192 will be in the neighborhood of .2319 in/µs . The SS309LSi will be in the neighborhood of .2228 in/µs.
The interface signal will be weak as those two are fairly close regarding their acoustical impedance.
However, the interface between the two will not be isotropic, and the dilution/intermetallic compounds at the interface will not have a uniform ultrasonic velocity.
You will likely get an interface signal, but it will be a weak one if you get it. Therefore you will need an A-scan presentation to perform this.
The simple solution is to produce a cal standard if your looking for backside wall loss. For this block, the 192 side would receive the step machining.
If your looking looking to measure amount of cladding, the same block, except the cladding would receive the step machining.
For the former, an echo to echo cal will be needed.
For the latter, you will need to pick up the interface signal which would be weak.
If it's simply measuring the overall T, cut the 192 side.
Dunno of that helps you but there it is.
Here's an interesting thread:
