Final Report for Grant DE-FG02-86ER45229

Weertman, Julia R.

Northwestern University (Evanston, Ill.)

关键词: 36 Materials Science Nanocrystalline Metals;    Nanocrystalline Metals;    Mechanical Properties;    Synthesis;    Characterization;   

DOI  :  10.2172/790810
RP-ID  :  N/A
RP-ID  :  FG02-86ER45229
RP-ID  :  790810

美国|英语

来源: UNT Digital Library

【 摘 要 】

This final report of DOE Grant DE-FG02-86ER45229 summarizes the work performed over the life of the grant, from 1 December 86 to 28 February 99. The first part of the grant concerned several topics on strength and damage in 3 steels. A technique using anomalous small angle X-ray scattering (ASAXS) was developed to separate out the contribution of a particular species of scattering entity in a material and quantify its number density and size. The measurements were applied to the large Cr23C6 carbides in Fe9C1Mo+(V,Nb). Small angle neutron scattering (SANS) and TEM were used to follow the nucleation and growth of M2C carbides in AF1410, an ultra-high strength, high toughness steel. These carbides are important in giving the steel its favorable properties, so it is of interest to determine the optimum composition and heat treatment to produce a large number of very small M2C carbides. The mechanism responsible for a compression hold time being more damaging than an analogous tensile hold time during elevated temperature fatigue in some steels was elucidated. It was found that the behavior of the oxide film following a compressive hold time can hasten crack initiation. The second part of the grant was devoted to the synthesis, characterization and study of the mechanical behavior of nanocrystalline metals. The samples, produced by inert gas condensation and compaction, were characterized by precision density measurements and SANS (porosity), XRD (grain size, grain size distribution, RMS strains), TEM and HREM (check on grain size distribution, study of special boundaries). Improvement in the synthesis conditions led to samples with greatly increased mechanical strength. Hardness and compressive strength measurements for nanocrystalline copper as a function of grain size give a Hall-Petch plot that is close to the extrapolation of coarse-grain Cu data. Tensile data show smaller strengths, probably due to flaws but also to strain localization and plastic in stability resulting from lack of work hardening. Yield strength in nanocrystalline copper was measured as 850 MPa, ultimate strength in Ni at over 2 GPa. It was shown that short anneals lead to significant strengthening, which can cause an apparent negative Hall-Petch slope.