Structure Transformations and Mechanical Properties of the Ultra-High-Strength M54 Steel Produced by Spark Plasma Sintering

Ultra-high-strength M54 steel has been considered a promising candidate for structural applications in spacecraft and aircraft because of its excellent match of strength and toughness. Spark plasma sintering (SPS) technique characterized by simultaneous uniaxial pressure and pulsed current allows achieving fully dense bulk materials at low temperature with short heating, soaking, and cooling times. SPS has been widely used to produce metal materials due to its efficiency and advantages caused by its distinctive heating mode. The sintering behaviors, structural transformations, and mechanical properties of the ultra-high-strength M54 steel prepared by spark plasma sintering (SPS) were studied in this work. The actual density of the SPSed specimen was measured according to Archimedes’ principle, and X-ray diffraction (XRD) analysis was used to identify the phases of the raw powders and SPSed specimens. The microstructure of the SPSed specimens was characterized by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) coupled with an energy-dispersive spectrometer (EDS). After SPS consolidation, metallurgical bonding between powders was completed, and the ultra-high-strength M54 steel adjacent to nearly full densification was obtained directly. The quasistatic tensile tests indicated that the SPSed M54 steel exhibited better ultimate tensile strength (UTS) of 1933.88 MPa compared to the wrought M54 steel. According to TEM analysis, the primary strengthening mechanism was its lath martensite structure with high-density dislocations. The elongation was not significant due to the presence of micro-voids and inclusions.