Abstract
To improve the oxidation resistance of near α-titanium alloy IMI834, TiAl-(Cr, Nb, Ta) coatings were deposited by applying high-velocity oxy-fuel (HVOF) and warm spray (WS). Comparison was made in terms of microstructure, surface morphology as well as isothermal and cyclic oxidation behaviors in the air at 750 °C up to 100 h and 100 cycles, respectively. The results show that smoother and less oxidized coatings were deposited by warm spraying. The microstructure of all coatings underwent an appreciable change during the oxidation tests, as in as-sprayed state it occurred in the nonequilibrium state. It was revealed that a small difference in the initial oxidation between the two spraying processes as well as microstructure, the level of porosity and surface roughness significantly influences the oxidation kinetics of the sprayed coatings at high temperature, which should affect the service lifetime as an oxidation-resistant layer for potential applications. After exposure at 750 °C in air, rutile TiO2 was found in addition to α-Al2O3 in the oxide scale formed on the HVOF and warm sprayed coatings. However, isothermal and cyclic oxidation tests of all WS TiAl-(Cr, Nb, Ta) coatings showed improved oxidation resistance of IMI 834 as well as good adherence to the substrate alloy.
Highlights
Needs for enhancements of turbine engines power, efficiency and weight reduction have stimulated the development of temperature- and creep-resistant materials with reduced density (Ref [1,2,3,4])
To improve the oxidation resistance of near atitanium alloy IMI834, TiAl-(Cr, Nb, Ta) coatings were deposited by applying high-velocity oxy-fuel (HVOF) and warm spray (WS)
scanning electron microscopy (SEM) images of the gas-atomized TiAl-(Cr, Nb, Ta) alloys with powder size below \ 45 lm are shown in Fig. 1(a), (b) and (c)
Summary
Needs for enhancements of turbine engines power, efficiency and weight reduction have stimulated the development of temperature- and creep-resistant materials with reduced density (Ref [1,2,3,4]). Such requirements have driven the development of a wide range of titanium alloys culminating more recently IMI 834 alloy (Ti-5.8Al-4Sn3.5Zr-0.7Nb-0.5Mo-0.35Si), which is one of the most developed titanium alloys, operating industrially today as compressor disks and blades of advanced gas turbine engines for lightweight aircrafts (Ref [5, 6]). The properties of the titanium aluminides that make them attractive as a coating include outstanding oxidation resistance, low density and microstructural stability at elevated temperatures derived from their intermetallic
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