Synthesis of Al2O3 coatings on Ti(C,N)-based cermets by microwave plasma CVD using Al(acac)3

Aluminum acetylacetonate (Al(acac)₃) was used as a precursor to synthesize aluminum oxide (Al₂O₃) coatings on Ti(C, N)-based ceramic by microwave plasma CVD (MPCVD). Al₂O₃ coatings transformed from γ phase to δ phase and α phase and as microwave power (p_M) and total pressure (P_tot) increased. The effects of p_M and P_tot on the microstructure of the Al₂O₃ coating and oxidation of the substrate have been investigated. The relationship between phase structure and adhesive strength of the coatings was also studied. Coatings deposited at p_M = 1.0-1.2 kW and P_tot = 400 Pa exhibited good adhesion strength (Class 1).     

Formation of (Al2OC)1−x(AlN)x solid solution starting from Al–Si–Al2O3 powder matrix at 1300°C in flowing nitrogen

(Al₂OC)_1−x(AlN)_x solid solution-reinforced Si–Al₂O₃ composite was successfully synthesized by designed heating of the Al–Si–Al₂O₃ composite to 580°C and held for 8 hours, followed by heating to 1300°C at a rate of 12°C/h in flowing nitrogen. The reaction mechanism is as follows: after the Al–Si–Al₂O₃ composite is heated to 580°C and held for 8 hours, an AlN cladding is formed on the surface of the Al powder, thus the composite is preconverted into (Al–AlN cladding structure)–Si–Al₂O₃ system. With increasing temperature, the AlN cladding ruptures and the reactive Al(l) flows out. The Al(l) preferentially undergoes active oxidation to form metastable Al₂O(g), which lowers P_O2 inside the composite and inhibits the active oxidation of Si. Moreover, ultrafine carbon is produced by the pyrolysis of the phenolic resin binder. Both metastable Al₂O(g) and ultrafine carbon are highly reactive. Therefore, under the induction of AlN and N₂, (Al₂OC)_1−x(AlN)_x solid solution is formed by the reaction which easily occurs at a relatively low temperature. In the presence of a large amount of Al₂O(g), the P_O2 in the composite does not satisfy the condition required for both Si nitridation and active oxidation, so the free Si remains stable in the composite, forming a metal-non-oxide-oxide composite. The cold crushing strength of the composites is up to 305 MPa, and the composites do not show hydration after 20 months of storage in the environment.     

Al2O3-C材料中Ti(C,N)的形成及其抗气化炉渣侵蚀性能研究

水煤浆气化炉内衬材料的无铬化势在必行.基于碳氮化钛对高炉渣的增稠机理,本工作在前期开发水煤浆气化炉用Al2O3-C无铬化内衬材料的基础上,拟通过在Al2O3-C材料中引入一定量的TiO2,使之在高温下材料内原位反应形成碳氮化钛相,提高材料的抗气化炉渣侵蚀性能.结果表明:当Al2O3-C材料引入适量的TiO2时,可以发现在烧成过程中材料中原位形成了Ti(C,N)相,优化材料的孔结构;当材料与渣发生反应时,提高了在侵蚀过程中渣的粘度,改善材料的抗侵蚀性能.当材料中引入的过量的TiO2,TiO2易与气化炉渣发生反应,降低渣的粘度,从而降低材料的抗侵蚀性能.     

In situ reaction synthesis and characterization of Ti3Si(Al)C2/SiC composites

The reaction route, microstructure, and properties of Ti₃Si(Al)C₂/SiC composites with 5–30 vol.% SiC content prepared by in situ hot pressing/solid–liquid reaction synthesis process are investigated. In contrast to monolithic Ti₃Si(Al)C₂, the SiC particle-reinforced composites exhibit higher elastic modulus, Vickers hardness, fracture toughness, improved wear, and oxidation resistance, but have a slight loss in flexural strength. The improvement in the properties is mainly ascribed to the contribution of SiC particles, and the strength degradation is due to the residual tensile stresses in the matrix.     

