SURFACE RELIEF EFFECTS ASSOCIATED WITH PROEUTECTOID ALPHA-PLATES IN A TI-7.15 WT-PERCENT CR ALLOY

Surface relief effects associated with 'normal alpha ' and the black plates formed during the proeutectoid alpha reaction have been investigated. Approximately 80% of the reliefs examined were tent-shaped; the remainder were of the invariant plane strain (IPS) type. Both types of proeutectoid alpha plate yielded similar tilt angles for a given type of relief effect. All plates were laterally monocrystals, hence the tent-shaped reliefs could not have been caused by two plates formed back-to-back. TEM also showed that proeutectoid alpha plates contain no twins, whereas martensite plates formed in a comparable Ti-Cr alloy do. All plates formed above the T//0 temperature. Implications of these observations and related information with respect to whether growth takes place by a shear or a diffusional mechanism are considered.