Wear-resistant multilayered diamond-like carbon coating prepared by pulse biased arc ion plating

Diamond-like carbon coatings have been deposited by a pulse biased arc ion plating. In order to improve their adherence to metal substrate, two systems of graded transition layers, namely Ti/TiN/TiC and Ti/TiCN/TiC, have been applied. The structure and composition of the diamond-like carbon/transition composite coatings were studied by scanning electron microscopy, Raman spectroscopy and energy dispersive X-ray spectroscopy. The total thickness of the coatings was within a range of 1.0–2.0 μm. Such multi-layer coatings showed excellent properties including high hardness, low friction coefficient and long wear-resistant lifetime. Diamond like carbon coatings as well as their wear tracks developed by sliding steel balls have been investigated by scanning electron microscopy. The results of the analysis, particularly that of the tribological study showed that the wear resistance and film-to-substrate adherence of diamond like carbon coatings with stainless steel surface were dramatically improved by using a graded transition layer and pulse biased arc ion plating.     

一种新型镍基高温合金的动态再结晶行为

采用等温热压缩实验研究了一种新型镍基高温合金在不同热变形条件下(变形温度1040～1120℃、应变量0.35～1.2、应变速率0.1 s^-1)的动态再结晶行为。通过光学显微镜(OM)、扫描电子显微镜(SEM)和电子背散射衍射仪(EBSD)研究变形温度和应变量对合金热变形过程中组织演变和动态再结晶(DRX)形核机制的影响。结果表明,根据加工硬化率曲线能够准确确定DRX出现的临界应力和临界应变。合金的DRX晶粒体积分数随变形温度和应变量的增加而增加。在高温低应变速率下,不连续动态再结晶(DDRX)和连续动态再结晶(CDRX)形核机制同时发生。随着变形温度的升高,CDRX形核机制减弱,而CDRX机制在高温条件下占据主导。随着应变量的增加,合金中DDRX机制逐渐变强。热变形后期,CDRX仅作为辅助形核机制发挥作用。另外,Σ3孪晶界的形成有助于DRX晶粒的形核。     

超窄间隙焊接中送进焊剂片与电弧相互作用机制分析

送进式焊剂片约束电弧超窄间隙焊接中,连续送进的焊剂片与电弧相互作用的关系影响着焊接过程的稳定性.采用一种快速中断电弧的方法,得到了熄弧位置处焊缝熔池形态和焊剂片瞬时熔化形貌,分析了焊剂片对电弧的作用长度与电弧受约束程度的关系.结果表明,增加焊剂片送进速度或减小电弧电压,可使焊剂片对电弧的作用长度增加,当增至一定程度时,电弧被有效约束在坡口底部对侧壁根部进行均匀加热,获得根部熔合良好的平焊缝.当焊剂片对电弧的作用长度过小时,电弧的受约束程度减弱,电弧加热区域集中在两侧壁上,很难在坡口根部形成有效熔池,最终形成孔洞焊缝.     

气体流量和耦合度对GPCA-TIG焊电弧特性影响的数值模拟

根据磁流体动力学理论和组分守恒建立气体熔池耦合活性TIG焊电弧二维数学模型,采用简化阴极边界层模型将阴极与电弧耦合求解,计算得到了不同外层氧气流量与耦合度下电弧等离子的温度、氧气分布、阳极表面电流密度和热流密度等特征参数。结果表明,与TIG电弧相比,气体熔池耦合活性TIG电弧收缩,流速增大,阳极表面电弧压力升高;增大外层氧气流量或增大耦合度,电弧最高温度均上升,氧气向电弧区域扩散趋势更明显,电弧形貌略有收缩,阳极表面电流密度与热流峰值均略有增大。     

C/SiC复合材料与抗氧化陶瓷涂层的优化匹配

目的 快速筛选与C/SiC复合材料界面热应力最低匹配的抗氧化涂层材料。方法 在原用于单层陶瓷材料热冲击计算模型的基础上改造建立了一个简易但能合理解释热冲击下抗氧化涂层失效的解析模型。采用有限元模型对解析模型得到的界面热应力加以验证,二者结果基本一致。结果 当裂纹长度小于30 μm时,裂纹对涂层-基体界面热应力的影响几乎可以忽略,然而,当涂层表面预制长度大于30 μm的微裂纹或增加涂层中的微裂纹密度均能够有效降低涂层-基体界面的热应力,提高涂层在服役条件下的断裂临界温差,改善涂层材料的抗热震性,提高涂层的使用寿命。利用该解析模型计算出各温度下涂层-基体体系具体的断裂临界温差,并预测涂层-基体体系最危险的工作温度区间。结论 解析模型可以用来方便地计算涂层材料的热应力和断裂临界温差,从而筛选出热应力最小匹配的涂层材料。C/SiC复合材料的抗氧化涂层中预制长度大于30 mm的微裂纹,可有效提高涂层抗热震性能。     

Annealing temperature dependence of local piezoelectric response of (Pb,Ca)TiO3 ferroelectric thin films

