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A Review on Superplastic Forming of Ti-6Al-4V Alloy

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A Review on Superplastic Forming of Ti-6Al-4V Alloy JournalMaterials of Science Alloys andand Technology Compounds AA Review Review on on Superplastic Superplastic Forming Forming of of Ti-6Al-4V Ti-6Al-4V Alloy Alloy --Manuscript Draft-- Manuscript Number: MST16321 Full Title: A Review on Superplastic Forming of Ti-6Al-4V Alloy Article Type: Review Keywords: Superplastic forming; Superplasticity; Ti-6Al-4V; Microstructure; Multi step forming dies Corresponding Author: Sai Pratyush Akula, B.E. Mechanical Engineering Birla Institute of Technology and Science Hyderbad, Telangana INDIA Corresponding Author Secondary Information: Corresponding Author's Institution: Birla Institute of Technology and Science Corresponding Author's Secondary Institution: First Author: SaiAkhil Pratyush Agnihotri Akula First Author Secondary Information: Order of Authors: SaiAkhil Pratyush Agnihotri Akula AkhilSai Akula Agnihotri Pratyush AmitAmit Kumar Gupta Order of Authors Secondary Information: Abstract: This paper presents a review on the superplastic forming of Ti-6Al-4V alloy, which has been used to manufacture parts of complex shapes and geometries. This paper outlines the major work carried out on this front in the past three decades. It covers various aspects related to experimental setups, including the manufacture of dies and their modifications to maintain alloy thickness uniformity after forming. A detailed study of the process parameters has also been done to note the most important physical conditions required for successful forming. This is followed by the influence of microstructure, modern applications of superplastic forming of different titanium alloys and is concluded with an insight into the future work and progress in this field. Additional Information: Question Response Please state the novelty of your 1. Elaborates on the latest advancements in the field of SPF of Ti-6Al-4V submission by providing (at least) four 2. Dedicated to processing of Ti-6Al-4V for aerospace and prosthetic applications aspects of originality or uniqueness in 3. First paper in over three decades to cover the SPF of Ti-6Al-4V alloy your article. Please keep each point to a 4. Consolidated work on theoretical and experimental aspects of SPF of Ti-6Al-4V maximum of 12 words. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Manuscript Click here to download Manuscript A review on superplastic forming of Ti-6Al-4V alloy.docx 1 2 3 4 5 A Review on Superplastic Forming of Ti-6Al-4V Alloy 6 7 8 Sai Pratyush Akula, Akhil Agnihotri, Amit Kumar Gupta 9 10 11 Department of Mechanical Engineering, BITS Pilani, Hyderabad Campus, Telangana, India - 500078 12 13 14 Keywords: Superplastic forming, Superplasticity, Ti-6Al-4V, Microstructure, Multistep forming dies, etc. 15 16 17 ABSTRACT 18 19 20 This paper presents a review on the superplastic forming of Ti-6Al-4V alloy, which has been used to 21 manufacture parts of complex shapes and geometries. This review paper serves as a means to give an 22 23 outline on all the major work that has been carried out on this front in the past three decades. It covers 24 various aspects related to superplastic forming of Ti-6Al-4V alloy like experimental setups which include 25 the manufacture of dies and their modifications to maintain alloy thickness uniformity after forming. A 26 27 detailed study of the process parameters has also been done to note the most important physical 28 conditions required for successful forming. This is followed by the influence of microstructure, modern 29 30 applications of superplastic forming of different titanium alloys and is concluded with an insight into the 31 future work and progress in this field. 32 33 34 1 INTRODUCTION 35 36 37 Metal forming process involves changing the shape of a metal into a desired one without any loss of mass 38 by the means of plastic deformation. It is one of the most important manufacturing techniques due to its 39 40 cost effectiveness, enhanced mechanical properties, flexible operations, high productivity and metal 41 saving. A general forming process is said to include a punch and die mechanism, where the metal takes 42 the shape of the die due to the application of pressure. This mechanical process need not rely on 43 44 temperature to get the desired geometry. Various forming techniques such as forging, rolling (hot and 45 cold) and extrusion etc. are being used today in automotive, appliances, aerospace and other industries. 46 However, a unique kind of forming technique known as superplastic forming is being studied lately, which, 47 48 with the help of elevated temperatures, achieves higher plastic deformation in the metal. 