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L. Wagner - One of the best experts on this subject based on the ideXlab platform.
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Mean stress effect on fatigue strength in titanium alloys
1999Co-Authors: J. Lindemann, L. WagnerAbstract:The mean stress sensitivity of the fatigue strength is evaluated for the various titanium alloy classes, i.e., {alpha}, near-{alpha}, ({alpha}+{beta}) and Metastable {beta} alloys. It is shown that an anomalous mean stress sensitivity (AMSS) is restricted to near-{alpha} and ({alpha}+{beta}) alloys. Methods for reducing AMSS in duplex microstructures of near-{alpha} and ({alpha}+{beta}) alloys by varying thermomechanical treatments are determined.
Sergey V. Prikhodko - One of the best experts on this subject based on the ideXlab platform.
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Effect of Severe Hot Forging and Rolling on Microstructure, Texture and Tensile Properties of Titanium Metastable Beta-Alloys
Volume 2A: Advanced Manufacturing, 2013Co-Authors: Orest M. Ivasishin, P.e. Markovsky, Marta Pozuelo, Sergey V. PrikhodkoAbstract:The influence of specific method of severe hot deformation, forging plus rolling, that ensures true deformation |e| = 1.39 in single pass was studied on two Metastable β-class titanium alloys VT22 (Ti-5.0Al-4.79Mo-4.70V-0.97Fe-0.71Cr) and TIMETAL-LCB (Ti-1.50Al-6.82Mo-4.47Fe), wt%. The results on microstructure, crystallographic texture and tensile properties are presented. It was found that this type of severe deformation forms elongated not-recrystallized β-microstructure with sharp axial (110)β texture, and fine α-precipitates inside the β-grains. In as-deformed condition both alloys are characterized by high tensile strength (above 1500 MPa) and very low ductility. Additional annealing at α + β temperatures does not change β-grain microstructure and crystallographic texture, but gives the structure a balance of strength and ductility. It looks very attractive for practical application of the alloys. Results are discussed in terms of specific mechanism of deformation accommodation.Copyright © 2013 by ASME
Mark David Richardson - One of the best experts on this subject based on the ideXlab platform.
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Microstructural and Mechanical Property Development in Metastable Beta Titanium Alloys
2016Co-Authors: Mark David RichardsonAbstract:Titanium alloys represent an ever increasing proportion of the materials employed in aerostructural applications. Metastable beta alloys in particular, offer high specific strength and good corrosion resistance that allow them to compete with steels. Ti-5Al-5Mo-5V-3Cr and Ti-10V-2Fe-3Al are two such alloys used in the main landing gear of large commercial aircraft. Thermomechanical processing of Metastable beta alloys is critical in obtaining the desired microstructure, which in turn governs the mechanical properties. This therefore demands a thorough understanding of the relationship between processing, microstructure and mechanical properties in order to optimise the final product and process route. This project characterises the microstructural and mechanical property variation within forged Ti-5553. Microstructural variables are quantified in order to examine their relative influence on mechanical properties. This reaffirmed the importance of microstructural control during materials processing. Gradual changes in primary alpha morphology, beta volume fraction and grain structure were observed throughout the forgings. However, it was also found that the size of secondary alpha precipitates could fluctuate rapidly over relatively short distances. The effect on mechanical properties was significant enough to completely reverse the general trends exhibited over the entire forging. It was also found that the heat treatment response varied with orientation. It would appear that unspecified microstructural variables limited the maximum achievable properties in certain orientations, preventing the heat treatment from further affecting them. However, changes in work hardening behaviour were observed which increased the proof stress while leaving the tensile strength essentially unchanged. The influence of subtransus thermomechanical processing on the microstructural evolution of Ti-10-2-3 was also investigated. Flow curves exhibited an initial peak at low strain followed by extensive flow softening. Microstructural analysis would suggest that the fragmentation and globularisation of acicular alpha particles is at least partially responsible for this softening effect. The use of torsion tests demonstrated that non-linear strain paths may not represent an efficient means of globularising primary alpha. The Burger’s Orientation Relationship (BOR) was found to break down at a linear strain of about 0.5. However, the process of ‘strain reversal’ could partially restore this up to an original linear strain of around 0.8. Solution treatment and ageing revealed that more highly strained regions were less responsive to age hardening.
John R. Scully - One of the best experts on this subject based on the ideXlab platform.
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Effect of pre-dissolved hydrogen on fracture initiation in Metastable beta Ti-3Al-8V-6Cr-4Mo-4Zr
Scripta Materialia, 1997Co-Authors: Michalle A. Gaudett, John R. ScullyAbstract:Hydrogen embrittlement (HE) in certain {beta}-Ti alloys has been conclusively attributed to either the formation of a brittle hydride or the raising of the ductile to brittle transition temperature (DBTT) by hydrogen. Yet there remains a need to understand the mechanism(s) governing HE in solution heat treated + aged (STA) Metastable beta alloys that do not show either of these two phenomena. Therefore, the possibility of additional mechanisms needs to be addressed to understand HE of {beta}-Ti alloys at these intermediate H concentrations.
Mark Whittaker - One of the best experts on this subject based on the ideXlab platform.
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Titanium in the Gas Turbine Engine
Advances in Gas Turbine Technology, 2011Co-Authors: Mark WhittakerAbstract:The development of the gas turbine engine over the past 60 years has been mirrored by the success of the titanium industry, with a clear symbiant relationship existing between the two industries. Immediately apparent in the early days of the evolution of the gas turbine was the need for a material which could provide the strength required for component operation, whilst at the same time providing a low enough density to allow for successful flight applications. Whilst aluminium based alloys offer an excellent strength to weight ratio, their operation is limited to temperatures below approximately 1300C, reducing possible applications within the gas turbine to a minimum. 300 series stainless steels offer a similar strength to most conventional titanium alloys, but come with a significant density penalty of over 50% and, whilst offering reductions in cost, do not provide significant benefits in terms of operating temperatures. Titanium however, has long been viewed as having a desirable balance of properties for applications towards the front end of the gas turbine engine (i.e. fan discs/blades, compressor discs/blades, along with other smaller components). Titanium has a density of 4.5g/cm3 (which, apart from a limited number of alloys such as Ti811, does not vary significantly in alloys considered for aerospace applications) which is higher than aluminium, but lower than nickel and steel alloys. Titanium is allotropic with a HCP lattice ( phase) stable to 8820C, transforming to a BCC (β phase) lattice above this temperature. Alloying elements act to stabilize either of these phases (Al, Sn for example stabilize the alpha phase, whereas Mo, V, Cr stabilize the beta phase) meaning that the transformation temperature can be altered, and subsequently the proportions of each phase existing at room temperature can be varied. The morphology of these phases may however vary, dependent on the process history, with alpha phase material being classed as primary alpha (persisting during heat treatment in the phase field) or secondary alpha (structures arising from the → phase transformation). This allows for the development of a range of bimodal microstructures which provide titanium alloys with inherent strength and also allows for further refinement of properties through various heat treatment and processing regimes. For example designers requiring creep strength and good elevated temperature properties may choose to opt for alloys with more alpha stabilizers (alpha or near alpha alloys), whereas Metastable beta alloys, which are heavily beta stabilized offer improved forgeability. Alphabeta alloys contain a more balanced mix of stabilizers and are widely used due their balance of properties. Ti6-4 (Ti-6Al-4V) for example has been a stalwart of the titanium industry since the 1950s due to its good weldability, relatively high strength and good fatigue properties.