High-temperature oxidation behavior of Al2O3/TiAl matrix composite in air

Abstract

The oxidation behavior of Al 2 O 3 /TiAl in situ composites fabricated by hot-pressing technology was investigated at 900℃ in static air. The results indicate that the mass gains of the composites samples decrease gradually with increasing Nb 2 O 5 content and the inert Al 2 O 3 dispersoids effectively increase the oxidation resistance of the composites. The higher the Al 2 O 3 dispersoids content, the more pronounced the effect. The primary oxidation precesses obey approximately the linear laws, and the cyclic oxidation precesses follow the parabolic laws. The oxidized sample containing Ti 2 AlN and TiAl phases in the scales exhibits excellent oxidation resistance. The oxide scale formed after exposure at 900 for ℃ 120 h is multiple-layered, consisting mainly of an outer TiO 2 layer, an intermediate Al 2 O 3 layer, and an inner TiO 2 +Al 2 O 3 mixed layer. From the outer layer to the inner layer, TiO 2 +Al 2 O 3 mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed layer. Near the substrate, cross-section micrograph shows a relatively loose layer, and micro-and macro-pores remain on this layer, which is a transition layer and transferres from Al 2 O 3 +TiO 2 scale to substrate. The thickness of oxide layer is about 20 μm. It is also found that continuous protective alumina scales can not be observed on the surface of oxidation scales. Ti ions diffuse outwardly to form the outer TiO 2 layer, while oxygen ions transport inwardly to form the inner TiO 2 +Al 2 O 3 mixed layer. Under long-time intensive oxidation exposure, the internal Al 2 O 3 scale has a good adhesiveness with the outer TiO 2 scale. No obvious spallation of the oxide scales occurs. The increased oxidation resistance by the presence of in situ Al 2 O 3 particulates is attributed to the enhanced alumina-forming tendency and thin and dense scale formation. Al 2 O 3 particulates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface, thereby the TiO 2 growth rate decreases, which is also beneficial to improve the oxidation resistance. Moreover, the multi-structure of the TiO 2 +Al 2 O 3 mixed layer decreases the indiffusion of oxygen ions and also avails to improve the high temperature oxidation resistance of the as-sintered composites.Al 2 O 3 /TiAl matrix composite, oxidation resistance, high temperature

Characterisation and oxidation of LVOF sprayed Al2O3–40%TiO2coating on superni 601 and superni 718 superalloys at 800 and 900°C

“…Similar phases in case of plasma sprayed Al 2 O 3 –TiO 2 coating has been reported by Gok. 20 According to Ai et al 24 TiO 2 phase forms along the splat boundaries and contact each other, and Al 2 O 3 phase forms inside the splats.…”

“…The intact phases might be of Al 2 O 3 and Al 2 O 3 –TiO 2 phases, which remained adherent on the surface. According to Ai et al 24 the multi-structure of the TiO 2 –Al 2 O 3 mixed layer decreases the diffusion of oxygen ions inside the subsurface region of the coating thus improving the high temperature oxidation resistance. They further suggested that the continuous protective alumina scales do not form on the surface of oxidation scales.…”

“…Similar phases in case of plasma sprayed Al 2 O 3 -TiO 2 coating has been reported by Gok 20. According to Ai et al24 TiO 2 phase forms along the splat boundaries and contact each other, and Al 2 O 3 phase forms inside the splats. Measurement of average coating thickness, average surface roughness and average microhardness of as sprayed coating Thickness of the coatings was continuously monitored during the process of LVOF spraying with Minitest-2000 made in Germany.…”

The Flexural Strength and Fracture Toughness of TC4-Based Laminated Composites Reinforced with Ti Aluminide and Carbide

“…Their working temperature can reach 750–900 °C, which is close to that of the widely used Ni-based alloys, but the density is only half of the latter. Therefore, TiAl-based alloys have the potential to replace Ni-based alloys as aerospace structural components and transmission parts of power systems, which can greatly improve the thrust-weight ratio and fuel efficiency of the engines [1,2,3,4,5]. However, the intrinsic brittleness results in poor processing performance; thus, it hinders their further applications.…”

Low-temperature synthesis and characterization of Ti2AlC/TiAl in situ composites via a reaction Hot-Pressing Process in the Ti3AlC2-Ti-Al system

“…Intermetallic matrix composites (IMCs) can provide the right combination of HighTemperature strength and creep resistance and overcome the problem of poor ductility and toughness at ambient temperature [9]. Compounds such as Al 2 O 3 , TiB 2 , Ti 5 Si 3 , and Ti 2 AlC have been previously identified as compatible and thermochemically stable reinforcements for TiAl intermetallics [4,[10][11][12][13][14][15][16][17][18]. However, much more attention has been given to Ti 2 AlC reinforcement [11,17,18].…”