Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys. Edited by: Mark Hardy, Eric Huron, Uwe Glatzel, Brian Griffin, Beth Lewis,.
Superalloys 2016: Proceedings of the 13th International Symposium on Superalloys Edited by: Mark Hardy, Eric Huron, Uwe Glatzel, Brian Griffin, Beth Lewis, Cathie Rae, Venkat Seetharaman, and Sammy Tin TMS (The Minerals, Metals & Materials Society), 2016
RESONANT ULTRASOUND SPECTROSCOPY FOR DEFECT DETECTION IN SINGLE CRYSTAL SUPERALLOY CASTINGS B.R. Goodlet1, L.H. Rettberg1, and T.M. Pollock1 1
Materials Department, University of California, Santa Barbara, 93106, USA
Keywords: nondestructive evaluation, NDE, recrystallization, resonant ultrasound spectroscopy, RUS, finite element, FE, modeling. beam sources [8]. Ultrasonic methods are more affordable than xray methods and more quantitative than a visual inspection. Pulseecho ultrasonics [11] and ultrasonic array [10] both have potential as quantitative inspection techniques for grain structures, but they are typically local inspection tools tailored to identify small flaws in particular regions of a specimen. Alternatively, ultrasonic resonance samples the full volume of a specimen with a single measurement [9], potentially enabling the detection of bulk, subsurface, and surface grain defects with a single measurement. To enhance the inspection capabilities of resonant ultrasound spectroscopy (RUS), a rigorous predictive capability for quantifying the influence of grain defects on resonance is essential. Herein, Finite Element (FE) models are used to inform RUS measurements and establish a rapid and reliable NDE framework for identifying recrystallization and analogous grain structure defects.
Abstract Resonant ultrasound spectroscopy (RUS) has been combined with forward finite element (FE) models of resonance for detection of grain structure defects in single crystal Ni-based superalloys. The nondestructive evaluation (NDE) potential of RUS is demonstrated with experiments on Mar-M247 single crystals that were shot peened and solution heat treated to induce surface recrystallization. FE models using self-consistent elastic properties and variable recrystallization depths show excellent agreement with RUS measured results, allowing for the effect of recrystallization on resonance to be isolated and quantified. The validated FE modeling framework is then extended to a turbine blade model for exploring RUS as a NDE technique of grain structure defects in complex geometry components. Extension of RUS to evaluate defects, anomalies, and damage mechanisms relevant to manufacturing process control and component lifecycle management is also discussed.
Fundamentals of Resonance
Introduction
Resonant ultrasound spectroscopy (RUS) was developed at Los Alamos National Lab in the 1980’s and was first licensed for development of commercial nondestructive evaluation equipment in 1992 [12]. Finding early success for inspection of geometric defects in very-high precision ball bearings on the order of 1 part per million [12,13], RUS for NDE has remained largely relegated to niche applications due to the lack of tractable, reliable, and precise forward modeling methods capable of explaining the complex relationship between damage and resonance. RUS techniques excite low-energy elastic waves that travel through the specimen until opposite-traveling waves of a particular frequency constructively interfere to generate a standing wave in the specimen, causing the amplified harmonic deflections that are the hallmark of mechanical resonance. A single broadband RUS scan may excite tens or even hundreds of individual resonances that collectively contain a wealth of information about the specimen. Low-order resonances effectively probe large volumes of the specimen and are quite sensitive to small global changes in material properties, or perturbation of the specimen geometry [14]. Higher-order modes can be quite localized in their deflection character, making them ideal for probing local properties and defects, assuming these modes are properly identified from the broadband spectrum [13,15]. It is also understood that the resonance frequencies of both low-order and higher-order modes can be measured with high precision. With different modes sensitive to different aspects of the specimen’s intrinsic properties, RUS affords the most accurate characterization of elastic properties in solid media [16,17].
