Direct ion implantation of radioactive isotopes, such as 7Be or 22Na, has recently been of interest as a means of surface layer activation for purposes of wear-rate measurement in material systems for which activation by conventional proton irradiation is ineffective. Though direct implantation doses anticipated for adequate wear measurement sensitivity are expected to be quite low (∼1012 cm−2), the potential for alteration of wear properties by ion damage cannot be ignored. The present work was designed to simulate 22Na implantation with non-radioactive 20Ne irradiations into specimens of 17–4PH stainless steel which had been deliberately heat treated to contain 98 vol% metastable martensite. Specimens were subjected to doses of 2×1012, 2×1013 and 2×1014 cm−2 of 20Ne2+, applied at a total energy of 50 MeV, giving a projected ion range (determined by TRIM-91 computations) of approximately 10 μm. Nanoindentation surface hardness traverses were conducted to detect any material softening which may have resulted from ion-solid interactions within the projected range. Though doses of > 1014 cm−2 produced a detectable softening (apparent as a dip in the hardness level corresponding to locations near the end of the ion range) the maximum dose for a negligible effect on nanoindentation hardness was found to be approximately 1013 cm−2, well above the doses anticipated for use in wear studies employing direct ion implantation of radioisotopes.