纳米锰方硼石粒径分布对铜基摩擦材料的影响

采用高能球磨法制备粒径小于200 nm的微细锰方硼石颗粒,将其作为摩擦填料添加到铜基摩擦材料中,利用放电等离子烧结(SPS)的方法制备出铜基摩擦材料。通过扫描电镜(SEM)、透射电镜(TEM)以及X射线衍射(XRD)研究纳米颗粒的形貌、显微结构与成分。在铜基摩擦材料中添加不同粒径的纳米锰方硼石,并通过摩擦磨损试验测试其磨损性能。结果表明:高能球磨法可以有效地细化锰方硼石;添加球磨处理的锰方硼石后所有样品的致密度均在97%以上,添加球磨50 min的纳米锰方硼石的样品致密度达到99%以上;稳定了摩擦因数(平均摩擦因数为0.187),磨损量为1.049×10-14 m3·J-1,抗压强度达到167 MPa;随着锰方硼石的细化,摩擦的样品磨损机理从剥层磨损与粘着磨损逐渐转向轻微的磨粒磨损。     

锰方硼石对铜基摩擦材料摩擦性能的影响

为了拓展锰方硼石的应用领域,提高铜基摩擦材料性能,将锰方硼石高能球磨处理30min后(颗粒尺寸<1μm),按照0.5%和1.0%的质量分数分别添加于铜基摩擦材料,用SPS烧结制得试样;并与不含锰方硼石的摩擦试样进行比较,分析3种样品的硬度、相对密度、摩擦系数及磨损率。结果表明:当锰方硼石的质量分数为0.5%时,摩擦试样的硬度较大,摩擦系数最平稳(平均摩擦系数为0.218)且磨损率最低;SEM分析发现其磨损机理为粘着磨损和磨料磨损。     

成型工艺对树脂基摩擦材料及其摩擦学性能的影响

以碳纤维2.5D浅交弯联结构为预制体,分别采用树脂传递成型工艺(RTM)和热压成型工艺(HPM)制备了碳纤维增强酚醛树脂基摩擦材料.通过MS-T3001摩擦磨损试验机考核了材料的摩擦磨损性能,采用扫描电子显微镜、激光三维形貌扫描仪观测了材料的磨损形貌,对比分析了两种成型工艺对材料摩擦学性能的影响.结果表明:随着滑动速度和工作载荷的增大,材料的摩擦系数均减小.热压成型工艺成型摩擦材料的主要磨损形式为磨粒磨损,摩擦系数0.085~0.130,磨损率1.5×10^-8 g·N^-1·m^-1.树脂传递成型工艺成型摩擦材料的主要磨损形式为黏着磨损和疲劳磨损,摩擦系数0.075~0.120,磨损率7.5×10^-8 g·N^-1·m^-1.     

电感耦合等离子体原子发射光谱法间接测定锰方硼石中氯

建立了电感耦合等离子体原子发射光谱法（ICP-AES）间接测定锰方硼石中氯的新方法。采用HNO₃分解矿石样品, 并向样品溶液中加入过量的AgNO₃溶液, 使Ag⁺与Cl^-生成AgCl沉淀, 溶液澄清后选择328.068{102}nm波长的光谱线作为分析线, 以ICP-AES测定了溶液中剩余的Ag, 通过计算, 间接地测定了锰方硼石中氯。实验发现, 溶液中Ag原子发射光谱强度与ρ（Ag）在0～40μg/mL范围内呈良好的线性关系, 校准曲线相关系数r为0.9999, 方法检出限为0.024μg/mL。本方法用于实际样品锰方硼石中氯的测定, 加标回收率在98.8%～99.6%之间, 相对标准偏差（n=6）为0.11%～0.54%。     

球磨时间对锰方硼石显微结构和发光特性的影响

使用三维震动高能球磨机对选矿后的锰方硼石粉末进行球磨, 球磨时间设定为30、40及50 min, 采用透射电子显微镜(transmission electron microscope, TEM)、扫描电子显微镜(scanning electron microscope, SEM)以及X射线衍射仪(X-raydiffraction, XRD)对球磨后锰方硼石粉末的形貌和结构进行表征, 利用Scherrer公式计算样品半高宽和晶粒尺寸, 并讨论球磨时间对锰方硼石发光特性的影响。结果表明, 锰方硼石经30、40、50 min高能球磨后, 样品粒径分别达到0.37、0.29、0.28 μm; 随球磨时间增加, 锰方硼石衍射峰明显宽化, (202)、(114)、(404)晶面的衍射峰强度明显降低, 晶面为不完全解理面; 锰方硼石样品发光强度随球磨时间增加明显降低。     

