Hi pradeep

You have many options to choose in M tech after completion of b tech in mechanical engineering like

Refrigeration and Air Conditioning

Computer Aided Design.

Mechanical Systems Design

Computer Aided Manufacturing,

Manufacturing engineering,

Maintenance management,

Metallurgy & Material Science Engineering,

Mining Engineering,

Mechatronics,

Operations management,

Petroleum Engineering,

Project management,

Thermal Engineering,

Automotive Engineering etc....

If you have any doubts drop out the comment

Best of luck!!

Thank you::)