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Ni3Al shows like many other L12 alloys an anomalous increase of the yield stress up to a peak temperature of about 800°C. This increase is generally explained by a thermal activated cross slip process of superlattice screw dislocations from (111) to (010). To study the influence of the external stress on this process two orientations were selected: compression axis % MathType!MTEF!2!1!+- % feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaai4waiqaig % dagaqeaiaaikdacaaIZaGaaiyxaaaa!3A03! $[\bar 123]$ and [001]. They show a large difference of the Schmid factors for cube cross slip. Single crystals of Ni3Al were deformed at RT and 400°C, and TEM foils cut parallel to (111) and (010) were studied. At RT which is below the anomalous temperature regime the dislocation structures are in both cases similar to those of fee structures without an order. At 400°C the TEM results show a distinct difference: dislocations bowing out on (010) are a typical feature for the % MathType!MTEF!2!1!+- % feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaai4waiqaig % dagaqeaiaaikdacaaIZaGaaiyxaaaa!3A03! $[\bar 123]$ axis; whereas in the case of the [001] axis dislocation reactions and long straight screws are predominant. They occur in the form of KW locks and contain frequently SISF converted KW locks. Therefore, despite of the different appearance, in both cases strong obstacles are contained in the observed dislocation structures. To overcome these strongly locked segments an Orowan type source model is proposed. When the stress is sufficiently high the dislocation can bow out between obstacles, move on and leave the locked segments behind, which are stored. |
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