Chemical vapour deposition (CVD) diamond coated tools performance in machining of PEEK composites

This paper presents a study about the chemical vapour deposition (CVD) diamond coated tool performance in machining unreinforced PEEK and composite PEEK CF30 (reinforced with 30% of carbon fibres).

The experimental procedure consisted of turning operations, during which cutting forces and surface roughness obtained in composite workpieces were measured.

The obtained results showed a best cutting performance for CVD diamond coated tool in machining PEEK composites, particularly in terms of cutting forces and power consumption, when compared with polycrystalline diamond (PCD) and cemented carbide (K10) cutting tools. This fact is very important due to the minor production costs of CVD diamond coated tools in comparison with PCD tools.     

Influence of rotational speed during centrifugal casting on sliding wear behaviour of the Al-2Si alloy

The microstructures and dry sliding wear behaviour of an Al-2Si alloy cast centrifugally are studied. Results indicate that at optimum speed the cast has a microstructure consisting of uniformly distributed α-Al grains and fine eutectic silicon grains. The cast exhibited better wear resistance compared to the same cast prepared at different rpms. This paper attempts to investigate the influence of the microstructural changes in the Al-2Si alloy by varying the rotational speed of the mould and its combined action on the dry sliding wear behaviour.     

CVD金刚石薄膜在钨丝和碳纤维上的制备

用CVD方法在钨丝和碳纤维上沉积金刚石薄膜,约含有10000根纤维的纤维束经特殊处理后分离为单根,生长条件使碳纤维中心在CVD生长结束后仍保持固态,CVD金刚石在纤维上生长的平均激活能为93.15KJ/mol。SEM照片给出了纤维涂层在不同生长条件下的表面和中心的形貌。纤维内部的石墨碳和外部的金刚石层有很大的不同。钨丝的断裂强度和杨氏模量的测量表明,具有金刚石涂层的钨丝的断裂强度为0.567GPa,非常接近不具有金刚石涂层的钨丝的断裂强度,但具有金刚石涂层的钨丝的断裂应变为4.8%,比没有金刚石涂层的钨丝的新裂应变7%要小得多,这表明了金刚石涂层可以减少钨丝的断裂应力,提高其机械性能。     

Al—12.7%Si共晶中硅相的形态与分枝特征

用SEM考察了生长速度R=30～2500μm/s时Al-12.7％Si共晶中硅相的形态与分枝特征。对深腐蚀样品的观察表明,共晶硅相具有连续生长、成束分布特征,随生长速度R增大,共晶硅逐渐由粗大片状向片状、条状转变。硅相生长与分枝特征与局部生长条件密切相关,从整体上看,随生长速度增大,晶体学生长与分枝特征减弱。     

钠盐变质及振动对Zn - 27Al - Si合金组织和性能的影响

为了提高锌铝合金在干摩擦条件下的耐磨性以进一步拓宽其应用范围,在Zn-27Al合金中加入3%～4%Si,并通过钠盐变质及振动处理,制得Zn-27Al-Si合金.利用显微镜和电镜观察分析了试验合金中硅相形貌,并对合金的力学性能进行了测定.研究结果表明:钠吸附在硅晶体的生长台阶上使初晶硅产生大量分枝,最终生长成为球团状;振动一方面改变了结晶的温度场,抑制了共晶硅的析出,另一方面产生的"扰动"作用使硅球表面辐射生长的杆状共晶硅机械碎断,从而减少了硅相对基体的割裂作用,使试验合金在其他性能不变的情况下耐磨性提高3～4倍.     

用高能球磨法制备的细晶Al-50Si合金的组织与性能

用高能球磨工艺制备Al-50Si合金粉末,将粉末经冷压、烧结、热压等工艺制备出Al-50Si合金块体材料,对球磨粉末和块体样品进行了显微组织观察、EDS分析和XRD分析,测定了块体样品的密度、硬度和热扩散系数.结果表明:高能球磨后Al-50Si合金粉末的硅粒子明显细化,其尺寸分布为1-15μm;在烧结过程中块体样品的硅粒子长大,其尺寸增大到5-30μm;Al-50Si合金块体材料具有较高的密度和硬度,其室温热扩散系数为55mm2·s-1.     

