Evaluating Mechanical Properties of CoNiCrAlY Coating from Miniature Specimen Testing at Elevated Temperature
CoNiCrAlY alloys have been widely used as bond coats for thermal barrier coating (TBC) systems because of low cost, improved control of composition, and the feasibility to tailor the coatings microstructures. Coatings are in general very thin structures, and therefore it is impossible to characterize the mechanical responses of the materials via conventional mechanical testing methods. Due to this reason, miniature specimen testing methods, such as the small punch test technique, have been developed. This paper presents some of the recent research in evaluating the mechanical properties of the CoNiCrAlY coatings at room and high temperatures, through the use of small punch testing and the developed miniature specimen tensile testing, applicable to a range of temperature, to investigate the elastic-plastic and creep behavior as well as ductile-brittle transition temperature (DBTT) behavior. An inverse procedure was developed to derive the mechanical properties from such tests for the coating materials. A two-layer specimen test method is also described. The key findings include: 1) the temperature-dependent coating properties can be accurately determined by the miniature tensile testing within a wide range of temperature; 2) consistent DBTTs can be identified by both the SPT and miniature tensile tests (~ 650 °C); and 3) the FE SPT modelling has shown good capability of simulating the early local cracking. In general, the temperature-dependent material behaviors of the CoNiCrAlY coating has been effectively characterized using miniature specimen testing and inverse method.
 Lugsheider E, Herbst C, Zhao L. Parameter studies on high-velocity oxy-fuel spraying of MCrAlY coatings. Surf. Coat. Technol. 1998; 108-109:16–23.
 Higuera V, Belzunce FJ, Riba J. Influence of the thermal-spray procedure on the properties of a CoNiCrAlY coating. Surf. Coat. Technol. 2006; 200: 5550–5556.
 Chen H, Jackson GA, Sun W. An overview of using small punch testing for mechanical characterization of MCrAlY bond coats. J. Therm. Spray Technol. 2017; 26: 1222-1238.
 Tillmann W, Selvadurai U, Luo W. Measurement of the Young’s modulus of thermal spray coatings by means of several methods. J. Therm. Spray Technol. 2013; 22: 290-298.
 Waki H, Oikawa A, Kato M, Takahashi S, Kojima Y, Ono F. Evaluation of the accuracy of Young’s moduli of thermal barrier coatings determined on the basis of composite beam theory. J. Therm. Spray Technol. 2014; 23: 1291-1301.
 Itoh Y, Saitoh M. Mechanical properties of overaluminized MCrAlY coatings at room temperature. J. Eng. Gas Turb. Power. 2005; 127:807–813.
 Hemker KJ, Mendis BG, Eberl C. Characterizing the microstructure and mechanical behaviour of a two-phase NiCoCrAlY bond coat for thermal barrier systems. Mat. Sci. Eng. A. 2008; 483-484:77–730.
 Eskner M, Sandstrom R. Mechanical properties and temperature dependence of an air plasma-sprayed NiCoCrAlY bondcoat. Surf. Coat. Technol. 2006; 200(8): 2695 – 2703.
 Chen H, Hyde TH, Voisey KT, McCartney DG. Application of small punch creep testing to a thermally sprayed CoNiCrAlY bond coat. Mater. Sci. Eng.: A. 2013; 585:205–213.
 Jackson GA, Sun W, McCartney DG. The Application of the Small Punch Tensile Test to Evaluate the Ductile to Brittle Transition of a Thermally Sprayed CoNiCrAlY Coating. Key Eng. Mater. Vol. 2017; 734: 144-155.
 Jackson GA, Sun W, McCartney DG. The influence of microstructure on the ductile to brittle transition and fracture behaviour of HVOF NiCoCrAlY coatings via SP tensile testing. Mater. Sci. Eng. A. 2019; 754: 479-490.
 Mao X. Small punch test to predict ductile fracture toughness JIC and brittle fracture toughness KIC. Scripta Metallurgica et Materialia. 1991; 25:2481–2485.
 Cao L, Bürger D, Wollgramm P, Neuking K, Eggeler G. Testing of Ni-base superalloy single crystals with circular notched miniature tensile creep (CNMTC) specimens. Mater. Sci. Eng. A. 2018; 712: 223-231.
 Farrukh H, Desmukh MN, Husain Asif, Sehgal DK. Miniature test technique for acquiring true stress–strain curves for a large range of strains using a tensile test and inverse finite element method. Applied Mech. Mater. 2011; 110-116: 4204-4211.
 Kundan K, Arun P, Madhusoodanan K, Singh RN, Arnomitra C, Dutta BK., Sinha RK, Optimisation of thickness of miniature tensile specimens for evaluation of mechanical properties. Mater. Sci. Eng. A. 2016; 675: 32-43.
 Wen W, Becker AA, Sun W. Determination of material properties of thin films and coatings using indentation tests: a review. J. Mater. Sci. 2017; 52: 12553-12573.
 Kang JJ, Becker AA, Wen W, Sun W. Extracting elastic-plastic properties from experimental loading-unloading indentation curves using different optimization techniques. Int. J. Mech. Sci. 2018; 144: 102-109.
 Lu J, Campbell-Brown A, Tu Shan-Tung, Sun W. Determination of creep damage properties from miniature thin beam bending using an inverse approach. Key Eng. Mater. 2017; 734: 260-72.
 Husain Asif, Sehgal DK, Pandey RK. An inverse finite element procedure for the determination of constitutive tensile behaviour of materials using miniature specimen. Comput. Mats. Sci. 2004; 31: 84-92.
 Saeidi S, Voisey KT, McCartney DG. The effect of heat treatment and the oxidation behaviour of HVOF and VPS CoNiCrAlY coatings. J. Therm. Spray Technol. 2009; 18. 209–216.
 CEN CWA 15627 Worskshop Agreement: Small punch test method for metallic materials. European Committee for Standardization, Brussels, December 2006.
 Kameda J, Mao X. Small-punch and TEM-disc testing technique and their application to characterization of radiation damage. J. Mater. Sci. 1992; 27(4):983–989.
 Eskner M, Sandstrom R. Measurement of the ductile-to-brittle transition temperature in a nickel aluminide coating by a miniaturised disc bending test technique. Surf. Coat. Technol. 2003; 165(1):71 – 80.
 Lancaster RJ, Illsley HW, Davies GR, Jeffs SP, Baxter GJ. Modelling the small punch tensile behaviour of an aerospace alloy. Mater. Sci. Technol. 2017; 33 (9).
 Rasche S, Kuna M. Improved small punch testing and parameter identification of ductile to brittle materials. Int. J. Pre. Ves. Pip. 2015; 125: 23-34.
 Wen W, Jackson GA, Li H, Sun W. An experimental and numerical study of a CoNiCrAlY coating using miniature specimen testing techniques. Int. J. Mech. Sci.2019; 157–158: 348-356.
 Ray AK. Failure mode of thermal barrier coatings for gas turbine vanes under bending. Int. J. Turb. Jet. 2000; 17: 1–24.
 Johnson GR, Cook WH. A constitutive model and data for metals subjected to large strains, high strain rates, and high temperatures. Proc. 7th Int. Symp. on Ballistics, Hague, Netherlands, 1983 April.
 Mathworks. Global Optimization Toolbox: User's Guide (r2015a). 2015.
 Abaqus Analysis User's Manual. (2009) Providence, RI: Simulia.
 Wen W, Sun W, Becker AA. Development of a two-material miniature specimen testing technique and the associated inverse approach. Theor. Appl. Fract. Mech. 2019; 99: 1-8.