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ABSTRACT: The oxidation behaviors of TiB and TiC particle-reinforced, titanium-matrix composites (TMCs) were studied in air at 550–650°C, The oxidation kinetics follow approximately a parabolic rate law. The oxidation rates, which were lower than those of Ti6242, decrease gradually as oxidation proceeds. The oxide scales formed on TMCs were predominantly rutile and α-Al2O3. No B2O3 and other oxides were observed within the oxide scale. The in situ-synthesized TiB and TiC reinforcements can increase the oxidation resistance of TMCs. The oxide scales that formed exhibited excellent spallation resistance under all testing conditions. No scale cracking or spallation could be observed, implying that growth and thermal stresses generated during heating and cooling have been effectively released. The mechanisms of the decrease in oxidation rate and the improvement on spallation resistance are discussed based on microstructure studies.
Oxidation of Metals 01/2006; 66(5):253-268. · 1.40 Impact Factor
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ABSTRACT: The oxidation behavior of an in situ synthesized TiB reinforced Ti-Al-8(vol%)B composites (TMCs) and Ti-Al were studied at 823, 873, and 923K in atmospheric
air. The oxidation kinetics follows a parabolic rate law. The oxidation rate decreases gradually as the oxidation proceeds.
Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry, and transmission electron microscopy (TEM) were
used to identify oxidation products and characterize oxide scale morphology. The oxide scale formed on TMCs was predominantly
rutile TiO2 and α-Al2O3. No B2O3 and other oxides were observed within the oxide scale. The in situ synthesized TiB particles can increase the oxidation resistance of TMCs. It is attributed to the enhanced alumina-forming
tendency, the formation of thin and dense oxidation, and the interface cohesion and the clean interfacial microstructure before
and after oxidation between the reinforcements and the titanium matrix alloy.
Journal of Materials Science 11/2005; 40(24):6553-6558. · 2.02 Impact Factor
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ABSTRACT: In the present work, (TiBw+ TiCp)/Ti6242 composites were fabricated via common casting and hot-forging technology utilizing the SHS reaction between titanium and B4C. The XRD technique was used to identify the phases of composites. The microstructures were characterized by means of OM and TEM. Results from DSC and analysis of phase diagram determine solidification paths of in situsynthesized Ti6242 composites as following stages: -Ti primary phase, monovariant binary eutectic -Ti + TiB, invariant ternary eutectic -Ti + TiB + TiC and phase transformation from -Ti to -Ti. In situsynthesized reinforcements are distributed uniformly in titanium matrix alloy. Reinforcement TiB grows in whisker shape whereas TiC grows in globular or near-globular shape. TiB whiskers were made to align the hot-forging direction after hot-forging. The interfaces between reinforcements and Ti matrix alloy are very clean. There is no any interfacial reaction. Moreover, the mechanical properties improved with the addition of TiB whiskers and TiC particles although some reduction in ductility was observed. Fractographic analysis indicated that the composites failed in tension due to reinforcements cracking. The improvements in the composite properties were rationalized using simple micromechanics principles. The strengthening mechanisms are attributed to the following factors: undertaking load of TiB whiskers and TiC particles, high-density dislocations and refinement of titanium matrix alloy''s grain size.
Journal of Materials Science 07/2001; 36(15):3707-3714. · 2.02 Impact Factor
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ABSTRACT: In the present work, a novel titanium matrix composite reinforced by TiB and Nd2O3 was prepared through the synthesis reaction from Ti, B2O3 and Nd with nonconsumable vacuum arc melting. The result shows that the reinforcements are TiB and Nd2O3. TiB grows in needle shape, while Nd2O3 grows in sphere and dendritic shapes.
Materials Letters.
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ABSTRACT: TiC reinforced titanium matrix composites were produced by non-consumable arc-melting technology utilizing the self-propagation high-temperature synthesis (SHS) reaction between titanium and graphite. X-Ray diffraction (XRD) was used to identify the phases in the composites. Microstructures of the composites were observed by optical microscope (OM) and transmission electron microscope (TEM). The results show that there are two phases in the composites: TiC and titanium matrix alloy. TiC has two different shapes: dendritic shape, equiaxed or near-equiaxed shape. The in situ synthesized TiC grows by dissolution–precipitation. Analysis of the binary phase diagram determined that the solidification path undertook the following three stages: primary TiC, binary eutectic β-Ti+TiC and solid transformation. Primary TiC grows in dendritic shape due to the formation of composition undercooling. Binary eutectic TiC grows in equiaxed or near-equiaxed shape. A small quantity of TiC may form twin structure during nucleation and growth. The twin plane is the (111) plane.
Journal of Alloys and Compounds.
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ABSTRACT: Titanium matrix composites reinforced with TiB and TiC were fabricated by a non-consumable arc-melting technology utilizing self-propagation high-temperature synthesis reaction between titanium and B4C. Microstructural characterization of in situ synthesized TiB was observed by scanning electron microscope (SEM), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HREM). The TiB shows a typical whisker shape and the crystallographic planes of the TiB at transverse cross-section are always of the planes (100), (101) and (10). Stacking faults are observed in the TiB. The TiB forms in a way of nucleation and growth. The growth morphologies and formation of the stacking faults are related to crystal structure of the TiB. Due to its B27 structure, the TiB is likely to grow along [010] direction and form the whisker shape. The stacking faults are also likely to form in the (100) plane. The formation of above morphologies and the stacking faults serves to minimize the lattice strain at the interface between the TiB and the titanium matrix alloy.
Journal of Alloys and Compounds.
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ABSTRACT: Titanium matrix composites reinforced with TiB and Y2O3 were prepared by a non-consumable arc-melting technology. X-ray diffraction (XRD) was used to identify the phases in the composites. Microstructures of the composites were observed by means of optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that there are two kinds of reinforcements formed in the titanium matrix, needle-shaped TiB and Y2O3 with near-equiaxed and dendritic shape. The interfaces between reinforcements and titanium are clear and there is no evidence of interfacial reaction. The hardness of the composites decreases with the increasing contents of yttrium in the composite.
Materials Research Bulletin. 39(6):873-879.
