Simulated Thermal Cycles Research Articles

Design of novel Fe–Mn–Ni cryogenic steel: microstructure-property relationship during simulated welding

ABSTRACTWe describe here the microstructural evolution during simulation of welding thermal cycles in novel Fe–Mn–Ni cryogenic steel and elucidate the mechanism of cryogenic toughness. The original microstructure was tempered martensite and ∼10% retained austenite. Electron backscattered diffraction indicated that the frequency of large-angle boundaries with misorientation >15° was similar at peak temperatures of 1320, 870 and 760°C. The volume fraction of retained austenite determined by X-ray diffraction was ∼11% at 760°C, 9% at 870°C and 1% at 1320°C. Retained austenite was film-like near the bainite lath, and it was enriched with Mn and Ni at peak temperatures of 760 and 870°C. The enrichment with Mn and Ni stabilised the austenite and softened the bainitic matrix. The higher volume fraction of stable retained austenite was the dominant factor responsible for superior cryogenic toughness at the peak temperature of 760°C.

Effect of Zr Addition on the Microstructure and Toughness of Coarse-Grained Heat-Affected Zone with High-Heat Input Welding Thermal Cycle in Low-Carbon Steel

Microstructures and toughness of coarse-grained heat-affected zone (CGHAZ) with high-heat input welding thermal cycle in Zr-containing and Zr-free low-carbon steel were investigated by means of welding thermal cycle simulation. The specimens were subjected to a welding thermal cycle with heat inputs of 100, 400, and 800 kJ cm−1 at peak temperature of 1673 K (1400 °C) using a thermal simulator. The results indicate that excellent impact toughness at the CGHAZ was obtained in Zr-containing steel. The Zr oxide is responsible for AF transformation, providing the nucleation site for the formation AF, promoting the nucleation of AF on the multi-component inclusions. High fraction of acicular ferrite (AF) appears in Zr-containing steel, acting as an obstacle to cleavage propagation due to its high-angle grain boundary. The morphology of M-A constituents plays a key role in impact toughness of CGHAZ. Large M-A constituents with lath form can assist the micro-crack initiation and seriously decrease the crack initiation energy. The relationship of AF transformation and M-A constituents was discussed in detail.

Three-dimensional thermal analysis of multi-layer metallic deposition by micro-plasma transferred arc process using finite element simulation

Manufacturing of complex 3D-parts by micro-plasma transferred arc (μ-PTA) powder deposition process involves repeated heating and cooling at the same location causing thermal distortion and residual stresses in the substrate and deposited material. Simulation of temperature distribution, thermal cycles and temperature gradient can be helpful to predict thermal distortion and residual stresses. This paper describes 3D-analysis of temperature distribution and thermal cycles in multi-layer metallic deposition by μ-PTA process by finite element simulation using temperature dependent properties of the deposition material. Analysis was also done to study influence of deposition direction on temperature distribution and temperature gradient in multi-layer metallic deposition. The simulated results were experimentally verified on the μ-PTA process experimental apparatus developed for temperature measurement depositing powder of titanium alloy (Ti-6Al–4V) on substrate of the same material. Good agreement is observed between the simulated and experimental results. The results showed that temperature increases with increase in the deposition height and the temperature gradient in parallel deposition is higher than that in back and forth deposition. This implies that parallel deposition exhibits better heat diffusion than back and forth deposition. This work will be helpful in selection of optimum heat input, process parameters and deposition direction in multi-layer metallic deposition by μ-PTA process.

Thermal Cycle Simulation of Welding Process in INC 738 LC Superalloy

This paper is a contribution to the study of the microstructure in welded joint of INC 738 LC. It presents the microstructures obtained after real welding and also after thermal cycle simulation of welding by rapid heating and cooling treatments in specific simulation equipment. We were focusing on the temperature range [900°C, 1100°C] which is the temperature range of main phases occurrence, as coarse γ’primary, fine γ’ secondary and carbides. Optical microscopy and microhardness measurements were used as characterization techniques. We have found that the obtained microstructures by thermal cycle simulation of welding correspond to those observed in the same zone of the real welded joint performed by real welding.

Creep properties of simulated heat-affected zone of HR3C austenitic steel

Tensile creep tests on austenitic stainless HR3C steel pipe in an as-received state and after heat affected zone (HAZ) thermal cycle simulation by means of the GLEEBLE 3800 physical simulator were carried out at 923 and 1023K and an applied stress range between 100 and 350MPa to evaluate the effect of welding on its creep properties and behaviour. It was found that creep testing was conducted in a power-law creep regime. The results show a clear detrimental influence of the HAZ simulation on creep properties of HR3C steel at 923K and for very short creep exposure. However, with increasing time to fracture, the effect of weld simulation becomes less significant. By contrast, no such deterioration of creep properties was detected at 1023K. The evaluated similar values of the stress exponents of the minimum creep rate and the time to fracture are explained using the assumption that both creep deformation and the fracture process are controlled by the same mechanism. The main creep fracture mode was intergranular brittle fracture due to grain boundary creep damage.

PREDICTION OF STRENGTH REDUCTION FACTOR FOR WELDED JOINTS OF REDICTION OF STRENGTH REDUCTION FACTOR FOR WELDED JOINTS OF TURBINES WITH ULTRA SUPERCRITICAL STEAM PARAMETERS URBINES WITH ULTRA SUPERCRITICAL STEAM PARAMETERS

During long-term operation heat-resistant ferrite and martensitic steel welds have type IV cracking in a so-called ‘soft layer’, which contains part of fine grain region and inter-critical region of heat-aff ected zone (HAZ). The rupture of dissimilar welds occurs in the carbonless soft layer near fusion line. Therefore the strength reduction factor of welds decreases significantly with increasing lifetime and operating temperature. Based on experimental investigations the design model is constructed to predict the welds strength reduction coefficient at the design stage, taking into account different structural and technological factors, also changes creep and fracture mechanisms. Creep strength tests of martensitic steel P91 welds and dissimilar welds P91 + Cr-Mo-V steel were performed at temperature of 620°С. The HAZ metal investigation was performed after the thermal welding cycle simulation at the «IMETCKTI» and «Gleeble-3800» units. In addition, numerical modeling was carried out, using the Kachanov-Rabotnov constitutive equations, taking into account the three stages of creep, the influence of complex stress state, changes creep and fracture mechanisms. Based on the calculation results, the life time of P91 welds depends from the soft layer relative width and the creep rate ratio the base metal vs. the soft layer metal. A quantitative evaluation of the dissimilar welds creep strength is obtained using a sample model with two soft layers. Both have the same properties corresponding to the weakened region HAZ metal of the similar weld. According to the calculation results, the dissimilar welded samples rupture location moves to carbonless zone at lower stress level. Calculation results have good agreement with the experimental data. The obtained dependences are in good agreement with the theoretical and experimental studies of L. M. Kachanov, D. R. Hayhurst, V. N. Zemzin, R. Z. Schron et al.

A study on the thermal cyclic behavior of thermal barrier coatings with different MCrAlY roughness

Thermal cycling behavior of thermal barrier coatings (TBCs) with different MCrAlY (M for Ni and Co) interface roughness was studied under two thermal cycling simulation conditions, namely thermal shock with short heating time and high cooling rate, and thermal-ageing fatigue with long heating time but low cooling rate. MCrAlY powders with various sizes were used to obtain different bond coat interface roughness for the TBCs. The MCrAlY bond coat (BC) was sprayed by HVOF, APS, or the combination of them, and the top coats (TCs) with different thickness (300 or 1000 μm) were made. It was found that while the coarser MCrAlY powder gave higher BC roughness, the APS spraying provided more micro-roughness. The increased BC roughness was found to improve the thermal cycling resistance of the TBCs under both testing conditions. The failure mechanism of the TBCs with various MCrAlY roughness was investigated by analyzing microstructures and via finite-elemental modeling.

