What is the shiny structure under a metal coating?
Likely an intermetallic , I think there are a couple different ones. I am more familiar with "spray and diffuse"  or vapor deposition ( Alon). Alonizing is very long ( > 24 hr) but gives a high integrity coating , can't remember the thickness.  As I remember the "diffuse" cycle takes a couple hours. I expect your process produced a thinner coating but still with some intermetallics.