High-temperature Resistance Properties Research Articles

Tailoring the microstructure and properties of tungsten-copper composites by minor addition of SiC particles for nuclear fusion reactor application

In this work, minor addition of SiC ceramic particles were tested to tailor the microstructure and properties of infiltrated tungsten-copper (W–Cu) composites. The resultant microstructure, density, electrical conductivity, compressive behavior and arc resistant property of the WCu-x wt%SiC (x = 0.5, 1, 2, 3) composites were studied in comparison. The phase constituents of bcc-W, fcc-Cu and hcp-SiC were confirmed by X-ray and electron diffraction techniques. It is also revealed that gradual sintering growth of W particles occurred with the increasing content of SiC under the same processing and sintering parameters. Besides, with the increase of the mixed SiC, the density and electrical conductivity showed a steady decreasing trend due to the retarded rearrangement of W during sintering and the inherently low conductivity of SiC. Specifically, the composite of WCu–2%SiC exhibited the highest room-temperature strength of 1323 MPa and the highest particle-particle contiguity value of 0.373. Moreover, it showed excellent high-temperature arc resistance and compressive properties. Electron backscattering diffraction (EBSD) analysis further validated that the origin of its high damage tolerance can be attributed to its hierarchical microstructure both in grain size and misorientation.

Novolac/Phenol-Containing Phthalonitrile Blends: Curing Characteristics and Composite Mechanical Properties.

The phenol-containing phthalonitrile resin is a kind of self-curing phthalonitrile resin with high-temperature resistance and excellent properties. However, the onefold phthalonitrile resin is unattainable to cured completely, and the brittleness of the cured product is non-negligible. This paper focuses on solving the above problems by blending novolac resin into phenol-containing phthalonitrile. Under the action of abundant hydroxyl group, the initial curing temperature and gelation time at 170 °C decrease by 88 °C and 2820 s, respectively, monitored by DSC and rheological analysis. FT-IR spectra of copolymers showed that the addition of novolac increased the conversion rate of nitrile. When the novolac mass fraction is 10%, the peak of nitrile group disappears, which means the complete reaction. The mechanical test of blends composites shows that the maximum fracture strain of 10 wt% novolac addition is 122% higher than those of neat phthalonitrile composites on account of the introduction of flexible novolac chain segments. The mechanical properties are sensitive to elevated post-cured temperature; this is consistent with the result of morphological investigation using SEM. Finally, the dynamic mechanical analysis indicated that the glass transition temperature heightened with the increase of novolac content and post-curing temperature.

Assessment of Asphalt Binders and Hot Mix Asphalt Modified with Nanomaterials

In the recent times, asphalt binder modification has emerged an inevitable alternative in the paving industry to ensure better performing pavements against the distresses caused by common factors such as; moisture susceptibility and high-temperature sensitivity of asphalt binders. Nanomaterials, as asphalt-modifiers, have proved to be the most promising materials in the industry owing to their higher active surface area and small particle size. This study was devoted to assessing the modification influence of three different types of nanomaterials, including nano-Bentonite, nano-CaCO3, and ZycoTherm, on the properties of asphalt binder and HMA. Conventional and rheological tests on asphalt binders, as well as, Marshall mix design and modified Lottman test on laboratory-prepared HMA specimens were conducted in order to signify the influence of nanomodification. The research findings suggested that nanomaterials can potentially enhance the high-temperature susceptibility resistance, storage stability, and rheological properties of asphalt binder samples. Mix design results revealed that the optimum binder contents decreased and Marshall stabilities were slightly improved with nanomodification. Moreover, the modified Lottman test results indicated that 0.1 % of ZycoTherm increased the TSR by 22 % as compared to the control mixture that infers its efficiency in terms of improving the HMA resistance against the moisture-induced damages.

