Hi, I am a Materials Science Engineer and I am working on a project where aluminum substrate is plated with nickel-phosphorour (through electroless process). After polishing the disks, we see few worm-like pit defects (Which are very shallow) on the plating surface. I tried finding similar defects in internet but in vain. Have anyone experienced the same type of worm pit defect on electroless nickel plated layer on aluminum substrate?

Thanks.