Hong Liang Sun

In Situ Fabrication of Particles Reinforced Al-Si-Al2O3 Composites by Hot Isostatic Pressing

Particles reinforced Al-xwt.%Si-Al2O3 (x=10,20) composites are fabricated through in situ reaction sintering of Al and SiO2 powder by hot isostatic pressing. Outgassing process and the microstructure of composites under different sintering processes are studied.XRD analysis confirms that the best hot outgassing temperature is 500°C,in situ reaction achieves completely and samples A2 and B2 have better microstructure at 550°C then heating-up to 700°C only for 1h.The microstructure analysis indicates that the reinforcement particulates distribute uniformly in the aluminum matrix.The mechanical properties test results show that the tensile strength of A2 is higher than B2. when x=10,the Al-Si-Al2O3 composites have better performance.

Oxidation Behaviors of TiB2-TiCX and TiB2-TiCX/15SiC Ceramics

Fully dense samples of TiB2-TiCX and TiB2-TiCX/15SiC ceramic composites were fabricated by in-situ synthesis under hot isostatic pressing from TiH2, B4C and SiC powders. Their oxidized behaviors at different temperatures were tested. Optical micrograph studies and thermo-gravimetric analyses show that the highest effective temperature of oxidation resistance is 700°C for TiB2-TiCX, and 1100°C for TiB2-TiCX/15SiC. The weight gain of TiB2-TiCX/15SiC below 1100°C is quite low, and it rises up suddenly when the temperature reaches 1200°C. Thus, the highest effective temperature of oxidation resistance is 1100°C for TiB2-TiCX/15SiC. The oxidation dynamic curves of TiB2-TiCX/15SiC ceramics accord with the parabola’s law. The activation energy of TiB2-TiCx/15SiC (189.87kJ.mol-1) is higher than that of TiB2-TiCx (96.44kJ.mol-1). In the oxidation process of TiB2-TiCx/15SiC, TiB2 reacts with oxygen and generates TiO2 and B2O3 at first. A layer of whole homogeneous oxide film cannot be formed, in the mean time, the oxidation of TiC begins. When temperature goes up to 1000°C, TiC phase is totally oxidized. SiC is oxidized to SiO2 at about 900°C, Meanwhile, TiO2 forms denser film than B2O3, which grows and covers the surface of the material, and gives better property of oxidation resistance.

In Situ Synthesis of TiB2-TiC0.8-40vol%SiC by Hot Pressing

TiB2-TiC0.8-40vol%SiC multiphase ceramics were prepared by in-situ hotpressing sintering. The phase composition and microstructures of the materials were characterized by optical mic- oscope, X-ray diffraction and scanning electron microscopy. The effects of sintering temperature on the phases, microstructures and mechanical properties of the ceramics were investigated. The results show that density, bending strength and fracture toughness of the ceramics are increased with the elevation of sintering temperature (1800-1950°C). High densified TiB2-TiC0.8-40vol%SiC multipha- se ceramics and optimized microstructure is obtained by sintering at 1900°C, in which the uniform distribution of lath-shape TiB2 and bulk TiC0.8 grains can be observed obviously. Nano-SiC particles distributed dispersively in the TiB2 and TiC0.8 grains and at boundaries. The Vickers hardness, fract- ure toughness, flexural strength and electrical conductivity of the TiB2-TiC0.8-40vol%SiC multipha- se ceramics sintered at 1900°C are 24.055GPa, 8.27±1.0MPa∙m1/2, 516.69MPa and 2.2×106S∙m-1, respectively. However, up to 1950°C, TiB2 and TiC0.8 grains gradually grew up, the bending stren- gth of multiphase ceramics was decreased greatly. In addition, TiB2, TiC0.8 and SiC particles were incorporated together to improve the particulate strength and toughness of composite material by the synergistic mechanism effects among the crystal phases in the multiphase ceramics, such as crack deflection, grain’s pull-out and fine-grain toughening.

