The free titles that you'll get in March with your PS Plus membership have been announced. The list of games can be seen below and Sony has also announced that starting March 2019 their service will no longer include free PS3 and Vita games so that they can focus solely on PS4 titles.
Ratchet & Clank
Legend of Kay
Mighty No. 9 (Cross Buy with PS4)
Claire: Extended Cut (Cross Buy with PS4)
Bombing Busters (Cross Buy with PS4)