Thermocyclic Tests Research Articles

Unveiling the humidity effect and achieving an unprecedented 12% PCE in MAPbBr3 solar cells

Fabricating high-efficiency MAPbBr3 solar cells is challenging due to substantial recombination losses within the perovskite layer and at interfaces with charge transport layers. Here, we investigate the critical role of ambient humidity in improving device performance and stability. We varied humidity levels from dry N2 to 80 % relative humidity (RH) and identified that maintaining the environment at 25 % ± 0.82 % RH optimally enhances the morphological, structural, optical properties of MAPbBr3 films. Our novel analyses demonstrate that this specific humidity level significantly reduces bulk defect densities and interface recombination sites without any additive, leads to the formation of larger crystal grains, and improves optical qualities as well. Consequently, devices fabricated under these conditions achieved the highest device efficiency of 12.14 % for the MAPbBr3 solar cells. Additionally, they exhibited remarkable long-term stability, retaining nearly 90 % of the initial efficiency after 1000 h damp-heat and 100 cycles of thermo-cycling tests with encapsulated devices.

ULTRA-JET DIAGNOSTICS OF DAMAGE TO CARBON FIBER PANELS AS A RESULT OF THERMAL CYCLING

The article is devoted to the development of a method of ultra-jet diagnostics of damage to carbon fiber panels, based on the high-speed impact of a liquid jet on the surface of a sample, the results of which are judged on its quality indicators. It is shown that the informative criteria for assessing the quality of carbon fiber panels as a result of ultra-jet diagnostics are the amount of stratification of the composite material and the depth of the cavity. Based on the analysis of experimental data, it is proved that the method of ultra-jet diagnostics makes it possible to assess the level of defectiveness of a carbon fiber panel formed as a result of thermocyclic tests of samples of various durations. Dependences are constructed according to which it is possible to observe a change in the informative (geometric parameters) of samples depending on the formed damage as a result of previously conducted thermocyclic tests. The presented material is part of the ongoing comprehensive research on the assessment of the possibility of using the proposed method of ultra-jet diagnostics to assess the quality of composite materials used in rocket and space technology.

Forming and heat resistance study of NiAl‒ZrO<sub>2</sub> gradient thermal barrier material for superalloys

In this work the spark plasma sintering (SPS) technique was used to forming a functionally gradient thermal barrier material based on nickel aluminide (VKNA) and zirconium oxide (YSZ). Layer-by-layer powders of VKNA / mixtures VKNA + 15 (30) % YSZ / YSZ were consolidated in a graphite matrix at 1070°C in a vacuum atmosphere for 5 minutes and at a pressure of 30 MPa. It is determined that the sintered material has good adhesion of layers, there are no interlayer boundaries. To check the functionality of the material, thermocyclic tests were carried out at 1100°C in the air. The results showed that the material containing the sublayer VKNA + 30 % YSZ has better heat resistance. Ill. 5. Ref. 28. Tab. 2.

Enhancing Resin Cement Adhesion to Zirconia by Oxygen Plasma-Aided Silicatization.

The combinations of alumina particle air abrasion (AA) and a 10-methacryloyloxyidecyl-dihyidrogenphosphate (MDP) primer and a tribochemical silica coating (TSC) and a silane–base primer are contemporary pre-cementation treatments for zirconia restorations for bonding with resin cements. However, the stability of zirconia resists the mechanical or chemical preparations. The purpose of this study was to develop an atmospheric-pressure oxygen plasma (OP)-aided silicatization method to enhance the adhesion of resin cements to zirconia. Zirconia discs were prepared to receive surface treatments of different combinations: (1) AA or TSC (2) with or without OP treatment, and (3) a chemical primer (no primer, silane, or a silane–MDP mixture). The surface morphology, hydrophilicity, and chemical compositions were characterized, and the resin–zirconia bond strengths were examined either after 24 h or a thermocycling test. The results indicated that the OP treatment after the TSC facilitated the homogeneous distribution of silane and crosslinking of silica particles, and effectively improved the hydrophilicity. The OP increased the O and Si and reduced the C elemental contents, while the combination of TSC, OP, and silane induced SiOx generation. Among the groups, only the TSC-OP–silane treatment effectively enhanced the bond strength and maintained the adhesion after thermocycling. With these results, the OP aided the silicatization protocol effectively, generated silane crosslinking, and resulted in superior resin–zirconia bond strength and durability compared to the current treatments.