锰方硼石结构与性能的研究进展

锰方硼石(Mn_3B_7O_(13)Cl)是一种应用前景巨大的锰氯硼酸盐矿物,我国是世界上目前唯一拥有锰方硼石矿床的国家,开发利用天然锰方硼石及人工合成纳米锰方硼石,并对其性能展开研究具有重要的理论和实际意义。本文首次对锰方硼石的显微结构、光致发光性能、电磁性能和摩擦磨损性能的研究进展进行概述,为我国进一步开发应用锰方硼石提供理论基础。     

Hastelloy G3管材热挤压模具磨损有限元分析

基于修正的Archard磨损模型,利用DEFORM-2D有限元软件分析了镍基耐蚀合金(Hastelloy G3)管材热挤压成形时挤压工艺参数对模具磨损的影响规律.结果表明,挤压模具的磨损主要集中在锥模出口处.模具最大磨损深度随着挤压速度、坯料预热温度的升高而降低,随摩擦因数的增大而升高.模具表面磨损深度随着模角的增大而升高.最佳热挤压工艺参数是:挤压速度200mm·s^-1,坯料预热温度1180℃,摩擦因数0.05,界面换热系数5N·mm^-1·s^-1·℃^-1.此时,模具最大磨损深度为0.0515mm,模具可重复使用20次.     

纳米锰方硼石的合成与结构性能表征

通过溶胶?凝胶（Sol?Gel）法成功合成了纳米锰方硼石并对其进行了稀土Eu3+掺杂。使用X射线衍射、透射电子显微镜和高分辨透射电子显微镜等表征了锰方硼石晶体结构,并通过荧光光谱测试对其发光性能进行了研究。结果表明:合成纳米锰方硼石为粒径小于50 nm的球状颗粒,与天然锰方硼石的物相结构相同,属于斜方晶系,与尖晶石类似,（010）晶面的晶面间距为0.8565 nm。在490 nm激发光激发下,天然锰方硼石、合成锰方硼石和稀土Eu3+掺杂锰方硼石晶体中的Mn2+发光,其中发绿光的Mn2+在晶体中占据四面体格位中心,发红光的Mn2+在晶体占据八面体格位中心。合成的锰方硼石随激发波长变长,产生发射光谱的红移现象,有利于实现冷暖发光转换;在稀土Eu3+掺杂的纳米锰方硼石光谱的发光强度得到了提升。      

电子封装用高体积分数SiCp/Al复合材料的制备

采用粉末注射成形制备SiC预成形坯和Al合金无压熔渗相结合的工艺,用单一粒度的粉末成功地制备出了致密度为98．7%的60% SiCp/Al高体积分数复合材料．SEM分析表明,所制备的复合材料增强体和基体分布均匀,组织致密,热膨胀系数在100℃到400℃范围内介于(7．10-7．75)×10^-6K^-1之间,室温热导率为170W·m^-1·K^-1,能够完全满足电子封装的技术要求．     

纳米锰方硼石的制备及其电磁特性

为了开发利用锰方硼石,采用柠檬酸法结合表面活性剂成功制备了纳米锰方硼石粉体,并探讨了纳米锰方硼石的形成过程与机理。利用XRD,TEM等对制备的锰方硼石进行了表征,并研究了利用纳米锰方硼石粉末制得陶瓷基片的电磁特性。结果表明,干凝胶在550℃下焙烧可以获得粒径分布较为均匀、平均粒径在50 nm左右的Mn3B7O13Cl纳米粉体。纳米Mn3B7O13Cl有较好的电磁性能,在1~9 GHz下,锰方硼石主要以磁损耗为主,在9~18 GHz下以电损耗为主,通过加入适当的吸收剂,可用于制备微波衰减材料。     

