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Titanium alloys on the F-22 fighter airframe
Abstract
The F-22 air superiority fighter utilizes more titanium alloy than any other United States Air Force aircraft. Stringent F-22 performance requirements led to the extensive application of titanium alloys. The F-22 product mix consists of cast and wrought versions of six different alloys and multiple heat treatments.
... When considering Ti alloy use in aerospace industry, they are often utilized in constructing airframe parts, and gas turbine engines parts [2][3][4][5]. In order to meet the present day demand for improved mechanical properties and also to manufacture low cost Ti alloys, various Ti metal matrix composites (MMC) with particle reinforcements of borides, carbides, nitrides, and graphene were studied [6][7][8]. ...
... (www.preprints.org) | NOT PEER-REVIEWED | Posted: 7 March 2024 doi:10.20944/preprints202403.0401.v15 ...
Additive manufacturing (AM) techniques are widely investigated for the cost-effective use of titanium (Ti) alloys in various aerospace applications. One of the AM techniques developed for such applications is plasma transferred arc solid free-form fabrication (PTA-SFFF). Materials manufactured through AM techniques often exhibit anisotropies in mechanical properties due to the layer-by-layer material build. In this regard, the present study investigates the isothermal directional fatigue of Ti-TiB metal matrix composite (MMC) manufactured by PTA-SFFF. This investigation includes rotating beam fatigue test, electron microscopy, and fatigue calculations. The fatigue experiments were performed at 350 ºC using specimen with the test axis oriented diagonally (45º) and parallel (90º) to the AM builds directions. The fatigue values from the current experiments along with literature data find that Ti MMC manufactured via PTA-SFFF exhibit fatigue anisotropy reporting highest strength in 90º and lowest in perpendicular (0º) AM build directions. Further, the electron microscopy investigations on 0º, 45º, and 90º AM build specimens reveal frequent TiB clusters in all three AM build directions and suggest that the spread of these TiB clusters play a role in fatigue anisotropy. Moreover, the fatigue calculations were performed using both the Paris’ and recently reported modified Paris’ equations. Comparison of R^2 values for these calculations show that modified Paris’ equation predicts the fatigue life of AM Ti-TiB MMC more accurately than the Paris’ equation.
... Lockheed Martin used Sciaky's 3D-printed titanium alloy parts on the aileron spar of the F-35 fighter jet and conducted flight test verification [71]. The two companies (British BAE & Lockheed Martin) also jointly developed the F-22 fighter's titanium alloy support, which passed the fulllife spectrum fatigue test and load test [72]. The British Royal Air Force has successfully tested a Tornado fighter jet with 3D-printed metal parts. ...
FDM Printing Additive Manufacturing Military
... Lockheed Martin used Sciaky's 3D-printed titanium alloy parts on the aileron spar of the F-35 fighter jet and conducted flight test verification [71]. The two companies (British BAE & Lockheed Martin) also jointly developed the F-22 fighter's titanium alloy support, which passed the fulllife spectrum fatigue test and load test [72]. The British Royal Air Force has successfully tested a Tornado fighter jet with 3D-printed metal parts. ...
... In this regard, titanium (Ti) alloys are often selected as candidate materials in such applications due to their high specific strength and good corrosion resistance at elevated temperatures [2,3]. When considering Ti alloy use the in aerospace industry, they are often utilized in constructing airframe parts and gas turbine engines parts [2][3][4][5]. In order to meet the present-day demand for improved mechanical properties and to reduce the production costs of Ti alloys, research has been conducted on various Ti MMCs [6][7][8][9][10]. ...
Additive manufacturing (AM) techniques are widely investigated for the cost-effective use of titanium (Ti) alloys in various aerospace applications. One of the AM techniques developed for such applications is plasma transferred arc solid free-form fabrication (PTA-SFFF). Materials manufactured through AM techniques often exhibit anisotropies in mechanical properties due to the layer-by-layer material build. In this regard, the present study investigates the isothermal directional fatigue of a Ti-TiB metal matrix composite (MMC) manufactured by PTA-SFFF. This investigation includes a rotating beam fatigue test in the fully reversed condition (stress ratio, R = −1), electron microscopy, and calculations for fatigue life predictions using Paris’ and modified Paris’ equations. The fatigue experiments were performed at 350 °C using specimen with the test axis oriented diagonally (45°) and parallel (90°) to the AM builds directions. The fatigue values from the current experiments along with literature data find that the Ti MMC manufactured via PTA-SFFF exhibit fatigue anisotropy reporting highest strength in 90° and lowest in perpendicular (0°) AM build directions. Furthermore, calculations were performed to evaluate the optimum values of the stress intensity modification factor (λ) for fatigue life prediction in 0°, 45°, and 90° AM build directions. It was found that for the specimens with 45°, and 90° AM build directions, the computed intensity modification factors were very similar. This suggests that the initial fatigue crack characteristics such as location, shape, and size were similar in both 45°, and 90° AM build directions. However, in 0° AM build direction, the computed stress intensity modification factor was different from that of the 45°, and 90° AM build directions. This indicates that the fatigue crack initiation at 0° AM build direction is different compared to the other two directions considered in this study. Moreover, the quality of fatigue life prediction was assessed by calculating R² values for both Paris and modified Paris predictions. Using the R² values, it was found that the fatigue life predictions made by the modified Paris equation resulted in improved prediction accuracy for all three builds, and the percentage improvement ranged from 30% to 60%. Additionally, electron microscopy investigations of 0°, 45°, and 90° AM build specimens revealed extensive damage to the TiB particle compared to the Ti matrix as well as frequent TiB clusters in all three AM build directions. These observations suggest that the spread of these TiB clusters plays a role in the fatigue anisotropy of Ti-TiB MMCs.
