Papers by Author: Wan Jiang

Abstract: Joining of TE material to electrode is the key technique in the construction of TE device for the practical applications. In this study, a suitable alloy electrode was introduced into CoSb3-based element by means of spark plasma sintering (SPS). Finite element analysis showed that the maximum thermal residual stress appeared at the cylindrical surface zone close to the CoSb3/electrode interface. Microstructure of CoSb3/electrode was investigated by EPMA and the intermetallic compound (IMC) layers were found. The shear strength of CoSb3/electrode joints was tested and the results show that the joints have sufficient strength for reliability of TE device. Electrical contact resistance between CoSb3 and electrode was measured by means of four-probe technique. The results show that the contact resistance was minimal and below the 50μΩ.cm2, which meant the joint exhibited a good electrical contact. The high temperature reliability evaluation showed good thermal duration stability of the CoSb3/electrode joints.

Abstract: Ga-substituted Ge based type-I clathrates with the general formula A8X16Y30 display promising thermoelectric performance. Using high purity elemental Sr, Ba, Ga, and Ge as starting materials, polycrystalline co-filled type-I clathrate compound (Sr,Ba)8Ga16Ge30 were successfully achieved by combining melting and Spark Plasma Sinter (SPS) method. The temperature dependence of thermal conductivity, electronic conductivity and Seebeck coefficient were reported. The calculated ZTmax is 0.28 at 700K. Enhanced thermoelectric performance would be expected through adjusting Sr/Ba ratio and framework atoms.

Abstract: In this study, we designed a suitable electrode material was designed, Cu-W alloy, which achieved a good thermal match with CoSb3 thermoelectric (TE) material. By means of spark plasma sintering (SPS), Cu-W alloy was introduced into CoSb3/Ti/Cu-W TE element successfully. Finite element analysis showed that the maximum thermal residual stress appeared at the cylindrical surface zone close to the CoSb3/electrode interface. SEM and EPMA results showed that an intermetallic compound (IMC) layer formed at the CoSb3/Ti interface and EDS analysis confirmed the IMC layer was TiSb phase. Shear tests showed that the shear strength of CoSb3/Ti/Cu70W30 joint was about 50Mpa. The potential profile of the interface area was measured by the four-probe method and the result showed no abrupt change in voltage was found around the interface. The high temperature reliability evaluation showed the joint had high thermal duration stability.

Abstract: Fatigue behaviors of conventional alumina ceramics in cyclic loading with hemisphere and cylinder punches are investigated with modified small punch (MSP) tests. Residual strengths are used to quantify the degree of fatigue damage. The dependences of the residual MSP strength on loading mode, cyclic loading magnitude, frequency, and puncher shape have been discussed in detail. Fatigue behavior studies could be very convenient and effective because MSP tests could perform the cyclic loading and then evaluate the residual strength consistently and effectively.

Abstract: Ti5Si3-TiC-Ti3SiC2 composites containing different Ti3SiC2 volume fractions from 0 to 50% were in-situ fabricated by spark plasma sintering using Ti and SiC powders through adjusting the molar ratio of Ti to SiC. The morphologies of the fracture surfaces were analyzed by scanning electron microscopy (SEM). The room temperature mechanical properties of composites including hardness, bending strength and fracture toughness were tested.

Abstract: Ti3SiC2/20vol%SiC composite was synthesized by spark plasma sintering (SPS) under a pressure of 50MPa at 1350°C using Ti, Si and C as starting powders. The phase constituents and microstructures of the composite were investigated. X-ray diffraction (XRD) results demonstrated that Ti reacted with C to form TiC firstly, then TiSi2 formed from Ti and Si. The formation of Ti3SiC2 might come from two reactions. One was that TiSi2, Ti and TiC reacted directly to form monolithic Ti3SiC2. The other one was that TiSi2, Ti and C reacted to form Ti3SiC2 and SiC. The EPMA results showed that the main phases were Ti3SiC2 and SiC with a minor content of TiC as impurity. TiC particles less than 1μm in diameter distributed in SiC phase.

Abstract: In-situ toughened TiC-Ti5Si3 composites were fabricated using reactive sintering of Ti and SiC via spark plasma sintering (SPS). The focus of this work on the content of TiC in final composites was different. The phase constituents and microstructures of the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Fracture toughness at room temperature was also measured by indentation tests. The results showed that the corporation of TiC greatly enhances the fracture toughness of TiC-Ti5Si3 composites.

Abstract: The room temperature fracture toughness and the high temperature DBTT of MoB particle-reinforced MoSi2 composites were investigated using Vickers indentation technique and MSP testing method， respectively. Modified Small Punch (MSP) test is a method for evaluation of mechanical properties using very small specimens, and it’s appropriate for the determination of strength and DBTT. It was found that the approximate fracture toughness of the composite is 1.3 times that of monolithic MoSi2, and its DBTT is 100°C higher than that of monolithic MoSi2 materials. Cracks deflection is a probable mechanism responsible for this behavior.

Abstract: A combustion front quenching (CFQ) technique was used to investigate the mechanism of selfpropagating high-temperature synthesis (SHS) of MoSi2 from Mo and Si powders. Based on the experimental results, a combination of reactive diffusion and dissolution-precipitation mechanism of the formation of MoSi2 was proposed, and a model corresponding to this mechanism was drawn.

Abstract: Lanthanum-modified lead zirconate-titanate (PLZT5/54/46) powders were prepared from the commercial PbO, La2O3, TiO2 and ZrO2 powders by high-energy ball milling process. The synthesized powders milled for different hours were characterized using XRD and SEM. Thedesigned PLZT perovskite phase was formed from the mixture of the starting materials after milling for 20 hours. PLZT(5/54/46) ceramics were obtained using the produced powders milled for 20 h followed by sintering at temperatures ranging from 1000 to1200°C. Ferroelectric property of the PLZT ceramics was also measured.