Advanced casting methods have enabled fabrication of Ni-based superalloy turbine blades with weight-saving geometries and serpentine internal cooling passages that permit operation at higher thermal and mechanical loads [1,2]. However, these complex single crystal airfoil designs are prone to grain structure defects that may arise during the directional solidification process, e.g. stray grains or misoriented single crystals [1]. Residual stresses and plastic strains induced during solidification as a result of metal shrinkage around rigid cores, or impact damage during mold removal may also initiate recrystallization during subsequent heat treatment [3]. Recrystallization, stray grains, and blades with crystal orientations rotated away from the desired [001] axis are all of particular concern due to their deleterious impact on both creep and fatigue properties [3–5]. Process controls that minimize the occurrence of these life-limiting grain structure defects and effective nondestructive evaluation (NDE) tools to reliably detect defective components before entering service are critical. There are a variety of nondestructive techniques for evaluating grain structure in Ni-based superalloys including: etching and visual inspections [6], x-ray diffraction, radiography and tomography [7,8], and ultrasonic methods [9,10]. Visual inspections after etching are commonly employed to identify high-angle grain boundaries, stray grains, recrystallization, and freckles that are present on the surface [6], however they can be subjective and prone to error, and are incapable of assessing defects below the surface. X-ray methods based on diffraction include the classical Laue technique to produce diffraction spots for a quantitative determination of single crystal orientation [7]. X-ray computed tomography and radiography methods generally rely on absorption contrast and require more expensive brighter
The physical underpinnings of resonance can be derived from time-independent solutions of the 3D wave equation of motion [9]. In this work models of mechanically resonating 3D elastic bodies assume a simply supported (free), undamped, stress-free body. These assumptions, in conjunction with homogenization
303
304
bending and torsional characteristics, and appear to be related to each other such that a unique mode type classification is warranted. The designation “plate mode” is simply due to the fact that modes with a similar appearance have been observed in plate geometries, whereby sinusoidal deflections arise along thin exterior sections of the plate. These plate modes are common at low frequencies for the given turbine blade model, and exhibit a strong positive or negative ΔfR that depends on the location of recrystallization along the TE of the airfoil. In fact, these modes appear to be quite diagnostic of defects along the trailing edge of the blade, and with further study it may be possible to identify specific regions that contain damage based on which plate modes are most affected. As a rigorous modal analysis was not conducted for the turbine blade model results, Figures 12 and 13 focus on the first 20 resonance modes where mode order switching is less likely. In lieu of mode order matching as before, ΔfR results for the turbine blade parametric studies are calculated according to each modes appearance in the frequency regime, thus the “frequency order” designation in the abscissa of Figures 12 and 13. Note that failing to account for mode order switching would result in modeled ΔfR that appear smaller than they actually are, which could obscure resonances that are particularly diagnostic of damage.
•
Acknowledgements This work was supported by the U.S. Air Force Research Laboratory (AFRL) through Research Initiatives for Materials State Sensing (RIMSS) Contract FA8650-15-C-5208, under the Universal Technology Corporation. The authors would like to thank program collaborators Chris Torbet of UCSB, John Aldrin of Computational Tools, Eric Biedermann, Julieanne Heffernan and Leanne Jauriqui of Vibrant NDT, and the program coordinator Siamack Mazdiyasni of AFRL. Finally, thanks to Jesse Keller, Art Peck, and Jon Schaeffer of GE Power & Water for shot peening the specimens examined in this work.
References 1. Roger C. Reed, The Superalloys (Cambridge: Cambridge University Press, 2006).
Conclusions A combined RUS measurement and FE modeling framework has been developed and validated as a NDE technique for detecting grain structure defects in Ni-based superalloy specimens. FE models using self-consistent elastic properties between the recrystallized and single crystal regions predicted changes in resonance with very good agreement to measured results across a broad spectrum of frequencies and mode types. The FE model framework was experimentally validated with a Mar-M247 single crystal quarter-cylinder specimen that was shot peened to induce recrystallization on subsequent 1225 °C (2237 °F) heat treatments for 2 to 320 minutes. Through the validation process recrystallization was determined to be the single dominant mechanism affecting resonance in the measured specimen. Secondary mechanisms affecting resonance during high temperature exposure, e.g. annealing of imparted dislocations and surface oxidation, were deemed to have a negligible impact on resonance frequencies in this study. Definitive conclusions as to the relative impact of high-temperature mechanisms affecting resonance are only possible with the inclusion of FE models that are capable of assessing the impact of individual mechanisms, or a few select mechanisms concurrently. Finally, the validated modeling framework was extended to explore the NDE potential of RUS for recrystallization in turbine blade geometries. The following are key conclusions from this study: •
•
Small volumes of recrystallized material on order of 1% the total volume of the single crystal turbine blade result in significant and characteristic changes in resonance that are two orders of magnitude greater than the RUS measurement sensitivity reported.
