Abstract

Attempts to improve tribological properties of titanium generally employ laser cladding with ceramic reinforcements. Here, we present an alternative weld deposition-based technique for surface hardening of titanium substrates through hard intermetallic compounds (IMCs) formed in situ. Using pure nickel as a filler in a gas metal arc welding (GMAW) setup, we produced Ti-Ni IMC reinforcements in near-surface regions of the substrate with concomitant increase in hardness. The alloyed region exhibited considerable microstructural heterogeneity that could be traced back to solidification events taking place in a compositionally and thermally inhomogeneous melt. Fusion interface in the substrate is characterized by consecutive bands of Ti₂Ni and NiTi. Two different morphologies of the NiTi + Ni₃Ti eutectic, along with some isolated regions of primary NiTi and primary Ni₃Ti, constitute rest of the alloyed zone. The eutectic morphologies differ significantly in their length scale originating from non-reciprocal heterogeneous nucleation found in faceted/non-faceted eutectic systems. We constructed a hardness map of the alloyed zone that highlighted a wide hardness variation that correlated well with the observed microstructural heterogeneity. The interaction of macroscopic transport phenomena with the system thermodynamics is shown to have a profound influence on solidification of inhomogeneous melts, resulting in unusual solidification modes and microstructures.

Graphic Abstract

中文翻译：

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通过镍熔敷​​过程中原位形成的Ni-Ti金属间化合物提高钛的表面硬度

摘要

试图改善钛的摩擦学性能的尝试通常采用具有陶瓷增强材料的激光熔覆。在这里，我们介绍了一种通过基于原位形成的硬金属间化合物（IMC）的钛基底表面硬化的替代性基于焊接沉积的技术。在气体金属电弧焊（GMAW）装置中，使用纯镍作为填料，我们在基材的近表面区域生产了Ti-Ni IMC增强材料，并随之提高了硬度。合金区域表现出相当大的微观结构异质性，这可以追溯到在成分和热不均匀熔体中发生的凝固事件。基材中的熔融界面的特征是连续的Ti _2能带镍和镍钛。NiTi + Ni ₃ Ti共晶的两种不同形态以及初级NiTi和初级Ni ₃ Ti的一些隔离区域构成了其余的合金区。共晶形态的长度尺度显着不同，这是由于在多面/非多面共晶系统中发现的非可逆异质成核所致。我们构建了合金区域的硬度图，该图突出显示了与观察到的微观结构异质性很好相关的宽广的硬度变化。宏观传输现象与系统热力学的相互作用被证明对不均匀熔体的凝固具有深远的影响，从而导致异常的凝固方式和微观结构。

图形摘要