... Additionally, titanium alloys are highly valued in the aerospace industry for their excellent strength-to-weight ratio, corrosion resistance, and ability to withstand high temperatures. They are commonly used in critical components of aircraft in demanding conditions characterized by high cyclic loads and harsh environmental factors [82]. For instance, Ti-6A1-4V (Ti-6-4) finds applications in aircraft components such as airframes, engine components, and critical structural elements while Ti-6A1-2Sn-2Zr-2Cr-2Mo-0.2Si (Ti-6-22-22), Ti-6A1-2Sn-4Zr-2Mo-0.lSi (Ti-6242), and Ti-10V-2Fe-3A1 (Ti-10-2-3) are employed in applications requiring elevated temperature capabilities, such as gas turbine components. ...
This study explores the thermal-structural design elements of military aircraft, encompassing important areas such as the advancement of fighter jets, the influence of high temperatures, airframe construction, and the vital significance of thermal structural testing. From the early days of flight to the present day, the pursuit of supersonic speeds has brought about significant changes in the field, revolutionizing speed, maneuverability, and military readiness. Airframe durability is greatly affected by high temperatures, leading to issues like material degradation and the formation of thermal fatigue cracks. This study also highlights the significance of choosing materials that can withstand extreme thermal conditions, which are crucial for preserving the structural integrity and functionality of advanced combat aircraft. The construction of aircraft airframes is an intriguing field that combines the demands of combat with the latest advancements in technology. It calls for creative design solutions to effectively manage thermal stresses caused by rapid temperature fluctuations. In addition, the study emphasizes the importance of conducting thermal structural tests to validate designs and ensure the safety, reliability, and performance of aircraft. Through a detailed analysis of crucial aircraft components, the research enhances our comprehension of the complex interplay between design, materials, construction, and testing in influencing the thermal-structural design of military aircraft. Briefly, this comprehensive study not only contributes to our understanding of improving aircraft performance but also makes a significant contribution to our awareness in the field of military aviation.
... Titanium and titanium composites have extensive applications in the biomaterial [1], aerospace, and military fields owing to their excellent strength, high corrosion resistance [2], and outstanding heat resistance [3]. The titanium contents of F-22 and F-35 jets have reportedly reached 41% and 25% [4], respectively, and the titanium contents of Boeing passenger jets have also hugely increased from 0.5% to 14% [5]. The rapid development of aerospace technology demands superior materials for the weight reduction and structural optimization of aircraft engines [6] and fuselage parts [7]. ...
Titanium matrix composite (TiB+TiC)/TC4 has excellent physical properties and is a completely new composite material with great application prospects in the next generation of the aerospace field. However, there are problems, such as tool loss and material overheating, when using conventional processing methods. Electrochemical milling is a low-cost, high-efficiency processing method for difficult-to-machine metal materials with no tool wear. In this research, the feasibility of the electrochemical milling of (TiB+TiC)/TC4 and removal mechanisms during processing was reported for the first time. The feasibility of electrochemical milling is verified by the current efficiency experiment and basic processing experiment. Through the adjustment of the processing parameters, the final material removal rate increased by 52.5% compared to that obtained in the first processing, while the surface roughness decreased by 27.3%. The removal mechanism during processing was further performed based on the current efficiency experiment; three stages were observed and concluded during the electrolytic dissolution. This research proved that electrochemical milling is an excellent low-cost method for roughing and semi-finishing (TiB+TiC)/TC4 composites and provides guidance for better electrochemical milling in the titanium matrix composites.
