Xin Ying Teng

New Thought for Designing the Multi-Phase and Multi-Scale Nanocomposite Ceramic Tool Materials

The new thought for designing the multi-phase and multi-scale nanocomposites was proposed to improve the comprehensive mechanical properties. Multi-phase and multi-scale particles are added to the matrix, and one of the additives is nano-scale particle, thus the comprehensive mechanical properties can be improved by the synergic effects of micro-scale toughening, nano-scale strengthening and mutual benefit between multi-phases. The ideal microstructure of multi-phase and multi-scale nanocomposites was designed. With this microstructure, the trans/intergranular fracture modes can be formed, which will consume more fracture energy during the crack propagation, therefore, both the flexural strength and fracture toughness can be improved. An advanced ceramic tool material has been fabricated based on this new thought.

Preparation of Graphene and Graphene/Al Composites

Metal matrix composites reinforced by graphene particles exhibit physical and mechanical property and are developed and qualified for use in aerospace structure, bioengineering, energy storage material and photoelectric device. In the present paper, graphene was fabricated by modify Hummers method, and then was surface modified by chemical plating copper. The graphene/Al composites were fabricated by powder metallurgic method. Morphology characterization of graphene and composites were detected by XRD and SEM,the fabrication parameters of composites were optimized by testing harness and density. The volume fraction of graphene particles was 3%, the density of composites was maximum of 96.5%. The hardness had a maximum of HB 42.6, and the hardness of graphene/Al composites increased by 33.5%.

Thermal Aging Behavior of CoSb3 with Protective Mo Coating

In order to prevent the sublimation of Sb, protective Mo coatings were deposited on the CoSb3 substrate by DC magnetron sputtering. Thermal aging behavior of CoSb3 with Mo coating was investigated by accelerated experiment at 650oC for 24h. The results indicated that Mo coatings exhibit columnar crystal and body-centered cubic structure. It was found that the weight loss decreases with the increasing thickness of Mo coating. In comparison with naked CoSb3 material, the degradation of thermoelectric properties of CoSb3 with Mo coatings decreases under accelerated thermal aging test.

Study on the Multi-Phase and Multi-Scale Nanocomposite Ceramic Tool Material

An advanced ceramic cutting tool material Al2O3/TiC/TiN is developed by means of adding micro-scale TiC particle and nano-scale TiN particle dispersion. With an optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite may get both higher flexural strength and fracture toughness, especially the fracture toughness may reach to 7.8 MPa·m1/2. The micro-scale TiC particle will form the framework microstructure with other particle and the particles will inlay each other. That is why the flexural strength of Al2O3/TiC composite is improved. Another phase such as nano-scale TiN may lead to fining the grains further more, and promote the sintering to get higher density. The uniform and densified microstructure is obtained, the coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN can result in remarkable strengthening and toughening effect.

Effects of Rare Earth Y Addition on Microstructural and Properties of Pure Copper

The effects of rare earth Y addition on microstructure and properties of pure copper were investigated. Mechanical test, electrical test, oxidation resistance test, metalloscope, scanning electronic microscope (SEM) and X-ray difffraction (XRD) were performed to study the properties, microstructure and constitution. The results showed that both the hardness and antioxidant properties obviously increased with the increase of Y, confirmed the successful refinement role of Y. A small amount of Y (less than 0.5 wt.%) could improve the electrical conductivity of pure copper. When the Y content reached 0.2 wt.%, pure coppers obtained optimum electrical conductivity which is 96.8% IACS. However, over-added Y (>0.5 wt.%) resulted in second phase of Cu7Y coarsening and non-homogeneous microstructures forming, which reduces the conductivity of copper. In addition, Y can effectively purify the organization of molten copper.

Effect of Nd Addition on the Microstructure, Mechanical and Corrosion Properties of Mg-Zn-Y-Nd Alloys

The microstructure of as-cast Mg97-xY2Zn1Ndx (x = 0, 0.5, 1.0 and 2.0 at. %) alloys was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mechanical properties were measured by universal testing machine. The corrosion behavior was evaluated by Tafel curves and hydrogen evolution reaction. The results showed that the α-Mg, MgZn, Mg12Nd and Mg12YZn phases exist in the Mg-Zn-Y-Nd alloy. Mg12YZn is a long period stacked ordered (LPSO) phase. When x is, the addition of less than 1at. % Nd can promote the formation of LPSO phase. The addition of more than 1at. %Nd could result in the formation of Mg12Nd phase, and the volume fraction of the Mg12Nd phase in Mg95Zn1Y2Nd2 alloy is larger than that of others. The ultimate tensile strength (UTS) of Mg96ZnY2Nd1 alloy reaches 197.8MPa because of small grain size and uniform distribution of the LPSO and MgZn phases. The corrosion rate of Mg96.5Zn1Y2Nd0.5 alloy is lower than that of other alloys due to its lower self-corrosion current density and hydrogen evolution rate.

