Papers by Author: De Liang Zhang

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Authors: Gorgees Adam, De Liang Zhang, Jing Liang, I. Macrae
Abstract: Titanium and titanium alloys are the materials of choice for many industrial applications because of their attractive combination of low density, good mechanical properties, and high corrosion resistance, and titanium is the fourth most abundant metal in the earth crust (0.86 % by weight) behind aluminum, iron, and magnesium. However, titanium and titanium alloys are not widely. The reason for this is the high cost of titanium and titanium alloys! The cost gap for titanium and titanium alloys widens when they are used for fabricating components and structures. Consequently, much effort has been expended to reduce the cost of titanium and titanium alloys. In conjunction with the University of Waikato, Titanox Development Limited-New Zealand has been successful in creating a modified novel process to produce TiAl based alloy powders with different particle sizes and compositions at low cost. The process offers several benefits to the titanium industry the most significant one of which is that it displays the potential to significantly reduce the commercial production costs of Ti-Al based alloys. This paper describes the Titanox Development Limited technology in brief, and shows how it can economically produce titanium alloy powders for different industrial applications and making titanium alloys affordable. The process has been disclosed in a PCT (Patent Corporation Treaty) application which was approved in 2004 [1], and the related patent applications either have been approved or are being filed in different countries.
Authors: G. Thavanayagam, De Liang Zhang, K.L. Pickering, Stiliana Raynova
Abstract: Metal injection moulding (MIM) is an innovative injection moulding technique widely used to produce complex shaped components from feedstock composed of metal powders and thermosetting or thermoplastic binders. In MIM, binder selection and formulation are considered as critical processes since binder characteristics dictate the success of MIM. The purpose of this study is to determine the feasibility of polyvinyl butyryl (PVB) based binder system in Ti-6Al-4V(wt.%)/binder feedstock, as well as to understand the effects of key parameters, such as powder loading and mixing conditions on the rheological properties of a feedstock. In this study, PVB, polyethylene glycol (PEG), and stearic acid (SA) were chosen to formulate a multi-component binder system to prepare Ti-6Al-4V based feedstock with the aid of three types of mixers: a compounder, a modified mechanical mixer and a twin screw extruder. Further, morphological analysis was performed using optical microscopy and scanning electron microscopy. Thermal analysis was performed using simultaneous differential thermal analysis and thermogravimetric analysis. Results showed that binder formulation was reasonably successful with the aid of both mechanical mixer and a twin screw extruder under certain mixing conditions, and the critical powder loading was 68 vol.%, resulting in an optimum powder loading of 63 vol.% .
Authors: De Liang Zhang, Carl C. Koch, Ron O. Scattergood, K. Youssef
Authors: Asma Salman, Brian Gabbitas, De Liang Zhang, Peng Cao, Stiliana Raynova
Abstract: A feedstock of Ti(Al,O)-Al2O3 composite powders was produced by high energy milling of a mixture of Al and TiO2 powders followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxygen-fuel (HVOF) technique on H13 steel substrates to produce Ti(Al,O)-Al2O3 composite coatings. The performance of the coatings was assessed in terms of thermal fatigue behaviour and reaction with molten aluminium (soldering). The composite powders and coatings were characterised using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses characteristics and potential applications of the composite coatings.
Authors: Ming Tu Jia, De Liang Zhang, Brian Gabbitas
Abstract: Ti-6Al-4V rocker arms for internal combustion engines were produced by forging of compacts of blended powder consisting of elemental hydride-dehydride (HDH) titanium powder and Al60V40 (wt%) master alloy powder or mechanical alloyed (MA) powder synthesized by high energy mechanical milling of a mixture of HDH titanium and Al60V40 master alloy powders. The powder compacts were made by warm compaction, and their relative density was 90%. The mechanical properties and microstructures of as-forged parts made using blended powder were improved significantly with increasing holding time at forging temperature, and close to those of as-forged parts produced by powder compact forging of HDH Ti-6Al-4V pre-alloyed powder. However, the as-forged part produced by powder compact forging of MA powder was brittle, and fractured prematurely during tensile testing.
Authors: Peng Cao, Brian Gabbitas, Asma Salman, De Liang Zhang, Z.H. Han
Abstract: Thermal spray deposition has been widely used as a coating process for applying thin protective layers to the need-to-protect materials, or substrates. Recent technological developments in thermal spray processing, particularly cold gas spraying (CGS) and supersonic plasma spraying (S-PS), have enabled some emerging applications for making structural components. This paper reports on the results of our recent attempts to obtain thick TiAl coatings using three coating techniques: atmospheric plasma spraying (APS), S-PS and CGS. We successfully achieved a 3 mm thick coating using both APS and S-PS techniques, but failed in cold spray. A significant phase change was observed of the powder particles experienced during both APS and S-PS processes. Nevertheless, a considerable quantity of titanium oxides was observed in the APS coating.
Authors: Aamir Mukhtar, De Liang Zhang, C. Kong, P. R. Munroe
Abstract: Cu-(2.5 or 5.0vol.%)Al2O3 nanocomposite balls and granules and Cu-(2.5vol.% or 5.0vol.%)Pb alloy powder were prepared by high energy mechanical milling (HEMM) of mixtures of Cu and either Al2O3 or Pb powders. It was observed that with the increase of the content of Al2O3 nanoparticles from 2.5vol.% to 5vol.% in the powder mixture, the product of HEMM changed from hollow balls into granules and the average grain size and microhardness changed from approximately 130nm and 185HV to 100nm and 224HV, respectively. On the other hand, HEMM of Cu–(2.5 or 5.0vol.%) Pb powder mixtures under the same milling conditions failed to consolidate the powder in-situ. Instead, it led to formation of nanostructured fine powders with an average grain size of less than 50nm. Energy dispersive X-ray mapping showed homogenous distribution of Pb in the powder particles in Cu–5vol.%Pb alloy powder produced after 12 hours of milling. With the increase of the Pb content from 2.5 to 5.0 vol.%, the average microhardness of the Cu-Pb alloy powder particles increases from 270 to 285 HV. The mechanisms of the effects are briefly discussed.
Authors: Fei Yang, De Liang Zhang, Brain Gabittas, Hui Yang Lu
Abstract: Ti-6Al-4V (wt%) alloy rods were prepared successfully using a low-cost method that combines mixing HDH titanium, elemental aluminum and Al-V master alloy powders and powder compact extrusion. The microstructure and mechanical properties of Ti-6Al-4V alloy and the effects of powder compact holding time on them were investigated. The results showed that powder compact holding time had a significant effect on the microstructure and mechanical properties of the extruded Ti-6Al-4V alloy rods. With increasing powder compact holding time from 2 to 10 min., the microstructure of the extruded rods became more homogeneous, and their UTS decreased from 1300 to 1215MPa and the elongation to fracture increased from 7.1 to 10.2%. 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.
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