Plasma nitriding of titanium alloy: Effect of roughness, hardness, biocompatibility, and bonding with bone cement

Abstract

Titanium (Ti) alloys have been widely used in orthopedics and orthodontic surgeries as implants because of their beneficial chemical, mechanical, and biological properties. Improvement of these properties of a Ti alloy, Ti-6Al-4V Eli, is possible by the use of plasma nitriding treatment on the Ti alloy. The novelty of this study is the evaluation of a DC glow discharge nitrogen plasma treatment method on the surface, mechanical and biological properties of Ti alloy. Specifically, this study measured the chemical states, roughness, hardness, and biocompatibility of plasma nitride treated Ti-6Al-4V Eli as well as determined the effect of plasma treatment on the fracture strength between the Ti alloy and bone clement. This study hypothesized that DC glow discharge nitrogen plasma treatment may alter the surface chemical and mechanical states of the Ti alloy that may influence the fracture strength of implant/cement interfaces under static load. This study found that plasma nitride treatment on Ti alloy does not have effect on the roughness and biocompatibility (P value > 0.5), but significantly effect on the hardness and fracture strength of Ti-bone cement interfaces compared to those values of untreated Ti samples (P value < 0.5). Therefore, the DC glow discharge nitrogen plasma treated Ti alloy can potentially be used for orthopedic applications.

Microstructure and Phase Transformation of Pure Titanium During Nitriding Process by High Density Plasma

“…This is in accordance with the data resulting increase in surface hardness, which is depicted in Figure 8. From these data, it appears that the surface hardness of nitrided samples increases with increasing concentration of TiN [3][4]6].…”

“…There are two important stages in this nitriding process. First, the pre-nitriding process was carried out using plasma that generated by a DC generator with a high voltage of -500 V. At this stage, the plasma of the gas mixture of nitrogen and hydrogen with a flow rate of 160/40 ml/min was utilized in 1 h. The plasma ion in high voltage was used to sputter the surface of specimens in order to remove titanium oxide from the outermost surface [4,17]. Meanwhile, a surface activation process was also carried out before the main nitriding process.…”

“…For the last few decades, titanium has attracted tremendous interest in many fields of industry, such as aerospace, industrial, consumer applications, and production of implants [1][2][3]. It because titanium is a lightweight metal owing to such properties as low density, high corrosion stability, and biocompatibility [1,4,5]. However, the low surface hardness, high friction coefficient, and low wear resistance prevent the use of titanium in friction pairs restrict their use of application where sliding is inevitable [6].…”

“…The nitriding process of titanium typically involves a high temperature of 700-1000 C which can harden the surface material up to 1300 HV [5,11]. Plasma nitriding is a thermo-chemical method that can control the phase formation and the depth of the nitrided layer [3][4][5]13]. It also requires short periods of nitriding time and can avoid oxidation, but the high temperature in the process can reduce the fatigue strength and cause detrimental micro-structural changes in titanium substrates [5].…”

“…The gas pressure and DC bias were controlled as process parameters in order to gain the optimum result of the low temperature plasma nitriding process [15]. The purpose of this study was to determine how the influence of the phase change that occurs in titanium that allows the formation of TiN as an agent that can cause the increasing of surface hardness [4,6,10] of titanium at the low temperature plasma nitriding process.…”