Current PM Literature for Engineers and Users

Abstract

Fine tin powders were produced in a pilot plant gas atomiser. Nitrogen gas at 1·56 MPa pressure was used as the atomising agent in a ‘confined design’ nozzle which operated vertically upwards. A range of metal flowrates from 0·864 to 1·425 kg min^?1 was studied at a melt temperature of 450°C. Powders were sized using dry sieving down to 45 μm and wet sieving for smaller sizes. The Sauter mean diameter of the powders varied from 9·01 to 10·28 μm, depending on the rate of production. The size distribution was bimodal (albeit not very well defined) with the peak separation at ～44 μm. In the fine size range, particles were spherical, while those in the coarse range were more elongated or irregular in shape and free of satellites. Comparison of the tin powders with copper powders from another study, AA 2014 aluminium alloy powders, and magnesium and zinc powders from previous work showed that the differences in mean diameter and standard deviation are small among these common metals at a given volumetric production rate. This confirms the overriding importance of liquid metal volume flowrate under fixed gas flow conditions in gas atomisation, while the actual physical properties of the liquid playa secondary role. Although surface tension is secondary to volume flowrate in importance for controlling particle size, the study has shown that a liquid metal with lower surface tension and viscosity than AA 2014 alloy, together with a higher density, yields finer particles. PM/0667A     

Measurement of friction for powder compaction modelling – comparison between laboratories

Abstract

A ‘round robin’ assessment of methods for measuring friction for die compaction of powders has been undertaken as part of the European PM Modnet programme. Measurements have been made on a Distaloy AE with 0·5% graphite and 1·0% wax using five different shear based techniques and six techniques using instrumented dies. The potential accuracy of friction measurement required as input to models of the compaction process has been assessed using results from modelling sensitivity studies where friction was varied, together with specifications from industry of the accuracy of model output required. These studies suggest that an accuracy of measurement of friction coefficient of ±0·01 is preferred, but that an accuracy of ±0·02 will still give predictions of acceptable levels of accuracy. Friction data have been compared by separating the measurements into three regimes, respectively relevant to: ? surfaces perpendicular to punch movement during compaction (Type 1), ? surfaces parallel to punch movement during compaction (Type 2), ? surfaces parallel to punch movement during ejection (Type 3). The majority of data relate to the second of these cases. Type 2 friction data from shear techniques fall within a band of ±0·02 around a linear relation with normal pressure and density. Mean friction falls from 0·14 to 0·07 as density increases from 4 to 7·5 g cm^-3 and from 0·11 to 0·06 as normal pressure rises from 0 to 600 MPa. Type 2 friction data from dies show a wider variation than data from shear techniques. A number of reasons for this has been suggested. The use of a varying ratio of radial to axial pressure at die surfaces during compaction has been demonstrated to bring closer agreement between data from die and shear techniques, especially at pressures above 200 MPa.     

Characteristics of rapidly solidified Cu–10%Sn alloy powders produced by water jet cooled rotating disc atomisation

Abstract

In the present work, an experimental water jet cooled rotating disc centrifugal atomiser was designed and constructed and used to produce rapidly solidified Cu–10%Sn alloy powders. The characteristics of rapidly solidified Cu–10%Sn alloy powders have been investigated with respect to powder size and disc surface condition. Uncoated and ZrO₂ coated copper discs were used to investigate the effect of disc surface conditions on the microstructure and cooling rate of the powders. The produced powders appeared in the shape of sphere, rounded, ligament, irregular and flaky, depending on the particle size. The powders exhibited fine grained microstructure, cell size increased with increasing powder size and higher cooling rates were obtained using uncoated disc. The results indicated that cooling rates of 20 μm powder produced with uncoated and ZrO₂ material coated discs were estimated as 5·82×10⁵ and 1·44×10⁵ K s^?1 respectively.     

