PNNL

Abstract

Fusion-based additive manufacturing (AM) technologies, such as wire arc, laser powder bed, selective laser melting, and electron beam, enable intricate designs but face challenges when applied to steel fabrications. These challenges include residual stress buildup, microstructure anisotropy, porosity, chemical composition segregation, and vaporization of alloying elements. Solid-phase AM technologies, operating below melting points, significantly mitigate these issues. Notable methods include ultrasonic, cold spray, and friction-based AM, with additive friction surfacing (AFS) standing out by eliminating the need for costly tooling and feedstock. This study demonstrates the use of AFS to produce high-strength low-alloy steel depositions. The microstructural evolution is explored as the tempered martensite condition of the feedstock results in a freshly deposited martensitic layer after AFS. As AFS progresses, the previously deposited martensitic layer undergoes post-deposition tempering and phase transformation into tempered martensite, ferrite, or a combination of these phases. These transformations are influenced by multiple thermal cycles during each layer deposition process, demonstrating that AFS can potentially achieve local microstructure control by tuning its parameters. Moreover, AFS shows promise for other high-strength, high-temperature metallic materials that are traditionally considered "unprintable" through melt-based processes.