Papers by Author: De Liang Zhang

Abstract: Ti-6Al-4V (wt%) alloy rods were prepared successfully using a low-cost method that combines mixing elemental and master alloy powders and powder compact extrusion. The microstructure and mechanical properties of the rods and the effects of extrusion temperature on them were investigated. The results showed that the microstructure and mechanical properties of the extruded rods were strongly affected by the extrusion temperature. With increasing extrusion temperature from 1200°C to 1300°C and keeping the powder compact holding time unchanged at 2 minutes, the fraction of undissolved V rich particles in the microstructure of the extruded rod decreased substantially to zero, the level of composition homogenization increased dramatically to the highest level, and the UTS and elongation of the extruded rods increased significantly from 886MPa and 1.2% to 1300MPa and 7.1%, respectively. The tensile properties of the Ti-6Al-4V alloy rods produced by powder compact extrusion of the powder mixture are comparable to those of Ti-6Al-4V alloy produced by ingot metallurgy and thermomechanical processing.

Abstract: This work investigates the debinding process of powder compacts formed by metal injection moulding (MIM) of feedstocks comprised of HDH Ti or HDH Ti-6Al-4V powder mixed with a binder of a predetermined ratio of water soluble polyethylene and wax. The full debinding process has three stages: a solvent debinding process to leach the water soluble component, a drying phase allowing the removal rate to be measured and a thermal treatment step for removing the wax components, leaving the backbone components to retain part geometry prior to sintering. Leaching of the water soluble component was monitored and the results were consistent with the general correlation which predicts that binder removal time increases by a factor of 4 when the section thickness is doubled. Uniformity of binder removal, defect formation and particle surface degradation in Ti MIM parts are also discussed.

Abstract: Ti-43Al-5V-4Nb (at.%) intermetallic compounds with fully lamellar structure were fabricated by forging method without canning using the blended elemental powders. The process route consisted of powder blending, compacting, sintering and final fabrication by hot forging. During sintering, there existed expansion, which is detrimental to forging process. In order to overcome the difficulty, two-step forging was introduced. The total reduction of two-step forging was up to 65%. Nearly fully lamellar structure of TiAl alloy was obtained. Overall, an optimized and potentially lower cost processing route could be identified.