铝合金表面微/纳米结构构筑研究进展

铝合金以其优异的性能而被广泛应用于工业生产的各个领域,通过一系列方法可以在铝合金表面构筑多种类型的微纳米结构。这些微纳米结构可以提高铝合金的摩擦学性能、耐蚀性能、界面结合力、抗结冰性以及装饰性能,对将铝合金应用到更广阔和更苛刻的环境中具有重要意义。介绍了铝合金表面微/纳结构的主要构筑方法。化学刻蚀法制备出了凸台和凹坑的迷宫形貌;阳极氧化法构筑出了高度有序的孔洞结构;微弧氧化法制备出了表面布满微孔的氧化膜;水热法可以构筑形状多样的纳米花朵形貌;电解加工对阴极材料的表面结构进行复刻,可以采用不同比例的阴阳极材料进行大面积的制备。阐述了这些微纳米结构的生长过程,并分析了实验条件(如温度、处理时间、电参数、溶液成分及浓度等因素)对铝合金表面微纳米二元结构生长的影响规律,重点总结分析了其研究现状和影响微纳米结构的因素。通过对现有铝合金表面结构制备方法的总结和分析,展望了其今后的发展趋势。     

Friction-induced physical and chemical interactions among diamond-like carbon film,steel ball and water and/or oxygen molecules

Friction and wear behaviors of diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig at different relative humidity (RH) in a nitrogen environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), while the chemical states of some typical elements on the worn surface of DLC film were investigated by means of X-ray photoelectron spectroscopy (XPS). The result showed that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity from 5% to 100%. In dry nitrogen (RH < 5%), thick and compact transferred carbon-rich layer was observed covering on the worn surface of steel ball, while the chemical states of the original and worn film surface showed no obvious change. In humid nitrogen, distinct changes of the chemical states on the worn surface of DLC film took place, indicating that tribochemical reactions such as the oxidation of DLC film and the interactions between DLC film and steel ball were involved in the friction process. Therefore, it was proposed that the friction and wear behaviors of DLC film were dependent on the friction-induced physical and chemical interactions among DLC film, steel ball and water and/or oxygen molecules. The roles of environment in the friction and wear behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions.     

Preparation and properties of different types of sputtered MoS2 films

MoS₂ is widely used as a dry lubricant. For special applications, for example bearings for space mechanisms, it is applied in the form of sputter-deposited films. The lamellar structure of this material, the orientation of the lamellae and the stoichiometry of the coating are important in the sliding process and thus for the tribological performance.It is shown that these properties can be varied to a large extent by the variation of a single parameter in the deposition process. This parameter, which is usually not controlled quantitatively, is the amount of H₂O present in the plasma. Furthermore, it is shown for the first time that all three different types of sputtered MoS₂ films, namely type I, type II and amorphous, can be produced by a variation in this parameter solely.     

Large-area silicon detection in hadronic sampling calorimetry

The usage of a maximum size silicon wafer area was optimized by using a geometry with two trapezoidal detectors, each of 28 cm². In order to enable the use of silicon detectors for hadron calorimeters a mosaic module consisting of 18 trapezoidal detectors was developed and assembled. Laser cutting technique was employed to minimize the dead area of the mosaic. In the performed investigations no physical deterioration was observed.     

Tribological performances of the boron carbide coatings sliding against silicon carbide and silicon nitride balls under various relative humidity conditions

Boron carbide (B₄C), silicon carbide (SiC) and silicon nitride (Si₃N₄) can achieve low coefficient of friction (Cof) under high relative humidity condition. Therefore, B₄C/SiC and B₄C/Si₃N₄ tribo-pairs may exhibit outstanding tribological behaviors, while the tribological investigation is poor. In present investigation, we performed the friction tests of the B₄C/SiC and B₄C/Si₃N₄ tribo-pairs under various relative humidity conditions, and revealed that the B₄C/SiC tribo-pair is a promising candidate for high relative humidity engineering applications. Surprisingly, the B₄C/SiC tribo-pair exhibited much better tribological behaviors than the B₄C/Si₃N₄ tribo-pair with the same test condition and tribochemical products. This is mainly attributed to less wear debris on the SiC ball and the formation of a stable tribochemical film containing boric acid and silica gel.     

Improving the mechanical and tribological properties of TiB2/a-C nanomultilayers by structural optimization

A novel nanomultilayered architecture was developed through magnetron sputtering to simultaneously achieve excellent mechanical and tribological properties in TiB₂/a-C film. Structural optimization was conducted by adjusting the modulation period from 1 to 10.5 nm. Film hardness and toughness were significantly improved and reached the optimal value at Λ = 6.6 nm. Combination of a sufficient number of heterointerfaces and appropriate individual layer thickness played a key role in hardening and toughening. The internal stress increased linearly with the increase in modulation period, which may be related to the reduction in the number of interfaces. Furthermore, a low friction coefficient of about 0.1 was achieved in the steady state at Λ ≤ 6.6 nm due to the formation of a uniform and compact transfer film on the worn ball surface. The improved mechanical performance and the presence of an effective transfer film resulted in an outstanding anti-wear performance at Λ = 6.6 nm.     

Preparation and tribocorrosion performance of CrCN coatings in artificial seawater on different substrates with different bias voltages

The CrCN coatings have been prepared by multi-arc ion plating technology with different bias voltages on 316?L, TC4 and H65 substrates, respectively. The prepared CrCN coatings have been characterized by XRD, SEM, and EDS, respectively. The mechanical properties, electrochemical corrosion behavior, and tribological performance of prepared coatings were tested by microhardness tester, scratch tester, electrochemical workstation, and friction and wear tester, respectively. Results show that the CrCN coatings with bias voltage of ?50?V presented the finer grain size, denser structure, better comprehensive mechanical properties and friction, and better corrosion resistance than the CrCN coatings with a bias voltage of ?30?V. The coating on TC4 substrate show the lower hardness, the better adhesion, the better electrochemical properties and tribological properties than that on 316?L substrate. The coatings based on H65 Cu substrate presented the worst electrochemical and wear properties. The CrCN coating with a bias voltage of ?50?V on TC4 substrate is an optimal candidate in artificial seawater for tribocorrosion.     

Oxidation behaviour of the MAX-phases Ti2AlC and (Ti,Nb)2AlC at elevated temperatures with and without fluorine treatment

MAX-phase materials have shown great potential for different technical applications due to their mechanical properties. If the main group element is aluminium their excellent oxidation resistance also makes them attractive for several high temperature applications. As an example the thermodynamically stable MAX-phase Ti₂AlC forms a thin, protective alumina layer in oxidising atmospheres at elevated temperatures. This alumina layer is formed due to the high Al activity within the material and prevents further attack by the environment. However, high temperature oxidation tests at 900 °C in air of “technical” Ti₂AlC which is not pure single-phase Ti₂AlC led to the formation of a non-continuous alumina scale which is intersected by a mixed TiO₂/Al₂O₃ scale. Furthermore, internal oxidation was observed. This “technical” material consists of two phases namely Ti₂AlC plus γ-TiAl due to the manufacturing route. Such γ-TiAl-grains are preferentially oxidised. This type of internal attack can be suppressed by a preceding fluorine treatment.