Xuan Hui Qu

Powder Injection Molding of Ti6Al4V Alloy

An improved wax-based binder was developed for powder injection molding of Ti6A14V alloy. The molding behavior, debinding kinetics and sintering process were studied. Components with relative density of 96.5% were produced with PIM process. The density of the components was increased up to 99% by HIP treatment. The tensile properties of the alloy were as follows: tensile strength 1060MPa, yield stress 960MPa, elongation 9.5%, which are equivalent to those of the same alloy made with traditional press-sintering process. The dimension deviation of the sintered samples could be controlled in the range of ±0.03mm with the optimized processing parameters.

Analysis of Density and Mechanical Properties of Iron Powder with Upper Relaxation Assist through High Velocity Compaction

For producing higher density PM parts a new method, High-Velocity Compaction process with additional upper relaxation assist (URA) device is presented in the paper. Using zinc stearate as a die wall lubricant, iron powder was pressed with and without upper relaxation assist device of mass 0.14 Kg focusing to investigate the density and mechanical properties. To explain a compaction process in loading stage a conservation of momentum principle has been introduced during collision of hammer, upper piston and upper relaxation assist device in die compaction. To observe the morphological characteristics and mechanical properties, a scanning electron microscopy (SEM) and computer controlled universal testing machine were used. The experimental results showed that the samples compacted with URA device had an improved green density and mechanical properties compared to the samples compacted in the absence of URA device.

Microstructure and Tensile Properties of Tungsten Heavy Alloys

Mechanical properties of tungsten heavy alloys are dependent on many factors including the purity of the raw materials, their tungsten content, manufacturing parameters and the microstructure of the final compact. The main object of this research was to examine the effect of sintering conditions (temperature and time) on the microstructure of tungsten heavy alloys and how the resulting modification of the microstructure can be used to optimize their mechanical properties. Alloys composed of 88%, 93% and 95% wt. of tungsten with the balance of Ni: Fe in the ratio of 7:3 were consolidated into green compacts. Samples of each of the three resulting alloys were sintered at different temperatures (1350°C,1450°C and 1500 0C) for different sintering holding times (3 and 30 minutes) in hydrogen atmosphere. Standard metallographic procedures were used to obtain SEM micrographs. The mechanical properties of tungsten heavy alloys were found to be dependent on the microstructural parameters such as W particle size, solid volume fraction, connectivity and w-w contiguity. It was shown that the mechanical properties of the alloys, and especially their ductility, are harmed when tungsten grains are contiguous.

Effect of Si on the Wettability of SiC/Al System

In this paper, Si was added to the Al alloy to research its effect on the wettability between SiC and Al at 1000°C. The results showed that the contact angle decreased with the increase of Si content in the Al alloys and it droped from 570 to 370 with the Si content from 0 to 12wt% and reached equillibrium with the further addition of Si to 18wt%. The improvement mechanism of Si on the wettabitliy is also discussed in this paper.

Effect of TiC Intermediate Layers on the Thermal Conductivity of Copper/Diamond Composites

TiC intermediate layers were formed on the surface of diamond particle with reaction of Ti powders in mixed molten NaCl-KCl salts. The copper/diamond composites with TiC-coated diamond particles were fabricated by pressure infiltration. Then the microstructure and thermal conductivity of the obtained copper/diamond composites were studied. The results showed the thermal conductivity of the composites with a density of 5.65 g/cm3 reached 514 Wm-1 K-1, which is much higher than with uncoated diamond. The TiC layers synthesized on diamond particles is shown to be an effective way to enhance the thermal conductivity of copper/diamond composite.

Effect of SiC Powder Characteristic on the Rheological Properties of Feedstock

In this study, the effect of SiC powder characteristic on the rheological properties of the feedstock was investigated. It was found that the viscosity of the feedstock decreased with the increase of the particle size. For the binary powder mixtures, the viscosity of the feedstock decreased with the increase of the particle size ratio of the larger particle to finer particle, which is attributed to the increase of the tap density of the powder.