水热还原法制备W-Cu复合粉体的工艺研究及表征

利用XRD、SEM、TEM等检测手段,对制备新型W-Cu合金过程中的产物显微组织进行研究和标定。结果表明:水热过程中,Na_2WO_4·2H_2O和Cu(NO_3)_2·3H_2O发生反应,水热反应产物主要由球形Cu WO_4·2H_2O和Cu_2WO_4(OH)_2的复合络合物组成,该络合物粉末分散性好,粒度均匀,平均粒径10~15 nm;煅烧后,水热产物转变为由CuWO_(4-x)、CuO和WO_3组成的混合氧化物粉体;经H2还原,氧化物粉末完全转化成W-Cu复合粉末,呈一种特别的W包覆Cu的近球形结构,平均粒径为20~60 nm,且Cu的存在对WO3的还原起催化作用。     

液氮球磨制备Al-Zn-Mg-Cu纳米晶粉末及组织分析

利用液氮球磨技术制备了Al-Zn-Mg-Cu纳米合金粉末.采用X射线衍射对材料在球磨过程中的固态相变、晶粒尺寸和微观应变进行了研究,利用金相显微镜和透射电镜观察了微观组织.研究表明,随着球磨的进行,雾化粉末中的MgZn₂第二相逐步减少,并最终完全超饱和固溶于α-Al之中.低速(200r·min^-1)球磨10h后仍有少部分粗晶存在于粉末心部;高速(400r·min^-1)球磨能够使粉末纳米晶粒更加均匀.材料经过低速液氮球磨6h以后平均晶粒大小稳定在45nm,并保持到10h不再变化;增加主轴转速到400r·min^-1继续球磨5h后,粉末平均晶粒大小降到34nm.微观应变随着球磨进行呈现先增大后降低的趋势.     

氢爆工艺(HD)对钕铁硼磁粉粒度和形状的影响研究

采用热处理态钕铁硼平板铸锭作为母合金,通过氢爆工艺将平板铸锭破碎成磁粉.研究了氢爆工艺过程中温度、氢压对钕铁硼磁粉的破碎程度、粒度和形状的影响.实验发现,随着温度和氢压的提高,吸氢过程活化时间逐渐缩短,当温度为300℃,氢压为0.1 MPa时,活化过程消失,铸锭一旦暴露在氢气中,吸氢过程直接发生.热处理态平板铸锭吸氢之...     

Modification of Ag-doped BaTiO3 powders through La gaseous penetration route

The Ag-doped BaTiO₃ (BATO) polycrystalline powders were fabricated by Sol-Gel method. Further modification by rare earth La was done through gaseous penetration route. Changes in constitution, structure, and electrical conductivity before and after modification of Ag and La were characterized. The acceptor dopant Ag owned the ability to decrease the resistivity of the doping samples from 4.30×10⁹ Ω·m to 6.14×10⁵ Ω·m where the resistivity fell by 4 orders of magnitude when the Ag doping ratio was 0.10%. And more doping of Ag enhanced the resistivity dramatically even beyond 2.0×10⁷ Ω·m. Yet, gaseous penetration of La successively reduced the resistivity of BATO to the lowest point of 2.45×10⁵ Ω·m. XRD analysis indicated that the doping process of Ag did not change the perovskite structure and main phases of the powders. However, new compound BaLa₂O₄ generated from complex reactions during the penetration process, which manifested that La³⁺ penetrated into the crystal lattices in the form of substituting the Ti⁴⁺ site. And this substitution strengthened the Ti-O bond, which led to the inhibition of blue shift in FTIR spectrum caused by doping of Ag. The morphology of La penetrated BATO powders detected by SEM and EDAX suggested that La did penetrate into the powders and this penetration process progressed the partly sintering of the powders which is in favor of the conductivity.     

Recyclability assessment of Al 7075 chips produced by cold comminution and consolidation using spark plasma sintering

A solid-state recycling route for processing aluminium alloy 7075 chips is proposed. This process involves pulverizing the chips using an industrial scale comminution line to produce a broad particle size distribution of granulated products and powders. Upon sieving, the ?140 mesh fraction of the pulverised material was consolidated by spark plasma sintering into fully dense compacts, i.e. >99%. The properties of the pulverised powders and compacts were compared to commercially available aluminium alloy 7075 powder used in industrial press-sinter applications. The comminution line produced powder particles which possessed a 7·9?±?0·6-nm thick native oxide layer with adhering exogenous contaminants, and aluminium oxide particles dispersed throughout the powder. The presence of the oxide layer and exogenous contaminants was found to be deleterious to the powder consolidation and mechanical properties. A flexural strength and strain and hardness of 94·7?±?7·2?MPa, 2·1?±?0·3% and 69·3?±?5·2 HV were obtained, respectively.