We performed high-precision mass measurements of the proton-rich nuclei ${}^{52}\mathrm{Ni}$ and ${}^{51}\mathrm{Co}$ with the LEBIT Penning trap at the Facility for Rare Isotope Beams. For ${}^{52}\mathrm{Ni}$, a mass excess of $-22474.8\left(2.2\right)$ keV was determined, which is consistent with a recent storage-ring measurement at the Cooler-Storage Ring (CSRe) but has a factor 37 improved precision. For ${}^{51}\mathrm{Co}$, we obtained a mass excess of $-27375.1\left(5.7\right)$ keV, agreeing with a recent CSRe result, while reducing the uncertainty by a factor 2. Combining our mass value for ${}^{52}\mathrm{Ni}$ with the known two-proton decay energy of ${}^{54}\mathrm{Zn}$, we determined the mass excess of ${}^{54}\mathrm{Zn}$ to be $-6463\left(42\right)$ keV. These new mass values reveal a substantial breakdown of the isobaric mass multiplet equation for $A=52$ and $A=54$, and provide stringent benchmarks for isospin-symmetry-breaking effects in the proton-rich $fp$-shell, favoring theoretical descriptions that omit the Coulomb-exchange term.

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• Binding energy & masses
• Nuclear binding
• Nuclear forces
• Nuclear structure & decays
• Nucleon-nucleon interactions
• Rare & new isotopes
• 39 ≤ A ≤ 58
• Nuclear mass ranges
• Nuclear many-body theory
• Radioactive beams
• Shell model
• Spectrometers & spectroscopic techniques