Short Communication
Manana Mikaberidze, George Gor
Abstract
New corrosion resistant Ti-8Ni-Cr system alloys with increased hardness and strength have been developed for medical tools and implants. The development was made based on study of chromium influence on the phase constituents, microstructure, mechanical properties, corrosion resistance and electrochemical characteristics of Ti- 8Ni alloy. Optimum condition of thermal treatment, providing high strength, hardness and corrosion resistance of alloys has been defined – quenching from 950°C with content of chromium in alloys 1 – 3% (by addition of Yttrium in quantity 0,001 – 0,01 mass%). The cause is that alloys after quenching from 950°C have structure of transformed β-solid solution and contain ω-phase, which is micro dispersive during concentration of chromium up to 1-3%. On the base of studying of the phase equilibrium by microstructural, x-ray investigations and differential thermal analysis of Ti-8Ni-Cr system alloys polythermal sections of phase diagram of this system have been constructed, which is in complete accordance with the phase diagram formed by thermodynamic calculations. Study of mechanical properties of Ti-8Ni-(0-3) Cr quenching alloys show, that chromium increases the tensile strength (1000MPa) and hardness (48 HRC) and slightly influences on plastic properties of the Ti-8Ni alloy. Tensile strength of titanium commercial alloys: Ti-6Al-4V and Ti-5Al-3Sn do not exceed 900 MPA. Corrosion tests in medium containing human body: blood, physiological solution, gastric juice, tissue liquid and also corrosion testing according to the following regime: cleaning+disinfection+sterilization in aggressive solutions with addition of hydrogen peroxide reveal high corrosion resistance of Ti-8Ni-(0-3)Cr alloys, without the changing of surface. After 20 cycles corrosion losses of the commercial titanium alloys are ~ one order more than the losses of new alloys. Study of toxic properties of alloys Ti- 8Ni-(1-3)Cr during their implantation in muscles and abdominal cavity of animals show, that they do not cause local irritative actions on different tissues, they do not suppress local tissue reactions and do not have any toxic effects during short or long term implantation conditions. High corrosion resistance of alloy Ti-8Ni-1Cr is established also by the modeling and prediction of corrosion behavior in the physiological solution at the temperature 37oC with using of electrochemical investigations, spectral analysis, regression and variance analysis of the mathematical statistics. Alloys Ti-8Ni-(1-3)% Cr are recommended for manufacturing high-strength medical tools of multiply usage and surgical implants. Application of new alloys will allow improving functional properties and increase quality, reliability, service life of medical tools and implants.