Stress corrosion cracking of beta-brasses in water
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STUART S. BIRLEY, formerly Graduate Student at the University of British Columbia, is now Senior Scientific Officer at the Military Vehicles and Engineering Establishment, Chersey, Surrey, England, and DESMOND TROMANS is Associate Professor, Department of Metallurgical Engineering, The University of British Columbia, Vancouver, B.C. Canada, V6T 1W5. Manuscript submitted August 7, 1980. METALLURGICAL TRANSACTIONS A
Some metastable/5'-brasses undergo a martensite transformation upon sub-zero cooling, the M s temperature being dependent upon Zn concentration. 4 Above 41 at. pct Zn, no martensite forms upon cooling to liquid nitrogen temperature. Below 41 pct Zn, the Mi temperature rises linearly with decreasing concentration of Zn to - 0 ~ at 37.3 at. pct Zn. However, the M d temperature below which martensite forms in severely cold worked/5'-phase is considerably higher than Ms and also rises with decreasing Zn concentraion. 4 The Ma temperature is reported to be near room temperature at - 4 9 at. pct Zn. 4 The martensite transformation product is a faulted closed packed structure with a unit cell of uncertain symmetry. 4,5 The unit cell has been described aS being face centred tetragonal by Hornbogen et al 6 and orthorhombic by Jolley and Hull. 7 The observations of Jolley and Hull 7 also appear to be consistent with a 3 R / 1 R structure, 8 which consists of a lamellar mixture of alternating close packed planes with a 3R rhombohedral stacking sequence (ABCBCACAB) and 1R sequence (ABC). In addition, Kajiwara 9 reported three deformation induced Cu-Zn martensite structures: 1R twinned, 3R, and 3 R / 1 R . s A pseudoelastic behavior has been reported in some Cu-Zn based metastable B'-brasses containing small ternary additions of either Si 1~ or Sn. 1~ In this phenomenon, martensite forms upon application of stress and disappears when the stress is removed. Depending upon the alloy composition, the pseudoelastic phenomenon may be obtained at room temperature. The structure of the pseudoelastic martensite is not clear. However, the analysis of Eisenwasser and Brown H indicated an orthorhombic unit cell of similar size to that reported by Jolley and Hull. 7 The present study reports some initial observations on SCC of Cu-Zn binary/5'-brasses and a ternary CuZn-Sn/5'-brass in water, particularly with respect to the possible influence of the martensite transformation. 1. EXPERIMENTAL PROCEDURE 1.1 Alloy Preparation Four Cu-Zn and one Cu-Zn-Sn alloy were prepared in the laboratory from high purity starting materials, namely Cu and Zn of 99.999 pct purity, Sn of 99.9 pct
ISSN 0360-2133/81/0713-1215500.75/0 9 1981 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 12A, JULY 1981--1215
purity, and a high purity Cu-Zn master alloy containing 28.8 at. pct Zn. Appropriate quantitites of starting material were melted in evacuated and sealed cylindrical quartz capsules. The melts were allowed to mix for 3 h at 980 ~ with occasional agitation, and the products were quenched vertically into ambient temperat
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