Microstructure and Oxidation Performance of TiAl-(Cr, Nb, Ta) Coatings Fabricated by Warm Spray and High-Velocity Oxy-Fuel Spraying

Abstract

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). 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 TiO 2 was found in addition to a-Al 2 O 3 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.

A review on Ti-based metal matrix composite coatings

“…This coating had wear resistance performance at room temperature and higher temperature. TiAl-(Cr, Nb, Ta) coatings were fabricated by thermal spraying in Ar atmosphere in Y 2 O 3 crucibles in induction coil with high frequency and different nitrogen flow rates by Sienkiewicz et al [32]. All coatings had relatively small porosity, which was located between the particles and during spraying, the particles hitting the substrate and form microstructures.…”

Cyclic oxidation of slurry silicide-aluminide coatings formed on Ti-6Al-4V alloy

“…From the ductility viewpoint, α 2 -Ti 3 Al and γ-TiAl phases demonstrate the most favourable properties (typical room temperature tensile ductility is 0.3% and 0.9%, respectively), and they can manifest across a broad spectrum of aluminium compositions. This characteristic enables the incorporation of alloying elements, thereby facilitating additional enhancements in both strength and ductility [11]. The phase with the largest amount of aluminium, TiAl 3 , is not used in industry due to its high brittleness (typical room temperature tensile ductility is 0%).…”

A Comparative Study of Aluminium and Titanium Warm Sprayed Coatings on AZ91E Magnesium Alloy

“…Although the HVOF is mentioned as competitive to WS due to its high process temperature, it is not used to spray pure Al and Ti metals in practice. It can be used only for spraying metals with much higher melting points, such as intermetallic powders based on TiAl [ 18 , 19 ]. The high HVOF spray temperature was the main reason for developing the WS system to control the spray temperature over a wide range.…”