Thermal Exposure Tests Research Articles

Strength characterization of cohesionless soil treated with cement and polyvinyl alcohol

Lime, cement, and bitumen are well-known traditional binders for improving the bearing capacity of soils. However, the production of these binders results in a massive impact on the environment due to the emission of greenhouse gases, such as carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). In this study, a novel cement–polyvinyl alcohol (PVA) mixture is proposed to fabricate strong composite geomaterials. The advantage of the proposed materials is that they can increase the unconfined compressive strength (UCS) and, combined with cement hydration, producing PVA glue, can be used to fill up the soil pores. Laboratory tests indicate a threefold increase in UCS with the cement–PVA-combined mixture compared to a cement-stabilized one. The results of scanning electron microscope (SEM) observations suggest that the cement–PVA composite can ameliorate the pore structure that is more solid than the cement-stabilized one. Moreover, by curing at 80 °C, the strength of the cement–PVA stabilized soil decreases by threefold, plateauing at the same strength as the non-PVA stabilized soil. In addition, the results of cyclic thermal exposure tests suggest that, with the increase in the number of heating/cooling cycles, the UCS gradually decreases compared to the initial one. However, the loss of UCS is less than 25 % under the three cycles of exposure. Thus, these composites have the potential to promote urban renewal projects in an ecofriendly manner.

Evaluation of the synergistic effect of plant-based components on the stability of curcuminoid emulsion

In this study, the effect of matrix compounds from natural curcuminoid resources on the stability of curcuminoids and emulsions thereof was evaluated. Curcuminoid emulsions were prepared curcuminoid rich sources (curcuminoid extract, an aqueous turmeric concentrate and turmeric powder) with medium-chain triglyceride oil as lipid phase, lecithin, and pectin as emulsifiers. The curcuminoid emulsions were exposed to light in the visible wavelength range (300 nm–800 nm) at the specific energy input of 0.47 kW/m2 for 7 days and to the temperature of 4 °C, 25 °C, 40 °C for 49 days. The total curcuminoid retention (TC), droplet size (DS) change, instability index (InI), and yellowness reduction (YR) was observed during the storage time. The half-life of curcuminoids in emulsions was increased to 21 h, while the half-life of free curcuminoids was 1.3 h in the light exposure test. The co-compounds from the curcuminoid sources contributed to the emulsion stability by increasing the viscosity. In the thermal exposure test, the matrix compound system retained more than 93% curcuminoids after 49 days of storage at 40 °C, whereas the phase separation increased significantly. However, the TC reduction was independent of the InI change and droplet agglomeration. The YR depended on the TC and the amount of co-components in the emulsion.

Microstructure and Nanoindentation Evolution of (Ni,Pt)Al Coating on IC21 Substrate at 1100 °C

In this study, a ~20 μm (Ni,Pt)Al coating was applied to an IC21 substrate via electroplating followed by aluminizing. A thermal exposure test at 1100 °C in air was used to investigate the microstructure evolution and nanoindentation behavior of samples with and without coating. The experimental results show that the (Ni,Pt)Al coating caused a phase change from β-(Ni,Pt)Al to Ni3Al, and the Topologically Close-Packed (TCP) phase at the interdiffusion zone grew larger after thermal exposure for 200 h at 1100 °C, while a layer of γ’ phase was formed on the surface of the IC21 substrate. The nanoindentation test indicated that the elastic modulus was reduced in both annealed samples (with and without coating), and after annealing the sample with coating had higher elastic modulus than the sample without coating. This result reveals that the coating effectively prevented the precipitation of refractory metal elements and the coarsening of the microstructure in the substrate, and thus shows that the coating had advantages not only in terms of improving the high-temperature oxidation properties of the substrate, but also played a significant role in improving the mechanical properties of the substrate.

