Preparation and tribological properties of thin oxide coatings on an Al383/SiO2 metallic matrix composite

A new Al383/SiO₂ metal matrix composites (MMC) was designed to improve the wear properties of the aluminium (Al) alloys with manufacturing cost much lower than the hypereutectic Al-Si alloys. However, like the hypereutectic Al alloys, the MMC was also subject to large plastic deformation of the soft Al matrix under high contact stress during lubricated sliding wear tests. As a result, the reinforced SiO₂ particles detached from the matrix and promoted the third-body wear. In this paper, to improve the wear performance of the MMC under high contact stress but also to avoid the honing process, a new proprietary approach based on a modified Plasma Electrolytic Oxidation (PEO) process was used to produce oxide coatings on the MMC. The effect of both oxide coating thickness and the volume content of SiO₂ particles on the wear behaviour of the MMC was investigated. It was found that with a proper combination of the volume content of SiO₂ and coating thickness, the coated MMC presented a much higher wear resistance and lower friction coefficient than the uncoated MMC.     

Influence of oxygen on the tool wear in machining

High temperatures generated in machining are known to facilitate oxidation wear. A controlled atmosphere chamber was developed to investigate the effects of oxygen on tool wear and high speed machining tests were conducted on air and in argon. Cemented carbide, cermet and cubic boron nitride tooling was used on alloyed steel, hardened tool steel and superalloy Alloy 718. Machining in argon resulted in higher flank wear, higher cutting forces, and larger tool–chip contact length on the rake face. However, in hard machining, argon atmosphere reduced rake cratering. Transmission electron microscopy of tools worn on air showed formation of nanocrystalline Al₂O₃ film on the rake when machining aluminium containing Alloy 718, while no oxide films was detectable in the other cases.     

镁合金石墨砂型铸件表面氧化膜的组成与结构

利用XPS(X射线光电子能谱 )对镁合金石墨砂型铸造时的表面氧化膜进行了分析 ,探讨了表面氧化膜的组成与结构。结果表明 :镁合金表面氧化膜呈层状结构 ,主要由MgO和Mg(OH) 2 组成 ,由于表面氧化膜中有大量C原子的渗入 ,增加了致密度 ,使其具有较好的防护性能     

镁合金石墨砂型铸件表面氧化膜的组成与结构

利用XPS（X射线光电子能谱 ）对镁合金石墨砂型铸造时的表面氧化膜进行了分析 ,探讨了表面氧化膜的组成与结构。结果表明 :镁合金表面氧化膜呈层状结构 ,主要由MgO和Mg（OH） 2 组成 ,由于表面氧化膜中有大量C原子的渗入 ,增加了致密度 ,使其具有较好的防护性能。     

石墨-AZ91镁基复合材料及其摩擦磨损性能的研究

研究了不同石墨颗粒含量对AZ91镁合金基复合材料摩擦磨损性能的影响。结果表明:在所研究的范围内,复合材料的摩擦磨损特性明显优于基体合金;随着石墨颗粒含量从5%增加到20%,镁合金基复合材料的耐磨性得到明显的改善,磨损质量损失与摩擦系数都降低到较低水平。在不同磨损阶段,对应着不同磨损机制。随着磨损过程的进行,在磨损试样表面逐渐形成一层连续黑色润滑膜,这层润滑膜有效隔离两摩擦副的直接接触,有效地延迟了镁合金基复合材料由轻微磨损向严重磨损的转变过程。     

Fretting contact study of Ti-6Al-4 V/graphite couples in a dry shaft/bearing contact with thrust: Influence of plasma nitriding of the titanium alloy