Control of High-Temperature Static and Transient Thermomechanical Behavior of SiMo Ductile Iron by Al Alloying

Silicon and molybdenum (SiMo) ductile iron is commonly used for exhaust manifolds because these components experience thermal cycling in oxidizing environment, which requires resistance to fatigue during transient thermomechanical loads. Previous studies have demonstrated that alloying elements, such as Al, to SiMo ductile iron reduces the amount of surface degradation during static high-temperature exposure. However, deterioration of sphericity of the graphite nodules and a decrease in ductility could affect the tendency of cracking during thermal cycling. In this article, the effect of Al alloying on static and transient thermomechanical behavior of SiMo ductile iron was investigated to optimize the amount of Al alloying. A thermodynamic approach was used to confirm the effect of the Al alloying on the phase transformations in two SiMo cast irons, alloyed by 1.8% Al and 3% Al. These two alloys were cast in a laboratory along with the baseline SiMo ductile iron. Several experimental methods were used to evaluate the dimensional stability, physical properties, static oxidation, and failure resistance during constrained thermal cycling testing to compare their high-temperature capability. Experimental results verified that Al alloying increases the temperature range and decreases volume change during eutectoid transformation, which together with enhancement of oxidation protection improved the dimensional stability. Thermocycling tests showed that the number of cycles to failure depends on the amount of Al alloying and the applied high-temperature exposure during each cycle. SEM/EDX, high-resolution TEM and µCT analysis were used to verify the mechanism resulting from the Al alloying protection. It was shown that an optimal level of Al alloying for balancing oxidation and thermal cracking resistance depends on thermomechanical conditions of application.

Test technique for turbine cooled blades of gas turbine engines

Test technique for turbine cooled blades of gas turbine engines is developed. The new approaches during development of inductor structures, induction heating devices, cooling systems, hydraulic force loading system and methods for their design to provide the prescribed nonuniform heating the turbine cooled blades and to carry out more effective the thermocyclic tests are presented taking into account the developed test technique. Study of effect of the clearances between inductor and blade surface and change of inductor efficiency on the thermal state of blade is presented. The test rig and improved systems of induction heating and mechanical loading are used to improve accuracy and simulate more complete the operating thermomechanical loading the full-scale cooled and uncooled blades at the thermocyclic tests. The results of rig testing the turbine cooled monocrystalline blades of gas turbine engine are received according to the developed test technique.

Reducing the risk of formation of the eutectic Cu-Cu2O during welding of copper with steel by improving treatment preparation technology

ABSTRACT The water-cooled nozzle works in quite difficult conditions: on the one hand, it comes into contact with liquid metal or slag, on the other it is cooled by water, receives and transmits large heat fluxes and experiences frequent heat changes. When welding copper with steel, an eutectic is formed at the grain boundaries, which reduces the efficiency of the weld. Scientific work has been performed to reduce the risk of eutectic formation. The method of preparation of metal edges by rolling was investigated. The calculation and analysis of the stress-strain state of the metal was done for rolling the edges of copper. The optimal values were set when analysing and comparing the results of rolling at different compressions. The performed thermocyclic tests confirmed the results of the study when rolling the edges of copper intracrystalline shifts interfere with the formation of eutectic in large quantities. Calculation of the field of equivalent plastic deformations was done for rolling the edges of copper depending on the compression. Preparation of copper edges before welding by rolling reduces the risk of formation of a large number of eutectic compounds. This method increases the quality of the weld, durability and efficiency of the blast furnace.

ВЛИЯНИЕ ЭКСПЛУАТАЦИОННЫХ ФАКТОРОВ НА ОСНОВНЫЕ ФИЗИКО-МЕХАНИЧЕСКИЕ СВОЙСТВА ИЗДЕЛИЯ ИЗ СТЕКЛОПЛАСТИКА ВПС-31

The results of the work performed at NRC «Kurchatov Institute» – VIAM in research on aspects of the influence of operational factors (high humidity and temperature) on the physic-mechanical properties of glass fiber composite VPS-31. The main physical and mechanical properties of samples obtained from the spar of the helicopter's main blade are presented (including the glass transition temperature, strength and modulus of elasticity in tension, elongation at break at various test temperatures in the initial state and after exposure to moisture). We studied the fragments of the spar, successfully passed thermocyclic tests («day/night»). The results of the research confirmed the possibility of exploitation of glass fiber composite VPS-31in a humid tropical climate.

