Interactions between lattice dislocations and grain boundaries in Ni3Al investigated by means of in situ TEM and computer modelling experiments

Abstract

Abstract--The interaction between lattice dislocations and grain boundaries in Ni3A1 has been investigated by means of in situ TEM deformation experiments. The interaction between screw dislocations and a coherent twin boundary could be analyzed in detail. The interaction mechanism found experimentally was compared to the results of a computer modelling study. In the computer modelling study, many-body potentials representing Ni3A1 were used. The results of the in situ straining indicate that (110) screw dislocations impinging on a Z = 3 coherent twin boundary that have a Burgers vector that is parallel to the grain boundary plane can be transmitted to the symmetric slip plane in the other grain under influence of an applied stress. A one-to-one comparison with the results of a computer modelling study of exactly the same system in Ni3AI can be made and the experiment agrees with the simulations. Also, observations were made of superlattice intrinsic stacking faults (SISF) that were formed as a result of the interaction between gliding dislocations and the dislocations of a low angle grain boundary (cell wall). The creation of jogs in the line of the gliding dislocation may be the cause of the SISF formation.R~sum~-On 6tudie l'interaction entre les dislocations du r~seau et les joints de grains dans Ni3A1 au moyen d'essais de d&ormation in situ en MET. L'interaction entre les dislocations vis et un joint de macle coh6rent peut ~tre analys~e en d&ail. Le m~canisme d'interaction trouv6 exp6rimentalement est compar~ aux r6sultats d'une 6tude mod61is6e par ordinateur. Dans l'~tude mod6lis6e, on utilise des potentiels fi n corps pour repr6senter Ni3AI. Les r6sultats des d&ormations in situ montrent que les dislocations vis (110) qui rencontrent un joint de macle coh6rent Z = 3, ayant un vecteur de Burgers parall61e au plan du joint de grains, peuvent &re transmises sur le plan de glissement sym6trique de l'autre grain sous Faction de la contrainte appliqu~e. Une comparaison point par point avec les r6sultats de l'6tude num6rique du m~me systdme dans Ni3AI peut fitre effectu6e et l'exp6rience est en accord avec les simulations. De plus, on observe des d~fauts d'empilement intrins6ques de surstructure qui se sont form,s par suite de l'interaction entre les dislocations qui glissent et celles d'un joint de grains de faible d~sorientation (paroi de cellule). La cr6ation de crans sur la ligne de la dislocation qui glisse peut ~tre la cause de la formation d'un tel d6faut.Zusammenfassung--Die Wechselwirkung zwischen Gitterversetzungen und Korngrenzen in Ni3AI wird mit in-situ-Verformungsexperimenten im Durchstrahlungselektronenmikroskop untersucht. Die Wechselwirkung zwischen Schraubenversetzungen und einer koh~renten Zwillingsgrenze kann ausf/ihrlich analysiert werden. Der gefundene Wechselwirkungsmechanismus wird mit den Ergebnissen einer Computer-Modellstudie verglichen. In dieser werden Vielk6rperpotentiale, die das Ni3A1 darstellen, benutzt. Aus den Ergebnissen geht hervor, dab eine auf die koh~rente Zwillingsgrenze 2...

Controllable fatigue cracking mechanisms of copper bicrystals with a coherent twin boundary

“…Since the TB could be penetrated by the S1 SBs 14,15 , there is good strain compatibility near the TB which is parallel to the loading direction. So the TB shows higher fatigue cracking resistance than high-angle GB and the fatigue crack nucleates along the SB like in single crystals 3,5 .…”

“…Due to the special crystallographic characteristics, the TB possesses specific interactions with the dislocations 13 . The TB could provide barrier to the dislocation motion like the conventional GB to enhance the strength 9,10,13 and it is also a slip plane, which could accommodate 10,11,13 or be penetrated by the dislocations 12,14,15 to improve the plasticity. On one hand, the incorporation of nanoscale TBs into materials can partly turn the trade-off relationship between the strength and ductility of the nano-grained materials [9][10][11][12]16 .…”

Slip transfer at coherent twin boundaries in Ni3Al and ordered Cu3Au

“…However, part of the dislocations were absorbed in the boundary plane. This was explained by a local change of the boundary structure if the superdislocation is absorbed in the boundary plane which lowers the energy of the configuration (see also the discussion in [17]). …”

“…the boundary and a subsequent dissociation into grain boundary dislocations (GBDs) which can possibly glide on the GB plane; (2) slip transfer into the second crystal: the incoming dislocation dissociates into a lattice dislocation of the second crystal and a residual GBD which possibly can glide on the boundary plane; (3) nucleation of dislocations into the second crystal, after an accumulation of residual GBDs in the boundary occurred [9]; (4) crack nucleation at the boundary, followed by GB failure as in pure NiaA1. A number of studies were devoted to the interaction of lattice dislocations with GBs in order to assess the stress relief mechanism at GBs in different alloys, in many cases using in situ deformation in the transmission electron microscope (TEM) of NiaA1 [3,[9][10][11][12][13][14][15][16][17], of NiaFe [18], or of CusAu as a model material for the L12-ordered structure [19,20].…”

“…Also in Ni3AI in situ deformation experiments near CTBs have been carried out in the electron microscope [17], together with a simulation of the interaction of dislocations with a CTB with and without an applied stress. In this paper a TEM investigation of ex situ deformed Cu3Au and Ni3AI is reported which makes a comparison possible with the in situ deformation experiments.…”