Nitride coatings were formed on Ti-6Al-4V alloy by thermodiffusion treatment. The corrosion-electrochemical behaviour of Ti-6Al-4V alloy with nitride coatings I and II was investigated in physiological solutions (0.9% NaCl and Tyrode's) at temperatures of and . It is determined that nitride coating I provides Ti-6Al-4V alloy the higher corrosion resistance in Tyrode's solution at both temperatures of solution while nitride coating II in isotonic 0.9% NaCl. 1. Introduction Titanium and its alloys are widely used in dentistry and orthopedics [1–4]. They provide high biomechanical properties and chemical stability in biological systems than other materials such as stainless steel and cobalt-chromium alloys. Ti-6Al-4V alloy has better physical and mechanical properties than titanium, but has a low corrosion resistance [2, 5, 6]. Surface treatment is widely used to enhance abrasion, corrosion resistance, and surface hardness [2, 3, 7, 8]. Nitriding is often used to harden the titanium alloy surface [3, 9–11]. Good biocompatibility of titanium nitride is shown in the blood and bone tissue [11]. In addition, the titanium nitride is characterized by good mechanical, tribological, and anticorrosion properties. That is why the titanium nitride is the most suitable to protect the surface of medical implants. One of the main criteria to use material as implant is its corrosion resistance in physiological solution that simulates the environment of the human body [12]. In particular, isotonic 0.9% NaCl solution simulates blood plasma and Tyrode’s solution biological tissue. The temperature increase is a protective reaction to the penetration of infection or inflammation. When the physiological solution temperature changes, the transition from normal to inflammatory state of the human body can occur. Purpose is to examine the corrosion-electrochemical behaviour of Ti-6Al-4V alloy with nitride coatings in physiological solutions at 36°C and 40°C. 2. Experimental Samples of ( ) Ti-6Al-4V alloy (wt%: C-0.1; H-0.015; N-0.04; O-0.15; Fe-0.25; Al-6.0; V-4.0; Ti-bal.) with dimensions ？mm were investigated. Before chemical-thermal treatment, the samples were polished by diamond paste to a surface roughness of ？ m. Then, they were washed in alcohol and dried. Thermodiffusion saturation by nitrogen was carried out at for ？h. The samples were heated to the nitriding temperature in a vacuum of ？Pa. Heating rate was 0.040°C/s. After the isothermal exposure, the samples were cooled in nitrogen with the furnace at an average cooling rate of 0.028°C/s. After cooling to 500°C, the
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