Effect of Isothermal Forging on Microstructure and Mechanical Properties of TiAl-Based Alloys

The effect of isothermal forging on microstructure and mechanical properties of Ti-44Al-4Nb-4Zr-0.2Si-1B alloys were investigated by means of BSE, TEM, tensile and the high cycle fatigue test at room temperature. The results showed that the lamellar thickness and volume fraction of equiaxed γ phases and B2+ω phases decreased, the grain size and volume fraction of lamellar α2+γ colonies was raised after isothermal forging. The lamellar was bending. The tensile strength and yield strength was increased by 80MPa although the total elongation hardly changed. The fatigue limit was increased by 230MPa. The effect of boride, lamellar thickness and B2+ω phases on the mechanical properties were studied.

Effect of Tungsten Addition on Microstructure and Mechanical Properties of TiAl-Based Alloy

The effect of different tungsten addition on microstructure and mechanical property of TiAl-based alloy was investigated. The results indicate that the size and amount of β (B2) phase and equiaxed γ phase gradually increase with increasing content of tungsten. The grain size and lamellar spacing obey a parabolic law. The tungsten addition can increase the room temperature strength, high temperature strength but have a little effect on the ductility. The creep rupture life has inverse correlation relationship with the content of tungsten.

Preparation of the BaO-B2O3 Matrix Low-Temperature Sintering Ceramics via an Aqueous Suspension Route

Due to the low-meting characteristics of the BaO-B2O3 binary composition, the dense ceramics with peculiar properties, so called low-temperature sintering ceramics, were prepared by the introduction of other oxides, e.g., SiO2, Al2O3, ZnO, CaO to the BaO-B2O3 binary compositions at a sintering below 1000°C. The low-temperature preparation of the ceramics are achieved by milling the aqueous suspension mixtures of Ba (OH)2·8H2O, H3BO3 ,H2SiO3, Al (OH)3, ZnO. By the aqueous suspension process, some compounds with a low-melting point such as hydrated barium borate, and the precursor compounds of the functional mineral phases, e.g., BaSiO3, ZnSiO3, BaAl2Si2O8, etc. can be formed easily from a suspension solution, which consequently supply more possibilities to fabricate the low-temperature sintering ceramics with peculiar physical properties.

Peritectic Reaction of High Nb and W Pentatomic TiAl-Based Alloy

The effect of different aluminum content on peritectic reaction and mechanical properties of pentatomic TiAl-based alloy was investigated. The results indicate that the grain size gradually increase with increasing content of aluminum and addition 45.7% aluminum in TiAl-based alloy results in that the peritectic reaction can increase grain size greatly, respectively. The content of aluminum can increase the room temperature strength, high temperature strength but peritectic reaction can effectively reduce tensile strength. Aluminum content has a little effect on the ductility. The stress rupture life has positive correlation relationship with the content of aluminum.

High Temperature Properties of Ti3SiC2-SiC Composites

Fully dense Ti3SiC2-64vol.%SiC(0.5m) composite materials are successfully fabricated by in situ synthesis under hot isostatic pressing. The high temperature flexure, tension and creep of Ti3SiC2-SiC composites were studied, and the results indicated that the composite had a high tensile strength under high temperature. Above 1000°C the composite were displayed a good high temperature plastic. The creep behavior is characterized by two regimes: an initial transient regime, where έ(dε/dt) decreases with t (time); a secondary creep regime in which έ is more or less constant with time.

In Situ Synthesis of TiB2-TiCx Ceramic Matrix Composites by Hot Isostatic Pressing

TiB2-TiC ceramic matrix composites were fabricated by in situ synthesis under hot isostatic pressing (HIP) with 3TiH2-B4C and 11TiH2-3B4C being the raw materials, respectively. The XRD analysis indicates that the samples synthesized from 3TiH2-B4C have TiB2 and TiC phases, while those from 11TiH2-3B4C have not only TiB2 and TiCx phases, but also Ti3B4 phase. TiB2-TiCx ceramic matrix composites obtained from 11TiH2-3B4C have better mechanical properties than those from 3TiH2-B4C. The microstructures of the composites are investigated with SEM and TEM. TiB2 grains are platelet grains; Ti3B4 grains have two different morphologies. Ti3B4 phases are formed through two different paths: fine grain Ti3B4 is formed through TiB+B=Ti3B4 at low temperature; large plate-like grain Ti3B4 is formed through TiB2+TiB=Ti3B4 at high temperature.