Ultra-high Temperature Amorphous Metals: INTRINSIC and EXTRINSIC Approaches to Discovery and Processing of Tough Hybrids.

摘要

Metallic glasses have been designed in order to tune the elastic constants to a condition favorable for increasing the toughness of these glasses. Initial experiments were conducted on a model Ca-based glass to demonstrate the concept, followed by extension to a higher Tg glass. Suction casting in collaboration with AFRL has produced bulk Ca-based glasses. Elastic constants have been measured acoustically and reveal chemically induced changes to the shear- and bulk-modulus, resulting in favorable increases to the poisson s ratio, producing increases to the fracture toughness. Fracture toughness was measured on both notched- and fatigue precracked bend bars and revealed significant increases to the fracture toughness via chemical tuning of the elastic constants. This approach has been extended to higher temperature metallic glasses based on Ni, Ta, and other refractory metal systems. Similar improvements to the damage tolerance have been recorded in these higher Tg metallic glasses. XRD, Hot hardness, elastic constant measurements, and fracture toughness testing followed by SEM analyses of fracture surfaces were used to document the behavior of the model Ca-based glasses as well as the higher Tg glasses.