Microstructure,interfacial reaction behavior,and mechanical properties of Ti_3AlC_(2)reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti_3AlC_(2)at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated.The results show that the addition of3.0 wt.%Ti_3AlC_(2)refines the average grain size ofα(Al)in the composite by 50.1%compared to Al6061 alloy.Morphological analyses indicate that an in-situ Al_(3Ti)transition layer of-180 nm in thickness is generated around the edge of Ti_3AlC_(2)at 720℃,forming a well-bonded Al-Al_(3Ti)interface.At this processing temperature,the ultimate tensile strength of A16061-3.0 wt.%Ti_3AlC_(2)composite is 199.2 MPa,an improvement of 41.5%over the Al6061 matrix.Mechanism analyses further elucidate that 720℃is favourable for forming the nano-sized transition layer at the Ti_3AlC_(2)edges.And,the thermal mismatch strengthening plays a dominant role in this state,with a strengthening contribution of about 74.8%.

Ti_3AlC_2-Al_2O_3-TiAl_3 composite fabricated by reactive melt infiltration

Porous preforms were fabricated by cold-pressing process using powder mixture of TiC,TiO2 and dextrin.After pyrolysis and sintering,Al melt was infiltrated into the porous preforms,leading to the formation of Ti3AlC2-Al2O3-TiAl3 composite.Effects of cold-pressing pressure of preforms on microstructures and mechanical properties of the composites were studied.Synthesis mechanism and toughening mechanism of composite were also analyzed.The results shows that TiO2 is reduced into Ti2O3 by carbon,the decomposition product of dextrin,which causes the spontaneous infiltration of Al melt into TiC/Ti2O3 preform.Then, Ti3AlC2-Al2O3-TiAl3 composite is in-situ formed from the simultaneous reaction of Al melt with TiC and Ti2O3.With the increase of cold-pressing pressure from 10 MPa to 40 MPa,the pore size distribution of the preforms becomes increasingly uniform after pre-sintering,which results in the reduction of defects,and the decrease of property discrepancy of composites.Nano-laminated Ti3AlC2 grains and Al2O3 particles make the fracture toughness of TiAl3 increase remarkably by various toughening mechanisms including stress-induced microcrack,crack deflection and crack bridging.

Synthesis of Y_2O_3 particle enhanced Ni/TiC composite on TC4 Ti alloy by laser cladding

A Y2O3 particle enhanced Ni/TiC composite coating was fabricated in-situ on a TC4 Ti alloy by laser surface cladding. The phase component, microstructure, composition distribution and properties of the composite layer were investigated. The composite layer has graded microstructures and compositions, due to the fast melting followed by rapid solidification and cooling during laser cladding. The TiC powders are completely dissolved into the melted layer during melting and segregated as fine dendrites when solidified. The size of TiC dendrites decreases with increasing depth. Y2O3 fine particles distribute in the whole clad layer. The Y2O3 particle enhanced Ni/TiC composite layer has a quite uniform hardness along depth with a maximum value of HV1380, which is 4 times higher than the initial hardness. The wear resistance of the Ti alloy is significantly improved after laser cladding due to the high hardness of the composite coating.

Morphology and Frictional Characteristics Under Electrical Currents of Al_2O_3/Cu Composites Prepared by Internal Oxidation

Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.

Microstructure and evolution of(TiB_2+Al_2O_3)/NiAl composites prepared by self-propagation high-temperature synthesis

（TiB2＋Al2O3）/NiAl composites were synthesized by self-propagation high-temperature synthesis, and their phase compositions, microstructures and evolution modes were studied. The microstructures and shapes vary with the TiB2＋Al2O3 content in the NiAl matrix. TiB2 particles take a great variety of elementary shapes such as white bars, plates, herringbones, regular cubes and cuboids. These results outline a strategy of self-assembly processes in real time to build diversified microstructures. Some TiB2 grains in sizes of 2-5μm are embeded in Al2O3 clusters, while a small number of TiB2 particles disperse in the NiAl matrix. It is believed that the higher the TiB2＋Al2O3 content is, the more the regular shapes and homogeneous distributions of TiB2 and Al2O3 will be present in the NiAl matrix.

Hot deformation and processing maps of Al_2O_3/Al composites fabricated by flake powder metallurgy

The deformation behaviors of Al2O3/Al composites were investigated by compressive tests conducted at temperature of 300-450 °C and strain rates of 0.001-1.0 s-1 with Gleeble-1500 D thermal simulator system. The results show that the flow stress increases with increasing strain rate and decreasing temperature. The hyperbolic sine constitutive equation can describe the flow stress behavior of Al2O3/Al composites, and the deformation activation energy and constitutive equations were calculated. The processing maps of Al2O3/Al-2 μm and Al2O3/Al-1 μm composites at strain of 0.6 were obtained and the optimum processing domains are in ranges of 300-330 °C, 0.007-0.03 s-1 and 335-360 °C, 0.015-0.06 s-1 for hot working, respectively. The instability zones of flow behavior can also be recognized by the maps.

Preparation of Al_2O_3/Au nano-laminated composite coatings and their oxidation resistance on stainless steel

Al2O3/Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al2O3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al2O3/Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.

Effect of CuO particle size on synthesis temperature and microstructure of Al_2O_(3p)-Al composites from Al-CuO system

Al2O3p-Al composites were synthesized using an in-situ reaction in the 80%Al-20%CuO （mass fraction） system. The effects of the CuO particle size on the synthesis temperature and microstructure of the composites were investigated by various methods. The results indicate that the CuO particle size has a significant effect on the temperature at which the complete reaction in the Al-CuO system occurs：the temperature is 200 ℃ lower in the Al-CuO system containing CuO particles with sizes less than 6μm than that containing CuO particles with sizes less than 100μm. The interfacial bonding between Al2O3 particles and Al is not complete when the temperature is below a critical value. The morphology of the Al2O3 particles varies from ribbon-like shape to near spherical shape when the temperature is above a critical value. These two critical temperatures are affected by the particle size of CuO, and the critical temperature of the sample containing CuO particles with sizes less than 6μm is 100 ℃ lower than that of the sample containing CuO particles with sizes less than 100μm.

Al/TiO_2/TiC体系原位合成Ti_3AlC_2/Al_2O_3/TiAl_3复合材料的反应机理

通过分析机械球磨Al/TiO_2/TiC复合粉末的放热反应及原位合成动力学,确定Ti_3AlC_2/Al_2O_3/TiAl_3复合材料的合成路径。在此基础上,结合球磨后复合粉末的微观形貌和物相演变分析,提出复合材料的原位合成机理。结果表明:复合材料原位合成过程中存在中间产物TiO和TiC_x;机械球磨形成的"核壳结构"对原位合成组织细小均匀的Ti_3AlC_2/Al_2O_3/TiAl_3复合材料至关重要。

In-situ Synthesis of Ti_3AlC2/TiC-Al_2O_3 Composite from TiO_2-Al-C System

Ti3AlC2/TiC-Al2O3 composite was synthesized by a combustion reaction in TiO2-Al-C system. The effect of the compositions in raw materials on the products was investigated. Ti3AlC2/TiC-Al2O3 composite was obtained at the molar ratio of TiO2：Al：C=3.0：5.0～5.1：1.8～2.0. The reaction path for the 3TiO2-5Al- 2C system was proposed. Al3Ti, Ti203, TiO, and 6-Al2O3 are found to be transitional phases. Finally, Ti3AlC2/TiC-Al2O3 composite forms at～900℃ of furnace temperature. The measured Vickers hardness, fracture toughness, and flexural strength of the nearly dense sample from 3TiO2-5Al-2C are 13.3±1.1 GPa, 5.8±0.3 MPa.m^1/2, and 466±39 MPa, respectively.

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF IN-SITU Al_2O_3/TiAl COMPOSITES BY EXOTHERMIC DISPERSION METHOD

In-situ Al2O3/TiAl composites were fabricated by pressure-assisted exothermic dispersion （PAXD） method from elemental powder mixtures of Ti, Al, TiO2, and Nb2O5. The microstructures and mechanical properties of the as-sintered composites are investigated. The results show that the as-sintered products consist of γ-TiAl, α2-Ti3Al, Al2O3, and NbAl3 phases. Microstructure analysis indicates that Al2O3 particles tend to disperse on the grain boundaries. Application of a moderate pressure of 35 MPa at 1200℃ yields Al2O3/TiAl composites with fine Al2O3 reinforcement and a discontinuous network linking by Al2O3 particles. The aluminide component has a fine submicron γ ＋α2 lamellar microstructure. With increasing Nb2O5 content, Al2O3 particles are dispersed uniformly in the matrix. The hardness of the composites increases gradually, and the bending strength and fracture toughness of the composites reach to the maximum value, respectively.

Preparation of TiAl/Al_2O_3 composites by combustion synthesis

Studies the combustion synthesis of Al Ti TiO 2 system and concludes that, due to its low exothermic nature, a stable combustion wave can be maintained only when the system is ignited at a certain preheating temperature, and coupled with appropriate pseudo HIP process, dense TiAl/Al 2O 3 composites with density as high as 97% of the theoretical value can be produced, and points out. Microstructure observation shows in situ formed Al 2O 3 particles are of an average size smaller than one micron, and the hardness of TiAl matrix is enhanced by introduction of these particles.

Fabrication and Mechanical Properties of Sm2O3 Doped CeO2 Reinforced Ti3AlC2 Nano Composite

The fabrication process of Sm2O3 doped CeO2 reinforced Ti3AlC2 nano composites including the nano particle dispersion process by a hetero-coagulation process was developed using in-situ synthesis and densification process of Ti3AlC2. The effects of Sm2O2 doped CeO2 nano particles on mechanical properties of Ti3AlC2 were investigated. It was found that the presence of 20SDC nano particles in Ti3AlC2 was very effective to improve the mechanical properties of Ti3AlC2 without spoiling the unique characteristics of Ti3AlC2temary carbide.

Fabrication and Mechanical Properties of Al_2O_3/TiAl Composites

Al2O3/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO2 and Nb2O5, and the microstructure and mechanical properties were investigated. The results indicate the fine Al2O3 particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb2O5 content. The bending strength and fracture toughness reach to a maximum when Nb2O5 content is 6 wt%, under 642 MPa and 6.69 MPa·m^1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al2O3 particles.

In-situ Preparation of Al/TiAl_3(P) Composite by Direct Reaction between Molten Al and TiO_2 Powder

TiAl3 particle reinforced pure Al composite has been made by direct reaction among molten Al, TiO2 and a flux. The composite exhibits high Synthetically properties. The strength and hardness are higher than those of pure Al matrix by 71.5% and 134% respectively However, the elongation is 20.36%, slightly lower than that of the Al matrix.

原位合成Al_2O_3颗粒增强双相TiAl基复合材料的组织与性能

以Ti-Al-TiO2反应体系为基础,添加不同含量的Nb2O5粉,采用压力协助原位合成Al2O3颗粒增强的双相TiAl基复合材料,对复合材料的组织和力学性能进行了分析讨论,并探讨了其增韧机制。结果表明:Nb2O5的掺杂使复合材料的相对密度和硬度得到提高,抗弯强度和断裂韧性在Nb2O5掺杂量为6%(质量分数)时达到最大,分别为398.38 MPa和6.992 MPa.m1/2。微观组织分析表明,获得了双相组织,Al2O3颗粒分布于基体晶界处;随Nb2O5的掺杂量增大,Al2O3颗粒呈细小弥散分布,同时基体晶粒尺寸也减小。双相基体晶粒的细化及Al2O3颗粒的弥散分布是赋予材料高韧性的主要增韧机制。

