粉末冶金组合烧结中空凸轮轴的组织与性能

采用粉末冶金组合烧结技术制备由Fe-Cr-Mo-P-Si-Cu-C凸轮和16Mn钢管为芯轴组成的中空凸轮轴,对凸轮的密度、硬度等物理性能、摩擦磨损性能和微观组织进行测试与分析,研究烧结致密化机理,并与传统凸轮材料球墨铸铁的摩擦磨损性能进行对比。结果表明:Fe-Cr-Mo-P-Si-Cu-C凸轮材料在烧结过程中产生Fe-C-P三元液相,Cr、Mo元素溶解于液相中使得液相量显著增加,促进液相烧结,体积收缩率高达19.1%。凸轮材料的平均密度为7.51 g/cm3,平均硬度(HRC)53.7,与钢制芯轴形成牢固的冶金结合,扭矩高达1 150 N·m,连接可靠性较好;该凸轮材料的硬度与传统球墨铸铁凸轮材料相近,耐磨性是球墨铸铁的3倍,质量减轻35%,满足发动机使用要求。     

镍与石墨含量对新型铜基粉末冶金受电弓滑板材料性能的影响

采用粉末冶金法,在N2和H2混合气氛保护下烧结,制备以石墨和镍等为主要合金元素的新型铜基受电弓滑板材料,研究石墨含量对该材料电阻率、冲击韧性、硬度、摩擦因数和磨损性能的影响,以及镍含量对其硬度和冲击韧性的影响,并分析烧结过程中形成的弥散相和固溶体对材料的增强增韧效果。结果表明:石墨对材料密度影响较明显,石墨含量越高,材料的电阻率越大,冲击韧性越小,并且摩擦因数越小,减磨和耐磨性越好,但石墨含量超过5%时材料性能下降;随镍含量增加,受电弓滑板材料的硬度和冲击韧性都提高,但电阻率增大。石墨和镍的含量(质量分数)均为3%时,材料的电阻率为0.22μΩ·m,硬度为HB60,冲击韧性为7.1J/cm2,摩擦因数为0.19,能满足铜基受电弓滑板的使用要求。     

混料时间对含石墨的铜基摩擦材料性能的影响

本文采用粉末冶金方法制备了含石墨的铜基粉末冶金摩擦材料,通过调整加入石墨后的混料时间,采用布氏硬度计、摩擦磨损试验机和扫描电镜等设备研究了混料时间对含石墨的铜基摩擦材料性能的影响。研究结果表明:随着加入石墨后混料时间的增加,烧结后摩擦材料中的石墨颗粒分布更加均匀,铜基体的连续性变差,材料密度和硬度均下降,材料的摩擦因数先增大后减小,磨损量先减小后增大。加入石墨后,混料8 h的烧结体的摩擦磨损性能最佳(较其他试样摩擦因数增加了10%左右,磨损量降低了30%左右)。     

粉末冶金烧结硬化凸轮材料的摩擦磨损性能研究

本研究将铁基Fe-Cr-Mo-Cu-Si-P-C粉末冶金材料用于组合烧结式粉末冶金中空凸轮轴的凸轮制备,使用MR-H5型高速环块磨损实验机进行摩擦磨损性能测试,并通过白光干涉形貌法对该凸轮材料在不同转速下的摩擦磨损性能进行研究。结果表明,凸轮材料烧结后密度可达7.5 g/cm3以上,硬度HRC达到53.7;材料的磨损状况与转速密切相关,在1 000~2 000 r/min转速范围内,磨损机制主要为磨粒磨损,随着转速提高,微凸体啮合程度不断降低,摩擦因数降低。磨损量则呈现先增加后减少的趋势。当转速达到3 000r/min时,以粘着磨损为主,材料磨损严重。在同样的实验条件下,该粉末冶金凸轮材料的磨损量仅为传统球墨铸铁凸轮材料的1/3,显示了优异的耐磨性。     

Fe含量及摩擦组元对铜基粉末冶金摩擦材料性能的影响

以电解Cu粉、还原Fe粉、石墨等为主要原料,采用粉末冶金加压烧结工艺制备了Cu基粉末冶金摩擦材料,研究了Fe含量及SiO2、Al2O3、SiC等摩擦组元对烧结合金的显微组织、力学性能和摩擦磨损性能的影响。结果表明:Fe主要影响摩擦材料的力学性能,随Fe含量的增加,摩擦材料的硬度、抗压强度和抗弯强度显著提高,Fe含量为15%(质量分数,下同)时具有高摩擦系数、较低磨损量和稳定的摩擦过程;添加摩擦组元SiC后的材料强度最高、摩擦系数最大、磨损量最小,但增加了对偶材料的磨损,加SiO2后材料摩擦系数最小、磨损量最大,Al2O3所起作用介于二者之间。     

粉末烧结Cu-C-SnO2多孔材料摩擦磨损特性研究

铜-石墨复合材料是一种优良的导电耐磨材料,但铜与石墨润湿性很差,导致材料的耐磨性能不足。本文通过向原料中加入与石墨亲和性良好的SnO₂,利用粉末冶金的方法制得Cu-C-SnO₂多孔材料,研究了烧结温度及成分配比对烧结体孔隙率、物理特性及摩擦磨损性能的影响。结果表明：烧结体的孔隙率随烧结温度升高而降低,随石墨/SnO₂质量比增大而增大,随非金属/Cu质量比增大而减小;烧结体的密度、硬度、渗油率等与孔隙率密切相关,随孔隙率升高,密度和硬度呈降低趋势,渗油率呈上升趋势;但试样硬度受Cu₂O产生和Cu颗粒再结晶的影响而变化复杂,在烧结温度830℃附近出现突变。干摩擦条件下,试样摩擦磨损特性受材料硬度和石墨相自润滑作用等多重因素影响而变化复杂,随试样硬度和石墨含量的升高而降低;渗油后试样的摩擦磨损特性则主要受油膜润滑控制,与干摩擦相比,相对摩擦因数和磨损率均显著减小,试样磨损率随渗油率的增大而减小,但在石墨/SnO₂质量比0.155附近存在突变。     

石墨含量对铜基摩擦材料摩擦磨损性能的影响

采用粉末冶金压烧技术制备了含不同质量分数石墨的铜基摩擦材料,研究了石墨含量对摩擦材料微观组织、磨损性能和磨损机理的影响。结果表明:铜基体的连续性随石墨含量增加而降低,动摩擦系数随石墨含量的增加先增加后降低,磨损量随着石墨含量的增加而减小;材料的磨损机理为犁沟式磨料磨损;石墨质量分数为16%时,试样动摩擦系数和静摩擦系数最高并且稳定,具有最好的摩擦磨损性能。     

Ti、石墨含量对铁基粉末冶金烧结材料的组织与性能影响

本文以雾化铁粉、羰基镍粉、钼粉、电解铜粉、钛粉及石墨粉为实验原料,在Fe-2%Ni-0.5%Mo-2%Cu-0.3%C基础上,按Ti和C原子比1∶1同时添加Ti和石墨(Ti的添加量为质量分数0～4%),利用粉末冶金与原位烧结合成技术制备了TiC颗粒增强铁基粉末冶金烧结材料,并用光学显微镜(OM)和扫描电子显微镜(SEM)等手段研究了实验材料的显微组织及性能。研究结果表明:实验粉末冶金烧结材料的组织主要为珠光体、铁素体及贝氏体。随着Ti加入量的增加,珠光体含量增多,且珠光体片间距更细小,而铁素体及贝氏体组织逐渐减少。原位合成的TiC颗粒尺寸约在0.3μm,主要分布在珠光体晶粒边界处。随Ti加入量的增大,材料的表观硬度提高,而抗弯强度和密度下降。断口形貌没有表现出明显的塑性变形,属于脆性断裂。     

含石墨的青铜-钢背双金属材料的微摩擦学特征

通过粉末冶金工艺制备了含石墨的青铜-钢背复合材料,采用多功能微摩擦磨损测试仪和扫描电镜等检测分析手段,研究了石墨含量对材料的硬度、显微组织和摩擦磨损性能的影响,并考察了摩擦磨损机理。结果表明:随着石墨含量的增加,材料的硬度逐渐降低;材料的摩擦磨损性能是随着石墨含量的增加先逐渐提高,后逐步降低;在石墨含量为3%(质量分数)时,材料的平均摩擦系数、最大摩擦系数和摩擦系数变化幅度等摩擦磨损性能最佳;在既定试验条件下,合适的石墨含量和材料硬度是保证石墨能够在摩擦面上成膜良好和充分发挥固体润滑剂作用的关键。     

ZrB_2含量和烧结温度对ZrC-ZrB_2复合材料组织与性能的影响

以ZrC和ZrB_2粉末为原料,采用放电等离子烧结法在1 750℃和1 850℃烧结制备ZrB_2含量(质量分数)分别为5%,10%,15%的ZrC-ZrB_2复合陶瓷材料,研究ZrB_2含量对材料组织与性能的影响。结果表明:ZrC-ZrB_2复合材料表面形貌呈鳞片状,随ZrB_2含量增加,晶粒变细。当烧结温度为1 750℃时,随ZrB_2含量增加,材料密度降低,但断裂韧性提高,ZrB_2含量为15%时断裂韧性达到11.972MPa·m~(1/2),而ZrB_2含量为10%时,材料硬度最大,为16.868 GPa。与1750℃烧结的ZrC-ZrB_2复合材料相比,烧结温度为1 850℃时材料发生再结晶与晶粒长大,整体力学性能下降,随ZrB_2含量增加,材料密度降低,但仍有晶粒细化与力学性能升高的趋势。     