高分子材料涂覆金属方法研究进展

综述了几种镁合金表面改性的方法,主要包括电沉积、等离子体表面技术、浸涂法、喷涂法,并分析了它们的优缺点,以及今后的发展方向。     

Dry machining of silicon-aluminium alloys with CVD diamond brazed and directly coated Si3N4 ceramic tools

Silicon-aluminium alloys (Al-Si), with Si contents up to 20%, are important materials in automotive and aeronautical industries due to their low density and high wear resistance. The turning of these alloys has been done mainly by superhard tools like polycrystalline diamond (PCD). CVD diamond either as thin coatings on silicon nitride ceramics or as thick brazed tips on hard metals is alternative material. In this work, CVD diamond thin films were grown on Si₃N₄ ceramic substrates and thick CVD diamond plates were brazed onto WC-Co tools. These different inserts were used in dry turning of silicon-aluminium alloys with 12 wt% and 18 wt% Si. Both directly diamond coated and brazed tools are able to machine the Al-12 wt% Si alloy with negligible wear. In turning of Al-18 wt% Si, sharp edged tools yield lower cutting forces than the chamfered ones, with the occurrence of tool failure at about 500 and 100 m, respectively. CVD brazed tools proved to be able for dry turning this hypereutectic alloy, keeping the cutting forces below 60 N. Minimal wear was observed after 1500 m of cutting length, mainly caused by diamond chipping at the flank face.     

Correlation between diamond grain size and hydrogen incorporation in nanocrystalline diamond thin films

Hydrogen-incorporated nanocrystalline diamond thin films have been deposited in microwave plasma enhanced chemical vapour deposition (CVD) system with various hydrogen concentrations in the Ar/CH₄ gas mixture. The bonding environment of carbon atoms was detected by Raman spectroscopy and the hydrogen concentration was determined by elastic recoil detection analysis. Incorporation of H₂ species into Ar-rich plasma was observed to markedly alter the microstructure of diamond films. Raman spectroscopy results showed that part of the hydrogen is bonded to carbon atoms. Raman spectra also indicated the increase of non-diamond phase with the decrease in crystallite size. The study addresses the effects of hydrogen trapping in the samples when hydrogen concentration in the plasma increased during diamond growth and its relation with defective grain boundary region.     

Microstructural refinement of Al-10.2%Si alloy by intensive shearing

Al-10.2%Si alloy when cast near the liquidus temperature has tremendous potential for producing fine grain structure. However, for casting applications, it requires casting at higher superheating, where this alloy results in large dendritic grain structure. Here, we show that, by applying intensive shearing to the liquid metal prior to casting, dendritic growth can be largely suppressed and fine grain structure can be achieved at higher casting temperature.     

采用MPCVD法在硅衬底上选择性生长金刚石膜

采用微波等离子体化学气相沉积（MPCVD）法在附有SiO2掩摸的硅衬底上选择性沉积出了金刚石膜。采用扫描电子显微镜（SEM）和Raman光谱仪对金刚石膜的表面形貌和结构进行了表征。并讨论了衬底温度对金刚石薄膜选择性沉积的影响。得出了较佳的沉积条件。     

TC11微弧氧化膜制备及其结构性能研究

在Na2SiO3-Na2WO4-NaOH混合电解液中,利用微孤氧化(MAO)技术在TC11合金表面制备了氧化膜.用扫描电镜(SEM),X射线能谱仪(EDS),X射线衍射仪(XRD)对氧化膜微观结构、化学成分、厚度以及相组成进行了分析,采用HVS-1000维氏显微硬度计、MFT-4000划痕试验机、电化学测量系统完成氧化...     

喷射沉积Al-30Si组织及其半固态保温转变规律

对喷射沉积Al-30%Si合金组织及其在半固态保温过程中的转变进行了试验研究,喷射沉积Al-30%S合金沉积态组织是由细小的Si相与α基体组成,提出这种组织是由于离异共晶引起的,并运用该机制对组织中Si相的集聚进行了解释,认为其形成机制为,欺 一,在沉积阶段凝固过程中大量细小的Si发生了粗化和团聚;其二,大量的Si在沉积时会发生碰撞而靠在一起,在随后的离异共晶凝固过程中,共晶硅附着在初生硅上从而将原来相互独立的Si联结在一起,在半固态保温过程中,基体发生熔化而出现球形α,而Si相则发生粗化,且粗化速度与保温温度和时间有关。     

强磁场对Al-18Si合金凝固组织的影响及其机理研究

研究了过共晶Al-18Si合金在稳恒强磁场中的凝固行为.实验表明,在稳恒强磁场作用下,过共晶Al-18Si合金中的初生Si发生显著偏聚.为解释初生Si的偏聚机理,建立了相应的量子理论模型.模型认为:初生Si在Al-18Si合金中的偏聚是由于部分Si原子在磁场中获得附加能后,沿磁场方向做旋进运动所致.Si原子在10T磁场中获得的附加能为1.854×10-22J.     

