Influence of the Degree of Hydration on the Relaxation Microheterogeneity of Segmental Mobility in PVA

The study of local dissipative processes by the method of free-damped torsional oscillations excited in polyvinyl alcohol (PVA) showed the presence of three loss peaks in the internal friction spectrum in different temperature ranges of this spectrum [1].

Anelastic Effects on Martensitic Carbon Steels during First Stage of Tempering

The evolution of martensitic carbon steel during low temperature tempering was studied using internal friction. The steel containing 0.71wt.% carbon was heated at 1093K for 5min and then rapidly cooled into water (quenched), and tempered for 10 min at 340, 380, 420 and 460K. Additionally, other samples were tempered at 380K for 1 and 20 hours. Internal friction was measured by using a forced vibration pendulum, in a temperature range from 300 to 600K, with deformation amplitude 3 x 10-6 and temperature rate of 0.8 K/min. The internal friction spectrum is decomposed into three Debye peaks: P1 at 380K, P2 at 420K and P3 at 480K, for 3 Hz. P1 is attributed to the epsilon carbide precipitation. P2 and P3 are associated to the dislocation relaxation process. P2 appears when dislocations are pinning with epsilon carbide and P3 appears when dislocations are pinning with cementite carbide.

Anelastic Effects of Phase Decomposition in 14-Carat AuAgCu Alloy

A relaxation peak has been observed in the internal friction spectrum of 18-carat AuAgCu yellow gold alloys at about 750K for 0.5Hz. It is related to the presence of grain boundaries, since it is absent in the spectrum of single crystals. For the 14-carat yellow gold alloy (Au38%Ag32%Cu30%), a phase decomposition between silver-rich and copper-rich solid solution occurs in the same temperature range. The effects of the phase decomposition on the internal friction and the dynamic modulus are studied by isochronal and isothermal measurements and correlated with the microstructure evolution. Upon cooling, the phase decomposition starts at grain boundaries at about 840K, producing a fine lamellar structure, and the grain boundary peak amplitude strongly decreases. As the phase decomposition progresses at the interior of the grains upon further cooling, the internal friction background increases. It remains very high in heating until solid solution homogenisation, which occurs above 890K. Such an increase of the internal friction background is observed also in the single crystalline alloy and may be attributed to the interfaces between lamellae of the silver and copper-rich phase.