Ti Alloy with Enhanced Machinability in UAT Turning
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INTRODUCTION
LIGHT-WEIGHT materials such as titanium alloys have gained popularity in modern aerospace structures due to their excellent mechanical and physical properties. Some of the well-documented advantages of titanium alloys are high strength-to-weight ratio, relatively low density, excellent corrosion resistance, and a low modulus of elasticity. However, titanium alloys have been classified as difficult to machine due to their physical properties.[1] Also, their chemical reactivity with tool materials and consequent adhesion to the cutting tool during machining can lead to excessive tool chipping and/or premature tool failure and poor surface finish. Titanium alloys also maintain their high strength levels at elevated temperature in addition to their low modulus of elasticity and thermal conductivity. These characteristics cause high temperatures at the cutting interfaces during machining and result in higher tool wear rates.[2] Finally, automated machining of such alloys is almost impossible due to formation of long chips, especially during drilling and turning operations. As a result, during component manufacturing, the cutting process has to be interrupted as often as necessary to remove chips from the process zone to avoid poor surface quality or fatal tool failure.[3] Metastable-b alloys like Ti 15V 3Al 3Cr 3Sn (Ti-153-3-3), Ti 10V 2Fe 3Al (Ti-10-2-3), or Ti 5Al 5V AGOSTINO MAUROTTO, Research Associate, is with the Nuclear Advanced Manufacturing Research Centre, University of Sheffield, S60 5WG Rotherham, U.K. Contact e-mail: [email protected] CARSTEN SIEMERS, Senior Research Scientist, is with the Institut f¨ur Werkstoffe, Technische Universit¨at Braunschweig, 38106 Braunschweig, Germany. RIAZ MUHAMMAD, Associate Professor, is with the Department of Mechanical Engineering, CECOS University of IT and Emerging Sciences, Peshawar, KPK, Pakistan. ANISH ROY, Senior Lecturer, and VADIM SILBERSCHMIDT, Professor, are with the Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough LE11 3TU, U.K. Manuscript submitted September 28, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
5Mo 3Cr 0.5Fe (Ti-5-5-5-3) are nowadays intensively investigated, since their fatigue strength can be raised up to 800 MPa by age-hardening.[4] Those beneficial effects identify this family of alloys as one of the most important for manufacturing processes since its widespread adoption in aerospace industry. However, titanium alloys show poor thermal conductivity and high chemical reactivity with tool materials. Those effects impair machinability at high cutting speeds, while at low-to-medium cutting speeds, those alloys produce long helicoidal chips, which are undesirable in modern automated machining processes.[5] Production costs could be reduced by improving the material removal rate (MRR) and by reducing the chip length and, hence, enable automated manufacturing. In machining, three different types of chips are known to form, namely, continuous chips having a constant chips thickness, segment
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