Improving the Fracture Toughness of Constituent Phases and Nb-Based In-Situ Composites by a Computational Alloy Design Approach

摘要

A computational alloy design approach has been used to identify a ductile matrix for Nb-based in-situ composites containing Ti, Hf, Cr, Si, and Ge additions. Candidate alloys in the form of cast buttons were fabricated by arc melting. Coupon specimens were prepared and heated treated to vary the microstructure. Backscattered electron (BSE) microscopy, quantitative metallography, energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were utilized to characterize the morphology, volume fraction, composition, and crystallography of individual phases in the microstructure. The fracture toughness of the composites was characterized by three-point bending and compact-tension techniques, while the fracture toughness of individual phases in the in-situ composites was determined by an indentation technique. The composition, crystallography, and volume fraction of individual phases were correlated with the fracture-toughness results to assess (1) the role of constituent properties in the overall fracture resistance of the composites and (2) the effectiveness of the computational design approach. The results indicated that the effects of alloy addition and plastic constraint on fracture toughness were reasonably predicted, but the conditions for relaxing plastic constraint to attain higher fracture toughness were not achieved.