CrB颗粒增强MMC涂层的组织及其耐磨机理

用超音速电弧喷涂方法制备CrB颗粒增强的MMC涂层,利用金相显微镜、扫描电镜(SEM)及电子探针(EPMA)分析方法,对涂层的微观组织及微区成分进行分析;在实际循环流化床锅炉水冷壁上进行现场试验以检测涂层的耐高温冲蚀磨损性能,对涂层冲蚀表面的微观形貌进行分析,研究涂层的耐磨机理。结果表明:涂层具有复合材料的典型层状组织特征,金属基体在涂层中连续分布;增强颗粒主要为Cr的硼化物和Cr的氧化物。硬质相颗粒均匀弥散分布在涂层中,起到强化作用,并可阻挡冲蚀划痕的扩展,减缓了涂层金属基体受磨损的进程;塑、韧性较好的金属基体可缓冲冲蚀粒子对硬质相颗粒的冲击,使涂层具有优良的耐冲蚀磨损性能。     

Molten salt synthesis of orthorhombic CrB and Cr2AlB2 ceramics

High-purity and fine CrB powders are firstly synthesized from Cr and B powders in (Na, K)Cl molten salt at 850 °C for 2 h. Then the as-achieved CrB powders are used as precursors to synthesize homogeneous and size-controlled Cr₂AlB₂ powders in (Na, K)Cl molten salt at 900 °C for 2 h. Additionally, the formation mechanisms of CrB and Cr₂AlB₂ in (Na, K)Cl molten salt are also investigated. Results show that the Cr atom, formed by disproportionation of Cr²⁺ ions in molten salt, reacts in-situ with B powders to form CrB. For the formation of Cr₂AlB₂, Al and CrB migrate mutually and assemble firstly in the molten salt, and then Al intercalates into CrB to generate Cr₂AlB₂.     

原位生成WB-CrB增强镍基激光熔覆层的耐蚀性研究

采用静态浸泡法对原位生成WB-CrB增强镍基激光熔覆层的耐腐蚀性进行研究.使用扫描电镜和X射线衍射仪对熔覆层进行显徽组织和物相分析,在光学显微镜下观察样品表面腐蚀形貌.结果表明:WB-CrB增强镍基激光熔覆层(Ni60+16 wt.%(WO3/B2O3+C))在10%H2SO4(质量百分数)溶液中表现出较好的耐腐蚀性能...     

沉积温度对CrB_2涂层结构与性能的影响

为了研究沉积温度对涂层微结构与力学性能的影响,采用直流磁控溅射技术制备了CrB_2涂层。通过XPS、XRD、SPM、SEM、HRTEM、纳米压痕仪和维氏压痕仪分别分析了涂层的成分、结构、微观形貌和力学性能。结果表明:在不同沉积温度下,CrB_2涂层均由CrB_2和少量Cr相组成。涂层具有致密的纳米柱状结构,其直径大约为7nm,且沿着生长方向贯穿整个涂层截面。随沉积温度升高,涂层晶体取向由(101)和(001)的混合取向逐渐转变为(001)择优取向,涂层由纤维状结构转变为柱状晶结构,且柱状晶尺寸随沉积温度的增加逐渐细化,致密化程度增加。涂层的力学性能随沉积温度的升高而显著增加;当沉积温度达到400℃时,涂层具有最高硬度(50.7±2)GPa和最高弹性模量(513.6±10)GPa。微观结构和力学性能随沉积温度的演变归因于沉积原子运动的逐渐增强和结构的致密化。     

钛合金表面等离子弧熔覆原位自生镍基耐磨涂层的制备及微观结构表征

目的 在钛合金表面制备陶瓷相增强复合耐磨涂层。方法 采用等离子弧熔覆技术,在Ti6Al4V钛合金表面制备了原位自生TiB2、TiC、CrB陶瓷相增强镍基耐磨涂层。采用X射线衍射仪、扫描电镜、能谱仪检测了涂层的物相组成、组织组织以及微区化学成分,采用显微硬度计测试了涂层的硬度。结果 涂层靠近熔合线区域由Ni-Ti树枝晶及枝晶间的共晶组成,在涂层的中上部,大量原位增强相分布于镍基固溶体基体之中。在熔覆过程中,钛合金基材中的Ti元素同熔覆粉末中的B、C元素发生原位冶金反应形成TiB2、TiC增强相,CrB增强相为Ni基熔覆粉末中Cr、B元素反应形成,增强相的形态由各自的晶体结构及熔池凝固热力学与动力学条件决定。涂层的显微硬度得到显著提高,最高达1037HV0.2。结论 采用等离子弧熔覆技术,利用熔池内Ni-Cr-Ti-B-C合金体系的原位冶金反应,可以在钛合金表面制备原位自生TiB2、TiC、CrB增强镍基复合耐磨涂层。同Ti6Al4V基材相比,由于涂层具有大量增强相分布于镍基固溶体的组织特征,其显微硬度得到了显著提高。     

MODE I AND MIXED MODE I/II FATIGUE CRACKING IN Ni3Al(CrB) SINGLE CRYSTALS

Abstract— Nominal mode I and mixed mode I/II fatigue tests were carried out using the intermetallic compound Ni₃Al(CrB) in the form of single crystal specimens. The effects of crystal orientation and load mode on fatigue crack initiation and growth were studied. The fracture surfaces of the single crystals were characterized by a cleavage-like appearance and cracking occurred either on a single {111} plane or on multiple {111} planes irrespective of whether mode I or mixed mode I/II loadings were applied. It was found that the crack initiation and growth behaviour are dependent on both crystal orientation and applied loading mode. The cracking behaviour predicted by three mixed mode fracture criteria (MTS, SED and G criteria) in polycrystalline materials under mixed mode loading can be understood from the present results on single crystals.     

