Cr含量对炭/炭复合材料SiC/Al-Si抗氧化涂层的影响(英文)

采用料浆法在已制得SiC内涂层炭/炭(C/C)复合材料(SiC-C/C)表面,制备了不同Cr含量(质量分数分别为0%,31.85%,44.95%及55.57%)的Al-Si合金涂层。分别采用X射线衍射法(XRD)、扫描电子显微镜(SEM)及1773K静态空气气氛中的恒温氧化试验,测试了所得涂层试样的微观结构及抗氧化性能。结果表明:Cr元素可以显著提高Al-Si合金涂层的抗氧化性能;Cr含量为44.95%的Al-Si合金涂层SiC-C/C复合材料试样在1773K空气气氛中氧化197h后的氧化增重为0.079%(质量分数)。     

渗硅对Mo-12Si-8.5B-(8Cr)合金抗高温氧化性能的影响

在Mo-12Si-8.5B-(8Cr)两种合金表面包埋渗制备硅化钼涂层,以改善Mo-12Si-8.5B合金的高温抗氧化性能,分析了材料的微观组织结构及其高温氧化行为。结果表明:通过包埋渗技术在Mo-12Si-8.5B合金表面获得了一层致密的硅化物涂层,添加Cr的合金表面硅化物涂层生长速率约是不含Cr合金的2倍。未渗硅处理的合金在800~1200℃的高温抗氧化性能较差。渗硅后Mo-12Si-8.5B和Mo-12Si-8.5B-8Cr合金在1200℃氧化60 h质量仅减少0.22和0.24 mg/cm~2。渗硅处理大幅度地改善了合金的高温抗氧化性能,归因于硅化钼涂层表面连续致密氧化膜的形成。     

纳米CeO2改性渗Cr涂层在5%O2 - 0.1%SO2-N2气氛中的高温氧化

用Ni-CeO2复合电镀后包埋渗Cr的方法在低碳钢上制备了CeO2改性的渗Cr涂层.在900℃、含与不含0.1%SO2的5%O2+N2气氛中,与低碳钢渗Cr及镀Ni渗Cr涂层的氧化行为进行了对比研究,获得如下结果：（1）CeO2改性的渗Cr涂层抗高温氧化性能最好,低碳钢渗Cr涂层最差;（2）SO2促进了碳钢渗Cr及镀Ni渗Cr涂层的退化,而对CeO2改性渗Cr涂层的氧化影响不大.利用光学显微镜（OM）、X光衍射（XRD）、扫描电镜与能谱（SEM/EDAX）对氧化前后试样分析表明：CeO2通过细化改性渗Cr涂层晶粒以及改变渗层Cr含量,避免氧化膜/涂层界面附近由于Cr的贫化而析出Ni2Cr相,延缓α相向γ相的快速转变,来提高氧化膜的抗剥落性能;同时,CeO2还通过改变涂层氧化膜的生长机制降低了SO2对涂层抗高温氧化性能的影响.     

TA2表面等离子渗铌合金层在700~900 ℃的氧化行为

采用双辉技术在TA2基体表面渗入铌形成结构致密、与基体形成冶金结合的钛铌合金层。结合XRD、SEM及EDS等手段分析渗铌和未渗铌TA2试样分别在700、800、900℃的高温氧化行为。实验结果表明:随着氧化温度的提高,氧化增重增加,渗铌比未渗铌的氧化增重降低,抗高温氧化性能改善,特别在900℃铌的作用明显;对渗铌和未渗铌TA2在900℃分别氧化20、40、100 h后氧化层的表面及截面进行分析,获得对合金层成分、结构、氧化性能之间关系的认识。钛铌合金层高温氧化后的氧化层是由三部分组成:外层是由高浓度合金层氧化而形成,其氧化产物主要是Nb2O5/TiO2,中间层主要由TiO2/TiO和Nb2O5组成,内层是分布着条状的富铌相。     

