A01 – Solid Solution Effects on the Formation of Defect phases in metallic Ni-X solid solution alloys

PIs: Stefanie Sandlöbes-Haut (RWTH Aachen University, IMM)

SFB researcher: Pia Huckfeldt (RWTH Aachen University, IMM)

In the first funding period, project A01 has investigated the interactions of dislocations and stacking faults with solutes in Mg-Al-Ca. Specifically, seven ternary Mg-Al-Ca, one binary Mg-Al and one binary Mg-Ca alloys were tested mechanically and characterised microstructurally using x-ray diffraction (XRD), scanning electron microscopy (SEM)-based methods and conventional transmission electron microscopy (TEM). The results show, that only the joint addition of Al and Ca substantially increases the room temperature ductility with respect to pure Mg. Slip trace analysis, micropillar compression and conventional TEM revealed that this is related to the activation of <c+a> dislocations. To identify the underlying defect phases, the samples were shared with projects (A03), (B01), and (B03) for high resolution analysis of the local structure and chemistry.

In the second funding period, project A01 will focus on investigating the dislocation-, stacking fault-, and grain boundaries solute interactions and their effects on the mechanical properties in Ni-X solid solutions. More specifically, the solute-dependent nucleation mechanisms and mobility of dislocations, as well as the formation of stacking faults will be studied considering also aspects related to the change in dislocation core structure and cross slip, solute clustering, and ordering phenomena. Further, the segregation of alloying elements to grain boundaries and their effects on the recrystallisation and grain growth behaviour will be investigated.

For this purpose, we will employ systematic tests and characterisation of solid solution bulk and thin-film Ni-X samples. Micro-mechanical testing and (in-situ) annealing will be utilised to identify promising alloy compositions revealing property jumps and related to the predominant defect phases formed at dislocations, stacking faults and grain boundaries. To this end, scanning electron microscopic methods, such as electron backscatter diffraction (EBSD), conventional TEM (this project), high resolution scanning transmission electron microscopy (HRSTEM) (A03) and atom probe tomography (APT) (B03) will be employed.