Microstructure evolution and interdiffusion behaviors of (Ni,Pt)Al coating with and without Re-diffusion barrier on IC21 substrate at 1100°C

The degradation of high temperature oxidation resistance and mechanical properties caused by the high temperature interdiffusion between the coating and the single crystal intermetallic superalloy substrate has become a heavily researched topic within aeronautical materials research in recent years. In order to study the microstructural evolution and interdiffusion behaviors of the coating and superalloy, the (Ni, Pt)Al coating with and without Re-diffusion barrier (Re-DB) was prepared on the Ni3Al based superalloy (Grade: IC21). The thermal exposure tests were carried out on the specimens in air at 1100 °C for 200 h. The results revealed that the Al content in the coating gradually reduced during thermal exposure, and both coatings underwent phase transformation from β-(Ni, Pt)Al to Ni3Al. The coating with Re-DB had a lower phase transformation ratio. Moreover, the coating with Re-DB had smaller and fewer TCP phases precipitated in the inter-diffusion zone (IDZ) and secondary reaction zone (SRZ), showing that the Re-DB contributed to a lower extent of interdiffusion. Based on the actual measured composition-distance data, the interdiffusion coefficients between the (Ni, Pt)Al coating and the IC21 substrate with and without Re-DB were determined using HitDIC software, which verified that Re-DB impeded the diffusion of Re, Mo and Cr from substrate to the coating.

Characterisation and properties of class C-fly ash based geopolymer foams: Effects of foaming agent content, aggregates, and surfactant

In this study, GFs were first prepared in two forms; foamed mortars using the graded (GS-) and the river (RS-) sand as aggregates, and a foamed paste (P-). Aluminum (Al) powder, used as the foaming agent, had effects on porosity, pore morphology, and pore size distribution. When the amount of Al was increased, there cracks had formed in the P-GFs so the strength reduction was more drastic than that of the foamed mortars of both types. The sand aggregates acted as the skeletal structure of the GFs strengthening the materials. The attempt to improve the porosity characteristics of the foamed mortars by the addition of the dishwashing liquid surfactant was successful. The pore size of the GS-GFs became smaller and the distribution was more uniform. However, the compressive strength had degraded. Assessment on initial and final setting times, phase formation, and microstructure showed that the geopolymerisation and the C-S-H phase (tobermorite) formation had been retarded when this surfactant was incorporated. This GF also showed the most severe strength degradation in the thermal exposure test. Although all GFs mortars did not show disintegration or spalling of the pieces, microcracks appeared after exposure at 800 °C, and became more remarkable after 1000 °C. The fire resistance test on the 10 mm thick-GF mortar panels showed that the reversed-side temperature remained around 400–450 °C after 30 min of exposure without spalling or catastrophic cracks.

Thermal damage evaluation of nickel-based superalloys based on ultrasonic nondestructive testing

Ultrasonic nondestructive technique was used to assess the thermal degradation in a nickel-based superalloy in this research. Thermal exposure tests were carried out at an elevated temperature of 1050 °C to introduce controlled levels of damage, while the linear ultrasonic parameters (sound velocity and attenuation coefficient) and nonlinear ultrasonic parameters were observed. The evolution of the microstructure and the subsequent degradation in macro-mechanical properties of the material were quantitatively researched. The results suggest that the nonlinear parameters show hypersensitivity and high-credibility compared with the traditional linear parameters. The monotonic increase of the ultrasonic nonlinear parameters was explained by the evolution of the lattice mismatch and the volume fraction of the γ′ and carbide precipitated phase based on the dislocation precipitation interaction model.

Effect of shot peening and vibration finishing on the fatigue behavior of TC17 titanium alloy at room and high temperature

The effect of shot peening (SP) and vibration finishing (VF) on the fatigue performance of TC17 alloy at room-temperature was investigated. Meanwhile, to match the high-temperature service environment of the blade, the thermal exposure test and high-temperature fatigue test were also performed. The improvement in fatigue performance at room-temperature by SP + VF process was more than that by SP alone. After thermal exposure at 300 °C for 100 h, the high-temperature (300 °C) fatigue strength of the composite-treated sample remained 18.2% higher than that of the substrate. This is mainly because that SP + VF can induce lower surface roughness and remaining relatively stable gradient microstructure and compressive stress residual layer compared with SP.