Biomedical Ti-24Nb-4Zr-7.9Sn Alloy Fabricated by Conventional Powder Metallurgy and Spark Plasma Sintering

Ti-24Nb-4Zr-7.9Sn alloy was prepared by Powder Metallurgy (PM) and Spark Plasma Sintering (SPS) using titanium hydride powder, niobium powder, zirconium powder and tin powder as raw materials. The effect of sintering process on microstructure and mechanical properties was investigated by mechanical measurement and SEM. The results showed that the best sintering process by PM was at 12500C for 2 h. The relative density, tensile strength and elongation of the alloy reached 97.2%, 705MPa and 6.2%, respectively. The microstructure was a typical Widmannstatten microstructure, which possessed β-matrix and α-precipitation. The best process by SPS was at 12500C. The relative density, tensile strength and elongation of the alloy sintered by SPS reached 99.4%, 788.5MPa and 6.4%, respectively. The grain size was about 100µm and the microstructure was uniform. The fracture morphology of the alloy was ductile rupture. Compared to PM, Ti-24Nb-4Zr-7.9Sn alloy fabricated by SPS exhibited better comprehensive properties and more uniform microstructure.

Microstructural Characterization of Diamond/SiC Composites Fabricated by RVI

Diamond/Si/C porous preform was prepared with phenolic resin, Si, Diamond and graphite. Subsequent reactive vapor infiltration (RVI) of gaseous silicon at 1600 °C for 2 h in vacuum atmosphere resulted in the formation of a compact Diamond/SiC composite. The influence factors of perform porosity were investigated, including process pressure and raw materials. Density and microstructure of Diamond/SiC composites were also discussed. The results showed that the open porosity of preform was mainly influenced by the pressing pressure. It can also be affected by the content, morphology and the particle size of diamond. The preform with open porosity higher than 20% after RVI treatment can obtain Diamond/SiC composites with high density. However, over-high porosity of the perform will cause a mass of unreacted Si exists in the composite which is unfavorable for its application. In order to reduce the content of residual Si, open porosity of preform should be no higher than 40%.

Application Status and Market Analysis of Non-Aero Titanium in China

China is abundant in titanium mineral reserves, with ~870 million tons identified to date. After more than 50 years of development, China has established its own complete titanium industry chain and become one of the three largest titanium producers and consumers in the world. This article presents an overview of China’s titanium industry from the aspects of production capability, output, consumption and market profiles. The current status of non-aero titanium in China is highlighted because about 90% of the titanium consumption is China is for non-aero industrial applications. The consumption of titanium in various industrial sectors and the main technological improvements are introduced. Meanwhile, the application prospects, national policies and existing problems of China’s titanium industry are discussed. With its fast and sustained economic growth, an unprecedented opportunity exists for Chinas non-aero titanium industry.

A Novel Process for Making Spherical Powders of High Nb Containing TiAl Alloys

A novel process was developed to make micro-fine spherical high Nb containing TiAl alloyed powders in quantity. Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y(at%) ingot prepared by vacuum induction melting was heat-treated for homogenization, and then machined with a crusher. The chippings were refined by fluidized bed jet milling, and subsequently spheroidized with radio frequency (RF) argon plasma. The effects of processing parameters on powder characteristics were studied. By fluidized bed jet milling, the particle size and distribution uniformity both decline with the rise of classifier frequency. Above 5800rpm, the number-average diameter is lower than 20μm with a bimodal particle size distribution. The powders consist of coarse plate-shaped particles and some finer flaky debris, and with the further rise of the frequency, the amount of debris gradually increases. The plasma-spheroidized powders are found to possess good sphericity and composition homogeneity with phase dominated by supersaturated α2-Ti3Al. The granulometric characteristics of the spherical powders strongly depend on those of the feed powders. For the jet milled powders below 5800rpm, due to the relatively lower size distribution uniformity, the fine particle fraction reduces after spheroidization, which causes an obvious improvement of distribution uniformity and the corresponding increase of number-average diameter