Interfacial Oxides Evolution of High‑Speed Steel Joints by Hot‑Compression Bonding

The interfacial oxidation behavior of Cr4Mo4V high-speed steel (HSS) joints undergoing hot-compression bonding was investigated by using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In the heating and holding processes, dispersed rod-like and granular Al2O3 oxides were formed at the interface and in the matrix near the interface due to the selective oxidation and internal oxidation of Al, while irregular Si–Al–O compounds and spheroidal SiO2 particles were formed at the interface. After the post-holding treatment, SiO2 oxides and Si–Al–O compounds were dissolved into the matrix, and Al2O3 oxides were transformed into nanoscale Al2O3 particles, which did not deteriorate the mechanical properties of the joints. The formation and migration of newly-formed grain boundaries by plastic deformation and post-holding treatment were the main mechanism for interface healing. The tensile test results showed that the strength of the healed joints was comparable to that of the base material, and the in-situ tensile observations proved that the fracture was initiated at the grain boundary of the matrix rather than at the interface. The clarification of interfacial oxides and microstructure is essential for the application of hot-compression bonding of HSSs.