A Game-Changing Innovation in Crystal Viscoplasticity Modeling of Directionally Solidified Nickel-Base Superalloys

Significance 

Superalloys are high-performance alloys that can operate at exceptionally high temperatures, often exceeding 0.7 of the absolute melting temperature. These alloys exhibit remarkable mechanical properties, creep, oxidation and corrosion resistance, which are also considered important design parameters for high-temperature applications. Superalloys can be based on different metals, mostly cobalt, iron and nickel. Notably, nickel-base superalloys are the best suited for gas turbine and airplane applications.

Directionally solidified (DS) nickel-base superalloys (NBSAs) are widely used in developing gas turbine components owing to their remarkable mechanical properties at extremely high temperatures. DS NBSAs generally consist of columnar grain structures aligned in a parallel direction to the stress axis to enhance their strength at high temperatures. In most cases, the in-service failure of different components, such as gas turbine blades, is induced by the high mechanical and thermal cycling loads. Thus, in order to improve the service life of these materials, it is important to pair the mechanical design process with the material modeling process for a detailed evaluation of the material behaviour for a wide range of loading conditions.

In most studies involving DS NBSAs, the crystal viscoplastic (CVP) model is one of the methods used to simulate the effects of temperature and orientation dependence under different loading conditions. Though initially developed for single crystal material, DS materials have been extended to represent columnar grain structure and model the individual grains. However, CVP models for DS materials have been mainly developed by implicitly or explicitly applying SX CVP model to DS materials. Additionally, these approaches require the application of the SX-CVP model to multiple grains, which makes these approaches computationally expensive.

Herein, Professor Navindra Wijeyeratne, Dr. Firat Irmak and Professor Ali Gordon from the University of Central Florida presented a comparative study of the implicit and explicit approaches for modeling NBSAs with the DS-CVP model. The DS-CVP model for DS materials was developed to circumvent the expensive modeling of individual grains. Their main objective was to use three types of DS-CVP models to investigate the performance of the same materials. The previously developed single-crystal CVP model was the basis of the present study. Comparisons were performed at different temperatures and orientations to establish the advantages and disadvantages as well as the applicability of the models. Their research work is currently published in the research peer-reviewed Journal of Engineering for Gas Turbines and Power.

The authors revealed that CVP theory simulated the material response with higher precision compared with other modes. This was mainly attributed to its ability to integrate the effects of plasticity at the slip system level, allowing more accurate description of the underlying material physics. Moreover, all three approaches accurately fitted the monotonic experimental data for a wide range of temperatures and orientations. The main notable differences were in the computational processing time. Compared with the explicit and implicit approaches, the DV-CVP required less computational time, which was evident when performing cyclic and thermomechanical fatigue simulations. Furthermore, the explicit model requires complex geometry to represent material grains, making it unsuitable for practical applications.

In summary, this study utilized constitutive modeling to simulate the material behaviour under different loading conditions. It is worth noting that the study is the first comparison of these three modeling approaches for the same material. The comparison showed the superiority of DS-CVP model. However, both the DS-CVP model and implicit approaches were suitable for practical applications, while explicit approaches were not due to their disadvantages. In a statement to Advances in Engineering, Professor Navindra Wijeyeratne pointed out that the study findings would provide excellent insights into the usability of these constitutive models and the design of superalloys.

A Game-Changing Innovation in Crystal Viscoplasticity Modeling of Directionally Solidified Nickel-Base Superalloys - Advances in Engineering

About the author

Ali P. Gordon serves as an associate professor in mechanical and aerospace engineering at University of Central Florida (UCF). Just prior to joining UCF, he earned a Ph.D. in mechanical engineering from Georgia Tech. His principal research activities are focused on the development of continuum-level models to predict behavior of materials subjected to complex operating environments. This research has been funded by NSF, ONR and AFRL, among others, and various industrial partners. He has led or co-authored over 100 articles, and is a recipient of the Orr Award and the Widera Award for best papers in journals of the American Society of Mechanical Engineering.

In the classroom, he instructs curricula related to theoretical and experimental mechanics of materials and structures and was twice awarded UCF’s highest honor for teaching. During the summer of 2012, he was selected as the first Visiting Scientist of Structural Integrity with Siemens Energy. He has been appointed an AFOSR Summer Faculty Fellow at Wright-Patterson Air Force Base on multiple occasions. Gordon is an active member of ASME, and is the advisor of UCF’s NSBE chapter.

Research Interests: Mechanical Behavior of Materials and Structures, Fatigue, Creep, Fracture, Consitutive Modeling, Plasticity, Failure Analysis, Corrosion, Machine Design and Analysis

About the author

Dr. Navindra Wijeyeratne is an Assistant Professor of Mechanical Engineering at Florida Polytechnic University. He holds a Ph.D. in Mechanical Engineering from the University of Central Florida. He also holds a Master of Science in Mechanical Engineering and Bachelor of Science in Aerospace Engineering from the University of Central Florida and Embry-Riddle Aeronautical University respectively.

Dr. Wijeyeratne’s expertise lies in the field of mechanics of materials, solid mechanics, fatigue analysis, constitutive modeling, and computational modeling using finite element analysis (FEA). His research aims to enhance the effectiveness of next-generation engineering materials and manufacturing processes by utilizing multiscale material modeling approaches to investigate material deformation and failure. With a particular emphasis on additively manufactured superalloys, Dr. Wijeyeratne’s research utilizes physics-based constitutive models to develop data-driven models through the application of artificial neural networks (ANN) methods, with the goal of improving computational efficiency. He has extensive experience in experimental and computational constitutive modeling of Nickel-base superalloys, including the use of crystal viscoplasticity (CVP) theory to more accurately describe the material behavior. Dr. Wijeyeratne’s current research plans include the development of constitutive models for additively manufactured Nickel-base superalloys to address the uncertainty in the resulting fatigue life performance of these materials in safety-critical components for the aerospace industry.

Research Interests: Mechanics of materials and structures, plasticity, Fatigue, Creep, and Thermomechanical Fatigue analysis, Constitutive modeling, Computational modeling using finite element analysis (FEA), Nickel-base Superalloys

Reference

Wijeyeratne, N., Irmak, F., & Gordon, A. P. (2022). A comparative study of Crystal Viscoplastic Modeling of directionally solidified nickel-base superalloys. Journal of Engineering for Gas Turbines and Power, 145(2), 021017–7.

Go To Journal of Engineering for Gas Turbines and Power

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