Metastable Beta Alloy Research Articles

Effect of Strain Rate on Deformation Behaviors of Ti-12.1Mo -1Fe Metastable Beta Alloy

The addition of expensive elements to β titanium alloys, which are widely used in the aerospace and automobile industries, causes their price to increase. Low-cost, high-strength alloy (Ti-12.1Mo-1.0Fe) was designed in this study and the compressive behaviors of this alloy were evaluated for application to automobile parts, etc. As a result of ambient compression in the quasi-static and dynamic strain rate range (1×10<sup>-4</sup>/s~6×10<sup>3</sup>/s), twinning occurred at all strain rates, and in particular, adiabatic shear bands were observed, which cause cracks and fractures under dynamic strain rate conditions. In addition, when the relationship between these bands and mechanical characteristics was evaluated, an increase of compression strength and Vickers hardness was confirmed to occur, due to the strain rate hardening effect under compression loading. Some twins were formed by the deformation behavior during compression plastic deformation of the Ti-12.1Mo-1.0Fe alloy, and it exhibited excellent compression strength characteristics, showing a very high strain rate hardening effect at a high strain rate.

Evaluation of high-temperature formability for Ti-xMo-4Fe metastable beta alloys based on Mo contents

High-temperature formation technology is widely used to fabricate components with metastable β titanium alloys, a material characterized by balanced mechanical properties, including superb formability, corrosion resistance, and high strength. In high-temperature formation, it is crucial to control the formation conditions by linking the changes in those conditions caused by processing variables with microstructures and identifying the optimal conditions for high-temperature formation. As such, in this study, a Ti–Mo–Fe alloy was designed that is different from conventional metastable β titanium by adding molybdenum (Mo) and iron (Fe), which are relatively economical β stabilization elements. The mechanical characteristics of the alloy at room temperature were also examined by varying the Mo content, and a high-temperature compression test was conducted to evaluate its high-temperature characteristics and formability. The high-temperature compression test was performed at five different temperatures (700 °C, 750 °C, 820 °C, 900 °C, and 950 °C) to avoid β-transus and with four different strain rates 1 × 10−3/sec, 1 × 10−2/sec, 1 × 10−1/sec, and 1 × 100/sec. Then, the test results were utilized to create a processing map, which evaluated formability by examining plastic instability and energy distribution efficiency at different temperatures, strain rates, and reduction rates, the processing variables for high-temperature formation. Afterward, their connections with the microstructures were analyzed to determine the optimal conditions for the temperature formation of the newly designed Ti–Mo–Fe metastable β titanium alloy.

Tensile Flow Behaviour and Fracture Studies of Beta Titanium Alloys at Elevated Temperatures

Tensile testing on metastable beta alloy with various microstructures was carried out in this study. Beta 21S is a metastable alloy that exhibits a wide range of material characteristics depending on the processing techniques used. Three different sheets that have been used in this paper which has the same substance but three different microstructures. At a strain rate of 0.001/s, the tensile test was done on a single sheet at five different temperatures. The sheet has developed varied microstructures, the tensile nature of the material varies the alloy’s characteristics. Mechanical characteristics for 400°C, 500°C, 600°C, and 7000°C are described for 21S sheets. The alpha phase sheet elongated at room temperature by 1-3 %, whereas the pure beta phase sheet elongated by 22-24 %. There is a significant improvement in the extension of the sheet with the variation in temperature for the alpha phase. The elongation of the pure beta phase does not alter as the temperature rises. The fracture surface was tested at all temperatures and the optimal temperature for forming the sheet has been determined

CARTECH Ti-3Al-8V-6Cr-4Mo-4Zr (BETA C)

Abstract CarTech Ti-3Al-8V-6Cr-4Mo-4Zr, also known as Ti-3-8-6-4-4 and Beta C, is a metastable beta alloy used in the solution heat treated or solution heat treated and aged condition. It is appropriate for applications where very high strength, minimum weight, and corrosion resistance are important. Ti-3Al-8V-6Cr-4Mo-4Zr has gained in popularity among beta alloys because it is easier to melt and process, exhibiting low segregation, good workability, and good heat-treating properties. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Ti-172. Producer or source: Carpenter Technology Corporation.

Fatigue Life Enhancement of Titanium Alloy by the Development of Nano/Micron Surface Layer Using Laser Peening.

