  The distribution of metals in the intra-cluster medium encodes important
information about the enrichment history and formation of galaxy clusters. Here
we explore the metal content of clusters in IllustrisTNG - a new suite of
galaxy formation simulations building on the Illustris project. Our cluster
sample contains 20 objects in TNG100 - a ~(100 Mpc)^3 volume simulation with
2x1820^3 resolution elements, and 370 objects in TNG300 - a ~(300 Mpc)^3 volume
simulation with 2x2500^3 resolution elements. The z=0 metallicity profiles
agree with observations, and the enrichment history is consistent with
observational data going beyond z~1, showing nearly no metallicity evolution.
The abundance profiles vary only minimally within the cluster samples,
especially in the outskirts with a relative scatter of ~15%. The average
metallicity profile flattens towards the center, where we find a logarithmic
slope of -0.1 compared to -0.5 in the outskirts. Cool core clusters have more
centrally peaked metallicity profiles (~0.8 solar) compared to non-cool core
systems (~0.5 solar), similar to observational trends. Si/Fe and O/Fe radial
profiles follow positive gradients. The outer abundance profiles do not evolve
below z~2, whereas the inner profiles flatten towards z=0. More than ~80% of
the metals in the intra-cluster medium have been accreted from the
proto-cluster environment, which has been enriched to ~0.1 solar already at
z~2. We conclude that the intra-cluster metal distribution is uniform among our
cluster sample, nearly time-invariant in the outskirts for more than 10 Gyr,
and forms through a universal enrichment history.
