The effect of recovery heating rate on shape memory effect of the up-quenched Cu-8.88Al-10.27Mn（mass fraction, %） alloy was investigated by optical microscopy, electron transmission microscopy（TEM） and electrical ...The effect of recovery heating rate on shape memory effect of the up-quenched Cu-8.88Al-10.27Mn（mass fraction, %） alloy was investigated by optical microscopy, electron transmission microscopy（TEM） and electrical resistivity measurement. It is found that the shape recovery rate decreases as the heating rate decreases. It can reach 75% when the heating rate is 20 ℃/min, while it is only 8% when the heating rate is 1 ℃/min. In situ microstructure observation indicates that the dependence of shape memory effect on recovery heating rate is caused by the stabilization of twinned martensite induced by deformation. The analysis of electrical resistivity shows that the stabilization of twinned martensite may be ascribed to formation of compound defects of vacancies and dislocations at the boundaries of twinned martensite during the slow heating. The compound defects prevent the reverse transformation of twinned martensite.展开更多
The effects of different contents(0.4%, 0.7%, and 1.0%, mass fraction) of Mn or Ti additions on the micro structure, shape memory effect and the corrosion behaviour of Cu-Al-Ni shape memory alloys were studied by fiel...The effects of different contents(0.4%, 0.7%, and 1.0%, mass fraction) of Mn or Ti additions on the micro structure, shape memory effect and the corrosion behaviour of Cu-Al-Ni shape memory alloys were studied by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and electrochemical and immersion tests in NaCl solution. It was observed that the microstructure, shape memory effect and corrosion characteristics are highly sensitive to the composition variations. It was found that the highest strain recovery was with 0.7% addition of Mn or Ti. This may be attributed to the presence of precipitation with a high volume fraction and the grain refinement. The electrochemical test showed that the formation of oxide layers in both Cu-Al-Ni-Mn and Cu-Al-Ni-Ti shape memory alloys(SMAs) provided good passivation which enhanced the corrosion resistance of the alloys. Immersion test showed that in Cu-Al-Ni-Mn SMAs, pitting corrosion occurred through feebleness in the oxide layer. A corrosion product adjacent to the pits was rich in Al/Mn oxide and depleted in Cu while inside of the pit it was rich in Cu. In Cu-Al-Ni-Ti SMAs, localized corrosion occurred on the surface of the specimens and dealuminization attack was also observed in the matrix.展开更多
文摘The effect of recovery heating rate on shape memory effect of the up-quenched Cu-8.88Al-10.27Mn（mass fraction, %） alloy was investigated by optical microscopy, electron transmission microscopy（TEM） and electrical resistivity measurement. It is found that the shape recovery rate decreases as the heating rate decreases. It can reach 75% when the heating rate is 20 ℃/min, while it is only 8% when the heating rate is 1 ℃/min. In situ microstructure observation indicates that the dependence of shape memory effect on recovery heating rate is caused by the stabilization of twinned martensite induced by deformation. The analysis of electrical resistivity shows that the stabilization of twinned martensite may be ascribed to formation of compound defects of vacancies and dislocations at the boundaries of twinned martensite during the slow heating. The compound defects prevent the reverse transformation of twinned martensite.
基金the Malaysian Ministry of Higher Education (MOHE) and Universiti Teknologi Malaysia for providing the financial support and facilities for this research, under Grant No. R.J130000.7824.4F150
文摘The effects of different contents(0.4%, 0.7%, and 1.0%, mass fraction) of Mn or Ti additions on the micro structure, shape memory effect and the corrosion behaviour of Cu-Al-Ni shape memory alloys were studied by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and electrochemical and immersion tests in NaCl solution. It was observed that the microstructure, shape memory effect and corrosion characteristics are highly sensitive to the composition variations. It was found that the highest strain recovery was with 0.7% addition of Mn or Ti. This may be attributed to the presence of precipitation with a high volume fraction and the grain refinement. The electrochemical test showed that the formation of oxide layers in both Cu-Al-Ni-Mn and Cu-Al-Ni-Ti shape memory alloys(SMAs) provided good passivation which enhanced the corrosion resistance of the alloys. Immersion test showed that in Cu-Al-Ni-Mn SMAs, pitting corrosion occurred through feebleness in the oxide layer. A corrosion product adjacent to the pits was rich in Al/Mn oxide and depleted in Cu while inside of the pit it was rich in Cu. In Cu-Al-Ni-Ti SMAs, localized corrosion occurred on the surface of the specimens and dealuminization attack was also observed in the matrix.
