A Belleville washer is generally used as a spring, or to have a flexible preload range for a bolt or bearing installation.
Belleville washers could be used as a bolt locking method but only in very low dynamic load applications within the range of the Belleville washer spring compression length. You can stack the washers to change the spring rate and depending on the configuration the range where spring load is available.
A Belleville washer is not what you need to lock the bolt/nut on your shaft.
I suggest for locking the fastener, either a split lock washer, thread lockers, or an interference or locking thread. Also, you may be able to modify the shaft to accept a cotter pin and use a castle nut/bolt as a locking method.