| Abstract Scope |
Two intrinsic properties of multi-principal element alloys(MPEAs), local lattice distortion (LLD) and local chemical ordering (LCO), significantly influence dislocation-based plastic deformation. LLD and LCO can affect the mobility of edge and screw dislocations in different amounts, allowing deformation to occur with edge and screw cooperation, resulting in more homogeneous deformation and good work hardening ability. This finding is surprising because plasticity in BCC elemental metals and dilute alloys is mainly controlled via 1/2 <111> screw dislocations. In this study LLD and LCO have been manipulated via alloying and some heat treatment procedures. After these alloys were mechanically deformed, their dislocation characters were determined by postmortem TEM studies. Thus, we provided an experimental insight into the effects of LLD and LCO on dislocation based plastic deformation. For example, we added Ti to the MoNbTaW system in one case. The choice of NbMoTaW is due to its tunable lattice distortion, which can be precisely controlled through alloying. Ti, with its low elastic modulus and hexagonal close-packed (hcp) structure, is introduced to distort the body-centered cubic (BCC) lattice. Our preliminary compression tests show a significant improvement in the mechanical properties of the alloy. The yield strength increased from approximately 950 MPa to 1200 MPa, and compressive ductility rose from 2% to 20%. Additionally, our ultrasonic wave measurements indicate a reduction in the shear modulus from 69 GPa to 53 GPa. Later, in the standard g.b analyses we conducted on dislocations in deformed microstructures with post-mortem TEM studies, we saw that there were plenty of dislocations in non-screw and edge characters in addition to screw dislocations. In general, it is noteworthy that in systems with LLD introduced, unlike systems with low LLD, they do not create band formations that cause strain localization, but distribute the dislocations more homogeneously and provide more enhanced dislocation interaction, thus distributing the deformation more homogeneously. Thus, we can say that edge screw collaboration prevents strain localization and delays crack formation. Besides, another feature to notice is the appearance of Frank-Read sources in the microstructures of LLD introduced systems. This is also an explanation of increased deformability and is thought to be a result of edge screw collaboration. |