A demand for high-strength alloys in aerospace, marine and off-shore industries has stimulated development of new and efficient machining techniques. In the recent past, a novel machining technique known as ultrasonically assisted turning (UAT) has been introduced; in it low-energy ultrasonic vibration is superimposed on movement of a cutting tool. In the present work, a comparative study of machining of two advanced alloys - Ti15V3Cr3Al3Sn and Inconel 718 - is carried out numerically by developing a two-dimensional finite-element model of the turning process. A non-linear material description is used in the FE model to incorporate plastic deformation behaviour of the high-strength alloys. The model is employed to investigate the effect of tool geometry and contact conditions on cutting forces, temperature of the cutting region and the chip shape in orthogonal turning of modern alloys.