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Ni47Ti44Nb9 alloys were successfully fabricated by laser powder bed fusion (LPBF) technique with different laser powers. The phase transformation behavior, tensile properties and shape memory response before and after heat treating were also investigated. The Ni47Ti44Nb9 LPBF alloys have good shaping properties, though a few defects were discovered. Phase transformation peaks did not appear in the as-built samples, but were observed in the heat-treated samples. The phase transformation temperatures of the heat-treated samples increase with the increase in laser power. The tension test at room temperature indicates that the LPBF samples exhibit poor tensile ductility, which may be related to the existence of pores and Ti2Ni or Ti4Ni2Ox phase during the LPBF process. However, the LPBF samples after heat treating still possess good shape memory effect (with recovery strain about 7.82–8%) and relatively high reverse transformation temperature (about 36–52.6 °C) when deformed to 8%. [ABSTRACT FROM AUTHOR]

The evolution of phase composition and microstructure such as grain size, dislocation and crystallographic texture in austenite-martensite duplex Ni 47 Ti 44 Nb 9 rolled sheets during the annealing was systematically investigated. The influence of annealing temperature on shape memory effect was also examined. The strong {001} fiber texture tested in as-rolled sheets is identified as a wrong result, which is mistakenly introduced by X-ray Diffractometer, due to the interference of martensite. Different annealing temperatures result in variation of phase composition and microstructure. For instance, in the case of 600 °C, the phase fraction of austenite increases and the dislocations develop to form tiny sub-grains due to reverse martensitic phase transformation and recovery. The texture of NiTi austenite mainly concentrates on {111}〈110〉. In the case of 950 °C, the sub-grains develop to trigger recrystallization, resulting in larger grains and decreasing of dislocations and {111}〈110〉 texture intensity. In addition, the sheets annealed at 600 °C possess higher recoverability than those of 950 °C, which can be attributed to the combined role of grain size, dislocation and crystallographic texture. • The preferred orientation of as hot-rolled sheets concentrates on {111} <110>. • Phase transformation, recovery and recrystallization determine the microstructure. • The sheets annealed at 600 °C possess higher recoverability than those of 950 °C. • Grain size, dislocation and crystallographic texture determine the recoverability. [ABSTRACT FROM AUTHOR]

This work aims to clarify the influence of texture type and intensity on the shape memory effect (SME) in NiTiNb shape memory alloy (SMA) pipe joints, especially revealing the causes for the anisotropy of SME via texture changes. Three NiTiNb rods with different intensities of the {111}<110> texture were fabricated, and their microstructures, crystalline orientation distribution functions and inverse pole figures were obtained by X-ray diffraction and electron backscatter diffraction measurements. Simultaneously, the SME was characterized by inner-diameter recoverability of the corresponding pipe joints. For a given intensity of the {111}<110> texture, the SME of the NiTiNb pipe joints strongly depended on the expansion direction due to {111}<110> orientation-induced anisotropy of SME. In addition, both the SME and anisotropy of NiTiNb pipe joints increased with the increased intensity of the {111}<110> texture. Therefore, a suitable expansion direction and strong texture intensity should be considered for high SME in NiTiNb pipe joints. [ABSTRACT FROM AUTHOR]

The NiTiHf-Nb alloy exhibits good workability as well as high-temperature shape memory property. In this work, effects of cooling rate on martensitic transformation behavior and shape memory property for Ni-rich (Ni 50.1 Ti 34.9 Hf 15) 85 Nb 15 alloy were investigated. For comparison, the martensitic transformation behavior and shape memory property of Ni 50.1 Ti 34.9 Hf 15 alloy were also investigated. As the cooling rate decreased from water cooling to furnace cooling after solution treatment, the martensitic transformation temperatures (TTs) of (Ni 50.1 Ti 34.9 Hf 15) 85 Nb 15 alloy decreased gradually, whereas the decrease was not obvious for Ni 50.1 Ti 34.9 Hf 15 alloy. The increased valence electron concentration (c v) should account for the decrease in TTs of (Ni 50.1 Ti 34.9 Hf 15) 85 Nb 15 alloy. The shape memory effect strain increased with the decrease in the cooling rate for both two alloys, and the largest shape memory effect strain of 2.6% can be obtained in furnace-cooled (Ni 50.1 Ti 34.9 Hf 15) 85 Nb 15 alloy. This enhancement in the shape memory property should be ascribed to the precipitation of H-phase in furnace-cooled (Ni 50.1 Ti 34.9 Hf 15) 85 Nb 15 alloy. • Higher shape memory effect strain could be obtained by slow cooling after solution treatment. • Higher martensitic transformation temperatures could be obtained by fast cooling after solution treatment. • The martensitic start transformation temperatures were c v dependent. • Precipitation of H-phase could be improved by addition of Nb. [ABSTRACT FROM AUTHOR]

In Fe-Mn-Al-based shape memory alloys, the essential strategy for obtaining good superelasticity is precipitating coherent B2 nano-particles by adding Ni element. In the present paper, we investigated the effect of Ni contents on the precipitation behavior of nano-ordered particles in Fe-Mn-Al-Ni alloys subjected to solution treatment followed by water quenching and air cooling, respectively. D0 3 nano-particles were precipitated in water-quenched and air-cooled specimens with the Ni content of 2.1 at.%. However, coherent B2 nano-particles were precipitated in the water-quenched and air-cooled specimens with the Ni contents of 4.0–10.8 at.%. In addition, their average diameters increased linearly with increasing Ni contents, and were 3.4–14.5 nm for the water-quenched specimens and 9.5–32.3 nm for the air-cooled specimens. The precipitation of B2 nano-particles cannot be suppressed even by water quenching owing to the formation of a miscibility gap after adding Ni element in Fe-Mn-Al-Ni alloys. • Precipitation of nano-phase could be controlled by Ni contents in FeMnAlNi alloys. • D0 3 nano-particles were precipitated when Ni content was 2.1 at.%. • Average diameters of B2 nano-phase increased linearly with increasing Ni contents. • A miscibility gap was formed by adding Ni element in FeMnAlNi alloys. [ABSTRACT FROM AUTHOR]