TiAl合金表面激光重熔Al_2O_3-13wt%TiO_2复合陶瓷涂层组织结构

采用等离子喷涂和激光重熔复合工艺在TiA l合金表面制备了A l2O3-13wt%TiO2复合陶瓷涂层。为了减少重熔层裂纹等缺陷,采用较低的激光功率和能量密度进行重熔。用扫描电镜(SEM),能谱仪(EDS)和X射线衍射仪(XRD)分析了涂层形貌、微观结构和相组成。结果表明,经过激光重熔处理后,陶瓷涂层颗粒细化,片层状组织得以消失,致密性提高,获得了基本没有裂纹等缺陷的重熔层;激光重熔亚稳相-γA l2O3转变为稳定相-αA l2O3;由于陶瓷材料导热系数较低的影响,激光重熔时无法使整个陶瓷层实现重熔,重熔后的陶瓷涂层形成了晶粒细小的等轴晶重熔区、烧结区以及片层状残余等离子喷涂区。

添加TiAl对燃烧合成Ti_3AlC_2粉体的影响

采用 Ti,Al和C粉末为反应物原料,研究了添加金属间化合物TiAl对燃烧合成Ti3AlC2的影响.从动力学和热力学的角度探讨了TiAl对燃烧合成Ti3AlC2的影响机理.实验结果表明,仅以单质粉末Ti,Al和碳黑为原料,按Ti3AlC2化学计量比配料,燃烧产物的主要物相是TiC,只能得到少量Ti3AlC2相,但在保持原料配比不变的情况下,在反应物原料中添加金属间化合物TiAl(20%～35%)(质量百分数)后,燃烧合成产物中Ti3AlC2的含量显著增加,成为燃烧产物的主要物相,而TiC的含量则显著减少.燃烧产物中Ti3AlC2的含量随添加TiAl量的增加而显著增多.

Al_2O_3/TiAl复合材料的原位合成及反应机制的研究

利用Al-Ti-TiO2体系的放热反应,原位合成了Al2O3/TiAl复合材料。借助示差热分析法探讨了体系的反应机制,采用XRD、SEM和OM分析了复合材料的相组成及显微组织。结果表明,原位合成Al2O3/TiAl复合材料由TiAl、Ti3Al和Al2O3相组成,Al2O3颗粒分布于TiAl和Ti3Al双相交界处,并存在一定团聚。随其含量增加,团聚程度加剧,晶粒尺寸减小。Ti和Al反应生成TiAl3放出的热量使部分TiAl3相处于液相状态,熔融的体积分数约为87.87%,液相的存在提高了颗粒间的润湿性,同时放出的热量是引发后续反应的原因之一。TiAl3与Al-TiO2的还原反应生成的活性Ti原子结合最终生成了TiAl和Ti3Al相。

原位热压合成Nb掺杂Al_2O_3/TiAl复合材料

利用Al-Ti-TiO2-Nb2O5体系的放热反应,原位热压合成了Nb掺杂Al2O3/TiAl复合材料。借助DTA结合XRD探讨了Al-Ti-TiO2-Nb2O5体系的反应过程,并采用XRD、OM和SEM研究了复合材料的物相组成及显微结构。结果表明:Al熔化的同时,体系发生了Al和Nb2O5的铝热反应,生成了NbO2和Nb等中间产物,并放出了较多热量,这些热量促使Ti和Al较早化合生成TiAl3,随即引发Al和TiO2较早的还原反应,进而促使材料在较低温度下致密烧结;产物由-γTiAl、α2-Ti3Al、Al2O3和NbAl3相构成,Al2O3颗粒分布于基体交界处,存在一定的团聚;Nb2O5的引入,对基体-γTiAl相和α2-Ti3Al相的的分布有一定的影响,使得基体晶粒细化,较好地改善了材料的力学性能。