The effects of incident ion/metal flux ratioJi/JMeand ion energyEion the microstructure, texture, and phase composition of polycrystalline metastable Ti0.5Al0.5N films produced by reactive magnetron sputtering have been investigated using x‐ray diffraction (XRD), plan‐view and cross‐sectional transmission electron microscopy, and Rutherford backscattering spectroscopy. The films, typically &bartil;1 &mgr;m thick, were deposited at a pressure of 20 mTorr (2.67 Pa) in pure N2on thermally oxidized Si(001) substrates at 250±25 °C. The N2+ion flux to the substrate was controlled by means of a variable axial magnetic field superimposed on the permanent magnetic field of the magnetron. Films deposited atEi=20 eV (&bartil;10 eV per incident accelerated N) withJi/JMe=1 exhibited a complete (111) texture with a porous columnar microstructure and an average column size of &bartil;30 nm. IncreasingEifrom 20 to 85 eV, while maintainingJi/JMeconstant at 1, resulted in a small change in texture as the XRD intensity ratioI002/(I111+I002) increased from &bartil;0 to 0.14, a decrease in average column size to 25 nm, and a reduction in intracolumn porosity.The stoichiometric ratio N/(Ti+Al) increased from 1 atEi=20 eV withJi/JMe=1 to 1.23 atEi=85 eV indicating trapping of excess N while the lattice constanta0increased from 0.4157 to 0.4188 nm due to compressive stress.Eivalues ≥100 eV led to alloy phase separation. In contrast, maintainingEiat &bartil;20 eV and increasingJi/JMefrom 1 to ≥5.2 resulted in a change from a porous (111) texture to a dense completely (002)‐oriented microstructure with an increase in the average column size to 35 nm. N/(Ti+Al) anda0remained essentially constant and the alloy remained single phase. Mechanistic pathways leading to microstructure and texture changes through variations inEiat constantJi/JMeand inJi/JMeat constantEiwere found to be quite different. The average energy deposited per metal atom, ⟨Ed⟩=Ei(Ji/JMe), is therefore not a universal parameter, as has been previously proposed, for describing film growth.