Superalloy DZ125 Research Articles

Exploring the mechanical and electronic properties of skeletal and blocky carbides in DZ125 superalloy through first-principles and experiments

The diverse shapes and multi-component characteristics of complex carbides in nickel-based superalloys play a crucial role in determining their mechanical properties. However, relying solely on experimental evaluations poses challenges, making analog simulations essential. This study investigates the structural, mechanical, and electronic properties of skeletal and blocky carbides in the DZ125 superalloy using first-principles calculation and experimental methods. The carbides analyzed include Ti0.125Ta0.625Hf0.25C and Ti0.125Ta0.25Hf0.625C, which differ in their Ta and Hf ratios. The results indicate that Ti0.125Ta0.625Hf0.25C exhibits superior mechanical properties compared to Ti0.125Ta0.25Hf0.625C, along with enhanced fracture toughness and higher energy requirements for crack propagation. Electronic characteristic analysis reveals that Ti0.125Ta0.625Hf0.25C possesses greater thermodynamic stability due to the presence of more valence electrons in Ta atoms, which form stronger covalent and metallic bonds. Additionally, quasi-in-situ tensile testing confirms that skeletal carbides exhibit higher cracking resistance compared to blocky carbides. This study enhances our understanding of the stability of these carbides and provides valuable insights for the design and optimization of DZ125 superalloys.

Effects of thickness debit and stress concentration on superalloy DZ125 subjected to cyclic loading

AbstractIn this paper, the thickness debit and stress concentration effects of a nickel‐based directionally solidified superalloy were investigated through strain‐controlled low cycle fatigue (LCF) and creep–fatigue interaction (CFI) experiments. Compared to the fatigue lives of solid specimens provided in the existing literature, the results of this paper indicate that when the wall thickness of the specimen is reduced from 5 to 1.125 mm, the fatigue life with different strain amplitudes decreases by about 45%. When film‐cooling holes (FCHs) are introduced into the hollow specimens, the fatigue life is further reduced by about 25%. Based on the observation of the scanning electron microscope (SEM), the formation mechanisms of the thickness debit and stress concentration effects under LCF and CFI loads were revealed. Subsequently, two parameters, the “wall‐thickness coefficient” and “hole coefficient,” were proposed to establish a new fatigue life prediction method.

Experimental Study and Creep-Fatigue Life Prediction of Turbine Blade Material DZ125 Considering the Nonholding Effect and Coupling Effect of Stress and High Temperature

Abstract In response to the problem of creep-fatigue interaction damage failure of aero-engine turbine blade material, based on the modified damage evolution model of Kachanov-Rabotnov and Chaboche, a creep-fatigue life prediction model for nickel-based superalloy DZ125 is constructed considering the nonholding effect and coupling effect of stress and high temperature with the nonlinear interaction and superposition of creep damage and fatigue damage according to the continuum damage mechanics theory. Simultaneously, the microfracture morphology of DZ125 was analyzed using a scanning electron microscope, revealing the micromechanism of creep-fatigue interaction. The research results manifest that the creep-fatigue life prediction model has a high life prediction ability within ±2.0 times the dispersion band of the prediction results. Concurrently, a large number of intertwined tearing edges, microcracks, and microvoids appear in the fracture morphology, and creep and fatigue interact with each other in the form of effective stress. The above research can provide theoretical support for predicting the lifespan of mechanical structures in a high-temperature environment.

Study on creep-fatigue interaction mechanism and life prediction of aero-engine turbine blade

Aiming at the creep-fatigue interaction damage failure problem of turbine blades in aeronautical engineering, firstly, based on the modified Kachanov-Rabotnov-Chaboche (MKRC) damage mechanics theory, the creep-fatigue life prediction model of turbine blade material was constructed with the experimental verification completion of nickel-based superalloy DZ125. Meanwhile, the creep-fatigue interaction behavior was investigated with the mechanism revelation. Then, considering the shape, size and microscopic defect difference effect from the material to the structure, the creep-fatigue life prediction model of turbine blade structure is proposed by introducing the comprehensive correction factor with experimental verification. Finally, the research results show that there are a large number of interwoven tear edges, micro-cracks and micro-pores in the fracture morphology, and creep and fatigue interact with each other in the form of effective stress. Simultaneously, the creep-fatigue life prediction model has a high life prediction ability with an error of 3%, which can provide a theoretical reference for the damage tolerance design of the turbine blade.

