Effect of carbon and oxygen on microstructure and mechanical properties ofTi-25V-15Cr-2Al (wt%) alloys

The effect of carbon additions on microstructure and mechanical properties of alloys with different levels of oxygen was studied in beta titanium allo ys of the general composition Ti-25V-15Cr-2Al (all compositions are in wt% unless otherwise indicated). The microstructures were studied using optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that titaniu m carbides with vacancy-ordered structure formed in all alloys with C addit ions of over 1000 w.p.p.m. Grains were refined by carbides. Wavelength-disp ersive X-ray (WDX) analysis showed that oxygen was much higher in carbides than in beta matrix. After long-term exposure at 550 degrees C alpha precip itation was significantly reduced in samples with titanium carbides compare d with those without. A significant improvement in room temperature tensile ductility was achieved by the addition of carbon to the alloys. Elongation s of similar to 10% were obtained in samples which were exposed at 550 degr ees C for 500 h following heat treatments at 1050 and 700 degrees C. (C) 19 99 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights res erved.