Influence of processing parameters on density, surface morphologies and hardness of as-built Ti-5Al-5Mo-5V-3Cr alloy manufactured by selective laser melting

Abstract

Demand for new Ti alloys for AM is immense. Ti–5Al–5Mo–5V–3Cr (wt%), a β type Ti alloy is chosen for this study as it possesses excellent properties. Samples are manufactured using SLM technique. Relative density, surface morphologies and hardness of samples produced by varying laser processing parameters, e.g., laser scan speed and laser power, are thoroughly investigated. Top surface of the as-built samples shows adhered powder particles and discontinuous ripple patterns. A change in scan speed from 1200 to 1400 mm.s-1 drastically deteriorates top surface quality in terms of ripples patterns and adhered powders. Surface roughness (Sa/Ra) of the side surface of the produced samples shows a value of below 20 μm. Side surfaces show adhered powder particles, open surface pores, microcrack and interlayer crack. Substantial increase in adhered powder particles is evident when both laser power and laser scan speed are increased distinctively. These results are discussed with the help of the thermodynamic and metallurgical phenomena involved in the SLM processing. Hardness of the as-built samples is measured, the value is in agreement with con- ventional processing. This fundamental study will be useful for producing Ti-5553 alloy AM parts with optimum surface. © 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0 1. Introduction Ti–5Al–5Mo–5V–3Cr (wt%) (Ti-5553) is a near β Ti alloy that has a nominal density of 4.67 gm/cm3. It offers a very high strength, good ductility, excellent corrosion resistance properties and proved weldability [1–4]. The high strength and good ductility together positively affect fatigue behaviour of Ti-5553 [5]. Due to excellent hardenability, a second phase called hcp Ti phase (α-phase) pre- cipitates from metastable bcc Ti phase (β-phase) during heat treat- ment. As a result, a two-phase microstructure is achieved which can displays very high ultimate tensile strength of 1.4 GPa. Because of these properties, this alloy has been using in many engineering applications especially aerospace (landing gear and airframe in Boeing 787) and automotive industries [6]. In addition, a recent study shows that it can be a potential candidate for biomedical ap- plication especially in bone implantation [7]. Additive manufacturing (AM) technique has already shown a great potential producing near net-shape components. As proven, AM saves both material and machining cost. Selective laser melting (SLM) is one of the popular AM processes that are extensively used in metal applications [8,9]. It is a layer-by-layer technique where a laser system consisting of high laser power is used for melting the powder, and produces parts using the input CAD drawing. To date, two Ti materials (CP Ti and Ti-6Al4V) have attracted significant re- search interest. Besides, there are Ti alloys that are being used in engineering applications. These motivate us to find new Ti alloys for AM process. Due to the above mentioned excellent properties of Ti- 5553, this alloy is chosen for this study. A few studies has been re- ported on this material focusing build up relationship between processing, microstructure and mechanical properties [10–13]. Regardless of the application, surface of the SLM produced parts is crucial for determining its properties, useability and feasibility. Since this is a new in AM field, the surface morphologies of as-built Ti-5553 alloy need to be thoroughly understood. The present study aims to evolute the surface morphologies of as-built SLM Ti-5553 alloy with respect to laser processing parameters, such as laser power and scanning speed.