Fundamental Role of Grain Boundaries: Meso-Scale Simulation and Measurement; Final rept. 1 Jan 2005-31 Dec 2007

摘要

Collaborative Projects FA9550-05-1-0068 and FA9550-05-1-0088 were aimed at solving one of the outstanding problems in the mechanical behavior of metallic materials: understanding, quantifying, and predicting the role of grain size and grain boundary character on strength and ductility. This is an essential component required for the design of high-temperature alloys to resist stresses. Current models for polycrystals address only the grain texture (i.e. the statistical orientation of crystal lattices), not the presence or character of grain boundaries, nor the size of the grains. Novel simulation methods and materials characterization techniques were developed and verified. Noteworthy progress and results may be summarized as follows: * Identification of the underlying physics of grain-size effects in metals and alloys. * First quantitative prediction of Hall-Petch slopes from first principles (without introducing arbitrary length scales). * First comparison of measured and independently predicted lattice curvatures at grain boundaries. (Good agreement was discovered: within 20%.) * First simulations and presentations of dislocation density distributions within grains * Introduction of a new single- crystal constitutive representation that is more accurate and uses fewer parameters than existing equations. (Outstanding agreement was found with measurements.).