CVD金刚石膜/硅为基板的微条气体室性能研究

提出了一种新型的CVD金刚石膜/硅(ρ～1010Ω·cm)为基板的微条气体室,阳极宽度7μm阴极100μm,间距200μm。室温下,充以1.01×10-5PaAr+CH4混合气体时,采用5.9keV55FeX射线测量了探测器在不同高压和气体比例时的脉冲高度分布,详细讨论了高压和气体比例对能量分辨率的影响,结果表明该探测器具有较高的信噪比和能量分辨率。在Ar+10%CH4混合气体、-1100V漂移电压和-650V阴极电压工作条件下,微条气体室能量分辨率可达12.2%。     

凝固条件对Al-Si复合材料中共晶Si形貌的影响

为了优化压铸态Al2O3f／Al—15Si复合材料中Si相组织，利用金相和SEM分析了Al—15Si合金和Al2O3f/Al—15Si复合材料中Si相在不同冷却方式下的形貌特征．结果表明：压铸态和重熔后炉冷态的Al—15Si合金中共晶Si均为片状，而Al2O3f／Al—15Si复合材料内共晶Si由片状转变为棒状；Al2O3f／Al—15Si复合材料750℃重熔后在水淬、模具中冷却和炉冷冷却条件下分别获得了细小变质态、针状及棒状等形态的Si相；炉冷处理可作为优化压铸态复合材料组织的一种途径．     

喷射沉积连续挤压Al-20Si合金的微观组织及磨损性能

喷射沉积连续挤压技术是由喷射成型和连续挤压复合而成的新技术。本试验采用自制的喷射沉积连续挤压设备,在多种过热度条件下完成了Al-20Si合金的喷射沉积连续挤压试验,获得了8mm的铝合金杆件制品,分别对其显微组织和摩擦磨损性能进行研究。结果表明:喷射沉积连续挤压工艺可有效抑制初生硅的形核和生长,制备的铝硅合金中初生硅的尺寸约3~8μm,较铸态组织有明显细化,使得其耐磨性能提升1~2倍;随过热度的增加,喷射沉积连续挤压铝硅合金中初生硅的尺寸不断减小且分布更加弥散,使得合金的耐磨性更加优良。     

Undercooling and supersaturation of alloying elements in rapidly solidified Al-8.5% Fe-1.2% V-1.7% Si alloy

Dispersion-strengthened Al-8.5% Fe-1.2% V-1.7% Si alloy was produced by inert gas atomization and atomized melt deposition processes. Differential scanning calorimetry was used to estimate the extent of undercooling in the alloy powders as a function of powder size and in the atomized melt-deposited alloy as a function of process parameters. The estimated undercooling was found to be a strong function of powder size and processing conditions and varied from 380–200 °C. Alloy powders of diameter greater than 180 jam did not experience any undercooling during solidification. X-ray diffraction analysis was performed to study the dependence of supersaturation of alloying elements and metastable phase formation on the extent of undercooling. When the undercooled alloy was heated to about 400 dgC, formation of Al₁₂(Fe, V)₃Si phase with b c c crystal structure from the supersaturated matrix was observed.     

Influence of the supersaturated silicon solid solution concentration on the effectiveness of severe plastic deformation processing in Al-7 wt.% Si casting alloy

A comparative study of room temperature severe plastic deformation (SPD) of a hypoeutectic Al-7 wt.% Si casting alloy by high pressure torsion (HPT) and equal channel angular pressing (ECAP) has been performed. Microstructural parameters and microhardness were evaluated in the present work. Three different initial Si solid solution contents have been considered: as cast (C sample, 1.6 wt.% Si), annealed and quenched (Q sample, 1.2 wt.% Si) and annealed and furnace cooled (S sample, 0.7 wt.% Si). The samples processed by ECAP have smaller average Si particle sizes (0.9-1.7 μm), than those for samples processed by HPT (2.4-4.4 μm). The initial supersaturated Si solid solution is the major factor affecting the microstructure and the mechanical properties of the material. Fine deformation-induced Si precipitates from the supersaturated solid solution were responsible of the large grain refinement obtained by both SPD processing methods, which was considerably higher than that reported for pure aluminium. Q samples, processed by both SPD methods, containing an intermediate concentration of Si in solid solution, show the highest hardness due to the finest and most homogeneous microstructure. The finest and homogeneous grain size was ∼0.2 μm for the HPTed and ∼0.4 μm for the ECAPed Q samples.     

Crystal growth of the primary silicon in an Al-16 wt % Si alloy

Studies on the crystallographic growth habit of primary silicon crystals in an Al-16 wt% Si alloy were carried out by X-ray micro focus Laue analysis and ECP (electron channelling pattern) analysis. The plate-like primary silicon crystals grow by the same mechanism as that for germanium dendrites, i.e. the TPRE (twin plane re-entrant edges) mechanism. The spherical primary silicon crystal in sodium treated melts is composed of several pyramidal grains with tops at the centre of the sphere. Many of these grains have a twin relation to each other. The sodium enriched regions are found at the boundaries of these pyramidal silicon grains. The external surfaces of the spherical primary crystals exhibit regular crystal facets. The surface facets are most frequently parallel to {111} plane but there are also some facets parallel to other less densely packed planes such as {100}, {211} and so on.