A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting.This is attributed to the change from a layer-by-layer to vo...A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting.This is attributed to the change from a layer-by-layer to volume solidification mode with Al content increasing,which causes a change in grain shape from columnar to equiaxed.Furthermore,when compared with conventional casting,suction casting optimizes the microstructure of the alloy by refining the grain size and ensuring a homogeneous distribution of Ti2 Ni and Ni_(2)TiAl phases.The high cooling rate of suction casting also delays the formation ofβ'-Ni_(2)TiAl phase.Finally,this fine microstructure and uniform distribution of intermetallic phases result in the ultimate compressive strength of up to 2463.7 MPa,representing an improvement of 370 MPa over conventionally cast NiTi-Al alloy.展开更多
BACKGROUND Colonic stents are increasingly used to treat acute malignant colonic obstructions.The Wall Flex and Niti-S D type stents are the commonly used self-expandable metallic stents available in Japan since 2012....BACKGROUND Colonic stents are increasingly used to treat acute malignant colonic obstructions.The Wall Flex and Niti-S D type stents are the commonly used self-expandable metallic stents available in Japan since 2012.Wall Flex stent has a risk of stentrelated perforation because of its axial force,while the Niti-S D type stent has a risk of obstructive colitis because of its weaker radial force.Niti-S MD type stents not only overcome these limitations but also permit delivery through highly flexible-tipped smaller-caliber colonoscopes.AIM To compare the efficacy and safety of the newly developed Niti-S MD type colonic stents.METHODS This single-center retrospective observational study included 110 patients with endoscopic self-expandable metallic stents placed between November 2011 and December 2018:Wall Flex(Group W,n=37),Niti-S D type(Group N,n=53),and Niti-S MD type(Group MD,n=20).The primary outcome was clinical success,defined as a resolution of obstructive colonic symptoms,confirmed by clinical and radiological assessment within 48 h.The secondary outcome was technical success,defined as accurate stent placement with adequate stricture coverage on the first attempt without complications.RESULTS The technical success rate was 100%in Groups W,N,and MD,and the overall clinical success rate was 89.2%(33/37),96.2%(51/53),and 100%(20/20)in Groups W,N,and MD,respectively.Early adverse events included pain(3/37,8.1%),poor expansion(1/37,2.7%),and fever(1/37,2.6%)in Group W and perforation due to obstructive colitis(2/53,3.8%)in Group N(likely due to poor expansion).Late adverse events(after 7 d)included stent-related perforations(4/36,11.1%)and stent occlusion(1/36,2.8%)in Group W and stent occlusion(2/51,3.9%)in Group N.The stent-related perforation rate in Group W was significantly higher than that in Group N(P<0.05).No adverse event was observed in Group MD.CONCLUSION In our early and limited experience,the newly developed Niti-S MD type colonic stent was effective and safe for treating acute malignant colonic obstruction.展开更多
By liquid metal cooling(LMC) process,the Ni-43Ti-4Al-2Nb-2Hf(%,atomic fraction) alloy was directionally solidified(DS).The microstructure and tensile properties at room and elevated temperature were investigated.It wa...By liquid metal cooling(LMC) process,the Ni-43Ti-4Al-2Nb-2Hf(%,atomic fraction) alloy was directionally solidified(DS).The microstructure and tensile properties at room and elevated temperature were investigated.It was found that the DS process significantly improves the room temperature tensile strength,increasing by 70% compared with the as-cast alloy.After appropriate heat treatment(HT),the average tensile strength reaches above 1900 MPa,nearly twice of the as-cast one.At 800 and 900 ℃,the tensile strengths are about 308 and 169 MPa,respectively.展开更多
NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The...NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The microstructure and mechanical properties at room temperature and high temperature were investigated through scanning electron microscope （SEM）, X-ray diffraction （XRD）, and tensile tests. Results show that the micro- structure of as-forged Ni-43Ti--4AI-2Nb-2Hf alloy con- sists of NiTi matrix, Ti2Ni phase, and Hf-rich phase. The simultaneous addition of Nb and Hf, which have strong affinities for Ti sites, promotes the precipitation of Hf-rich phases along the grain boundaries. The tensile strengths of Ni-43Ti-4A1-2Nb-2Hf alloy are dramatically increased compared with the ternary Ni-46Ti-4A1 alloy. At room temperature and 650℃, the yield stress of Ni--43Ti-4Al- 2Nb-2Hf alloy reaches 1,070 and 610 MPa, respectively, which are 30 % and 150 % higher than those of Ni--46Ti- 4Al alloy. The improved tensile property results from the solid solution strengthening by Nb and Hf, as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.展开更多
