I just learned the PLA+ filament obtains a strong mechanical performance. So, can I use it to 3d print a gear？
It is not only the material. The print orientation is key, too. Printing flat makes the teeth strong, but may cause trouble at the axle mount.
And of course the use case. The gear may be strong enough, but could melt, when mounted to a hot motor. Same goes for friction due to speed and UV light.
So there is no clear answer for that. It always depends on the environment where the gear is used.