Materials Letters 355 (2024) 135546 Available online 10 November 2023 0167-577X/© 2023 Elsevier B.V. All rights reserved. Hot deformation characteristics and microstructural evolution of Ti-900 alloy Dipayan Chakraborty a, * , Gyan Shankar b , Akanksha Prajapati a , BR Chandra Obul Reddy c , Ajay Kumar a a Department of Mechanical Engineering, Indian Institute of Technology, Tirupati 517619, India b Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India c Gas Turbine Research Establishment, DRDO, Bangalore 560093, India A R T I C L E INFO Keywords: Metals and alloys Hot deformation Processing maps Microstructure ABSTRACT Hot deformation behaviour of Ti-900 (Ti-6.5Al-3.2Mo-1.8Zr-0.25Si) alloy has been analyzed by conducting an isothermal hot compression test at 850 ◦ C to 1050 ◦ C temperatures and strain rates between 0.001 s 1 to 10 s 1 . The effect of strain rates and deformation temperature on fow stress is investigated. The processing maps are constructed, and constitutive equations are studied to understand the formability of the novel titanium alloy in the different temperatures and strain rates regimes. Results suggest that temperatures and strain rates between 880 ◦ C to 950 ◦ C and 0.001 s 1 to 0.01 s 1 are the optimal processing window for this alloy. The kinetic rate equation indicates that the apparent activation energy for deformation is 531 kJ/mol in the α + β region. Post deformation microstructure formation is also studied. 1. Introduction Titanium alloys are widely used in aerospace and biomedical felds due to their excellent characteristics like high strength-to-weight ratio, corrosion resistance, fatigue, and creep resistance. Ti-900 is a newly developed α + β titanium alloy suitable for aerospace applications. Hot deformation characteristic of this alloy has not been explored system- atically and yet to be established. Optimizing the hot working parame- ters is important to successfully forge the alloy. Flow behaviour, processing map, and kinetic analysis are used in hot working processes to optimize the deformation condition for a material by graphically displaying the relationship between process variables like temperature, strain, and strain rate [1,2]. The commonly used alloy, Ti-6Al-4 V, is typically processed at 870 ◦ C and 0.001 s 1 [3]. Although Ti-900 and TC11 alloy are quite comparable, they differ chemically, and there are limited studies on the hot working processing of TC11 alloy. Slight variation in concentrations of the alloying elements in titanium can strengthen the alloy by hindering dislocation movement and mitigating the risk of cracking at high-temperature and strain rate deformation. Initial microstructure of the material affects its deformation parameters and fow stress [4]. The coarse lamellar microstructure of TC11 alloy poses challenges during processing. Optimum conditions for processing of this alloy are observed at 950 ◦ C and 0.001 s 1 . Dynamic recrystall- izing and globularization are the primary deformation mechanism in α + β feld [5–7]. Chen et al. have designed the processing maps of equiaxed TC11 alloy for β phase deformation, and in another study, kinetic analysis is discussed in only α + β region [8,9]. The current study aims to investigate the high temperature deformation behaviour of Ti- 900 alloy starting with equiaxed microstructure (equiaxed α + small acicular β phase), establish a processing map, and detailed microstruc- tural analysis is carried out to manufacture a defect free part. 2. Material and methods Chemical composition of Ti-900 alloy is listed in Fig. 1(c). Vacuum arc remelting (VAR) is used to manufacture the ingot. Then it is rolled to 15 mm diameter, followed by solution treatment and ageing. The β transus temperature of this alloy is 1000 ◦ C ± 20 ◦ C. As received alloy consists of equiaxed microstructure (Fig. 1(a)) with α vol % =65 % (black region) and β vol% =35 % (white region) phase fraction (Fig. 1(b)). Hot compression cylindrical samples with 10 mm diameter and 15 mm length (Fig. 1(d)) are prepared from homogenized cylindrical billet. Then, isothermal hot compression test is carried out on a Gleeble 3800 * Corresponding author. E-mail address: me21d004@iittp.ac.in (D. Chakraborty). Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet https://doi.org/10.1016/j.matlet.2023.135546 Received 22 July 2023; Received in revised form 13 October 2023; Accepted 7 November 2023