Effect of consolidation and oxide dispersoid addition on phase formation and mechanical properties of WTi ODS alloy

WTi alloys are presently considered promising candidates for plasma facing components in advanced nuclear energy systems. The mechanically alloyed WTi model alloys consolidated by different techniques were investigated. The effect of different amounts of the dispersed oxide particles on characteristics and properties of the WTi materials was also discussed. The results show that a homogeneous fine grain structure without formation of Ti-rich oxides is obtained in the model alloy sintered by spark plasma sintering. The (W,Ti)C solid solution and α″-Ti martensite phase are also found in the alloy confirmed by TEM investigation, which can be contributed to the effect of the carbon contamination and cooling rate during the process. In this work, it is clear to demonstrate that the presence of different carbides and Ti phases plays an important role in determining hardness and elastic modulus of the materials. The microstructure homogeneity and mechanical properties of the alloys can be further improved by increasing numbers of oxide dispersoids.     

合金元素含量对汽车大梁用610L钢组织与性能的影响

采用“调Si、降Nb、加Ti”的合金设计理念,结合优化的控轧控冷工艺,开发出一种新型汽车大梁用610 MPa级Ti-Nb-Si系低碳微合金钢。结果表明,当Si、Nb和Ti的质量分数分别为0.04%、0.03%和0.06%时,试验钢在热轧后水冷(15～20℃/s)至卷取温度时的显微组织为铁素体+珠光体,且在铁素体基体内分布着高密度的纳米析出相,综合力学性能较好,屈服强度为539 MPa,抗拉强度为633 MPa,伸长率为20.5%,扩孔率为66.4%,各项力学性能和扩孔性能均满足汽车大梁用610L钢的性能要求。     

A New High-Efficiency Experimental Design for Optimizing Various Flow Velocities Testing in Extremely Aggressive Formation Water

Compared to the traditional one-by-one method, a new high-efficiency method is used to characterize large numbers of regulations varying samples.Accordingly, bump-shaped electrodes are designed using the computational fluid dynamics model, and the effect of the height and placement of these electrodes is discussed.The experimental feasibility is certified by weight loss measurement.Results indicate that flow velocities of different bump-shaped electrode surfaces are significant differences.Thus, each surface can be analyzed independently; the thickness loss of each electrode surface is consistent with that using one-by-one method, which can effectively improve the experimental efficiency 12 times.     

Oxidation Performance and Interdiffusion Behavior of a Pt-Modified Aluminide Coating with Pre-deposition of Ni

To refrain the interdiffusion of elements while holding good oxidation resistance,a(Ni,Pt)Al/Ni composite coating was prepared by sequential treatments of electroplating Ni and Pt and successive gaseous aluminization.In comparison with normal(Ni,Pt)Al coating,high-temperature performance of the composite coating was evaluated in isothermal oxidation test at 1100℃.Both the two coatings exhibited good resistance against high-temperature oxidation,but the interdiffusion of elements between composite coating and single-crystal(SC) superalloy substrate was greatly relieved,in which the thickness of secondary reaction zone(SRZ) and the amount of precipitated topologically close-packed phase in the SC alloy matrix were significantly decreased.Mechanisms responsible for delaying rate of coating degradation and SRZ growth/propagation are discussed.     

Fabrication of carbon-coated boron carbide particle and its role in the reaction bonding of boron carbide by silicon infiltration

To tackle the dissolution problem of boron carbide particles in silicon infiltration process, carbon-coated boron carbide particles were fabricated for the preparation of the reaction-bonded boron carbide composites. The carbon coating can effectively protect the boron carbide from reacting with liquid Si and their dissolution, thus maintaining the irregular shape of boron carbide particles and preventing the growth of boron carbide particles and reaction formed SiC regions. Furthermore, the nano-SiC particles, originated from the reaction of the carbon coating and the infiltrated Si, uniformly coated on the surfaces of boron carbide particles, thus forming a ceramic skeleton of the nano-SiC particles-coated and -bonded boron carbide particles. The Vickers hardness, flexural strength and fracture toughness of the composites can be increased by 26 %, 45 %, and 37 % respectively, by using carbon-coated boron carbide particles as raw materials.     

Ultra-high temperature oxidation resistance of a novel (Mo,Hf, W,Ti)Si2 ceramic coating with Nb interlayer on Ta substrate

In order to solve the challenge of recyclability of tantalum substrates in high temperature oxidation environments, a novel MoSi₂-WSi₂-HfSi₂-TiSi₂ composite ceramic coating containing an Nb interlayer was prepared on the surface of tantalum substrate by a three-step method. The mix ceramic silicide coating exhibited superior performance and effective protection for 10.2 h at 1800 °C, possibly due to the formation of an outer SiO₂-HfO₂-HfSiO₄ composite oxide film with low oxygen permeability, moderate viscosity and thermal expansion coefficient, as well as good self-healing ability. Furthermore, the coating successfully passed 537 thermal cycles from room temperature to 1800 °C. The presence of Nb interlayer significantly mitigated the thermal mismatch between the ceramic coating and the tantalum substrate, and the bidirectional diffusion of Nb element during the high temperature oxidation and thermal shock process further reduced the tendency of the coating to crack.     

Control of barium ferrite decomposition during spark plasma sintering: Towards nanostructured samples with anisotropic magnetic properties

The sintering of barium ferrite (BaM) nano-sized powders by spark plasma sintering was studied. At the surface of the samples, an iron-rich layer (magnetite) was formed due to the decomposition of BaM and segregation in the secondary phases. To prevent the formation of secondary phases different protection layers between the graphite mould and the sample were used. Their effect on the sample microstructure was studied by X-ray diffraction and scanning electron microscopy. The most suitable protection layer was a highly dense sintered disc of aluminium oxide. Using this dense protection layer, sintered discs of BaM with 82% of theoretical density and grains of 90 ± 50 nm were obtained. A magnetic anisotropy was achieved from the sintering of the BaM particles with the largest shape anisotropy.     

Strain rate dependent mechanical properties of new albany reference shale

Drilling, mining and blasting of rock-like materials, in situ fracturing, rock fragmentation size and permeability extension are strongly affected by strain rates of loading. For low strain rates, fragment sizes are large, and cracks propagate further. For high strain rates, fragment sizes are small and cracks are localized. The purpose of the present investigation is to determine the effects of strain rate on the initial (linear) value of Young's modulus and on Poisson's ratio for different grades of New Albany oil shale, a reference oil shale designated by the U.S. Department of Energy. Material anisotropy is considered. Cylindrical specimens cored in a particular orientation of the oil shale formation are tested in compression, and the rate effects are investigated. An efficient data acquisition/reduction system is developed, interfacing with an Instron closed-loop hydraulic testing machine. Strain gauge instrumentation is used to measure lateral and longitudinal strains. Strain rates of about 10⁻⁵–10⁰/sec are studied.     

Dynamic delamination fracture toughness of a graphite/epoxy laminate under impact

Dynamic delamination fracture toughness in a [90/0]_5s T300/934 graphite/epoxy laminate was investigated using impact loading. Delamination cracks of three different sizes were embedded at the mid-plane of the composite specimen. The threshold impact velocity that causes propagation of the delamination crack was used in the dynamic analysis with the finite element method. From the finite element solution, the time-history of the strain energy release rate was calculated. The critical strain energy release rate was taken to equal the maximum value of the response history.