2. M.S. Titus, A. Suzuki, and T.M. Pollock, “High Temperature Creep of New L12 Containing Cobalt-base Superalloys” (Proceedings of the International Symposium on Superalloys, 2012), 823–832. 3. D. Goldschmidt, U. Paul, and P.R. Sahm, “Porosity Clusters and Recrystallization in Single-crystal Components” (Proceedings of the International Symposium on Superalloys, 1992), 155–164. 4. J. Meng et al., “Effect of Surface Recrystallization on the Creep Rupture Properties of a Nickel-base Single Crystal Superalloy,” Mater. Sci. Eng. A, (527) (2010), 6119–6122. 5. N.K. Arakere et al., “Investigation of Three-dimensional Stress Fields and Slip Systems for FCC Single-crystal Superalloy Notched Specimens,” J. Eng. Gas Turbines Power, (127) (2005), 629-637. 6. F.L. Versnyder and M.E. Shank, “The Development of Columnar Grain and Single Crystal High Temperature Materials through Directional Solidification,” Mater. Sci. Eng., (6) (1970), 213–247. 7. J.M. Winter, K.G. Lipetzky, and R.E. Green, “Optimization of X-ray Techniques for Nondestructive Characterization of Single Crystal Turbine Blades,” MRS Proc., (591) (1999), 3-14.
FE models with self-consistent elastic properties provide an accurate description of the influence of recrystallization on resonance over a wide range of frequencies, improving the predictive capability of RUS measurements for NDE.
8. E. Maire and P.J. Withers, “Quantitative X-ray Tomography,” Int. Mater. Rev., (59) (2014), 1–43. 9. A. Migliori and J. Sarrao, Resonant Ultrasound Spectroscopy: Applications to Physics, Materials Measurements, and Nondestructive Evaluation (New York: Wiley-Interscience, 1997).
Recrystallization in [001] single crystal Ni-based superalloys introduces local changes in elastic properties that result in modes with bending and extensional character to occur at higher frequencies while torsional modes shift to lower frequencies. The magnitude of the frequency shift scales with the recrystallization depth.
311
25. “Abaqus/CAE Version 6.12-1 User Manual”, Dassault Systèmes Simulia Corp. Providence, RI., (2012).
10. Christopher Lane, The Development of a 2D Ultrasonic Array Inspection for Single Crystal Turbine Blades (Cham, Switzerland: Springer International Publishing, 2014).
26. L.H. Rettberg, B.R. Goodlet, and T.M. Pollock, “Detecting Recrystallization in a Single Crystal Ni-base Alloy Using Resonant Ultrasound Spectroscopy”, NDT&E Int., (2016).
11. L.J. Bond, M. Punjani, and N. Saffari, “Review of Some Recent Advances in Quantitative Ultrasonic NDT,” IEE Proc., (131) (1984), 265–274.
27. Z. Hashin, “The Elastic Moduli of Heterogeneous Materials,” J. Appl. Mech., (1962) 143–150.
12. A. Migliori and Z. Fisk, “Crystals and Ultrasound, OldFashioned Materials Science,” Los Alamos Sci., (1993), 182–194.
28. E. Kröner, “Elastic Moduli of Perfectly Disordered Composite Materials,” J. Mech. Phys. Solids, 15 (1967) 319–329.
13. G. Rhodes et al., “Detection of Defects Using Resonant Ultrasound Spectroscopy at Predicted High Order Modes,” (US Patent No. 5,992,234, 1999).