Al对等离子放电烧结法合成Ti3SiC2的影响研究

以元素为原料，Al为助剂，采用等离子放电烧结(SPS)工艺合成Ti3SiC2块体材料，通过X射线衍射分析和对SPS过程参数的研究表明：适量A1能促进Ti3SiC2的反应合成，提高合成材料的纯度，但Al也会使Ti3SiC2的热稳定性降低。     

In situ reaction and solid solution induced hardening in (Ti,Zr)B2-(Zr,Ti)C composites

(Ti,Zr)B₂ - (Zr,Ti)C ceramics were synthesized by reactive hot-pressing and solid solution coupling effect using ZrB₂ and TiC powders as starting materials. Effects of sintering temperature on phase relations, microstructure and mechanical properties were reported. The equimolar ZrB₂ and TiC reactants ensured a complete in situ reaction to form (Ti,Zr)B₂ and (Zr,Ti)C solid solutions. The (Ti,Zr)B₂ - (Zr,Ti)C composite sintered at 1750°C was fully densified, and exhibited a high hardness of 29.1 GPa due to fine-grain hardening and solid solution hardening. The optimized comprehensive mechanical properties such as a hardness of 27.9 GPa, a strength of 705 MPa and an indentation fracture toughness of 5.3 MPa m^1/2 were achieved in (Ti,Zr)B₂ - (Zr,Ti)C composites sintered at 1800°C for 1 hour.     

The synthesis and mechanical properties of high pure Ti2Al(Sn)C solid solution

High pure Ti₂Al_(1?x)Sn_xC (x = 0‐1) powders were synthesized using Ti, Al, Sn, and TiC powders as raw materials by pressureless sintering method. The influence of sintering temperature and raw material ratio on the purity of Ti₂AlC and Ti₂Al_0.8Sn_0.2C powders were investigated. The results show that pure Ti₂AlC and Ti₂Al_0.8Sn_0.2C powders were obtained from the mixed raw materials ratio of Ti:1.1Al:0.9TiC and Ti:0.9Al:0.2Sn:0.9TiC at 1450°C, respectively. Subsequently, fully dense Ti₂AlC and Ti₂Al_0.8Sn_0.2C bulks were prepared using mechanically alloying and hot pressed sintering method. The Vickers hardness of Ti₂AlC and Ti₂Al_0.8Sn_0.2C approaches approximately about 6 GPa and 4 GPa, the flexural strength was measured to be 650 ± 36 MPa and 521 ± 33 MPa, respectively. Microstructural analysis reveals that grain delamination, kink bands, and crack deflection occurred around the indentation area and at the fracture surface.     

Oxidation resistance of Ti3AlC2 and Ti3Al0.8Sn0.2C2 MAX phases: A comparison

Ti₃AlC₂ and Ti₃Al_0.8Sn_0.2C₂ MAX phase powders are densified using Spark Plasma Sintering (SPS) technique to obtain dense bulk materials. Oxidation tests are then performed over the temperature range 800°C-1000°C under synthetic air on the two different materials in order to compare their oxidation resistance. It is demonstrated that, in the case of the Ti₃Al_0.8Sn_0.2C₂ solid solution, the oxide layers consist in TiO₂, Al₂O₃, and SnO₂. The presence of Sn atoms in the A planes of the solid solution leads to an easy diffusion of Sn out of the MAX phase which promote the formation of the nonprotective and fast growing SnO₂ oxide. Moreover, the small Al/Ti atom's ratio promotes the growth of a nonprotective rutile-TiO₂ scale as well. In the case of the Ti₃AlC₂ MAX phase, the oxide layer consists in a protective alumina scale; a few TiO₂ grains being observed on the top of the Al₂O₃ layer. The parabolic oxidation rate constants are about 3 orders of magnitude smaller for Ti₃AlC₂ compared to Ti₃Al_0.8Sn_0.2C₂.     

Ti3AC2(A=Si,Al)结构、弹性和电子性质的第一性原理研究

采用第一性原理方法,系统地研究了MAX相材料Ti3AC2(A=Si,Al)的结构、弹性和电子性质.对比LDA和GGA计算结果可知,采用GGA近似得到的结果更接近实验值.计算分析了Ti3AC2(A=Si,Al)的弹性性质,并根据弹性常数证明了其力学稳定性.此外,还从电子态密度和Mulliken布居分析的角度考察了Ti3AC2(A=Si,Al)的电子性质和价键特性,认为其具有共价键、离子键和金属键的综合性质.本文计算结果与文献报道吻合较好.     

放电等离子烧结制备Ti/Al2O3复合材料

Ti基金属复合材料是一种新型高温结构材料.本文利用放电等离子烧结技术,在温度1250℃、压力30MPa、真空度6Pa,保温时间10min条件下,制备了相对致密度较高的Ti/Al2O3复合材料.借助XRD,SEM,EDS等测试手段对该复合材料的物相组成、界面反应、微观结构以及致密度进行了观察与分析.结果表明:利用SPS技术制备Ti/Al2O3的复合材料,晶粒细小且分布均匀,结构致密、2相之间结合状态良好,相对致密度随材料中陶瓷相含量的增多而有所降低.Ti,Al2O32相之间无明显界面化学反应发生.     

