Effects of Surface Roughness on Interface Bonding Performance for 316H Stainless Steel in Hot-Compression Bonding

The metallurgical bonding quality of bonding joints is affected by the substrate surface state in hot-compression bonding(HCB),and the surface roughness is a core indicator of the surface state.However,the effects of surface roughness on interface bonding performance(IBP)in the HCB process are unclear for substrates with refractory oxide scales.This study presents the effects of surface roughness on IBP for 316H stainless steel joints fabricated by HCB.A set of HCB parameters for interface bonding critical state of 316H stainless steel joints was determined.The HCB experiments were carried out under parameters of interface bonding critical state to amplify the effect of surface roughness.The interface morphologies,element distribution,and tensile properties were used to characterize the IBP.As a result,the formation mechanisms of the interface pits were revealed and the variation trend of pit number with the roughness was summarized.Finally,the mapping relation between surface roughness and IBP was established.The results show that the degree of rotational dynamic recrystallization becomes weaker with the decrease in the surface roughness and the interface bonding mechanism is completely transformed into discontinuous dynamic recrystallization when the roughness is lower than 0.020μm Sa.The number of interfacial pits decreases as the roughness decreases owing to the weakening of oxide scale aggregation and abrasive inclusion mechanism.The elongation of the tensile specimen cannot increase significantly while the roughness is lower than 0.698μm Sa.

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

The interfacial oxidation behavior of Cr_(4)Mo_(4) V 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 granularδ-Al_(2)O_(3) 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 SiO_(2) particles were formed at the interface.After the post-holding treatment,SiO_(2) oxides and Si-Al-O compounds were dissolved into the matrix,andδ-Al_(2)O_(3) oxides were transformed into nanoscaleα-Al_(2)O_(3) 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.