Controllable additive manufacturing of gradient bulk metallic glass composite with high strength and tensile ductility

Introducing ductile crystalline dendrites into glassy matrix to produce in situ bulk metallic glass composites (BMGCs) is an effective strategy to enhance the ductility of bulk metallic glasses (BMGs). However, the microstructural control of the crystalline dendrites is a challenge, and potent toughening of BMGs often requires a high volume fraction of the crystalline phase that impairs the strength and causes the strength-ductility tradeoff. Moreover, existing processing techniques of BMGCs mostly rely on liquid metal casting, which imposes an inherent size limitation due to the required rapid cooling for glass formation. Here we fabricate a multi-layered Zr-based BMGC with a well-controlled gradient in volume fraction of the crystalline dendrites via laser additive manufacturing (LAM) that allows site-specific control of the cooling rate and the resultant microstructure. The gradient BMGC shows an exceptional combination of yield strength (>1.3 GPa) and tensile ductility (~13%). Such enhanced strength-ductility synergy is attributed to the synergetic strengthening from the interaction of the adjacent layers and the asynchronous deformation mode associated with the heterogeneous microstructure. The gradient or functionally-graded structure design motif, enabled by the versatile LAM technology, opens a new window to the development of high-performance BMGCs on a large scale for structural applications.