Thermal characteristics and amorphization in plasma spray deposition of Ni-Si-B-Ag alloy

Crystalline-amorphous matrix composites preserve the amorphous material high strength and additionally gains on plasticity. Substituting hard crystalline precipitates with soft ones should even more improve the latter. Therefore, this work was aimed at verifying, whether Ag and Ni-Si-B alloy shows liquid immiscibility and consequently, if they might form crystalline Ag/Ni-Si-B amorphous/crystalline composite. Firstly, a mixture of 95 wt% of Ni-Si-B (1559-40) and 5 wt% of Ag powders was arc-melted in argon and cooled at copper plate. The solidification process was documented by IR mid-wave camera and Time/Temperature graph. The microstructure of the ingot was studied using a scanning electron microscope (SEM) and light microscope (LM). Secondly, the powders mixture was plasma sprayed on a cooled copper plate. The cross-section microstructure and the phase composition of the plasma spray deposit were analyzed with a transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffractometer (XRD). The thermal characteristics of the plasma sprayed deposit and the Ni-Si-B powder were analyzed using differential thermal analysis (DTA) and compared. The results show that the melted Ag and Ni-Si-B powders form immiscible liquids at high temperatures used both during arc-melting and plasma-spraying. The proved that that the plasma spraying enables production of a Ni-Si-B/Ag composite with high strength Ni-based matrix with dispersed in it fine soft Ag-FCC flake-like particles.