Effect of N–Cr compounds on the brazing of high nitrogen steel with Ag-based filler metal: first-principles calculation

The Cr element is present in the form of CrN and Cr2N compounds in the brazing of high nitrogen steel with Ag-based filler metals. The Cr compounds have a strong influence on the strength of the brazed joints. In this paper, the mechanical properties of CrN and Cr2N are evaluated based on first-principles. The results show that Cr2N has a stronger covalent bonds than CrN, resulting in higher Young's modulus and hardness of Cr2N than CrN. The 7 atomic layers Ag(111) surface, 9 atomic layers CrN(111) surface and 9 atomic layers Cr2N(0001) surface can represent the block structure. The Ag(111)/CrN(111) interface and Ag(111)/Cr2N(0001) interface were constructed. The Ag(111)/CrN(111) B-site interface was found to have the largest work of adhesion(Wad). The chemical bonding strength of Ag–N in the Ag(111)/CrN(111) interface is stronger than that in Ag(111)/Cr2N(0001) interface, indicating that the formation of Cr2N phase is more likely to produce microcracks in brazing joints. Hence, the formation of the Cr2N phase should be suppressed.