Ghost microstructure evolution and identification in the coarse grain heat affected zone of 2.25Cr-1Mo-V-Ti steel using tint etching

Microstructural characteristics of the CGHAZ (coarse grained heat affected zone) made of the 2.25Cr-1Mo-V-Ti material for the thermal power plant boiler tube were discussed using the technique of tint etching. To conduct the micro structural characterization, the sample on which CGHAZ was produced by using a high temperature thermal cycle simulator, Gleeble 3500 equipment was used for comparative analyses using the existing Nital etching (ASTM E407-74) and the alkaline etching (ASTM E40785). The latter was used to observe a specific phase. For the microstructure on which the alkaline etching was experimented, the shape of a black strip (Ghost microstructure) in a few microns was observed, which was not observed from the Nital etching. It was found from the phase identifications based EPMA, EBSD and TEM experiments that the image of the black strip in a few microns represented the alpha phase in which C, Cr and Mo became segregated. In addition, it was verified that austenite and M23C6 phase were present around the segregated zone. Based on such results, the mechanism by which the image of the black strip in a few microns was formed at the CGHAZ. In this study, we have investigated the mechanism of the appeared black strip in the CGHAZ.

Vertically aligned CNT-Cu nano-composite material for stacked through-silicon-via interconnects

For future miniaturization of electronic systems using 3D chip stacking, new fine-pitch materials for through-silicon-via (TSV) applications are likely required. In this paper, we propose a novel carbon nanotube (CNT)/copper nanocomposite material consisting of high aspect ratio, vertically aligned CNT bundles coated with copper. These bundles, consisting of hundreds of tiny CNTs, were uniformly coated by copper through electroplating, and aspect ratios as high as 300:1 were obtained. The resistivity of this nanomaterial was found to be as low as ∼10−8 Ω m, which is of the same order of magnitude as the resistivity of copper, and its temperature coefficient was found to be only half of that of pure copper. The main advantage of the composite TSV nanomaterial is that its coefficient of thermal expansion (CTE) is similar to that of silicon, a key reliability factor. A finite element model was set up to demonstrate the reliability of this composite material and thermal cycle simulations predicted very promising results. In conclusion, this composite nanomaterial appears to be a very promising material for future 3D TSV applications offering both a low resistivity and a low CTE similar to that of silicon.

A thermo-mechanical stress prediction model for contemporary planar sodium sulfur (NaS) cells

We introduce a comprehensive finite-element analysis (FEA) computational model to accurately predict the thermo-mechanical stresses at heterogeneous joints and components of large-size sodium sulfur (NaS) cells during thermal cycling. Quantification of the thermo-mechanical stress is important because the accumulation of stress during cell assembly and/or operation is one of the critical issues in developing practical planar NaS cells. The computational model is developed based on relevant experimental assembly and operation conditions to predict the detailed stress field of a state-of-the-art planar NaS cell. Prior to the freeze-and-thaw thermal cycle simulation, residual stresses generated from the actual high temperature cell assembly procedures are calculated and implemented into the subsequent model. The calculation results show that large stresses are developed on the outer surface of the insulating header and the solid electrolyte, where component fracture is frequently observed in the experimental cell fabrication process. The impacts of the coefficients of thermal expansion (CTE) of glass materials and the thicknesses of cell container on the stress accumulation are also evaluated to improve the cell manufacturing procedure and to guide the material choices for enhanced thermo-mechanical stability of large-size NaS cells.

Two-body wear simulation influence on some direct and indirect dental resin biocomposites - A qualitative analysis.

