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Microstructural Characterization of Several Coatings Deposited on TiAlNb Intermetallic Alloy

Góral M., Pytel M., Dychtoń K.

Archives of Metallurgy and Materials

2014

Vol. 59, iss. 4

1547--1551

Titanium alloys based on the γ -TiAl intermetallic phase are a type of material which may replace nickel supperalloys in high temperature applications. Not enough resistance to corrosion at temperatures above 900°C remains the biggest limitation in industrial practices. The paper presents results of preliminary research into application of new type heat resistant coatings on the basis of γ -TiAl alloy. MeCrAlY and Si coatings were formed by pack cementation method. Aluminide coatings were deposited by pack cementation method and VPA. Research results have shown that except for the coating formed by VPA, coatings were characterized by high porosity and therefore would not ensure appropriate protection against oxidation. Further research will be necessary into application of the VPA method in protecting γ-TiAl titanium alloys in order to improve their heat resistance.

Stopy na osnowie fazy międzymetalicznej γ-TiAl stanowią materiał, który może stanowić zamiennik nadstopów niklu w aplikacjach wysokotemperaturowych. Nadal największym ograniczeniem w ich przemysłowym zastosowaniu jest niewystarczająca odporność na utlenianie w temperaturze powyzej 900°C. W artykule przedstawiono wyniki wstępnych badań nad zastosowaniem nowych rodzajów powłok żaroodpornych na podłożu stopu γ-TiAl. Wytworzono powłoki MeCrAlY oraz Si metodą zawiesinową a także powłoki aluminidkowe metodą pack cementation oraz VPA. Wyniki badań wykazały że poza powłoką wytworzoną metodą VPA pozostałe charakteryzowały się dużą porowatością przez co nie moga zapewnić odpowiedniej ochrony przed utlenianiem. Wskazano na konieczność dalszych badań nad zastosowaniem metody VPA do ochrony stopów tytanu γ-TiAl w celu poprawy ich żaroodporności.

Thermal stability of protective coatings produced on nickel based superalloy

Pytel M., Góral M., Motyka M., Miziniak T

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 51, nr 2

67--77

Purpose: In this paper the results of high temperature cyclic oxidation tests of the protective diffusion coatings were presented. One of the main purposes of this work was to produce three different types of protective coatings by three different methods, i.e. slurry method, vapour phase aluminizing (VPA) and chemical vapour deposition (CVD), applied on nickel based Rene 80 superalloy substrate. Design/methodology/approach: The high temperature cyclic oxidation tests were carried out in 23h cycles at constant temperature 1100°C using Carbolite CWF 1300 chamber furnace. The samples were removed outside and were weighted after each cycle. The microstructure investigations of all kinds of the coatings were conducted by the use of light microscope (Nikon Epiphot 300) and a scanning electron microscope (Hitachi S-3400N). In the analysis influence of each method have been taken into consideration, i.e. especially influence of the kind of process on microstructure, coating thickness, chemical composition, first of all aluminium content (in outer β-NiAl layer so-called additive layer, diffusion layer and substrate). For the chemical composition examination x-ray energy dispersive (EDS) method was applied using Thermo equipment. Findings: It was found that the best high cyclic oxidation resistance of coating was obtained using CVD method (the maximal increase of samples weight after 28th cycle was observed, whereas in case of the slurry sample after 3rd and VPA after 5th). Research limitations/implications: The research results will be used in the future in order to increase coating thickness, aluminium content and to produce Pt, Pd, Zr, Hf and Si modified aluminide coatings. Practical implications: The CVD method will be used to coat internal passages of turbine blades, for example to produce modified aluminide bond coats on single crystal nickel based superalloys. Originality/value: Chemical vapour deposition is an unique method which is a “pure method” and allows to coat hardly accessible locations/areas.