Oxidation Resistance Of TiAl Alloys Research Articles

Enhancement of mechanical properties and oxidation resistance of TiAl alloy with addition of Nb and Mo alloying elements

In this study, small button-shaped ingots were prepared by a non-self-consuming vacuum arc melting method. The effect of the content of Nb and Mo elements on the microstructure, mechanical properties and oxidation resistance of TiAl alloys were investigated. The as-cast TiAl alloy presented laminar microstructure. When only adding Nb element, a small amount of β phase was distributed in the form of dots at the grain boundaries of α2/γ lamellar structure. When adding both Mo and Nb, the precipitated β phase started to precipitate in lines inside the α2/γ lamellar structure. The microhardness of the alloy increased with the increasing Nb and Mo content. The compressive strength of the alloys increased firstly with the increasing Nb content and decreased when the content of Nb exceeded 7 wt%. However, with the addition of Mo, the compressive strength of the alloys decreased drastically. The optimal compressive strength of the alloy, i.e. 2250 MPa, was obtained with 5 wt% Nb and 5 wt% Mo addition. The oxidation resistance of the alloys were enhanced with the addition of Nb and Mo elements and the TiAl–5Nb–5Mo alloy also showed the best oxidation resistance at 800 °C.

Improving high temperature oxidation resistance of TiAl alloy via hierarchical Ti5Si3-Ti2AlC precipitation strategy

In-situ precipitated ceramic particles with excellent oxidation resistance acted as a barrier, which can improve the high temperature oxidation resistance of TiAl alloys. Herein, hierarchical Ti5Si3-Ti2AlC particles reinforced TiAl composite was designed and prepared by spark plasma sintering, where micron-Ti5Si3 particles were mainly precipitated at grain boundaries, and nano-Ti2AlC particles were mainly precipitated at the interfaces of α2/γ lamellae. The mass gain of TiAl alloy was decreased by 38.5% after oxidation at 850 ℃ for 100 h. The various atoms inward and outward diffusion were inhibited by the hierarchical micron-Ti5Si3 and nano-Ti2AlC particles, which suppressed TiO2 fast-growing and promoted Al2O3 slow-growing.

Cyclic Oxidation Kinetics and Thermal Stress Evolution of TiAl Alloys at High Temperature

The oxidation resistance of TiAl alloys is crucial for their commercial application. In this paper, a cyclic oxidation test with stable air circulation was designed to investigate the cyclic oxidation behavior of the TNM alloy and 4822 alloy at 800 °C and to analyze the phase, morphology, and thermal stress evolution of the oxide layer. The oxidation weight gain curves of both alloys are found to be in parabolic form, and the oxidation reaction orders of the TNM alloy and 4822 alloy are 2.374 and 1.838, respectively. The Nb and Mo elements enhance the antioxidant performance of the TNM alloy by inhibiting the dissolution and diffusion of oxygen, Ti, and Al atoms in the TiAl alloy. The thermal stress evolution of the two alloys during the heating and cooling phases of the cyclic oxidation process are calculated separately, and it is found that the thermal stresses in the TNM alloy are smaller than those in the 4822 alloy, while the maximum thermal stresses appear at the oxide/substrate interface rather than inside the oxide scale, which quantitatively explains the oxidation peeling resistance of the two alloys.

High-temperature oxidation behavior of ceramic particles-reinforced TiAl composites with multilayered structure

To investigate the effect of different reinforcements on high-temperature oxidation resistance of TiAl alloys, ceramic particles-reinforced (graphene oxide (GO), SiC, BN) TiAl composites with a multilayered structure were prepared by spark plasma sintering (SPS) using high throughput concept. The TiAl composite was fully lamellar structure, including GO, SiC and BN reinforcements each layer respectively. The effect of different reinforcements on oxidation layer of TiAl composites was observed directly after cyclic oxidation testing at 950 °C. The mass gain of TiAl composites was 2.09 mg/cm2 lower than that of 2.81 mg/cm2 for TiAl alloy oxidized 100 h, corresponding to a lower oxidation rate. The oxidation layer of TiAl composites was composed of TiO2 and Al2O3, and presented a multi-layer structure. The results showed that SiC and GO reinforcements improved the high-temperature oxidation resistance of TiAl alloy, while BN reinforcement played a negative role. The effect of different reinforcements on oxidation mechanism of TiAl alloys was mainly attributed to the ceramic particles-inhibited oxygen diffusion and ceramic particles-indued the nitridation susceptibility.