TC4合金双辉等离子渗Cr高温氧化行为

研究了双层辉光等离子渗Cr对TC4合金650、750、850℃恒温氧化性能的影响。结果表明：渗Cr后,表面梯度合金层显著提高了TC4合金的高温氧化性能,Ti-Cr互扩散层可有效阻止氧向基体扩散。氧化过程中,Ti、Cr向外扩散形成TiO2/Cr2O3氧化膜,其形态与氧化温度有关。850℃氧化100 h后,渗Cr试样表面形成致密Cr2O3膜,恒温氧化性能优于NiCrAlY热障涂层。     

新型SiC-MoSi2/Al-O-Ti炭/炭抗氧化复合涂层的制备及其性能研究

采用包埋和涂刷法制备出一种新型的炭/炭复合材料抗氧化涂层,它由自愈合内涂层、热膨胀系数匹配过渡层、氧阻挡层三层复合而成.用SEM,XRD对它的组分和形貌进行了表征,同时测试了涂层在1 000,1 300和1 400℃下的抗氧化性能和抗热震性能.实验结果表明:该涂层能在1 400℃下有效保护炭/炭材料达50 h以上,经过...     

多弧离子镀AlTiYN涂层的高温氧化性能及高温摩擦学行为

为研究添加0.76%Y元素对AlTiN涂层结构、高温氧化行为及摩擦学性能的影响规律及作用机制,采用多弧离子镀技术于硬质合金(YG3X)表面沉积AlTiN及AlTiYN涂层。利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)研究涂层组织结构;采用纳米压痕仪、划痕仪进行力学性能表征;通过高温氧化试验分析涂层的高温抗氧化性能;利用高温摩擦磨损试验机研究涂层的摩擦磨损行为。结果表明:添加Y元素后,AlTiYN涂层发生晶粒细化、组织结构致密化、硬度及韧性增加、结合强度显著提升。AlTiN涂层经900℃/2 h氧化处理后已完全氧化;而AlTiYN涂层经900℃/2 h氧化处理后未完全氧化,氧化层厚度为1.1μm,表明添加Y元素可以增强AlTiN涂层的高温抗氧化能力。此外,AlTiYN涂层在900℃下其摩擦因数及磨损率均低于AlTiN涂层,表明添加Y元素可有效增强涂层高温耐磨损性能。     

炭/炭复合材料声电沉积钙磷生物活性涂层的生长机理

通过声电沉积在炭/炭复合材料表面制备钙磷生物活性涂层,采用SEM（带EDAX）,XDR,FTIR研究电沉积时间对钙磷生物活性涂层的形貌、结构和组成的影响.实验结果表明：沉积初始先在炭/炭表面形成无定形层,片状磷酸氢钙（DCPD）在其表面生长,随着电沉积时间的延长,逐渐向针状的羟基磷灰石Ca10（PO4）6（OH）2（HA）转变,涂层厚度和n（Ca）/n（P）不断增加,涂层的结晶度和电解液的pH值下降.涂层为缺钙磷灰石.同时探讨了在炭/炭复合材料表面钙磷生物活性涂层的生长机理.     

TiAl合金表面机械研磨渗铝涂层的制备及高温性能

利用机械研磨渗在TiAl合金表面制备了铝化物涂层。在600℃经过150 min的振动处理后,TiAl合金表面形成了约为30μm的涂层。该涂层均匀致密,Al和Ti元素沿涂层均匀分布。XRD分析表明该涂层的相结构为Al3 Ti相。在900℃下,经过300 h的循环氧化后,该铝化物涂层表面形成了一层连续均匀的Al2 O3膜,表现出良好的抗氧化和抗剥落性能。相比之下,TiAl合金空白样表面形成了分层结构的氧化层,主要由Al2O3和TiO2混合氧化物组成,因此表现出较差的高温性能。     

阴极弧离子镀AlCrN涂层高温氧化后XPS分析

采用阴极弧离子镀方法在Ti C基金属陶瓷刀具表面沉积了Al Cr N涂层,进行了900℃下2 h高温氧化试验。通过SEM、EDS、XRD、XPS等手段分析了Al Cr N涂层高温氧化前后表面形貌、元素组成、物相组成及元素结合能,并讨论了Al Cr N涂层高温氧化及失效机理。结果表明,氧化前Al Cr N涂层由Al N、Cr N和Cr2N物相组成,其中Cr N表现出(200)的择优取向,氧化后其物相转变为抗高温的Al2O3、Cr3O4和Ti4O3氧化物;氧化前Al Cr N涂层中Al和N以Al—N键、Cr和N以Cr—N键存在,氧化后Al与O以Al—O键、Cr与O以Cr—O键方式存在,在涂层-基体结合界面处形成了致密的扩散层。     