New BN/SiOC aerogel composites fabricated by the sol-gel method with excellent thermal insulation performance at high temperature

Although pure silicon oxycarbide (SiOC) aerogels have unique properties of low density and high temperature resistance, they are still difficult to apply at a large scale due to brittleness. To overcome this drawback, a strong boron nitride/silicon oxycarbide (BN/SiOC) aerogel composite with high-temperature resistance and thermal insulation was prepared by the sol-gel method and pyrolysis of the precursor aerogel. The microstructural, mechanical and thermal insulation properties of the composites were investigated, and the effect of the BN content on the microstructure and properties was also clarified. The results indicate that the obtained mesoporous composites exhibit low thermal conductivity (0.04–0.20 Wm−1 K−1) and high-temperature resistance (∼1300 °C). As the BN content increased from 0 to 15 vol %, the compressive strength of the composites increased from 2.2 to 20.3 MPa. The obtained composites exhibit considerable promise in high-temperature thermal insulation applications.

Pulse Reverse Alloy Plating for Increased Lifetimes for Biocombustors

Biomass embodies tremendous potential as a renewable energy resource. According to the biomass Thermal Energy Council (BTEC), biomass energy is renewable, carbon neutral, domestic and technologically mature. In addition, the low cost per BTU of wood chips and pellets relative to fossil fuels makes biomass an attractive thermal energy source. Furthermore, ~7% of global energy consumption comprises small-scale biomass combustion,[1] representing a tremendous market for technologies that facilitate enhanced biomass utilization. However, a major challenge associated with utilization of biomass is its combustion behavior. The moisture content, chemical composition, and combustion efficiency varies depending on the source of biomass. Small scale biomass combustors (Figure 1) which for cost reasons are often constructed of mild or low-alloy steels, during operation are subjected to corrosive environments which include alkali halides (borne, e.g., by fly ash particulates), mineral/halogen acids and water; as well as various others such as sulfur and nitrogen oxides. There is a need to create more efficient, longer lasting, cleaner, and cost effective cookstoves for use in burning biomaterials. The materials used for cookstoves must improve burning efficiency, must be able to operate at higher temperatures, and should be low cost material systems to durably perform in the corrosive environments. Within this context, Faraday Technology is working on developing low cost and high value corrosion-resistant alloy coatings for existing bio-combustors or lower cost steels with the goal of increasing their functional lifetime, while reducing the component cost. The manufacturing process involves electrodeposition of binary/ternary/quaternary alloys consisting of [Ni/Co]-Cr-[Mo/Fe] onto a low cost substrate and subsequent accelerated high temperature corrosion evaluation. A wide array of electrolytes and processing parameters were evaluated in order to understand these effects on the deposit composition, structure, and high-temperature corrosion resistance properties towards the goal of developing an ideal alloy coating. Specifically, 100 wt% Cr, 7 wt% Co- 93 wt% Cr binary and 15 wt% Ni – 20 wt% Cr – 55 wt% Co (NiCoCr) ternary alloy coatings demonstrated enhanced corrosion resistance when exposed to an aggressive environment (~700°C, 1000 hr, coating surface salted with ~1 mg/cm2 every 100 hours). When compared to the SS base material the Cr/CoCr alloy coatings exhibited effective protection to the substrate and over 10 times lifetime improvement to its base material. Acknowledgements: The financial support of DOE Contract No. DE-SC0013870 is acknowledged. [1] Biomass Production Now 10 Percent of World Energy, http://www.realclearenergy.org/charticles/2013/09/26/biomass_production_now_10_percent_of_world_energy_107257.html. Accessed 12 Jan 2015. Figure 1

A novel process with the characteristics of low-temperature bonding and high-temperature resisting for joining Cf/SiC composite to GH3044 alloy

Taking advantages of reaction composite brazing, transient liquid phase bonding (TLP) and partial transient liquid phase bonding (PTLP), a novel process with the characteristics of low-temperature bonding and high-temperature resisting was developed for joining Cf/SiC composite to GH3044 alloy by using (Cu-Ti) + C + Ni mixed powder filler. Under the bonding temperature (980 °C), the reaction between the liquid Cu-Ti alloy and C particles (reaction composite mechanism), composition homogenizations between the joining layer and Ni particles (PTLP mechanism) as well as Ni-based substrate (TLP mechanism) occurred to complete the transformation (Cu,Ti)l + Cs + Nis → TiCs + (Cu,Ni)s. Thereby, a joint with high-temperature resistance and excellent mechanical properties was obtained in relatively short holding time. The melting-point of the joint (1050 °C) was obviously higher than that of Cu-Ti alloy (898 °C) in the filler. The bonded joints exhibited shear strengths of 229, 225 and 104 MPa at room temperature, 600 °C and 1000 °C, respectively.

