Fig. 1. (a) Secondary electron micrograph (SEM) of Ti47Ni53 powders, (b) schematic diagram of the stripe rotation scanning strategy with a stripe width of 4 mm and a hatch rotation degree of 67°, (c) SLM-fabricated Ti47Ni53 block samples built on TiNi substrate, and (d) some opt-Ti47Ni53 gear parts fabricated by SLM with optimized parameters.

Fig. 2. (a) Summary results of the process parameter optimization. (b) Summary results of the internal quality varied with energy density E (E = p/(vht)), illustrated by an increased order of the laser scanning speed.

Fig. 3. (a) The phase composition of the opt-Ti47Ni53 alloy at room temperature identified by 1D HE-XRD pattern. (b) Electric resistance curves and DSC curves during the cooling and heating process.

Fig. 4. TEM images of opt-Ti47Ni53 alloy. (a) Bright-field image obtained at low-magnification. (b) High-magnification bright-field image showing the microstructural characteristics in grains. (c) Dark-field image of Ni4Ti3 precipitates obtained by double-beam analysis and a corresponding SAED pattern. (d) STEM-HAADF image of Ni4Ti3 precipitates. Dark-field images of R-phase obtained after (e) heating to a high temperature (350 K) and (f) cooling to a low temperature (120 K), respectively.

Fig. 5. (a) High-resolution TEM image of opt-Ti47Ni53 alloy. (b) Phase identification results according to the diffraction points of the FFT image in (a). The detailed distributions of (c) Ni4Ti3precipitate and (d) R-phase as well as (e) whole distribution of them are shown in the IFFT image and marked by red area. GPA strain maps for εxx the components of (f) Ni4Ti3 & B2, (g) R-phase & B2, and (h) Ni4Ti3 & R-phase.

Fig. 6. Tribological properties of the opt-Ti47Ni53 alloy. (a) The friction coefficient curves of the samples varying with time, including opt-Ti47Ni53, casting Ti47Ni53 treated by water quenching after the solution (C&Q), and commercial 20CrMnTi. (b) Summary results of the max-width and max-depth at three sampling positions after scratch testing. Schematic diagrams of (c) the ball-in-disc wearing test and (d) the scratch test. (e) Three photographs of opt-Ti47Ni53, (f) C&Q Ti47Ni53, and (g) commercial 20CrMnTi after scratch testing.

Fig. 7. Compression properties and the microscopic deformation behavior of opt-Ti47Ni53 alloy during compressive loading and unloading. (a) The compressive stress-strain cyclic curves obtained at 293 K. 1D HE-XRD patterns obtained along (b) the full azimuthal circle and (c) longitudinal direction (Φ = 90°). (d) The X-ray intensity of the B19′ (100) plane along the full azimuthal circle and (e) the lattice strain of Ni4Ti3 precipitate along the loading direction as the function of applied strain. (f) Comparison of the elastic strain of Ni4Ti3 precipitates achieved in this work and other reported hard inclusions embedded in conventional metal matrices which deform by dislocation slip [32].

Fig. 8. Multiple crystal plane diffractions of precipitation phase Ni4Ti3, R-phase, and B19′ phase along the full azimuth circle (0°-360°) at different applied strains. 180° and 360° are paralleled to the transverse direction (TD = 0°), 270° is paralleled to the direction of the longitudinal direction (LD = 90°).

Fig. 9. Diffraction intensity distributions along the azimuth circle to show (a) the texture and (b) the spatial orientation of Ni4Ti3 precipitate and B19′.

Fig. 10. (a) and (b) Schematic distributions of high-density precipitation particles with or without R-phase surrounded. (c) Spatial orientation of four precipitation variants characterized by TEM and HE-XRD, respectively. (d) The diffraction intensity distribution of the B2 along the azimuth circle obtained by in-situ HE-XRD at 373 K. (e) The crystal structure of B2 in space originated from (d). (f) Schematic diagram showing that the main reason for precipitation texture formation is the inherent B2 texture and the selected growth of precipitates formed during SLM processing.