Ferromagnetic shape memory alloys （FSMAs） such as NiMnGa, FePd and FePt are attractive as a new magnetic actuator material. They show a large magnetic-field-induced strain of 3% 9% due to the variant rearrangement. ...Ferromagnetic shape memory alloys （FSMAs） such as NiMnGa, FePd and FePt are attractive as a new magnetic actuator material. They show a large magnetic-field-induced strain of 3% 9% due to the variant rearrangement. Recently, the present authors have reported that in the Ni-Ga-Fe alloy the martensitic transformationfrom the B2 and/or the L21 structures into a seven-layer or five-layer modulated structure occurs upon cooling. In this alloy system, however, it is impossible to obtain a martensite phase at RT with a Curie temperature （TC） higher than 100 ℃. In this work,the effects of substitution of Co for Ni on the martensitic and magnetic transformations,crystal structures and phase equilibria in Ni-Ga-Fe alloys were studied.Ni-Ga-Fe-Co alloys were prepared by induction melting under an argon atmosphere.Small pieces of specimens were taken from the ingot and homogenized at 1433 K for 24 h followed by quenching in water. The obtained specimens were aged at 773 K for 24 h and then quenched. The compositions of each phase were determined by energy dispersion X-ray spectroscopy （EDX）. The martensitic transformation temperatures and TC were measured by differential scanning calorimetry （DSC） and vibrating sample magnetometer （VSM） measurement. The crystal structure of martensite phase was observed by X-ray diffractmeter （XRD） and transmission electron microscope （TEM）.The Curie temperature TC was increased with increasing Co content while the martensitic transformation temperature slightly decreased. In the Ni<sup>54-x Ga<sup>27 Fe<sup>19 Cox ,TC increases from 303 K to 408 K with increasing Co content from x=0 to x=6. The crystal structure of the martensite phase and the phase equiribria in the Ni-Fe-Ga-Co alloys will be also presented.展开更多
It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few system...It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp rnartensitic transformation and the SM effect were investigated in Co-A1 binary alloys(mole fraction of Al=0-16%). The γ/ε rnartensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60℃ at x(Al)=0 to 150℃ at x(Al) = 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4% (mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcpfee → reverse transformation above 200℃. The SM effect was significantly improved by precipitation of β (I32) phase and the max[real shape recovery strain of 2.2 % was obtained, which can be explained by precipitation hardening. The crystallographic orientations between the β, εand γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690℃ and 120 emu/g, respectively. It is concluded that the Co-A1 alloys hold promise as new high-temperature and ferromagnetic SM alloys.展开更多
Recently, minimally invasive surgeries using guide-wire, catheter, stent etc. have spread rapidly as the diagnosis and the medical treatment for a cancer, a disease in a circulatory organ etc. Currently, further maneu...Recently, minimally invasive surgeries using guide-wire, catheter, stent etc. have spread rapidly as the diagnosis and the medical treatment for a cancer, a disease in a circulatory organ etc. Currently, further maneuverability and functionability of those devices are strongly desired in order to be used widely and safely. Although Ti-Ni shape memory alloys have been used in medical devices such orthodontic wire, guide-wire, it has been suspected that Ni is allergenic and carcinogenic to the human body. Thus the development of Ni-free shape memory alloys has been strongly required. Recently, several Ni-free beta-titanium alloys such as Ti-Mo-Al, Ti-Mo-Ga, Ti-Nb-Al have been developed as new-type shape memory alloys. We have been studying Ti-Mo based beta-titanium alloys and Ti-Mo-Sn alloy has constantly super elasticity of 3%.The purpose of present study is to propose the micro catheter with thin wall and high flexibility using To-Mo-Sn alloys tube on the basis of its mechanical properties.展开更多
文摘Ferromagnetic shape memory alloys （FSMAs） such as NiMnGa, FePd and FePt are attractive as a new magnetic actuator material. They show a large magnetic-field-induced strain of 3% 9% due to the variant rearrangement. Recently, the present authors have reported that in the Ni-Ga-Fe alloy the martensitic transformationfrom the B2 and/or the L21 structures into a seven-layer or five-layer modulated structure occurs upon cooling. In this alloy system, however, it is impossible to obtain a martensite phase at RT with a Curie temperature （TC） higher than 100 ℃. In this work,the effects of substitution of Co for Ni on the martensitic and magnetic transformations,crystal structures and phase equilibria in Ni-Ga-Fe alloys were studied.Ni-Ga-Fe-Co alloys were prepared by induction melting under an argon atmosphere.Small pieces of specimens were taken from the ingot and homogenized at 1433 K for 24 h followed by quenching in water. The obtained specimens were aged at 773 K for 24 h and then quenched. The compositions of each phase were determined by energy dispersion X-ray spectroscopy （EDX）. The martensitic transformation temperatures and TC were measured by differential scanning calorimetry （DSC） and vibrating sample magnetometer （VSM） measurement. The crystal structure of martensite phase was observed by X-ray diffractmeter （XRD） and transmission electron microscope （TEM）.The Curie temperature TC was increased with increasing Co content while the martensitic transformation temperature slightly decreased. In the Ni<sup>54-x Ga<sup>27 Fe<sup>19 Cox ,TC increases from 303 K to 408 K with increasing Co content from x=0 to x=6. The crystal structure of the martensite phase and the phase equiribria in the Ni-Fe-Ga-Co alloys will be also presented.
文摘It is known that pure Co undergoes martensitic transformation from γ phase (fcc) to ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400 ℃, however, there have been few systematic works on the SM effect in Co and Co-based alloys. In this study, the fcc/hcp rnartensitic transformation and the SM effect were investigated in Co-A1 binary alloys(mole fraction of Al=0-16%). The γ/ε rnartensitic transformation temperatures were found from the DSC measurements to decrease with increasing Al content, while the transformation temperature hystereses were observed to increase from 60℃ at x(Al)=0 to 150℃ at x(Al) = 16%. The SM effect evaluated by a conventional bending test was enhanced by the addition of Al over 4% (mole fraction) and Co-Al alloys containing over 10%(mole fraction) exhibit a good SM effect associated with the hcpfee → reverse transformation above 200℃. The SM effect was significantly improved by precipitation of β (I32) phase and the max[real shape recovery strain of 2.2 % was obtained, which can be explained by precipitation hardening. The crystallographic orientations between the β, εand γ phases were also determined. Finally, the magnetic properties were investigated and it was found that the Curie temperature and saturation magnetization of Co-14% Al(mole fraction) are 690℃ and 120 emu/g, respectively. It is concluded that the Co-A1 alloys hold promise as new high-temperature and ferromagnetic SM alloys.
文摘Recently, minimally invasive surgeries using guide-wire, catheter, stent etc. have spread rapidly as the diagnosis and the medical treatment for a cancer, a disease in a circulatory organ etc. Currently, further maneuverability and functionability of those devices are strongly desired in order to be used widely and safely. Although Ti-Ni shape memory alloys have been used in medical devices such orthodontic wire, guide-wire, it has been suspected that Ni is allergenic and carcinogenic to the human body. Thus the development of Ni-free shape memory alloys has been strongly required. Recently, several Ni-free beta-titanium alloys such as Ti-Mo-Al, Ti-Mo-Ga, Ti-Nb-Al have been developed as new-type shape memory alloys. We have been studying Ti-Mo based beta-titanium alloys and Ti-Mo-Sn alloy has constantly super elasticity of 3%.The purpose of present study is to propose the micro catheter with thin wall and high flexibility using To-Mo-Sn alloys tube on the basis of its mechanical properties.