Improvements in miniaturized Hall Thrusters by use of high-temperature SmCo magnets and additive manufacturing techniques

This work presents the difficulties associated with the miniaturization of Hall Thruster engines and how state of the art materials and new manufacture techniques can potentially solve these problems. Hall Thrusters are electric propulsion systems that require specific magnetic field topography and uniform propellant distribution for optimal operation which is difficult to achieve with typical materials and by conventional manufacturing methods in miniaturized engines. To keep the optimal magnetic field distribution at small thruster sizes, it is shown that new alloys of SmCo permanent magnets can generate the desired magnetic field distribution and that their high-temperature resistance properties assure its operation temperature will be under the maximum operational temperature. In addition, whereas for the small dimensions required for the anode traditional manufacture methods only allow for simple designs, it is explained how the implementation of 3D-printing techniques can improve the uniformity in the azimuthal distribution of the propellant by allowing complex geometries in the design of the anode that are unattainable with traditional manufacturing.

Experimental research on the performance of lightweight concrete containing foam and expanded clay aggregate

This work addresses the preparation of self-flowing lightweight aggregate foamed concrete (LAFC) resulting from the mixing of stable foam, expanded clay aggregate (ECA) and silica fume (SF) as main raw materials. Formulated LAFC mixtures were tested for the mechanical, thermal, sorption and high-temperature resistance properties. Results showed that the increase in the volume of foam from 0% to 20% considerably improved the flowability of LAFC and LAFC mixtures were categorized into high stable visual stability index. Compressive strength of LAFC mixtures was reduced from 24.75 MPa to 21.10, 15.95 and 12.05 MPa respectively when foam volume was increased from 0% to 10, 15 and 20%. Thermal conductivity of LAFC mixtures was 0.84, 0.77, 0.65 and 0.53 Wm−1K−1 for the 0, 10, 15 and 20% foam volume respectively. The addition of SF enhanced the strength and thermal conductivity of LAFC mixtures. Sorption coefficient and porosity of LAFC were gradually increased from 0.22 to 0.85 kgm−2min−0.5 and 25.68–39.74% by increasing the volume of foam from 0% to 20%. However, incorporation of SF reduced the sorptivity and porosity of LAFC. Effect of high temperature was more prominent on the compressive strength of LAFC as compared to the density of LAFC.

A Polymer-based Drilling Fluid with High Temperature, Salt and Calcium Resistance Property

Filtrate reducer is facing higher requirements and challenges in temperature and salt resistance. A novel polymer filtrate reducer was synthesized by free radical polymerization in aqueous solution. By filtration experiments, the results show that the polymer has good filtration loss performance under high temperature and saturated salt. Through the optimization with filtrate reducer and inhibitor, the optimum components of drilling fluids are water, 4.0wt% bentonite, 0.3wt% Na2CO3, 2.0wt% DAADS, 3.0wt% SMP-II, 3.0wt% SPNH, 3.0wt% SMC, 1.0wt% SDJA and 2.0wt% RH-3. The drilling fluid system has temperature resistance up to 220°C, salt resistance to saturation and calcium resistance up to 1.0%. The API fluid loss of the drilling fluids with the addition of saturated NaCl and 1wt% CaCl2 respectively after aging at 220°C was 6.0 mL and 4.4 mL.

