Electron beam melting (EBM) is a metal powder bed fusion additive manufacturing (AM) technology that facilitates the production of metal parts by selectively melting areas in layers of metal powder. The electron beam melting process is conducted in a vacuum chamber environment regulated with helium (He) at a pressure on the scale of 10⁻³ mbar. One of the disadvantages of vacuum environments is the effect of vapor pressure on volatile materials: indeed, elements in the pre-alloyed powder with high vapor pressure are at risk of evaporation. Increasing the He pressure in the process can improve the thermodynamic stability of the pre-alloyed components and decrease the composition volatility of the solid. However, increasing the pressure can also attenuate the electrons and consequently reduce the energy deposition efficiency. While it is generally assumed that the efficiency of the process is 90%, to date no studies have verified this. In this study, Monte Carlo simulations and detailed thermal experiments were conducted utilizing EGS5 and an Arcam Q20+ machine. The results reveal that increasing the gas pressure in the vacuum chamber by one order of magnitude (from 10⁻³ mbar to 10⁻² mbar) did not significantly reduce the energy deposition efficiency (less than 1.5%). The increase in gas pressure will enable the melting of alloys with high vapor pressure elements in the future.

Additive manufacturing is a novel and breakthrough technology by which parts can be manufactured for various purposes and services. As in any production process, the desired properties of additively manufactured components, particularly in electron beam melting processes, ultimately depend on the manufacturing process parameters. Process parameters should be designed accordingly to manufacture parts with specific and desired characteristics. This study focuses on examining the effect of process parameters, such as beam current and velocity, focus offset, and line offset, at three different values each, on the properties of Ti-6Al-4V alloy. The study on the effect of the process parameters on the as-built material’s performance was performed using the Taguchi approach using an L₉ (3⁴) orthogonal array. The properties of printed parts (density, surface roughness, elastic moduli, hardness, tensile characteristics, fractography, and microstructure) were tested. A wide range of properties was obtained and analyzed; namely, porosity varied from 8% to almost fully dense materials with density higher than 99.9% and a range of yield and ultimate tensile strength values and brittle samples with less than 1% elongation to ductile samples with an elongation greater than 16%. The overall performance of printed parts was determined based on an evaluation criterion. Several parameter combinations were found and yielded the fabrication of parts with high density and relatively fine microstructure. The comparison of the best parameter combinations determined in this study and the parameters recommended by the machine manufacturer showed that improved results were obtained, and even when using the optimal parameters, they can be improved even more. This result highlights the ability of the proposed DOE method to further develop existing results and even for development of manufacturing parameters for new materials.

Hot Isostatic Press (HIP) post-processing is widely employed to enhance the performance of additive manufacturing components. However, its impact on 316L Electron Beam Powder Bed Fusion (EB-PBF) materials remains unexplored. This study investigated the effects of HIP temperature on 316L EB-PBF materials compared to as-built (AB) and powder metallurgy (PM) counterparts. In-situ neutron diffraction during tensile testing, performed with the loading direction parallel to the build direction, along with microstructural analysis, was conducted to assess the influence of HIP temperature on dislocation evolution, stress distribution, and the resulting mechanical behavior during deformation. The results revealed variations among the different product states. Differences in microstructural features, including grain size, twinning, lattice strain, and dislocation density, were observed and linked to the mechanical response. The PM product exhibited higher stiffness (193 GPa) than the AB EB-PBF product (120 GPa) while showing similar flow strength. HIP treatment significantly influenced the stress-strain behavior of EB-PBF products, affecting dislocation density and stress distribution amongst various grain orientations. These findings provide valuable insights into the behavior of EB-PBF products subjected to HIP post-processing and highlight the differences compared to PM products.