Simulation of Phase transformation behavior of NiTi doped with Cu during loading using classical molecular dynamics S. Aich, A. Behera and S. Ghosh Department of Metallurgical and Materials Engineering Indian Institute of Technology Kharagpur

CONTENT  Introduction  Literature review and objectives  Procedure of simulation  Results and discussion  Conclusions  Future study

INTRODUCTION  Ti-Ni thin films are considered to be an attractive alloy for miniaturization of functional materials in modern technology. Now a days the addition of third metal in the Ni-Ti matrix is also a very attractive issue.  Use of Ti-Ni-X thin film as SMA is greatly influenced by its composition.  The Sputtering technique is widely accepted for processing of Ti-Ni and Ni-Ti-X alloy thin film, because it is efficient to work in a very high vacuum and easy to control the composition of the films also the targets with very high melting point can sputtered easily. Shape Memory Alloy Actuator

Ni-Ti ALLOY FOR MICROACTUATOR

IMPORTANCE OF Ni-Ti-X ALLOY  Most commercial SMAs are only applicable around room temperature, or below because of its relatively low transformation temperature.  Increasing this transformation temperature would enable many new applications in various industries where elevated temperature actuation is desirable.  NASA is investigating the possibility of using these alloys in place of traditional actuators in jet engines.

TYPES OF Ni-Ti-X ALLOYS  Ni-Ti and Ni 50 Ti 50-x M x (where M=Hf,Cu,Zr) greater shape memory strain (8% vs. 4 to 5% for Cu-based Alloys),  More Thermally Stable.  Excellent Corrosion Resistance.  Higher Ductility.  Very excellent mechanical and electrical property. Application  Superelastic Applications in Military Aerospace.  Surface coatings and functional gradients for control of fatigue, erosion and wear degradation.  High Temperature Applications.

Effect of Cu addition Narrowing of hysteresis loop while heating and cooling The narrowing becomes significant when wt.% Cu is higher than 5. Study on the effect of Cu on the stress-strain behavior needs to be understood Plan Molecular dynamics simulation of nano-indentation Experimental validation of simulation Study on the effect of Cu on the stress-strain behavior needs to be understood

6/11/20168 MD-Introduction MD simulation is a technique by which one generates the atomic trajectories of a system of N particles by numerical integration of Newton’s equation of motion for specific interatomic potential, for certain initial conditions (IC) and boundary conditions (BC) Consider N atoms in volume Ω. Internal energy E=K+U K=kinetic energy and U= potential energy N particles X i (t) z y x

Simulation of Nano-indentation Embedded Atom Potential Number of atoms: 4000 NVT Diameter of indentor: 20 nm

Load displacement

Load

displacement

Load displacement

The previous plots after superposition Load displacement

Experimentally generated load displacement curves for different percentages of Cu

2% Cu

4% Cu

6% Cu

8% Cu

Conclusion Cu doesn’t play significant role in changing the stress required to initiate the transformation (psuedo-elastic deformation) The area of the load displacement curve is not modified by the addition of Cu