An Investigation on the Microstructure, Interface, and Mechanical Properties of Spark Plasma Sintered Ni/Ni-Ni₃Al/Ni Compound

This study investigates the interface, microstructure, and mechanical properties of layered Ni/Ni-Ni₃Al/Ni composite, fabricated by spark plasma sintering (SPS). Crack propagation behavior and joining mechanisms of particles in this layered composite were comprehensively studied and discussed. Ni₃Al powders were first synthesized using mechanical alloying. Particulate Ni-Ni₃Al composite was then produced by mixing 60 wt.% Synthesized Ni₃Al and 40 wt.% Ni powders. The layered composite was then synthesized by SPS. Samples were held at 970°C for 10 minutes to do sintering. Results showed that a uniform interface has been formed between different layers of composite, without any obvious evidence of delamination, cracks, or flaws in-between layers. Moreover, there was hardly any sharp boundary/interface and necking between particles is discernible, inferring that applied sintering has resulted in rather complete densification. Based on the obtained results, interfaces were categorized into three different interface types: Ni-Ni, Ni₃Al-Ni₃Al, and Ni-Ni₃Al. Results showed that intermetallic joints were less diffused and were less sintered, while metallic interfaces were much more diffused. Overall, complete sintering and diffusion for metal and kiss bonding or even cavities for intermetallic interfaces are more usual. The attribution of different interface structures to the mechanical properties and fracture behavior of the fabricated composite was thoroughly discussed. Results showed that a sample with a mixed Ni/Ni₃Al mid-layer has an improved shear strength, when compared to the case where pure Ni₃Al is used as the mid-layer.