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

Abstract

γ-TiAl has been a hot topic of research for more than a few decades now, since it is a potential candidate for high temperature structural applications. In this paper, dispersion strengthening of γ based TiAl alloy, produced by means of centrifugal casting, has been performed to increase its mechanical properties beyond those of standard TiAl alloys. After a careful selection of the alloy composition based on the desired properties, several samples were produced by means of investment casting. This work focused on the effect of Al2O3 nano- and micro-dispersoids on the mechanical properties of the considered TiAl alloy. Microstructural investigations were carried out to study both the alloy microstructure and the Al2O3 dispersion homogeneity. Samples of the produced alloy were subjected to four-point bending tests at different temperatures for evaluating the effect of dispersed particles on mechanical properties. The results of this study were promising and showed that Al2O3 dispersion determined an increase of the mechanical properties at high temperatures. The Young’s modulus was 30% higher than that of the reference alloy in the lower temperature range. Over the temperature range 800–950 °C the dispersion strengthening affected the yield stress by increasing its value of about 20% even at 800 °C. A detailed evaluation of fracture surfaces was carried out to investigate fracture mechanisms.

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

“…At 850 and 900 °C, the reference specimens bent but did not fracture when tested in 4-point bending, while the strengthened alloy fractured both at 850 °C and 900 °C and bent at 950 °C (Figure 11). By comparing the results obtained in this research with the results obtained in a previous published work, 18 in which we tested a TiAl alloy reinforced with nanometric alumina particles, it is evident that in situ formed alumina allows to obtain better mechanical properties. Yield stress obtained with nanometric alumina dispersion is 372 MPa at 850 °C and 267 MPa at 900 °C, while yield stress obtained with in situ formed alumina reaches 435 MPa at 850 °C and 329 MPa at 900 °C.…”

“…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). 18 Dispersion strengthening is a widespread practice in the industry, and it is extensively used to reinforce materials from steel to superalloys. This process is already being used to harden nickel-based superalloys used for aerospace engines 19 above 1000 °C.…”

A review on fabrication and characteristics of functionally graded aluminum matrix composites fabricated by centrifugal casting method

“…The strengthening is due to dislocation motion in the metal being impeded by the presence of small, hard particles. The Orowan bypassing [50][51][52][53] of the particle by the movement of dislocation increases the material's strength:…”

“…This nucleation is followed by grain growth, which continues until the particle impedes the grain boundary movement [57]. The following expression, which shows the relationship between the particle size (d), the grain size of the matrix (D), and the volume fraction of the particle (V r ), is expressed as [51]:…”

Diffusion Aluminide Coatings for Hot Corrosion and Oxidation Protection of Nickel-Based Superalloys: Effect of Fluoride-Based Activator Salts

“…Materials used in hot sections of aero-and land-based gas turbines are designed to endure severe operating conditions and must be able to resist both hot corrosion and high temperature oxidation. Nickel-based superalloys are usually employed in high temperature sections of the engine, whereas TiAl components have aroused great interest in recent decades for the less thermally stressed areas [1][2][3]. A great scientific and technological interest is thus devoted to thermal barrier coatings (TBCs) [4][5][6][7][8][9] as heat resistant surface layers deposited on metallic components of gas turbine engines (usually made of Ni-or Co-based superalloys), allowing for efficient protection from high temperature inlet gases and therefore providing improved engine performance.…”