Improving the high temperature oxidation resistance of TiAl alloy by SiOC coating

To improve the high temperature oxidation resistance of TiAl alloy, silicon oxycarbide (SiOC) coating was fabricated by dip-coating using polydimethylsiloxane (PDMS) as the precursor. The oxidation behavior of the coating was evaluated at 850 °C. The morphology and chemical structure of the SiOC coating were characterized by scanning electron microscopy (SEM) equipped with an energy dispersive spectroscopy (EDS), Fourier Transform infrared spectroscopy (FT-IR), X-ray photo electron spectroscopy (XPS), and X-ray diffraction (XRD). Results showed that the SiOC coating exhibited good oxidation resistance. During the thermal exposure, the selective oxidation of Al at the SiOC/TiAl alloy interface resulted in the generation of protective Al2O3, which suppressed the inward diffusion of oxygen and outward diffusion of the alloy matrix elements. However, the cracks on the surface of SiOC coating were observed, which would provide channels for the oxygen and form thermally grown oxide layer (mainly consisting of TiO2 and Al2O3) above the Al2O3 layer.

Effect of Ni in SiO2 coating on the oxidation resistance of TiAl alloy at 900 °C

In this study, a novel SiO2 coating with the incorporation of nickel was prepared on Ti48Al2Nb2Cr alloy by co-electrodeposition. The effect of Ni in SiO2 coating on the oxidation resistance of Ti48Al2Nb2Cr alloy at 900 °C was investigated. Due to the incorporation of nickel, the high temperature performance of the SiO2 coating is promoted. For the Ni-modified SiO2 coating, diffusion of oxygen to the substrate is effectively inhibited by a compact oxide scale composed of SiO2 outer layer, Al2O3 middle layer, and Ti5Si3 inner layer. The incorporated Ni reinforces the structure and withstands the stress change of the SiO2 coating. Moreover, the occurrence of cracking is impeded by NiO which is formed during oxidation.

Effect of Sn addition on the mechanical properties and high-temperature oxidation resistance of intermetallic TiAl alloys by first principles study and experimental investigation

Tin (Sn) can be used as an effective TiAl powder sintering aid, but it is unclear whether Sn will deteriorate its properties as a micro-alloyed element in TiAl intermetallic. This work focuses on the influence of Sn on the mechanical properties and oxidation resistance of TiAl alloys. The effect of Sn on the mechanical properties of TiAl alloys is investigated by experiments and first-principles calculations. Sn atoms preferentially occupy the Al sites in γ-TiAl alloys and increase the lattice volume, which is consistent with the XRD pattern. The elastic constants of TiAl alloys with different Sn contents are also systematically presented. It is found that 1.85 at.% Sn addition improves the ductility of TiAl, but a higher Sn content reduces the ductility. This result is also verified by room temperature compression test. The density of states is also used to prove the ductility improvement of TiAl alloys with a certain amount of Sn. Last, the diffusion barrier of O and Al/Ti–O bond strength were calculated to evaluate the oxidation resistance of TiAl–Sn alloys. The addition of Sn markedly increases the O diffusion barrier and Al–O bond force constant, indicating that Sn can improve the oxidation resistance of TiAl alloy.

Effects of oxygen addition on the microstructure, phase transformations, and oxidation resistance of TiAl alloys

This study investigated the effects of oxygen addition on the microstructure, phase transformations, and oxidation resistance of TiAl alloys at 1023 K. The addition of oxygen stabilized the α (α2) phase at the expense of the γ phase and reduced the oxidation mass gains of the TiAl alloys by more than 20%. Oxide scales composed of external scattered Ti-rich oxide particles/Al-rich/Ti-rich mixed Ti/Al oxides, and internal affected zones with Al-rich precipitates were observed in all oxidized samples. The results showed that the microstructure and phase transformations of the alloys were altered by adding 1 at% oxygen. The addition of O accelerated the α → α2 chemical ordering reaction and partly suppressed the α → γ massive phase transformation. The oxidation resistance of the TiAl alloys in air at 1023 K was not significantly affected by the addition of oxygen.

Improvement in oxidation resistance of TiAl alloys by in-situ precipitation of Ti2AlC at the interface of α2 and γ lamellae

Herein, in-situ sintered micro-nano Ti2AlC/TiAl composite with fully lamellar structures were designed by spark plasma sintering to improve the high-temperature oxidation resistance of TiAl alloys. The Ti2AlC/TiAl composite exhibited lower oxidation rate and thinner oxide scale enriched Al2O3 compared to TiAl alloy after 750 ℃ and 850 ℃ oxidation, suggesting that oxidation resistance of the Ti2AlC/TiAl composite was improved. The superior oxidation resistance of the Ti2AlC/TiAl composite was mainly attributed to Ti2AlC particles hindered the diffusion of O atoms and stabilized the Al-rich oxide layer by the formation of more Ti-Al-N layers due to the nitridation susceptibility of Ti2AlC.