A novel SiC nanowire aerogel consisted of ultra long SiC nanowires

SiC nanowire aerogel (SNA) with highly porous 3D nanowire architecture was synthesized by polymer pyrolysis chemical vapor deposition (PPCVD) process to deposit SiC nanowires in the pores of carbon foam, followed by high temperature oxidation of carbon foam. The microstructure of the prepared SNA was characterized by SEM, TEM and a large number of interweaving SiC nanowires with a diameter of 80–100 nm and a length of hundreds of micrometers form the highly porous 3D nanowire architecture of SNA. The prepared SNA possesses the performance combination of ultra-low density (30 ± 7 mg · cm−3), high-temperature oxidation resistance (750 °C), noncombustible and fire resistance property in the fire, excellent thermal insulating property (0.03 W · m−1 · ·k−1 at room temperature in He) and compressive strength of 0.11 MPa, which is applicable as high-temperature heat insulator, ceramic matrix composite, high temperature flue gas filter, fire-proofing material and catalyst carrier.

Microstructure Control and Mechanical Properties of New Developed C&W Superalloy GH4175 at 800°C

As the thrust-weight ratio continues to increase, the aero-engine turbine disk material required both high strength and high temperature resistant properties which were often not compatible; Besides the working temperature of the turbine disk rim had reached 800 °C, the existing superalloys can not to meet the requirements, which was the reason that GH4175 alloy was produced. GH4175 was derived from Russian BK175 alloy, and the volume content of γ’ was over 58%. For the new GH4175, the low-segregation melting ingot with diameter of as large as 508mm could be prepared by the Double vacuum melting or Triple metlting process, in which the macro segregation and various metallurgical defects could be effectively controlled, then the conversion of as-cast microstructure and fine-grained billets were achieved on open-die hydraulic press by multi-times upsetting and drawing process and the novel temperature control technology with high efficiency, next, with the multi-cycle thermos-mechanical processing technology, the full-size turbine disks with a diameter of 600mm or more could be produced on hot die forging or isothermal forging. After standard heat treatment, the alloy combines high strength and high temperature characteristics, and balances the relationship between fatigue and creep. The long-term working temperature of the alloy reaches 800 °C.

Rheological Performance of Bio-Char Modified Asphalt with Different Particle Sizes

To improve the performance of petroleum asphalt, bio-char was used as a modifier for a petroleum asphalt binder, in this study. The rheological properties of bio-char modified asphalt binders were compared with different particle sizes and contents, with one control and one flake graphite modified asphalt binder. Specifically, the bio-char modifiers with two particle sizes (ranging from 75 μm–150 μm and less than 75 μm) and three contents of 2%, 4%, and 8% were added into the asphalt binder. A flake graphite powder with particle sizes less than 75 μm was used as a comparison modifier. The Scanning Electron Microscopy (SEM) image showed the porous structure and rough surface of bio-char as well as dense structure and smooth surface of flake graphite. A Rotational Viscosity (RV) test, Dynamic Shear Rheometer (DSR) test, aging test, and Bending Beam Rheometer (BBR) test were performed to evaluate the properties of bio-char modified asphalt in this study. Both modifiers could improve the rotational viscosities of the asphalt binders. The porous structure and rough surface of bio-char lead to larger adhesion interaction in asphalt binder than the smooth flake graphite. As a result, the bio-char modified asphalts had better high-temperature rutting resistance and anti-aging properties than the graphite modified asphalt, especially for the binders with the smaller-sized and higher content of bio-char particles. Furthermore, the asphalt binder modified by the bio-char with sizes less than 75 μm and about 4% content could also achieve a better low-temperature crack resistance, in comparison to other modified asphalt binders. Thus, this type of bio-char particles is recommended as a favorable modifier for asphalt binder.