转炉炉壳热应力分析

根据实际转炉建立实体模型。以有限元为手段,考虑了炉衬和炉壳材料的物性参数随温度变化的特点和炉衬与炉壳之间膨胀间隙,计算了转炉炉壳在温度载荷和炉衬膨胀压力同时作用下的热应力。所得结果可为转炉炉壳设计提供依据。     

焦炭热性能指标意义浅析

通过对焦炭在高炉内的历程及其变化规律的剖析,阐述焦炭热性能指标的意义,形象地把焦炭在高炉内的损耗分为三部分(M1,M2,M3)。指出M2对焦比及焦炭价格有一定的指导作用。     

Results of treatment of cancer of the cardia

Cancer of the cardia is traditionally discussed with cardiac cancer of the lower portion of the esophagus and upper gastric cancer invading the esophagus, and the specific characteristics of cancer of the cardia have never been clearly defined. We reviewed the outcome of 172 patients with adenocarcinoma of the cardia who had undergone radical surgery between 1949 and 1994 in the Division of Gastrointestinal Surgery of the Cancer Institute Hospital. The centers of the tumors were located within 2 cm above and below the boundary between the esophagus and the stomach, and their longitudinal diameter was less than 8 cm. We divided the patients into an early period (1949-1979; n = 79) and a late period (1980-1994; n = 93), and focused on the historical transition. There were no differences in patient gender or histology between the two periods. However, the late period was associated with fewer cases of esophageal invasion and shorter longitudinal diameter, as the age of the population advanced. The number of advanced cancers such as the localized and infiltrative type had decreased, and early cancer and early clinical stage had become more common, but despite the fact that the number of early cancers had increased, extended dissection, such as thoracic and paraaortic lymph node dissection, was performed more frequently. By clinical stage, the long-term outcome markedly improved in Stage I patient in the late period, and tended to improve in Stage II and III patients. This appears to have been attributable to the prevention of micrometastasis by extended dissection, although the number of early cancers is another major potential cause. There were no differences in the outcome of Stage IV patients between the two periods, and further advances in multimodality therapy must be awaited. The range of resection is basically proximal gastrectomy, and if there are adequate indications, the prognosis is favorable. In view of the status of lymphatic flow and lymph node metastasis, and long-term results, lateroaortic lymph node dissection is important. Since the number of early cancer patients has been increasing, if intraabdominal recurrence is prevented, intrathoracic lymph node dissection will contribute greatly to the outcome of such patients.     

The effect of amount of possession of the trait of hostility on accuracy of perception of hostility in others.

Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of rates of infection of two methods of emergency ventricular drainage

The rates of infection of two methods of external ventricular drainage in use at Atkinson Morley's Hospital--namely, (a) percutaneous drainage with Rickham reservoirs and (b) tunnelled ventriculostomies--were compared in this retrospective review. Percutaneous drainage of CSF with Rickham reservoirs was associated with a 27% rate of infection as identified by positive microbiological cultures; tunnelled ventriculostomy catheters had a 10% infection rate. The difference in the infection rate between the two methods was statistically significant (P < 0.015). Other variables examined, including the age and sex of the patients and the reasons for ventricular drainage, were not associated with an increased rate of infection. Most infections from either method were caused by a coagulase negative staphylococcus. The average duration of ventricular drainage before identification of positive cultures was 5.7 days for Rickham reservoirs and 6.0 days for ventriculostomies.     

浅析《野草》的版画特征

鲁迅先生一生热爱美术作品,对版画中木刻兴趣尤甚.<野草>作为其"写心之作",亦呈现出一些与木刻版画一致的审美特征:一是具有木刻版画的色彩特征,多对比、多冷色,有阴郁的美感;二是具有木刻版画的力度特征,环境描写、人物刻画处处刀锋毕现,遒劲有力,有一种"力之美".     

四辊破碎机车刀架的改造

针对四辊破碎机车刀架车削中存在的几个问题,详细介绍了电动车刀架的结构和工作原理,建立主要设计参数的数学表达式,并进行适当的分析。改造后,这种电动车刀架运行平稳、可靠、方便、省力,取得了预期的效果。     

Effect of antibiotics of chemotaxis of human leukocytes

The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed.