石材锯切加工机理的研究

本文介绍了70年代以来，德国在石材锯切加工机理、石材可锯性研究方面的一些重要成果，着重介绍了汉堡工业大学加工技术和工艺研究所的一些最新研究成果。1石材加工机理采用金刚石工具锯切花岗岩，是石材加工中常用的工艺方法之一。金刚石颗粒与石材矿物之间的作用，决定了石材切除率、金刚石磨损和加工表面质量。多年来，为了不断提高金刚石工具锯切加工石材的能力，对石材锯切加工机理进行了持久的研究。从早期即开始使用的单颗粒划伤表面形貌观察方法，逐渐发展到综合使用偏光显微镜和扫描电镜观察矿物成份及划痕形貌、用声发射信号评价…     

湿化学法制备W-TiC复合粉体及其SPS烧结行为

采用湿化学法制备W-TiC复合粉体,然后采用放电等离子体烧结(SPS)技术制备超细晶W-TiC复合材料,并对其复合粉体形貌和烧结复合材料组织结构进行研究。结果表明,对原始TiC粉进行活化预处理,使TiC粉表面获得均匀分布的缺陷,提高TiC粉表面的的亲水性,通过化学还原获得第二相TiC颗粒,且均匀弥散分布于W基体晶界和晶粒内。采用SPS烧结技术获得的超细晶W-TiC复合材料晶粒尺寸为400 nm,致密度为95%,维氏显微硬度值HV0.2达到1280。     

种分法制备超细氢氧化铝过程中的粒度控制

超细氢氧化铝具有许多优点,应用广泛。超细氢氧化铝的粒度分布和颗粒形貌对产品的性能有很大影响。根据湿化学法颗粒成核与生长机理从理论上分析了超细氢氧化铝制备过程中需控制的工艺条件,研究了二段分解工艺中晶种添加量和温度等对分解产品粒度分布的影响,得出了温度和种子添加量对氢氧化铝粒度分布的影响规律。     

放电等离子烧结制备超细晶粒W-TiC复合材料

采用机械合金化和放电等离子烧结(SPS)技术制备了纳米TiC颗粒弥散增强超细晶W-TiC复合材料,对超细晶W-TiC复合材料的显微组织和室温力学性能进行了研究。研究表明,采用SPS工艺于1700℃下烧结1min可获得烧结颗粒结合良好,致密度高达约98.6%的超细晶W-TiC复合材料。通过添加纳米TiC,不仅能抑制W晶粒的长大,还能促进W的致密化。当TiC的加入量为0.7%时(质量分数,下同)可获得晶粒尺寸为0.5μm,抗弯强度和维氏硬度分别为1262MPa,6.45GPa的超细晶W-TiC复合材料。     

种分制备超细氢氧化铝过程分解率影响因素及结晶机理分析

研究铝酸钠溶液种子分解生产超细氢氧化铝过程中各因素对分解率影响及其结晶机理,对于控制氢氧化铝的粒度分布、颗粒形貌和优化生产工艺有重要的指导作用。本文通过研究温度、苛性碱浓度和种子率等主要因素对分解率的影响,揭示其影响规律,并对超细氢氧化铝的结晶机理进行了分析。     

超细TiCN基金属陶瓷的制备及其微波烧结工艺研究

采用微波烧结技术制备了超细TiCN基金属陶瓷材料,研究了烧结温度和保温时间对超细TiCN基金属陶瓷材料力学性能的影响,并利用扫描电镜观察了断口形貌及其组织结构。结果表明:随着烧结温度的升高,超细TiCN基金属陶瓷的收缩率、致密度、横向断裂强度和硬度均先增大后减小。该材料经1500℃保温30 min,可获得晶粒细小、组织均匀、性能优异的超细TiCN基金属陶瓷,此时其横向断裂强度和硬度分别为1547 MPa和90.6 HRA。     

表面活性剂对超细银粉分散性能的影响

在以抗坏血酸为还原剂、银氨配合物为前驱体、PVP为保护剂及表面活性剂为分散剂的液相化学还原体系中制备超细银粉,研究阳离子、阴离子和非离子表面活性剂在银粉制备过程中的防团聚作用和分散作用,并采用扫描电镜(SEM)和X射线衍射等对还原产物进行形貌观察和结构表征.结果表明:表面活性剂的种类对制各样品的纯度、分散性和颗粒大小有着重要的影响,其中阳离子表面活性剂和阴离子表而活性剂的分散效果不明显,非离子表面活性剂的分散效果最好.对吐温(TW)系列分散剂的研究表明:TW相对分子质量的大小对银粉颗粒的分散效果、形貌和大小也有显著影响;采用TW80分散剂可制备出高分散、窄粒级的超细银粉.     

高能球磨法制备Fe-C超细晶/纳米晶粉末的研究

采用高能球磨法制备出了平均颗粒尺寸为纳米级的超细Fe-C粉末。利用SEM、XRD等分析手段研究了球磨时间和转速对Fe-C超细晶/纳米晶粉末颗粒形貌、尺寸和合金化效果的影响。结果表明,Fe-C超细晶/纳米晶粉末的过程中,颗粒尺寸随球磨时间和转速的增加而得到有效细化。当球料比为20:1、转速350r/min、球磨70 h时,颗粒细化效果最好。将球磨后平均颗粒尺寸为纳米级的粉末进行SPS烧结,烧结温度700℃时,能实现烧结体完全致密,并可有效避免晶粒的长大,该烧结体材料抗压强度达2800MPa。     

切削速度对切屑形态和加工表面微观形貌的影响

为了研究钛合金车削过程中切削速度和切屑形态特征对已加工表面微观形貌的影响。采用硬质合金涂层刀具车削钛合金TC4,研究了切削速度对切屑形态特征、已加工表面粗糙度和轮廓最大高度的影响规律,分析了切屑底部毛边形貌、已加工表面形貌与表面粗糙度三者之间的关系。结果表明:在切削速度40~120m/min时,切屑底边出现锯齿形毛边,且随切削速度增大锯齿越明显。切屑底部锯齿毛边的形成是造成已加工表面波峰损伤形成的主要原因。影响已加工表面粗糙度的微观形貌特征包括硬质颗粒、粘结现象和波峰损伤。因此,为了获得高质量的加工表面,加工参数选择时必须规避硬质颗粒和严重的粘结现象,并控制切屑底部毛边形态特征。     

铝酸钠溶液晶种分解制备超细氢氧化铝结晶机理初步研究

采用铝酸钠溶液加凝胶晶种分解工艺制备出粒度分布窄、颗粒均匀的超细氢氧化铝,主要研究了温度、添加剂、晶种添加量等对分解率和晶体颗粒形貌的影响,并对晶体生长机理进行了分析研究。     

电子束辐照下铜超微粒子氧化与还原过程的高分辨电子显微镜观察

利用电子显微镜中的电子束对铜超微粒子进行了连续地照射和跟踪观察，结果表明电子束使Ｃｕ与镜筒中的低氧压气氛发生了反应，电子束的辐照使纳米量级的Ｃｕ粒子发生了氧化并被消耗，首先生成一种类非晶膜，然后生成Ｃｕ的晶态氧化物，新生成的Ｃｕ的晶态氧化物，在电子束的进一步照射下，又发生了还原反应，不断地还原为铜     

Fabrication of cast carbon steel with ultrafine TiC particles

The carbon steels dispersed with ultrafine TiC particles were fabricated by conventional casting method. The casting process is more economical than other available routes for metal matrix composite production, and the large sized components to be fabricated in short processing time. However, it is extremely difficult to obtain uniform dispersion of ultrafine ceramic particles in liquid metals due to the poor wettability and the specific gravity difference between the ceramic particle and metal matrix. In order to solve these problems, the mechanical milling (MM) and surface-active processes were introduced. As a result, Cu coated ultrafine TiC powders made by MM process using high energy ball milling machine were mixed with Sn powders as a surfactant to get better wettability by lowering the surface tension of carbon steel melt. The microstructural investigations by OM show that ultrafine TiC particles are distributed uniformly in carbon steel matrix. The grain sizes of the cast matrix with ultrafine TiC particles are much smaller than those without ultrafine TiC particles. This is probably due to the fact that TiC particles act as nucleation sites during solidification. The wear resistance of cast carbon steel composites added with MMed TiC/Cu-Sn powders is improved due to grain size refinement.     

Fabrication of cast carbon steel with ultrafine TiC particles

The carbon steels dispersed with ultrafine TiC particles were fabricated by conventional casting method. The casting process is more economical than other available routes for metal matrix composite production, and the large sized components to be fabricated in short processing time. However, it is extremely difficult to obtain uniform dispersion of ultrafine ceramic particles in liquid metals due to the poor wettability and the specific gravity difference between the ceramic particle and metal matrix. In order to solve these problems, the mechanical milling (MM) and surface-active processes were introduced. As a result, Cu coated ultrafine TiC powders made by MM process using high energy ball milling machine were mixed with Sn powders as a surfactant to get better wettability by lowering the surface tension of carbon steel melt. The microstructural investigations by OM show that ultrafine TiC particles are distributed uniformly in carbon steel matrix. The grain sizes of the cast matrix with ultrafine TiC particles are much smaller than those without ultrafine TiC particles. This is probably due to the fact that TiC particles act as nucleation sites during solidification. The wear resistance of cast carbon steel composites added with MMed TiC/Cu-Sn powders is improved due to grain size refinement.     

超细纯镁及镁钛粉体的制备及储氢性能

采用直流电弧等离子体方法制备超细纯Mg及Mg-Ti粉体。运用X射线衍射（XRD）,透射电子显微镜（TEM）,压力成分温度（PCT）方法和TG/DTA技术研究粉体吸放氢前后的相组成、微观结构和吸放氢性能。结果表明,大部分超细Mg和Mg-Ti颗粒呈六角形,颗粒大小在50700nm范围内。根据范特霍夫方程计算由PCT曲线获得的吸氢平台压力,Mg-Ti粉的氢化焓约为67kJ/mol H2,显著高于纯镁粉的氢化焓78.6kJ/mol H2。TG/DTA分析表明,氢化后Mg-Ti粉的放氢起始温度为386°C,低于氢化纯镁粉的放氢温度（423°C）。通过电弧蒸发法直接向Mg中添加Ti而获得的Mg-Ti超细粉体可以显著改善镁的储氢热力学性能。     

磨料微粉的颗粒整形技术

为提高磨料微粉的振实密度,需要对粉末的颗粒形貌进行控制,使其接近于球形.本文通过分析球磨机和流化床气流磨两种设备的粉碎机理,调整粉碎工艺参数,减小破碎强度,增加介质与粉末之间的摩擦作用,利用研磨方式对碳化硅和碳化硼微粉分别进行颗粒整形.整形后的颗粒球形度高,产品的振实密度较之整形前有较大提高,并得到每种设备的最佳整形工...     

The measurement of ultrafine particles: A pilot study using a portable particle counting technique to measure generated particles during a micromachining process

