Fig. 1. Two types of additive manufacturing processes mostly used in shape memory alloys (SMAs) forming. (a) L-PBF process principle^[64]; (b) L-PBF process parameters^[65]; (c) L-PBF system^[65]; (d) L-DED process principle^[64]; (e) L-DED process parameters^[66]; (f) L-DED system^[67]

Fig. 2. Mechanism of elastocaloric effect of SMAs^[71]. (a) Stress loading accompanies temperature increasing; (b) stress unloading accompanies temperature decreasing

Fig. 3. Elastocaloric performance of additive manufactured elastocaloric materials with excellent refrigeration capacity. (a)‒(b) Laser-directed energy deposited NiTi alloys exhibit quasi-linear superelasticity with less energy dissipation and a large adiabatic temperature drop of -7.5 ℃^[74]; (c) adiabatic temperature drop of NiMnSn materials under an additional applied magnetic field is greater than that under a single stress field because the applied magnetic field stabilizes the austenitic phase and reduces the residual martensite phase after stress unloading^[77]; (d) NiTi alloys with three porous structures fabricated by L-PBF exhibit smaller working driving forces than bulk NiTi alloys of the same size^[78]

Fig. 4. Elastocaloric materials with long fatigue life^[66]. (a)‒(b) Compressive stress‒strain curves and elastocaloric effect of Ni_51.5Ti_48.5/Ni₃Ti nanocomposites prepared by L-DED after aging treatment; (c) relationship between ∆E/E and fatigue life

Fig. 5. Effects of scanning speeds, scanning spacing, and laser power on phase transition behavior, respectively^[86]. (a)‒(c) Variations in the DSC curves when the scanning speed, scanning spacing, and laser power are changed; (d) linear relationship between each parameter and the peak temperature of martensitic transformation

Fig. 6. Phase transformation temperature of SLM Ni_50.8Ti_49.2 alloy regulated by aging treatment^[88]. (a) Changes in DSC curves after aging treatment for 1 h at different temperatures; (b) evolution in DSC curve after extended aging treatment time at 350 ℃; (c) superelasticity of as-fabricated SLM Ni_50.8Ti_49.2 alloy; (d) good superelasticity at body temperature (37 ℃) obtained after aging treatment at 350 °C for 1 h

Fig. 7. Effect of remelting process on the properties of additively manufactured metal functional materials. (a)‒(b) Effect of remelting of SLM Cu-Al-Ni-Mn alloy interlayers on the microstructure and austenite phase transformation peak temperature^[90]; (c) principle of laser in-situ heat treatment in L-DED^[91]; (d) NiTi alloy with in-situ laser heat treatment behaves larger enthalpy of phase transition^[91]

Fig. 8. Micro-defects formed during the preparation of NiTi alloys by L-PBF^[99]. (a) Good formation; (b) keyholing; (c) lack of fusion; (d) balling

Fig. 9. Process parameters optimization of laser additive manufactured SMAs. (a) Laser processing diagram^[101], with solid lines indicating parameter areas applicable to different class processes and dashed lines indicating treatment depths. (b)‒(d) Eager‒Tsai model predicts the forming quality^[99,103]: (b) high-density NiTi alloy and NiTiHf alloy fabricated according to the quality distribution map; (c)‒(d) quality distribution maps of Ni_50.8Ti_49.2 and Ni_50.3Ti_29.7Hf₂₀ alloys, where the contour line means the maximum hatch spacing with unit of μm

Fig. 10. Inverse pole figure (up) and respective pole figure texture (down) of columnar-grained NiTi alloy^[106]. (a) Hatch spacing of 80 μm; (b) hatch spacing of 120 μm; (c) hatch spacing of 180 μm

Fig. 11. In-situ synchrotron XRD was used to characterize the stress-induced martensitic phase transformation of NiTi SMAs^[66]. (a) Changes in XRD diffraction patterns during stress loading‒unloading; (b) volume fraction of the primary phases in the alloy changes with the evolution of stress

Fig. 12. In-situ synchrotron XRD characterization platforms for L-PBF process. (a) Schematic of the in-situ high-speed X-ray imaging and diffraction characterization platform at the 32-ID-B beamline of the APS; (b) schematic of in-situ XRD characterization platform for SSRL 10-2 beamline; (c) schematic of in-situ XRD characterization platform for DESY PETRA III P07 beamline; (d) schematic of in-situ XRD characterization platform for ESRF ID-31 beamline; (e)‒(g) in-situ XRD characterization platforms for SLS MicroXAS and MS beamlines, where (e) is the in-situ L-PBF device mounted at MicroXAS beamline, (f) is the in-situ L-PBF device mounted at MS beamline, and (g) is schematic of the in-situ L-PBF device and diffraction geometry

Fig. 13. Schematics or pictures of in-situ synchrotron XRD characterization platforms for L-DED process. (a)‒(c) Schematics of in-situ XRD characterization platform for DESY PETRA III P07 beamline: (a) in-situ L-DED device picture; (b) picture of the processing head and a build sample; (c) sketch of in-situ L-DED. (d)‒(e) Schematics of in-situ XRD characterization platform for DLS JEEP beamline: (d) schematic of in-situ XRD of the L-DED process; (e) blown powder additive manufacturing process replicator designed to reproduce the operation of a commercial L-DED system. (f)‒(g) schematics of in-situ XRD characterization platform for BSRF 3W1 beamline: (f) schematic of in-situ XRD of the L-DED process; (g) picture of the L-DED device

Fig. 14. In-situ XRD studies on phase transition dynamics during additive manufacturing process. (a)‒(c) Characterization of phase transition dynamics of commercial additively manufactured 17-4 stainless steel (C_17-4) during laser melting^[50]: (a) schematic illustration of in-situ laser-melting XRD experiment; (b) room temperature XRD pattern of as-solidified C_17-4 after laser melting; (c) XRD intensity map (XRD peak intensity evolution as a function of time) during laser melting of C_17-4 from 0 s to 20 s. (d) In-situ XRD characterization on martensitic hot working tool steel during different modes of laser melting process^[49]: the left image shows XRD intensity map of solidification in thin plate melting mode (frame rate: 250 Hz) and the right image shows XRD intensity map of solidification in flat plate melting mode (frame rate: 20000 Hz)

Fig. 15. Texture evolution with repeated laser passes over the seventh layer within a sample manufactured with a laser power of 55 W^[55]

Fig. 16. Time series of the representative Laue diffraction patterns during laser remelting processes^[112]. (a)‒(e) Laue diffraction images collected at 0, 225, 250 , 350, and 1000 ms; (f) Local enlarged drawings of the diffraction spots of γ(3¯1¯1¯) and γ(3¯1¯1) lattice planes at 0 and 1000 ms; (g)‒(h) variation diagrams of γ(113) crystal plane with time in the χ direction (g) and 2θ direction (h). The laser was switched on at 150 ms and off at 250 ms