Erosion behaviors and the control of fiber structure in Al2O3,f/TiAl composites

Continuous Al2O3 fiber reinforced TiAl composite (Al2O3,f/TiAl) is expected to be promising to satisfy the tougher conditions in space industry. However, the thermostability of Al2O3 fibers in TiAl alloy has not been well studied. In this work, continuous Al2O3 fibers (containing 28 mol.% SiO2) have been introduced in Ti-48Al-4Nb-2Cr alloy by powder metallurgy technology at different hot pressing temperatures. The erosion reactions of Al2O3 fibers in TiAl matrix have been investigated by thermodynamic calculation. A evolution model of the interface regions has been established. It has been determined in this study that micropores can be eliminated completely at hot pressing temperature of 1050 °C while ensuring the integrity of Al2O3 fibers. Thermal exposure tests revealed the erosion reaction of fibers was mainly dominated by element diffusions of Ti and Si, and the erosion product was determined to be Ti5Si3. Based on the regulation of erosion reactions, a novel multilayer fiber structure with higher modulus has been achieved which could be matched with TiAl alloy and expected to improve strength/toughness of the Al2O3,f/TiAl composite. This structure contains a core of original fiber and coated by three composite ceramic layers, which can be obtained at hot pressing condition of 1050 °C/50 MPa/2 h and thermal exposure of 1050 °C/60 min

Preliminary development of a conceptual first wall for DEMO

The first wall is one of the key components in a tokamak, in particular, for DEMO in the future. The conceptual first wall for a DEMO reactor is designed, fabricated and tested in this paper. It has a sandwich-like structure, which consists of a reduced activation ferritic/martensitic (RAFM) substrate, an interlayer and a plasma-facing material of tungsten produced by chemical vapor deposition (CVD-W) due to its characteristics of high density, high purity and superior thermal shock resistance. The interlayer is required to not only have good adhesion between CVD-W and the CLF-1 substrate, which is a type of RAFM developed by the Southwestern Institute of Physics, but also the capability of tritium transport prevention due to the great importance of controlling the tritium buildup in the first wall, improving the fuel efficiency and conforming to the safety regulations of tritium. Titanium nitride (TiN), a well-known tritium barrier, is selected as the interlayer material in this work. In total, eight sandwich-like first wall samples have been fabricated, and thermal cycle tests and plasma exposure tests are implemented. The results of material analysis show that the quality of the TiN coating layer is critical for good adhesion and tritium prevention. At the defects of the TiN interlayer, fluorine (F) penetrated into the CLF-1 during the CVD-W fabrication and, as a result, the sandwich-like structure was broken near the CLF-1 side. For some samples, the TiN interlayer made by CVD has sufficient adhesion as an interlayer between CVD-W and CLF-1 during tests so far. These encouraging test results support further examination of TiN as an interlayer material for W on an RAFM steel as a first wall material. Preliminary results indicate that the design and fabrication of the conceptual first wall are feasible. Further tests, including the improvement of the interlayer quality and the tritium permeation test, are necessary in the future.

Effect of ultrafine-grained microstructure on creep behaviour in 304L austenitic steel

The austenitic stainless steel 304 L was subjected to severe plastic deformation using high-pressure torsion technique at room temperature. The severe plastic deformation led not only to the grain size reduction but also to the transformation of austenite into deformation-induced martensite. At high imposed strains the martensitic boundaries disappeared and misorientation distribution exhibited nearly random misorientation distribution. The thermal exposure and tensile creep tests under constant load performed at 923 K and stresses ranging from 50 to 150 MPa revealed that austenitic microstructure contains σ phase. The ultrafine-grained microstructure coarsens during creep testing but the mean grain size is significantly finer than the predicted stationary subgrain. The results demonstrate that during creep testing new grains at precipitates of σ phase are formed and texture changes. The formation of new grains during creep keeps the microstructure of being ultrafine-grained and thus grain boundary mediated processes are enhanced in this steel.