Postoperative biliary strictures are the most common cause of benign biliary stricture in Western countries, secondary to either operative injury or bile duct anastomotic stricture following orthotopic liver transplan...Postoperative biliary strictures are the most common cause of benign biliary stricture in Western countries, secondary to either operative injury or bile duct anastomotic stricture following orthotopic liver transplantation(OLT).Surgery or endoscopic interventions are the mainstay of treatment for benign biliary strictures.We aim to report the outcome of 2 patients with refractory anastomotic biliary stricture post-OLT,who had successful temporary placement of a prototype removable covered self-expandable metal stent(RCSEMS).These 2 patients(both men,aged 44 and 53 years)were given temporary placement of a prototype RCSEMS (8.5 Fr gauge delivery system,8 mm×40 mm stent dimensions)in the common bile duct across the biliary stricture.There was no morbidity associated with stent placement and removal in these 2 cases.Clinical parameters improved after the RCSEMS placement.Longterm biliary patency was achieved in both the patients. No further biliary intervention was required within 14 and 18 mo follow-up after stent removal.展开更多
The microstructural evolution of Ni–42Ti–7Al and Ni–41Ti–7Al alloys as a function of solution and aging heat treatment was investigated using transmission electron microscopy（TEM）, electron probe, and X-ray diff...The microstructural evolution of Ni–42Ti–7Al and Ni–41Ti–7Al alloys as a function of solution and aging heat treatment was investigated using transmission electron microscopy（TEM）, electron probe, and X-ray diffraction（XRD）. The results reveal that the volume fraction of Ti2 Ni phase as well as its composition does not change significantly after as-solution treated at 1200 °C and aged at 850 °C. At the early stage of the aging treatment at 850 °C for 1 h, the cuboidal β＇ precipitate keeps coherency with the matrix; further aging, β＇ precipitate coarsens, and the semicoherency between the β/β＇ two phases are observed.The shape of coarsened β＇ precipitates changes to the globule, and the interface dislocations are introduced accompanied by the occurrence of semicoherent precipitates. Under the same heat treatment, compared to the Ni–42Ti–7Al alloy, the lattice misfits of the Ni–41Ti–7Al alloy between the β and β＇ two phases are larger, so the β＇ precipitates in Ni–41Ti–7Al alloy are coarsened severely and easily lose coherency with the matrix. The thermal stability of Ni–41Ti–7Al alloy is much worse when aging at 850 °C.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos.51101003 and 51471012)
文摘A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting.This is attributed to the change from a layer-by-layer to volume solidification mode with Al content increasing,which causes a change in grain shape from columnar to equiaxed.Furthermore,when compared with conventional casting,suction casting optimizes the microstructure of the alloy by refining the grain size and ensuring a homogeneous distribution of Ti2 Ni and Ni_(2)TiAl phases.The high cooling rate of suction casting also delays the formation ofβ'-Ni_(2)TiAl phase.Finally,this fine microstructure and uniform distribution of intermetallic phases result in the ultimate compressive strength of up to 2463.7 MPa,representing an improvement of 370 MPa over conventionally cast NiTi-Al alloy.
文摘BACKGROUND Colonic stents are increasingly used to treat acute malignant colonic obstructions.The Wall Flex and Niti-S D type stents are the commonly used self-expandable metallic stents available in Japan since 2012.Wall Flex stent has a risk of stentrelated perforation because of its axial force,while the Niti-S D type stent has a risk of obstructive colitis because of its weaker radial force.Niti-S MD type stents not only overcome these limitations but also permit delivery through highly flexible-tipped smaller-caliber colonoscopes.AIM To compare the efficacy and safety of the newly developed Niti-S MD type colonic stents.METHODS This single-center retrospective observational study included 110 patients with endoscopic self-expandable metallic stents placed between November 2011 and December 2018:Wall Flex(Group W,n=37),Niti-S D type(Group N,n=53),and Niti-S MD type(Group MD,n=20).The primary outcome was clinical success,defined as a resolution of obstructive colonic symptoms,confirmed by clinical and radiological assessment within 48 h.The secondary outcome was technical success,defined as accurate stent placement with adequate stricture coverage on the first attempt without complications.RESULTS The technical success rate was 100%in Groups W,N,and MD,and the overall clinical success rate was 89.2%(33/37),96.2%(51/53),and 100%(20/20)in Groups W,N,and MD,respectively.Early adverse events included pain(3/37,8.1%),poor expansion(1/37,2.7%),and fever(1/37,2.6%)in Group W and perforation due to obstructive colitis(2/53,3.8%)in Group N(likely due to poor expansion).Late adverse events(after 7 d)included stent-related perforations(4/36,11.1%)and stent occlusion(1/36,2.8%)in Group W and stent occlusion(2/51,3.9%)in Group N.The stent-related perforation rate in Group W was significantly higher than that in Group N(P<0.05).No adverse event was observed in Group MD.CONCLUSION In our early and limited experience,the newly developed Niti-S MD type colonic stent was effective and safe for treating acute malignant colonic obstruction.