Effect of Cooling Rates on the Solidification and Microstructure of Rapidly Solidified Mg 70.8 Zn 28 Nd 1.2 Quasicrystal Alloy

The influence of cooling rates on the solidification and microstructure of rapidly solidified quasicrystal alloy Mg70.8Zn28Nd1.2(at.%) was investigated. The microstructure, phase constitution, phase transition and phase structure of the alloys were examined by means of scanning electron microscopy, x-ray diffraction, energy dispersive spectrometer, differential scanning calorimetry. The experimental results showed that the phase composition of as-cast Mg70.8Zn28Nd1.2 alloy includes quasicrystal I-phase and Mg7Zn3 phase. For the rapidly solidified alloy ribbons, when the speed is not higher than 400 r/min, the microstructure includes I-phase, Mg7Zn3 phase and α-Mg phase. When the speed is at the range of 400-2000r/min, the Mg7Zn3 phase disappears and only quasicrystal with α-Mg phase exist. With the increase of cooling rate, the grain size decreases and there are a large number of microcrystals in the microstructure. When the speed reaches higher than 2500 r/min, amorphous phase appeared. Differential thermal analysis showed that quasicrystal exist at about 340°C.

Effect of Nd Content and Heat Treatment on Microstructure and Mechanical Properties of Mg-Zn-Nd Alloy

In this paper, the microstructure and mechanical properties of the as-cast and heat treatment of Mg-Zn-Nd alloy was investigated. The alloy was manufactured by a conventional casting method, and then subjected to a heat treatment. The results showed that the microstructure of as-cast alloy was comprised of α-Mg matrix and Mg12Nd phase. With increase of Nd content, the grain size gradually decreased from 25.38 μm to 9.82 μm. The ultimate tensile strength and elongation at room temperature of the Mg94Zn2Nd4 alloy can be reached to 219.63 MPa and 5.31%. After heat treatment, part of the second phase dissolved into the magnesium matrix and the grain size became a little larger than that of the as-cast. The ultimate tensile strength was declined by about 2.5%, and the elongation was increased to 5.47%.

Microstructure and Mechanical Properties of Mg-Er-Zn Alloys with LPSO Phase

As-cast Mg-3Er-xZn (x = 0, 0.5, 1 and 2 at.%) alloys were prepared by a cast ingot metallurgy process. The effect of Zn contents on the microstructure and phase constitution of the alloys was investigated by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and transmission electronic microscope (TEM). The results revealed that the as-cast Mg-3Er alloy mainly consisted of α-Mg phase and MgEr eutectic phase. Typically, a small amounts of LPSO phase was precipitated at grain boundaries by adding 0.5 at.% Zn into Mg-3Er alloy. With the addition of 1 at.%Zn, the volume fraction of LPSO phase increased obviously. When the addition of Zn increased to 2 at.%, the volume fraction of LPSO phase decreases and Mg8ZnEr phase forms at grain boundaries. Tensile test indicated that Mg-3Er-1Zn alloy exhibits the excellent mechanical properties. The tensile strength, yield strength and elongation of Mg-3Er-1Zn alloy are 213 MPa, 187.6 MPa and 5.52%, increased by 38.8%, 60% and 3.19%, respectively, corresponding to the alloy without Zn addition. The excellent mechanical properties could be attributed to the introduction of Zn element in alloys, which leads to the strengthening of LPSO phase and grain refinement of α-Mg.

Influence of Yb Modification on the Microstructure and Mechanical Properties of A356.2 Aluminum Alloy

A356.2 aluminum alloy (Al–7Si–0.35Mg) has been widely used in automotive and aircraft industries. Previous studies found that the metamorphism effect of rare earth is better than other type of elements because of long modification time and good stability. The influence of Yb addition (0%, 0.2%, 0.4% and 0.6%) and T6 heat treatment on A356.2 alloy has been investigated in this work. The microstructures and mechanical properties of the specimen after T6 treatment were examined by optical microscope, scanning electronic microscope and tensile tests. Experimental results showed that Yb could reduce the size of α-Al and change the Si morphology from needle-like to fine spheroidal particles. With the increase of Yb content, the ultimate tensile strength increased gradually. When adding 0.4%Yb, the alloy achieved the highest ultimate tensile strength (252 MPa) and hardness (97.3HB), 10.12% and 37.66% higher than the alloy with no Yb addition. Tensile fracture analysis showed that the fracture mechanism for A356.2 aluminum alloy after T6 treatment is transgranular/intergranular mixed mode of fracture.