Effect of near beta-transus forging parameters on the mechanical and microstructural properties of Ti-6Al-4V: Application to hammer forging

Abstract

Ti-6Al-4V is a widely employed material in the aerospace, power generation and bioengineering industries due to its low density, excellent corrosion resistance and outstanding mechanical properties. Hammer forging is one of the most utilized manufacturing processes to produce high-performance titanium components and it is known that the process parameters highly affect the microstructure, and thus, the mechanical properties of the manufactured parts. Ti-6Al-4V alloy has a temperature dependent dual structure and forging below or above the β-transus transition temperature (≈980ºC) highly influences the resultant microstructure. Due to the significant adiabatic heating in high-speed hammer forging processes the β-transus temperature can be exceeded during the process. Therefore, it is of vital importance to study the phase transformation limits and the resultant effects on the mechanical properties to establish the optimum processing window for the hammer forging of Ti-6Al-4V. In this work, the Direct-Impact Drop Hammer (DIDH), a purpose-built laboratory hammer with a maximum blow speed of 5 m/s is employed to perform intermediate strain rate (≈200 s-1) uniaxial compression tests of Ti-6Al-4V at 900ºC, 940ºC, 980ºC, 1000ºC and 1020ºC. The flow behaviour of this titanium alloy is experimentally characterized under a wide range of hammer forging conditions, and the microstructure of the tested samples is analysed to study the influence of the adiabatic heating on the phase transformation of Ti-6Al-4V.