Ti-15V-3Cr-3Al-3Sn (Ti-15-3) is a metastable beta alloy which is considered to be a potential alternative for Ti-6Al-4V alpha+beta alloy for aerospace applications, especially for sheet products. This paper describes the work carried out to enhance the fatigue life of Ti-15-3 in an economical way by means of laser peening without coating (LPwC) using Nd:YAG laser operating at a power density of 5 GW cm-2. In order to have a sufficient bulk hardness and high compressive stresses on the surface, as-received beta solution treated (ST) Ti-15-3 was subjected to aging (520 °C/10 h/Air-cooled) and then to LPwC. Laser peening induced a notable increase in Ra (arithmetic mean roughness), which was measured using MAHR GD-120 profilometer. The Electron Back Scatter Diffraction (EBSD) analysis of the aged sample (STA) revealed a significant increase in the alpha precipitation (20 vol%), and this led to a substantial increase in the hardness (~40%) and UTS (~50%). In addition to this, peening of aged (STA+LPwC) sample resulted in a considerable increase (~12%) in near-surface microhardness and compressive residual stress (maximum stress of -195 MPa at a depth of 150 μm). This increase in compressive stress and microhardness led to an enhancement in the fatigue life of the STA+LPwC sample by 210% when compared to STA sample. In spite of high surface roughness induced by the LPwC, fractography studies revealed that crack initiation was independent of surface roughness.

Study of the radiation damage effect on Titanium metastable beta alloy by high intensity proton beam

A foil of a metastable β Titanium alloy Ti-15V-3Cr-3Sn-3Al was irradiated at the J-PARC neutrino experimental facility with 1.4 × 1020 30 GeV protons at low temperature (100–130 °C at most), and microstructural characterization and hardness testing were conducted as an initial study on the radiation damage effects of Titanium alloy by the high energy proton beam exposure. Expected radiation damage at the beam center is about 0.06–0.12 displacement per atom. A high density (> 1023 m−3) of a nanometer-sized precipitate was observed by TEM studies, which would be identified as martensite α-phase and athermal ω-phase formed during the solution-treatment process to fabricate metastable β alloy. They did not appear to change substantially after irradiation with protons. In the irradiated specimen, we could not identify an obvious signature of radiation damage distributed along the proton beam profile. Very small, nanometer-scale black dots were present at a low density in the most highly irradiated region, and may be small dislocation loops formed during irradiation. The micro-indentation test indicated that the radiation exposure led to tiny increase in Vickers micro-hardness of ΔHV = 20 at beam center. Atom probe tomography reveals compositional fluctuations that reach a maximum amplitude of 10 at% Ti within a space of < 5 nm both before and after irradiation, which may also indicate presence of rich precipitates. These experimental results suggest this specific β alloy may exhibit radiation damage resistance due to the existence of a high density of nano-scale precipitates, but further studies with higher exposure are required to explore this possibility.

Exploitation of Field-Assisted Sintering Technology (FAST) to Produce Pre-Forged Billets from Metastable Beta Titanium Alloy Powder

Powder produced by gas atomisation of metastable beta alloy Ti-5Al-5Mo-5V-3Cr has been consolidated using field-assisted sintering technology (FAST) to examine the suitability of the process to produce pre-forged billets as opposed to the conventional multi-step Kroll-VAR-forging route. FAST testing was performed using an FCT Systeme GmbH spark plasma sintering furnace type HP D 25 at The University of Sheffield. The dwell temperature was varied between 800 and 1200°C and the dwell time between 3 and 60 minutes. The process was found to allow very precise control over the beta grain size in Ti-5Al-5Mo-5V-3Cr by variation of the dwell time and dwell temperature, producing grain sizes between ~40 and ~350 μm. However, it was found that the grain size was increased more by increasing the dwell temperature than increasing the dwell time. The porosity was found to be between 99.5 and 100 % for all dwell temperatures at dwell times of 30 minutes or above. FAST has the ability to produce almost fully consolidated Ti-5Al-5Mo-5V-3Cr pre-forged material from powder with a controlled beta grain size, which is not possible by other methods.

