Beta 21S Research Articles

Directed energy deposition processing of titanium alloys Ti-6242 and Beta 21S

ABSTRACT The objective of this research was to assess the response of two titanium alloys to directed energy deposition (DED). The alloys considered were Ti-6242 (near-alpha alloy) and Beta 21-s (beta alloy). The same experimental methods were employed for each alloy with different variable ranges. The first design of experiments (DOE) varied the laser power and traverse rate, with sample density as the dependent variable. A second DOE then varied laser power, traverse rate, hatch spacing, layer thickness and powder feed rate. The optimal parameter set determined was then utilised to prepare specimen for tensile testing and heat treatment studies. Both alloys were successfully processed, producing samples with densities >99.8% of full theoretical. The alloys also responded favourably to heat treatments, with resultant microstructures comparable to wrought. Mechanical properties were near wrought in terms of tensile strength but suffered from somewhat inferior tensile ductility.

Reduced-Order Models Correlating Ti Beta 21S Microstructures and Vickers Hardness Measurements

Ti Beta 21S alloy is a metastable Ti Beta alloy commonly used in the aerospace industry, especially in jet engines. Components made from this alloy are usually subjected to various thermal histories during service, which leads to significant changes in their microstructures and associated mechanical properties. The central goal of this study is to demonstrate the feasibility of correlating the optical images of the microstructure obtained from heat-treated samples of Ti Beta 21S to their respective Vickers hardness measurements using recently established analyses and statistical quantification approaches based on the principal components of the rotationally invariant 2-point spatial correlations. The correlations extracted in this work can be used for non-destructive diagnostics of in-service components.

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

Single step heat treatment for the development of beta titanium composites with in-situ TiB and TiC reinforcement

Titanium matrix composites have been attracting great interest from aerospace industry due to favorable properties like thermal stability, high specific strength, corrosion, and wear resistance. Optimal relation between mechanical properties demands complex processing routes and, in this context, the effects of a single-step processing route on microstructure and mechanical properties of β titanium matrix composites was placed on focus in this study. The commercial TIMETAL Beta 21S alloy and its modification with the addition of B4C were developed, allowing in-situ formation of TiB and TiC particles in a β matrix. The composites presented highest values of mechanical strength and hardness, and the addition of 3% of B4C provided a significant reduction in grain size, and compressive yield strength and ultimate compressive strength values of 1205 MPa and 1636 MPa, respectively, with a maximum deformation of 20.5%. An orientation relationship investigation provided information about some unconventional relation between the present phases.

Development of High Temperature Oxidation Resistant Titanium Alloy Arconic-THORTM

The aeroengine and airframe applications of titanium alloys are often limited by their insufficient oxidation resistance to the aggressive environment at higher temperatures. A high temperature oxidation resistant titanium alloy (Arconic-THORTM) has been developed. This alloy is an alpha-beta alloy with superior oxidation resistance and improved creep resistance. The oxidation weight gain of Arconic-THORTM is much lower than Ti-6242 and Beta 21s in the temperature range up to 750˚C. The room and elevated temperature properties of Arconic-THORTM are comparable to those for Ti-6242. Arconic-THORTM also shows superior, post-thermal-exposure tensile strength, ductility, and fatigue properties, and is capable of being cold formed, hot formed, and superplastic formed, welded and heat treated to different product geometries. The microstructures and mechanical properties for sheet manufactured from the production ingots are presented and discussed in this study.

Protective aluminide coating by pack cementation for Beta 21-S titanium alloy

Pack cementation method was used to form high activity aluminide coating on titanium alloy Beta-21S using a cement activated by CrCl3 at 760 °C for a period of 9 h. Thermodynamic computations showed that growth mechanism of TiAl3 occurs in tree steps involving different chemical reactions. The effectiveness of the TiAl3 coating to protect Beta-21S alloy was demonstrated through oxidation tests performed at 750 and 850 °C during 300 h. The elevated resistance against oxidation of the TiAl3 layer is provided by a protective Al2O3 scale having low growth kinetics.

