THE FORMATION OF POROSITY DURING DIFFUSION PROCESSES IN METALS (thesis)
Evidence is presented which indicates that the porosity formed during diffusion processes in Cu--Ni and Ag--Au couples is heterogeneously nucleated in the presence of a relative excess concentration of vacancies resulting from the unequal mass flow of the two participating constituents. The nature and extent of porosity is dependent on the purity of the sample and thus appears to be related to the number or potency'' of nuclei available for vacancy agglomeration. From metallographic observations on the distribution of porosity, it is estimated that pores will form when vacancies are pumped into any small region of the diffusion zone at the rate of about 10/sup 15//cm/sup 3//sec in oxygen-free high conductivity copper and 10/sup 17//cm/sup 3//sec in spectroscopically pure copper. The higher supersaturation required for the nucleation of pores in spectroscopically pure copper is consistent with all the qualitative observations made on the formation of porosity. Estimates of the relative fraction of the excess vacancies which condense to form pores on the copper-rich side were obtained in two ways: (1) from the ratio of the overall expansion of the couple to the normal Kirkendall shift, and (2) from the ratio of the measured pore volume to that associated with the net vacancy flux, as derived from concentration-penetration profiles. Both estimates are in reasonable agreement and indicate that upwards of 90% of the excess vacancies agglomerate as pores rather than being annihilated at jogs on dislocations or other sinks; in spectroscopically pure copper; about 50% of the excess vacancies end their lives at pores. It is concluded that, contrary to the usual assumption, dislocations are not very effective sinks for vacancies under conditions (e.g., relatively low vacancy supersaturations) which prevail within the diffusion zone. The observed differences in the extent of porosity in the two grades of copper are believed to be due to differences in nucleating sites availahle for vacancy condensation rather than to differences in the ease with which dislocation climb can take place in these two materials. Additional observations indicate that the presence of aluminum oxide particles or clusters in silver has influenced the normal distribution of porosity in silvergold diffusion couples. These particles or clusters may be acting as favorable sites for vacancy condensation. (auth)
- Research Organization:
- California Univ., Berkeley, CA (US). Lawrence Radiation Lab.
- DOE Contract Number:
- W-7405-ENG-48
- NSA Number:
- NSA-18-010544
- OSTI ID:
- 4102252
- Report Number(s):
- UCRL-10383
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- United States
- Language:
- English
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