Anisotropic Phase Transformation Mechanism on Coarse-Grained and Fine-Grained Pure Titanium at Low-Temperature Plasma Nitriding
J. M. Windajanti$^1$, M. S. Rajapadni$^1$, D. J. D. H. Santjojo$^1$, M. A. Pamungkas$^1$, A. Abdurrouf$^1$, and T. Aizawa$^2$
$^1$Physics Department, Faculty of Mathematics and Natural Sciences, Brawijaya University, Jalan Veteran Malang, East Java, Indonesia
$^2$Surface Engineering Design Laboratory, Shibaura Institute of Technology, Ota-City, Tokyo, Japan
Received 04.02.2022; final version — 09.02.2022 Download PDF
The nitriding process of the coarse-grained and fine-grained pure titanium proceeded by multidirectional forging technique has been investigated at temperatures of 623, 673, and 723 K. The process was carried out by high-density radiofrequency-direct current plasma combined with a rectangular hollow cathode device. The result obtained is a significant increase in surface hardness with increasing holding temperature. The surface hardness increases due to forming a surface layer composed of δ-Ti2N, ε-Ti2N and TixNx observed from x-ray diffraction results. This paper explains the mechanism of surface layer formation. We also observed anisotropic phase transformation of titanium nitride through the right shift of the x-ray diffraction peaks. Diffused nitrogen atoms during the nitriding process cause a change in crystal orientation through structural transformation of the metastable δ-Ti2N to the stable ε-Ti2N. The structural reconstruction will continue by forming TixNx to achieve stoichiometric equilibrium. More compacting of the surface microstructure is also obtained by increasing nitriding temperature.
Keywords: plasma nitriding, low temperature, pure titanium, fine-grained, anisotropic phase transformation.
Citation: J. M. Windajanti, M. S. Rajapadni, D. J. D. H. Santjojo, M. A. Pamungkas, A. Abdurrouf, and T. Aizawa, Anisotropic Phase Transformation Mechanism on Coarse-Grained and Fine-Grained Pure Titanium at Low-Temperature Plasma Nitriding, Prog. Phys. Met., 23, No. 1: 90–107 (2022)