Abstract

In the course of the selective laser melting (SLM) process, the part is built layer by layer involving partial re-melting/heating of the previous layer, called as intrinsic heat treatment. Therefore, superficial properties of as-built parts are somewhat different from that of the inside of the part. In this work, the nano-tribological behavior of commercial pure Ti (CP-Ti) samples built using SLM was investigated considering the near-surface regions with focus on the effect of intrinsic heat treatment. Microstructure and nano-wear testing allowed identifying specific sliding behaviors in three regions: (I) surface (0 to 50 µm); (II) subsurface (50 to 200 µm); (III) inner-part (below 200 µm). Regions (I) and (III) promote a stick-and-slip behavior while sliding is smooth and continuous in Region (II). This gradient microstructural characterization enabled associating the behavior of region (II) to large-sized lath martensite a' morphologies, which is different from the region I and III with finer microstructure. A FEA thermal model suggests that the existence of the three identified regions is the consequence of the intrinsic heat treatment induced by the SLM process, in which the re-melting/heating and recrystallization has been considered as the main reason for microstructure coarsening and refinement between region I and II, region II and III, respectively.

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