Electrochemical boriding and characterization of AISI D2 tool steel

D2 is an air-hardening tool steel and due to its high chromium content provides very good protection against wear and oxidation, especially at elevated temperatures. Boriding of D2 steel can further enhance its surface mechanical and tribological properties. Unfortunately, it has been very difficult to achieve a very dense and uniformly thick boride layers on D2 steel using traditional boriding processes. In an attempt to overcome such a deficiency, we explored the suitability and potential usefulness of electrochemical boriding for achieving thick and hard boride layers on this tool steel in a molten borax electrolyte at 850, 900, 950 and 1000 °C for durations ranging from 15 min to 1 h. The microstructural characterization and phase analysis of the resultant boride layers were performed using optical, scanning electron microscopy and X-ray diffraction methods. Our studies have confirmed that a single phase Fe₂B layer or a composite layer consisting of FeB + Fe₂B is feasible on the surface of D2 steel depending on the length of boriding time. The boride layers formed after shorter durations (i.e., 15 min) mainly consisted of Fe₂B phase and was about 30 μm thick. The thickness of the layer formed in 60 min was about 60 μm and composed mainly of FeB and Fe₂B. The cross sectional micro-hardness values of the boride layers varied between 14 and 22 GPa, depending on the phase composition.     

HIPIMS制备Cr-B涂层及摩擦学性能

为研究Cr-B涂层在多测试环境(干摩擦、蒸馏水和海水环境)下摩擦磨损行为,采用高功率脉冲磁控溅射沉积技术制备Cr-B涂层,分析涂层成分、结构、微观形貌和力学性能,重点考察涂层在不同环境下的摩擦磨损性能。结果表明:制备的Cr-B涂层,B/Cr的原子比为1.8,结构主要由CrB2和自由Cr相组成,硬度和弹性模量分别为(26.9±1.0)GPa和(306.7±6.0)GPa。摩擦测试结果显示:涂层在干摩擦时具有较高的摩擦因数为0.75,发生严重磨损失效,归因于摩擦过程中涂层剥落而导致严重的磨粒磨损;与干摩擦相比,涂层在蒸馏水和海水环境中的摩擦因数均显著降低,分别为0.26和0.22,这主要由于蒸馏水和海水的边界润滑作用所导致,在蒸馏水中摩擦的磨损机制为磨粒磨损,而在海水中的磨损机制为磨粒磨损和腐蚀磨损的协同作用。     

Phase pure and well crystalline Cr2AlB2: A key precursor for two-dimensional CrB

Phase pure and well crystalline Cr₂AlB₂ powders are synthesized by heating the mixtures of CrB and Al powders at 900 °C. Cr₂AlB₂ exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-like grain with the increase of holding time. The morphology-structure relationships of Cr₂AlB₂ are delicately discussed. Meanwhile, as the precursor for fabrication of Cr₂AlB₂, high purity CrB powders are also prepared by high-temperature reaction of B and Cr elemental powders at 1800 °C. CrB grains grow into regular plate-like morphology. Through Rietveld structure refinement, new sets of diffraction data are presented for both CrB and Cr₂AlB₂ and overlapped peak positions and intensities are revealed which make up for the deficiency of the existing data in ICDD PDF ^#32-0277 (CrB) and ICDD PDF ^#72-1847 (Cr₂AlB₂). Moreover, since MAB phases are precursors for preparing MBenes, 2D-CrB nanosheets are successfully prepared by completely etching out Al atomic layers from Cr₂AlB₂. 2D-CrB crystalizes in CrB structure with two-dimensional lamellar morphology. Simultaneously the formation mechanism of 2D-CrB is vividly depicted. A system of materials preparation from CrB to Cr₂AlB₂ and then to 2D-CrB is well established.     

First demonstration of possible two-dimensional MBene CrB derived from MAB phase Cr2AlB2

In this communication, the possibility for the preparation of two-dimensional MBene CrB from MAB phase Cr₂AlB₂ is demonstrated for the first time. Herein M is a transition metal, A is a group III_A or IV_A element and B is boron; MAB phases are layered transition metal ternary borides, MBene is used to emphasize the loss of A group element from the parent MAB phases and to highlight the 2D nature. The possible 2D CrB nano sheets are prepared by selectively etching out Al layers from Cr₂AlB₂ by immersing the Cr₂AlB₂ powders in dilute HCl solution at room temperature. The as-prepared 2D CrB nano sheets are examined using X-ray diffraction and scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). In addition, different structure models are built to explain the observed phenomena. The discovery in this work opens a door to the synthesis of a large number of new 2D MBenes from MAB phases.