Hot compression bonding of a 9Cr oxide dispersion strengthened alloy and a 9Cr reduced-activation ferritic/martensitic alloy

Abstract

An innovative method of hot compression bonding is proposed in this work for the joining of 9Cr oxide dispersion strengthened (ODS) alloy and 9Cr reduced-activation ferritic/martensitic (RAFM) alloy. The microstructural evolution of the bonding interface was investigated by scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM). The results verify that the pinning effect of nano-oxides particles (NPs) in 9Cr ODS alloy significantly enhances its dynamic recrystallization (DRX) temperature and deformation resistance. Continuous DRX (CDRX) first occurred on the 9Cr RAFM alloy side, and the areas near the bonding interface were composed of recrystallized grains. With increasing strain, CDRX also showed up on the 9Cr ODS alloy side. Inevitable slight oxidation occurred at the bonding interface during the hot compression bonding (HCB) process, and the interfacial oxides transformed from initial coarse CrO to TiO and finally to Y-Ti-O nanoparticles with sizes comparable to pre-existing NPs dispersed in the 9Cr ODS alloy matrix. It is believed that interfacial oxide transformation and grain structure consistency contributed to the excellent interface healing of the two dissimilar alloy pieces. The effectiveness of the bonding was tested by tensile tests and fractography analysis, revealing that ideal metallurgical bonding could be achieved under a controlled strain level of 10 % at 800 °C followed by soaking at 1000 °C for 4 h.