  Mass measurements continue to provide invaluable information for elucidating
nuclear structure and scenarios of astrophysical interest. The transition
region between the $Z = 20$ and $28$ proton shell closures is particularly
interesting due to the onset and evolution of nuclear deformation as nuclei
become more neutron rich. This provides a critical testing ground for emerging
ab-initio nuclear structure models. Here, we present high-precision mass
measurements of neutron-rich chromium isotopes using the sensitive
electrostatic Multiple-Reflection Time-Of-Flight Mass Spectrometer (MR-TOF-MS)
at TRIUMF's Ion Trap for Atomic and Nuclear Science (TITAN) facility. Our
high-precision mass measurements of $^{59, 61-63}$Cr confirm previous results,
and the improved precision in measurements of $^{64-65}$Cr refine the mass
surface beyond N=40. With the ab initio in-medium similarity renormalization
group, we examine the trends in collectivity in chromium isotopes and give a
complete picture of the N=40 island of inversion from calcium to nickel.
