Non-Destructive Evaluation of Defects in Structural Materials Using Long-Wavelength Neutrons.
Annual rept. no. 3, Nov 80-Dec 81,
NAVAL RESEARCH LAB WASHINGTON DC
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Small-angle neutron scattering SANS measurements have been performed on several structural alloys to study voids and microporosities in powder consolidates of Al- and Fe-base alloys. The evolution of precipitates in Al-4Cu and in beta-III Ti Ti-11Mo-7Zr-5Sn-0.08Fe-.015C-0.012-0.1O alloys subjected to varying annealing temperatures and times, and the nucleation and growth of voids formed during creep and superplastic forming in Cu-3Al-2Si-.5Zn-0.4Co alloys. The theta to theta phase transformation in Al-4Cu has been measured and analyzed. Calculated size density distributions show the coarsening of theta phase with simultaneous disappearance of theta as a function of annealing times at 190 C. From these observations, the average size of precipitates at each stage has been calculated and compared with electron micrographic results. Similarly the precipitation of omega-phase in beta-III titanium has been observed for several annealing temperatures 600 F to 800 F and aging times 2 min. to 100 hrs.. The observation of pronounced peaks in the small-angle profiles leads to an evaluation of the coherence length resulting from a clustering of precipitates. Microporosity in powder consolidates has been studied in two alloys Fe-21Cr-6Ni-9Mn-0.02C-0.25N Wt and Ti-6Al-4V. The analysis shows a variation of Guinier slopes consistent with the expectations of pore size and density variation as a function of the compaction pressure and temperature. Finally, preliminary measurements on superplastically deformed alloys of Cu-3Al-2Si-.5Zn-.4Co have been made under varying conditions of strain and strain rates to determine creep-induced void densities.
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