Fundamental Electronic Structure Characteristics and Mechanical Behavior of Aerospace Materials

Abstract

Public reporting burden for this collection of ieformation is estimated to average 1 hour per response. including the time for revI ig the data needed, and completing and reviewing this collection of information Send comments regarding this burden estimate or ar ducAng this burden to Department SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)Air To fulfill the great potential of intermetallic alloys for high temperature structural applications, it is essential to understand the mechanisms controlling their mechanical behavior on the microscopic level. We focus on the mechanical behavior of homogeneous intermetallics with L I 2 and B2 structures, two-phase y/y' alloys, and bcc transition metals and their alloys. Based on highly-accurate total energy calculations and large-scale Peierls-Nabarro and atomistic modeling, we investigated the relation between electronic structure, dislocation properties, and brittle-ductile behavior in these metals and alloys. We demonstrated that Ir-and Rh-based alloys are intrinsically brittle and established the dislocation structure in Ir and Rh-based Li 2 alloys. We determined the temperature dependence of the lattice misfit parameter in y/y' superalloys, and established its simple relation with the alloy phase diagram. We studied the structure of dislocations in bcc Nb, Ta, Mo and W alloys, analyzed the effect of alloying with 3d and 5d transition metal elements on dislocation energetics, and established the electronic origins of the solid solution softening/hardening phenomena. We investigated the effect of topologically close packed phase formation on the solubility of interstitial impurities in Cr-and Mo-based alloys and demonstrated their effect in preventing the formation of embrittling phases. We showed that Co-and Y-based B2 intermetallics are intrinsically ductile, established the dislocation structure in Co-based alloys, analyzed the origins of their unusual mechanical behavior, and identified the microscopic origins of the yield stress anomaly. IS. SUBJECT TERMSHigh temperature structural materials, intermetallic alloys, y/y' superalloys, large-scale modeling, electronic structure calculations, dislocation properties, brittle-ductile behavior, alloying, solid solution softening, yield stress anomaly