Enabling Bulk High-Temperature Additive Friction Stir Deposition of Steels with Polycrystalline Cubic Boron Nitride-Based Tools

Forgings currently have long lead times, motivating technology developments that produce parts with forge-like properties and have shorter timelines. Solid-state processes such as additive friction stir deposition (AFSD) offer this potential; however, large-scale deposition of high-temperature materials remains limited by tool durability, thermal management, and process stability. In this study, new polycrystalline cubic boron nitride (PCBN) AFSD tools, integrated with a liquid-cooled tool holder, are developed and evaluated for bulk deposition of 316 L stainless steel. Tool geometry modifications, including increased puck diameter and a drafted feed exit orifice, enabled graphite-free deposition by mitigating feedstock swaging. A minimum deposition rate is identified that maintains stable material flow and avoids excessive actuator forces. Comparing the use of PCBN tools with different shank materials shows that tungsten carbide shanked tools have improved thermal management relative to tools with a nickel-based shank. This improved thermal regulation resulted in more stable deposition, reduced tool wear, and successful multi-layer builds. Additionally, the use of a fully enclosed inert gas environment reduces surface oxidation and interlayer oxide formation. Electron microscopy was used to reveal limited tool-related contamination in the deposition. The contamination observed was dispersed boron nitride particles rather than continuous interfacial layers of tool material as observed in other literature. These results demonstrate that PCBN tooling combined with active cooling can enable stable, bulk AFSD of high-temperature alloys.