Oxidation and embrittlement of Ti-6Al-2Sn-4Zr-2Mo alloy

Shenoy, R. N.; Unnam, J.; Clark, R. K.

doi:10.1007/bf00664276

Cited by 64 publications

(40 citation statements)

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“…[7] For shortterm elevated-temperature applications such as thermal protection systems and hot structures that include thinwall components, rapid degradation across the entire cross section could occur due to a-case formation. [8] The high-temperature application of conventional titanium alloys is therefore limited to a temperature regime below which diffusion rates through the oxide scale are slow enough to prevent excess oxygen content being dissolved in the bulk material, resulting in no significant a-case depth.While the a-case formation and its deleterious effects on component life are well known, [9] quantitative studies on a case are scant. Shamblen and Redden [10] determined the air contamination rates using microhardness traverses and approximated diffusion of oxygen in the a phase of high-temperature titanium alloy Ti-6Al-2Sn-4Zr-2Mo (Ti-6242, all compositions are given in weight percent unless noted otherwise) bar stock based on a relationship between oxygen concentration and microhardness.…”

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“…Shamblen and Redden [10] determined the air contamination rates using microhardness traverses and approximated diffusion of oxygen in the a phase of high-temperature titanium alloy Ti-6Al-2Sn-4Zr-2Mo (Ti-6242, all compositions are given in weight percent unless noted otherwise) bar stock based on a relationship between oxygen concentration and microhardness. Shenoy et al [8] studied the oxidation kinetics in Ti-6242 sheet and foil using thermogravimetric analysis and estimated the substrate contamination from empirical relations using weight gain and microhardness measurements. Similar studies were performed on other high-temperature Ti alloys Ti-5.8Al-4Sn-3.5Zr-0.5Mo-0.7Nb-0.35Si-0.06C (IMI 834) [11] and Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si (Ti-1100).…”

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A Study on Alpha-Case Depth in Ti-6Al-2Sn-4Zr-2Mo

McReynolds

Tamirisakandala²

2011

Metall Mater Trans A

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Isothermal oxidation experiments in air were performed on Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) with a bimodal microstructure in the temperature range 811 K to 922 K (538°C to 649°C) for up to 500 hours, and a-case depths were quantified using metallography. Alpha-case depth followed a parabolic variation with time. Alphacase depths in excess of 10 lm formed above 811 K (538°C) and 100-hour exposures. An activation energy of 244 kJ/mol was estimated for diffusion of oxygen in the a phase of Ti-6242.The high chemical affinity of titanium to oxygen (indicated by Ti-O bond energy of 2.12 eV, comparable to the Ti-Ti bond energy of 2.56 eV [1] ) and the high interstitial solid solubility of oxygen in a-titanium (about 14.5 wt pct or 34 at. pct in pure titanium [2] ) cause significant oxygen ingression during air exposure at high temperatures, resulting in the simultaneous formation of an oxide (TiO 2 ) scale on the surface and an oxygen-rich a layer underneath the scale. Formation of an oxygen-rich a layer is a result of the oxygen gradient, oxygen migration through the n-type anion-defective TiO 2 scale, and the relative ease of interstitial diffusion. This layer is commonly referred to as a case, since it is a continuous, hard, and brittle zone of oxygen-stabilized a phase. Alpha-case forms during casting, [3] processing, [4] and elevated temperature exposure in service. Alphacase formed during casting or processing is completely removed via machining or chemical milling. [5] Alphacase formed during service often limits the maximum service temperature of titanium alloys, since a significant amount of less ductile a case results in the formation of surface cracks under tensile loading. Incorporation of oxygen leads to anisotropic lattice distortions, thus hindering dislocation mobility and changing the deformation behavior from a wavy to a planar slip mode. [6] The low local ductility and the large slip offsets at the surface can cause low overall ductility or early crack nucleation under cyclic loading conditions. The service conditions that affect the oxidation kinetics are environment, temperature, stress, and exposure time. For long-term elevated-temperature applications such as blades, disks, and impellers in gas turbine aero-engines, a-case depth is critically important in addition to creep resistance and strength. [7] For shortterm elevated-temperature applications such as thermal protection systems and hot structures that include thinwall components, rapid degradation across the entire cross section could occur due to a-case formation. [8] The high-temperature application of conventional titanium alloys is therefore limited to a temperature regime below which diffusion rates through the oxide scale are slow enough to prevent excess oxygen content being dissolved in the bulk material, resulting in no significant a-case depth.While the a-case formation and its deleterious effects on component life are well known, [9] quantitative studies on a case are scant. Shamblen and Redden [10] determined the air contamination rate...