The abrasive waterjet machining process was introduced in the 1980s as a new cutting tool; the process has the ability to cut almost any material. Currently, the AWJ process is used in many world-class factories, producing parts for use in daily life. A description of this process and its influencing parameters are first presented in this paper, along with process models for the AWJ tool itself and also for the jet–material interaction. The AWJ material removal process occurs through the high-velocity impact of abrasive particles, whose tips micromachine the material at the microscopic scale, with no thermal or mechanical adverse effects. The macro-characteristics of the cut surface, such as its taper, trailback, and waviness, are discussed, along with methods of improving the geometrical accuracy of the cut parts using these attributes. For example, dynamic angular compensation is used to correct for the taper and undercut in shape cutting. The surface finish is controlled by the cutting speed, hydraulic, and abrasive parameters using software and process models built into the controllers of CNC machines. In addition to shape cutting, edge trimming is presented, with a focus on the carbon fiber composites used in aircraft and automotive structures, where special AWJ tools and manipulators are used. Examples of the precision cutting of microelectronic and solar cell parts are discussed to describe the special techniques that are used, such as machine vision and vacuum-assist, which have been found to be essential to the integrity and accuracy of cut parts. The use of the AWJ machining process was extended to other applications, such as drilling, boring, milling, turning, and surface modification, which are presented in this paper as actual industrial applications. To demonstrate the versatility of the AWJ machining process, the data in this paper were selected to cover a wide range of materials, such as metal, glass, composites, and ceramics, and also a wide range of thicknesses, from 1 mm to 600 mm. The trends of Industry 4.0 and 5.0, AI, and IoT are also presented.
This paper studies the deformation and fracture mechanism of Ti-6Al-4V titanium under high velocity (970 m/s and 1590 m/s) and hypervelocity (2240 m/s) impacts. For the Ti-6Al-4V target, as the impact velocity increases, the volume of the crater increases, and the shape of the crater gradually changes from a shallow dish shape to a hemispherical shape. After impact at 970 m/s, dislocation slip and twining occur in the crater, forming a large number of dislocation cells and {10-12} tensile twins; several adiabatic shear bands (ASBs) are formed in the crater, and the grains inside the ASBs are severely elongated with few microvoids. After impact at 1590 m/s, the overall deformation degree of the crater increases, in addition, {11-22} compression twins are formed in some deformed grains and recrystallization occurs in some ASBs. When the impact velocity reaches hypervelocity (2240 m/s), in addition to the deformation characteristic above, FCC twins and martensitic transformation also occur in the crater, and the number of ASBs increases significantly, many microvoids are generated and connected to form macrocracks in ASBs; meanwhile, a few spallation cracks are also formed in the crater. The calculation results show that the recrystallization mechanism in the ASB is subgrain rotational dynamic recrystallization.
In the fabrication of aero-engine, the blade parts are difficult to cut, resulting in high energy consumption and pollution. Reducing energy consumption and improving material utilization are conducive to alleviating energy shortage and climate change problems. The blade billet is usually obtained by forging or casting, and then processed by computer numerical control (CNC) precision machining. They are widely used in the manufacturing industry with the characteristics of high precision and weak stiffness, resulting in long machining time and high energy consumption. The forging billet has a large allowance, low material utilization and high machining energy consumption. Therefore, this paper investigates the potential of allowance optimization to reduce carbon emissions in free-form surface machining. An innovative optimization model of reconstructing the machining model of free-form surface is proposed for the near-net-shape billet. By this way, the differences in energy consumption, material utilization and carbon emissions between the traditional method and the proposed method are compared. Finally, a group of blades of an aero-engine compressor is used to demonstrate the proposed method. The carbon emission reduced in the finishing phase is about 3.745 kgCO2 for a compressor. If 1100 unit compressors are produced one year, the reduction is equivalent to absorptive amount of 228 trees.
The F-22 Raptor is an air dominance fighter, with higher speed and longer range, greater agility, enhanced offensive and defensive avionics, and reduced observability as compared with current US Air Force aircraft. Its increased capability is due to the high performance materials in the engine, the structure, and the skin. Efficient processing methods also contribute to higher reliability, lower costs, and simplified maintenance. The F-22 raptor materials, composite parts, resin transfer molding, composite pivot shaft, electron beam welding, hot isostatic pressing, engine design and vectoring nozzle are described.
The occurrence of cavity initiation and gross, free-surface fracture during subtransus hot pancake forging of Ti-6Al-4V with a transformed beta (colony) microstructure was established. Cavity initiation mechanisms were one of two distinct types. At temperatures approximately 75 °C or more below the beta transus temperature (T
β
), cavity initiation occurred at relatively low strains in the beta phase lying between the grain-boundary alpha phase and the lamellar colonies. By contrast, at temperatures near the transus (i.e., T≈T
β
−25 °C), cavity initiation occurred at much larger strains as a result of microfracture of partially-to-fully globularized alpha phase. Finite element method (FEM) modeling of the pancake forging process revealed that secondary tensile stresses had been developed in the regions that had exhibited cavitation/fracture. The FEM analyses were used to correlate both the cavity initiation and the gross free-surface fracture results to previous observations from uniaxial hot tension tests in which identical damage mechanisms had been observed. The tensile work criterion of Cockcroft and Latham (C+L) gave moderately good (quantitative) correlation between the forging and uniaxial tension behaviors. An alternate comparison based on the Rice and Tracey cavity growth model gave reasonable predictions of free-surface fracture but tended to overestimate the incidence of subsurface cavity initiation.