Effect of boron and carbon on the fracture toughness of IN 718 superalloy at room temperature and 650 °C

The effect of B and C microadditions on the fracture toughness of IN 718 superalloy was investigated at room temperature (RT) and at 650 °C. At RT, the fracture toughness was observed to increase with increasing B and C concentrations. C had a relatively weak effect on the fracture toughness at 650 °C, but the influence of B was significant. At RT the highest fracture toughness value was obtained for the alloy with 29 ppm B and 225 ppm C at RT, and at 650 °C the alloy with 60 ppm B and 40 ppm C had the highest fracture toughness. An increase in the concentration of B to 100 ppm, however, resulted in a reduction in the fracture toughness at 650 °C. Fractographic observations showed that the formation and coalescence of microvoids was the predominant fracture mechanism at RT. In contrast, at 650 °C, the fracture surface exhibited intergranular cracking in the alloy with lower B concentrations and transgranular cracking coupled with fine dimples in the alloy with higher B concentrations. It is suggested that B impedes intergranular cracking by increasing the cohesion of grain boundaries and improving the grain boundary stabilization. The RT increase in the fracture toughness of the material caused by the addition of C is attributed to the formation of intergranular and intragranular carbides that increased the resistance to the plastic deformation.     

Effect of SI Content on the Oxidation Resistance of Ti3Al1-x Si x C2 (x⩽ 0.25) Solid Solutions at 1000–1400°C in Air

The oxidation behavior of Ti₃Al_1-x Si _x C₂ (x ⩽ 0.25) solid solutions was investigated in flowing air at 1000–1400°C for up to 20 hrs. Similar to Ti₃AlC₂, Ti₃Al_1-x Si _x C₂ (x⩽ 0.15) solid solutions display excellent oxidation resistance at all temperatures because of the formation of the continuous α-Al₂O₃ protective layers. However, Al₂(SiO₄)O formed during oxidation of Ti₃Al_1-x Si _x C₂ (x=0.2 and 0.25) solid solutions at and above 1100°C, which is believed to be responsible for the deterioration of oxidation resistance of Ti₃Al_0.75Si_0.25C₂ at 1300°C. Additionally, Ti₅Si₃ was also found in the oxidized samples. This implies that Ti₅Si₃ precipitated from Ti₃Al_1-x Si _x C₂ solid solutions during oxidation. But it has been proven that Ti₅Si₃ has little effect on the oxidation resistance of the material, which is attributed to an interstitial carbon effect.     

XRD analysis and microstructure of milled and sintered V, W, C, and Co powders

In the current study, results of the milled and sintered V, W, C, Co powders are presented. Analytical techniques such as SEM equipped with EDS and XRD were used to study microstructure and phase evolution, respectively. In addition to B1 (VW)C solid solution, a rhombohedral V₂O₃ and new τ-type (Cr₂₃C₆) carbide were formed after sintering. The possible formation mechanisms behind detected phases are discussed. It is evident that complete MA process depends strongly on the starting compositions of pure elements, their lattice coherency according to Hume-Rothery rules on crystal structure and atomic size, and enough milling time that provides adequate kinetics.     

PREPARATION AND ANTI–OXIDATION PROPERTY OF SiC/SiC–MoSi2 COATING ON C/C COMPOSITE

采用包埋法和涂刷法在C/C复合材料表面依次制备了SiC内涂层和SiC--MoSi₂外涂层, 借助XRD与SEM对涂层的微观结构进行了分析, 研究了涂覆后的C/C复合材料在高温静态空气中的防氧化性能. 结果表明: SiC/SiC--MoSi₂复合涂层有效缓解了MoSi₂与C/C热膨胀不匹配问题, 涂层无裂纹; 复合涂层在900和1500℃静态空气环境下均可对C/C复合材料有效保护100 h以上; 涂层的多层、多相结构以及在高温氧化后表面生成的SiO₂薄膜是其具有优异防氧化性能的原因.     