Investigations of heat exchanger elements at tests

A method for modeling the thermal state and a method for conducting research on plate heat exchanger elements for an aircraft gas turbine engine using the developed test equipment during thermocyclic tests are proposed. The analysis of the operating conditions of the heat exchanger is carried out and the most thermally stressed sections of the heat exchanger are identified. Optimal inductor designs are selected. The methods and boundaries of the effective control and thermal state in the elements of the heat exchanger are determined. Studies have shown the possibility of using high-frequency induction heating when testing sections of a heat exchanger for thermocyclic durability. The results of testing elements of a plate heat exchanger for a gas turbine engine are presented.

On the thermocyclic tests of corset shape samples as a promising method for studying thermal fatigue

The dynamics of deformation and fracture of the corset shape flat samples under cyclic heating was analyzed. These tests allow us to trace metallographic changes in the substructure of the material that is a result of its plastic deformation. The cracks appear in the first test cycles, regardless of the length of their thermal cycle mode. It means that the material is currently in a state favorable for cracking, according to the commonly accepted terminology. The damage accumulation specific for the development of thermal fatigue was completed in the first few cycles, and possibly in the zero half-cycle of tests. Test results could be explained by an excessively large plastic deformation in the cycle and confirmed by the evaluation calculation. We believe that deformation under cyclic heating in the central part of the corset shape samples is of a different mechanism if compared with cylindrical Coffin samples. Deformation occurs as a result of “external force”, which is created by the shoulders of the sample itself. The analysis showed that the range of plastic deformation changes on corset shape samples is more considerable than in the Coffin method, and it is more consistent with what is happening. It seems that thermocyclic tests of corset shape samples are promising for studying the destruction in real products subjected to cyclic heating, so it is necessary to identify dangerous zones and simulate them in corset samples. Published results of thermocyclic tests of the ZhS32 alloy were used to demonstrate the features of fracture development in corset shape samples. For a visual representation of the process in semi-cycle tests, a deformation diagram has been developed, which is useful when planning the thermocyclic tests.

High-heat flux tests of tungsten divertor mock-ups with steady-state plasma and e-beam

Abstract Mock-ups of the ITER divertor plate are tested with the combination of steady-state plasma and e-beam loads: (1) thermocyclic tests with powerful electron beam load of up to 49 MW/m2 in the e-beam facility; and then (2) subsequent testing in the PLM plasma device with steady-state plasma loads of 0.5–1 MW/m2 and more. Such tests simulate the variable load on divertor plates in the ITER. Tungsten samples are irradiated with helium plasma in experiments on the PLM plasma device with discharge duration of up to 200 min. The tests of ITER-grade tungsten VM-P with the combination of steady-state plasma and thermocyclic e-beam loads led to erosion, cracking, and nanostructured “fuzz” structure growth on the material surface. Post-mortem scanning electron microscopy revealed a stochastic nanostructured surface with dimension of structural elements less than 100 nm. The growth of a nanostructured surface with a “fuzz”-type structure and high porosity is observed. The results of such tests are of interest to estimate the erosion of tungsten in fusion reactors, including ITER, fusion neutron source FNS and DEMO.

Performance of plasma-sprayed MoSi2-based coating as a heating element

Rollers covered with a thermally sprayed heater coating are an alternative to conventional stream heated and electromagnetic induction heated rollers. In this study, a heater coating was developed using a combination of a thermally sprayed NiAl bonding layer, an MgAl2O4 insulating layer, and an MoSi2-based conductive layer; for comparison, an optional thin MgAl2O4 top layer was applied to provide corrosion and wear protection. The microstructures and characteristics, particularly the electrical-thermal performance, were systematically investigated. The MgAl2O4 layer was found to provide excellent high-temperature insulation performance. Thermo-cycling tests indicate the MoSi2-based coating can be heated to 320 °C with a relatively uniform temperature distribution at the roller surface. The addition of the top layer as a protective mask is beneficial to the heating stability, and NiCr added as a bonding phase in the conductive layer significantly improves the electrical-thermal performance.

