Search

The phase constitutions of Ti–35·4Nb and Ti–35·4Nb–0·05C (wt-%) alloys with different heat treatments were detected using X-ray diffraction experiments. Compressive properties were tested using a 100 kN MTS testing machine for the two alloys. It was shown that the phases of the as sintered alloys consist of α and β phases. As sintered Ti–35·4Nb–0·05C alloy contains less β phase and more α phase compared with as sintered Ti–35·4Nb alloy. The phases of as quenched alloys are composed of α″ and βM phases. As quenched Ti–35·4Nb–0·05C alloy has more α″ phase and less βM phase compared with as quenched Ti–35·4Nb alloy. As quenched Ti–35·4Nb–0·05C alloy has a lower elastic modulus and yield stress than as quenched Ti–35·4Nb alloy, which is resulted of more α″ phase in as quenched Ti–35·4Nb–0·05C alloy. The elastic modulus and yield stress of as quenched Ti–Nb alloys are less than those of the as sintered Ti–Nb alloys with identical compositions since both α″ and βM phases in as quenched Ti–Nb alloys have...

The internal friction of Ti-35.4Nb-0.05C (wt.%) was investigated using a dynamic mechanical analysis (DMA) Q800 from TA Instruments. It has been shown that a relaxational peak is observed in the water-quenched Ti-35.4-Nb-0.05C alloy on tanδ-temperature curve. The activation energy and pre-exponential factor of the peak are Hq=1.82±0.1 eV and τ0q=1.7×10-19±1s, respectively. The activation energy value is a little larger than that of the water-quenched Ti-35.4-Nb alloy. The peak height is decreased compared with the water-quenched Ti-35.4-Nb alloy.

Binary Fe-Al alloy ingots with 29 at. %Al were prepared with commercially pure Fe and Al in a vacuum induction furnace. The specimens used in the internal friction measurement were cut using an electric sparkle machine from the ingots into a dimension 68×1.7×0.9 mm3. The heat treatment was performed in such regimes as heating temperature 900°C and holding time 1 hour in an argon atmosphere followed by furnace cooling or air cooling. The air-cooled samples were then aged at 350°C for different time to achieve the different degree of disorder. The internal fiction-temperature spectra of the air-cooled Fe71Al29alloy were measured during both heating and cooling using a computer-controlled automatic inverted torsion pendulum through free-decay and forced vibration methods. It has been found that three internal friction peaks appear during heating at 180°C termed as P1, 340°C termed as P2 and 510°C termed as P3 in air-cooled specimens, respectively. P1 and P2 peaks disappear and P3 is retained during cooling. XRD results show that the air-cooled Fe71Al29alloy is disordered and the furnace-cooled specimen possesses ordered structures. The air-cooled specimen presents similar diffraction peaks to the furnace-cooled specimen after it is heated to 650°C and then in-situ cooled to room temperature. Ageing has great influence on the P1 and P2 peaks for the air-cooled Fe71Al29alloy. The height of P1 and P2 peaks is decreased with increasing aging time, which is due to the reduction in the disorder degree of the air-cooled specimen.

The low frequency damping capacity of a strained Fe-31.36Mn-3.15Si (wt.%) alloy has been investigated using a multifunctional internal friction apparatus (MFIFA) through the free decay and forced vibration method. The high damping source is proposed to have originated from the irreversible movements of e/γ boundaries, being amplitude-dependent damping. An internal friction peak appears on the internal friction-temperature curves at about 280°C during heating from room temperature to 400 °C and the peak height is drastically reduced during subsequent in situ cooling. The peak height increases with increasing T/f. It has been suggested that the internal friction peak is resulted from the e → γ transformation during heating.

Low-frequency internal friction investigation of reverse martensitic transformation in oil-quenched Ni64Al36 alloy has been carried out using a multifunctional internal friction apparatus from room temperature to 400 °C and additionally differential scanning calorimetry and X-ray diffraction experiments were also completed. It has been shown that an internal friction peak presents at about 220 °C in the internal friction–temperature curve during heating for the oil-quenched Ni64Al36 alloy but not for the furnace-cooled Ni64Al36 alloy. The peak still appears during cooling and the peak temperature shifts to lower temperature. The changes of the peak temperature positions cannot be visibly observed when the vibration frequency is changed. The peak heights increase with decreasing vibration frequency and increasing heating rate, being linearly directly proportional to It has been suggested that the internal friction peak results from reverse martensitic transformation of L10 γ during heating and originates from martensitic transformation of γ L10 during the subsequent cooling process. The influence of the thermal cycles on the transformation is not observed for the limited thermal cycles. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The magnetomechanical hysteresis damping of Fe-Al alloys has been investigated using a computer-controlled automatic inverted torsion pendulum. It has been shown that Al content and heat treatment have a significant effect on the magnetomechanical hysteresis damping of the alloys. The Fe-10.5 (at.%)Al alloy has an optimal damping capacity after it was air-cooled from 900°C and the Fe-Al alloys with 29(at.)%Al and 38(at.)%Al exhibit rather low damping capacity after undergoing the same heat treatment because of decreasing magnetism. The water-quenched or as-cast specimens cannot form high damping due to high internal stress. An appropriate heating temperature in heat treatments is essential to obtain high damping.