Molecular dynamics simulation of phase transformation and wear behavior of Ni35Al30Co35 high temperature shape memory alloy

Ni–Al–Co alloys as one of the ferromagnetic high-temperature shape memory alloys (HTSMA) are attractive in aerospace and defense applications, due to their high phase transition temperature range (400–700K), high recoverable strain and good machinability. However, the underlying physics for the phase transformation behavior of β single-phase and β+γ two-phase Ni–Al–Co ternary alloys remain unclear. In this work, molecular dynamics simulation of phase transition, pseudoelasticity (PE) and wear behavior of Ni35Al30Co35 alloy were analyzed using the EAM potential. It shows that Ni35Al30Co35 alloy has a high martensite start temperature of 825K and an austenite start temperature of 631K, respectively. After five thermal cycles, martensite and austenite start and finish temperatures are stable around 500K and 700K. The initial structure of Ni35Al30Co35 alloy at 1000K is identified as BCC (β phase) and FCC (γ phase) structure, transforming to L10 structure through martensitic transformation. Furthermore, PE of Ni35Al30Co35 alloy exhibits about a 9.1% recoverable strain under <001> oriented uniaxial tension tests and about a 6.6% recoverable strain under <001> oriented uniaxial compression tests at a temperature of 1200K, showing the potential used in extreme environment. Moreover, spherical indenters with a radius of 15 Å were used to investigate the wear behavior of Ni35Al30Co35 alloy under different temperature. It was found that the PE effect affects the frictional behavior during nano-scratching. Combining the effect of high temperature softening and phase transition PE, the wear rate increases nearly by 5.3% when the temperature rises from 300K to 1000K. Furthermore, the friction force curve obtained is consistent with the friction force curve obtained by simulation at 300K.