Effect of heat treatment on microstructures and properties of a novel Al-Zn-Mg-Cu alloy for oil drilling

In view of the special requirements for strength, heat resistance and corrosion resistance of Al-Zn-Mg-Cu alloy for oil drilling, the Al-6.2Zn-2.5Mg-1.6Cu alloy was prepared by increasing Cu content on basis of Russian Series 1953 alloy. The effect of heat treatment on the microstructures and properties of the alloy was characterized by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM), and investigated by tensile test at room temperature, thermal exposure test and corrosion test. The results show that the strength after T6 aging treatment exhibit a decrease trend as an increase of the solution temperature from 465 °C to 480 °C. After the solution treated by the rate of 470 °C/1 h, second phases dissolve into the matrix very well and the strength property reaches optimum. The alloy has better comprehensive properties treated by a solution treatment of 470 °C/1 h and then followed by an aging treatment of 120 °C/24 h + 170 °C/1 h + 120 °C/24 h. Under the aging state, the precipitated phases inside the grains are suitable in size, while on the grain boundary distribute discontinuously and the precipitate-free zone is obvious. Besides, the alloy still maintain high tensile properties. The yield strength, tensile strength and elongation are 650 MPa, 686 MPa, 12.0%, respectively. The yield strength retention after heat exposure is 92%. The alloy has good corrosion resistance and the exfoliation corrosion degree. The average corrosion rate in the H2S and CO2 environment is 0.0024mm/a, which is far less than the required 0.12mm/a. It is insensitive to H2S and CO2 environments.

Failure Mechanism of Yttria Stabilized Zirconia Atmospheric Plasma Sprayed Thermal Barrier Coatings Subjected to Calcia-Magnesia-Alumino-Silicate Environmental Attack

The contribution focuses on the description of failure mechanism of atmospheric plasma sprayed multilayer thermal barrier coatings subjected to calcia-magnesia-alumino-silicate (CMAS) environmental attack. To identify exothermic and endothermic reactions which occurred during heating/cooling by means of calorimetry was also utilized initial yttria stabilized zirconia (YSZ) powder subsequently used for thermal spraying of multilayer thermal barrier coating system (TBCs), CMAS powder later on utilized for thin layer deposition and its mixture. Atmospheric plasma spray technique was used to produce the TBCs on a grit blasted nickel-based superalloy substrates, where CoNiCrAlY powder was used for deposition of a bond coat and YSZ powder was sprayed as a top coat. In accordance to the aerospace standard the thin layer of CMAS was deposited on as sprayed TBCs samples surface from its colloidal solution by paint brush method. Burner-rig test, utilizing direct propane-oxygen flame, was used for thermal cyclic exposition of the multilayer coated samples at the temperature of 1150 °C. Samples after thermal cyclic exposure test were investigated by means of materialographic analysis approaches. The significant reduction in life-time of CMAS coated YSZ top coat was observed due to lower melting point phase formation and molten silicate crystallization within the pores providing the spallation identified as a major mechanism of TBCs failure.

Performance of metal and polymeric O-ring seals during beyond-design-basis thermal conditions

This paper summarizes the small scale thermal exposure test results of the performance of metallic and polymeric O-ring seals typically used in radioactive material transportation packages. Five different O-ring materials were evaluated: Inconel/silver, ethylene-propylene diene monomer (EPDM), polytetrafluoroethylene (PTFE), silicone, butyl, and Viton. The overall objective of this study is to provide test data and insights to the performance of these O-ring seals when exposed to beyond-design-basis temperature conditions due to a severe fire. Tests were conducted using a small-scale stainless steel pressure vessel pressurized with helium to 2 bar or 5 bar at room temperature. The vessel was then heated in an electric furnace to temperatures up to 900 °C for a pre-determined period (typically 8 h–9 h). The pressure drop technique was used to determine if leakage occurred during thermal exposure. Out of a total of 46 tests performed, leakage (loss of vessel pressure) was detected in 13 tests.