Microstructures And Mechanical Properties Of In-Situ Al2o3/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.     

Densification and compressive strength ofin-situ processed Ti/TiB composites by powder metallurgy

In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB₂, B₄C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB₂ or B₄C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100, 1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB₂ compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of the composite made from TiB₂ reactant powder was higher than that of the composite made from B₄C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between matrix and reinforcement made from TiB₂ reactant powder was better than that made from B₄C.     

Mechanical alloying of dispersion-hardened Ni3Al-B from elemental powder mixtures

Mechanical alloying and hot extrusion were studied as a means to dispersion harden an intermetallic compound based on Ni ₃ Al- B from elemental powder mixture. The oxide used for the dispersoids was partially stabilized zirconia. During mechanical alloying the microstructure evolved according to the characteristic stages found in other mechanical alloying systems. Completion of the alloying reaction required 16 h, beyond which loss of the crystalline property set in. Experimental observation of the grain refinement during mechanical alloying agreed with a prediction based on an existing model. Compared to V- cone mixing, the mechanical alloying produced a homogeneous distribution of fine dispersoids. The refined grain structure and dispersoids resulted in a high tensile yield strength over a wide range of temperatures.     

Microstructural Analysis of TiAl x N y O z Coatings Fabricated by DC Reactive Sputtering

TiAl _x N _y O _z coatings were prepared by DC reactive sputtering on AISI D2 tool steel substrates, using a target of Ti-Al-O fabricated from a mixture of powders of Ti (22.60 wt.%), Al (24.77 wt.%), and O (52.63 wt.%). The coatings were deposited on substrates at room temperature in a reactive atmosphere of nitrogen and argon under a pressure of 8.5 × 10⁻³ mbar. X-ray diffraction, electron dispersive spectroscopy, Raman scattering, and nanoindentation techniques were employed to investigate the coatings. The results show that the increment in the nitrogen flow affects the structure and the mechanical properties of the coatings. The sample with the lowest nitrogen flow presented the highest hardness (10.5 GPa) and the Young’s modulus (179.5 GPa). The hardness of the coatings TiAl _x N _y O _z as a function of crystalline grain size shows a behavior consistent with the Hall–Petch relation.     

High temperature oxidation of a (Cr2N−Mo2S3)/Cr double-layered coating deposited on steel by D.C. magnetron sputtering

A coating consisting of (Cr₂N−Mo₂S₃) overlay coating and an underlying Cr coating was deposited on a steel substrate by D.C. magnetron sputtering. The oxidation characteristics of the deposited double-layered coating were studied at temperatures ranging from 400 to 900 °C in air. The oxidation product was primarily Cr₂O₃. The unreacted coating beneath the oxide scale had some dissolved oxygen, sulfur, and iron. Oxidation of the coating occurred via complex routes such as the outward diffusion of chromium and nitrogen from Cr₂N and iron from the substrate, and the inward transport of oxygen from air, chromium from Cr₂N, and S from Mo₂S₃. This counter diffusion of various ions occurred easily via fine crystallites that constituted the coating, which had some solubility of S, O, and Fe.     

Effect of C and milling parameters on the synthesis of WC powders by mechanical alloying

In the current study, the amount of carbon and the effects of milling parameters in production of tungsten-carbide (WC) powder were evaluated. Mechanical alloying (MA) of elemental W and C powders at different carbon-rich and carbon-deficient compositions was studied. XRD results showed that the higher the carbon content the longer the milling period for the formation of WC powder. We also report on the effect of milling parameters on the phase formation. In stoichiometric composition, WC was synthesized faster than in compositions with higher carbon amount. Furthermore, W₂C phase was observed in compositions with higher carbon content milled at low speed and ball-to-powder ratio (BPR), as well as in carbon-deficient composition milled for shorter period. The ab initio calculations were performed in attempt to explain the destabilization of W₂C on further milling.