Analysis of Thermal Treatment Zirconia as Spacer Layer on Dye-Sensitized Solar Cell (DSSC) Performance with Monolithic Structure

Monolithic dye-sensitized solar cells (DSSC) offer the prospect of lower material cost and require a simpler manufacturing process compared with conventional DSSC. Fabricated on a single fluorine tin oxide (FTO) glass substrate consists of a nanoporous TiO2 photoanode layer, a ZrO2 spacer layer, a carbon counter electrode layer, a dye, and an electrolyte. The spacer layer on the monolithic DSSC serves as electrolyte storage and insulating layer to separate between photoanode and counter electrode. Zirconia is often used as a spacer because it has high temperature resistant properties, high dielectric constant and adhesive as an insulator that has band gap between 5-6 eV. The effects of the thermal treatment of zirconia layer as a spacer electrolyte on the performance of monolithic DSSC have been investigated. The cell’s performance increases with the sintering temperature as well as indicated by the decreased in particle size and increased in quantum efficiency in the absorption region of the titania layer. Co-sintering treatment tends to drastically reduce cell’s performance. The highest performance was obtained at a temperature sintering of 500o C with an PCE of 0.22%, Isc = 0.16 mA and Voc = 0.71 V.

Electrodeposited Inconel and Stellite like Coatings for Improved Corrosion Resistance in Biocombustors

Biomass embodies tremendous potential as a renewable energy resource. According to the biomass thermal Energy Council (BTEC), biomass energy is renewable, carbon neutral, domestic and technologically mature. In addition, the low cost per BTU of wood chips and pellets relative to fossil fuels makes biomass an attractive thermal energy source. Furthermore, ~7% of global energy consumption comprises small-scale biomass combustion,[1] representing a tremendous market for technologies that facilitate enhanced biomass utilization. However, a major challenge associated with utilization of biomass is its combustion behavior. The moisture content, chemical composition, and combustion efficiency varies depending on the source of biomass. Small scale biomass combustors (Figure 1) which for cost reasons are often constructed of mild or low-alloy steels, during operation are subjected to corrosive environments which include alkali halides (borne, e.g., by fly ash particulates), mineral/halogen acids and water; as well as various others such as sulfur and nitrogen oxides. There is a need to create more efficient, longer lasting, cleaner, and cost effective cookstoves for use in burning biomaterials. The materials used for cookstoves must improve burning efficiency, must be able operate at higher temperatures, and should be low cost material systems to durably perform in the corrosive environments. Within this context, Faraday Technology Inc. is working on developing low cost and high value corrosion-resistant alloy coatings for existing bio-combustors or lower cost steels with the goal of increasing their functional lifetime, while reducing the component cost. The manufacturing process involves electrodeposition of binary/ternary/quaternary alloys consisting of [Ni/Co]-Cr-[Mo/Fe] onto a low cost substrate and subsequent accelerated high temperature corrosion evaluation. A wide array of electrolytes and processing parameters were evaluated in order to understand these effects on the deposit composition, structure, and high-temperature corrosion resistance properties towards the goal of developing an ideal alloy coating. Specifically, 60 wt% Ni – 40 wt% Cr (NiCr) binary and 25 wt% Ni – 20 wt% Cr – 55 wt% Co (NiCoCr) ternary alloy coatings demonstrated enhanced corrosion resistance when exposed to an aggressive environment (~700°C, 1000 hr, coating surface salted with ~1 mg/cm2 every 100 hours). When compared to the 441 SS base material the NiCoCr coating exhibited an significant lifetime improvement over its base material and other alloys. Acknowledgements: The financial support of DOE Contract No. DE-SC0013870 is acknowledged. [1] Biomass Production Now 10 Percent of World Energy, http://www.realclearenergy.org/charticles/2013/09/26/biomass_production_now_10_percent_of_world_energy_107257.html. Accessed 12 Jan 2015. Figure 1

Electrodeposited Inconel and Stellite like Coatings for Improved Corrosion Resistance in Biocombustors