The aim of this study was to qualitatively assess the outcomes of two in vitro aging methods, thermal-cycling and twobody wear simulation accomplished with a dual-axis chewing device, on the surface characteristics of eight direct and indirect dental resin biocomposites. Eighty mesial-occlusal-distal dental cavities were restored with four direct nanohybrid composite materials and with four nano- and micro-hybrid lab-fabricated resin composite inlays. After the restored teeth were subjected to thermal-cycling and wear simulation based on mechanical loading, the surface texture features of the restorations were separately analysed for each of the methods, on epoxy resin models using a digital camera, computer-aided-design system, optical stereo-microscopy and scanning electron microscopy. All the dental restorative resin based composites used in this investigation displayed different cyclic wear patterns after undergoing mechanical loading. After thermal-cycling, the group of resin composite inlays showed a better adaptation, a smoother and more polished occlusal surface compared with direct restorative materials. Only two of direct nanohybrid resin composites performed better after two aging methods. One nanohybrid and the other two microhybrid resin inlays did not perform as expected when they were subjected to simulated wear compared to the rest of test materials. The use of the two-body wear simulation method revealed important information about the behavior of the dental resin-based composites when multiple oral factors are involved in a lab-simulated condition. Furthermore, the macro- and micro-morphological analysis showed different abrasion patterns among the materials being tested according to the filler percentage and distribution of the particles within the resin matrix.

Is There a Correlation Between Tensile Strength and Retrievability of Cemented Implant-Retained Crowns Using Artificial Aging?

The main goal of this in-vitro study was to evaluate whether tensile strength and retrievability of cemented implant-retained crowns correlate when using artificial aging. A total of 128 crowns were fabricated from a cobalt-chromium alloy for 128 tapered titanium abutments (6 degrees taper, 4.3 mm diameter, 4 mm length, Camlog). The crowns were cemented with glass-ionomer (Ketac Cem, 3M) or resin cements (Multilink Implant, Telio CS Cem [Ivoclar Vivadent], Retrieve [Parkell]). Multilink Implant was used without priming. The experimental groups were subjected to either 37,500 thermal cycles between 5°C and 55°C, 1,200,000 chewing cycles, or a combination of both. Control groups were stored for 10 days in deionized water. The crowns were removed with a universal testing machine or a clinically used removal device (Coronaflex, KaVo). Data were statistically analyzed using nonparametrical tests. Retention values were recorded between 31 N and 362 N. Telio CS Cem showed the lowest retention values, followed by Retrieve, Ketac Cem, and Multilink Implant (P≤.0001). The number of removal attempts with the Coronaflex were not significantly different between the cements (P>.05). Thermal cycling and chewing simulation significantly influenced the retrieval of Retrieve Telio CS Cem, and Ketac Cem specimens (P≤.05). Only for Multilink Implant and Telio CS Cem correlations between removal with the universal testing machine and the Coronaflex could be revealed (P≤.0001). Ketac Cem and Multilink Implant (without silane) can be used for a semipermanent cementation. Retrieve and Telio CS Cem are recommendable for a temporary cementation.

페라이트계 스테인리스강 재현 용접 열 영향부의 석출거동 및 열피로 특성에 미치는 구속응력의 영향

Abstract Thermal fatigue life of the automobile exhaust manifold is directly affected by the restraint force according to the structure of exhaust system and bead shape of the welded joints. In the present study, the microstructural changes and precipitation behavior during thermal fatigue cycle of the 18wt% Cr ferritic stainless steel weld heat affected zone (HAZ) considering restraint stress were investigated. The simulation of weld HAZ and thermal fatigue test were carried out using a metal thermal cycle simulator under complete constraint force in the static jig. The change of the restraint stress on the weld HAZ was simulated by changing the shape of notch in the specimen considering the stress concentration factor. Thermal fatigue properties of the weld HAZ were deteriorated during cyclic heating and cooling in the temperature range of 200to 900due to the decrease of Nb content in solid solution and coarsening of MX type precipitates, laves phase, M 6 C with coarsening of grain and softening of the matrix. As the restraint stress on the specimen increased, the thermal fatigue life was decreased by dynamic precipitation and rapid coarsening of the precipitates.Key Words : Thermal fatigue, Ferritic stainless steel, Heat affected zone, Precipitation

