Mechanism of magnetic fragmentation effect on mechanical properties of TiAl alloy modified by combined magnetic-thermal treatment

This paper presents a method of pulse magnetic field combined with heat treatment (PMT-HT) to improve the room temperature elongation of the TiAl-4822 alloy. Prior to heat treatment, the application of the pulsed magnetic field induces a phenomenon known as the "magnetic fragmentation effect," which breaks down the initially coarse grains. Additionally, the stacking faults promoted by the magnetic field facilitate phase transformations, resulting in a transition from the coarse near-γ microstructure of the original sample to a fine, lamellar arrangement of γ and α 2 phases in the PMT-HT sample, characterized by high interfacial matching and the emergence of fine equiaxed γ particles. Furthermore, the magnetic field activates and promotes the conversion of electron pairs from singlet to triplet states, which assists in dislocation recovery and alleviates dislocation and stress concentration during heat treatment, thereby increasing the amount of recrystallization. The elongation rates of the original sample, the heat-treated sample, and the PMT-HT sample are 0.62 %, 1.32 %, and 1.72 %, respectively, while their strengths are 227.13 MPa, 222.52 MPa, and 264.17 MPa. Notably, the PMT-HT sample exhibits increase in elongation and strength of 177.4 % and 16.3 % compared to the original sample, respectively. This significant enhancement in both strength and elongation can primarily be attributed to grain refinement, phase transformation strengthening, and dislocation strengthening.