## 4 Conclusions  
In this work, we selected a variety of parameter combinations to prepare NiTiNb by LSF, the results show that LSF can play a better role in the preparation of NiTiNb. We have obtained the feasible parameter combination of NiTiNb prepared by LSF, preliminarily obtained the microstructure and phase transformation temperature of NiTiNb prepared by LSF using mixed powder, which provides an experimental basis for the preparation of NiTiNb by LSF. The main conclusions of this work are as follows:  
Figure 13: Tensile properties of heat-treated part of sample L7.  
1. The LSF process parameter combination of 2000 W laser power and 900 mm/min scanning speed can fully melt the Ni + Ti + Nb mixed powder, and obtain a sample with a small size deviation, no serious oxidation on the surface, and a good metallurgical bond between the powder and the substrate.
2. The microstructure of LSF-NiTiNb alloy is mainly composed of NiTi matrix and Nb phase, and Nb is mainly enriched in grain boundaries. As the laser power increases, the grain size increases, and the proportion of equiaxed crystals increases, the martensite transformation temperature increases.
3. Heat treatment at 850 \({}^{\circ}\)C for 3 h will increase the phase transformation temperature and hysteresis of LSF-NiTiNb and change the phase transformation behavior from one-step B2-B19\({}^{\prime}\) to two-step B2-R-B19\({}^{\prime}\). However, the inhomogeneity of the microstructure results in different phase transformation temperatures and phase transformation behaviors in the same sample.
4. The tensile properties of the heat-treated LSF-NiTiNb samples with different building heights are significantly different due to the uneven microstructure. The maximum elongation reaches 8% and the minimum elongation is only 0.8%.  
In this work, LSF used Ni/Ti/Nb mixed powder to prepare NiTiNb alloy, and the prepared samples show uneven microstructure, which further affects the phase transformation and mechanical properties. To obtain the required phase transformation performance and mechanical properties with high repeatability, and then obtain samples with good shape memory effect, the most important issue is to solve the problem of uneven microstructure. It is possible to obtain a uniform microstructure or improve the microstructure from uniform powder, a good combination of process parameters, appropriate substrate, and the subsequent heat treatment or other processing methods, to realize the controllability of the preparation of NiTiNb by LSF.  
Conceptualization: H.L.; methodology: H.L.; validation: Y.Z.; X.L.; investigation: Q.G.; resources: H.L.; G.L.; data curation: Q.G.; writing--original draft preparation: Q.G.; writing--review and editing: Z.Y.; supervision, project administration, funding acquisition: H.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Natural Science Foundation of China (51775441).  
The data presented in this study are available on request from the corresponding author.  
The authors would like to thank the National Natural Science Foundation of China (51775441) for their support for this experimental project. At the same time, we would like to thank the Analytical & Testing Center of Northwestern Polytechnical University for the XRD, SEM, DSC, and other related testing services.  
The authors declare no conflict of interest.