A phase field – Finite element approach to model the interaction between phase transformations and plasticity in shape memory alloys

The coupling between phase transformations and plasticity in shape memory alloys (SMAs) is studied by developing a finite element framework in which the constitutive relation captures both phase transformations at the martensite correspondence variant (CV) scale and rate-dependent crystal plasticity in austenite. Load-free and load-biased thermal cycling simulations involving a model cubic-to-tetragonal transformation system are carried out to study how slip in austenite can affect the resulting martensite microstructure. Three key questions are answered. First, where does austenite slip predominantly occur during phase transformation? Second, at what stage during a thermal cycle is plastic deformation most pronounced? Third, what is the effect of plastic deformation on measurable parameters like transformation temperature and subsequent transformation microstructure? The model can also be generalized to study the coupling between phase transformations, twining, and slip.

Influence of simulated heat-affected zone thermal cycle treatment on mechanical performances and microstructural stability of Ni–17Mo–7Cr based superalloy

In the work, a Ni–17Mo–7Cr (wt.%) based superalloy was prepared, and its high-temperature (800 °C) mechanical properties and microstructural stability was evaluated when subjecting to the treatment of simulated heat-affected zone (HAZ) thermal cycle. The results reveal that a lamellar-like structure, which occurs in the alloy, is actually the mixture of Ni matrix and carbides (mainly MoC). When the peak temperature is elevated up to 1350 °C during the HAZ simulation, an equivalent excellent mechanical property is obtained relative to that of the alloy without treatment, due to formation of the typical structures in the alloy. After tensile tests, the hybrid fracture behavior appears on the fracture surfaces, in which the inter-granular fracture with torturous fracture surfaces in company with the ductile fracture are concurrently found. At last, the simulated microstructure can maintain its stability during the tests of isothermal stress relaxation. Based on the results of tensile tests and stress relaxation, we can infer that the simulated microstructure can preserve its excellent mechanical properties and stability at high temperatures.

Effect of high-temperature aging on microstructure and mechanical properties of Ni–Mo–Cr based superalloy subjected to simulated heat-affected zone thermal cycle

In the work, the effect of high-temperature (800–1100 °C) aging treatment on microstructural evolution and mechanical properties of the Ni–17Mo–7Cr based superalloy subjected to heat-affected zone (HAZ) thermal cycle. When the aging temperature is in excess of 800 °C, massive tiny MoC particles and a few chromium carbides are precipitated in the alloy. The lamellar-like structures grow in the alloy and tiny MoC are precipitated around them. In addition, some nano-sized chromium carbides with needle-like morphology are formed in the MoC. With increasing the aging temperature, the tensile and yielding strength decrease slightly due to increased precipitates in the alloy. In comparison with the alloy that does not go through the HAZ simulation, both of their mechanical properties share the close value at each temperature. The retention interval above 1300 °C during the HAZ simulation also influences the alloy's microstructure and mechanical properties. More lamellar-like structures are produced when elevating the retention interval over 5 s. Due to the increase of solidification defect and stress concentration, the tensile and yielding strength decrease sharply when the interval is increased from 5 s to 10 s. Further improving the interval has a limited influence on the alloy's mechanical properties.

