Invited Speaker

Abstract: Gradient structures (GSs) have been increasingly introduced to engineering metal alloys to enhance the mechanical strength and ductility simultaneously. However, current GSs have limitations of localized and simple gradients due to the disadvantages of applied conventional manufacturing approaches (CMAs). To tackle this issue, additive manufacturing (AM) is utilized to fabricate gradient stainless steel 316L using one-material AM apparatus. The results show that quadruple gradients, i.e., grain size, type of grain boundaries, precipitates and chemical composition, can be achieved via AM. Such high gradients have never been reached in the GSs produced by CMAs. The mechanical strength is significantly enhanced while maintaining the ductility of the gradient steel, meaning that the strength-ductility trade-off is defeated in this work via the introduction of GSs. The combination of strength and ductility bypasses that of the gradient and gradient-free 316L produced by AM, further confirming the advantage of introduction of GSs. The mechanical properties at elevated temperatures are also investigated and shown greater strength than the gradient-free 316L. The deformation mechanisms are revealed by electron backscattered diffraction. Finally, a temperature-dependent strength model is proposed to explain the decrease of yield strength of our gradient 316L. The findings in this research provide new insights into designing advanced gradient metal alloys with excellent mechanical properties across large temperature range.

Keywords: Gradient structure, additive manufacturing, mechanical strength, deformation mechanisms, temperature-dependent strength model