<b>Microstructure and properties of Ni-Ti-Cu alloy fabricated in situ by treble-wire arc additive manufacturing</b>

This study is the first attempt to manufactureTi50Ni45Cu5, Ti50Ni35Cu15, Ti50Ni25Cu25 alloys by treble-wire arc additive manufacturing (T-WAAM) using pure Ti, pure Ni and pure Cu wires as raw materials. The objective is to study the hysteresis of phase transformation, the microstructure evolution and properties of as-built Ni-Ti-Cu alloy. The results show that for Ti50Ni45Cu5 alloy, NiTi2, (Ni, Cu)2Ti, B2 with CsCl structure and B19′ phases are formed. For Ti50Ni35Cu15 alloy, NiTi2, B19′, Ni4Ti3, CuTi2, (Cu, Ni)Ti2 and (Cu, Ni)Ti phases are formed. For Ti50Ni25Cu25 alloy, Ti2Ni, B19′, R, (Cu, Ni)Ti, Ti2Cu, Ni4Ti3 phases are formed.With an increase of Cu content from 5 at.% to 25 at.%, the phase transition temperature increases sharply. The ultimate tensile strength of Ti50Ni45Cu5, Ti50Ni35Cu15, Ti50Ni25Cu25 are 248.2 MPa, 534.8 MPa and 261.8 MPa, respectively. Their strain is 1.71%, 6.42%, and 3.36%, respectively. For Ti50Ni45Cu5, Ti50Ni35Cu15, Ti50Ni25Cu25 alloy,the fracture mode of the Ti-Ni-Cu alloy is brittle fracture.本研究首次采用纯钛、纯镍及纯铜丝作为原材料，通过三丝电弧增材制造（T-WAAM）工艺制备Ti50Ni45Cu5、Ti50Ni35Cu15及Ti50Ni25Cu25三种合金，旨在探究沉积态Ni-Ti-Cu合金的相变滞后现象、微观组织演化规律与力学性能。结果表明，Ti50Ni45Cu5合金中生成了NiTi2、(Ni, Cu)2Ti、具有氯化铯（CsCl）结构的B2相以及B19'相；Ti50Ni35Cu15合金中生成了NiTi2、B19'、Ni4Ti3、CuTi2、(Cu, Ni)Ti2及(Cu, Ni)Ti相；Ti50Ni25Cu25合金中则生成了Ti2Ni、B19'、R相、(Cu, Ni)Ti、Ti2Cu及Ni4Ti3相。当铜元素原子百分比从5 at.%提升至25 at.%时，相变温度显著升高。Ti50Ni45Cu5、Ti50Ni35Cu15及Ti50Ni25Cu25合金的极限抗拉强度分别为248.2 MPa、534.8 MPa与261.8 MPa，断后伸长率分别为1.71%、6.42%及3.36%。上述三种Ti-Ni-Cu合金的断裂模式均为脆性断裂。