Fusing gear improves their stats at a cost of shards and Power Credits. The cost goes up for every upgrade. Fusing a gear piece 10 times will give you an option to evolve it, turning it into a stronger form with additional abilities. It can then be upgraded further for even higher stats up to a total of 21 fuses. Shards can be obtained by either shattering gear or through Surviror Mode. Shattering higher level gear yields more shards.