Fretting wear or wear by small displacements is defined when two contacting surfaces (first-bodies) are subjected to small amplitude reciprocating motion of micron order. This phenomenon is observed in many mechanical assemblies and it can significantly reduce the contact mechanisms life.This paper reports on the influence of nitriding treatment of the titanium alloy on the fretting tribological behaviour of graphite/Ti-6Al-4 V couple in a dry shaft/bearing contact with thrust. Two contact geometries are investigated: cylinder-in-cylinder and flat/flat. These fretting contacts are subjected to low-amplitude oscillatory movements, with temperature reaching 270 °C.The nitriding treatment for the Ti-6Al-4 V was carried out with a gas mixture N₂/H₂ at moderate temperature (700 °C) for 12 h. In these conditions, the maximum surface hardness was improved by a factor three.In this study, the mechanism of transfer and wear of graphite against Ti-6Al-4 V nitrided or not, have been studied with a scanning electron microscope, an optical microscope and an interferential microscope.The morphological and profile analysis performed on rubbing surfaces showed various aspects of wear: prints, craters, transfer ... and allowed to explain the location, development and origin of the degradation.The friction couples have showed differences between the tests realised with the shafts with or without nitriding and especially at an elevated temperature.We discuss the experimental results and we suggest several possibilities in order to understand some specific tribological behaviour: impact of the third body, of the abrasion, etc.     

Oxidation and wear behaviors of Ti-based thin films

The degradation of Ti-based coatings is known to be due to the formation of titanium oxide (TiO₂) at their surfaces. In this study, wear and thermal oxidation behaviors of various magnetron sputtered Ti-based thin films were studied after static oxidation and sliding wear. The oxidized surfaces after the static oxidation and the wear debris generated from pin-on-disc wear tests with alumina ball were characterized to identify the compounds, particularly titanium oxides, to gain a better understanding of the tribochemical reactions. The coatings that were examined include TiN, TiCN (N rich), TiCN (C rich), TiAlN, AlTiN, TiSiN, and TiCNO thin films. These coatings were characterized using Raman spectroscopy, scanning electron microscopy, and X-Ray diffractometer. The results show that TiSiN and AlTiN have the highest oxidation resistance, comparing with other coatings. As for the analyses of wear debris, all of the Ti-based coatings are worn by the mechanism of forming TiO₂, except AlTiN. AlTiN is worn by ploughing wear.     

SiC对熔铝石墨坩埚抗氧化性能的影响

采用鳞片状石墨、SiC、硅粉和高岭土等主要原料制备含SiC的熔铝石墨坩埚,试样分别在1050、1100、1150和1200℃保温3h烧成,随后将试样分别加热到700、800和900℃保温6h进行氧化试验。研究了SiC的加入量、烧成温度、氧化温度和时间对试样抗氧化性能的影响。结果表明,随着SiC含量的增加,坩埚的抗氧化性能得到明显的改善,这种作用在较高温度下尤为显著;SiC含量较多的试样,失重曲线平缓,失重率较小;试样的最佳烧成温度应控制在1100～1150℃之间;随着氧化温度的升高和氧化时间的延长,试样的失重率增加,尤其是在700～800℃氧化温度下。     

钢铁渗铝及渗铝钢的性能

铝原子向钢中的渗透,完全遵守Ｆｉｃｋ扩散定律;同时探讨了渗铝层耐氧化、耐腐蚀、耐磨损的机理。     

乙醇润滑条件下含石墨铝合金的磨损性能

以Al-Mg2Si合金为基体,添加铜包石墨颗粒及Al-Ce中间合金制备了新型含石墨铝合金。研究了含石墨铝合金铸态及固溶时效后的微观组织,并测定了其布氏硬度;重点考察了其在不同载荷、乙醇润滑条件下的磨损性能。结果表明,石墨均匀分布于铸态合金基体中,固溶时效后,组织细化,硬度提高。在载荷为100N、乙醇滴入量为20mL/min时,铝合金表面磨损轻微。摩擦界面的石墨颗粒及乙醇的综合润滑作用影响了合金的磨损性能。     

铝合金表面微弧氧化陶瓷层耐磨性

利用微弧氧化技术在7075铝合金表面形成微弧氧化陶瓷膜层,通过SEM、XRD手段分析了微弧氧化陶瓷层的显微结构、表面形貌和相组成,并在HIT-Ⅱ摩擦磨损试验机上测试了陶瓷膜层的摩擦学性能.结果表明:7075铝合金表面的微弧氧化陶瓷膜层由疏松层、致密层构成,其相组成主要是α-Al2O3和γ-Al2O3两相;氧化陶瓷层与基体结合良好,厚度为25～45μm,表面硬度可达到1900HV0.1左右;微弧氧化表面处理技术可以显著提高铝合金的表面耐磨性,在与GCr15钢球对磨时,膜层具有较低的磨损率,但摩擦因数相对较高.     

