The Novel Scanning Strategy For Fabrication Metallic Glasses By Selective Laser Melting

摘要

Metallic Glasses (MGs) can be described as a stable in the room temperature metallic materials with a disordered liquid-like structure produced during rapid cooling of a molten alloy. Due to the limited Glass Forming Ability (GFA), most of the MGs are produced as a thin ribbons through melt-spinning or as a fine powder during atomization processes. Certain multicomponent alloys with exceptionally high GFA, known as Bulk Metallic Glasses (BMGs), can retain disordered structure during copper-mold casting. The size and the complexity of objects produced in a such way is limited by the critical cooling rate. Additive Manufacturing (AM) methods like Selective Laser Melting (SLM) have been shown in a few studies as very perspective for producing BMGs without such limitations. In this work Realizer SLM-50, a desktop SLM machine, was used to selectively melt Kuamet52 Fe-Si-B-Cr-C metallic glass powder with various laser parameters. Material was rescanned with high power density and a novel Pulse-Random (P-R) strategy to achieve high content of glassy phase, despite low GFA of the alloy. Optical Microscopy (OM) was used to preliminary determine material structure. Amorphous structure was confirmed by the Differential Scanning Calorimetry (DSC) while residual crystalline phases were identified by the X-Ray Diffraction (XRD). Microstructural observations revealed, after the first melting in conduction mode, mostly crystalline phases made in samples. After the second melting in key-hole mode, which was performed with P-R strategy, there was observed great increase of amorphous phase content. Samples fabricated with new scanning strategies had amorphisation degree exceeding 60%, with retained a-Fe_3Si and FeB_2 crystalline phases. Model of the laser melted MGs crystallization, focused on devitrification during laser heating in Heat Affected Zone (HAZ), has been proposed to explain observed phenomena.