Microstructure and properties of in situ nanostructured ceramic matrix composite coating prepared by plasma spraying

In situ nanostructured ceramic matrix composite coating toughened by metallic phase was fabricated by reactive plasma spraying micro-sized Al–Fe₂O₃ composite powders. The microstructure of the composite coating was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The adhesive strength, microhardness, toughness, and wear resistance of the composite coating were explored. The results indicated that the composite coating exhibited dense microstructure with a lot of spherical α-Fe and γ-Al₂O₃ nano-sized grains embedded within the equiaxed and columnar FeAl₂O₄ nano-grains matrix. The adhesive strength, toughness, and wear resistance of the composite coating were significantly enhanced despite its lower microhardness compared with the micro-sized Al₂O₃ coating, which were attributed to the inclusion of ductile metallic phase Fe in the composite coating and the nanostructure of the composite coating.     

Study of the structure and adhesive properties of ceramic coatings prepared by plasma spraying

We study the influence of technological parameters on the formation and structure of ceramic coatings based on Al₂O₃ and deposited by plasma spraying. We present the results of investigations of the adhesive properties of plasma-sprayed coatings based on Al₂O₃ and ZrSiO₄ that form tribological couples with 19,436 and 12,050 steels and polyamide. It is shown that the parameters of an A-160 plasma torch with aqueous plasma stabilization are suitable for the high-quality melting of ceramic materials based on Al₂O₃ if we use powders with particles 40–100 μm in size and perform spraying from a distance of 200–600 mm. Ceramic layers are formed by three types of particles of different shapes with different arrangements. Defects in the structure of the layers (pores, hollows, branched cracks, and large particles) deteriorate the properties of the coatings. The coatings based on Al₂O₃ and ZrSiO₄ exhibit the best properties under the conditions of abrasive wear, and this material, in combination with 19,436 steel, is suitable for application in friction couples. The degree of wear corresponds to the the value of the friction coefficient for the investigated tribocouples determined by the hardness of the material surfaces in the couple. The ceramics-polyamide couple seems to be quite promising due to the low friction coefficient and minimum wear. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 2, pp. 62–70, March–April, 2008.     

自反应火焰喷涂梯度过渡陶瓷涂层研究

以Ti-B4C-C和Ni-Al自粘结复合粉为自蔓延反应喷涂体系,采用反应火焰喷涂技术,在金属表面制备了Ti(Cx,Ny)-TiB2-NimAln梯度过渡涂层.整个涂层以Ti(C0.7,N0.3)、TiC、TiN和TiB2构成陶瓷主结构,NimAln金属间化合物作为过渡相连续分布其中,涂层具有沿厚度方向宏观连续分布和微观成分突变的特征,并存在孔隙与夹杂,呈典型的多相非均质结构.涂层经梯度过渡后,与基体的结合强度由14.38 MPa增加到30.27 MPa,抗热震性能由2次增加到16次,孔隙率由原来的32%降至19%,显微硬度由底层的Hv545增加到表层的Hv1253.涂层耐磨损性能是45号钢的14倍.     

超音速等离子高铝青铜磷光粒子复合发光涂层的性能研究

采用超音速等离子喷涂技术在45#钢基体表面制备了Cu-14Al-X与SrAl_2O_4∶Eu~(2+),Dy~(3+)复合发光涂层,研究了不同喷涂工艺参数(H_2气流量)对制备涂层性能的影响。利用XRD、SEM、EDS及荧光/磷光发光光度计研究分析了喷涂层物相组织、形貌结构及其发光性能。结果表明,涂层均由Al_(0.5)Fe_(0.5)、AlFe_3、Cu_9Al_4、SrAl_2O_4相及少量SrAl_4O_7和SrFe_2O_4构成。随着H_2气流量从1L/min到16L/min增加,喷涂材料沉积率增大,磷光粒子沉积率增加明显,同时,涂层的发光强度随H_2气流量增加而增强,涂层结合强度、显微硬度及致密性也随H_2气流量增加而显著提高。     

Ti-Al球磨粉反应等离子喷涂涂层的组织与性能

为制备Ti-Al金属间化合物复合涂层并研究其性能,以机械球磨的Ti-Al混合粉在Q235钢表面进行反应等离子喷涂实验,分别采用X射线衍射、扫描电子显微镜对涂层的成分、显微组织进行了分析,并测试了涂层的结合强度、显微硬度和耐腐蚀性能.结果表明:涂层由Al3Ti、TiN、Al2O3、少量TiAl与Ti3Al、以及残留的Al和Ti组成;球磨可促进喷涂时的反应,但喷涂时Al和Ti仍未完全反应,且在空气环境中喷涂容易氧化和氮化;涂层与基体之间是镶嵌式的机械结合,结合强度平均为30.24 MPa;涂层表面的显微硬度平均为206.1 HV,涂层的耐腐蚀性优于基体.总体上看,当球磨时间较长、电流较大、喷涂距离较大、气流量较小时,喷涂时的反应较充分,且涂层比较均匀、致密,其强度、硬度以及耐腐蚀性能较高.     

