magnitude from 650 to 750 °C. Furthermore, the side of rod-shaped Cu-rich phase maintains incoherent interface with the matrix, however, the tip of Cu-rich phase exhibits a coherent interface with the matrix with an orientation relationship of 011¯α//1¯11Cu. The Nb-rich phase includes Fe2Nb, Fe3Nb4Si5, CrNbSi, (Fe,Cr,Si)2Nb, and Nb2C phase after thermal aging. At T < 750 °C, both sides of the Nb-rich phase provide nucleation points for the Cu-rich phase. At T = 850 °C, the tip of Cu-rich phase provides a nucleation site for Nb-rich precipitation. A coherent interface can be found between (Fe,Cr,Si)2Nb and Cu-rich phases, and the Cu-rich phase grows along (311) crystal planes of (Fe,Cr,Si)2Nb. Finally, the hardness change with aging time shows a single peak feature at T < 750 °C and a double-peak at 850 °C. The occurrence of aging peak is delayed and the peak values gradually decrease with the increase of aging temperature.

Phase-field simulation of early-stage kinetics evolution of γ' phase in medium supersaturation Co-Al-W alloy

The early precipitation of γ'-Co3(Al, W) phase affects the spatial distribution and kinetic evolution of precipitates for the morphology transmission effect, but the nucleation and concomitant growth are not studied still by aging experiments due to the expeditious precipitation of γ' phase in Co-Al-W alloy. By using the phase-field simulation with sublattice free energy, the early-stage kinetics evolution of γ'-Co3(Al, W) phase in a medium supersaturation Co-9Al-8W (at.%) alloy aged from 1023 K to 1173 K is investigated. The influences of aging temperature on the evolution of morphology and composition of γ' phase, and the kinetics of nucleation and growth to coarsening are clarified. It is found that the rates of composition evolution of W in γ phase are two or three times that of γ' phase, and the W compositions in γ and γ' phases show a linear relationship with time t–1/3, which means that the coarsening takes place earlier at high temperature. In addition, the equilibrium partitioning ratios indicate Al and W partition into the γ' phase and the ratios decrease with elevated temperature. The compositional variations across the γ/γ' phase interfaces suggest that low aging temperature makes the stoichiometric ratio closer to 3:1. Moreover, the precipitation evolutions from early nucleation to growth and coarsening in Co-Al-W alloy are distinguished, and the rate constants of square and cube of average particles radius increase with temperature. In later growth stage, the relationship of the square of average particles radius and time is obeyed, while the steady-state coarsening stage follows the cube law. The time exponents of particles number density at the coarsening stage are close to –1 of Kuehmann-Voorhees (KV) theory. The study demonstrates that the early-stage evolution of γ' phase which is undiscovered in the experiment can be captured by the phase-field simulation, and the resultant kinetics laws agree well with the experimental and theoretical results.

Influence of Aging Temperature on Precipitation Kinetics, Morphology and Hardening Behavior of Al-7475 Alloy

In this research, the precipitation hardening behavior of Al-7475 alloy is investigated by a comprehensive experimental study on the relationship between thermal aging and evaluation of the kinetics and hardening properties of the alloy. The investigation was carried out using X-ray diffraction analysis (XRD), differential scanning calorimetry, scanning and transmission electron microscopy investigations and Vickers hardness (HV) test. The XRD results show that increasing the aging temperature, from 273 to 620 K, enhances the coarsening and evolution of precipitates which leads to an increase in the particle size. The thermal analysis shows the precipitation kinetics of the observed phases such as $$\upeta '$$ , $${T}'$$ , and $$\upeta $$ , based on the correlation between migration and diffusion of spread atoms in the Al matrix. In addition, the TEM micrographs indicate that needle-shaped precipitates distinguish the development of $$\upeta '$$ and/or $${T}'$$ - precipitates which at most contribute to the material strengthening. Moreover, the reaction order values of $$\upeta '$$ and $$\upeta $$ -precipitate nucleation indicate that the developed phases are radially grown.

The influence of ageing temperature on carbide phases precipitation at grain boundaries of P/M Ni-base superalloys

The way to set ageing regimes of P/M Ni-base superalloy for disk application was demonstrated. The optimal ageing temperatures were identified by microstructure investigations. Mechanical tests of the material with different volume ratio of carbide phases were carried out. The obtained results confirm the correctness of the detected patterns.

Microstructure and property of laser additive manufactured alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si after aged at different temperatures

The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures. In this study, the influence of aging temperatures (600, 700 and 800 °C) on microstructure and mechanical properties of titanium alloy Ti–6Al–2V–1.5Mo–0.5Zr–0.3Si was investigated. The results indicate that after solid solution treatment at 970 °C followed by water quenching, the alloy mainly consists of coarsening lamellar α phase in martensite α′ matrix. Aging at 600 °C will not change the size of primary lamellar α phase but lead to huge amount of secondary α phases (αs) generating with very fine microstructure. By increasing the aging temperature, the number of αs decreases but with coarsened microstructures. When aged at 800 °C, the width of the αs phase reaches 350 nm, almost 7 times wider than that aged at 600 °C. The changing size of αs obviously influences the property of the alloy. The fine αs leads to high strength and microhardness but low plasticity, and specimen aged at 700 °C with suitable αs size has the best comprehensive properties.