Microstructure and Properties of the Tribaloy T-800 Coating Fabricated by Laser Cladding on the DZ125 Superalloy

Microstructure and Properties of the Tribaloy T-800 Coating Fabricated by Laser Cladding on the DZ125 Superalloy

Dependence of microstructural evolution on the geometric structure for serviced DZ125 turbine blades

The turbine blades were directionally solidified by a high-rate solidification process by the Bridgman technique using directional solidified Ni-based master superalloy DZ125 and operated on the engine bench with a high-temperature gas environment of more than 1500 °C from combustor and high-speed rotation of more than 13500 rpm for 400 h. A service-environment-based model was put forward to simulate the distribution of temperature and stress on the DZ125 blade in service. It was found that the distribution of temperature and stress on the serviced DZ125 blade was closely related to its geometric structure. The microstructural evolution of the serviced DZ125 blade was analyzed and the variations of microstructures with temperature and stress were investigated by using a scanning electron microscope. The results revealed that the evolution process of microstructures on the serviced DZ125 blade was different from that of the standard sample tested at constant temperature and uniaxial tensile stress. The reason for this discrepancy was explored using a combination of finite-element calculation and diffusion coefficient calculation.

Microstructural evolution and creep mechanism of a directionally solidified superalloy DZ125 under thermal cycling creep

In this study, thermal cycling creep tests under (950 °C/15 min+1100 °C/1 min)/100 MPa were performed to simulate the overheating service condition of a directionally solidified superalloy DZ125. The microstructural evolution and creep mechanism at each creep stage were revealed by systematic microstructure characterization after the interrupted creep tests. The results indicated that DZ125 superalloy exhibited three creep stages: the decelerating stage, the slow accelerating stage and the rapid accelerating stage. During creep, the un-recovered γ′ volume fraction at the lower temperature stages and the deterioration of grain boundary caused by the overheating stages were harmful to the creep resistance. During the decelerating stage, a few dislocations moved on the γ matrix. The rafted γ′ microstructure and dislocation networks formed near the minimum creep rate. Simultaneously, some dislocations sheared the γ′ phase as well. During the slow accelerating stage, the rafted γ′ microstructure and dislocation networks could prevent dislocations from moving. However, the dislocations shearing the γ′ phase, facilitated by the overheating and thermal cycling process, was conducive to creep deformation. During the rapid accelerating stage, more dislocations shearing the γ′ phase, severe γ′ phase degradation and increasing PFZs (precipitate free zones) along the grain boundary accelerated the creep deformation. The coupled effect of overheating and thermal cycling damage accelerated the deformation during the thermal cycling creep.

Machine learning-based prediction for time series damage evolution of Ni-based superalloy microstructures

The Directionally Solidified (DS) superalloy DZ125 developed time-series related microstructure damage with serve time. The conventional grey prediction model (GM (1,1)), the fractional order accumulation grey prediction model (FAGM (1,1)), and the long short-term memory (LSTM) neural network prediction model were used to forecast the values of the time-related damage variables. The damage variables of the superalloy microstructure evolution were obtained through experimental observations of the evolution characteristics of the γ' precipitates and γ matrix. The microstructure damage variables were predicted by three machine learning models, and the fatigue damage evolution mechanism of the superalloy was analyzed. It was found that the root mean square error of the three prediction models was 0.072, 0.001, and 0.008, respectively. Finally, a model to predict fatigue life was established based on the Chaboche fatigue damage theory, and the fatigue life was obtained using the damage variables predicted by machine learning. The results revealed that the fractional order cumulative grey model and the long short-term memory neural network prediction model were both more accurate, with the conventional grey model being better for exponentially small sample time series data. • Damage variable was predicted with time-series small sample using grey model. • The prediction accuracy of the GM (1,1), FAGM (1,1), and LSTM were compared. • Fatigue life prediction model of DZ125 superalloy containing damage was developed.