Wide temperature spectrum self-lubricating coatings prepared by plasma spraying

Self-lubricating, multicomponent coatings, which lubricate over a wide range of operating conditions, are described. The coatings have been successfully applied by plasma spraying mixed powders onto superalloy substrates. They have been evaluated in friction and wear experiments and in sliding contact bearing tests. These coatings are wear resistant by virtue of their self-lubricating characteristics rather than because of extreme hardness; a further benefit is low friction. Experiments with simple pin-on-disk sliding specimens and oscillating plain cylindrical bearing tests were performed to evaluate the tribological properties of the coatings. It was shown that coatings of Nichrome, glass and calcium fluoride are self-lubricating from about 500 to 900°C, but give high friction at the lower temperatures. The addition of silver to the coating composition improved the low temperature bearing properties and resulted in coatings which are self-lubricating from cryogenic temperatures to at least 870°C; they are therefore “wide temperature spectrum” self-lubricating compositions.     

Effect of Zr on microstructure of metallic glass coatings prepared by gas tunnel type plasma spraying

Metallic glass is one of the most attractive advanced materials, and many researchers have conducted various developmental research works. Metallic glass is expected to be used as a functional material because of its excellent physical and chemical functions such as high strength and high corrosion resistance. However, the application for small size parts has been carried out only in some industrial fields. In order to widen the industrial application fields, a composite material is preferred for the cost performance. In the coating processes of metallic glass with the conventional deposition techniques, there is a difficulty to form thick coatings due to their low deposition rate. Thermal spraying method is one of the potential candidates to produce metallic glass composites. Metallic glass coatings can be applied to the longer parts and therefore the application field can be widened. The gas tunnel plasma spraying is one of the most important technologies for high quality ceramic coating and synthesizing functional materials. As the gas tunnel type plasma jet is superior to the properties of other conventional type plasma jets, this plasma has great possibilities for various applications in thermal processing. In this study, the gas tunnel type plasma spraying was used to form the metallic glass coatings on the stainless-steel substrate. The microstructure and surface morphology of the metallic glass coatings were examined using Fe-based metallic glass powder and Zr-based metallic glass powder as coating material. For the mechanical properties the Vickers hardness was measured on the cross section of both the coatings and the difference between the powders was compared.     

机械振动对SHS陶瓷内衬复合管显微结构和力学性能的影响

通过在重力分离SHS法制备陶瓷内衬复合管过程中施以不同振幅与振频的单自由度上下往复式机械振动 ,研究了机械振动对SHS铝热燃烧、陶瓷凝固及复合管组织性能的影响 .研究发现 ,机械振动并相应提高振频可以提高燃烧温度、燃烧速率和反应转化率 ,促进Al2 O3 Fe液相重力分离和陶瓷致密过程 ,并使陶瓷层的凝固组织发生改变 ;性能测试结果表明机械振动并相应提高振频可以提高复合管的各项力学性能指标和内衬陶瓷层的表面质量 .     

粒度对超音速等离子喷涂高铝青铜合金微观结构的影响

采用超音速等离子喷涂技术在45号钢表面制备粒度范围为-280~+320目、-320~+360目、-360~+400目、-400目的4种高铝青铜合金粉体涂层。采用XRD、SEM等手段对涂层的物相组成、组织结构、显微硬度等进行了分析,研究了粒度对涂层组织及性能的影响。结果表明,粉体的粒度对涂层显微组织结构及性能有着重要影响。粉体粒度越细小,涂层的组织及性能越优良。-400目的粉体制备的涂层组织致密均匀,层流状结构明显,显微硬度可达367.5HV。     

Influence of in-flight particle characteristics and substrate temperature on the formation mechanisms of hypereutectic Al-Si-Cu coatings prepared by supersonic atmospheric plasma spraying

