Some effects of structure and composition on the properties of electron beam vapor deposited coatings for gas turbine superalloys

Abstract

Multi-element overlay coatings applied by electron beam vapor deposition to gas turbine superalloys have been the subject of intensive research and development programs for the past eight years. Such coatings have proven to be superior to diffusion coatings in a number of critical applications primarily because of the ease with which compositional variations can be effected to meet unique protection and mechanical requirements. Overlay coating structural features have been identified (i.e., open columnar structure, vapor source spit marks, flakes and pits), along with present and future methods for their control. Laboratory observations have indicated that in a line-of-sight process, the open columnar structure is the result primarily of shadowing effects and the limited surface diffusion of the depositing atoms. Point defects (spits, flakes, and pits) result from pool behavior and substrate contamination. Methods of minimizing these defects range from in-process controls to post-coating processing. Current development areas for improved processing techniques such as gas randomization and ion plating should result in further improvements and elimination of some present post-coating processing requirements.

Influences of chromium and hafnium additions on the microstructures of β-nial coatings on superalloy substrates

“…It is also expected that further modifications to the processing method such as post-deposition peening and aging would lead to further improvements in coating microstructure and performance. Low impact surface peening has been used for more than 30 years to heal defects and to improve the quality of vapor deposited overlay coatings [60,61,106,107]. Such methods have been employed recently to modify the microstructures of b-NiAl-based overlay coatings, yielding positive results [108,109].…”

The influence of oxides on the performance of advanced gas turbines

“…[26][27][28] (b) A second consists of a two-phase, ␥/␤-alloy, usually deposited onto the substrate by plasma spraying or EB-PVD. [29][30][31] (c) The third is a two-phase ␥/␥ alloy made by infusing Pt (and Hf) into the substrate. 32,33 Systems made using these bond coats perform differently with durability governed by different mechanisms.…”

A kinetic Monte Carlo simulation of film growth by physical vapor deposition on rotating substrates

“…1) that enables the accommodation of the thermal expansion mismatch with the metallic substrate as the assemblage is thermally cycled during the operation of the engine [3]. Each columnar grain in the microstructure is bonded to the TGO but separated from its neighbors by voided boundaries or "gaps", broadly acknowledged to result from insufficient surface diffusion to overcome "self-shadowing" during deposition [4,5]. The films, however, are typically grown at ∼1000 • C [6], a temperature corresponding to the upper end of zone 2 (∼0.4T M ) in the Movchan and Demchishin structure map [7].…”