Cyclic oxidation behavior of Pt-modified aluminide coating treated with ultrasonic nanocrystal surface modification (UNSM) on Ni-based superalloy

Abstract The effect of ultrasonic nanocrystal surface modification (UNSM) on Pt-modified aluminide coatings on Ni-based superalloy was investigated. UNSM was applied to make the grain size finer and to release compressive stress on the Al oxide film by reducing surface roughness. A Pt layer, with a thickness of 10–11 μm, was coated on a superalloy and transformed to a Ni-Pt alloy layer by annealing, at 1050 °C for 3 h. Before pack aluminizing, the surface of the Ni-Pt alloy layer was shocked by UNSM. The grain size of this UNSM-shocked Ni-Pt alloy layer was finer than the grain size on the untreated specimen. During pack aluminizing, the treated Pt-modified aluminide coating had more Al uptake and greater thickness than the untreated Pt-modified aluminide coating, because many grain boundaries and volume increase were incurred by UNSM. Furthermore, the treated coating displayed a smoother surface before, and after, pack aluminizing. The treated coating showed superior cyclic oxidation resistance. The decrease of surface roughness in the treated coatings diminished compressive stress, which caused spallation of the thermally grown oxide (TGO) and faster depletion of Al. Faster Al depletion in the untreated coating led to a phase transformation, from β-NiAl to γ′-Ni 3 Al, and then to changes in volume and solubility of the alloying element, Cr. The increase of the surface and interface roughness was a result of the change in volume as well as the increased stress and strain between the TGO and the coating. Additionally, the increasing solubility of the alloying element, Cr, in the coating, resulted in the formation of a large amount of Cr- and Ni-related oxides, which are unstable in the TGO during cyclic oxidation. Spallation of the TGO caused an accelerated rate of Al depletion in the untreated coating, and a faster degradation rate than in the treated coatings.

[1]  Chang-Min Suh,et al.  Fatigue and mechanical characteristics of nano-structured tool steel by ultrasonic cold forging technology , 2007 .

[2]  F. Xie,et al.  A novel powder aluminizing technology assisted by direct current field at low temperatures , 2008 .

[3]  S. Joshi,et al.  Evolution of aluminide coating microstructure on nickel-base cast superalloy CM-247 in a single-step high-activity aluminizing process , 1998 .

[4]  A. Evans,et al.  Effect of interface undulations on the thermal fatigue of thin films and scales on metal substrates , 1997 .

[5]  A. Evans,et al.  The ratcheting of compressed thermally grown thin films on ductile substrates , 2000 .

[6]  Pierre Villars,et al.  Pearson's handbook of crystallographic data for intermetallic phases , 1985 .

[7]  F. Pettit,et al.  Oxidation of Ni ‐ Cr ‐ Al Alloys Between 1000° and 1200°C , 1971 .

[8]  A. Gafurov,et al.  Development of evolutionary cone type LSD for SUV/RV utilizing the axiomatic approach and the ultrasonic nano crystal surface modification technology , 2008 .

[9]  Manish Roy,et al.  Microstructural degradation of plain and platinum aluminide coatings on superalloy CM247 during isothermal oxidation , 1999 .

[10]  Jian Lu,et al.  An investigation of surface nanocrystallization mechanism in Fe induced by surface mechanical attrition treatment , 2002 .

[11]  David R. Clarke,et al.  Surface rumpling of a (Ni, Pt)Al bond coat induced by cyclic oxidation , 2000 .

[12]  S. Joshi,et al.  Role of Pt content in the microstructural development and oxidation performance of Pt–aluminide coatings produced using a high-activity aluminizing process , 1998 .

[13]  M. R. Jackson,et al.  The aluminization of platinum and platinum-coated IN-738 , 1977 .

[14]  P. K. Datta,et al.  Shot peening effect on aluminide diffusion coating formation on alloy steels at low temperatures , 2006 .

[15]  V. Lesnikov,et al.  Influence of instability of the β-phase of the aluminide coating on the condition and scale resistance of the surface layer of Ni−Al alloys , 1986 .

[16]  N. Ridley,et al.  On dislocation accumulation and work hardening in Hadfield steel , 2006 .

[17]  K. F. Badawi,et al.  Microstructure of Pt modified aluminide coatings on Ni-based superalloys without prior Pt diffusion , 2005 .

[18]  W. Han,et al.  The effect of Pt contents on the surface morphologies of Pt-modified aluminide coating , 2009 .

[19]  T. Girardeau,et al.  Study by complementary X-ray techniques of in-depth microstructure in Ni-based superalloys after Pt diffusion treatment , 2002 .

[20]  A. Evans,et al.  On the mechanical behavior of brittle coatings and layers , 1983 .

[21]  G. W. Goward,et al.  Mechanisms of formation of diffusion aluminide coatings on nickel-base superalloys , 1971 .

[22]  Kwang-Lung Lin,et al.  Interdiffusion of the aluminized and Pt-aluminized coatings on MAR-M247 superalloy , 1992 .

[23]  H. M. Tawancy,et al.  Thermal stability of a platinum aluminide coating on nickel-based superalloys , 1992, Journal of Materials Science.

[24]  S. Joshi,et al.  Effect of prealuminizing diffusion treatment on microstructural evolution of high-activity pt-aluminide coatings , 2000 .

[25]  Jian Lu,et al.  Chromizing behaviors of a low carbon steel processed by means of surface mechanical attrition treatment , 2005 .

[26]  D. Das,et al.  Effect of Al Content on Microstructure and Cyclic Oxidation Performance of Pt-Aluminide Coatings , 2002 .

[27]  F. Pettit,et al.  Thermal Barrier Coatings for the 21st Century , 1999, International Journal of Materials Research.