固体电解质Li_(1.3)Al_(0.3)Ti_(1.7)(PO_4)_3烧结片的制备与表征

以固相法合成固体电解质Li1.3Al0.3Ti1.7(PO4)3(LATP)粉末。研究了烧结温度以及烧结时间对LATP离子电导率的影响。采用X射线衍射、扫描电子显微镜和交流阻抗技术对材料粉末以及烧结片相组成、结构和离子导电性进行表征。结果表明,900℃条件下合成的粉末为纯相LATP,颗粒均匀,当LATP电解质基片在900℃下烧结4 h,得到的LATP烧结片表面致密光滑,而且离子电导率较高,为3.03×10-4S/cm。     

Intermediate phases in synthesis of Ti3SiC2 and Ti3Si(Al)C2 solid solutions from elemental powders

In this paper, we investigated the reaction path to synthesize Ti₃SiC₂ by the in situ hot pressing/solid–liquid reaction method. The effect of different content of Al addition on this process was also examined. Ti₃SiC₂ mainly formed from the reaction between Ti₅Si₃C_x, TiC_x, TiSi₂ and graphite at 1400–1500 °C. As an inescapable impurity in Ti₃SiC₂, TiC_x was removed by addition of small amounts of Al. This was owing to the fact that the addition of a minor quantity of Al increased the amount of “effective TiC_x” and relatively decreased that of “invalid TiC_x”. Further increasing Al content, however, resulted in the presence of TiC_x again in the final product. This was due to the fact when significant amounts of Al was added, the stoichiometric ratio of silicon and graphite has been deviated from that for Ti₃SiC₂. More Si and less graphite were needed to prepare a monolithic Ti₃Si(Al)C₂ solid solution with high Al content.     

Investigation of preparation and properties of Ti3SiC2/Al2O3 multilayered composites

Ti₃SiC₂/Al₂O₃ multilayered composites were prepared by the combination of tape casting and hot pressing sintering. The slurry was produced by adjusting the amounts of each organic material, including triethyl phosphate (TEP) as a dispersion, polyvinyl butyrate (PVB) as a binder, dioctyl phthalate (DOP) as a plasticizer, and anhydrous ethanol as an organic solvent. When TEP content was 3 wt.%, PVB content was 4.5 wt.%, R-value (DOP/PVB) was 1.4, and solid content was 38 wt.%; the cast film with a smooth surface, good flexibility, and uniform thickness was obtained after defoaming, tape casting, and drying. Three samples were prepared, namely, S1–S3. The S1 was monolithic Ti₃SiC₂/Al₂O₃ (mass ratio is 1:1) composites. S2 and S3 were Ti₃SiC₂/Al₂O₃ multilayered composites, which matrix layers were Ti₃SiC₂/Al₂O₃ composites (mass ratio is 1:1) and Al₂O₃, respectively, and their interface layer was Ti₃SiC₂. S1–S3 were also sintered at 1550°C. The bending strength of multilayered materials were lower than that of monolithic material, but the fracture toughness of multilayered materials significantly increased. Due to the introduction of Ti₃SiC₂ interface layer, the friction coefficient and wear rate of Ti₃SiC₂/Al₂O₃ multilayered composites were reduced by 30.7% and 33.8%, respectively, compared with monolithic material.     

加入Si,Si/Al对高碳Al2O3-C材料抗热震性的影响

以电熔白刚玉、熔融石英(粒度≤0.5 mm)为骨料,鳞片石墨(粒度≤0.15 mm)、电熔白刚玉粉(粒度≤0.088mm≤0.045 mm)、Si粉(粒度≤0.074 mm)、Al粉(粒度≤0.088 mm)为基质,热固性酚醛树脂作结合剂,压制成25 mm×25 mm×125 mm的试样,经200℃固化24 h后,在埋炭条件下经1200℃下保温3 h制成碳含量为30%的高碳Al2O3-C材料.分别用5%、10%、15%、20%的Si粉替代高碳Al2O3-C材料中的石墨研究其对试样抗热震性的影响;根据Si粉替代石墨的结果又研究了不同比例Si/Al粉(总量10%)替代石墨后对试样抗热震性的影响,并用SEM和XRD分析热震后试样的显微结构和物相组成.结果表明:(1)Si替代石墨量在5%～10%之间,试样的抗热震性基本保持不变,替代量大于10%以后试样的抗热震性下降.(2)Si/Al替代石墨量为10%时,改变Si/Al比例对试样抗热震性的影响不大.(3)适量Si,Si/Al基本保持Al2O-C材料抗热震性的原因是原位生成非氧化物.     