Probabilistic lifetime model for atmospherically plasma sprayed thermal barrier coating systems

Calculations of atmospherically plasma sprayed thermal barrier coating durability were facilitated by the development of a numerical lifetime model including probabilistic fracture mechanical analyses of thermally induced topcoat stress field evolutions. The stress distributions were determined in finite element analyses taking into account oxide scale growth and topcoat sintering as transient degradation effects. The influence of interface microstructure was investigated by implementing two different interface approximation functions. Subsequent fracture mechanical analyses of subcritical crack growth were performed at numerous different and permanently assigned abstract crack positions. A comparison of the transient energy release rate to its critical value, which depends on crack length and therefore position, results in statistical distributions of system lifetime as a function of simulated thermal cycling conditions. The model was calibrated by presetting an experimental lifetime distribution which was determined in thermal cycling experiments performed at a burner rig facility. The associated cycle-dependent calibration parameter reflects the effect of fracture toughness increase for increasing crack lengths. Experimental reference values for system lifetime were found to be reproduced by the lifetime model. The stress field inversion directly correlated to oxide scale growth rate was identified as the main failure mechanism. The expectation values and standard deviations of the calculated lifetime distributions were found to be in accordance to the experimentally obtained lifetime data and the data scattering typically observed in thermal cycling.

Evaluation of nanoalumina coated germanium black polyimide membrane as sunshield for application on the communication satellite antenna

Alumina thin coatings were grown on Germanium (Ge) coated black polyimide (GBP) or Kapton which has been used as a sunshield membrane on communication satellite antennas to protect it from environmental degradation during ground storage and implementation. The deposited nanoalumina coatings were found to be optically transparent in solar regime in spectral window while RF characteristic revealed negligible losses. Space worthiness of the coating was examined by simulated environments, e.g. humidity, thermal cycling and thermovacuum tests. No degradation was observed in its microstructural, thermo-optical, electrical, chemical state and RF characteristic in particular Ku and Ka bands. The aforesaid study indicates that the alumina thin coating is able to prevent surface degradation of GBP retaining the thermo-optical properties of the Ge coated Kapton and RF transparency which are functional requirements for communication antenna. The thickness of the optimized alumina coating was ~60nm.

Numerical Simulation and Artificial Neural Network Modeling for Predicting Welding-Induced Distortion in Butt-Welded 304L Stainless Steel Plates

In the present study, artificial neural network modeling has been employed for predicting welding-induced angular distortions in autogenous butt-welded 304L stainless steel plates. The input data for the neural network have been obtained from a series of three-dimensional finite element simulations of TIG welding for a wide range of plate dimensions. Thermo-elasto-plastic analysis was carried out for 304L stainless steel plates during autogenous TIG welding employing double ellipsoidal heat source. The simulated thermal cycles were validated by measuring thermal cycles using thermocouples at predetermined positions, and the simulated distortion values were validated by measuring distortion using vertical height gauge for three cases. There was a good agreement between the model predictions and the measured values. Then, a multilayer feed-forward back propagation neural network has been developed using the numerically simulated data. Artificial neural network model developed in the present study predicted the angular distortion accurately.

Hydraulic performance of compacted clay liners under simulated daily thermal cycles

Compacted clay liners (CCLs) are commonly used as hydraulic barriers in several landfill applications to isolate contaminants from the surrounding environment and minimize the escape of leachate from the landfill. Prior to waste placement in landfills, CCLs are often exposed to temperature fluctuations which can affect the hydraulic performance of the liner. Experimental research was carried out to evaluate the effects of daily thermal cycles on the hydraulic performance of CCLs under simulated landfill conditions. Hydraulic conductivity tests were conducted on different soil specimens after being exposed to various thermal and dehydration cycles. An increase in the CCL hydraulic conductivity of up to one order of magnitude was recorded after 30 thermal cycles for soils with low plasticity index (PI = 9.5%). However, medium (PI = 25%) and high (PI = 37.2%) plasticity soils did not show significant hydraulic deviation due to their self-healing potential. Overlaying the CCL with a cover layer minimized the effects of daily thermal cycles, and maintained stable hydraulic performance in the CCLs even after exposure to 60 thermal cycles. Wet-dry cycles had a significant impact on the hydraulic aspect of low plasticity CCLs. However, medium and high plasticity CCLs maintained constant hydraulic performance throughout the test intervals. The study underscores the importance of protecting the CCL from exposure to atmosphere through covering it by a layer of geomembrane or an interim soil layer.