Protective coatings on turbo engine blades from titanium alloys, for service temperature of 850°C

摘要

The new challenges in aircraft materials engineering, are now driven, especially, by energy and pollution aspects pressures. The contemporary tendencies concerning aircraft materials aim to the light alloys, from which the most important are the titanium base alloys. The most important thing is to choose an optimal combination between base alloy and thermal barrier coating for turbo engine applications knowing the high aggressivity of the environment, the high temperature and gases resulting from burned fuel. Our study focussed on titanium aluminide with mixed structure, α_2 /γ (Ti50Al40Nb6,0Ta0,5Crl,0Si0,2Ni0,5 with 25% of α_2 phase) and two types of coatings with double roles, thermal and diffusion barrier. The coatings have been obtained by spraiyng using two different techniques: atmospheric plasma (APS) and high velocity oxygen fuell (HVOF). The main characteristic of coatings systems are: Bilayer system with Bond coat (Amdry 997 (Ni40Co 25Cr20 Al10Ta4Yl) obtained using HVOF technique (combustion gases: O_2 + propane; p O_210 bar; PC_3H_8 - 8 bar; W O_2-250 nlpm, W C_3H_8- 60 mLpm; W powder 38 g/min; Driving gas for powder- N2 with 6 bar and 28 nlpm; projection distance 220 mm Outer coat (Metco 204 (ZrO_2Y_2O_3) obtained using APS technique (Plasma gas: Ar+H_2; Pat - 5 at and Ph_2 - 5at; War= 44 nlpm, W H_2=13nlpm; Driving gas (powder):Ar = 3,5 nlpm; projection distance 90 mm; Current (I)=630 A; tension (V)= 78 V Monolayer system -Diamalloy 2001 (Ni76Crl7B3,0Si3,5C0,5) obtained using HVOF technique combustion gases: O_2 + propane; p O_210 bar; PC_3H_8 - 8 bar; W O_2-250 nlpm, W C_3H_g- 60 mLpm; W powder: 38 g/min; Driving gas for powder- N2 with 6 bar and 28 nlpm; projection distance 220 mm. Oxidation resistance of the specimens coated with the layers described above has been carried out by thermal oxidation at 850 °C for 500 hours. Thermal oxidation tests were conducted in an oven VulcanTM 3-130 (Ney), in static air atmosphere. Subsequently analyzed specimens were placed in ceramic crucibles (Al2O3) for oxidation tests. Ceramic crucibles have previously been calcined at temperatures of 1000 °C for 2 hours to eliminate organic contaminants and humidity. Three specimens were tested from each type of coating. Waistlines of each sample was checked using an analytical balance after every 100 hours. To determine oxidation products and properties of oxide layers resulting from thermal oxidation have used different characteri2ation techniques: 1. morfologia and elemental analysis of oxide films are made with SEM and EDS; 2. Identify types of oxides after thermal oxidation resulting with Raman spectroscopy; Were studied interfacial aspects between base alloy and coatings and between layers (in the case of bilayered system), especially.