[SY-J3] Symposium J-3

[SY-J3] The effect of layer thickness ratio on the plastic deformation mechanisms of nonoindented Ti/TiN nanolayered composite: A molecular dynamics study

^○Georges Y Ayoub¹, Wei yang², Iman Salehinia³, Bilal Mansoor², Hussein Zbib⁴ (1.Dept. of Industrial and manufacturing system Engineering, Univ. of Michigan, United States of America, 2.Dept. of Mechanical Engineering, Texas A&M Univ., United States of America, 3.Dept. of Mechanical Engineering, Northern Illinois Univ., United States of America, 4.School of Mechanical and Materials Engineering, Washington State Univ., United States of America)

Molecular dynamics simulations were performed to identify the underlying deformation mechanisms controlling the plastic behavior of nanoindented nanoscale multilayered Ti/TiN. MD simulations were conducted on pure Ti and pure TiN as well as on four different layer-thickness ratios of Ti/TiN multilayers, Ti:TiN=1, 2.5, 4, and 7.5. The Ti layer thickness varied from 2nm to 15nm. The plastic deformation of nanoindented pure Ti was dominated by the formation of dislocation loops resulting from basal partial dislocations, while very few perfect dislocations that tie dislocation loops together were observed. The plastic deformation of nanoindented pure TiN was controlled by the activation of perfect dislocation propagation along the 111 plane that dissociates into two partials. Depending on the thickness ratio, either dislocation pile-up or single dislocation crossing through the interface was the controlling plastic deformation mechanism of nanoindented Ti/TiN multilayers. For metal layer thicknesses above 5nm, significant dislocation pile-ups were observed at the interface of the quad-layered samples. The Ti/TiN multilayer with a thickness ratio of 1:1 with individual layer thickness of 2nm exhibited the highest strain-hardening rate. At this length scale, the activation of dislocation sources requires very high stresses, and the single dislocation crossing process is the most dominant deformation mechanism. The initiation of plasticity in the TiN layer occurs at a high level of stress since there is no dislocation pile-up at the interface.