Low-temperature Test Research Articles

Recommended Changes to the Precision Estimates of AASHTO T 313 (BBR)

A comparison of precision estimates in the 2019 AASHTO T 313 (BBR) with those of 2012 indicates that the 2019 multilaboratory precision values are notably smaller than those of 2012. This decrease has a significant effect on the percentage disagreements between contractors’ test results and those of state departments of transportation (DOTs). A review of state DOT and contractors’ bending-beam rheometer (BBR) results indicated that 39% of contractors' data were in disagreement with the state DOT’s data, primarily because the allowable difference between the BBR results of two laboratories (d2s) is set too low. This could cause unnecessary additional costs of testing and delay in a project. Another shortcoming of the AASHTO T 313 precision statement is that the current precision values are for creep stiffness (S) and slope (m-value) at the PG+10°C test temperature only. With the increased applications of continuous low-temperature performance grade (LTPG) and delta Tc (ΔTc), asphalt binders are also required to be tested at the lower temperature of PG+4°C. Therefore, addition of precision values for the lower test temperature is necessary. This study aimed at reevaluating BBR precision properties at PG+10°C, preparing new sets of precision values for PG+4°C, and determining precision of LTPG and ΔTc. An interlaboratory study involving seven laboratories testing six binders was conducted. The new and improved sets of precision values at PG+4°C and PG+10°C have reduced disagreements between the BBR results of two laboratories to about 5%, which better represents the 95% reliability anticipated in the analysis of precision.

Temperature dependence of the deformation behavior and mechanical properties of a Fe–Mn–Al–C low-density steel for cryogenic application

The temperature dependence of the deformation behavior and mechanical properties of a Fe–20Mn–6Al-0.6C-0.15Si austenitic low-density steel was studied by tensile test and Charpy impact test at −196 °C, −77 °C and room temperature (RT), followed by microstructure analyses. The results indicate that the decreased tensile temperature, which is corresponding to reduced stacking fault energy (SFE), promotes the planar glide of dislocations. This led to larger fraction of low-angle grain boundaries (LAGBs) at lower tensile temperature. Consequently, both the tensile strength and elongation were improved as temperature decreased. At lower impact test temperature, the load and energy of crack initiation were larger, indicating a higher resistance to crack initiation. However, the transition from stable to unstable crack propagation occurred more rapidly at lower temperature, resulting in lower crack propagation energy and reduced resistance to crack propagation. This is because less region experienced planar glide. Due to the rapid unstable crack propagation, the Charpy absorbed energy at −196 °C was the lowest. The smaller fracture surface area, larger fibrous zone and more obvious ductile fracture characteristics in radial zone suggest that the toughness is better at higher temperature. Additionally, the presence of secondary cracks at RT delayed fracture, therefore benefitting toughness.

Preparation and Characterization of Preformed Polyelectrolyte and Polyampholyte Gel Particles for Plugging of High-Permeability Porous Media.

Excessive reservoir water poses significant challenges in the oil and gas industry by diminishing hydrocarbon recovery efficiency and generating environmental and economic complications. Conventional polymer flooding techniques, although beneficial, often prove inadequate under conditions of elevated temperature and salinity, highlighting the need for more resilient materials. In this research, two types of acrylamide-based preformed particle gels (PPGs) were synthesized, as follows: polyelectrolyte and polyampholyte. These PPGs were engineered to improve plugging efficiency and endure extreme reservoir environments. The polyelectrolyte gels were synthesized using acrylamide (AAm) and sodium acrylate (SA), while the polyampholyte gels incorporated AAm, AMPS, and APTAC, with crosslinking achieved through MBAA. The swelling properties, modulated by temperature, salinity, and pH, were evaluated using the Ritger-Peppas and Yavari-Azizian models. The mechanical characteristics and surface morphology of the gels were analyzed using SEM and BET techniques. In sand pack experiments designed to mimic high-permeability reservoirs, the inclusion of 0.5 wt.% of fine PPGs substantially reduced water permeability, outperforming traditional hydrogels. Notably, the polyampholyte PPGs demonstrated superior resilience and efficacy in plugging. However, the experiments were limited by the low test temperature (25 °C) and brine salinity (26.6 g/L). Future investigations will aim to apply these PPGs in high-temperature, fractured carbonate reservoirs.

