Yuan Yuan Li

Glass-forming ability of Pr-(Cu, Ni)-Al alloys in eutectic system

A eutectic point in Pr-rich Pr-(Cu,Ni)-Al alloys was experimentally determined by measuring the solidus temperature (T m ) and liquidus temperature (T,). It was found that Pr 6 8 (Cu 0 . 5 Ni 0 . 5 ) 2 5 Al 7 (at.%) is at the eutectic composition in the pseudoternary Pr-(Cu 0 . 5 Ni 0 . 5 )-Al alloys. The alloy Pr 6 8 (Cu 0 . 5 Ni 0 . 5 ) 2 5 Al 7 exhibits better glass-forming ability (GFA) than the ternary eutectic alloy Pr 6 8 Cu 2 5 Al 7 . However, the best GFA was obtained at an off-eutectic composition (Pr 5 4 [Cu 0 . 5 Ni 0 . 5 ] 3 0 Al 1 6 ) in the Pr-(Cu 0 . 5 Ni 0 . 5 )-Al alloys, which can be formed in fully amorphous rods with diameter of 1.5 mm by copper mold casting. Moreover, the glass-transition temperature T g increases quickly (from 367 to 522 K) with the increasing of the Al content (from 3 to 27 at.%). The deviation of the best GFA composition from the eutectic point [Pr 6 8 (Cu 0 . 5 Ni 0 . 5 ) 2 5 Al 7 ] was explained in terms of the asymmetric coupled eutectic zone, the competition between growth of crystalline phase and formation of amorphous, and the higher glass-transition temperature T g on the hypereutectic side.

Fabrication of biomedical Ti–35Nb–7Zr–5Ta alloys by mechanical alloying and spark plasma sintering

Abstract Ti–35Nb–7Zr–5Ta biomedical alloys were fabricated by spark plasma sintering of nanocrystalline powders by mechanical alloying. After 60 h milling, mixtures of respective elemental powders transformed into a homogeneous structure of completed β-Ti solid solution. The grain size of the milled powder was ∼9 nm. Subsequently, the obtained nanosized grained powder was consolidated into bulk form by spark plasma sintering at different sintering parameters. At a sintering temperature of 1373 K, the fabricated bulk alloys reached nearly full density. The microstructure of the fabricated alloys was of hcp α-Ti regions surrounded by bcc β-Ti regions. In addition, fracture strengths, Young’s modulus and microhardness of the fabricated alloys were investigated to explore the potential adaptability of the fabricated alloys as human implant.

Biomedical porous TiNbZrFe alloys fabricated using NH4HCO3 as pore forming agent through powder metallurgy route

Abstract Porous Ti59.38Nb26.6Zr8.7Fe5.32 (wt-%, referred to as TNZF) alloys with high strength and low modulus were successfully fabricated by space holder method through adding ammonium hydrogen carbonate (NH4HCO3). Results show that the fabricated porous TNZF alloys are of β type titanium alloy with adjustable pore characteristics and mechanical properties. Varied amount of NH4HCO3 exerts significant effects on phase constituents, pore characteristics and mechanical properties of the porous alloys. Fracture mechanism of the porous alloys, which is different from the typical brittle fracture as a result of high porosity, exhibits transgranular fracture accompanied with cleavage steps. Strain increased even under low stress during the compressive deformation, demonstrating that the porous alloys possess certain ductility. The porous TNZF alloys with a porosity of 39–53%, an average pore size of 300–800 μm and a compressive modulus of 7–16 GPa and a compressive strength of 117–204 MPa can well meet the requirements of biomedical implant materials.

Application of Polymer Plating to Inhibit Corrosion of Magnesium Alloy

An organic compound of dihexyl-contained triazine dithiol was specially synthesized for surface modification of magnesium alloy AZ91 in order to improve its corrosion resistance. The nano-scale polymer film on the surface of AZ91 was created with the synthesized compound by means of electrochemical measuring system called as polymer plating in the electrolytic solution. The modified surface of AZ91 had the peculiar functional characteristic of water repellency to inhibit corrosion. Corrosion tests were carried out with methods of polarization curve and electrochemical impedance. The corrosion resistance was evaluated from corrosive current density and reactive resistance. When concentration of the compound was set on 8 mol/m3, the good corrosion resistance was obtained for low corrosive current density and high reactive resistance in NaCl aqueous solution at 303K.

A new general equation of mean particle size for different atomization processes

In conventional studies, different empirical atomization equations are correlated for different kinds of atomization methods or even in the same method. In the present study, it was found that the basic law of melt breakup from bulky liquid into droplets can be universally applied to all atomization methods. Based on theoretical analysis, a new general equation of mean particle size applicable to both conventional atomization methods and new atomization processes is presented. The mean particle size in melt atomization is mainly controlled and decided by two key dimensionless parameter groups representing the liquid stability of melts and the breakup ability of atomizer respectively. Different specific atomization mechanisms result in different formulae in conventional atomization methods. In case of gas atomization, it is equivalent with and can be changed into Lubanska Equation. In case of centrifugal atomization, it can be changed into the equations that are currently the most widely used. In case of water atomization, it is similar to the equation proposed by Grandzol and Tallmadge. According to the universal equation, new correlations for mean particle size in novel atomization processes such as Hybrid Atomization and Multistage Atomization were proposed and agreed with our experimental data well.