49 50 Superplasticity refers to the property of metals to achieve elongation of over 1000% of without necking, 51 52 usually at elevated temperatures (about 900℃ for Ti-6Al-4V) under a constant, controlled strain rate. The 53 optimum strain rate varies with the superplastic material and is attributed to the viscous behavior shown 54 55 by metals and alloys with refined and stable microstructure at elevated temperatures. 56 57 Superplastic forming (SPF) of sheet metal has been used to produce complex patterns and integrated 58 59 structures that are light-weight and stronger than the assembled components [45]. This process of SPF is 60 often combined with diffusion bonding (DB) to manufacture multisheet structures [40]. This results in 61 62 63 1 64 65 1 2 3 4 reduction in the total number of parts and often gives post-processing benefits such as enhanced product 5 6 performance and cost reduction [7]. This process also has few disadvantages in terms of high working 7 temperature, non-uniform thickness distribution etc. [41]. Titanium has high specific strength and good 8 cold-formability, resulting in applications in the manufacturing of aircraft and automobile parts such as 9 10 compressor blades and turbine discs. However, the technique for improving its formability at elevated 11 temperatures is still a challenge at present [42]. Over the last few decades, a growing interest in the 12 13 superplasticity of Titanium has been seen, as shown in Figure 1 and Figure 2. 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Figure 1: SPF literature focus in the papers 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 Figure 2: Literature trends in SPF since 1980 57 58 59 60 61 62 63 2 64 65 1 2 3 4 Discontinuous Metal Matrix Composites (MMCs) possess high strength but low ductility, and are difficult 5 6 to form with traditional techniques such as rolling, forging or bending [23]. Moreover, due to high 7 hardness, there are only limited number of practically plausible machining techniques. Powder metallurgy 8 does not provide for high dimensional tolerances while casting is only possible in cases where the liquid 9 10 matrix is non-reactive with the reinforcing phase and the environment. In such cases, superplastic forming 11 is desired since it allows for large strains with limited necking and cavitation. 12 13 14 During SPF, differential straining across the sheet takes place, causing large amounts of variation in 15 thickness, thus reducing the sheet’s applicability and increasing post-processing costs [7]. This straining 16 17 occurs in two parts. First, during free forming (when the sheet has not come in contact with the die), 18 which can be controlled if the alloy exhibits high strain rate sensitivities of flow stress. Second, when the 19 alloy comes in contact with the die, and although differential straining is locally controlled, other parts 20 21 continue to experience this phenomenon. Thus, the last part of the alloy to come in contact with the die 22 has experienced the most strain and hence, has the least thickness. This can be controlled by ensuring 23 that the alloy, more or less, comes into contact with the die in a uniform manner and that the 24 25 experimental parameters such as load and forming temperature are specific to the local strain gradients. 26 27 28 Bellows expansion joints find application in areas involving expansions and contractions of pipes due to 29 temperature changes, mechanical vibrations, non-uniform support structure, etc. [24]. Superplastically 30 formed using gas pressure and compressive axial load, Titanium alloy Ti-6Al-4V is an ideal candidate for 31 32 U-type bellows expansion joints as it allows for more than 1000% elongation. The entire process was 33 divided into tube blank fabrication and the actual SPF process. 34 35 36 2 Applications of superplastic forming 37 38 39 40 Titanium alloys are widely used in biomedical applications like cranioplasty since they favour 41 osseointegration with bones, have excellent mechanical features and are biocompatible. This makes the 42 alloy suitable for the making of prostheses. Prostheses are machines which are usually expensive and take 43 44 a lot of time to manufacture. Due to this, superplastic forming has found its application in the making of 45 prostheses using titanium alloys [20]. Ambrogio et al., 2018; has work related to the testing and 46 manufacturing of cranial prosthesis using superplastic forming. The cranial prostheses developed by 47 48 Ambrogio et al., 2018 can be seen in Figure 3 and the die setup can be seen in Figure 4. 49 50 51 52 53 54 55 56 57 58 59 60 Figure 3: Prostheses a) made from incremental forming b) made from superplastic forming. Credits: [20] 61 62 63 3 64 65 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Figure 4: a) Die setup for SPF of cranial prostheses b) Formed part. Credits: [20] 19 20 21 22 Sorgente, Palumbo, Piccininni, Guglielmi & Aksenov, 2018; have performed a study on the thickness 23 distribution on the prostheses made with the help of finite element simulations and free inflation tests at 24 25 different pressures.
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