Microstructure design for blended feedstock and its thermal durability in lanthanum zirconate based thermal barrier coatings

The effects of microstructure design on the lifetime performance of lanthanum zirconate (La2Zr2O7; LZO)-based thermal barrier coatings (TBCs) were investigated through various thermal exposure tests, such as furnace cyclic thermal fatigue, thermal shock, and jet engine thermal shock. To improve the thermal durability of LZO-based TBCs, composite top coats using two feedstock powders of LZO and 8wt.% yttria-doped stabilized zirconia (8YSZ) were prepared by mixing in different volume ratios (50:50 and 25:75, respectively). In addition, buffer layers were introduced in layered LZO-based TBCs deposited using an air-plasma spray method. The TBC with the double buffer layer showed the best thermal cycle performance among all samples in all tests. For applications with relatively slow cooling rates, the thermal durability in single-layer TBCs is more effectively enhanced by controlling a composition ratio in the blended powder, better than introducing a single buffer layer. For applications with relatively fast cooling rates, the thermal durability can be effectively improved by introducing a buffer layer than controlling a composition in the top coat, since the buffer layer provides fast localized stress relief due to its high strain compliance. These research findings allow us to control the TBC structure, and the buffer layer is efficient in improving thermal durability in cyclic thermal environments.

Thermal durability and fracture behavior of layered Yb-Gd-Y-based thermal barrier coatings in thermal cyclic exposure

The effects of structural design on the thermal durability and fracture behavior of Yb-Gd-Y-based thermal barrier coatings (TBCs) were investigated through thermal cyclic exposure tests, such as furnace cyclic thermal fatigue (FCTF) and jet engine thermal shock (JETS) tests. The effects of composition in the bond coat and feedstock purity for the buffer layer on its lifetime performance were also examined. To overcome the drawbacks of Yb-Gd-Y-based material with inferior thermal durability due to poor mechanical properties and low coefficient of thermal expansion, a buffer layer was introduced in the Yb-Gd-Y-based TBC systems. In FCTF tests, the TBCs with the buffer layer showed a longer lifetime performance than those without the buffer layer, showing the longest thermal durability in the TBC with the Co-Ni-based bond coat and the buffer layer of regular purity. In JETS tests, the TBC with the Ni-based bond coat and the buffer layer of high purity showed a sound condition after 2000cycles, showing better thermal durability for TBC with the Co-Ni-based bond coat rather than that with the Ni-based bond coat in the single layer coating without the buffer layer. The buffer layer effectively enhanced the thermal durability in slow temperature change (in the FCTF test), while the bond-coat composition and the feedstock purity for the buffer layer were found to be important factor to improve the thermal durability of the TBC in fast temperature change (in the JEET test). Finally, these research findings allow us to control the structure, composition, and feedstock purity in TBC system for improving the thermal durability in cyclic thermal environments.

クレイ強化ナイロン6の熱曝露が及ぼす劣化解析

The thermal exposure tests are conducted to evaluate high temperature durability of nylon 6 clay hybrid nanocomposite (NCH). The degree of crystallinity is reduced by the thermal exposure at 120 °C and 150 °C, based on Differential Scanning Calorimetry (DSC) analysis. The tensile strength, elongation and fatigue strength are also decreased by the thermal exposure. The fracture origin is changed from the surface in as-received specimens to interior in the exposed specimens.