High Plastic Ti66Nb13Cu8Ni6.8Al6.2 Composites with in-situ β-Ti Phase Synthesized by Spark Plasma Sintering of Mechanically Alloyed Glassy Powders

High plastic Ti66Nb13Cu8Ni6.8Al6.2 composites with in situ precipitated ductile -Ti phase were firstly synthesized by mechanical alloying and subsequent consolidation by spark plasma sintering with crystallization. Microstructure analysis indicated that all composites contain soft (Cu, Ni)-Ti2 regions and hard -Ti regions, but the two regions have different scale and distribution. The synthesized composites exhibit high fracture strength of 2415 MPa and large plasticity as high as ~31.8%. The large plastic deformability was well explained based on the distinctive microstructure by a developed “hard-soft model”.

Direct Joining of Acrylic Rubber to Cast Iron with Functional Nanofilm by Polymer Plating

The nanoscale functional thin film with the affinity to acrylic rubber was formed on the surface of a high ductile spheroidal-graphite cast iron by means of polymer plating of 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium salt. The direct joining of acrylic rubber to the cast iron was achieved with the functional nanofilm during curing. High peel strength adherend of the rubber/cast iron was obtained with suitable film thickness and good film quality under curing at 453 K for 18 min. When the film thickness was 8.53 nm, peel strength of the adherend was high to 4.9 kNm-1, and its broken-out section was rubber cohesive failure. The film thickness considerably affected peel strength and rubber coverage. Moreover, the current density of polymer plating had largely influence on mass and quality of thin film, thereby on joining property of acrylic rubber to the cast iron. The good joining property results from chemical bond within interfacial layer of acrylic rubber chain and reactive groups of nanofilm polymer-plated on the surface of cast iron.

Effect of Si Content on the Synthesis of Ti3SiC2 Bulk Material by Pressureless Sintering

Ti3SiC2 is a bioinert material. The combination of high fracture toughness, excellent corrosion resistance and easy machinability make it a new class of potential biomaterials for orthopedic applications, dental implants, and fixation devices for the bone. In this paper, effect of Si concentration on the sintering of Ti3SiC2 bulk material was reported. Ti3SiC2 bulks were fabricated by pressureless reactive sintering of powder compacts made of Ti, Si and graphite powders. Nearly pure Ti3SiC2 bulk was obtained by reactive sintering of the powder compact, with a nominal composition of 3:1.1:2 in molar ratio of Ti:Si:C, at 1500 °C for 120 minutes. TiC, a non-preferable impurity was avoided by the appropriate addition of excess Si (relative to stoichiometric composition of 3:1:2 in Ti3SiC2). However, too much Si will result in the formation of significant amount of TiSi2 and SiC in the sintered Ti3SiC2. Microstructure of the prepared Ti3SiC2 bulks was analyzed by scanning electron microscope. Phase constituent analysis was carried out by x-ray diffraction. Effect of Si content on the density of sintered samples was also studied.

Spatial Structure Injection Molding Analysis of Suspended Bio-Carriers

The realizability for spatial structure of suspended bio-carriers should be considered in the process of structure designing. Injection molding analysis could obtain the injection performance of spatial structure, and provide the references for economic benefit of structure realization and structure optimization, so it become an important tool for structure designing and optimization. In oder to apply the injection molding analysis to the process of bio-carriers designing, three structures, multi-plane spherical structure, straight chip columnar structure, wing panel structure are designed. Their injection performances, such as best location of injection, fill time, and injection pressure are be compared, the results show that the multi-plane spherical structure has the best injection economic benefit.

A Study on Ti3SiC2 Reinforced Copper Matrix Composite by Warm Compaction Powder Metallurgy

Increasing density is the best way to increase the performance of powder metallurgy materials. Conventional powder metallurgy processing can produce copper green compacts with density less than 8.3g/cm3 (a relative density of 93%). Performances of these conventionally compacted materials are substantially lower than their full density counterparts. Warm compaction, which is a simple and economical forming process to prepare high density powder metallurgy parts or materials, was employed to develop a Ti3SiC2 particulate reinforced copper matrix composite with high strength, high electrical conductivity and good tribological behaviors. Ti3SiC2 particulate reinforced copper matrix composites, with 1.25, 2.5 and 5 mass% Ti3SiC2 were prepared by compacting powder with a pressure of 700 MPa at 145°C, then sintered at 1000°C under cracked ammonia atmosphere for 60 minutes. Their density, electrical conductivity and ultimate tensile strength decrease with the increase in particulate concentration, while hardness increases with the increase in particulate concentration. A small addition of Ti3SiC2 particulate can increase the hardness of the composite without losing much of electrical conductivity. The composite containing 1.25 mass% Ti3SiC2 has an ultimate tensile strength of 158 MPa, a hardness of HB 58, and an electrical resistivity of 3.91 x 10-8 Ω.m.