## 1 Introduction  
The combination of LSF parameters with \(P\) = 2000 W and \(v\) = 900 mm/min can obtain a good metallurgical bond. 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. Heat treatment at 850 \({}^{\circ}\)C for 3 h will increase the phase transformation temperature and hysteresis of LSF-NiTiNb. However, the inhomogeneity of the microstructure results in different phase transformation temperatures in the same sample and the tensile properties of the LSF-NiTiNb samples with different building heights are also significantly different. The maximum elongation reaches 8% and the minimum elongation is only 0.8%. NiTi-based shape memory alloy (SMA) is a smart material with shape memory effect (SME) and superelastic properties (SE). This is related to the reversible thermoelastic martensite transformation between the high-temperature austenite phase and the low-temperature martensite phase existing in NiTi-based shape memory alloys [1]. Because of the unique functional characteristics of NiTi-based SMA such as good biocompatibility [2], excellent corrosion resistance [3], excellent mechanical properties [4], NiTi-based SMA has a strong application potential [5] in aerospace [6], automation [7], medicine [8] as well as in daily life. NiTiNb shape memory alloy with Nb addition and NiTiFe shape memory alloy with Fe addition can be applied to pipeline connections of an aeroengine [9; 10]. While NiTiNb has more potential because of the characteristics of wide hysteresis, the maximum phase transformation hysteresis temperature of pre-deformed NiTiNb alloy can reach 150 \({}^{\circ}\)C. A connector made of NiTiNb alloy can be stored, transported, and installed at room temperature, saving economic and time costs. Therefore, NiTiNb shape memory alloy has a wide range of application prospects and research value in aviation hydraulic pipeline connection systems. However, because of the characteristics of high work hardening, high toughness, high strength, and high ductility of NiTi-based SMAs [11], it is sensitive to processing parameters, so the workability is poor [12; 13]. Powder metallurgy and casting usually cause pollution, chemical segregation, pores, and unsatisfactory functional properties [14; 15; 16]. It is difficult to manufacture NiTi-based components with complex structures using traditional processing techniques of subtractive or equivalent material manufacturing. This greatly limits its potential applications [17; 18]. AM shows the reality of being able to transfer three-dimensional (3D) designs created on computers to a machine that can replicate the geometry into a physical object. We don't need to consider the geometrical complexity or determine how each feature must be made and in what order, so AM has more advantages than conventional manufacturing like machining [19]. In aerospace field, a well-known example is the fuel nozzle for the GE LEAP engine which was manufactured by AM, when using AM, lead-time can be considerably reduced compared to conventional manufacturing. In volume production industries, such as the automotive sector, AM is able to prototype their models earlier and bring their products to the market as fast as possible [20]. In medical field, AM can convert patient-specific data for customized products and medical interventions [21]. Therefore, the use of AM technology to prepare NiTi-based alloys has attracted more and more attention [11; 22; 23; 24]. In general, metallic AM techniques can be divided into three types based on heat source, i.e. laser-based AM and arc-based AM.