Hypereutectic Al-Si-Cu coatings were prepared by supersonic atmospheric plasma spraying to enhance the surface performance of lightweight alloys.To find out optimum process conditions and achieve desirable coatings,this work focuses on the influence of three important parameters (in-flight par-ticle temperature,impact velocity,and substrate temperature) on the collected splats morphology,coatings microstructure and microhardness.Results show that appropriate combinations of temper-ature and velocity of in-flight particles cannot only completely melt hypereutectic Al-Si-Cu particles,especially the primary Si phase,but also provide the particles with sufficient kinetic energy.Thus,the optimized coating consists of 98.6 ％ of fully-melted region with nanosized coupled eutectic and 0.9 ％of porosity.Increasing the substrate deposition temperature promotes the transition from inhomoge-neous banded microstructure to homogeneous equiaxed microstructure with a lower porosity level.The observations are further interpreted by a newly developed phase-change heat transfer model on quan-titatively revealing the solidification and remelting behaviors of several splats deposited on substrate.Besides,phase evolutions including the formation of supersaturated α-Al matrix solid solution,growth of Si and Al2Cu phases at different process conditions are elaborated.An ideal microstructure (low frac-tions of unmelted/partially-melted regions and defects) together with solid solution,grain refinement,and second phase strengthening effects contributes to the enhanced microhardness of coating.This inte-grated study not only provides a framework for optimizing Al-Si based coatings via thermal spraying but also gives valuable insights into the formation mechanisms of this class of coating materials.     

Densification,microstructure and mechanical properties of multicomponent (TiZrHfNbTaMo)C ceramic prepared by pressureless sintering

A multicomponent (TiZrHfNbTaMo)C ceramic has been fabricated by pressureless sintering at temperatures from 2100 ℃ to 2500 ℃,using an equimolar multicomponent carbide powder synthesized by carbothermal reduction as the starting material.Influence of sintering temperature on densification,microstructure and mechanical properties of the ceramics was investigated.The relative density increases with increasing sintering temperature,and a nearly fully dense sample is achieved by pressureless sintering at 2500 ℃.Average grain size increases from 3.7 to 15.2 μm with increasing sintering temperature from 2300 to 2500 ℃.The (TiZrHfNbTaMo)C ceramic sintered at 2400 ℃ exhibits a single phase fcc structure with homogeneous chemical composition,an average grain size of 7.0 μm and a relative density of 96.5％,while its measured hardness is 33.2 GPa at 100 mN and 23.2 GPa at 9.8 N.     

Ni/SiO2纳米复合涂层的结构与光学性质研究

采用射频磁控溅射方法制备Ni/SiO2纳米复合涂层,获得了镍成分为7.25%(at)(LNi)、13.96%(at)(MNi)、19.20%(at)(HNi)3种复合涂层,研究了该复合涂层的组织结构与光学性质.结果表明LNi纳米复合涂层的晶粒尺寸为10～15nm,随着镍含量提高,涂层的晶粒尺寸增大,纳米Ni颗粒的形状发生变化;LNi复合涂层在300～350nm存在显著的光吸收,随着晶粒尺寸增大,光吸收边发生显著的红移.     

Investigation of composite hydroxyapatite powder for plasma spraying bioceramic coatings

Powder synthesis on the basis of a matrix from nanocrystalline titanium dioxide with incorporated HA particles was developed. Using scanning and transmission electron microscopy (SEM and TEM), the shape, size, and relief of TiO₂-HA powder particles are investigated. When calculating for the powder particles using the SEM photos and TEM negative films on a picture analyzer, the granulometrical composition and the average maximum particle diameter (0.7 μm) are determined.     

The microstructure and mechanical properties of yttria-stabilized zirconia prepared by arc-melting

The microstructure of ZrO₂-Y₂O₃ alloys prepared by arc-melting was examined mainly by electron microscopy. It was found that the microstructure changed markedly with yttria content between 0 and 8·7 mol%. Pure zirconia was a single monoclinic phase, while ZrO₂-8·7 mol% Y₂O₃ alloy was single cubic phase as expected from ZrO₂-Y₂O₃ phase diagram. Tetragonal phase was found in alloys with 1 to 6 mol% Y₂O₃ together with monoclinic or cubic phase. The tetragonal phase found in present alloys normally had a lenticular shape with a length 1 to 5m and a width 0.1 to 0.3m, which is much larger than that formed by annealing. The phase with a herring-bone appearance was found in alloys with Y₂O₃ between 2 and 3 mol%, which was recognized to be a metastable rhombohedral phase. The structure of the present alloys is likely to be formed by martensitic or bainitic transformation during fairly rapid cooling from the melt temperature. The change in hardness and toughness with yttria content of the alloys is discussed on the basis of microstructural observations.     