Achieving Fine Beta Grain Structure in a Metastable Beta Titanium Alloy Through Multiple Forging-Annealing Cycles

A coarse-grained (order of 1 mm) Ti-5553 metastable beta alloy was subjected to multiple passes of low-temperature forging and multiple forging plus annealing cycles, respectively. In the forging only processing, strain was concentrated in the shear bands formed and accumulated with each forging pass, resulting in a heterogeneous microstructure and eventual cracking along the shear bands. In contrast, the introduction of a short beta annealing after each forging step led to fine recrystallized grains (50 to 100 µm) formed in the shear bands, and a uniformly refined beta grain structure after four cycles. This is attributed to the strengthening effect of the fine grains, causing redistribution of most severe strains to the coarse grain region in the subsequent forging, consistent with the simulated results by finite element analysis. The analyses of the microstructures and simulated strain distributions revealed that the critical strain for recrystallization is between 0.2 and 0.5 and the strain to fracture to be ~0.8 to 0.9. The fine-grained (50 to 100 µm) beta alloy, however, fractured at a much smaller strain of <0.4 during the next forging step, owing to the formation of stress-induced martensitic α″ which is more prevalent in fine grains than in coarse ones.

Thermo Mechanical Working and Heat Treatment Studies on Meta-Stable Beta Titanium Alloy (Ti15V3Al3Sn3Cr) Plates

The beta titanium alloys are highly cold workable in annealed condition, due to presence of single phase bcc structure (beta) at ambient temperature. The Ti15V3Al3Sn3Cr alloy is a metastable beta alloy retains single beta phase at ambient temperature by beta annealing. The beta alloys are most hardenable among titanium alloys, due to the formation of hard alpha (hcp) precipitates in beta (bcc) grains in solution treated and aged (STA) conditions. The present paper brings out the hot forging and rolling studies carried above beta transus temperature and correlating microstructure with mechanical properties in heat treated conditions (a. 800°C for 30 minutes and b. 800°C for 45 minutes, subsequent water quenched from single phase beta region plus aged at 482°C/538°C). The results conclude that solution treatment carried for 45 minutes and aged at 482°C/538°C achieved high tensile strength with improvement in ductility. This is due to less nucleation sites of alpha precipitates along the grain boundaries for the 45 minutes solution treated specimens. The Young’s modulus evaluated for solution treated (78GPa), aged at 482°C (105GPa) and 538°C (103GPa), the increase in aged conditions is due to the formation of alpha precipitates throughout the matrix and makes the alloy two phase alpha-beta system.Keywords: Metastable beta, alpha precipitates, solution treatment, tensile strength, Young’s modulus.

Influence of grain size, aging conditions and tension rate on the mechanical behavior of titanium low-cost metastable beta-alloy in thermally hardened condition

Taking titanium low-cost metastable β alloy TIMETAL-LCB (Ti–1.5(wt.%)Al–4.5Fe–6.8Mo) as a program material, the influence of grain size, size of secondary α-phase precipitates after aging, and strain rate (in the range of 1.6×10−4–7.3×10−2s−1) on mechanical behavior was studied. Aging caused increase in strength and decrease in ductility parameters as compared to initial single-phase metastable (as-quenched) β condition with two different β grain sizes (Coarse Grained, CG, 200μm and Fine Grained, FG, 20μm), and these effects were more pronounced at higher strain rates. Aged FG conditions had essentially higher resource of ductility compared to CG ones after the same aging regimes. Obtained results are discussed in terms of mechanical properties changes induced by aging with respect to initial as-quenched condition. Analysis of area under the engineering stress–strain curves, characterizing the work expended on deformation until fracture and representing tensile toughness of the material, showed that it decreased after aging at all strain rates applied, with essential superiority of FG conditions over CG.

State of the Art in Beta Titanium Alloys for Airframe Applications

Beta titanium alloys were recognized as a distinct materials class in the 1950s, and following the introduction of Ti-13V-11Cr-3Al in the early 1960s, intensive research occurred for decades thereafter. By the 1980s, dozens of compositions had been explored and sufficient work had been accomplished to warrant the first major conference in 1983. Metallurgists of the time recognized beta alloys as highly versatile and capable of remarkable property development at much lower component weights than steels, coupled with excellent corrosion resistance. Although alloys such as Ti-15V-3Al-3Sn-3Cr, Ti-10V-2Fe-3Al and Ti-3AI-8V-6Cr-4Mo-4Zr (Beta C) were commercialized into well-known airframe systems by the 1980s, Ti-13V-11Cr-3Al was largely discarded following extensive employment on the SR-71 Blackbird. The 1990s saw the implementation of specialty beta alloys such as Beta 21S and Alloy C, in large part for their chemical and oxidation resistance. It was also predicted that by the 1990s, cost would be the major limitation on expansion into new applications. This turned out to be true and is part of the reason for some stagnation in commercialization of new such compositions over the past two decades, despite a good understanding of the relationships among chemistry, processing, and performance and some very attractive offerings. Since then, only a single additional metastable beta alloy, Ti-5Al-5V-5Mo-3Cr-0.5Fe, has been commercialized in aerospace, although low volumes of other chemistries have found a place in the biomedical implant market. This article examines the evolution of this important class of materials and the current status in airframe applications. It speculates on challenges for expanding their use.

