Diffusion bonding among hard alloy, tool steel, and alloy steel by hot isostatic pressing: Interfacial microstructure and mechanical properties

Abstract

In this study, the diffusion bonding among YG18 cemented carbide, 30Cr2Ni2Mo alloy steel, and M4 high-speed steel was successfully realized by hot isostatic pressing. The microstructure and element diffusion of 30Cr2Ni2Mo/M4, YG18/M4, and Y18/30Cr2Ni2Mo joints were studied by electron-probe microanalysis and field emission scanning electron microscope. The mechanical properties of the three joints were evaluated by a uniaxial testing machine. The results showed that significant element diffusion occurred at the three connection interfaces. Although Kirkendall voids appeared at the 30Cr2Ni2Mo/M4 interface due to the unbalanced interdiffusion of elements, the negative effect of the Kirkendall void on the interfacial bonding strength was negligible. The η phase with a thickness of ⁓1.5 μm was formed at the YG18/M4 and Y18/30Cr2Ni2Mo interfaces. A diffusion distance of ⁓20 μm was generated at these two interfaces, where Co diffused from YG18 to M4 or 30Cr2Ni2Mo, and Fe diffused from M4 or 30Cr2Ni2Mo to YG18. The ultimate tensile strength of the 30Cr2Ni2Mo/M4, YG18/30Cr2Ni2Mo, and YG18/M4 joints was 1300.4 MPa, 736.2 MPa, and 631.2 MPa, respectively and the corresponding shear strength was 879.9 MPa, 810.0 MPa, and 360.2 MPa. The tensile and shear strength of the 30Cr2Ni2Mo/M4, Y18/30Cr2Ni2Mo, and YG18/M4 joints reached 80% of that of YG18. The tensile specimens of the 30Cr2Ni2Mo/M4 and YG18/30Cr2Ni2Mo joints failed at the M4 or YG18 side rather than at the interface, indicating that the two interfaces achieved good metallurgical bonding. The tensile specimens of the YG18/M4 joint fractured at the interface due to the existence of cracks at the YG18/M4 interface. The hot isostatic pressing enabled reliable connection among YG18, M4, and 30Cr2Ni2Mo. This study provides valuable exploitation for the reliable connection of YG18 cemented carbide and steels by hot isostatic pressing.