How electron beam melting tailors the Al-sensitive microstructure and mechanical response of a novel process-adapted γ-TiAl based alloy

Additive manufacturing of lightweight intermetallic gamma-TiAl based alloys combines process-related free-dom of design with material-specific excellent high-temperature properties. Nevertheless, where locally melting the powder by an electron beam, there is a risk that Al evaporates due to its high vapor pressure, causing compositional and microstructural variations. This work investigates the impact of different process parameters on the total and local Al-content as well as the resulting as-built and heat-treated microstructure in a complex multiphase Ti-44.8Al-4.1Nb-0.7W-1.1Zr-0.4Si-0.5C-0.1B (at.%) alloy. The examinations applied are complementary, employing electron microscopy, X-ray spectroscopy and diffraction experiments with synchrotron X-ray radiation, supported by numerical simulations. The mechanical anisotropy of the heat-treated microstructure was analyzed by micro-hardness measurements. The results demonstrate that the amount of gamma-TiAl phase decreases with increasing energy input of the electron beam in the as-built and heat-treated microstructure owing to the total and local loss of Al. Besides, the investigations of the crystal orientations within the multiphase alloy reveal a preferred orientation of the gamma phase at high energy inputs. This follows from the fact that the preferred y orientation is inherited through directional solidification of the beta phase. The obtained process-microstructure-property relationships show that tailor-made material properties of additively manufactured gamma-TiAl com-ponents are achievable. (C) 2021 The Authors. Published by Elsevier Ltd.

Automated summary

This study investigates the impact of different process parameters on the aluminum content and microstructure of an alloy based on γ-TiAl during additive manufacturing, with examinations using electron microscopy, X-ray spectroscopy, and diffraction experiments. The results demonstrate a decrease in the gamma-TiAl phase content with increasing energy input, affecting the mechanical properties after heat treatment. The preferred orientation of the gamma phase at high energy inputs is attributed to the directional solidification of the beta phase.