New observations on wear characteristics of solid Al2O3/Si3N4 ceramic tool in high speed milling of additive manufactured Ti6Al4V

Additive Manufacturing (AM) technologies applied to the titanium alloys have attracted attention from industries in recent years. Despite one of the main goals of AM is the reduction of manufacturing steps, semi-finish/finish machining operations are still required so as to obtain the desired geometrical tolerance and surface features. In this study, the solid end mill was manufactured by Al₂O₃/Si₃N₄ (Sialon) ceramic materials and employed in high-speed slot milling of Ti6Al4V alloy fabricated by the Direct Metal Laser Sintering (DMLS) AM technology to study the tool wear characteristics during processing. The Raman spectroscopic method was employed to characterize the molecular structures of Sialon ceramics for the manufacturing of the cutting tool. The morphologies and elemental maps of wear region of the ceramic tool were examined by scanning electron microscope and energy dispersive spectroscopy techniques. The results show that the adhesion wear and diffusion wear are the dominant wear mechanisms, and the chemical stability of Al₂O₃/Si₃N₄ (Sialon) ceramics fabricated as the solid ceramic tool to the attack of the atoms from additive manufactured Ti6Al4V is relatively weak under the atmosphere. The difference of thermal expansion coefficients of diffusion layer and tool substrate accelerates the initiation and propagation of thermal cracks formed on the diffusion interface. Moreover, fracturing and crater-like groves near the tool edge were finally formed due to the removal of adhered workpiece material.     

均相共沉淀法制备草酸铈固溶体

以草酸二乙酯、Ce(NO3)3.6H2O、Y(NO3)3.6H2O为初始原料,以尿素为pH值调节剂,实现了Ce3 、Y3 的均相共沉淀。利用热重分析(TG-DTA)从多方面证实了n=0～35.5(n为尿素与草酸二乙酯的摩尔比)范围内得到的沉淀物为草酸铈的固溶体。经扫描及透射电子显微镜观察,生成的草酸盐固溶体沉淀颗粒尺寸随着n值的增大而减小,由n=0时约10μm下降到n=35.5时约0.5μm,沉淀物热分解后得到的氧化物经X射线衍射分析及晶格常数计算表明了为Y固溶CeO2,其结晶粒径约10 nm。     

氢氧化铝和氢氧化锶复合粉末的制备及热处理

采用活化铝-锶合金粉末水解反应制备氢氧化铝和氢氧化锶复合粉末，并在700℃下进行热处理，利用XRD，SEM，BET和TG—DTG等分析技术对复合粉末结构、性能及热处理进行研究。结果表明，铝-锶合金粉末水解反应产物为氢氧化铝和氢氧化锶的复合粉末，微观形貌为1～3μm片状小颗粒叠加的团聚颗粒，BET比表面积较大。达到45．2m^2／g。TG—DTG结果显示，在70～190℃，八水氢氧化锶中8个结晶水脱水，在190～650℃，氢氧化铝和氢氧化锶热分解。经700℃下热处理1h后，其相组成、微观形貌、BET比表面积都将发生较大的变化。     

无压烧结Al2O3/Si3N4纳米复合陶瓷的力学性能

本文对Al2O3／Si3N4体系进行无压烧结。获得试样相对密度大于98％，采用物相分析，烧结体中并没有Si3N4颗粒存在而是形成SIALON相。Si3N4和Al2O3反应生成的β-SIALON相颗粒不仅分布在Al2O3晶粒晶界处也存在于Al2O3晶粒内部，形成独特的“内晶型”结构。当受到外力时既能诱发穿晶断裂，又能引起裂纹偏转，从而起到增强的作用。由于产生晶界滑移，韧性有所下降。     

无压烧结Al2O3/Si3N4纳米复合陶瓷的力学性能

对Al2O3／Si3N4体系进行无压烧结。获得试样相对密度大于98％,物相分析烧结体中并没有Si3N4颗粒存在而是形成SIALON相。Si3N4和Al2O3反应生成的β-SIALON相颗粒不仅分布在Al2O3晶粒晶界处也存在于Al2O3晶粒内部,形成独特的“内晶型”结构。当受到外力时既能诱发穿晶断裂,又能引起裂纹偏转,从而起到增强的作用。由于产生晶界滑移,韧性有所下降。     

热压烧结Al2O3/Si3N4复相陶瓷的研究

采用热压烧结工艺制备了Al2O3/Si3N4复相陶瓷材料,对不同温度下、不同氮化硅用量时所制备的材料进行了硬度、断裂韧性等力学性能的测试,运用X射线衍射分析(XRD)和扫描电镜(SEM)技术对材料的微相组成与显微形貌进行表征.结果表明1600 ℃,30 MPa,保温1 h,Si3N4用量为3wt%时所制备的材料的各项力学性能达到了最佳值.