In this work, we have systematically investigated the piezo/ferroelectric response of (Pb, Ca)TiO₃ thin films prepared by polymeric precursor method using simultaneously topography, piezoresponse force microscopy (PFM) and local piezoelectric hysteresis loop measurements. The thin films were grown on Pt/Ti/SiO₂/Si substrates and annealed at 400, 500 and 600 °C and subjected to structural characterization using x-ray diffraction, infrared and micro-Raman spectroscopy. The ferroelectric domains structure and the piezoelectric response evolved as a function of thermal annealing temperature as well as the density of active grains (number of switchable domains) progressively increased. Another important characteristic of these films is the onset of large area showing the coexistence of active (stronger piezoresponse signal) and inactive (weak or non piezoresponse signal) grains embedded in the polycrystalline perovskite matrix. A combination of out-of-plane (OP) and in-plane (IP) PFM images revealed local features of polarization component magnitudes in samples surface. Well-defined local piezoelectric hysteresis loop was achieved on top of individual nanometer-scale grains in both samples annealed at 500 and 600 °C, and the switching behavior is evident.     

宽温域下LaF3对镍基自润滑材料摩擦学性能的影响

为增强材料在宽温域下服役的稳定性及减少摩擦与磨损对材料性能的影响,采用Ni60合金粉末作为基体材料,利用放电等离子烧结技术(SPS)制备出了不同LaF3含量的镍基自润滑复合材料。利用HT-1000型高温摩擦磨损试验机、GBS-SmartWLI白光干涉三维轮廓仪、SEM、XRD等对复合材料在大气环境下的宽温域摩擦学性能进行了研究。结果表明,所制备的镍基自润滑材料在宽温域下具有优良的摩擦学性能。复合材料摩擦系数与磨损率从200到800℃的范围内保持在一个较低水平。当LaF3的含量为6%(质量分数)时,平均摩擦系数在200到800℃之间为0.189到0.288且变化范围最小,在600℃下表现最低为0.189,平均磨损率在10-5mm3/N·m数量级,综合表现出最优的摩擦学性能。这是因为LaF3含量为6%的材料在高温下形成了SrSiO3、SrMoO4、La6MoO12等盐类,所形成的盐转移膜一方面防止了对偶材料表面直接接触,另一方面减小了接触薄层的抗剪切强度,从而显著地提高了宽温域环境下材料的稳定性。随着测试温度增加到800℃,由于高温氧化作用使得复合材料摩擦系数略微上升,但仍然保持在0.2左右的较低水平。     

First-principles study on electronic properties and lattice structures of WZ-ZnO/CdS interface

We theoretically investigated the lattice structure, interface bonding energy, optical absorption properties and electronic properties of WZ-ZnO (1 1 2)/CdS (1 1 0) interface from first-principles calculations. The interface lattice mismatch is less than 4.3%. The atomic bond lengths and atomic positions change slightly on the interface after relaxation. The WZ-ZnO (1 1 2)/CdS (1 1 0) interface has bonding energy about −0.61 J/m², suggesting that this interface can exist stably. Through analysis of the density of states, no interface state is found near the Fermi level. In addition, there are orbital hybridizations between different interfacial atoms, and these orbital hybridizations effectively enhance the bonding of Zn and S atoms, Cd and O atoms on the interface. By analysis of difference density charge and Bader charge, we find that electrons on the interface are largely redistributed and charges transport near the Fermi level which strengthen the adhesion of the interface.     

First principles insights into improved catalytic performance of BaTiO3- graphene nanocomposites in conjugation with experimental investigations

The present work aims to provide first principles insights into the catalytic performance of composites based on BaTiO₃ particles decorated over reduced graphene oxide (rGO). Examination regarding the orbital contributions of valence states, conduction states, interaction surface and anchoring of perovskite over rGO have been carried out. Theoretical results thus obtained have been validated using experimental investigation. Further experiments have also been conducted to analyze the catalytic performance of composites with respect to multiple advanced oxidation processes. Charge separation has been improved due to rGO acting as macromolecular photosensitizer. Degradation of xanthene dye (Rhodamine B) and methyl orange (MO) assisted in evaluation of the catalytic performance. Acoustic irradiation provides an additional route to improve degradation by ameliorating catalytic activity (from 0.036 min to 0.099 min in RhB especially). Synergistic effect obtained through conjugated benefits of oxidation processes with proposed composite, played a crucial role in improving the overall efficiency. The cumulative outcome of the results indicates superior performance of BaTiO₃-rGO composites for green and sustainable water treatment applications.     

不同驱动力对熔池表面变形行为影响的数值模拟

基于流体动力学方程,采用焓-孔隙度法来处理液-固相变,采用VOF方法追踪熔池自由表面变形,建立了固定电弧下的三维瞬态TIG焊熔池数学模型,求解获得了在浮力、Marangoni力、电磁力和电弧压力单独作用时的熔池表面变形行为及其温度场与速度场的分布.模拟结果表明,在大电流（I≥250 A）时,在浮力、表面张力温度系数为正时的Marangoni力、电磁力单独作用于熔池上表面将会产生凸起变形,在电弧压力、表面张力温度系数为负时的Marangoni力单独作用下,熔池上表面将会产生凹陷变形.在大电流下,TIG焊和活性TIG焊熔池均产生凹陷变形.TIG焊熔池的中心区域形成向内的涡流,边缘部位形成向外的涡流,而活性TIG熔池在熔池中心和熔池边缘则分别形成两种成因不同的内向涡流.熔池表面变形量并不是各个驱动力作用的简单叠加.