Papers by Author: František Hnilica

Abstract: The beta-titanium alloys are used mainly in bioapplications for artificial joints and other implants. They posses interesting properties such as, high corrosion resistance, low Young’s modulus, good plasticity or superelasticity etc. In this work the effect of solution treatment temperature on deformation and fracture properties has been studied. The alloy Ti-35Nb-2Zr was processed via powder metallurgy process (cold isostatic pressing, sintering and subsequent swaging). Swaged alloy was annealed at 800, 850, 900, 950 and 1000 °C. Tensile tests have been performed on such heat treated specimens and the fracture surface has been studied in correlation with microstructure. With increasing annealing temperature both tensile strength (from 925 MPa to 990 MPa) and elongation (from 13 to 25 %) increased where the maximum values were obtained for 900 °C annealed specimens and subsequently slight decrease has been observed. The simultaneous increase of strength and elongation was attached to change of deformation mechanisms which was described by studying fracture surfaces and microstructure of deformed (tensile tested) specimens.

Abstract:

The β – Ti alloy with 35 wt. % Nb and 6 wt. % with various oxygen addition (between 0.05 and 0.8 wt. %) has been studied in this work. The alloy was arc melted in a protective atmosphere of helium into water cooled copper crucible. Subsequently the material was thermo-mechanically treated (i.e. homogenized, hot forged, solution treated and cold swaged). Samples of the alloy with the lowest oxygen content were also subjected to aging treatment 450°C for 8 hours. The yield stress R_p0.2, tensile strength (R_m), elongation (A), reduction area (Z) and Young's modulus (E) depending on the oxygen content and on microstructure were studied. Also the microstructure analysis by using the light and electron microscopy has been performed.

Small oxygen addition increases both yield and tensile strength in cold swaged or solution treated conditions. The same can be also said in a lesser extent about Young’s modulus. The decrease in elongation is more distinct for oxygen addition higher than 0.5 wt. %. The oxygen content in this alloy should not exceed this value for practical applications. The increase of strength due to precipitation strengthening leads to significant increase in modulus in comparison with strengthening caused by oxygen addition (when comparing similar strength values achieved).