Two phase direct particle-high speed compressible gas flow simulation techniques developed by the author are extended to include the effects of particle deformation and plasticity with a focus on high speed impact of metallic steel particles moving in high speed air. The first part of the study involves the development of the necessary modeling techniques. Using the results of fluid independent finite element analyses, normal force functions were devised to simulate the effect of a collision of two 1.5 mm radius steel particles over a range of relative impact velocities from 12.5 to 200 m/s with an elastic and then an elastic perfectly plastic material model. Methods were introduced to model the deformation of the particles/objects. Use of the collision force model and the inclusion of deformation in a simulation of the collision between two particles in air replicated the appropriate short term post collision velocities of the corresponding finite element analysis. The parametric studies conducted during this model development demonstrated the importance of utilizing the proper material model in predicting the motion of the particles. A longer contact time and increasingly comparable post collision velocities for the two colliding particles develop with an elastic perfectly plastic based collision model, with the differences from the elastic based model results growing with collision velocity. The modeling techniques were then applied to analyze the motion of fourteen steel particles placed ahead of a gas driven piston in a flow channel 19.5 mm in width for three different piston driving pressures of 50, 75, and 100 MPa, implementing the elastic and then the elastic plastic based collision force models. The results clearly indicate that the incorporation of plasticity and particle deformation causes the particles to remain closer together both inside and outside of the flow channel. The modeling methods developed provide the ability to incorporate the plasticity/deformation effects of multiple interacting particles together with the local flow induced force to simulate the coupled gas flow and particle motion. The techniques developed offer a tool to capture more of the physical phenomena occurring in the two phase flow regime of interest, extending the capabilities to simulate the motion of gas-particles to a wider range of particle and flow velocities and providing information to assist in the understanding of particle motion and interaction characteristics. Published by Elsevier B.V.