Papers by Author: Chang Zhou Yu

Abstract: This paper reports the synthesis of porous titanium with a nominal composition of Ti-6 wt%Al-4wt%V through a press-and-sinter process. Blended elemental (BE) mixtures of Ti and master alloy Al-40V powders were uniaxially pressed and sintered in vacuum. Porosity of the sintered samples was determined in the range of 23vol. % to 37vol. % by the Archimedes method. Tensile strengths were found to range from 73 to 147MPa and Young’s moduli of the sintered samples varied from 3.4GPa to 13GPa. Both tensile strength and elastic modulus decreased with increasing porosity. Electrochemical assessment of the sintered porous samples showed deteriorated corrosion resistance, as compared to 95% dense Ti-6Al-4V prepared by sintering pre-alloyed powder. The challenge of using blended elemental powder sintering to fabricate porous Ti-6Al-4V alloys is discussed.

Abstract: This work aims to study sintering of elemental titanium and pre-alloyed Ti-6Al-4V powders in a graphite furnace which is operated with back-filled argon. The specific task is to investigate the effect of carbon, oxygen and nitrogen contamination in the furnace atmosphere during sintering. X-ray diffraction (XRD) reveals that the main phase on the surface of the sintered samples was a titanium oxycarbonitride – Ti(CNO). The surface of all samples was porous due to the reaction between titanium and contaminants. A close-up surface morphological observation with environmental scanning electron microscopy (ESEM) shows the presence of spherical particles in the sintered Ti specimens, but not observed in the Ti-6Al-4V alloy specimens. Energy dispersive spectrometry (EDS) results indicate that these spheres mainly contain carbon and titanium. It is postulated that residual chlorine (Cl), a common impurity for sponge Ti powder but not for pre-alloyed Ti-6Al-4V powder, may play an important role in the formation of these spheres. Microhardness is dependent on the contaminant content on the sample surface. The implication of using graphite furnaces for sintering is discussed.