The development of strong and ductile alloys for application in cryogenic temperatures has long been sought after. In this work, we have developed a face-centered cubic Ni₁₀Co_56.5V_33.5 multi-principal element alloy (MPEA) that exhibits a balanced combination of high strength and good ductility at 77 K, based on the considerations of large local lattice distortion (LLD) and low stacking fault energy. The small-grained Ni₁₀Co_56.5V_33.5 MPEA exhibits a yield strength of 1400 MPa and an ultimate tensile strength of 1890 MPa, while preserving a good ductility of 23%. Moreover, precession electron diffraction and transmission electron microscopy revealed multiple deformation mechanisms, including wavy dislocations, atypically severely twisted dislocation bands, hierarchical stacking faults, and deformation twins, which are implicated in the alloy’s outstanding mechanical performance. These insights offer a strategic guide for the design of strong and ductile alloys, particularly for utilization in extreme environments.

Laser-induced projectile impact testing (LIPIT) based on synchrotron imaging is proposed and validated. This emerging high-velocity, high-strain microscale dynamic loading technique offers a unique perspective on the strain and energy dissipation behavior of materials subjected to high-speed microscale single-particle impacts. When combined with synchrotron radiation imaging techniques, LIPIT allows for in situ observation of particle infiltration. Two validation experiments were carried out, demonstrating the potential of LIPIT in the roentgenoscopy of the dynamic properties of various materials. With a spatial resolution of 10 µm and a temporal resolution of 33.4 µs, the system was successfully realized at the Beijing Synchrotron Radiation Facility 3W1 beamline. This innovative approach opens up new avenues for studying the dynamic properties of materials in situ.

Internal defects, especially those caused by elemental segregation and minor phases in as-cast super-thick steel plates with large section sizes, can critically impact the subsequent manufacturing processes and the mechanical properties of final products, which may result in catastrophic failure during industrial applications. However, the effects of elemental segregation and the resultant phase structures on deformation behaviors and real-time microstructural evolution under tensile loading remain unexplored in as-cast super-thick steels. In this study, we employed in-situ synchrotron and neutron diffraction techniques during tensile tests to investigate the relationship between internal defects and deformation behaviors of segregated and non-segregated super-thick steels. Compared to the segregated sample, the non-segregated sample exhibited improved yield and tensile strengths, increasing from 407.5 and 590.5 MPa to 515.2 and 632.8 MPa, respectively, with a significant increase in elongation from 8% to 23.4%. Strip-like elemental segregations were observed in the central core area due to final solidification, and the stress partitioning between ferrite matrix and retained austenite was revealed to be beneficial for uniform plastic deformation and necking before fracture. Both ductile and brittle fractographies were identified in segregated conditions. Our findings address a critical knowledge gap in understanding how elemental segregation and minor phases affect deformation behaviors, and offer valuable insights for optimizing processing parameters for as-cast super-thick steels.