29. C. Zener, “Contributions to the Theory of Beta-phase Alloys,” Phys. Rev., 71 (12) (1947), 846–851.
14. B.R. Goodlet et al., “Forward Modeling of Resonant Ultrasound Spectroscopy for Nondestructive Evaluation of Mechanical Damage,” In Preparation, (2016).
30. H.A. Kuhn and H.G. Sockel, “Comparison Between Experimental Determination and Calculation of Elastic Properties of Nickel-base Superalloys Between 25 and 1200 °C,” Phys. Status Solidi, 110 (2) (1988), 449–458.
15. J.C. Aldrin, L. Jauriqui, and L. Hunter, “Models for Process Compensated Resonant Testing (PCRT) of Silicon Nitride Balls,” (39th Annu. Rev. Prog. Quant. Nondestruct. Eval., 2013), 1393– 1400.
31. B. Gairola and E. Kröner, “A Simple Formula for Calculating the Bounds and the Self-consistent Value of the Shear Modulus of a Polycrystalline Aggregate of Cubic Crystals,” Int. J. Eng. Sci., (19) (1981), 865–869.
16. R.G. Leisure and F.A. Willis, “Resonant Ultrasound Spectroscopy,” J. Phys. Condens. Matter., (9) (1997), 6001–6029.
32. H.A. Kuhn and H.G. Sockel, “Contributions of the Different Phases of Two Nickel-base Superalloys to the Elastic Behaviour in a Wide Temperature Range,” Phys. Status Solidi, 119 (1990), 93–105.
17. M. Radovic, E. Lara-Curzio, and L. Riester, “Comparison of Different Experimental Techniques for Determination of Elastic Properties of Solids,” Mater. Sci. Eng. A, (368) (2004), 56–70. 18. E2534-15: Standard Practice for Process Compensated Resonance Testing via Swept Sine Input for Metallic and NonMetallic Parts, (Annual Book of ASTM Standards Volume 03.03, American Society for Testing and Materials, 2015).
33. F.X. Kayser and C. Stassis, “The Elastic Constants of Ni3Al at 0 and 23.5 °C,” Phys. Status Solidi, 64 (1981), 335–342. 34. A. Granato, A. Hikata, and K. Lücke, “Recovery of Damping and Modulus Changes Following Plastic Deformation,” Acta Metall., (6) (1958), 470–480.
19. A. Migliori and J.D. Maynard, “Implementation of a Modern Resonant Ultrasound Spectroscopy System for the Measurement of the Elastic Moduli of Small Solid Specimens,” Rev. Sci. Instrum., (76) (2005), 1–7.
35. G. Li and J.R. Gladden, “High Temperature Resonant Ultrasound Spectroscopy: A Review,” Int. J. Spectrosc., (2010) 1–13.
20. P. Heyliger, and H. Ledbetter, “Detection of Surface and Subsurface Flaws in Homogeneous and Composite Solids by Resonant Ultrasound,” J. Nondestruct. Eval., (17) (1998), 79–87. 21. J. Plesek, R. Kolman, and M. Landa, “Using Finite Element Method for the Determination of Elastic Moduli by Resonant Ultrasound Spectroscopy,” J. Acoust. Soc. Am., (116) (2004), 282287. 22. G. Liu and J.D. Maynard, “Measuring Elastic Constants of Arbitrarily Shaped Samples Using Resonant Ultrasound Spectroscopy,” J. Acoust. Soc. Am., (131) (2012), 2068-2078. 23. W.M. Visscher et al., “On the Normal Modes of Free Vibration of Inhomogeneous and Anisotropic Elastic Objects,” J. Acoust. Soc. Am., (90) (1991), 2154-2162. 24. E. Biedermann et al., “Resonance Ultrasound Spectroscopy Forward Modeling and Inverse Characterization of Nickel-based Superalloys” (41st Annual Review of Progress in Quantitative Nondestructive Evaluation, 2015), 835–844.
312
