It highly depend upon the material you have or the instruments, as the previous guy mentioned, it's better to find the gap which takes time. You should read tons of papers by abstract and conclusions and narrowing them down. So, I suggest you to kick off with review papers, check this paper and the references it might give you an idea especially if you intend to work on metal AM or in-situ improvement.

Article Ancillary Processes for High-Quality Additive Manufacturing:...

Cheers,

Hossein

Thank dear for your valuable suggestion Hossein Aliyari

No worries! somehow I forgot to give you the paper!!

this is the link to it!

Article Ancillary Processes for High-Quality Additive Manufacturing:...