Performance evaluation and stability of silicide-based thermoelectric modules

Long-term studies on thermoelectric generators based on N-type magnesium silicide (Mg 2.01 Si 0.49 Sn 0.5 Sb 0.01 ) and P-type higher manganese silicide (Mn 0.98 Mo 0.02 Si 1.73 Ge 0.02 ) materials are presented, in the operating temperature range of 200 °C–400 °C. Emphasis is put on the performance and reliability of the current collector configuration, especially on the hot side of the module, and on the thermomechanical stresses that are created during operation and lifetime testing as a result of large temperature gradients experienced across the thermoelectric legs. With silver (Ag) paste as contact material, the long term-stability of the uni-couples was carried out on non-metalized legs and gold metalized legs under ambient conditions. Under isothermal and thermocycling tests, the non-metalized legs showed a gradual decrease in open circuit voltage (after a period of 200 h) and increase in internal resistance. Conversely, the module made of metalized legs was robust and stable for the same isothermal period. However, after 300cycles the n-type material showed mechanical failure (cracks) but the p-type resisted. Post-operation analysis by SEM/EDS and mechanical testing revealed that oxidation, adherence of the contact material and diffusion of the bonding material were the cause of performance degradation of the unicouples.

Influence of temperature conditions on wood polymer-sand composite

The subject of this research is new wood polymer-sand composite and the study of its frost resistance using computer experiment. Industrial waste in the form of sawdust, chips, lumpy waste and polyethylene terephthalate are used as the filler. A computer program has been developed for modelling the structure and physical properties of building blocks from wood polymer-sand composite. The program enables to set (in the windows of the interface form in the program code) geometric and physical parameters of building block and material components, as well as test conditions for cyclic heating and cooling to the maximum temperature during operation. It explores the effect of parameters on internal and surface destruction of building blocks. The program is applicable for a wide range of composite component concentrations, building blocks’ geometric parameters, variety of mechanical and thermal cycling tests. The influence of wood polymer-sand composite formulation on the structure has been studied during thermocyclic testing. The dependences of broken bonds on wood concentration, cartograms of bond breaking of wood polymer-sand composite with a wood concentration from 20 to 80% have been obtained. Recommendations for optimizing the formulation of wood polymer-sand composite blocks are given to minimize bond breaking during thermal cycling.

Tests of tungsten divertor mock-ups with plasma and e-beam high-heat fluxes

The tungsten divertor mock-ups were tested with high-heat fluxes in the e-beam facility and in the plasma device. The water-cooled mock-ups are tested with the combination of plasma and e-beam loads: (1) thermocyclic tests with the highpower electron beam load ranging from 5 to 40 MW/m2 and then (2) tests in the PLM plasma device with stationary plasma loads of up to 5 MW/m2. Such two tests are performed together for the first time. They simulate the variable loads onto the divertor plates, which can occur in the ITER during stationary discharges with transient ELM events. The duration of helium plasma discharges in the PLM amounted to 200 minutes. The temperature of the test targets heating amounted to 1000°C and more.

Tests of tungsten divertor mock-ups of tokamak-reactor with powerful plasma and e-beam loads

Plasma-facing materials of divertor and the first wall of a hybrid thermonuclear reactor are studied in plasma and beam facilities with extreme high thermal and beam load. Tests of tungsten divertor mock-ups of tokamak reactor are tested with high-heat flux in the plasma device and in the e-beam facility. Water-cooled mock-ups are tested with the combination of plasma and e-beam loads: (1) thermocyclic tests with electron beam powerful load from 5 to 10 MW/m2 and then (2) plasma tests in the PLM device with stationary plasma loads up to 1 MW/m2. These two tests are carried out for the first time and simulate the variable load on divertor plates in tokamak-reactor during stationary discharges with transient ELM events. The e-beam facility provides a complete simulation of the conditions of heating and cooling of the tested components. The advantages of the tests are stationary plasma discharges in the PLM plasma device modeling reactor conditions in the divertor and SOL.

The study of the degradation of refractories under the action of cyclic thermal loads

The results of thermocyclic tests of a number of products of higher refractoriness are given. It is shown that the most resistant to cyclic variable thermal loads are periclase products from fused powders coated with ZrO2. The structure of corundum products in the process of thermocyclic testing significantly degrades due to recrystallization and the formation of new phases. Products made of fused periclase powders modified with ZrO2 are recommended for the organization of the lining and heat exchange tips of test benches that are operated under conditions of variable thermal loads in pulsed piston systems. Ill. 5. Tab. 4.

The Influence of Silica Dioxide and Aluminum Oxide Nano Fillers Reinforced Heat Cured Acrylic Denture Base Material and Thermocycling on Tensile and Shear Bond to Denture Soft Lining Material

Background: Soft lining materials play an important role in modern prosthodonticstreatment because of their capability to restore the inflamed and distorted mucosa.The purpose of the research was to estimate the influence of acrylic denture basereinforcement with silanted nano fillers (Al2O3 and Sio2) separately on tensile andshear bond strength of soft lining material and studying effect of thermo cyclingon bonding strength.Materials and methods: Total 120 specimens were prepared; it divided into 60Specimens for shear bond strength test and 6o specimens for tensile bond strengthtest. Specimens were sub grouped into 30 Specimens without thermo cycling and30 specimens with thermo cycling. Each sub group is consisted from: 10Specimens control, 10 specimens were reinforced with 2 wt% of Al2O3 nano fillersand 10 specimens were reinforced with 5 wt% of SiO2 nano fillers. Samples wereprocessed depending on test applied. Soft lining material was applied for eachtesting group. Samples were immersed in distal water for 24 hours at 37°C beforetesting. For thermo cycling test, specimen were thermo cycled in thermo cyclingdevice. Bonding strength test was done using INSTRON universal testingmachine.Results: reinforcement of acrylic denture base with nano-fillers was significantlyincrease both tensile and shear bonding of lining material and thermo cyclingdecreases both bonding strength.Conclusion: reinforcement of acrylic denture base with nano fillers could improvebonding strength of lining material, while thermo cycling had a deleterious effecton bonding strength.

High temperature corrosion of commercial FeCrAl alloys (Kanthal AF) in nitrogen gas

In the present study, the corrosion mechanism of commercial FeCrAl alloy (Kanthal AF) during annealing in nitrogen gas (4.6) at 900?C and 1200?C is outlined. Isothermal and thermo-cyclic tests with varying total exposure times, heating rates, and annealing temperatures were performed. Oxidation test in air and nitrogen gas were carried out by thermogravimetric analysis. The microstructure is characterized by scanning electron microscopy (SEM-EDX), Auger electron spectroscopy (AES), and focused ion beam (FIB-EDX) analysis. The results show that the progression of corrosion takes place through the formation of localized subsurface nitridation regions, composed of AlN phase particles, which reduces the aluminum activity and causes embrittlement and spallation. The processes of Al-nitride formation and Al-oxide scale growth depend on annealing temperature and heating rate. It was found that nitridation of the FeCrAl alloy is a faster process than oxidation during annealing in a nitrogen gas with low oxygen partial pressure and represents the main cause of alloy degradation.

Joining of tungsten with low-activation ferritic–martensitic steel and vanadium alloys for demo reactor

The conceptual designs of the blanket and the helium-cooled divertor of the DEMO reactor require joining of reduced activation steel (for example RUSFER EK-181, EUROFER, etc.) and tungsten. Significant differences in their physical properties can lead to the generation of the stresses during cooling and, as a result, to the failure of the joint. In this paper, diffusion brazing of RUSFER EK-181 steel with tungsten using a V–4Ti–4Cr interlayer was obtained. Rapidly-quenched ribbon brazing alloys based on copper of various compositions were used. Brazing was carried out in vacuum furnaces at temperatures in the range of 800–1000 °C. The structural-phase states of the joints obtained were studied, the microhardness was measured, and thermocycling tests were performed in the interval of 700 to 25 °C. FEM simulation was used to calculate the optimal thickness of the interlayer.