Thermal-cycling behavior of CoNiCrAlY bonds coated with thermal barrier coatings (TBCs) produced with atmospheric plasma spraying (APS)

Abstract

Thermal barrier coatings (TBCs) are commonly applied as a thermal insulation in order to protect against environmental influences in the components of high-temperature gas turbines and jet engines. Gas-turbine components are affected by aggressive conditions of the environment during the service, being subjected to failures such as corrosion, thermal shock and oxidation. Plasma-spray technology is used to produce metallic bonds and ceramic top coats as a cost-effective method to prolong the lifetime of TBCs. In the present research, CoNiCrAlY bond-coat and YSZ top-coat powders included in the TBCs were deposited onto Inconel 718 superalloy substrates using atmospheric plasma spraying (APS). The TBCs were exposed to a furnace cycling test at 1150°C and one-hour cycles. The presence of porosity and cracks facilitating the diffusion of oxygen in the top-coating structure led to the formation of thermally grown oxides (TGOs) at the interface. In addition, the most effective factors of failures were the formation and growth of mixed oxides at the bond/top-coat interface and the presence of imperfections. According to the test results, an increasing number of thermal cycles resulted in a decrease in the lifetime of the TBCs related to the sintering of the top coating due to the effect of high temperature. Keywords: thermal barrier coatings (TBCs), thermal cycling, Inconel 718 superalloy, atmospheric plasma spraying (APS), CoNiCrAlY, ytrria-stabilized zirconia (YSZ) Prevleke s toplotno pregrado (angl. TBCs) se obi~ajno uporabljajo kot toplotna izolacija, ki {~iti komponente visoko temperaturnih plinskih turbin ali reaktivnih motorjev. Na komponente plinskih turbin vplivajo agresivni vplivi okolja, katerim so izpostavljene med obratovanjem, zato pride do okvar, kot so: korozija, termi~ni {ok in oksidacija. Tehnologija plazemskega napr{evanja je cenovno ugodna tehnologija za izdelavo kovinskih in kerami~nih prevlek. V~lanku avtorji predstavljajo raziskavo v kateri sta bila na podlago iz zlitine Inconel 718 s tehnologijo plazemskega napr{evanja v zra~ni atmosferi nane{ena vezivna prevleka CoNiCrAlY in prekrivni sloj iz YSZ prahu. Izdelani prevleki sta bili nato izpostavljeni termi~nem utrujanju v pe~i pri 1150°C z ve~imi enournimi cikli. Prisotnost poroznosti in razpok olaj{a difuzijo kisika v zgornjo plast prevleke kar vodi do nastanka termi~no induciranega oksida (TGO) na povr{ini prevleke. Poleg tega sta bila najpomembnej{a dejavnika za nastanek napak tvorba me{anih oksidov na meji med vezno in vrhno plastjo ter prisotnost drugih nepravilnosti. Rezultati preizkusov so pokazali, da pove~anje {tevila termi~nih ciklov zmanj{uje dobo trajanja TBC prevlek, zaradi sintranja zgornje plasti pri povi{anih temperaturah. Klju~ne besede: prevleke s toplotno pregrado, toplotni (termi~ni) cikel, superzlitina Inconel 718, plazemsko napr{evanje, CoNiCrAlY, cirkon stabiliziran z itrijem