HETEROGENEITY OF FUSION WELDS DETERMINED BY USE OF $sup 63$Ni-TAGGED FILLER METAL. Page: 2 of 35
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When high-alloy weldments are appraised for critical applications, it
no longer suffices to consider solely the soundness of the traditional weld
deposit and heat-affected zone. Savage  has stressed the importance of
distinguishing between discrete microregions within heterogeneous welds and
the use of proper terminology in 'discussions of their properties. Other
elusive features associated with weld quality are surface cleanliness and
freedom from internal fissures, pores, or segregates.
Delineation and study of the origin and character of the foregoing
weld features require highly complicated metallographic techniques, and
often many questions remain unanswered . Our purpose was to explore
these features autoradiographically and metallographically.
SELECTION OF RADIOISOTOPES
The radioisotopes considered fall into two classifications: (1) those
that are highly soluble in the matrix of the weld metal and. thus can be
evenly distributed in it, and (2) isotopes that concentrate in or are
stoichiometrically linked with secondary phases, and, hence, can be selec-
An important factor considered in selecting isotopes was. the charac-
teristic radiation, which determines the degree of photographic definition
and autoradiographic resolution. Isotopes that emit_ alpha or beta radia-
tion are useful  and should be especially suited when free of stray
gamma rays (which fog film); low-energy radiation helps assure good
Alpha rays, as a result 'of high energy release rates (short'particle
range) generally give very high photographic -rsolution. Unfortunately,
however, alpha sources are few :and usually emit supplemental rays that
produce undesirable background fogging.;.
Beta emitters offer the best 'compromise for autoradiographic use
Beta particles have fairly low ranges, and .those of lower intensity should
give' reasonably good photographic resolution. Fortunat'ely beta-emitting
sources are quite numerous and many of them do not have gamma or other
contamirating' rays (4]
The pure beta-emitting isotopes and the r energies are listed in
Table ;. The tracers, selected for our study are listed in Table II with
their characteristics. Note that the maximum energies of all the isotopes
selected are attractively low, and bnly 33P has an undesirably low half-life.
The.isotope 63,Ni wasused fe conferdrig evenly4ristributed betakactivity
to welding wires. The .stritcture aid extent of alloying between filler
metal and base metal in the ;variou's'regions Of .heterogeneous welds were
explored ,in welds prepared with:tracer containingfiller metals on untraced
base metals. : The iSotopes "C, 3S, and 3 link' with intermetallic com
pounds and their associated eutectics and are b' ing used to investigate
the role of microsegregates nLn wefd cxrapking artd geneifal weld 'behavior.
'I r1' , I
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Hammond, J.P.; Slaughter, G.M. & Gurtner, F.B. HETEROGENEITY OF FUSION WELDS DETERMINED BY USE OF $sup 63$Ni-TAGGED FILLER METAL., report, October 31, 1972; Tennessee. (digital.library.unt.edu/ark:/67531/metadc1035220/m1/2/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.