Microstructure degradation of service-exposed turbine blades made of directionally solidified DZ125 superalloy

The investigation about the degradation behavior of turbine blades exposed to complex and extreme environments for long-term service is of great importance to assess the remaining life of the blades. In our work, the microstructure at different positions of the service-exposed turbine blade was characterized from the micron scale to the nanoscale. The results showed that there are noticeable differences in the microstructure at different positions of the blade and the blade has a complex service history. These conclusions suggest that the most severely damaged part of the blade should be responsible for assessing the remaining life of the blade, moreover, the mechanical properties of materials should not be limited to life at constant temperature and stress, rather non-isothermal and variable stress tests are more instructive in assessing the performance or life of aircraft engine blade materials.

Thermal cycling creep properties of a directionally solidified superalloy DZ125

Aero-engine turbine blades may suffer overheating during service, which can result in severe microstructural and mechanical degradation within tens of seconds. In this study, the thermal cycling creep under (950 °C/15 min+1100 °C/1 min)-100 MPa was performed on a directionally solidified superalloy, DZ125. The effects of overheating and thermal cycling on the creep properties were evaluated in terms of creep behavior and microstructural evolution against isothermally crept specimens under 950 °C/100 MPa, 950 °C/270 MPa, and 1100 °C/100 MPa. The results indicated that the thermal cycling creep life was reduced dramatically compared to the isothermal creep under 950 °C/100 MPa. The plastic creep deformation mainly occurred during the overheating stage during the thermal cycling creep. The thermal cycling creep curve exhibited three stages, similar to the 1100 °C isothermal creep, but its minimum creep rate occurred at a lower creep strain. The overheating events caused severe microstructural degradation, such as substantial dissolution of γ' phase, earlier formation of rafted γ' microstructure, widening of the γ channels, and instability of the interfacial dislocation networks. This microstructural degradation was the main reason for the dramatic decrease in thermal cycling creep life, as the thermal cycling promoted more dislocations to cut into γ' phase and more cracks to initiate at grain boundaries, carbides, and residual eutectic pools. This study underlines the importance of evaluating the thermal cycling creep properties of superalloys to be used as turbine blades and provides insights into the effect of thermal cycling on directionally solidified superalloys for component design.

Effect of microstructures restoration on high temperature fatigue behavior of DZ125 superalloy

Combination of hot isostatic pressing (HIP) and rejuvenation heat treatment (RHT) technology was used to restore creep-damaged DZ125 directional solidified superalloy, and the influence of microstructure restoration on high temperature fatigue behavior of the samples was explored. The results show that the HIP+RHT process could effectively heal internal cavities and recover the degraded γ′ phase in creep-damaged DZ125 superalloy to cubic particles similar as in as-received sample. After restoration treatment, the stress concentration areas inside the sample eradicated with the healing of the internal cavities, and the fatigue source areas were limited only to near surface than initiating from inside as in the as-received and creep-damaged samples. As a result, the restored sample had higher crack initiation life and lower crack propagation rate compared to as-received and creep damaged samples. The TEM microstructure characterization near fatigue fracture showed that the restoration of the degraded γ′ phase eliminated tangled dislocation in creep damaged sample and produced evenly distributed dislocations in the γ channel with short curved line-like morphology, like the as-received sample, which effectively hindered the dislocations movement during subsequent deformation, and strengthen the fatigue resistant of alloy. Therefore, it can be concluded that the HIP-RHT process, through the combined effect of internal cavities healing and the restoration of the degraded microstructures, renders higher high temperature fatigue life than creep-damaged and even higher than as-received DZ125 superalloy.

Properties of alumina coatings prepared on silica-based ceramic substrate by plasma spraying and sol-gel dipping methods

