Papers by Author: Chang Xu Hu

Abstract: Ti, SiC and their composite materials have been widely used as high temperature structural material. The knowledge of interfacial stability between SiC and Ti is vital in high temperature applications. In this study, SiC/Ti diffusion couples were prepared to investigate the interfacial reactions between SiC and Ti at 1273 K. Phase forming sequence, microstructure and thermal stability of SiC/Ti interface were studied. It was indicated that after annealed at 1273 K for 10 days, 4 reaction layers were formed at the SiC/Ti interface. The diffusion path between SiC and Ti is SiC/Ti₃SiC₂/Ti₅Si₃/Ti₅Si₃+TiC/Ti₃Si/Ti. As the annealing time prolong, the thicknesses of these reaction layers increased.

Abstract: Mo-Ti₃SiC₂ layered composite was successfully prepared by spark plasma sintering at 1573 K for 20 min under a pressure of 50 MPa in vacuum. The Mo and Ti₃SiC₂ layers were metallurgically bound together without noticeable superficial defects and micro-cracks at the interface. The fabricated Mo-Ti₃SiC₂ layered composite was annealed at 1273 K under vacuum for 5, 10, 20 and 40 h to study the composite’s thermal stability. Three intermediate layers, Mo₂C, MoSi₂ and Ti₅Si₃C_x, were formed at the interface. Experimental results showed that the Mo-Ti₃SiC₂ layered composite prepared in this study has good interfacial stability at elevated temperature.

Abstract: Mo-Ti3SiC2 layered material was prepared by spark plasma sintering. Mixed Ti, Si, graphite and Al powder with molar ratio of 3Ti:1Si:2C:0.2Al was put into a graphite mould and pressed with a pressure of about 0.5 MPa, then, Mo powder was put on top of the mixed powder. Experimental results showed that Mo-Ti3SiC2 layered material could be fabricated successfully by sintering the above powder mixture at 1300°C for 20 minutes under a pressure of 50 MPa in vacuum. The surface and interfaces of the layered composite were tight and clear without any observable crack. In order to study the thermal stability at elevated temperature, the fabricated Mo-Ti3SiC2 layered composite was heat treated at 800°C for 5, 10, 20 and 40 hours. After 40 hours of annealing, the intermediate layers formed between the Mo and Ti3SiC2 matrix grew thicker. The interfaces are clean and tight with no obvious formation of voids and new phases. The initial 10 hours of annealing is the fast growing period, after that, the growth rate slowed down significantly.

Abstract: Powder metallurgy process is a net-shape manufacturing technique that can eliminate or reduce machining time. It is economical and environmental friendly since no scrap is being produced and no high energy consuming process such as melting is involved. Unfortunately, conventional powder metallurgy is not capable of producing complex parts. However, a recently developed binder-treated warm compaction technique can overcome this problem by increasing the flowability of the mixed powder. In this study, by using a commercially available water-atomized iron powder, a cross-shaped part was prepared by warm compaction of a binder-treated iron-base powder at approximately 80 °C and then sintered at 1120 °C. Microstructure, mechanical property and shape consistency of the prepared part were examined. Results showed that parts with high density and high green strength can be obtained without significant shrinkage or expansion. The present paper demonstrated that the binder-treated warm compaction process can expand the capability of powder metallurgy techniques to produce complex parts.

Abstract: A simple and economical powder metallurgy forming process known as warm compaction was employed to fabricate a Cu-Ti3SiC2 particulate reinforced copper matrix composite for electro-friction purpose. Copper matrix composites reinforced with 5, 10, 15 mass% Cu coated Ti3SiC2 particulate were prepared by compacting the powder mixture with a pressure of 700 MPa at 145°C, and then sintered at 1000°C under cracked ammonia atmosphere for 60 minutes. Their density, hardness, tensile strength, elongation and electrical resistivity were studied. Result showed that within a reasonable limit, the addition of Ti3SiC2 particulate can increase the hardness of the composite without losing much of electrical conductivity. Sintered composite with 5 mass% Ti3SiC2 has an ultimate tensile strength of 182 MPa with an elongation of 10%, a hardness of HB 68 and a resistivity of 8.0×10-8Ωm. Compared with the samples using uncoated Ti3SiC2 particulate, the resistivity of the samples prepared by using the Cu coated Ti3SiC2 particulate have a better conductivity, but have a slightly lower mechanical property.

Abstract: 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.