hi nitish,

you can do the following courses for M.TECH after completing b.tech in mechanical engineering,

• mechanical engineering
• mechatronics 
• robotics
• mechanical handling and automation
• mechanical systems design
• metallurgical engineering
• production engineering
• thermal engineering
• thermal energy and environmental engineering
• thermal and fluids engineering
• refrigeration and air conditioning
• manufacturing engineering
• manufacturing systems engineering
• machine design
• industrial engineering
• aerodynamics
• aerospace propulsion
• aerospace structure
• design engineering
• environmental engineering
• nanoscience

all the best!

note:if any links available,copy and paste it in the url bar of your browser.

I Hope this information will be useful to you.

if you need additional information,let us know to help you.

Thank you!!!:)