基金supported by the National Natural Science Foundation of China (No. 51101003)
文摘By liquid metal cooling(LMC) process,the Ni-43Ti-4Al-2Nb-2Hf(%,atomic fraction) alloy was directionally solidified(DS).The microstructure and tensile properties at room and elevated temperature were investigated.It was found that the DS process significantly improves the room temperature tensile strength,increasing by 70% compared with the as-cast alloy.After appropriate heat treatment(HT),the average tensile strength reaches above 1900 MPa,nearly twice of the as-cast one.At 800 and 900 ℃,the tensile strengths are about 308 and 169 MPa,respectively.
基金supported by the National Natural Science Foundation of China (No. 51201016)
文摘NiTi-Al-based alloys are promising high-tem- perature structural materials for aerospace and astronautics applications. A new NiTi-Al-based alloy Ni--43Ti-4AI- 2Nb-2Hf （at%） was processed via isothermal forging. The microstructure and mechanical properties at room temperature and high temperature were investigated through scanning electron microscope （SEM）, X-ray diffraction （XRD）, and tensile tests. Results show that the micro- structure of as-forged Ni-43Ti--4AI-2Nb-2Hf alloy con- sists of NiTi matrix, Ti2Ni phase, and Hf-rich phase. The simultaneous addition of Nb and Hf, which have strong affinities for Ti sites, promotes the precipitation of Hf-rich phases along the grain boundaries. The tensile strengths of Ni-43Ti-4A1-2Nb-2Hf alloy are dramatically increased compared with the ternary Ni-46Ti-4A1 alloy. At room temperature and 650℃, the yield stress of Ni--43Ti-4Al- 2Nb-2Hf alloy reaches 1,070 and 610 MPa, respectively, which are 30 % and 150 % higher than those of Ni--46Ti- 4Al alloy. The improved tensile property results from the solid solution strengthening by Nb and Hf, as well as the dispersion hardening of the Ti2Ni and Hf-rich phases.
文摘Postoperative biliary strictures are the most common cause of benign biliary stricture in Western countries, secondary to either operative injury or bile duct anastomotic stricture following orthotopic liver transplantation(OLT).Surgery or endoscopic interventions are the mainstay of treatment for benign biliary strictures.We aim to report the outcome of 2 patients with refractory anastomotic biliary stricture post-OLT,who had successful temporary placement of a prototype removable covered self-expandable metal stent(RCSEMS).These 2 patients(both men,aged 44 and 53 years)were given temporary placement of a prototype RCSEMS (8.5 Fr gauge delivery system,8 mm×40 mm stent dimensions)in the common bile duct across the biliary stricture.There was no morbidity associated with stent placement and removal in these 2 cases.Clinical parameters improved after the RCSEMS placement.Longterm biliary patency was achieved in both the patients. No further biliary intervention was required within 14 and 18 mo follow-up after stent removal.
基金financially supported by the National Natural Science Foundation of China (NSFC) (No. 5110100)
文摘The microstructural evolution of Ni–42Ti–7Al and Ni–41Ti–7Al alloys as a function of solution and aging heat treatment was investigated using transmission electron microscopy（TEM）, electron probe, and X-ray diffraction（XRD）. The results reveal that the volume fraction of Ti2 Ni phase as well as its composition does not change significantly after as-solution treated at 1200 °C and aged at 850 °C. At the early stage of the aging treatment at 850 °C for 1 h, the cuboidal β＇ precipitate keeps coherency with the matrix; further aging, β＇ precipitate coarsens, and the semicoherency between the β/β＇ two phases are observed.The shape of coarsened β＇ precipitates changes to the globule, and the interface dislocations are introduced accompanied by the occurrence of semicoherent precipitates. Under the same heat treatment, compared to the Ni–42Ti–7Al alloy, the lattice misfits of the Ni–41Ti–7Al alloy between the β and β＇ two phases are larger, so the β＇ precipitates in Ni–41Ti–7Al alloy are coarsened severely and easily lose coherency with the matrix. The thermal stability of Ni–41Ti–7Al alloy is much worse when aging at 850 °C.
