Meng Xiangkang

Deformation Induced Internal Friction Peaks in Nanocrystalline Nickel

We report the mechanical spectroscopy study of the cold-rolling induced dynamical behavior of crystalline defects in nanocrystalline (NC) nickel. The results show that internal friction (IF) peaks in NC nickel can be induced by cold-rolling. An IF peak, originating from dislocation activity, occurs when the strain is in the range of 9.7–32.8%. Two Bordoni peaks occur when the strain is 39.0% and an IF peak associated with deformation twinning appears when the strain is 42.6%. These results mean that deformation of NC nickel is mediated by different kinds of defects as the strain increases.

Curie Transition of NC Nickel by Mechanical Spectroscopy and Magnetization Study

Mechanical spectroscopy measurement is performed to study the internal friction of nanocrystalline ( NC) nickel with an average grain size of 23 nm from room temperature to 610 K. An internal friction peak is observed at about 550 K, which corresponds to the Curie transition process of the NC nickel according to the result of magnetization test. Moreover, the fact that the Curie temperature of NC nickel is lower than that of coarse-grained nickel is explained by an analytical model based on the weakening of cohesive energy.

The Anomalous Temperature Effect on the Ductility of Nanocrystalline Cu Films Adhered to Flexible Substrates

The effect of temperature, T, on the ductility of nanocrystalline (NC) Cu films of different thicknesses on flexible substrates is studied by uniaxial tension. It is found that the NC Cu films will fracture more easily with increasing T, exhibiting the anomalous T effect compared with that of bulk NC metals and freestanding films. Moreover, the T dependence of ductility becomes stronger for thinner films due to the larger decrement of the interfacial strength in thinner films. T-induced softening of the stretchable substrate reduces the interface constraint ability for suppressing strain localization, leading to the anomalous T effect.

FMAA-MS Investigation into Ni68Fe32 Nanoalloy with Sample Length Less than 30 mm

An investigation into the properties of nanocrystalline (NC) materials with sample lengths less than 30 mm seems to be a challenge by using conventional mechanical spectroscopy (MS). We use a newly developed frequency modulation acoustic attenuation mechanical spectroscopy (FMAA-MS) to investigate phase transition in Ni68Fe32 NC alloy (22 nm) where the length of the sample is 10 mm. An internal friction peak accompanied by an abrupt increase in resonant frequency occurs at 641 K, which originates from order-disorder phase transition, confirmed by a vibrating sample magnetometer and differential scanning calorimetry.

Internal Friction Of Bend-Deformed Nanocrystalline Nickel By Mechanical Spectroscopy

Internal friction of nanocrystalline nickel is investigated by mechanical spectroscopy from 360 K to 120 K. Two relaxation peaks are found when nanocrystalline nickel is bent up to 10% strain at room temperature and fast cooling. However, these two peaks disappear when the sample is annealed at room temperature in vacuum for ten days. The occurrence and disappearance of the two relaxation peaks can be explained by the interactions of partial dislocations and point defects in nanocrystalline materials.