Influence of alloying elements on the aging of economically alloyed metastable titanium beta-alloys

We use three commercial economically alloyed metastable titanium β-alloys (TIMETAL-LCB (wt.%): Ti–1.5Al–4.5Fe–6.8Mo, Ti–4.3Fe–7.1Cr–3Al, and Ti–1Fe–13Cr–3Al) to perform the comparative analysis of the influence of individual alloying elements on the kinetics of decomposition of the metastable β-phase quenched from the temperatures of the monophase β-region in aging. The roles played by alloying elements, such as molybdenum, iron, and chromium, are clarified. The experimental results are compared with the results of parallel computations by using the DICTRA software. We propose a new composition of economically alloyed titanium β-alloy in which Ti–1.5Al–4.5Fe–6.8Mo alloy is taken as the base and molybdenum is replaced with the equivalent amount of manganese (4%). It is shown that this alloy is promising for practical applications.

Effect of Cold Working and Heat Treatment on Recrystallization, Mechanical Properties and Microstructure of High Strength Ti15V3Al3Cr3Sn (Ti-Beta) Alloy

Ti15V3Al3Cr3Sn (Ti-15-3-3-3) alloy is a highly cold formable metastable beta alloy and attains very high strength by proper selection of cold working and heat treatment cycles. Due to the presence of softer BCC beta phase at ambient temperature in solution treated condition, this alloy is highly cold workable; to as much as 90% without need of any intermediate annealing. In the present work, cold working up to 83% was imparted to the sheet. Subsequently, cold worked sheet was solution annealed at various temperatures. Cold worked and solution annealed samples were provided with two types of aging cycles: 482°C/16hrs/AC (STA-1) and 538°C/8hrs/AC (STA-2). Hardness measurement, tensile property and microstructural evaluation in cold worked (CW), CW plus solution annealed (CWSA) and CWSA plus aged conditions were carriedout. Recrystallization temperature has been observed to be dependent on extent of cold working. Tensile properties are higher for STA-1 cycle as compared to STA-2 cycle. Hardness values in cold worked condition are higher than solution annealed samples whereas for cold worked and STA samples, an increase in hardness w.r.t. to annealed values has been observed. Corresponding volume fraction of alpha precipitates is found to be more with STA-1 cycle than STA-2 cycle. Also, distribution of the precipitates with STA-1 cycle is observed to be more uniform than STA-2 cycle. The present paper discusses the effect of cold working on recrystallization, mechanical properties and microstructure in Ti-15-3-3-3 beta alloy.

Advanced processing techniques for titanium base alloys and its aluminides for space applications

Indian Space programs require high specific strength materials with compatibility to various working fluids/environments. Titanium alloys possess these characteristics and hence are materials of choice for various space applications like high pressure gas bottles and upper stage propellant tanks of launch vehicles and satellites. For these applications, main contribution is from the workhorse two phase (α+β) Ti-6Al-4V alloy, which is used in annealed as well as STA (solution treated and aged) conditions. Further, application at extremely low temperature of 20K requires a special grade single phase (α) Ti-alloy, namely Ti-5Al2.5Sn-ELI (extra Low Interstitial). For these two alloys, processing techniques required for fabrication of various components is established through closed-die forging / plate-forming / ring rolling, machining and EB welding. Close control on the processing parameters are mandatory to achieve desired microstructure, mechanical properties and cost effective components. Indigenous development of a new high strength Ti-15-3 (metastable beta) alloy is accomplished, offering advantage of amenability to cold forming and attainment of very high strength through aging. This can lead to processing of lighter, cost effective and near net shape components and thin-sheet-structures.

Effect of precipitation from tweed matrix on the mechanical properties in a metastable beta alloy of Ti-15-3

The effects of aging treatment on the microstructures and mechanical properties of a metastable beta titanium alloy Ti-15-3 (Ti−15V−3Al−3Sn-3Cr) have been investigated with hardness measurements, tensile test, and optical and electron microscopy. Precipitate-free beta structure with average grain size of about 56 μm was obtained after solution treatment at 800°C for 15 min followed by air cooling. Solution treated specimens were aged up to 800 h in the temperature range between 350 and 600°C. The morphology of the precipitates was varied significantly, depending on the aging temperature. The fine aggregates of α precipitates were dominant above 450°C. Peak hardness values were maintained up to 800 h at 500°C, which showed the superior thermal stability of α precipitates. Tensile strength increased up to 1600 MPa along with the decrease of elongation after aging at 350 and 400°C.

