Effects of the manufacturing process on fracture behaviour of cast TiAl intermetallic alloys

Abstract

The γ -TiAl based intermetallic alloys are interesting candidate materials for high-temperature applications with the efforts being directed toward the replacement of Ni-based superalloys. TiAl-based alloys are characterised by a density (3.5-4 g/cm 3 ) which is less than half of that of Ni-based superalloys, and therefore these alloys have attracted broad attention as potential candidate for high-temperature structural applications. Specific composition/microstructure combinations should be attained with the aim of obtaining good mechanical properties while maintaining satisfactory oxidation resistance, creep resistance and high temperature strength for targeted applications. Different casting methods have been used for producing TiAl based alloys. In our experimental work, specimens were produced by means of centrifugal casting. Tests carried out on several samples characterised by different alloy compositions highlighted that solidification shrinkage and solid metal contraction during cooling produce the development of relevant residual stresses that are sufficient to fracture the castings during cooling or to produce a delayed fracture. In this work, crack initiation and growth have been analysed in order to identify the factors causing the very high residual stresses that often produce explosive crack propagation throughout the casting.

Mechanical Behaviour of an Al2O3 Dispersion Strengthened γTiAl Alloy Produced by Centrifugal Casting

“…Over the last few years, a lot of efforts 2 of 12 have been made in order to increase the low temperature ductility and toughness [12,13] of these alloys. Microstructural modifications and the addition of ternary elements are extensively used to optimize the mechanical and oxidation properties of γ titanium aluminides [14,15].…”

“…Considering that, a mixture of these two phases with an aluminium content of 37-49% has been found to be viable for structural applications. This is a dual phase of titanium aluminide with a mixture of α 2 and γ phases [11,14,15].…”

“…The mechanical properties of this dual α 2 + γ phase have been found to be very sensitive to its microstructure, grain size and microalloying elements [14]. For several years, our research team worked on the development and characterization of TiAl intermetallic alloys [12][13][14][15] produced by centrifugal casting for use at high temperatures as an alternative to superalloys. Worldwide research is remarkable [1][2][3][4][5] and usually these alloys are produced using technologies such as hot isostatic forming starting from powders, casting, additive manufacturing with already several industrial applications.…”

Enhanced High-Temperature Mechanical Behavior of an in Situ TiAl Matrix Composite Reinforced With Alumina

“…Our research team has worked, over the years, on the development and characterization of TiAl alloys produced by centrifugal casting for use at high temperatures. [15][16][17] Most recently, the focus has been on the methods that allow to increase mechanical strength, Young's modulus and creep resistance. Dispersion strengthening of the metal matrix has been studied by adding particles characterized by high thermal stability and elastic modulus, such as oxides (Al 2 O 3 , Y 2 O 3 , CeO 2 , ZrO 2 and ThO 2 ) and carbides (SiC, NbC, MoC, WC).…”

Fracture assessment of magnetostrictive materials

“…Thus, among all the giant magnetostrictive materials, the (Tb0.3Dy0.7Fe1.9) alloy has broadly gained interest in the last years. However, despite of the great attention that this alloy has gained in the industrial applications and though it is susceptible to in-service fracture due to its brittleness [2], very few works are available concerning the assessment of the influence of manufacturing induced defect and cracks on magnetostricitve material performances, notwithstanding the widely reported harmful effects of notches [3][4][5]. Moreover, the fracture behavior of these materials are highly affected by the presence of magnetic fields, since the fracture resistance uder mode I is inversely related to the intensity of the field Narita et al [6].…”