Can we export charts or images in excel

No, not with Appian’s built‑in Excel export features.

Appian's out‑of‑the‑box Excel exports only export data.
Recommend you would try, Create an Excel template with charts that reference a data range and then populate that data via a plugin or template‑based export, Excel will render the charts when opened, but the charts themselves are authored in Excel, not exported from Appian’s chart components.