Sreenivas,
In Fiori Client, if you are clicking on the link and nothing appears to be happening, the link is probably coded wrong. You can look at the sample on http://scn.sap.com/docs/DOC-65399 to see how to call attachment viewer. I've seen older Fiori Apps not call it correctly. What is happening when you click on the link?
One way to verify the correct code is being used is to use Chrome Debugger to verify.
Reagrds,
Kevin