Silica-based ceramic cores are widely used in the manufacturing of hollow, nickel-based, superalloy turbine blades. However, elemental Hf, Ti, Al, and other active metals in the superalloy can react with silica-based ceramic cores during casting, resulting in a reduction in the quality of the turbine blades. In this study, both plasma spraying and sol-gel dipping methods were used to prepare alumina coatings on silica-based ceramic substrates to prevent the interfacial reaction. The performance of the alumina coatings prepared by both methods was evaluated by comparative analysis of the surface roughness, bonding interface morphologies, and the adhesive characteristics of the coating. The plasma-sprayed alumina coating has a roughness greater than 5 μm and peeled away from the substrate due to the difference in thermal expansion between SiO2 and Al2O3 at temperatures above 1500 °C, rendering the silica-based substrate with the plasma-sprayed alumina coating unfit for the application requirements of the casting process. The alumina coating prepared by the sol-gel dipping method improved the roughness of the substrate from Ra 2.39 μm to Ra 1.83 μm, and no peeling was observed when heated to 1550 °C for 30 min due to the pinning characteristics of the coating on the substrate. Furthermore, the interfacial reaction between the DZ125 superalloy melt and the silica-based substrate coated with alumina by sol-gel dipping method were investigated. The alumina coating effectively inhibited the interfacial reaction and no reaction products were detected during the directional solidification with pouring temperature of 1550 °C and withdraw rate of 5 mm/min. While a uniform, 4–5 μm thick HfO2 reaction layer formed between the uncoated substrate and the DZ125 alloy melt. Two dipping-drying cycles were required to ensure the alumina sol completely covered the surface of the substrate.

RETRACTED: Creep behavior of a nickel-based superalloy under cyclic temperatures

Abstract In this paper, the thermal-cycling creep of Ni-based superalloy DZ125 is investigated at very high temperature. Experiments were conducted with various parameters including overheating duration, applied stress, temperature interval and heating/cooling frequency. Microscopic observation has revealed a modified thermodynamic equilibrium with lower γ’ content in comparison to isothermal creep situation. This phenomenon is discussed on the basis of Johnson-Mehl-Avrami-Kolmogorov law and pre-existing theoretical assumptions of dislocation density evolution during thermal transients. A linear relationship between overheating numbers and equilibrium γ’ content is obtained to develop a phenomenological life model of thermal-cycling creep. Life prediction results of proposed method are in good agreement with experimental ones.

Profile grinding of DZ125 nickel-based superalloy: Grinding heat, temperature field, and surface quality

• Increase of grinding speed and undeformed chip thickness decreases grinding heat. • Temperature field is characterized by experiments and simulation. • DZ125 is well ground by HEDG with good quality and residual compressive stress. • DZ125 blade root is ground with material removal rate over 50 mm 3 /(mm·s). During the high-efficiency deep grinding of a turbine blade root, localized thermal damage of the profile surface could easily occur owing to the complexity of the grinding dynamics and cooling conditions in the grinding zone. Therefore, it is worthwhile to investigate the generation of the grinding heat, the grinding temperature and its distribution, and the grinding surface quality, particularly for superalloys used to produce aero-turbine blades. In this study, the specific grinding energy and grinding heat flux during the profile grinding of a fir tree-shaped root of a DZ125 superalloy turbine blade were investigated. The grinding temperature at four points on the profile were measured and the results were used to conduct a three-dimensional simulation to analyze the temperature distribution on the machined surface and in the direction of the cutting depth. The effects of the heat source shape and contact length on the temperature distribution were also examined. A moderately high material removal rate was found to be beneficial to the surface quality, with a maximum material removal rate of 50.6 mm 3 /mm·s producing a surface roughness of Ra 0.6 μm without saturation or microstructural changes. Residual compressive stress was also achieved on the ground surface.

AIP multi-layer coating on DZ125 superalloy substrate

AIP multi-layer coating on DZ125 superalloy substrate

Directional solidification behavior of turbine blades in DZ125 alloy: design of blade numbers on assembly

The influence of blades assembly, i.e., the blade number on the solidification process, heat exchange and grain structure on a directionally solidified Ni-based superalloy DZ125 was investigated by combining the experimental and simulation results. The casting process was simulated thermodynamically by ProCAST software, where the interface heat transfer coefficient was precisely determined by a measurement with thermocouples. There is a good agreement between experimental and simulation results. It was interestingly found that with the number of blades increasing from 6 to 10, due to the decrease in radiation absorption efficiency, the maximum temperature and the heating rate decrease in the mold, during the preheat process. During the withdrawal procedure, increased assembly numbers reduce the radiation exchange from mold to the enclosure, resulting in the decrease in cooling rate and temperature gradient of the blades. At the end of withdrawal, the slower cooling rate of the outside balances the temperature distribution of internal and external surfaces on the rabbet of blade. The interface heat transfer coefficient (IHTC) values of DZ125 casting system were investigated by inverse method. Then, a series of assembly blade groups were designed and being cast and calculated. Values of IHTC are proved to be suitable for different assembly groups of casting in this case. Based on simulation and experimental results, it was interestingly found that: In the preheating process, with the number of blades increased, the maximum temperature on the mold becomes lower and the heating rate becomes slower, which result from the decrease in radiation efficiency between the mold and graphite heater. During the withdrawal, increasing assembly blade number reduced the radiation exchange from the mold to the enclosure, and it results in the cooling rate and temperature gradient on the blades getting decreased. At the end of withdrawal, the slower cooling rate leads to the temperature distribution maintaining uniformity for internal and external surfaces on the rabbet of the blade.

