The effect of ion implantation and of post-annealing treatments on the surface modifications of sapphire has been widely investigated. In particular, relationships between the microscopic state and the macroscopic properties of implanted sapphire have been established. High-dose ion implantation has been carried out in polycrystalline alumina to a smaller extent. Surface mechanical properties are modified due to surface segregation and precipitation of new phases induced by post-implantation heat treatments. These results are reviewed and a comparison between implantation and annealing effects on single-crystalline and polycrystalline materials is conducted. There have been a lot of reports on surface amorphization of sapphire which depends on the particular species implanted and on the implantation temperature. Observed results for polycrystalline alumina do not differ in this respect for the cases studied. The main differences that will be discussed in this article are attributed to grain boundaries. Charged particle bombardment notably disturbs charge equilibria between grain boundaries and grain bulk. Moreover, it has been shown that during post-implantation heat treatments the orientation relationships of newly created phases are strongly dependent on the initial sapphire orientation. These phase orientations are difficult to put in evidence for polycrystals for which each grain represents a single crystal itself. A comparison of the mechanical property changes obtained for both types of alumina structures is also discussed.