A critical appraisal of the nanoindentation creep 'nose' effect in Ni thin films.
The creep behaviour of polycrystal Ni thin films under the same maximum load (Pmax = 8000 microN) and different unloading periods (ranging from 1 to 250 s) has been investigated at room temperature using nanoindentation tests. A 'nose' has been observed in the unloading segment of the load-penetration depth curve when the holding time at peak load is short and/or the unloading rate is small, and when the peak load is sufficient high. When a 'nose' presents, the apparent unloading stiffness Su, defined as dP/dh, is negative, and the reduced modulus can no longer be calculated from the Oliver-Pharr method. Taking such uncertainties into account, a critical appraisal is proposed for ranking creep propensities exhibited during nanoindentation under specified conditions.
Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education, Faculty of Materials, Optoelectronics and Physics, Xiangtan University, Xiangtan 411105 China.
Zengsheng
Z
Ma
Yichun
Y
Zhou
Shiguo
S
Long
Yong
Y
Pan