Microstructure of additive layer manufactured Ti-6Al-4V after exceptional post heat treatments

The microstructure of Ti-6Al-4V components, which were produced by an additive layer manufacturing (ALM) process, typically consists of columnar prior beta-grains containing colony and/or basket-weave alpha + beta with martensite. The microstructure is equivalent to microstructures neither of wrought nor of cast parts. However, the post heat treatments applied for the present investigation are derived from heat treatment specifications of those materials. This paper presents the microstructure and hardness of additive manufactured Ti-6Al-4V after heat treatments, which are not standardized or commonly applied, in order to suggest new ways forward. The experiments show that columnar prior beta-grains can be transformed to globular prior beta-grains without cold or hot working. The hardness and microstructure in a prior beta-grain is a function of the cooling rate through beta transus temperature rather than of the duration at above beta transus. A heating cycle was determined which leads to a microstructure that is homogeneous in each prior beta-grain and does not significantly differ from grain to grain. (C) 2012 Elsevier B.V. All rights reserved.