Microstructure and Properties of Beta 21S Alloy with 0.2 wt. % of Carbon

Taking into account the high requirements of new structural materials the development of high-strength and high-temperature alloys based on titanium is a subject of great scientific interest. Carbon has usually been regarded as an impurity of titanium alloys. Increasingly however, it begins to play an important role as alloy addition and, taking into account its price, it is consistent with the global cost-cutting trend for production and processing of new alloys with improved properties. The addition of carbon creates new application opportunities for titanium alloys. The relationship between mechanical properties and microstructure of Beta 21S alloy with carbon addition were considered in this study. The alloy was produced traditionally by vacuum induction melting in cold crucible furnace and hot-deformed with further heat treatment. The effect of heat treatment on the conventional strength and creep resistance of researched alloy was also determined.

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.

In Vitro Corrosion Behavior and Apatite Growth of Oxygen Plasma Ion Implanted Titanium Alloy β-21S

Titanium alloy beta 21S was implanted with oxygen ions by plasma immersion ion implantation. The implanted surface was characterized by micro-Raman, XPS and FESEM before and after potentiodynamic polarization and electrochemical impedance studies in Hanks’ solution and after incubation in Hanks’ solution for 1 and 7 days. The investigations show that the native oxide on the sample is replaced by a compact oxide by implantation and the new oxide layer behaves in a different way in that a two layer model is required to explain the observed electrochemical impedance data. The analysis of layers formed in the electrochemical studies and after incubation in Hanks’ solution by XPS and FESEM shows that the new oxide surface is capable of inducing apatite growth on it.

Effect of gas composition on corrosion behavior and growth of apatite on plasma nitrided titanium alloy Beta-21S

Titanium alloy beta 21S with composition Ti–15Mo–3Nb–3Al–0.2Si was plasma nitrided using inductively coupled RF Plasma with 100% N2 and 80% N2–20% H2 at 800°C for 4h. XRD and micro Raman studies show the formation of titanium nitrides. Potentiodynamic polarization studies in Hank's solution show the corrosion resistance of the 80–20% (N2–H2) treated samples to be better than the 100% N2 treated samples. However, untreated samples show better corrosion resistance than the treated samples. Electrochemical impedance spectroscopy (EIS) studies show higher charge transfer resistance and lower double layer capacitance for the substrate compared to the nitrided samples. FESEM images of samples immersed in SBF show that growth of apatite is more and the size of deposits are larger on nitrided samples, especially on those nitrided with hydrogen dilution, as compared to that on the untreated substrate. EDS results show a decrease in nitrogen content and increase in oxygen content after corrosion experiments. XPS spectra from the nitrided and corrosion tested samples show the presence of oxide, nitride and oxynitride on the surface and after corrosion studies the samples are covered with oxide. Nitrided samples immersed in Hank's solution for one day show higher amount of calcium, phosphorous and oxygen in hydroxide form than the substrate.

Experimental study on the milling of a Ti Beta 21S

Ti Beta 21S is a new metastable beta titanium alloy which is generally known to be one of the most difficult materials to machine because of its high hardness, high strength at high temperature, affinity to react with the tool materials, and low thermal diffusivity. In this paper, the tool wear and cutting force in the milling process were studied by experiment together with machinablity assessment when using different cutting tools. The optimized machining parameters are provided for reference to actual production.

Interfacial reaction kinetics of coated SiC fibers with various titanium alloys

The kinetics of the reaction between the silicon carbide fibers and the titanium-based alloy matrix was investigated at temperatures from 800 to 1000 C for several titanium-based alloys (including Ti-1100 alloy and BETA 21S) and unalloyed Ti, reinforced with coated silicon carbide fiber SCS-6. The reaction zone growth kinetics was studied by exposing vacuum encapsulated samples to temperatures from 700 to 1000 C for times up to 150 hrs, followed by SAM observations of samples which were polished perpendicular to the fiber axis and etched. It was found that the reaction zone growth kinetics of the alpha (hcp) and beta (bcc) phases of unalloyed titanium reacting with SCS-6 fibers exhibited different values of the apparent activation energy and of the preexponential factor. Additions of other metals to Ti was found to slow down the reaction kinetics. Among the alloys studied, the Ti-1100 was the slowest reacting conventional alloy and the Ti-14Al-21Nb (in wt pct) was the slowest overall.