Materials Science and Engineering A 367 (2004) 225–233 Microstructure of diffusion aluminide coatings on Ti-base alloy IMI-834 and their cyclic oxidation behaviour at 650 ◦ C D.K. Das ∗ , S.P. Trivedi Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India Received 27 August 2003; received in revised form 1 October 2003 Abstract The present study describes the microstructural details of plain pack aluminide and Pt-aluminide coatings on Ti-base alloy IMI-834 and their cyclic oxidation performance at 650 ◦ C in air. While the plain aluminide coating consists of a single layer of Al 3 Ti phase, the Pt-aluminide coating is constituted of two layers, with the outer layer consisting of PtAl 2 and Al 3 Ti phases and the inner layer of Al 3 Ti phase. These two coatings display excellent cyclic oxidation resistance on IMI-834 alloy although the Pt-aluminide coating is found to be somewhat superior to its plain aluminide counterpart. Virtually no coating degradation occurs even after 500h of oxidation exposure at 650 ◦ C. In this study, a layer of pure Pt deposited by electroplating is also found to offer limited protection against oxidation to the above alloy. TiO 2 is found as the primary oxide phase in the oxidation of bare IMI-834 alloy. © 2003 Elsevier B.V. All rights reserved. Keywords: Oxidation; IMI-834; Ti alloy; Platinum-aluminide coating; Aluminide coating 1. Introduction Titanium and its alloys offer designers several attrac- tive properties such as exceptional corrosion resistance and high specific strength. However, their utilization has been restricted because of certain inherent shortcomings associated with these materials. They include poor high temperature oxidation resistance, susceptibility to adhesive and fretting wear, poor galvanic compatibility with less corrosion resistant materials, etc. High temperature oxida- tion is currently proving to be one of the stumbling blocks for the use of near- Ti alloys such as IMI-834, IMI-829 and TIMETAL 1100. Oxidation exposure of the above al- loys at high temperatures (above ∼600 ◦ C) is known to cause the formation of a brittle  casing which under- mines the mechanical properties of these alloys. There- fore, several coatings are being examined for providing oxidation protection to the near- Ti alloys in the tem- perature range of 600–750 ◦ C. Prominent among these are physical vapour deposited TiAlN coating, Al 3 Ti-type alu- ∗ Corresponding author. Tel.: +91-40-24586504; fax: +91-40-24341439. E-mail address: dipakd1004@yahoo.co.in (D.K. Das). minide coating, silicide coatings and MCrAlY-type coatings [1–7]. IMI-834 alloy is currently being used for compressor parts in modern gas turbine engines. The maximum tem- perature of use for this alloy is approximately 600 ◦ C and in order to protect this alloy from oxidation damage dur- ing application, several coatings have been reportedly used including some of those listed above. Diffusion aluminide coatings of the type Al 3 Ti (or plain aluminide coating as it is often called) and Pt-aluminide have been reported to offer very good oxidation resistance to IMI-834 alloy [1,8,9]. Nicholls et al. [8] and, more recently, Gurrappa and Gogia [9] have reported that Pt-aluminide coating can pro- tect IMI-834 alloy from oxidation damage over long-term exposure at high temperatures up to 800 ◦ C. Gurrappa and Gogia have also shown the superiority in oxidation re- sistance of Pt-aluminide coating over its plain aluminide counterpart in air at 800 ◦ C. Although such superior ox- idation performance of diffusion aluminide coatings on IMI-834 alloy has been highlighted in the above studies [8,9], the microstructural aspects of these coatings, espe- cially those of Pt-aluminide coating, have not been well investigated. In the present study, microstructures of a plain aluminide coating and a Pt-aluminide coating formed on 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2003.10.196