Here is a an image of the torque/speed curve. My guess is that increasing voltage will simply translate the curve up because the slope is the torque constant, which is a physical motor property that will not change with added voltage. I know from this post that increasing voltage will increase stall torque:
So does the increasing voltage not only increase the stall torque, but also the overall range of torques the motor can achieve? In other words, the same RPM now correlates to a higher torque in the higher voltage curve?
Additionally, if the above is true, here is another question. If the original stall torque in the lower curve is 2.5 N-m, but the stall torque of the higher curve is 3.5 N-m, does this mean that with the added voltage I can now run the motor at 2.5 N-m more safely than I could before since it is no longer the stall torque? Or is the power dissipation the same in both curves so that 2.5 N-m will still be dissipating the same heat? So, if the motor was going to burn up at 2.5 N-m, it will still burn up at 2.5 N-m at the higher voltage input?