Biomass embodies tremendous potential as a renewable energy resource. According to the biomass thermal Energy Council (BTEC), biomass energy is renewable, carbon neutral, domestic and technologically mature. In addition, the low cost per BTU of wood chips and pellets relative to fossil fuels makes biomass an attractive thermal energy source. Furthermore, ~7% of global energy consumption comprises small-scale biomass combustion,[1] representing a tremendous market for technologies that facilitate enhanced biomass utilization. However, a major challenge associated with utilization of biomass is its combustion behavior. The moisture content, chemical composition, and combustion efficiency varies depending on the source of biomass. Small scale biomass combustors (Figure 1), which for cost reasons are often constructed of mild or low-alloy steels, during operation are subjected to corrosive environments that include alkali halides (borne, e.g., by fly ash particulates), mineral/halogen acids and water; as well as various others such as sulfur and nitrogen oxides. There is a need to create more efficient, longer lasting, cleaner, and cost effective cookstoves for use in burning biomaterials. The materials used for cokstoves must improve burning efficiency, must be able operate at higher temperatures, and should be low cost material systems to durably perform in the corrosive environments. Within this context, Faraday Technology is working on developing low cost and high value corrosion-resistant alloy coatings for existing bio-combustors or lower cost steels with the goal of increasing their functional lifetime, while reducing the component cost. The manufacturing process involves electrodeposition of binary/ternary/quaternary alloys consisting of [Ni/Co]-Cr-[Mo/Fe] onto a low cost substrate and subsequent accelerated high temperature corrosion evaluation. A wide array of electrolytes and processing parameters were evaluated in order to understand these effects on the deposit composition, structure, and high-temperature corrosion resistance properties towards the goal of developing an ideal alloy coating. Specifically, 60 wt% Ni – 40 wt% Cr (NiCr) binary and 25 wt% Ni – 20 wt% Cr – 55 wt% Co (NiCoCr) ternary alloy coatings demonstrated enhanced corrosion resistance when exposed to an aggressive environment (~700°C, 1000 hr, coating surface salted with ~3 mg/cm2 every 100 hours). When compared to the SS base material the NiCr and NiCoCr alloy coatings exhibited a 70% lower weight loss and 3.4 times lifetime improvement over its base material. Acknowledgements: The financial support of DOE Contract No. DE-SC0013870 is acknowledged. [1] Biomass Production Now 10 Percent of World Energy, http://www.realclearenergy.org/charticles/2013/09/26/biomass_production_now_10_percent_of_world_energy_107257.html. Accessed 12 Jan 2015. Figure 1

The High-Temperature Resistance Properties of Polysiloxane/Al Coatings with Low Infrared Emissivity

High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (ΔL) of the coatings were characterized by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy, and thermal mechanical analysis (TMA), respectively. The results show that thermal decomposition of the resin and mismatch of ΔL between the coating and the substrate facilitate the high temperature failure of the coating. A suitable amount of flake aluminum pigments could restrain the thermal decomposition of the resin and could increase the match degree of ΔL between the coating and substrate, leading to an enhanced thermal resistance of the coating. Our results find that a coating with a pigment to binder ratio (P/B ratio) of 1.0 could maintain integrity until 600 °C, and the infrared emissivity was as low as 0.27. Hence, a coating with high-temperature resistance and low emissivity was obtained. Such coatings can be used for infrared stealth technology or energy savings in high-temperature equipment.

Renewable eugenol-based functional polymers with self-healing and high temperature resistance properties

A novel small molecule 1,3-bis(eugenyl) glycerol diether is synthesized from renewable eugenol and epichlorohydrin in 60% total yield, and its structure is confirmed by 1H–NMR spectrum. Then, this small molecule is utilized to prepare oligomer, linear polymer and the corresponding crosslinked polymer (denoted as P 2 ) by using thiol-ene and thiol-oxidation reactions. The polymer P 2 can form brown film on a glass substrate and can be easily put off from the substrate. Mechanical properties of P 2 show that tensile strength value is about 6 MPa, with elongation at break of around 300%. Glass transition temperature (Tg) of P 2 is −2.76 °C, meaning that P 2 is at rubber state. There are hydroxyl groups in the prepared linear polymer, which further reacts with 1,6-hexanediisocyanate (HDI) to form polyurethane P 4 with crosslinked structures. Compared with P 2 , the polyurethane P 4 forms yellow film on a glass substrate. But the film of P 4 is not so flexible as that of P 2 , presumably because of relatively higher Tg (5.85 °C) of P 4 than P 2 . Due to the existence of dynamic disulfide bonds as well as hydrogen bonds in both P 2 and P 4 , these thermoset resins show repeatable self-healing behavior stimulated by UV irradiation. Furthermore, the polyurethane P 4 exhibits ultrahigh temperature resistance performance, with Td5 = 375 °C and Td10 = 1000 °C according to TGA curve. This work is expected to expand research and potential applications of the renewable resource eugenol in preparation of smart materials.