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confidence: 99%

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confidence: 99%

A Study on Alpha-Case Depth in Ti-6Al-2Sn-4Zr-2Mo

McReynolds

Tamirisakandala²

2011

Metall Mater Trans A

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“…This value is much lower than the activation enthalpy (Q v = 295 kJ/mole [9,10], 330 kJ/mole [11]) for lattice diffusion of Ti in γ-TiAl. However, it is close to the activation enthalpy for diffusion of O in γ-TiAl (177 kJ/mole) [12], O in Ti (168 kJ/mole) [13], O in Ti-6Al-4Zr-2Mo-2Sn (167.2 kJ/mole) [14], and C in Ti (127.6 kJ/mole) [15]. Also, the value is also close to the activation enthalpy for dislocation core diffusion (Q c /Q v ≈ 0.6, i.e.…”

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confidence: 59%

Role of Interfacial Dislocations on Creep of a Fully Lamellar TiAl

Hsiung

Nieh²

1999

KEM

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“…Molybdenum was selected because it is an important element in high-temperature Ti alloys, such as b-21S (a b alloy) and Ti6242 (an a + b alloy). 31,[35][36][37][38][39] This approach allows for a systematic assessment of the influence of composition on the oxidation resistance of the binary titanium alloys independent of experimental variability. The materials were b-solutionized in argon, quenched, and polished prior to being subjected to the oxidation tests.…”

Section: Methodologiesmentioning

confidence: 99%

Discovery via Integration of Experimentation and Modeling: Three Examples for Titanium Alloys

Liu

Samimi

Ghamarian

et al. 2014

JOM

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One key aspect of any integrated computational materials engineering approach is the integration of experiments that provide critical information for the modeling activities. This article describes, using case studies, three examples of critical experiments that have been conducted in an integrated fashion with modeling activities for titanium alloys, providing valuable information in an accelerated manner. The first has been used to identify key microstructural features associated with fracture toughness in Ti-6Al-4V and integrates artificial neural networks and various experimental techniques. The second is associated with defect accumulation in highly constrained titanium structures and integrates a highly innovative characterization technique (precession electron diffraction) and dislocation dynamics. The third is a high-throughput combinatorial technique to understand the oxidation behavior of titanium alloys and couples the experimental effort with the CALPHAD approach. INTRODUCTIONThe composition, microstructure, and defect structures of advanced nonferrous structural alloys are the predominant factors that govern the response of the material to an externally applied stimulus. For example, there will be an elasticplastic response of the material to an externally applied load. Similarly, there will be a compositional and structural evolution in response to thermal excursions. Although these responses are expected to occur, the precise details of the responses are less well understood. integrated computational materials engineering (ICME), or integrated computational materials science and engineering (ICMSE), is a strategy to integrate knowledge, represented by both computation/simulation and high-fidelity experimental databases, from across the composition-microstructure-processing-property paradigm so as to engineer a solution to a design problem. ICME strategies are increasingly being put into service and adding value. 1-4 However, to be effective the individual components must accurately describe materials phenomena.For many structural materials, the precise details of materials response to external stimuli are not well understood. Often, an integrated experimental and computational approach can help elucidate these missing details. While not representing a complete ICME program, each of these integrated activities has provided knowledge that was otherwise lacking. Each of these programs is related to a different problem facing a particular class of nonferrous structural alloys-titanium-based alloys. These include efforts to understand the following: the influence of microstructure on the fracture toughness of a + b-processed Ti-6Al-4V, the influence of defect populations on performance of single-phase and two-phase titanium alloys, and the role of composition on the oxidation behavior of several titanium alloys. The motivation and details of each problem are described separately, as are the conclusions. It is seen that the integration of critical and careful experiments with various modeling schemes ca...

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Oxidation and embrittlement of Ti-6Al-2Sn-4Zr-2Mo alloy

Cited by 64 publications

References 9 publications

A Study on Alpha-Case Depth in Ti-6Al-2Sn-4Zr-2Mo

A Study on Alpha-Case Depth in Ti-6Al-2Sn-4Zr-2Mo

Role of Interfacial Dislocations on Creep of a Fully Lamellar TiAl

Discovery via Integration of Experimentation and Modeling: Three Examples for Titanium Alloys

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