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There is limited understanding of time-dependent plastic deformation behavior of amorphous alloys as a function of their structural state. Here, the creep behavior of Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glass was investigated in its as-cast and relaxed states using nanoindentation technique with applied load in the range of 500–1500 mN and temperature in the range of room temperature to 573 K. The creep displacement increased with increasing load and temperature since the creep process is thermally activated and diffusion rate is enhanced at elevated temperature and higher load. The creep strain rate sensitivity, which is a measure of the creep mechanism, increased with increase in temperature and decrease in applied load. This was attributed to the transition from localized to more homogeneous creep. Reduction in free volume for the relaxed alloy resulted in lower creep displacement and larger strain rate sensitivity compared to its as-cast counterpart. The results suggest that diffusion-based deformation dominate at higher temperature in contrast to shear transformation mediated plasticity at room temperature. The volume of shear transformation zone for the metallic glass was calculated using cooperative shearing model and correlated with the structural state for fundamental insights into the deformation process as a function of temperature and load.

Refractory high-entropy alloys have attracted widespread attention as potential structural materials for high temperature applications. However, there is limited understanding of their high temperature deformation behavior and tribological response. Here, the temperature dependence of strain rate sensitivity and wear behavior was evaluated for two refractory high-entropy alloys, namely HfNbTiZr and HfNbTaTiZr. HfNbTaTiZr showed higher hardness, strength, and lower strain rate sensitivity compared to HfNbTiZr. The extrinsic strain rate sensitivity of both alloys obtained from micro-pillar compression was higher compared to the intrinsic values from nanoindentation due to the larger surface to volume ratio in micro-pillars leading to annihilation of dislocations and their easier movement. The decrease in strain rate sensitivity with increase in temperature was attributed to activation of both edge and screw dislocations as well as phonon drag controlled screw dislocation motion at high temperatures. Wear rate for both alloys increased with increase in sliding cycle frequency due to frictional heating. Wear rate also increased with increase in temperature from 298 K to 423 K and then decreased with further increase in temperature to 573 K. The underlying mechanism changed from abrasive wear at room temperature to extensive ploughing with fine wear debris at intermediate temperatures and oxidative wear at the higher temperatures.

The electrodeposition route to obtain amorphous alloys offers a facile, low-cost, and versatile alternative to conventional melt quenching. However, there are significant knowledge gaps in tribological properties and wear mechanisms for electrodeposited metallic glasses (EMGs). Here, the wear behavior and the scratch response of a model binary amorphous alloy system were investigated. Electrodeposited Ni–P metallic glasses were systematically studied as a function of composition, with amorphous alloy formation over the narrow range of 10 at% to 20 at% phosphorus. The electrodeposited metallic glasses showed hardness values in the range of 6.6–7.4 GPa, modulus in the range of 155–163 GPa, and friction coefficient around 0.50. Among the studied alloys, electrodeposited Ni80P20 showed the lowest wear rate, which was two orders of magnitude lower than electrodeposited pure Ni. The wear mechanism was determined to be extensive plastic deformation along with mild ploughing, micro tears, and formation of discontinuous lubricious oxide patches. Scratch tests showed an increase in critical load for damage initiation with the increase in phosphorus content among the amorphous alloys following the trend: Ni80P20 > Ni85P15 > Ni90P10. The overall wear rate for the electrodeposited metallic glasses was found to be lower than most reported bulk metallic glasses (BMGs). This represents a fundamental study on structure-property correlations in electrodeposited metallic glasses and demonstrates the versatility of electrodeposition in tuning the surface properties of amorphous alloys.