Mechanical properties of SiNxCx ceramic films prepared by plasma CVD

The mechanical properties of Si₃N₄-SiC, SiN_x and SiC_y films prepared at a low temperature of 400 °C by plasma chemical vapour deposition are reported. Microhardness, internal stress of the film and adhesive strength between the film and glass or stainless steel substrate were evaluated as principal mechanical properties. Microhardness was measured to be about 10 to 20 G Pa dependent on the film composition in each system. Internal stress of the films on borosilicate glass substrates extensively varied from tensile to compressive with the film composition change from Si₃N₄ to SiC. Adhesive strength, as ascertained by the scratch test, was about 580 to 800 MPa for crown glass substrates, and about 210 to 310 M Pa for 316 stainless steel substrates. It is pointed out that tensile stress in these films brought about more abrupt decreases of the adhesive strength than did compressive stress.     

On some physical properties of nanostructured Cu-Pb alloy prepared by mechanical alloying

Cu-Pb alloys have no solubility in the whole solid state and their physical properties are very different from each other. In the present study, nanostructured Cu-Pb alloy powders were synthesized by the mechanical alloying process, and their nanostructural characteristics were evaluated in order to elucidate the relationship between structure and properties. By appropriate control of mechanical alloying process variables, the Pb solid solubility in Cu matrix was increased up to 10 wt.%. The monotectic temperature of Cu-Pb alloy was also decreased by decreasing the crystalline size. The relation between the structure and properties of this nanostructured Cu-Pb alloy is discussed on the basis of the experimental results.     

Mechanical properties of conventional and nanostructured plasma sprayed alumina coatings

The hardness and the elastic modulus measured by microindentation of three different types of plasma sprayed alumina coatings have been compared. Usually, such coatings present porosity and heterogeneity which affect the measurement of the mechanical properties. To take such effects into account along with the indentation size effect which is relevant to all hardness studies, the Proportional Specimen Resistance model is applied. The three alumina coatings show closely similar mechanical properties at indentation loads exceeding 1 N, i.e., macrohardness around 5.7 GPa, indentation size effect parameter around 5.5 MPa mm and elastic modulus around 160 GPa. For loads below 1 N, the extrapolated values of the macrohardness of crushed and agglomerated alumina coatings increased to 8.5 GPa, while the indentation size effect parameter has the same value, and the elastic modulus increased to 320 GPa. However, no significant change in the measured values of hardness and the elastic modulus of the nanostructured alumina coating has been observed. This result is attributed to porosity and the bimodal microstructure of the nanostructured coating where a semimolten phase coexists along with the fully molten phases.     

Study of titanium nitride deposition by supersonic plasma spraying

In this study, titanium nitride (TiN) deposition by reactive spraying was carried out under a low-pressure environment using a DC arc plasma jet generator with a supersonic expansion nozzle. Titanium powders were injected using a hollow cathode with argon gas, and nitrogen or nitrogen and hydrogen mixture was used as the plasma gas. Microstructure and properties of the coatings were examined using scanning electron microscope and X-ray diffraction. A dense TiN coating with a Vickers hardness of 2000 Hv was formed at a substrate temperature of 700 °C with a low input power of 5.3 kW. The results showed that the supersonic plasma jet in thermodynamic and chemical nonequilibrium state exhibits high potentials for reactive spraying.     

SiC whiskers-aluminium 6061 composite: microstructure and mechanical characteristic anisotropy

The correlation has been studied between the microstructure and the tensile and compressive properties of composite extruded bars of aluminium 6061 alloy matrix reinforced with silicon carbide whiskers. The material was tested before and after being subjected to T6 heat treatment. Different degrees of alignment and breakage in the whiskers and the texture of the metal matrix were observed, corresponding to different ratios of extrusion. The material also showed marked anisotropy in its mechanical characteristics: its compressive strength in the longitudinal direction was considerably higher than in the transverse direction.     

等离子喷涂法制备炭/炭复合材料硅酸钇涂层研究

采用等离子喷涂(Atmospheric plasma spraying,APS)法在炭/炭复合材料碳化硅(SiC)内涂层表面制备了硅酸钇涂层。分别采用XRD和SEM分析了所得涂层的微观结构,并测试了带有SiC/硅酸钇复合涂层的炭/炭复合材料试样在1500℃静态空气中的抗氧化性能。结果表明:通过调节喷涂粉料中的SiO2和Y2O3的摩尔比,可制得Y2SiO5、Y2Si2O7、Y2Si2O7/Y2SiO5和Y4Si3O12/Y2Si2O7/Y2SiO5四种不同结构的硅酸钇涂层;1500℃氧化73h后,SiC/Y4Si3O12/Y2Si2O7/Y2SiO5涂层试样的氧化失重速率相对较低,仅为1.01×10-4g.cm-.2h-1。