The Effect of Gd Additions on the Oxidation Resistance of TiAl Alloys Prepared by SPS

The Effect of Gd Additions on the Oxidation Resistance of TiAl Alloys Prepared by SPS

Improvement in Oxidation Resistance of Tial Alloys by In-Situ Precipitated Ti2alc at Interface of Α2 and Γ Lamella

Improvement in Oxidation Resistance of Tial Alloys by In-Situ Precipitated Ti2alc at Interface of Α2 and Γ Lamella

Microstructure and Oxidation Behavior of NiCoCrAlY Coating With Different Sm2O3 Concentration on TiAl Alloy

In order to improve the oxidation resistance of TiAl alloys, NiCoCrAlY coatings with different amounts of Sm2O3 were prepared by laser cladding on TiAl alloys. The microstructure and oxidation behavior of the coatings were investigated by isothermal oxidation tests at 900°C. The results indicated that the grains of the coatings were refined by Sm2O3. The fine grain reduced the crack sensitivity of the doped coatings and promoted the transformation of θ-Al2O3 to α-Al2O3. Therefore, the internal oxidation of the coatings and the growth rate of the oxide films were reduced. The segregation of Sm at grain boundary inhibited the outward diffusion of Ti, thus reducing the excessive oxidation of Ti. In addition, the oxidation mechanism of the coating was changed from simultaneous diffusion of Al and O to predominant inward diffusion of O. The oxidation resistance of the doped coatings was significantly improved. However, excessive Sm2O3 is detrimental to the improvement of the oxidation resistance. The oxidation resistance of 3 wt% Sm2O3 is the best.

Oxidation resistance of TiAl alloy improved by hot-pack rolling and cyclic heat treatment

The isothermal oxidation behavior of two TiAl alloys (as-HIP and as-RHT) were compared to explain the effect of microstructure on the oxidation resistance of TiAl alloy. After hot-pack rolling and cyclic heat treatment, the size of lamellar colonies was refined from 35.4 μm to 21.5 μm, and the β/B2 phase was effectively removed. It is concluded that the as-RHT TiAl alloy has better oxidation resistance than the as-HIP TiAl alloy. The main reason is due to refinement of lamellar colony size, elimination of β/B2 phase, uniform distribution of Nb and Mo, and the crushing of Y compounds.

A Short Review on the Phase Structures, Oxidation Kinetics, and Mechanical Properties of Complex Ti-Al Alloys.

This paper reviews the phase structures and oxidation kinetics of complex Ti-Al alloys at oxidation temperatures in the range of 600–1000 °C. The mass gain and parabolic rate constants of the alloys under isothermal exposure at 100 h (or equivalent to cyclic exposure for 300 cycles) is compared. Of the alloying elements investigated, Si appeared to be the most effective in improving the oxidation resistance of Ti-Al alloys at high temperatures. The effect of alloying elements on the mechanical properties of Ti-Al alloys is also discussed. Significant improvement of the mechanical properties of Ti-Al alloys by element additions has been observed through the formation of new phases, grain refinement, and solid solution strengthening.

High-temperature oxidation behaviour of TiAl alloys with Co addition

The challenge of enhancing the high-temperature oxidation resistance of TiAl alloys is hereby addressed by Co addition. Isothermal oxidation tests were conducted on the newly designed TiAl-Co alloys in laboratory air at 900 °C up to 100 h. Sintered microstructure, oxidation kinetics, scale structure, spallation resistance and oxidation mechanisms were systematically investigated. Results show that the original sintered microstructure of TiAl alloys mainly consists of matrix phases α2-Ti3Al/γ-TiAl lamellae, while the Co addition leads to the formation of the two additional Co-rich phases of CoAl2Ti and Ti (Al, Co, Cr and Nb) at grain boundaries. The Co-doped TiAl alloys exhibit an improved high-temperature oxidation resistance compared with the Co-free alloy. The presence of the Co-rich phases network along the grain boundaries and Co-rich layer at the scale/substrate interface can hinder the inward diffusion of oxygen and the outward diffusion of Ti and Al, thereby suppressing the growth of oxide scale and improving the spallation resistance of TiAl alloys. As a result, the TiAl-3Co alloy possesses excellent oxidation resistance, with the minimum mass gain of 4.08 mg/cm2, thinnest scale thickness of 17.8 μm and without surface spallation or crack formation after isothermal oxidation for 100 h. This result would pave the way for designing high-temperature oxidation-resistant TiAl-based alloys.

