DIFFUSION IN COLUMBIUM RICH COLUMBIUMTITANIUM ALLOYS WITH CONSIDERATION OF THE POSSIBILITY THAT THE DIFFUSION COEFFICIENT IS TIME DEPENDENT.
NAVAL RESEARCH LAB WASHINGTON D C
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Interdiffusion has been studied in Cb vs. Cb 8.5 atom percent Ti and Cb vs. Cb 35 ao Ti couples at temperatures of 1300 to 2000C and for times of 0.1 to 1000 hours. The electron microprobe has been used to obtain the penetration curves. Marker displacement toward and the development of porosity within the alloy at 1800 and 2000C demonstrate that a vacancy mechanism is operative in this b.c.c. alloy system. Porosity was also observed at 1500C. At 1500C for anneal times extending from 10 to 1000 hours for the more dilute alloy and from 10 to 120 hours for the 35 ao Ti alloy, the interdiffusion coefficient D computed by the BoltzmannMatano analysis is determined to be independent of time. The Arrhenius plot for results extrapolated to 100 ao Cb is a straight line and yields an activation energy of 110 k calg-atom. However, as composition is increased to 30 ao Ti, an increase in the concentration dependence of D is observed with decreasing temperature. This is manifest by curvature of the log D vs. 1T plots with increasing titanium content. Author