Spark assisted chemical engraving (SACE) mechanism on ZrO2 ceramics by analyzing processed products

Traditional machining processes are usually unworkable for ZrO2 ceramics due to the mechanical properties of fragility, high hardness and high-temperature resistance. The process of spark assisted chemical engraving (SACE) has been explored for machining ZrO2 ceramics, but up to now the processing mechanism has not been clearly understood yet. To understand the microscopic mechanism, the phase transition paths of ZrO2 ceramics under various physical and chemical conditions were analyzed. A backstepping approach based on structures and components of SACE processed products was proposed to verify the physical and chemical mechanisms. According to the crystal phase composition of the processed debris resulting from Raman spectrum analysis, it was found that the debris exhibited crystalline and amorphous forms which provided the evidence of physical crushing and chemical reactions. Furthermore, the chemical removal mechanism was proven by the nearly saturated concentration of Zr ion in the processed solution according to the ICP-OES assay of SACE electrolyte. The quantitative proportion of physical and chemical effect can be successfully determined by distinguishing and analyzing two kinds of debris with different crystal phase compositions which yield distinctly identifiable appearances under an optical microscope.

纳米Fe-Al/Cr3C2复合涂层及其抗高温腐蚀性能

制备纳米金属间化合物Fe-Al/Cr3C2复合涂层并测试其抗腐蚀性能，为利用热喷涂技术治理火电站易损部件腐蚀问题提供有效手段。运用自主研发的造粒系统，成功对高活性的纳米Fe-Al/Cr3C2复合喷涂粉体实施团聚造粒；运用高速火焰喷涂方法，在结构材料表面制备出了纳米Fe-Al/Cr3C2复合涂层，对比测试了微米、纳米Fe-Al/Cr3C2复合涂层的抗高温腐蚀性能，分别采用抛物线型和幂函数型对腐蚀动力学曲线进行拟合。纳米Fe-Al/Cr3C2复合喷涂材料的粒径由原始的50 nm团聚到最终的114~178 μm，团聚后的纳米颗粒呈圆形或椭圆形，各成分比例保持原始比例，团聚颗粒内部仍然保持纳米粉体状态；纳米Fe-Al/Cr3C2复合涂层表面致密、铺展均匀，截面元素过渡平缓、层片细小；运用幂函数方程对腐蚀动力学曲线的拟合效果更好。通过对腐蚀动力学拟合方程进行求导运算可推算出各复合涂层的腐蚀速率。团聚后的纳米颗粒满足热喷涂材料的相关要求，纳米Fe-Al/Cr3C2复合涂层的抗高温腐蚀性能显著高于微米Fe-Al/Cr3C2复合涂层。纳米Al、Cr优先氧化生成具有保护作用的氧化膜机理解释了纳米涂层抗高温腐蚀性能优异的原因。

Comparison of material specific rim zone effects of Ti6Al4V machined by wire EDM in water- and CH- based dielectrics

Because of their lightweight, high-temperature corrosion resistance and fatigue property, titanium alloys are ideal for use in turbomachinery, medical and chemical areas with corrosive environments and precision mechanics as used in aeronautical applications. Wire electro discharge machining (WEDM) is a nearly force free process and hence beneficial compared to classical production technologies when it comes to the production of filigree parts with high aspect ratios. Beside the well-known fact of the heat affected rim zone at WEDM machined parts, titanium alloys have another material specific drawback, called ‘alpha case’, which is developed by diffusion driven interstitials, such as carbon, nitrogen and especially oxygen. The alpha-case is a hard to remove superficial defect, which leads to crack initiation and propagation. The influence of water- and CH-based dielectrics as a source of diffusitives on the formation of alpha-case have to be investigated to predict the part’s fatigue strength.