Fabrication and Oxidation Resistance of TiAl Matrix Coatings Reinforced with Silicide Precipitates Produced by Heat Trea
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Fabrication and Oxidation Resistance of TiAl Matrix Coatings Reinforced with Silicide Precipitates Produced by Heat Treatment of Warm Sprayed Coatings Judyta Sienkiewicz1 • Seiji Kuroda2 • Hideyuki Murakami2 • Hiroshi Araki2 Maciej Gi_zyn´ski3 • Krzysztof J. Kurzydłowski3
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Submitted: 25 January 2018 / in revised form: 10 August 2018 The Author(s) 2018
Abstract Ti-Al-based intermetallics are promising candidates as coating materials for thermal protection systems in aerospace vehicles; they can operate just below the temperatures where ceramics are commonly used, and their main advantage is the fact that they are lighter than most other alloys, such as MCrAlY. Therefore, Ti-Al-Si alloy coatings with five compositions were manufactured by spraying pure Ti and Al-12 wt.% Si powders using warm spray process. Two-stage hot pressing at 600 and 1000 C was applied to the deposits in order to obtain titanium aluminide intermetallic phases. The microstructure, chemical composition, and phase composition of the asdeposited and hot-pressed coatings were investigated using SEM, EDS, and XRD. Applying of hot pressing enabled the formation of dense coatings with porosity around 0.5% and hard Ti5(Si,Al)3 silicide precipitates. It was found that the Ti5(Si,Al)3 silicides existed in two types of morphologies, i.e., as large particles connected together and as small isolated particles dispersed in the matrix. Furthermore, the produced coatings exhibited good isothermal and cyclic oxidation resistance at a temperature of 750 C for 100 h.
& Judyta Sienkiewicz [email protected] 1
Institute of Armament Technology, Faculty of Mechatronics and Aerospace, Military University of Technology, Kaliskiego 2, 00-908 Warsaw, Poland
2
National Institute for Materials Science, Research Center for Structural Materials, 1-2-1, Sengen, Tsukuba-Shi, Ibaraki-ken 305-0047, Japan
3
Faculty of Materials Science and Engineering, Materials Design Division, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland
Keywords applications,spray forming feedstock, coatings for engine components intermetallics testing
Introduction Titanium aluminides are promising as a coating material, especially for thermal protection on Ti alloys (e.g., IMI 834) used under high-temperature and harsh environmental conditions in aerospace, automobile, and gas turbine industries because of their high specific strengths and excellent properties at elevated temperature (Ref 1-6). Industrial application of such coatings, however, is limited due to the complicated production routes. TiAl-based coatings might be fabricated by thermal spray techniques which can either use aluminide powder or deposits consisting of Ti and Al powder mixtures followed by heat treatment (Ref 7-10). However, there are some problems with production of coatings using Ti and Al powder mixture as a feedstock. In our previous study, pure Ti and Al powders were deposited by warm spray, which is a modification of high-velocity oxy-fuel (HVOF) spray process,
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