The effect of well temperature on the microstructure and the mechanical performance of bismuth-based plugs in well plugging and abandonment operations

Bismuth-tin (BiSn) alloys are considered promising candidates as potential alternatives to cement for well plugging and abandonment (P&A) applications to prevent any uncontrolled flow of deep reservoir fluids to the surface. As the temperature in the well varies with depth, the final microstructure of the BiSn alloy after its solidification might be influenced, and consequently the mechanical performance of the alloy will also be affected. The aim of this study is to evaluate the microstructural evolution of the BiSn alloy after solidification, at temperatures between 20 °C and 90 °C, to reflect in situ conditions from approximately 800m to 3 km depth. Microstructural characterization was carried out by using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The microstructural analysis revealed that the plug subjected to the lower temperature resulted in finer microstructure, whereas the grain size of the material was increased at higher temperatures. Additionally, the theoretical lever rule was employed to validate the microstructural findings. The observed microstructures were also correlated with tensile tests, which showed that the plug at 20 oC had a yield strength of 67,25 MPa, whereas the yield strength of the plug at 90 oC was only 41,64 MPa. In addition, hydraulic push-out tests further confirmed that lower testing temperatures correlate with higher pressure tolerance of the plug. The plug at 20 oC could withstand 113,5 bar, compared to the plugs at 60 oC and 90 oC which could withstand 90,4 and 50,9 bar, respectively. From all the experimental tests conducted, the outcome was that the lower temperature of 20 oC resulted in a material with a finer microstructure, which plays an important role in enhancing the mechanical properties of the bismuth-based plug. This study aims to advance the understanding of BiSn alloy performance in plug and abandonment (P&A) operations, thereby supporting the industry's efforts to qualify BiSn alloys as effective well-barrier materials.

Intermediate temperature degradation of a SiC/BN/SiC (MI) composite with holes at 500–900°C in steam

AbstractSpecimens from a Hi‐Nicalon Type S/BN/SiC (MI) ceramic matrix composite with multiple machined holes were subjected to a furnace dwell and then tensile tested. The furnace temperature range was 500–900°C, and the atmosphere was pure steam to approximate the temperature and sea level partial pressure of water vapor in the cooling air going through turbomachinery cooling holes. Exposure of control specimens was done in laboratory air at the same temperatures. Tensile results along with microscopy and spectroscopy showed significant strength degradation in some conditions due primarily to oxidation of the boron nitride fiber coating, with coating volatilization at lower temperatures and probable fiber‐to‐matrix bonding and imposed fiber stresses at higher temperatures. The greatest strength degradation occurred in the 500–600°C steam range. The fiber coating oxidation/volatilization was especially evident near the holes and was exacerbated in the lower temperature tests by porosity networks that were open to the atmosphere at fiber tow ends at the specimen edges and along the inner walls of the holes.

Study on the Application of Kramers-Kronig Relation for Polyurethane Mixture.

Polyurethane (PU) mixture, which is a new pavement mixture, exhibits different dynamic properties compared to a hot-mixed asphalt mixture (HMA). This paper analyzed whether the Kramers-Kronig (K-K) relation and thermorheologically simple properties applied to the PU mixture. Based on the results, the PU mixture exhibited thermorheologically simple properties within the test conditions. The time-temperature superposition principle (TTSP) was applicable for the PU mixture to construct a dynamic modulus master curve using the standard logistic sigmoidal (SLS) model, the generalized logistic sigmoidal (GLS) model, and the Havriliak-Negami (HN) model. The Hilbert integral transformed SLS and GLS models for the phase angle can accurately fit the measured phase angle data with newly fitted shift factors and predict the phase angle within the viscoelastic range. The core-core and black space diagrams both displayed single continuous smooth curves, which can be utilized to characterize the viscoelastic property of the PU mixture. The K-K relation is applicable for the PU mixture to obtain the phase angle master curve model, storage modulus, and loss modulus from the complex modulus test results with the test temperatures and loading frequencies. The phase angle of the PU mixture at extremely high or low test temperatures cannot be derived from the dynamic modulus data.

Thermal creep properties of virgin and irradiated cladding tubes made of Ti-stabilised DIN 1.4970 (15-15Ti) austenitic stainless steel

ABSTRACT This paper presents assessments performed on a large database of virgin material and irradiated material thermal creep data from uniaxial and pressurised DIN 1.4970 Ti-stabilised austenitic stainless steel i.e. EN X10NiCrMoTiB15–15 or ‘15-15Ti’ cladding tubes. The data base incorporates multi-heat data from uniaxial and bi-axial (internal pressure) creep tests conducted during the fast reactor R&D program of the DeBeNe (Deutschland-Belgium-Netherlands) consortium between the 1960s to the late 1980s together with more recent data, for example, from the European projects MATTER and PATRICIA and the EERA JPNM pilot project TASTE. The data comprises of a virgin material data base and a data base with irradiated creep data. The virgin material data comprises of time-to-rupture and time-to-0.2% creep strain in a temperature range of 600–800°C and covers a large range of stresses. The irradiated data base has less data and does not cover all material heats tested for the virgin material properties. The irradiation conditions are also different depending on the test reactor specifics and the irradiation campaign targets. The attained ‘irradiation damage’ in displacements per atom (DPA) for the irradiated materials range from 0.1 up to 38.1. Un-irradiated ‘reference material’ models for tensile strength and creep strength are constructed from the current-state of the art literature data and more recent results from the Sandvik 24% cold worked 1515–Ti cladding tube currently used as the main material batch studied at SCK CEN. The tensile strength model is used throughout the paper for normalizing creep strengths by the tensile properties, needed when applying the Wilshire (WE) creep model. Time factors (TF), stress factors (SF) and temperature ratio factors (TRF) are calculated for different material states for describing the impact of heat treatments, (virgin and irradiated) and irradiation conditions. This initial study targets to give estimates for the thermal creep properties of cladding tubes with a cold work range of 16–24% in a non-annealed state, as it is the preferred option for future designs according to the state-of-the art knowledge base. However, the main bulk of the available data on irradiated material is on claddings with a cold work range of 0-16% with and without annealing and at various levels of irradiation damage, thus leading to the need for estimation by interpolation and extrapolation assuming that irradiation damage levels and trends, e.g. time reduction factors found on a lower cold worked material can also be applied on materials with higher cold work levels. The results of the assessments clearly show relative strength differences between chosen material heats and heat treatments and has enabled constructing simple multilinear models for estimating the life of irradiated material. The models show that low creep test temperatures (and irradiation temperatures), low stress levels, low levels of cold work and high irradiation doses are increasing the detrimental difference between the specific material condition and the reference material. Also, it was found that the general level of life reduction (time factor TF and stress factor SF) for irradiation damaged material failure, in relation to the reference material failure, roughly coincides the corresponding values of time to 0.2% creep strain for virgin material. The estimated ‘failure creep temperature limits’ for 30 000 hours of service are studied and compared for both virgin and irradiated materials at a reference stress level of 1/3 of the tensile strength (at temperature).

Study on the influence factors of fatigue properties of large-stone asphalt mixtures based on semi-circular bending tests

In order to alleviate the fatigue cracking problem of asphalt pavements. The development of large-stone asphalt mixtures (LSAM) is a worthwhile research direction. In this paper, different loading frequencies, test temperatures and stress ratios are designed to investigate the influence of semicircular bending (SCB) test conditions for LSAM fatigue properties. Comparative tests were also conducted with AC-13 fine-grained asphalt mixtures. The fatigue property of LSAM was analyzed by applying Paris' law, measuring fatigue crack length and using fatigue rupture energy theory. The test results indicated that fatigue life increased approximately 12 times with increasing loading frequency, 5 times with lower test temperatures, and 4 times with reduced stress ratio. Respectively, the magnitude of the single fatigue rupture energy and the total fatigue rupture energy also increased. Compared to AC-13 fine-grained asphalt mixtures, LSAM has a lower rate of rise in the displacement curve and smaller fracture displacement. After logarithmic transformation, the fatigue rupture energy and fatigue life of LSAM show an obvious linear relationship, specifically Wf=0.000806Nf1.12975. In summary, based on the SCB test conditions, LSAM exhibited superior fatigue performance compared to AC-13 fine-grained asphalt mixture. Additionally, LSAM demonstrated better resistance to fatigue loading-induced deformation.

Comparative study of reciprocating sliding wear of HNBR on the effects of temperature

The wear of the sealing rubber of packers, which are widely used in the field of oil production, has drawn more and more attention nowadays. This research conducted the reciprocating sliding wear tests of hydrogenated nitrile rubber (HNBR) at 20 °C, 60 °C, 100 °C and 140 °C in different downhole mediums (dry, water, crude oil). The results show that the coefficient of friction (COF) curves fluctuate greatly under dry sliding and water medium condition, but keep a stable state in crude oil medium. In dry sliding condition, the average COFs and wear volume increase firstly, then diminish and reach the minimum at 140 °C due to the reduced hardness and matrix binding force. Schallamach waves, little debris and pits feather the worn surface of HNBR at lower test temperature (20 °C and 60 °C). Plastic deformation and cracks occur at 100 °C and 140 °C, indicating the combined mechanism of abrasive wear and fatigue wear at this condition. Both the average COF and wear volume increase slightly with temperature in water and crude oil medium. This paper has guiding significance to improve the sealing performance of packer.

Environmental tests and reliability characterization of pixel-sized colloidal QDs for next-generation display technologies

This study investigates integrating pixelated colloidal quantum dot (QD) layers into LCDs to enhance color conversion and pixel-level enrichment for future display technologies. We developed miniature prototypes with pixel-sized QD color-converter layers seamlessly integrated into the backlight unit (BLU). The prototypes, featuring red- and green-emitting QD pixels with a single blue LED on glass substrates, underwent rigorous environmental tests such as Thermal Shock Test (TST), Thermal Cycle Test (TCT), High Temperature High Humidity Test (HHT), and Low Temperature Test (LTT). The assessment covered the uniformity of light, spectral radiance, and CIE color coordinates, revealing insights into the performance of the QD layers through the analysis of pre- and post-environmental tests. Despite a decrease in luminance, the QD layers exhibited resilience against rapid temperature variations, enduring thermal shock, and thermal cycle tests without cracking. However, high-temperature and high-humidity conditions revealed susceptibility. Low-temperature stress tests demonstrated stable color gamut coordinates with no discernible shifts. This research fills a notable gap in the existing literature by conducting comprehensive environmental tests on pixel-sized QD utilization in display technologies, providing valuable insights to enhance the stability, durability, and reliability of QD displays.

Leadfree SnAgCu Solder Materials Characterization at High Strain Rates at Low Test Temperatures and Drop and Shock Simulation Using Input-G Method

Abstract Electronics will experience high and low working temperatures during operations, handling, and storage in severe environments applications such as download drilling, aircraft, and transportation. Temperatures in the vehicle underhood applications can range from −65 °C to +200 °C. Lead-free solder materials continue to evolve under varying thermal workloads. Material characteristics may deteriorate if operating conditions are harsh or heavy. Nonetheless, lead-free solders are susceptible to high strains, which can lead to electronic device failure. A better understanding of solder alloys is needed to ensure reliable operation in harsh environments. New doped solder alloys have recently been created by adding Ni, Co, Au, P, Ga, Cu, and Sb to SnAgCu (SAC) solder alloys to improve mechanical, thermal, and other qualities. SAC-Q has recently been made using Sn–Ag–Cu and the addition of Bi (SAC+Bi). It was discovered that adding dopants to SAC alloys may enhance mechanical characteristics and reduce aging damage. There is no published data on SAC solder alloys after prolonged storage at high strain rates and low functioning temperatures. The materials characterization of SAC (SAC105 and SAC-Q) solder after extended storage at low working temperatures (−65 °C–0 °C) and high strain rates (10–75 per sec) is investigated in this article. To characterize the material constitutive behavior, the Anand viscoplastic model was utilized to derive nine Anand parameters from recorded Tensile data. The generated nine Anand parameters were used to validate the Anand model's reliability. A strong correlation was established between experimental data and Anand's predicted data. The Anand parameters were used in a finite element framework to simulate drop events for a ball-grid array package on printed circuit board assembly to calculate hysteresis loop and plastic work density. The plastic work per shock event measures the damage progression of the solder interconnects. Thermal aging effects have been studied in terms of the hysteresis loop and the evolution of PWD.

Effect of Temperature on Interface Characteristics between Compacted Recycled Asphalt Pavement and Geogrid

This study presents an experimental investigation of the interface behaviors of recycled asphalt pavement (RAP) reinforced with biaxial geogrid. A series of direct shear tests were conducted on compacted RAP specimens with or without geogrid under different normal stresses (50, 75, and 100 kPa) and test temperatures (0, 20, and 35°C) using an improved temperature-controlled direct shear apparatus. The effect of test temperature on interface shear strength and strength parameters was systematically examined. Test results showed that shear stress versus shear displacement curves of RAP specimens with or without geogrid show strain-softening characteristics. Under the same normal stress, the curve of the reinforced RAP sample with a high temperature is always below that with a low temperature, which indicates the test temperature has an adverse effect on the strength of the reinforced RAP sample. The shear strength consistently increases linearly with the increase of applied normal stress for all RAP samples. The shear strength with geogrid is greater than pure RAP under a given test temperature and normal stress. The shear strength of RAP samples at lower test temperatures is higher than that at a higher temperature. Both apparent adhesion intercept of RAP-geogrid and cohesion of RAP show a decreasing trend with the increase of the test temperature and tend to be stable with increasing temperature. Both the interface friction angle of RAP-geogrid and the internal friction angle of RAP slightly decrease with the increase of test temperature. For RAP-geogrid, the value of the apparent adhesion intercept is higher than that for sand and gravel with geosynthetics. The interface friction angle is close to that of sand and gravel with geosynthetics. Therefore, RAP material can be well used as alternative backfill materials in lieu of natural aggregates such as gravel and sand in geotechnical applications.

High Temperature Friction and Wear Behavior of PTFE/MoS2 Composites

High performance polymer matrix composites with low friction and wear rate are of urgent requirement in sliding bearings and gaskets. In this study, the PTFE/MoS2 composites were prepared and the effect of testing temperature on the tribological properties were investigated. Results show that the friction coefficient and wear rate are approximately (0.14–0.19) and (4.18–13.38 × 10−4 mm3/Nm) at testing temperatures from 25 to 250 °C, respectively. At testing temperatures above 200 °C, the coefficient of friction of the composite with the addition of MoS2 is lower than that of pure PTFE, while the wear rate of the composite material with the addition of 2 wt.% and 5 wt.% MoS2 is lower than that of pure PTFE at temperatures above 150 °C. At low testing temperatures (25–100 °C), the main wear mechanism is that of slight abrasive wear, while from 150 °C to 250 °C, the main wear mechanism transformed to fatigue and severe abrasive wear.

Size correction scheme to determine fracture toughness with mini-CT geometry in the transition regime

The mini-CT geometry is used to determine relevant fracture toughness data along with the master curve description within the transition regime. However, due to significant loss of constraint experienced at loadings close to J-levels corresponding to the reference temperature T0, the current size correction scheme from ASTM E1921 standard requires a better assessment in order to avoid censoring a large number of mini-CT specimens. Indeed, the current tight ASTM E1921 requirements on the KJc limit value set to ensure that the computed transition temperature T0 is reliable often implies that many samples have to be censored. A large number of censored specimens leads to a significant loss of time, money and material, and of unnecessary activated material in the case of irradiated specimens. Besides, because of the specimen size reduction, more mini-CT samples and lower test temperatures as compared to large sized samples are required to determine a reliable T0 value. In this study, an improved specimen size correction associated to the mini-CT geometry is proposed based on a local approach of brittle fracture combined with FEM simulations. The results show that the proposed size correction reduces the T0 bias compared to the 1T-CT geometry. It also contributes to relaxing the KJc limit for the mini-CT geometry as compared to the ASTM size corrected values.

Tribological investigation of graphene or/and MoDTC as additives in PAO base oil

In this work, the anti-friction and anti-wear capacity of 0.05 wt% graphene or/and 0.5 wt% MoDTC were investigated in PAO base oil at different test temperatures. Sliding surfaces were analyzed by scanning electron microscope, X-ray energy dispersive spectrometer, and Raman spectroscopy. Results indicated that graphene alone as an additive mildly reduced the friction coefficient at low test temperatures due to its easy shear and ultrathin lamellar structure. MoDTC alone effectively reduced the friction coefficient at different test temperatures because of the formation of MoS2 tribo-film. The excellent mechanical and thermal properties of graphene tribo-film and the good lubricity of MoS2 tribo-film contributed to the enhanced anti-wear capacity of graphene and MoDTC additives, respectively. Graphene-MoDTC dual additive further improved the lubricating performance of PAO base oil. It was shown that MoS2 tribo-film derived from MoDTC dominated the friction behavior of graphene-MoDTC dual additive and graphene nanosheets further improved the anti-wear characteristics of the dual additive. It suggests that the combination of graphene and MoDTC supplies a feasible additive formulation design for PAO base oil at steel/steel interface.

Excellent low temperature performance for modified asphalt by finely dispersed sidewall tire rubber

Low temperature performance of rubber asphalt in cold regions still has challenges for facing cracking. In this study, the modified asphalt by finely dispersed degraded sidewall tire rubber (STR) was prepared to study its low temperature performance by bending beam rheometer, differential scanning calorimetry, Fraass brittleness temperature and ductility. Results showed that low test temperature and Fraass brittleness temperature of STR-modified asphalt could be down to −24.0 °C, both of which were better than that of current crumb tire rubber modified asphalt. The ductility at temperature of 5 °C was 22.3 cm, which was higher than those of other tire section rubber modified asphalt, such as tread tire rubber modified asphalt (TTRMA, 19.8 cm) and bead tire rubber-modified asphalt (BTRMA, 15.6 cm). This was owing to that STR-modified asphalt had low glass transition temperature (Tg) of −33.1 °C, which was lower than those of TTRMA (−32.9 °C) and BTRMA (−31.2 °C). Modification mechanism proposed that flexible butadiene rubber (Tg of −110.0 °C) in STR strongly promoted the relaxation of rubber molecular segments through molecular orientation and conformation switching when suffering stress concentration. Accordingly, the STR-modified asphalt had excellent low temperature performance, and could be practically used for flexible pavement in cold region.

Rheological Characterization of Reclaimed Asphalt Binder Blended with The Neat And Sbs-pma Binders

Reusing reclaimed asphalt pavement material guarantees a substantial optimization of non-renewable material resources, emissions reduction, and decreasing landfill space, along with the economic benefits associated with saving the costs of purchasing and transporting new aggregate and asphalt binder for asphalt concrete mixture production. This study aims to investigate the influence of aged asphalt binder from reclaimed asphalt pavement on the virgin asphalt binder’s rheological properties. Therefore, different dosages of RAP binder (20%, 30%, and 40% by weight of the total mix) were blended with neat asphalt binder (40-50), penetration grade (P40), and SBS polymer asphalt (SBS-PMA) binder. Using both traditional and Superpave performance testing methods, the effects of RAP on the blend's consistency, viscosity, softening, elastic recovery, rutting (permanent deformation), fatigue cracking, and low temperature cracking were evaluated. The results revealed that the RAP binder decreased the penetration value of both neat and SBS-PMA binders. The neat asphalt binder’s viscosity and softening point increased with the increase in RAP content, whereas they decreased for SBS-PMA. The RAP binder decreases the SBS-PMA elastic recovery. where the neat asphalt experienced a little improvement in elastic recovery when blended with the RAP binder. The Superpave test results revealed that the RAP binder deteriorates the performance of the SBS-PMA binder at high, intermediate, and low testing temperatures. With the addition of 20%, 30%, and 40% RAP, the high-temperature PG grade of SBS-PMA blends decreased by 0.64%, 0.95%, and 1.10%, respectively, while the low-temperature PG grade increased by 23%, 31%, and 32%, respectively. In contrast, the RAP improves the neat asphalt blend's high-temperature performance grade and deteriorates intermediate and low-temperature performance grades. The addition of 20%, 30%, and 40% RAP increased the neat asphalt blends' high-temperature properties by 1.5%, 3.3%, and 4.5%, respectively. whereas the neat asphalt low-temperature PG grade increased by 5%, 11%, and 15% with the addition of 20%, 30%, and 40% RAP, respectively. In summary, the performance of virgin and RAP binder blends depends on the individual characteristics of the blended asphalt binders

TEMPERATURE DEPENDENCE OF THE DEFORMATION BEHAVIOR OF HIGH-ENTROPY ALLOYS CO20CR20FE20MN20NI20, CO19CR20FE20MN20NI20С1 AND CO17CR20FE20MN20NI20С3. MECHANICAL PROPERTIES AND TEMPERATURE DEPENDENCE OF YIELD STRENGTH

This paper discusses the temperature dependence of the mechanical properties of multicomponent alloys Co20Cr20Fe20Mn20Ni20 (Cantor alloy), Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 under uniaxial static tension in the temperature range from 77 to 473 K. It is shown that after thermomechanical treatment all the alloys have an fcc crystal structure, but unlike single-phase Co20Cr20Fe20Mn20Ni20 and Co19Cr20Fe20Mn20Ni20С1 alloys, the alloy with 3 at % carbon exhibits large incoherent chromium carbides. Alloying with carbon causes solid solution strengthening of the austenitic phase and dispersion hardening, and promotes grain refinement in the Cantor alloy. Solid solution strengthening contributes to an increase in the athermal and thermal stress components of σ0.2, leading to higher yield stress values and stronger temperature dependences σ0.2( T ) in Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 alloys than in the Cantor alloy. The results of X-ray diffraction and microscopic analysis indicate that despite the differences in the total concentration of interstitial atoms in Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 alloys, the concentrations of carbon dissolved in the crystal lattice of the austenite phase are close. However, the higher strength properties of Co17Cr20Fe20Mn20Ni20С3 compared to Co19Cr20Fe20Mn20Ni20С1 are determined primarily by grain boundary strengthening and, to a lesser extent, by dispersion hardening. Both factors such as lowering the deformation temperature and alloying with carbon contribute to an increase in the deforming stresses of the Cantor alloy. It is shown that alloying with carbon affects the staged plastic flow of the Cantor alloy: the tensile curves of Co19Cr20Fe20Mn20Ni20С1 carbon alloy exhibit a well-defined stage of microplastic deformation, and the flow curves of Co17Cr20Fe20Mn20Ni20С3 alloy at the initial stages of plastic flow have a parabolic shape, typical of the deformation of alloys with large incoherent particles. The elongation to failure of Co20Cr20Fe20Mn20Ni20 and Co19Cr20Fe20Mn20Ni20С1 alloys increases linearly with decreasing deformation temperature, i.e., the mechanical properties of single-phase alloys are improved in the region of low test temperatures. For Co17Cr20Fe20Mn20Ni20С3 alloy, an increase in strength properties during low-temperature deformation is accompanied by a decrease in ductile characteristics, and the alloy becomes brittle from the viewpoint of macromechanical behavior.

Excellent sensitivity of SnO2 nanoparticles to formaldehyde

The room temperature gas sensors have always been an important research direction of the gas sensor, and the room temperature gas sensors without the assistance of the light is more valuable. The SnO2 nanoparticles were synthesized by hydrothermal method, which showed good formaldehyde sensitivity, had the advantages of low test temperature, only [Formula: see text]C, good formaldehyde selectivity, and especially the good response to formaldehyde at room temperature. The nanostructure and gas-sensing properties were characterized by scanning electron microscopy, EDS mapping, nitrogen physical adsorption, and X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and WS-60B gas-sensing measurement system. Compared with the reported research results, we carefully discuss the physical mechanism of the SnO2 formaldehyde sensor with low operating temperature and good formaldehyde selectivity in this paper.

Deformation behavior at cryogenic temperature in extruded Mg–Al–Zn alloy

ABSTRACT The effect of grain size on tensile deformation behaviors at room- and cryogenic-temperatures was examined using extruded Mg–Al–Zn (AZ31) alloys with different average grain sizes of 3.7, 14.0, and 38.7 μm. The mechanical properties were influenced by the grain size as well as the testing temperature. Strength increased with a finer grained structure and a lower testing temperature. Regarding the elongation-to-failure in tension, all the alloys tested at cryogenic-temperature exhibited about half the values of those at room-temperature. Deformed microstructural observations revealed that deformation twins formed in the alloys with coarse- and meso-grained structures, but decreased with grain refinement. The reduction of twin formation at both room- and cryogenic-temperatures is due to enhancement of grain boundary plasticity. Contrary to our expectation, it is interesting to note that grain boundary compatibility contributes to activation of non-basal dislocation slips, irrespective of testing temperatures. In addition, dislocation slips lead to occurrence of strain hardening after yielding even at 77 K.