ALLVAC Ti-15Mo

Abstract Allvac Ti-15Mo is a metastable beta alloy melted in a vacuum arc remelting (VAR) furnace to minimize segregation. The alloy has a unique combination of properties and is used in the medical, chemical, and aerospace industries. This datasheet provides information on composition. Filing Code: TI-136. Producer or source: Allvac, an Allegheny Technologies Company.

A study on the laser forming of near-alpha and metastable beta titanium alloy sheets

Laser forming has been identified as a technique suitable for producing sheet metal products and for making on-site repairs. One application is the repair of titanium turbines for military airplanes, which consists of shaping distorted blades back to their original shape without removing them. This paper essentially analyzes the effects of consecutive scans at known beam parameters, and to a practical standpoint, it can help to select adequate forming conditions. Two titanium alloys were chosen: a near-alpha alloy, Ti–6Al–2Sn–4Zr–2Mo, and a metastable beta alloy, Ti–15V–3Cr–3Al–3Sn. Empirical equations for predicting bending and section thickening were derived so that series of experimental points could be reduced into two parameters. Effects of repeated scans on bending angle and thickening were first investigated. Second, these two geometric changes were correlated and the two materials compared. The reduced bending often observed after a few scans was related to the initial thickening. Alloy Ti–6Al–2Sn–4Zr–2Mo was found to bend more in the early stage of forming, but it also thickened more than alloy Ti–15V–3Cr–3Al–3Sn. It was concluded that gradual thickening reduced subsequent bendability. The greater initial bending in alloy Ti–6Al–2Sn–4Zr–2Mo was due to a lower yield temperature and a higher thermal expansion coefficient. Because lesser thickening occurred in Ti–15V–3Cr–3Al–3Sn, a better formability was found after many scans. It is also proposed that buckling could cause bending to decrease. As a result of this work, process parameters can be chosen to create the largest bending angles and minimize the number of scans.

Effect of pre-dissolved hydrogen on fracture initiation in metastable beta Ti-3Al-8V-6Cr-4Mo-4Zr

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.

An evaluation of fiber-reinforced titanium matrix composites for advanced high-temperature aerospace applications

The current capabilities of continuous silicon-carbide fiber-reinforced titanium matrix composites (TMCs) are reviewed with respect to application needs and compared to the capabilities of conventional high-temperature monolithic alloys and aluminides. In particular, the properties of a first-generation titanium aluminide composite, SCS-6/Ti-24Al-11Nb, and a second-generation metastable beta alloy composite, SCS-6/TIMETAL 21S, are compared with the nickel-base superalloy IN100, the high-temperature titanium alloy Ti-1100, and a relatively new titanium aluminide alloy. Emphasis is given to life-limiting cyclic and monotonic properties and to the influence of time-dependent deformation and environmental effects on these properties. The composite materials offer a wide range of performance capabilities, depending on laminate architecture. In many instances, unidirectional composites exhibit outstanding properties, although the same materials loaded transverse to the fiber direction typically exhibit very poor properties, primarily due to the weak fiber/matrix interface. Depending on the specific mechanical property under consideration, composite cross-ply laminates often show no improvement over the capability of conventional monolithic materials. Thus, it is essential that these composite materials be tailored to achieve a balance of properties suitable to the specific application needs if these materials are to be attractive candidates to replace more conventional materials.

Next Generation Titanium Alloys for Elevated Temperature Service.

There are many ongoing U.S. aerospace programs which have identified requirements for higher temperature capability from conventional titanium alloys. In order to meet these requirements, two new titanium alloys have been developed. A near alpha alloy, designated Ti-1100 (Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si), is a modification of the well known Ti-6242S alloy (Ti-6Al-2Sn-4Zr-2Mo-0.1Si). It offers roughly a 55°C (100°F) creep advantage over the older alloy and is currently being considered for sheet metal and forging applications in both turbine engine and airframe applications. On the other hand, a metastable beta alloy designated Beta-215S (Ti-15Mo-2.7Nb-3Al-0.2Si) has shown exceptional promise as a matrix in metal matrix composites for high temperature applications. Its key attributes are its ease of processing in foil production and its excellent oxidation resistance. This paper will review the development of these alloys and some of their more important mechanical properties.