Effect of Thermal Exposure on Tensile and Fatigue Properties of Clay Reinforced Nylon Nanocomposites

In this paper, both nylon 6 and 2 wt% clay reinforced nylon 6 matrix nanocomposite were used for thermal exposure tests at temperatures of 80 oC and 120 oC and 150 oC, respectively. Then, the tensile tests and fatigue tests of the exposed specimens were conducted at room temperature. It was shown that the tensile strength in both nylon 6 and NCH-2 decreased with an increase in thermal exposure temperature. The brittle fracture occurred in the specimens exposed at 120 oC and 150 oC. After pre-oxidation treatment at 80 °C for 100 hours, the fatigue strength decreased 14% in nylon 6, and 8% in NCH-2. From this result, it was understood that the addition of clay in nylon 6 could suppress the decrease of fatigue strengths.

On the performance and failure mechanism of thermal barrier coating systems used in gas turbine blade applications: Influence of bond coat/superalloy combination

Surface engineering plays a major role in achieving the performance and design lives of gas turbine components such as the high pressure turbine aerofoils which operate under the most arduous conditions of temperature and stress leading to a wide range of thermal and mechanical loading during service. In this study, emphasis is placed upon the role of composite systems consisting of bond coat and superalloy substrate in determining the performance and useful life of thermal barrier coatings using yttria-stabilized zirconia as top coat processed by electron-beam physical vapor deposition. Three platinum-modified bond coats of the diffusion type and three nickel-based superalloys are included in the study. Thermal exposure tests at 1150°C in air with a 24-hour cycling period to room temperature have been used to rank the performance of the coating systems. Various electron-optical techniques have been used to characterize the sequence of events leading to coating failure as marked by spallation of the top ceramic coat. It is shown that for a given superalloy substrate, the coating performance is dependent upon the type of bond coat. Conversely, for a given bond coat, the performance becomes a function of the superalloy composition used in the application. However, in both cases, coating failure is found to be predominated by loss of adhesion between the thermally grown oxide and bond coat indicating that the respective interface is the weakest link in the system. The results are interpreted in terms of the phase transformations which occur in the bond coats during exposure at elevated temperatures and the corresponding effects on their oxidation behavior.

Enhancing the Oxidation Properties of Gamma Prime + Gamma Platinum Bond Coat by Rhenium and Yttrium Additions for Improved Adhesion of Thermal Barrier Coatings on Nickel-Base Superalloys

A Re- and Y-modified γ′ + γ Pt bond coat was synthesized by diffusing 25 μm layer of Ni-6 wt%Re–0.5 wt%Y alloy and 5 μm layer of Pt into a Ni-based superalloy. It was observed that the modified bond coat can extend the useful life of thermal barrier coating systems with yttria-stabilized zirconia as top coat by more than double relative to the conventional bond coat synthesized by diffusing 8 μm layer of Pt into the same superalloy. The superior performance of the modified bond coat is explained in terms of the combined beneficial effects of Re and Y on the oxidation properties as determined from thermal exposure tests at 1150 °C and detailed microstructural characterization using various electron-optical techniques.

Oxidation Behavior of Selected Bond Coats Based on the γ′ + γ Structure and Their Performance in Thermal Barrier Coatings Deposited on a Nickel-Based Superalloy

Three bond coats based on the γ′-Ni3Al + γ-Ni microstructure were developed by diffusing pairs of Pt layers and metallic layers with selected compositions into a Ni-based superalloy. Thermal exposure tests at 1,150 °C with 24-h cycling period to room temperature were used to evaluate the thermal stability and oxidation behavior of the bond coats as well as their performance in thermal barrier coating systems utilizing zirconia-7 wt% yttria as the top coat. It is shown that a bond coat developed by a Pt layer and a layer of Ni-6 wt% Re-0.5 wt% Y alloy outperforms the conventional γ′ + γ Pt bond coats by more than two folds. Most evidence points out that the proper concentrations of Re and Y in the presence of balanced concentrations of other elements, particularly Al, Ti, Cr and Co can significantly enhance the thermal stability and oxidation resistance of γ′ + γ Pt bond coats.