The accurate measurement of airborne particles in the nanometer range is a challenging task. Because several studies have linked exposures to airborne ultrafine particles to elevated human health risks, the need to assess the concentrations of particles in the workplace that are below 100 nm in diameter is imperative. Several different techniques for monitoring nanoparticles are now available, and others are currently being tested for their merit. Laboratory condensation particle counters (CPC), field-portable CPC, nanometer differential mobility analyzers, electron microscopy, and other novel and experimental approaches to measuring nanoparticles have been recently used in investigations. The first part of this article gives an overview of these techniques, and provides the advantages and disadvantages for each. The second part of this article introduces a portable technique, coupling two particle measurement devices that are capable of characterizing microscale and nanoscale particles in the field environment. Specifically, this pilot study involved the use of a direct-reading CPC and a laser particle counter to measure airborne concentrations of ultrafine particles during a laboratory machining process. The measurements were evaluated in real time, and subsequently, decisions regarding human exposure could be made in an efficient and effective manner. Along with the results from this study, further research efforts in related areas are discussed. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

45钢在超细SiC颗粒作用下的正向冲蚀行为*

选用超细SiC颗粒作为磨料,研究了韧性材料45钢在正向冲击条件下的冲蚀行为并与7075-T6铝合金对比。使用高强度磁铁捕获了45钢冲蚀磨屑,利用扫描电子显微镜(SEM)对冲蚀磨损后试样表面以及磨屑形貌进行观测;采用质量分析法,分析45钢在不同冲蚀条件下的失重情况与材料去除率;利用X射线应力测定仪,分析45钢在不同冲蚀条件下的表层及深度方向的残余压应力分布情况。结果表明,正向冲击条件下,韧性材料表面主要发生塑性变形,偏向堆积脊部还存在片层剥落的材料去除形式,超细磨料产生的材料去除率相对较小,材料去除率随磨料量的增加呈先增加后减小的趋势;表层应力随磨料量呈先增加后降低的趋势,微磨料冲蚀残余压应力的影响深度约为10μm。     

Synthesis of BaCO3 Nano-particles Through a Polymer-Assisted Precipitation Method

BaCO₃ powders with different morphologies have been synthesized by a simple polymer-assisted precipitation method. The influence of diethylene glycol (DEG) as a modifier on the powder particle characteristics has been investigated using XRD, FESEM, FT-IR, and VSM techniques. It is revealed that both crystallinity and crystallite size of particles can be greatly affected through the change in DEG:water ratio. The crystallite size decreases from 32 nm for water solution to 20 nm for DEG’s solution. The FESEM images also show that DEG:water volume ratio causes the shape of particle to change greatly. While particle synthesized in presence of water solution has rodlike shape with 900 nm in length and 276 nm in width, particle synthesized in DEG solution has completely spherical shape with a mean particle size of 93 nm. Finally, the performance of barium carbonate nano-particles produced in this work has been examined in the processing of barium hexaferrite magnetic phase.     

Particle temperature measurement in the thermal spray process

Particle temperature is a fundamental parameter in the thermal spray process. The measurement of particle temperature usually relies on the measurement of the radiance of the hot, incandescent, particles in two or more wavelength or color bands. Measurement techniques can be categorized as single particle and ensemble methods. Single particle methods use high-speed pyrometry to estimate the temperature of individual particles. The mean and standard deviation of the particle temperature distribution can then be obtained from observations of sufficient numbers of individual particles. Ensemble methods observe large numbers of particles simultaneously and yield an estimated mean temperature directly, but cannot provide information on the shape or width of the particle temperature distribution. Both techniques have inherent errors, strengths, and limitations that are examined and discussed.     

Wear resistance of NiTi alloy after surface mechanical attrition treatment

An ultrafine grain layer consisting of nanocrystallites as well as submicrometer grains is produced on NiTi shape memory alloy by surface mechanical attrition treatment (SMAT) and the effects of the ultrafine grain layer on the tribological properties are investigated under dry sliding conditions. Compared to the coarse grain (CG) NiTi, the SMAT NiTi has smaller friction coefficients and improved wear resistance at applied loads from 5 to 15 N due to the grain refinement effect. Examination of the worn surfaces indicates that materials delamination and particles co-exist on both the CG and SMAT NiTi samples. Our results indicate that delamination is the main wear mechanism on CG NiTi whereas abrasive particles dominate the wear process on SMAT NiTi.