Papers by Author: Fan Tao Kong

Abstract: In this paper, the TiAl/Ti laminated (MIL) composite was fabricated via hot-pack rolling of the as-forged Ti-43Al-9V-0.3Y (at.%) plates and commercial Ti6Al4V (wt.%) sheet at 1250°C and then annealed at 90°C for 6 hours. The composite was analyzed by XRD and SEM techniques, respectively. Results showed that the interface between Ti and TiAl in the composite was consisted of four different microstructure areas and the phase constitutions for each area were: area 1: acicular β-Ti and α₂ phase; area 2: acicular α₂ phase; area 3: acicular α₂ phase and B2 matrix; and area 4: acicular γ, α₂ phase and B2 matrix. The fracture toughness of the TiAl/Ti MIL composite was tested, showing that the K_IC value was about 38.35MPa·m^1/2 at room temperature and higher than that of the pure Ti-43Al-9V-0.3Y alloy, which had a value of about 24.72 MPa·m^1/2. The possible toughening mechanism for the TiAl/Ti MIL composite was discussed.

Abstract: TiAl alloy with a composition of Ti-43Al-5V-4Nb-Y (at.%) was prepared by spark plasma sintering (SPS). The TiAl powders were sintered between 650°C and 1300°C for 5 min under different loads. With the increasing of the temperature, the diffusion of the elements can be observed. Full compaction is achieved in a short period of time and the overall processing duration does not exceed 30 min. A fully lamellar structure was seen in the TiAl alloy after heat treatment. The microstructures of the samples were determined by X-ray diffraction and scanning electron microscopy. Their mechanical properties were evaluated by tensile tests performed at room temperature

Abstract: In the present study, Ti-6Al-2.5Sn-4Zr-0.7Mo-0.3Si-0.3Y alloy matrix composites reinforced with TiB and TiC were fabricated by combustion-assisted cast utilizing the reaction between titanium and B₄C, graphite. The microstructure, room temperature mechanical properties were presented and discussed. Microstructural analysis of the composites revealed that the prior β grain size as well as the thickness of α colony significantly refined with increasing of volume fraction. At room temperature (RT), tensile strength and elastic modulus increase significantly, while the ductility drops gradually possibly because of the cracking of TiB whiskers and TiC particles.

Abstract: Investment casting technique presents more advantages in the production of accuracy and versatility components. The mechanical performance of the ceramic shell is crucial to the quality of the castings. The slurry parameters can affect the properties of the ceramic shell. The purpose of this paper is to investigate the physical properties of primary slurry for titanium and titanium alloy investment casting. Three different slurries (ZrO2, Y2O3 and Al2O3) were evaluated respectively by comparing the parameters: viscosity, bulk density, particle size distribution, thixotropy and suspension percentage of slurries. The results show that the physical properties of primary slurry were mostly determined by the type and content of refractory materials. Refractory particle morphology and the particle size distribution affect slurry rheology and viscosity.

Abstract: Ti-6Al-2.5Sn-4Zr-0.7Mo-0.3Si-0.3Y alloy matrix composite reinforced with 7%vol TiB whiskers was fabricated by Induction Skull Melting (ISM) technique and one-direction forged technology utilizing the reaction between titanium and TiB2. The microstructure, room temperature and high temperature mechanical properties have been presented and discussed. Microstructural analysis of the composites revealed that the microstructure was significantly refined and TiB whiskers were made to align the longitudinal direction after forging. It shows that the tensile strength and ductility of the composites has a significant improvement, especially at room temperature.

Abstract: Ti-47Al-2Cr-2Nb-Y alloy pancake were produced by hot-pack forging. The microstructure of as-forged Ti-47Al-2Cr-2Nb-Y alloy were investigated by optical microscopy and scanning electron microscopy, showing that the forged alloy was composed of fine γ grains and retain cast lamella colonies surrounded by elongated B2 phase. Tensile properties of the material showed that yield strength (YS) and ultimate tensile strength (UTS) were decreased from 500MPa and 612MPa at room temperature to 420 MPa and 462 MPa at 800°C, respectively. With the temperature increasing to 900°C, elongation reached 120%.

Abstract: Ti-43Al-5V-4Nb (at.%) intermetallic compounds with fully lamellar structure were fabricated by forging method without canning using the blended elemental powders. The process route consisted of powder blending, compacting, sintering and final fabrication by hot forging. During sintering, there existed expansion, which is detrimental to forging process. In order to overcome the difficulty, two-step forging was introduced. The total reduction of two-step forging was up to 65%. Nearly fully lamellar structure of TiAl alloy was obtained. Overall, an optimized and potentially lower cost processing route could be identified.

Abstract: Effects of different Mo contents on microstructures and properties of Ti-22.5Al-20Nb-2V(at.%) were analyzed in this paper. Experimental results showed that the grain size was refined and the amounts of equiaxed α2 phases decreased with increase of Mo from 0.6at.% to 1.5at.%. The size of (O+B2) lath was refined when Mo from 0.6at.% to 1.2at.%. However, it seems that Mo easily segregate especially in grain boundary and become seriously with Mo increased. Compression tests showed that the yield strength and ultimate strength of alloys were obviously improved with Mo addition from 0.6at.% to 1.2at.%. Microhardness tests showed the same trend with compression yield and ultimate strength.

Abstract: The paper outlines some research work that has been conducted in Harbin Institute of Technology, on the fabrication of TiAl alloys. The review is presented with special emphasis on some different manufacturing routes of TiAl alloys, including investment casting, canned forging and sheet rolling, mechanical milling and rapid solidification. Investment casting has been developed to manufacture near-net shape TiAl blades. Also included are current development of canned forging and rolling for TiAl sheets. Then, TiAl nanocrystalline powders gained through low temperature and two steps mechanical milling were researched. And considerably refined TiAl alloys with Y additions were produced by rapid solidification and the microstructure evolution with Y addition was studied. Details of the processing route and microstructure related to different processing method will be presented.

Abstract: γ-TiAl components due to their unique properties are on the verge of industrial application for increasing operation temperature and improving energy efficiency, especially in aerospace and automobile areas. This paper describes the recent developments of hot precision processing in ingot metallurgy technology including investment casting, canned forging and sheet rolling of TiAl alloys. Alloys development and the melting technology were discussed. Investment casting of TiAl alloys has been successfully developed to manufacture net-shape components. Research aimed at producing TiAl sheets through canned forging and rolling is introduced.