Effective thermal management is essential in metal additive manufacturing to ensure process stability and desirable material properties. Directed energy deposition using a laser beam and wire (DED-LB/w) enables the production of large, high-performance components but remains sensitive to adverse thermal effects during multi-layer deposition due to heat accumulation. While prior studies have investigated interlayer temperature control and substrate preheating in DED modalities, including laser-powder and arc-based systems, the influence of substrate preheating in DED-LB/w has not been thoroughly examined. This study employs substrate preheating to simulate heat accumulation and assess its effects on melt pool geometry, wire–melt pool interaction, and the microstructural evolution of Alloy 718. Experimental results demonstrate that increased substrate temperatures lead to a gradual expansion of the melt pool, with a notable transition occurring beyond 400 °C. Microstructural analysis reveals that elevated preheat temperatures promote coarser secondary dendrite arm spacing and the development of wider columnar grains. Moreover, Nb-rich secondary phases, including the Laves phase, exhibit increased size but relatively unchanged area fractions. Observations from electrical conductance measurements and coaxial visual imaging show that preheat temperature significantly affects the process dynamics and microstructural evolution, providing a basis for advanced process control strategies.

The combination of corrosion resistance and mechanical properties of martensitic precipitation hardening stainless steels (MPHSS) makes them well suited for demanding applications in aerospace, high-pressure gas bottles, or in injection molding of corrosive plastics. Directed energy deposition methods and specifically the laser metal deposition process with powder as feedstock (LMDp) have the potential to be applied in the production of such components. It is well-known that the geometrical features of the deposited beads such as aspect ratio and dilution are crucial for process efficiency and deposition quality. Therefore, this work aims at understanding the influence of the process parameters and the resulting microstructure of a MPHSS modified PH 13-8Mo alloy when using LMDp. Design of experiment (DoE) was used to plan and analyze the influence and interaction of the different LMDp process variables in the geometry of the deposits. It was found that height, width, and depth were statistically significantly influenced by speed, while height was also considerably influenced by the powder feeding rate. In terms of laser power, it was the most significant factor for the width and the depth, but it did not significantly affect the height of the beads. The results showed that the as-deposited microstructure of the modified PH 13-8Mo under the LMDp conditions investigated in this work consists of a martensitic matrix with some amount of primary δ ferrite. The presence of a low amount of retained austenite and aluminum-enriched inclusions was confirmed. This work enhances the fundamental process and material understanding of LMDp of the modified PH 13-8Mo alloy as a first stage in the fabrication of additively manufactured components.

The PH 13-8 Mo family of steels belong to the martensitic precipitation hardening stainless steels (MPHSSs) category, which exhibits a good combination of mechanical properties and corrosion resistance. Additive manufacturing (AM) offers advantages, including reduced material waste and the capability to produce complex, near-net-shape parts. Consequently, the application of AM techniques to the PH 13-8 Mo family is being increasingly explored across various industries. This review paper presents the existing literature on the topic and provides an overview. The review starts by presenting information about the PH 13-8 Mo family, including microstructure, chemical compositions, heat treatments, and mechanical properties. Afterwards, the work focuses on presenting the microstructure and resulting properties of PH 13-8 Mo family processed by three different additive manufacturing processes: Powder Bed Fusion using a Laser Beam (PBF-LB), Directed Energy Deposition using an Electric Arc (DED-Arc), and Directed Energy Deposition using a Laser Beam (DED-LB), both in their as-built condition and following post-processing heat treatments. The review concludes with a summary and outlook that highlights existing knowledge gaps and underscores the need for further research to tailor the microstructural evolution and enhance the properties. The findings indicate that AM of the PH 13-8 Mo family has the potential for industrial applications, yet further studies are necessary to optimize its performance.