Microalloying effects of Ho on microstructure evolution and high temperature properties of Ti46Al4Nb1Mo alloy

In order to improve high-temperature mechanical properties and oxidation resistance of TiAl alloys, Ho element was added into Ti46Al4Nb1Mo alloy. The microstructure, high-temperature tensile property and oxidation behavior of Ti46Al4Nb1Mo alloy with different Ho content (0, 0.15%, 0.3%, atomic percent, hereafter in at.%) were investigated in this study. The results showed that Ho2O3 particles with square and rod-like shape formed by internal oxidation and the α2/γ lamellar spacing was refined with 0.15% Ho addition. When Ho content was 0.3%, irregular and large Al2Ho phases appeared at grain boundaries. Compared with Ti46Al4Nb1Mo alloy, the high-temperature tensile strength was improved with 0.15% Ho and decreased with 0.3% Ho. The improvement of the strength resulted from the Ho2O3 second phase strengthening, the decreasing of the strength was caused by the formation of large irregular Al2Ho phase. Oxidation testing results indicated that 0.15% Ho improved oxidation resistance of Ti46Al4Nb1Mo alloy, which was due to suppression of inward diffusion of oxygen and better adhesion between oxide film and matrix.

Effect of Sn addition on the high-temperature oxidation behavior of high Nb-containing TiAl alloys

The effect of Sn addition on the oxidation behavior of high-Nb containing TiAl alloys was investigated with isothermal oxidation tests conducted in static air at 1000 °C. Sn addition can improve the high-temperature oxidation resistance of TiAl alloys by forming a protective Ti3Sn layer to diminish the inward oxygen diffusion. Moreover, the generated Al2O3 oxide pegs provide a mechanical locking to enhance the spallation resistance. The alloy containing 3 at.% Sn exhibits superior oxidation resistance, with no spallation occurring. The lowest mass gain after being oxidized for 100 h was 3.29 mg/cm2, which is 42.1 % lower than the Sn-free alloy.

The effect of Ta additions on the oxidation resistance of SPS-produced TiAl alloys

The influence of the environment on the properties of TiAl alloys is a concern for elevated temperature applications. One element that stands out in improving the resistance of TiAl alloys against high-temperature oxidation is Nb. Nb promotes the activities of Al and favors the formation of a more protective Al2O3 surface oxide which subsequently stymies oxygen diffusion to the alloy. Ta is an equal replacement of Nb. Thus, this study aims to evaluate the effect of 0.8, 4, and 8 at. % Ta additions on the oxidation resistance of spark plasma sintered Ti-46.5Al (at. %) alloy. Isothermal oxidation tests were carried out for 360 and 100 h at 1123 and 1273 K respectively. Surface oxides examination include scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray diffractometry. The results show that 4 and 8 at. % Ta additions significantly support the formation of an interconnected, non-porous Al2O3 layer at the metal-oxide interface. The continuous non-porous Al2O3 layer serves as a diffusion barrier which leads to superior oxidation resistance of the TiAl alloys.

Solid-State Processing Route, Mechanical Behaviour, and Oxidation Resistance of TiAl Alloys

A primary challenge associated with TiAl alloys is their low ductility at room temperature. One approach to overcome this flaw is attaining ultrafine grains in the alloy’s final microstructure. The powder metallurgy (PM) processing route favours the synthesising of ultrafine grains in TiAl alloys. This paper features the mechanical alloying (MA) process and rapid consolidation through the spark plasma sintering (SPS) technique, which comprises the PM process. Furthermore, a second approach discussed covers microalloying TiAl alloys. An evaluation of the influence of high oxygen content is also presented, including the formation of α-Al2O3. A section of the review delves into the dynamic recrystallisation mechanisms involved in elevated temperature deformation of TiAl alloys. The final section highlights the efficacy of ternary element additions to TiAl alloys against oxidation.

Improving the High-Temperature Oxidation Resistance of TiAl Alloy by Anodizing in Methanol/NaF Solution

An aluminum- and fluorine-enriched anodic film was fabricated on TiAl alloy by anodizing in NaF-contained methanol solution. The high-temperature oxidation resistance and protection mechanism of the anodized TiAl alloy were investigated. It showed that the formation of aluminum-enriched oxide scale originates from halogen effect and quite small anodization current density is essential to improving the high-temperature oxidation resistance. Upon oxidation at 850 °C for 100 h, no cracks and/or spallation were exhibited on the anodized TiAl alloy. At temperature higher than 300 °C, titanium fluoride will sublimate, accompanying with the transformation of aluminum fluoride into protective Al2O3 layer, as was indicated by XPS analysis. This freshly generated Al2O3 layer, together with the anodization formed one, can efficiently inhibit the outward diffusion of Al and inward diffusion of oxygen, thereby improving the high-temperature oxidation resistance of the TiAl.