HIPIMS deposition of TiAlN films on inner wall of micro-dies and its applicability in micro-sheet metal forming

For further enhancement of the tool life in microforming process, a high power impulse magnetron sputtering (HIPIMS) deposition technique, which has well-known advantageous features, such as dense and smooth surface, and three-dimensional uniformity on complex-shaped substrates, was applied to microforming die in this report. In view of the process tribology in sheet metal forming, the present study particularly focused on the thin film properties on the inner wall surface of the sub-millimeter scale tiny hole structure as micro-dies. TiAlN films were deposited by both HIPIMS and conventional direct current magnetron sputtering (dcMS) on the micro-hole structure, and its inner wall film properties were investigated in detail. Cross-sectional scanning electron microscopy (SEM) analysis, surface topographical analysis using atomic force microscopy, and micro-Vickers hardness test of TiAlN films deposited by HIPIMS demonstrated the highly dense microstructure with fine smooth surface (Rmax: 126 nm) and relatively high hardness (2288 Hv) even at the inner wall of micro-holes. Additionally, high wear resistivity and adhesion strength on the substrates were also shown via ball-on-disk tribology test and scratch test, respectively. The applicability of these advantageous features of HIPIMS deposition films to the practical forming behavior is further studied with micro-circular drawing test. Anti-adhesive performance of HIPIMS deposited micro-die leads to the better micro-formability than that deposited by the conventional dcMS process.