The Effect of Coolant Concentration on the Machinability of Nickel-Base, Nimonic C-263, Alloy

This paper investigates the effect of coolant concentration on tool performance when machining nickel-base, C-263, alloy with triple coated (TiN/TiCN/TiN) carbide insert at various (3–9%) coolant concentrations and under different cutting speed conditions. Tool life, tool-failure modes, wear rates, component forces and surface finish generated during machining were recorded, analyzed and used to formulate mechanisms responsible for tool wear at the cutting conditions investigated. Analysis of the recorded data shows that tool performance during machining is dependent on coolant concentration. 6% coolant concentration gave the best overall performance as effective combination of cooling and lubrication functions were achieved during machining. Increasing coolant concentration to 9% reduced tool performance due to a reduction of the tool-chip contact length area and the consequent increase in compressive stresses at the tool-chip and tool-workpiece interfaces. This action often leads to pronounced chipping of the tool cutting edge during machining. Friction coefficient between the workpiece material and substrate increases once the coating layer(s) is broken as a result of the direct contact between the tool substrate and the work material. This action increases mechanical wear of the tool, which in turn leads to a significant increase in the cutting force with negligible effect on the feed forces during machining.     

Atmospheric effects of friction,friction noise and wear with silicon and diamond. Part II. SEM tribometry of silicon in vacuum and hydrogen

Scanning electron microscope (SEM) tribometric data on polycrystalline silicon (poly-Si) vs. poly-Si, Si(100) vs. Si(100) and Si(111) vs. Si(111) interfaces, obtained in Torr and in 0.2 Torr partial pressure of hydrogen gas ( ) from room temperature to 850^°C, were performed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology described in part I of this paper series. The results indicate a highly beneficial friction- and wear-reducing regime within a relatively narrow thermal region. This desirable region coincides with some chemisorption of excited species of molecular hydrogen just before the mass thermal desorption of surface hydrides. These data represent the tribochemical equivalent of a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking in molecular hydrogen. The also exerts a moderating influence on the size of the friction noise at all test temperatures. However, the general level of friction beyond the beneficial thermal region is high. In parallel, the general wear rate of Si representative of the entire range of standard thermal ramping in both atmospheric environments is in the extremely high 10^-12m³/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude reduction in the wear rate over those measured under standard thermal ramping conditions. Although the results confirm previous findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microbearings and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen at surface temperatures between 100 and 300^°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

精磨硬质合金数控刀片切削与磨损性能的实验研究

对YT14三角形硬质合金数控刀片的切削与磨损性能进行了实验研究.在实验中,针对两种不同精度级的数控刀片进行了切削性能和磨损特性对比实验.实验表明：刀片精度级越高,其磨损速度越低.用高精度级刀片进行切削加工,不仅可以提高工件的加工表面质量,还可延长刀片的使用寿命,从而节省刀片的购置费用,具有可观的经济效益和社会效益.     

世界核电设备与结构将长期面临的一个问题--微动损伤

核电设备至仍面临许多不易解决的问题,经过对核电和结构部件多例事故的分析可知,核电设备中微动是不可避免的现象,核能工程中的相当一部分结构损伤事故与和微动损伤有着直接的关系;在反应力集中,腐蚀部位,微动又是许多核电设备提前损伤失效的直接原因。     

MoS_2对铝基材料摩擦磨损性能的影响

以Al,Fe,Zn等金属粉末和Si粉为原料,采用热压法制备MoS_2含量(质量分数)分别为0和3%的铝基复合材料,在滑动速度为0.377~1.131 m/s以及载荷为4~10 N的条件下进行摩擦试验,研究MoS_2对铝基复合材料摩擦磨损性能的影响。结果表明:在0.377 m/s的滑动速度下,3%MoS_2/铝基复合材料在10 N载荷下具有较低的平均摩擦因数0.4,比不含MoS_2材料的摩擦因数降低近一半;在0.755 m/s的滑动速度下,2种材料的摩擦因数和磨损率接近;在1.131 m/s的滑动速度下,载荷7~10 N时2种材料都严重磨损,3%MoS_2/铝基材料具有相对较低的磨损率,磨损机理为熔化磨损,未添加MoS_2材料的磨损机理为严重塑性变形磨损。添加3%MoS_2可显著改善铝基材料的摩擦磨损性能。     

WMnNbTa耐磨合金应用研究

介绍了通过添加WMnNbTa耐磨合金及利用热处理,提高破碎机齿板耐磨性能的新方法。     

蒸汽发生器传热管面内流体弹性失稳分析

流体弹性失稳是蒸汽发生器内最严重的传热管流致振动机理,一旦发生就会使传热管发生大幅振动并快速失效。流体弹性失稳可能在U形传热管束的面内及面外两个方向发生,为研究面内及面外流体弹性失稳发生的先后顺序,通过将蒸汽发生器U形传热管防振条支撑假设为单向简支,即仅在传热管面外方向对U形管进行约束,建立了完整的U形管模型;计算了弯曲半径及防振条支撑数量对U形管面内外固有频率的影响,基于成熟的流体弹性失稳经验模型,得到了面内流体弹性失稳先于面外方向发生的条件。结果表明,对弯曲半径在0.5 m-1.75 m范围内的U形传热管,当其弯管段支撑点超过4 h,面内流体弹性失稳将先于面外方向发生。     

喷油器针阀偶件的耐久性和可靠性

本文应用实际装机试验和试验室精密测量相结合的方法测得工程机械柴油机喷油器针阀偶件的实际使用寿命，并对影响针阀偶件耐久性的可靠性的各种因素做了分析研究，在此基础上提出了提高国产针阀偶件质量和使用寿命的方法和措施。     

CVC工作辊非对称磨损分析与预报模型建立

 CVC辊形以其较强的凸度控制能力在热连轧中有着广泛的应用,但是CVC辊形不具有均匀磨损的能力,其磨损往往比较严重,且呈现出非对称性。针对该特点提出CVC工作辊非对称磨损的表征方法,利用该方法对某1 800 mm CSP生产线下游机架CVC工作辊非对称磨损情况进行分析。统计结果表明,下游机架工作辊磨损多为非对称形式,并与CVC辊形呈现出一定的对应性。在此基础上,提出辊径对整体磨损影响系数及辊径对轧制力影响系数2个新的磨损模型参数,并建立针对CVC轧辊的非对称磨损预报模型,利用遗传算法对模型参数进行优化,并利用实测数据进行验证,改进后磨损模型精度比常规磨损模型精度平均提高了约35%。     

W-4.9Ni-2.1Fe 高比重合金的摩擦磨损行为

采用高能球磨和放电等离子体烧结技术制备W-4.9Ni-2.1Fe高比重合金,研究不同球磨时间对合金显微组织结构和摩擦磨损行为的影响. 结果表明:当球磨时间较短（2 h）时,合金粉末中Ni、Fe元素仍以单质的形式存在;随着球磨时间的延长,Ni(Fe)溶入W晶格中形成W的过饱和固溶体,W衍射峰强度逐渐变弱,峰形明显宽化,合金试样的相对密度呈下降趋势;适量的球磨时间（24 h）,既可以保证合金中黏结相的含量和均匀分布,又不至于引入过量的杂质元素而引起合金成分改变,合金拥有最优的耐摩擦磨损性能.