Increasing Test Temperature Research Articles

Magnesium nanocomposite: increasing copperisation effect on high temperature tensile properties

Hybrid nano reinforcement particles with increasing volume percentage of copper have significantly enhanced tensile properties of commercially pure magnesium when incorporated using blend-press-microwave sintering powder metallurgy process. Incorporated hybrid reinforcement maintained their strengthening effect on magnesium matrix up to the temperature limit used in this study although gradually declined with increasing test temperature. Reinforcement particle assisted dynamic recrystallisation and thermally activated deformation process induced near super plasticity in commercially pure magnesium matrix at incomparably lower temperature and suggested the potential of near net shape fabrication in to intricate shape. Limit in total volume fraction of nanometre size reinforcement resulted the hybrid nano reinforcement with 0.3 vol.-% of metal particle most effective to enhance tensile characteristics of commercially pure magnesium.

Deformation Characteristics of 6066 and 6069 Aluminum Alloys at Elevated Temperatures

Currently liners of high-pressure hydrogen storage container for fuel cell vehicles are manufactured from the 6061 aluminum alloy pipes through spinning at elevated temperatures. Since the surroundings of the containers are reinforced with a large amount of high-cost CFRP, the use of 6066 or 6069 aluminum alloy with higher strength than 6061 is demanded to lower the cost of the container. However, the formability of these aluminum alloys at elevated temperatures has not been elucidated yet. In this study, tensile deformation characteristics of 6066 and 6069 aluminum alloys at temperatures ranging from 25 to 550°C were investigated. The total elongation of 6066 aluminum alloy was higher than that of 6069 aluminum alloy at 450°C. This may be caused by the lower volume fraction of constituent particles. The flow stresses of the two alloys were almost the same, and were decreased with increasing testing temperature. The increase in elongation and decrease in strength observed in the two alloys were attributable to dynamic recovery.

高温環境下における DLC 膜の摩擦特性に及ぼす移着膜と膜構造の影響

Diamond-like carbon (DLC) coatings has found widespread application as a protective coating in many fields because its high hardness, low friction, chemical inertness and other properties. It was reported that tetrahedral amorphous carbon (ta-C) coatings showed lower friction at high temperature than at ordinary temperature. But the mechanism of ta-C coatings' lower friction at high temperature is not clarified. In this study, we clarified the effect of transfer layer and film structure on friction properties at high temperature. We conducted friction test at five temperature environment (23 ~ 400 ℃) and analyzed transfer layer. From the result, friction coefficient of ta-C coatings decrease with test temperature increase and friction coefficient of ta-C coatings become same value at over 200 ℃. And friction coefficient decrease with thickness of graphitized transfer layer calculated by atomic force microscope (AFM) become thicker. We also deposited three kind of sp3 bonding ratio ta-C coatings by changing bias voltage in T-shaped filtered arc deposition (T-FAD) method. And we conducted friction test at 200 ℃. From the result, friction coefficient of fewer sp3 bonding ratio decreased.

Effect of LaMgAl11O19 addition and temperature on the mechanical properties of Al2O3-based ceramics

In this study, the effect of the LaMgAl11O19 content on the mechanical properties of pressureless sintered Al2O3–LaMgAl11O19 composites, including room-temperature fracture toughness and flexural strength from room temperature to 1400°C, was systematically investigated. Results indicated that Al2O3–LaMgAl11O19 ceramics exhibit enhanced mechanical properties as compared with those of monolithic Al2O3 ceramics both at room and elevated temperatures, with the maximum fracture toughness and flexural strength values of 4.88MPam1/2 and 472.8MPa at room temperature, respectively. The flexural strength of Al2O3–LaMgAl11O19 ceramics gradually decreased with increasing test temperature below 1000°C and sharply decreased thereafter. The improved mechanical properties of Al2O3–LaMgAl11O19 composites at ambient temperature were primarily attributed to the combination of crack deflection and bridging of LaMgAl11O19 platelets, while under elevated temperatures, the presence of LaMgAl11O19 platelets also played a crucial role in effectively hindering the grain boundaries sliding, thereby endowing superior bending strength to the composites.

Fractographic analysis of austempered ductile iron

AbstractThis investigation involves a systematic study of the fracture surfaces of two grades of austempered ductile iron (ADI) broken under quasi‐static, dynamic and cyclic loading conditions. The study used electron microscopy, optical microscopy and image post‐processing. The results show that the predominating fracture mechanism in ADI upon impact loading changes from quasi‐cleavage to ductile (with little areas of cleavage facets) as the testing temperature increases. Noticeably, even at the lower temperatures tested, the fracture surface of ADI shows clear signs of ductile fracture mechanisms. In particular, graphite nodule cavities suffer marked plastic deformation. Fracture after bending tests at room temperature was characterized by a mix of quasi‐cleavage facets, deformation of the contour of nodular cavities and microvoid coalescence. In the case of fatigue fracture at room temperature, the fracture surfaces show a flat appearance which has notorious differences with those reported for other loading conditions, but the typical fatigue striations were not found. The particular features identified on the fatigue fracture surfaces can be used to identify fatigue failures.It was also shown that the determination of the direction of main crack propagation by using the experimental methodology proposed earlier by the authors is applicable to ADI fractured by impact and quasi‐static loads.The results provide information potentially useful to fractographic analyses of ADI, particularly in samples that fail in service under unknown conditions.

Impact toughness of 12Cr1MoV steel. Part 1 – Influence of temperature on energy and deformation parameters of fracture

In the paper, the study of the impact toughness of 12Cr1MoV steel Charpy specimens at the temperature range from 20°C to 600°C is presented. It was revealed that the increase of the testing temperature from 20°C to 375°C and then to 600°C causes the impact toughness to decrease by 1.2 and 2.42times, respectively. The maximum energy of crack propagation during impact loading was observed at T=375°C, which is related to the increased resistance to crack propagation (cracking resistance) and sufficient strength (load capacity) of 12Cr1MoV steel. An approach to the quantitative description of impact fracture process was developed that includes the measurement of shear lip size as a quantitative fracture parameter. Scanning electron microscopy (SEM) was used to reveal and justify the reduction of load capacity at increased testing temperature and simultaneous increase of ductility and to describe the rival influence of such factors on the behavior and work of impact fracture.

Impact toughness of 12Cr1MoV steel. Part 2 – Influence of high intensity ion beam irradiation on energy and deformation parameters and mechanisms of fracture

The impact toughness of initial and irradiated 12Cr1MoV steel Charpy specimens has been studied in the range of temperatures from 20°C to 600°C. In addition, it was found that ion beam treatment of steel deteriorates the impact toughness at the tested temperatures by 5–42%. Moreover, it was revealed that the increase of testing temperature decreases the difference between the fracture energies of initial and modified steel specimens. Also, the physical regularities of irradiation effect on microhardness and hardness of the treated surface were investigated. It was also revealed that irradiated specimens fracture via more brittle mechanism, which is related to both more severe stress–strain state at the notch tip and gradient alteration of properties in the subsurface layer.

Microstructure and mechanical properties at elevated temperatures of a new Al-containing refractory high-entropy alloy Nb-Mo-Cr-Ti-Al

In the present investigation, we provide results on the casting, homogenization, and deformation behavior of a new Al-containing refractory high-entropy alloy, namely the equiatomic Nb-Mo-Cr-Ti-Al. The alloy shows a dendritic microstructure after arc melting. The dendrites completely dissolve due to a heat treatment at 1300 °C for 20 h. Besides a major phase in the form of a solid solution of W prototype structure, identified by X-ray diffraction (XRD) measurements as well as electron backscatter diffraction (EBSD), additional phases of small volume fraction within the grains and at the grain boundaries were observed. Quasistatic compression tests, performed between room temperature and 1200 °C, reveal sustaining and high yield strength up to 800 °C and an increasing ductility with increasing test temperature. The dominant deformation mechanism for quasistatic compression loading between 800 °C and 1200 °C is the 〈111〉 pencil glide of dislocations within the solid solution which was proven by the according fiber texture components, evolving during deformation.

Improved tensile properties of a new aluminum alloy for high pressure die casting

This paper investigates the effects of strain rate and test temperature on the tensile properties and deformation behavior of a recently developed high-ductility cast aluminum alloy Al–5Mg–0.6Mn. The as-cast alloy tested at room temperature and the lowest strain rate of ~1.67×10−4s−1 shows the highest yield strength of ~212MPa, ultimate tensile strength of ~357MPa and elongation (~17.6%). Increasing strain rate reduces the ultimate tensile strength and ductility of the as-cast alloy. With the increasing of test temperature, the as-cast alloy shows significantly decreases in tensile strengths and improvements in elongation. The tensile failure of the alloy is mainly originated from the cracking and debonding eutectic particles. The Portevin–Le Chatelier effect occurs in the alloy tested at RT. Strain rate in current study ranges does not significantly affect the work-hardening behavior of the alloy. Increasing test temperature apparently reduces the strain-hardening exponent and coefficient. For the alloy tested at RT, all tensile failures occur prior to global instability, indicating the existence of localized damage. In contrast, for the alloy tested at HT, the global instability occurs at strains below the logarithmic fracture strains, suggesting that there is still a postnecking damage.

High temperature mechanical behavior of AZ61 magnesium alloy reinforced with graphene nanoplatelets

In present work, graphene nanoplatelets reinforced AZ61 magnesium alloy was synthesized by disintegrated melt deposition method. The synthesized materials were subjected to homogenization at 430°C for 24h and extruded at 350°C with the ratio of 5.2:1. Experimental results revealed that graphene nanoplatelets addition have significant effect on refining grain size and changing in basal textures due to their uniform distribution throughout the composite matrix, which results in significant improvement in room temperature micro hardness, tensile and compression strengths. In addition, tensile strength of as extruded graphene nanoplatelets-AZ61 composite was investigated at temperatures ranging from 75°C to 225°C with initial strain rate of 2×10−3s−1. The results show that total fracture strain increases and tensile yield strength decreases with increasing testing temperature. The increased fracture strain at high temperature is mainly attributed to significant grain refinement and uniform particle distribution. The fracture surface analysis revealed that deformation possibly occurs through grain boundary sliding accommodated by diffusional transport.

Effect of specimen thickness on DHC velocity for Zr-2.5Nb alloy pressure tube material

Zr-2.5Nb alloy pressure tubes used in pressurized heavy water reactors (PHWR) are susceptible to failure by Delayed Hydride Cracking (DHC), which is a form of localized hydride-embrittlement phenomenon manifested in the presence of a hydrostatic stress gradient and hydrogen concentration above a threshold limit as a sub-critical crack growth process in hydride forming metals. The DHC parameters used for safety assessment are DHC velocity (VDHC) and a threshold stress intensity factor (KIH). In this work DHC velocity was determined for Zr-2.5Nb pressure tube material at 250 and 280 °C using specimens of thickness between 1 mm and 4.5 mm. The DHC velocity was found to increase with increase in specimen thickness at 250 °C and 280 °C. Significant amount of tunneling of the crack was observed for 1-mm and 2-mm thick specimens at 250 °C and 280 °C, with the degree of tunneling increasing with decrease in thickness and increase in test temperature.

Electrical treeing behavior at high temperature in XLPE cable insulation samples

This paper reports on investigations aiming to understand the behavior of electrical trees formed in XLPE cable insulation at elevated temperatures. Samples cut from a real high voltage cable equipped with an embedded electrode system and composed of a needle separated by 2 mm from counter electrode were used. The temperature was varied between 50 and 90 °C and the range of voltage changed between 9 and 18 kV. The electrical treeing process was followed by means of microscopic observation from the moment of initiation until the leading branches connected the counter electrode and partial discharge (PD) activity was monitored simultaneously. The shape and fractal dimension of the resulting trees were analyzed. It was found that temperature and voltage level had pronounced effect on the process of electrical tree formation. At lower voltages different type of trees could be formed, whereas at higher voltages branch trees dominated. Increase of test temperature reduced the time for tree initiation, whereas the tree growth time was less affected, except for the lowest voltage level at which the slowest tree development was observed at the highest test temperature. It is postulated that the impeding effect of elevated temperature on tree growth is due to a change of tree channel sidewall conductivity, whereas the observed reduction of tree initiation time with the increase of temperature and voltage level is attributed to lowering of the threshold energy for damage at higher temperature as well as increasing of the injection current at higher voltage level.

Contribution on understanding the friction film development in the performance of a dry automotive clutch system

To investigate the effects of a developed friction film on clutch system performance, clutch samples tested in three different field conditions were characterized. The wear mechanisms identified were simulated in laboratory. For this, a commercial truck friction material and cast iron were tested in a pin-on-disc tribometer. Tribological tests were carried out at standard procedures and by cleaning the wear track of the counter-face. For both lab test conditions, the normal load ranged from 200N to 450N at constant sliding speed of 2.05ms−1 and 3.27ms−1. These parameters correspond to PV values between 3.08 and 11.08 (MPams−1), which cover part of the power release in real clutch systems (between 1.3 and 20MPams−1). The friction film simulated in laboratory showed similar characteristics with those observed in field and its development and morphology depend on the test severity. Standard tribometer tests presented a transition in the wear rate at temperatures of 250°C. Removing the wear debris, the wear rate decreased almost 31% at the lowest level and 45% at the highest level of energy. The friction material tested traditionally revealed a stable friction film for tests performed to 7.88 (MPams−1) and a damaged film was found in severe wear regimes. When removing the wear debris under the same conditions, a stable friction film was observed and a less developed friction film was noted on the disc surfaces by eliminating the wear debris. The friction coefficient decreased with increasing testing temperature and cleaning the sliding surface increased the friction levels.

Corrosion behavior of 5Cr0.5Mo steel in sulfur-bearing solution at high temperature

Corrosion behavior of 5Cr0.5Mo steel in sulfur-bearing solutions as a function of temperature, test time, and sulfur content was investigated by weight loss measurements in this study. The results indicate that the corrosion rate of the steel increases with increasing test temperature. Besides, the corrosion rate increases during the initial test time and then decreases with longer test duration. Moreover, the corrosion rate rises with a higher amount of sulfur in the solution, and consequently a lower amount of sulfur leads to a decreased corrosion rate. In addition, the effect of Cr and Mo elements has been discussed.

Evaluation of Rheological Properties and Field Applications of Buton Rock Asphalt

Abstract Buton rock asphalt (BRA) is a type of natural asphalt found in Buton Island, located at southeast of Sulawesi Island of Indonesia. Because of different situations during its sedimentation process, the content of bitumen in the rock varies. The BRA used in this study contained about 20 % of bitumen by weight, with loose, black fine particles. A laboratory testing program was carried out in this study to evaluate the effects of the BRA on both the asphalt binder and asphalt concrete mixture. In the first part, a commonly used asphalt binder in China for pavement construction was used as the control binder sample. Specimens containing 0, 25, 50, 75, and 100 % of BRA, by weight of the Pen60/80 binder, in addition to the base Pen60/80 binder, were subjected to penetration test, ring and ball softening test, and the dynamic shear rheometer (DSR) test to assess their rheological properties. All tests were performed on original asphalt binders as well as short-term aged asphalt binders after the rolling thin film oven test (RTFOT). Test results showed that, with increasing BRA content, the binder’s penetration decreased, softening point increased, dynamic viscosity at 60°C increased, and complex modulus increased. The incorporation of BRA in the binder also changed the viscoelastic property of the asphalt binder. For all binders, with increasing testing temperature, the elastic portion of the binder stiffness decreased; however, the rates of decrease were different for different combinations of binders. Within the temperature range of the testing, the BRA modified asphalt binder retained a more elastic portion than the unmodified binder did. The trend was more significant at higher temperatures. From testing on samples subjected to RTFOT, BRA can improve the binder’s ability in resisting aging. Furthermore, BRA was more effective in affecting the rheological properties when its content was more than 50 % of the weight of the Pen60/80 asphalt binder. It is therefore recommended that, during a paving operation, the BRA optimal content should be about 2.0 to 2.5 % of the total weight of the asphalt concrete mixture or more. In the second part of the testing, asphalt concrete mixture samples were prepared with the Pen60/80 asphalt binder and with binders containing 50 and 100 % of BRA by weight of the Pen60/80 binder (BRA: Pen60/80 = 0.5:1 and BRA: Pen60/80 = 1:1, respectively). For comparison purpose, styrene-butadiene-styrene (SBS) modified asphalt concrete mixture samples were also prepared and were subjected to the same tests. Results from the rutting tests indicated that the BRA modified asphalt concrete mixtures had better rutting performance as compared to the control asphalt concrete mixture sample. The immersion Marshall test and the freeze-thaw splitting tensile test were performed on the samples to evaluate the influences of the BRA and SBS on water stability of the various asphalt concrete mixtures. Results showed that the BRA modified asphalt concrete mixture had similar water stability as the SBS modified asphalt concrete samples and both were better than unmodified asphalt concrete mixture. The fatigue life of the BRA modified asphalt concrete mixture was longer than that of the unmodified and the SBS modified asphalt concrete mixture samples, as determined by the semi-circular bending test.

The environment-induced cracking of as-annealed Ni3(Si,Ti) and Ni3(Si,Ti) with 2Mo in sodium chloride solutions

The environment-induced cracking (EIC) of as-annealed Ni3(Si,Ti) and Ni3(Si,Ti) with 2Mo has been researched as functions of applied stress, chloride ion concentration, test temperature, and pH. The investigation of EIC was carried out by applying a constant method in NaCl solutions. The EIC susceptibility of both intermetallic compounds increased with increasing test temperature and Cl− ion concentration and increased with decreasing pH. The fracture surface morphologies of Ni3(Si,Ti) was intergranular while Ni3(Si,Ti) with 2Mo was a mixture of intergranular and transgranular, and the relationship between log t f (time to failure) and log l ss (steady-state elongation rate) became the identical straight line irrespective of applied stress, chloride ion concentration, test temperature, and pH, which means that l ss becomes a relevant parameter for predicting t f. The EIC susceptibility of Ni3(Si,Ti) with 2Mo was lower than that of Ni3(Si,Ti), which showed the advantageous effect of Mo. From the results acquired, EIC of both the compounds was indicated to take place by hydrogen embrittlement (HE).

