A quantitative study of thermal cycling along the build direction of Ti-6Al-4V produced by laser powder bed fusion

During laser-powder bed fusion (L-PBF) the printed material is subjected to multiple fast heating and cooling cycles when the laser interacts with neighboring tracks or layers above. The complex thermal his-tory influences the final microstructure and the macroscopic properties of the printed part. In this work, we demonstrate how high-speed in situ X-ray diffraction in transmission mode can be used to measure temperature profiles and cooling rates in a Ti-6Al-4V single-track wall. During the laser remelting of the top layer, a temperature exceeding the E. transus temperature (TE. ti 1252 K) is measured up to 150 gm below the surface. The maximum observed cooling rates vary from 106 K/s at the top surface, to 105 K/s at a depth of 135 gm and 104 K/s at a depth of 255 gm. Based on the temporal evolution of the various crys-tallographic phases, the dimensions of the melt pool and the high-temperature E. zone surrounding the melt pool are estimated. It is anticipated that the data obtained from in situ measurements in transmis-sion mode on a thin wall combined with in situ measurements in reflection mode on a bulk sample will allow verification and validation of finite element models used in L-PBF processing.(c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

In this study, high-speed in situ transmission X-ray diffraction was used to measure temperature profiles and cooling rates in a Ti-6Al-4V single-track wall. It was found that the temperature exceeded the eutectic temperature up to 150 μm below the surface during the laser remelting of the top layer. The maximum cooling rates were measured to be 106 K/s at the top surface, 105 K/s at a depth of 135 μm, and 104 K/s at a depth of 255 μm. The dimensions of the melt pool and the high-temperature zone surrounding the melt pool were estimated based on the temporal evolution of crystallographic phases. It is anticipated that these in situ measurements can help verify and validate finite element models used in laser-powder bed fusion (L-PBF) processing.