Hot working and damage behaviour of additively manufactured Ti6Al4V

点击翻译按钮获取中文摘要

Due to current trends in the use of CFRP, aluminum structural components are increasingly being replaced by titanium components in aviation, since the ultrahigh-strength Al-alloys tend to corrode in contact with CFRP. Currently, the share of titanium alloys in the Airbus A350 is already around 14% (compared to A320 -> 3%). For forged titanium components, the material utilization is sometimes less than 10%. Due to the complex production and high costs of titanium, the low material yield is intolerable. The currently investigated additive manufacturing (AM) processes offer great advantages in single-part and small-batch production, i.e., near-net shape production. Due to the low build-up rates and high costs, powder bed based AM processes are hardly usable for large-volume titanium components. As alternatives, AM processes using laser, arc and plasma welding processes (Directed Energy Deposition - DED) are currently being investigated. Here the industrial take-up is hindered by the long production times, the reproducibility and the high residual stresses. The central hypothesis of this proposal is that by manufacturing adapted preforms by means of AM, forging steps and tools can be saved and a high material utilization can be achieved. If the fine microstructure of the AM preforms can be transferred into the forged component, improved mechanical properties may be realized. Very little work on forging of additively manufactured preforms has been published up to now. Our own preliminary work shows that additively manufactured samples have significantly lower yield stress and higher globularization rates than conventional rolled bar stock. Thus, a reduction of the forming forces and tool load and a forging with a small oversize appears possible, since the required globularized volume fractions are already achieved at lower degrees of deformation. On the basis of the preliminary work it was hypothesized that the formation of martensite in the AM process and its decomposition upon heating are responsible for the unusual forming behavior. The aim of this project is to characterize the deformation, globularization, damage and anisotropy behavior by means of DED-produced Ti6Al4V samples under forging conditions as a function of the microstructure and the sample position relative to the weld beads. Also, a coupled material model for the forming and transformation behavior as well as the damage behavior and anisotropy of the additively produced preforms shall be developed. In order to allow for the widest possible variation of beta grain sizes and martensite fractions, preform production shall be carried out by means of powder-based laser metal deposition (small grains and fully martensitic structure possible) and wire-arc metal deposition (large beta grains and Widmannstätten structure). This research is intended to lay the foundations for the use of additively manufactured preforms for forging processes.