Effect of elevated temperature on PCB responses and solder interconnect reliability under vibration loading

In this paper, vibration tests are conducted to investigate the influence of temperature on PCB responses. A set of combined tests of temperature and vibration is designed to evaluate solder interconnect reliability at 25°C, 65°C and 105°C. Results indicate that temperature significantly affects PCB responses, which leads to remarkable differences in vibration loading intensity. The PCB eigenfrequency shifts from 290Hz to 276Hz with an increase of test temperature from 25°C to 105°C, during which the peak strain amplitude is almost the same.Vibration reliability of solder interconnects is greatly improved with temperature rise from 25°C to 105°C. Mean time to failure (MTTF) of solder joint at 65°C and 105°C is increased by 70% and 174% respectively compared to that of solder joint at 25°C. Temperature dominates crack propagation path of solder joint during vibration test. Crack propagation path is changed from the area between intermetallic compound (IMC) layer and Cu pad to the bulk solder with temperature increase.

Influence of Test Temperature on the Tensile Properties along the Thickness in a Friction Stir Welded Aluminum Alloy

The aim of this study was to evaluate microstructures and the influence of test temperature on the tensile properties, strain hardening behavior and fracture characteristics of friction stir welded (FSWed) 2219-T62 aluminum alloy thick plate joints. A fine and equiaxed recrystallized grain structure had no significant change in grains at the top of weld nugget zone (WNZ) at a rotational rate of 500 r/min compared with 300 r/min, but the grains and second-phase particles at the middle of WNZ exhibited obvious coarsening. The yield strength, ultimate tensile strength and joint efficiency were observed to decrease with increasing test temperatures. However, the elongation presented a contrast trend. Compared with the middle and bottom slices, the top slice (216 and 342 MPa) had a higher strength and a lower elongation (8.5%) at different test temperatures. Hardening capacity and strain hardening exponent of bottom slices were higher than those of the top and middle slices. Both of them at room temperature (RT) were bigger than those at higher temperature (HT) and lower temperature (LT). The FSWed joints basically failed in the border area between the thermo-mechanical affected zone (TMAZ) and heat-affected zone (HAZ) of the top slice, and in the HAZ of the middle or bottom slices, while the fracture surfaces exhibited dimple fracture characteristics at different test temperatures.

Finite Element Analysis of Deformation Due to Ball Indentation and Evaluation of Tensile Properties of Tempered P92 Steel

Ball indentation (BI) technique has been effectively used to evaluate the tensile properties with minimal volume of material. In the present investigation, BI test carried out on P92 steel (9Cr-0.5Mo-1.8W), using 0.76 mm diameter silicon nitride ball indenter was modeled using finite element (FE) method and analyzed. The effect of test temperature [300 K and 923 K (27 °C and 650 °C)], tempering temperature [1013 K, 1033 K, and 1053 K (740 °C, 760 °C, and 780 °C)], and coefficient of friction of steel (0.0 to 0.5) on the tensile strength and material pile-up was investigated. The stress and strain distributions underneath the indenter and along the top elements of the model have been studied to understand the deformation behavior. The tensile strength was found to decrease with increase in tempering and test temperatures. The increased pile-up around the indentation was attributed to the decrease in strain hardening exponent (n) with increase in the test temperature. The pile-up height determined from profilometry studies and FE analysis as well as the load depth curve from BI and FE analysis was in agreement. The maximum strain location below the indentation changes with the test temperature. Stress–strain curves obtained by conventional tensile, BI test, and representative stress–strain concepts of FE model were found exactly matching.

The investigation of factors affecting the water impermeability of inorganic sodium silicate-based concrete sealers

The composition and preparation process for an inorganic sodium silicate-based concrete sealer are introduced in the current paper. The factors affecting water impermeability of the concrete sealer are systematically explored. In addition to the concentration of sodium silicates and the viscosity of the concrete sealer, the surface tension and gelation time of the concrete sealer also affect the waterproofing efficacy of the concrete sealer. Some super-active fluorocarbon surfactants are very effective in reducing the surface tension of the concrete sealer to an ideally low value. The gelation time of the sodium silicate-based concrete sealer surprisingly increases as the concentration of the active ingredient increases but decreases as the concentration of the catalyst increases. Additionally, the gelation time decreases as the testing temperature increases. The good waterproofing properties of the developed sodium silicate-based concrete sealer result from its low surface tension and appropriate density, viscosity and gelation time.