Effects of Cooling Rates on Internal Friction in Cu-Al-Ni Ternary Alloys

Abstract

Measurements of internal friction and Young’s modulus were made by a bending vibration method with a frequency of about 520∼680 Hz in a temperature range from 293 K to 433 K on the Cu-13.8 wt%Al-7.9 wt%Ni alloys obtained at various cooling rates after solution heat-treatment at 1223 K for 1.8×10³ s, where effects of cooling rates on the temperature behavior and the values of internal friction were discussed.
It was found that the main-peak (P_m) always appeared at a constant temperature of 323 K in all specimens which were cooled at the rates between 3.8×10⁻² and 53 K/s, and besides P_m sub-peak (P_s) appeared above 323 K in the specimens which were cooled at the rate of 5.5 K/s or more.
With increasing cooling rates, the values of P_s increased and the temperature of P_s had a tendency to become lower. Curves of Young’s modulus and differential scanning calorimetry showed the minimum value and the maximum value respectively at the temperature appearing P_s; showing that P_s is the phase transformation peak.
The values of P_m kept constant at the rate of 5.5 K/s or more after showing a linear increase with increasing cooling rate less than 5.5 K/s, where the values of P_m depended on the contents of γ′ martensite, and the single phase of γ′ martensite could be obtained from the specimens cooled at the rates beyond 5.5 K/s.
From the above-mentioned considerations, it was suggested that the P_m was the twin-boundary relaxation peak of γ′ martensite.