The effect of cyclic loading on the creep fatigue life and creep strength of a DS superalloy: Damage mechanism and life modeling

In this paper, the creep-fatigue behavior of directionally solidified superalloy DZ125 has been investigated by stress-controlled experiments at high temperatures with different dwell times. The endurance life(i.e Cumulated dwell time) has shown consistent changing trend with different load conditions. Crack growth form and creep-fatigue interaction are analyzed on the basis of microscope observation results. A new continuum damage mechanics(CDM) model is proposed and the damage behavior of DZ125 under different dwell times is systematically analyzed by this new model. Secondly, a life prediction model of high precision with fully coverage of dwell time and hold stress is proposed based on material’s endurance strength decline and classical Larson-Miller life prediction method. Finally, the ultimate value of endurance strength decline of the superalloy affected by cyclic loads is determined for engineering application purpose.

Evaluation of service conditions of high pressure turbine blades made of DS Ni-base superalloy by artificial neural networks

Evaluating the service conditions of high pressure turbine blades in areoengine, which is the key point for component design and remaining life prediction, has always been a great challenge. In this study, we report a method, which is developed by back propagation artificial neural networks (BPANN), for service condition evaluation of turbine blades by establishing a quantitative correlation between the microstructural evolution and the temperature, stress and time. This method was successfully applied to a directionally solidified superalloy DZ125 based on microstructural datasets obtained from temperature-stress-time (T-σ-t) simulations. As an example, the service condition of a turbine blade made of DZ125 superalloy were evaluated by the BPANN model using the microstructural descriptors, including γ′ volume fraction (Vf), γ′ rafting degree (Ω) and thickness of the rafted γ′ precipitates (D), and service time. This study shows great potential in accurately assessing the degradation and predicting the remaining life for hot section components made from directionally-solidified and single crystal nickel-based superalloys.

High-temperature hot-corrosion effects on the creep–fatigue behavior of a directionally solidified nickel-based superalloy: Mechanism and lifetime prediction

Creep–fatigue experiments were performed at 850℃ on bare and salt-coated directionally solidified Ni-based superalloy DZ125. Experimental test results showed that the salt-coated sample exhibited lower lifetime than that of the bare sample under all stress conditions. This reduction is found to correlate directly with the higher probability of crack initiation, due to surface micro-structural degradation and higher actual stress as a result of the decrease in effective bearing area. A modified damage accumulation model considering the creep, fatigue, and hot-corrosion interaction effect was proposed to predict the corrosion–creep–fatigue lifetime. In this model, a critical high-temperature hot-corrosion exposure time was proposed and was introduced using the Miller linear damage accumulation model. The predicted lifetimes correspond remarkably well with the experimental results.

ICME Framework for Damage Assessment and Remaining Creep Life Prediction of In-Service Turbine Blades Manufactured with Ni-Based Superalloys

Accurate creep life prediction is necessary for the evaluation of the remaining creep lives of in-service turbine blades and for the design of new turbine blades in aircraft engines. In this study, an integrated computational material engineering methodology for predicting the remaining creep life of in-service turbine blades was developed by taking a microstructural criterion and creep strain criterion into consideration, and combining artificial neural networks with a modified θ projection model to assess the service temperature, stress, degradation time, and existing creep strain. To explore the application of the method and verify its accuracy, the microstructural degradations at different locations of two directionally solidified superalloy DZ125 turbine blades, which were in-service for 300 h and 980 h in different engines, were characterized and quantified. Using these results, the remaining creep life of the microstructures at different locations of the blade was predicted. Finally, these creep life prediction results were experimentally verified using miniature creep test specimens. The development of this new method provides a reference for the design and service evaluation of turbine blades made of directional solidified and single-crystal Ni-based superalloys.