KEYWORDS: Fretting Wear, Sliding Wear, Ti-6Al-4V, Cu-Ni-In, Plasma Spray, Coatings, Solid Lubricants, Graphite, MoS2.
Conventionally, plasma sprayed Cu-Ni-In coating along with solid lubricants like MoS2 are applied to the dovetails of Ti-6Al-4V compressor blades in order to reduce the fretting damage. The role of overlay MoS2 in service is very critical to the functional characteristics of compressor blades of gas turbine engines, which is bound to undergo progressive removal with time. In the present work, instead of overlay MoS2, solid lubricants such as MoS2 and graphite were incorporated in Cu-Ni-In coatings and studied. Cu-Ni-In powder, CoCrAlYSi-hBN powder, Cu-Ni-In + graphite composite powder and Cu-Ni-In + MoS2 composite powder were plasma sprayed on Ti-6Al-4V coupons of size 10 mm x 6 mm x 6 mm. Fretting wear tests were conducted at ambient temperature and high temperatures up to 450 oC. Also, an attempt was made to understand the performance of the proposed coatings under sliding wear conditions.
In general, CoCrAlYSi – hBN coating was found to be more effective in reducing friction coefficient compared to Cu-Ni-In coating at all temperatures studied. In case of coatings made using Cu-Ni-In mixed with 5 wt. % graphite, those prepared using 25 µm sized graphite was found to exhibit the lowest friction coefficient at room temperature. These coatings performed better than CoCrAlYSi – hBN coating in lowering the friction coefficient at room temperature and 450 oC. CoCrAlYSi – hBN and Cu-Ni-In mixed with 5 wt. % graphite (25 µm sized graphite) can be considered as the replacement for the currently used coating material of Cu-Ni-In to reduce friction coefficient at the blade-disk dovetail joints of compressors of gas turbine engines. Though the proposed coatings helped to reduce friction in fretting wear tests, they have not done so in sliding wear tests.