Hi
Do you mean Monel 60? and Nickel 61? If you do, then you would not normally require a buttering layer of Ni61. Monel 60 will give a suitable first layer, as long as the dilution of the base metal into the filler does not exceed about 60%. (This is quite high. For overlays, the dilution is typically around 30 - 50%, depending on the process and parameters used. With some low dilution processes and parameters, dilutions as low as 10% can be achieved.)
Hope this helps.
Regards
Niekie Jooste
Fabristruct Solutions