Owing to low-temperature deposition conditions and high deposition rate, cold spray offers unique advantages in manufacturing a wide variety of metallic and composite coatings including metal matrix composites produced from physically blended powders. One of the challenges of producing composite coatings using cold spray is the deviation of coatings composition from the blended feedstock powder composition. This is of utmost importance as it affects the composition and phase evolution of intermetallic forming coatings during post spray heat treatment. In this work, cold spray of composite Ni-Ti coatings and formation of intermetallics from post spray heat treatment were investigated as a first step to examine the potential of producing equiatomic bulk Ni-Ti by cold spray. Three different physically blended Ni and Ti powders mixtures were sprayed on titanium substrates to address the coating composition variation from the blended feedstock powder and study its influence on phase evolution during post spray heat treatment. High-density and well-dispersed composite coatings were achieved for each case. EDS analysis revealed as-sprayed coatings with 10.5, 35.9 and 56.9 at.% Ni (and with balanced Ti ratios) from the three powder mixtures. Annealing treatments were conducted at 400, 500 and 900 °C for 1 and 2 h and comparative studies of the intermetallic compound formations were carried out. Microstructural investigation showed that all three equilibrium intermetallics phases of binary Ni-Ti phase diagram (Ni3Ti, Ti2Ni and NiTi) formed in the two Ni-rich composite coatings with NiTi phase being maximum in the coating with the closest composition to equiatomic ratio while only Ti2Ni phase formed in the Ti-rich coating after annealing. Thermal etching analysis of coatings showed that NiTi phase forms with a gradient microstructure from Ti splats boundary toward the center of splats, which is attributed to the grain refinement of CS samples at splat boundary and intermetallic nucleation mechanism.

中文翻译：

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冷喷涂 Ni-Ti 复合涂层的金属间相演变：喷涂时化学成分的影响

由于低温沉积条件和高沉积速率，冷喷涂在制造各种金属和复合涂层（包括由物理混合粉末制成的金属基复合材料）方面具有独特的优势。使用冷喷涂生产复合涂料的挑战之一是涂料成分与混合原料粉末成分的偏差。这一点至关重要，因为它会影响喷涂后热处理过程中金属间化合物形成涂层的组成和相演变。在这项工作中，研究了复合 Ni-Ti 涂层的冷喷涂和喷涂后热处理形成的金属间化合物，作为研究通过冷喷涂生产等原子块状 Ni-Ti 的潜力的第一步。将三种不同的物理混合 Ni 和 Ti 粉末混合物喷涂在钛基材上，以解决混合原料粉末的涂层成分变化，并研究其对喷涂后热处理过程中相演变的影响。每种情况都实现了高密度和良好分散的复合涂层。EDS 分析揭示了三种粉末混合物中含有 10.5、35.9 和 56.9 at.% Ni（并具有平衡的 Ti 比率）的喷涂态涂层。在 400、500 和 900 °C 下进行了 1 和 2 小时的退火处理，并对金属间化合物的形成进行了比较研究。显微组织研究表明，二元 Ni-Ti 相图 (Ni3Ti, Ti2Ni和NiTi)在两种富Ni复合涂层中形成，NiTi相在组成与等原子比最接近的涂层中最多，而退火后富Ti涂层中仅形成Ti2Ni相。涂层的热蚀刻分析表明，NiTi 相形成从 Ti 片晶边界到片晶中心的梯度微观结构，这归因于 CS 样品在片晶边界处的晶粒细化和金属间成核机制。