Structure transformation of alpha-brass subjected to cold work
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transformation occurs not only in the commercial purity leaded alpha-brass but also in the high purity lead-free alpha-brass. EXPERIMENTS
Two b r a s s alloys of the following composition were tested: a commercial purity alloy of 35.66 pct Zn and 2.2 pct Pb, and a high purity lead-free alloy of 70.01 pct Cu, 29.99 pct Zn, and as trace elements Pb, Mn, Mg, and B with less than 0.001 pct of each. Specimens of the leaded alloy were annealed at 400~ for 4 h, specimens of lead-free alloy at 500~ for 1 h. Grain size of the leaded alloy was 0.01 mm and that of the lead-free alloy was 0.04 mm. Leaded specimens were strained to 9.3, 12, 13.5, 20, and 24 pct and lead-free specimens to 14, 60, 70, and 75 (fractured) pct. Specimens of a conventional shape for tests in tension were 3 in. long and 88by 88in. in c r o s s - s e c t i o n . The external surface of some specimens was examined in an X - r a y diffractometer before and after straining of the specimen. Annealed specimens as determined by X - r a y diffraction (Tables I and II) were of the fcc structure and corresponded to the alpha-brass alloys. From the middle part of the strained specimens, sections were cut by spark cutting and, after etching off about 0.05 mm of material, the c r o s s section of specimen was examined in an X - r a y diffractometer with copper radiation and a nickel filter. Chromium radiation with a vanadium filter was used in only a few experiments to confirm the results with copper radiation. Bragg angles of the observed intensity peaks were determined and the integrated intensity of the peaks measured. The obtained data were matched to the corresponding fcc or hexagonal structures and lattice p a r a m e t e r s " a " and " c " were determined. For leaded specimen No. 1, strained 12 pct, Bragg angles and the integrated intensity of the observed reflections are given in Table I. These reflections are taken from the external surface and from the face of the specimen in c r o s s - s e c tion. In the same table are given Bragg angles of the proposed structure which correspond to the observed reflections. Similar data are given in Table II for lead-free specimen No. 14, strained 70 pct. The angles ' % 0 " between reflecting planes are less affected by the experimental e r r o r s than Bragg's angles and therefore are more discriminating in determination of the type of structure. The values of observed " A O " between (200) and (111) or between (104) and superimposed (102) and (006) planes are given in VOLUME 5, APRIL 1974-881
Table I. Structure Determination of Specimen No. 1 Containing 2.2 Pct Lead
Annealed Specimen
12 Pct Strained Specimen External Surface
External Surface
Observed 0 (deg)
Comp fcc Str
I/1 m (pct)
(hkl)
Observed
a (A)
0 (deg)
Comp fcc Str
I/Im (pct)
15.78 18.15
20.90
100
(111)
3.74
3 1.5
21.15
100
21.65 24.38
48
35.87
46
(200)
(220)
Cross Section
(hkl) (111)* (200)*
(111)
4.5
a ()~)
(102)~ (006)~
24.65
55
(200)
3.72
26.15 31.15 36.15
2 4 48.5
(220)* (311)* (220)
5.5 3
(311)
3.69
.8
(
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