Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidifi...Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidification and extmpolating this function to zero. This limit was exceeded first in the binary alloy undereooled by about 320K.The effect of liquid undercooling on the respective microstructure evolution was studied by optical metallogrnphy. The hypercooled microstructure contains rcsidual fragments within grain boundaries and is quite different from those obtained at undercoolings below 310K. The finding indicated the existence of dendrite break up. The dendrite break up may be induced either by remelting or by stress. By considering hyperrooling conditions and comparing two grain ndnement microstructures observed at small and larpe undereoolings, the forms of dendrite break up and the grain refinement mechanism exceeding the hypereooling limit are further discussed.展开更多
Ni_(25)Ti_(50)Cu_(25) shape memory particle/Al matrix composite was prepared by hot pressing and further extrusion.The Ni_(25)Ti_(50)Cu_(25) particles embeded in Al matrix still keep B19 and B19 structure,and have a g...Ni_(25)Ti_(50)Cu_(25) shape memory particle/Al matrix composite was prepared by hot pressing and further extrusion.The Ni_(25)Ti_(50)Cu_(25) particles embeded in Al matrix still keep B19 and B19 structure,and have a good thermal-elastic martensitic transition with 6K thermal hysteresis,the phase transition temperatures remaining constant during cycling. The scratching force of Ni_(25)Ti_(50)Cu_(25) particle is two times that of Al matrix,When the scratching force is larger than 4.2N, the Ni_(25)Ti_(50)Cu_(25) particle is separated from Al matrix.展开更多
The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre- sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction...The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre- sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction (XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were prepared by mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas- eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most of their hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. The crystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphous Mg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep- tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on the crystallization of amorphous alloys was discussed.展开更多
The microstructure and transformation behavior of Ni50Ti45Ta5 shape memory alloy were investigated using optical microscope, EPMA, X-ray diffraction and DSC methods. The microstructures are primary NiTi dendrite and n...The microstructure and transformation behavior of Ni50Ti45Ta5 shape memory alloy were investigated using optical microscope, EPMA, X-ray diffraction and DSC methods. The microstructures are primary NiTi dendrite and net-like eutectic. The room temperature phases of this alloy are B2 austenite with lattice parameter a=0.302 5 nm, B19′ martensite with lattice parameters a=0.290 nm, b=0.412 nm and c=0.473 nm, β=98.2° and a body center cubic β-Ta with lattice parameter a′=0.330 4 nm. A maximal shape memory recovery strain of 5.6% is obtained after deformation to （6.4%.） The reverse transformation temperatures increase and the forward transformation temperatures decrease in the first heating/cooling cycle after deformation. The reverse transformation heat also increases with increasing deformation. The phenomenon disappears in the second heating/cooling cycle. It is closely related to the variation of elastic energy and irreversible energies during deformation.展开更多
文摘Undereooling eoperiments on binary Ni50 Cu50 alloy melts were conducted. The hypercooling limit of this alloy, which is about 310K, was evaluated by mcasuring plateau time needed for the interkendritic liquid solidification and extmpolating this function to zero. This limit was exceeded first in the binary alloy undereooled by about 320K.The effect of liquid undercooling on the respective microstructure evolution was studied by optical metallogrnphy. The hypercooled microstructure contains rcsidual fragments within grain boundaries and is quite different from those obtained at undercoolings below 310K. The finding indicated the existence of dendrite break up. The dendrite break up may be induced either by remelting or by stress. By considering hyperrooling conditions and comparing two grain ndnement microstructures observed at small and larpe undereoolings, the forms of dendrite break up and the grain refinement mechanism exceeding the hypereooling limit are further discussed.
文摘Ni_(25)Ti_(50)Cu_(25) shape memory particle/Al matrix composite was prepared by hot pressing and further extrusion.The Ni_(25)Ti_(50)Cu_(25) particles embeded in Al matrix still keep B19 and B19 structure,and have a good thermal-elastic martensitic transition with 6K thermal hysteresis,the phase transition temperatures remaining constant during cycling. The scratching force of Ni_(25)Ti_(50)Cu_(25) particle is two times that of Al matrix,When the scratching force is larger than 4.2N, the Ni_(25)Ti_(50)Cu_(25) particle is separated from Al matrix.
文摘The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre- sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction (XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were prepared by mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas- eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most of their hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. The crystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphous Mg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep- tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on the crystallization of amorphous alloys was discussed.
文摘The microstructure and transformation behavior of Ni50Ti45Ta5 shape memory alloy were investigated using optical microscope, EPMA, X-ray diffraction and DSC methods. The microstructures are primary NiTi dendrite and net-like eutectic. The room temperature phases of this alloy are B2 austenite with lattice parameter a=0.302 5 nm, B19′ martensite with lattice parameters a=0.290 nm, b=0.412 nm and c=0.473 nm, β=98.2° and a body center cubic β-Ta with lattice parameter a′=0.330 4 nm. A maximal shape memory recovery strain of 5.6% is obtained after deformation to （6.4%.） The reverse transformation temperatures increase and the forward transformation temperatures decrease in the first heating/cooling cycle after deformation. The reverse transformation heat also increases with increasing deformation. The phenomenon disappears in the second heating/cooling cycle. It is closely related to the variation of elastic energy and irreversible energies during deformation.