Zr-4合金微弧氧化层的生物摩擦学性能

采用含Ca、P电解液,450V微弧氧化在Zr-4合金表面制备氧化膜层,在25%小牛血清润滑条件下做球盘往复式摩擦磨损试验,重点研究了氧化膜层的摩擦磨损特性。结果表明,微弧氧化膜层含Ca、P,主要由立方相氧化锆、四方相氧化锆和少量单斜相氧化锆构成,膜层表面粗糙多孔,有少量的微裂纹。Zr-4合金微弧氧化层与Si3N4球的摩擦因数低于Zr-4合金与Si3N4球的,氧化膜层硬度较高,摩擦副间的接触面积较小,膜层微孔储存小牛血清湿式润滑作用,均有利于摩擦因数降低。Zr-4合金微弧氧化层磨损量明显低于Zr-4合金,微弧氧化层硬度高是主要原因。Zr-4合金摩擦磨损以显微切削机制为主,微弧氧化层摩擦磨损则兼有疲劳剥落和显微切削两种机制。     

纳米镍微粒在耐高温陶瓷涂层中的作用

为了提高钛及钛合金高温抗氧化能力,用流涂工艺在工业纯钛上得到含纳米镍微粒的高温超细陶瓷涂层,通过氧化动力学实验及结合力试验,纳米镍微粒在涂层中对涂层-基体的结合及涂层的抗氧化性有着重大作用,试验用光学显微镜(OM)、扫锚电子显微镜(SEM)及X射线衍射(XRD)进行分析,得知纳米镍微粒在涂层中的作用机制.当加入10%(质量分数)的纳米镍微粒时,其抗氧化力及与基体的结合力最佳.     

Oxidation behaviour of particle reinforced MoSi2 composites at temperatures up to 1700°C. Part I: Literature review

In the first part of this paper the results of a literature review are presented. An overview of the oxidation behaviour in air and in combustion environments of both pure MoSi₂ and MoSi₂ composites in the temperature range from 400 to 1650°C is given. The second part of this paper reports about our results from oxidation tests with selected MoSi₂ composites (containing 15 vol.‐% Al₂O₃, Y₂O₃, ZrO₂, HfO₂, SiC, TiB₂, ZrB₂, or HfB₂, respectively) from different development stages at temperatures in the pest region as well as up to 1700°C. The third part describes the oxidation behaviour of the optimised MoSi₂ composites developed on the basis of the results from part II.     

Si-W-Mo coating for SiC coated carbon/carbon composites against oxidation

In order to prevent carbon/carbon (C/C) composites from oxidation at 1773 K, a Si-W-Mo coating was prepared on the surface of SiC coated C/C composites by a simple pack cementation technique. The microstructures and phase composition of the as-received multi-coating were examined by SEM, XRD and EDS. It was seen that the compact multi-coating was composed of α-SiC, Si and (W_xMo_1 − x)Si_2. Oxidation behaviour of the SiC/Si-W-Mo coated C/C composites was also studied. After 315 h oxidation in air at 1773 K and thermal cycling between 1773 K and room temperature for 17times, no weight loss of the as-coated C/C composites was measured. The excellent anti-oxidation ability of the multi-coating is attributed to its dense structure and the formation of the stable glassy SiO₂ film on the coating surface during oxidation.     

A MoSi2-SiC-Si oxidation protective coating for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation, a dense coating has been produced by a two-step pack cementation technique. XRD and SEM analysis shows that the as-obtained coating was composed of MoSi₂, SiC and Si with a thickness of 80-100 μm. The MoSi₂-SiC-Si coating has excellent anti-oxidation property, which can protect C/C composites from oxidation at 1773 K in air for 200 h and the corresponding weight loss is only 1.04%. The weight loss of the coated C/C composites is primarily due to the reaction of C/C substrate and oxygen diffusing through the penetration cracks in the coating.