粉末热挤压SiC_p/2024铝基复合材料的显微组织和力学性能

利用粉末热挤压工艺制备SiCp/2024铝基复合材料,研究所制备复合材料的挤压态和热处理态的显微组织及力学性能,分析复合材料的断口形貌和断裂类型。结果表明:大部分SiC颗粒和析出的大量细小第二相粒子均匀地分布在基体合金中,部分区域的SiC颗粒存在轻微团聚现象,晶粒沿挤压方向被显著拉长,刚性的SiC颗粒长轴平行于挤压方向分布,形成热加工纤维组织。对复合材料进行T6(490℃固溶75 min+170℃时效8 h)热处理后,复合材料的晶粒比较细小,抗拉强度达470 MPa,主要的析出强化相为S′(Al2CuMg)。挤压比的提高有利于提高SiC颗粒和基体合金的界面结合强度。粉末热挤压法制备的SiCp/2024铝基复合材料热处理后的断裂方式主要有3种:SiC颗粒断裂、SiC颗粒与基体合金的剥离和基体合金的韧性断裂,该复合材料的断裂机制为韧性断裂和脆性断裂共存的混合断裂。     

B_4C颗粒对C/C-SiC复合材料微观结构与力学性能的影响

采用浆料浸渗结合先驱体浸渍-裂解法制备B_4C颗粒改性C/C-SiC复合材料,研究B_4C颗粒对C/C-SiC复合材料力学行为的影响。结果表明,B_4C颗粒改性的C/C-SiC复合材料的抗弯强度和断裂韧性分别为250.41 MPa和13.56 MPa·m~(1/2),与C/C-SiC复合材料相比,其抗弯强度下降45.5%,而断裂韧性提高46.0%。B_4C颗粒可促进SiC基体的烧结,但由于大量闭孔和基体弱界面的形成,导致材料抗弯强度降低。B_4C颗粒改性的C/C-SiC复合材料断裂韧性提高的主要原因在于,B_4C颗粒与SiC基体中的弱界面使裂纹在SiC基体中得到有效偏转,增加了裂纹在基体中的扩展路径,使得材料的断裂韧性提高。     

高压扭转制备SiC_p/Al复合材料的断裂行为

为了研究大塑性变形对颗粒增强复合材料断裂行为的影响规律,在不同高压扭转工艺(high-pressure torsion,HPT)工艺参数下制备SiC_p/Al复合材料,测量试样真应力-应变曲线和观察试样的断口形貌,并分析SiC-Al界面的EDS谱。在分析各参数下材料断口形貌和界面原子扩散的基础上,讨论颗粒增强复合材料的断裂机理。研究发现:SiC_p/Al复合材料包含韧性断裂和脆性断裂2种性质的断裂,断口韧窝的大小和数量与材料的工艺参数有关;HPT变形可以有效改善SiC颗粒与Al基体的界面连接强度,提高该类材料的断裂性质。基体内气孔和颗粒与基体间孔隙的连接是金属基复合材料的主要断裂机制。     

热等静压法制备SiC_p/Al复合材料的组织及性能研究

采用热等静压法制备SiC颗粒增强铝基复合材料,研究其显微组织和力学性能,分析复合材料的断口形貌及断裂机制,测定了其热膨胀系数。结果表明:热等静压后,复合材料中的SiC颗粒会出现颗粒团聚,形成硬质的SiC骨架。对于20%SiC_p/6061Al(体积分数)复合材料,其抗拉强度能达到304 MPa,而20%SiC_p/2024Al(体积分数)的抗拉强度为276 MPa,两种复合材料的抗拉强度都达到或超过其他制备方法的水平。复合材料的断裂方式为基体的韧性断裂、SiC颗粒的解理断裂、SiC颗粒与基体的界面脱粘3种方式并存的混合断裂形式。对比复合材料热膨胀系数的实际测量值和Turner、Kerner模型理论值,Turner模型理论值更接近实测值。     

包覆法制备Gp/SiC 复合材料的显微结构和性能

以不同粒径的石墨颗粒和SiC粉体为原料,采用SiC粉体包覆石墨颗粒的方法,于2000℃热压制备了石墨/碳化硅(Gp/SiC)复合材料.利用扫描电子显微镜(SEM,EDS)分析了材料的金相和断口显微结构.研究表明,石墨粒径较小且质量分数较少的复合材料比石墨粒径较大且质量分数较多的复合材料在热压工艺中更致密.石墨颗粒呈岛状紧密地镶嵌在SiC基体中,石墨与SiC界面处C和Si的扩散不明显.复合材料的相对密度、抗折强度,断裂韧性和硬度随石墨粒径和质量分数的减少而增加.断口形貌表明SiC陶瓷基体为脆性,石墨为韧性断裂.当石墨粒径为125μm、SiC与石墨的质量比为3.5时,复合材料的综合性能最佳,开口气孔率为0.3%,相对密度为97.9%,抗折强度为75±15 MPa,断裂韧性为5.4±0.5 MPa.m1/2,硬度为26.8±3GPa.     

颗粒尺寸对15%SiC_p/2009Al复合材料断裂韧性的影响

采用粉末冶金+挤压工艺制备了含不同粒径SiC颗粒(3.5, 5.0, 10.0和15.0μm)的15%SiC_p/2009A1复合材料挤压棒材,利用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)和万能试验机研究了SiC颗粒尺寸对15%SiC_p/2009Al复合材料力学性能的影响。结果表明, SiC颗粒尺寸对复合材料强度和韧性的影响效果十分显著。随着SiC颗粒从3.5μm增大至15μm,复合材料的强度逐渐减小,而延伸率则逐渐增大。SiC颗粒尺寸为5.0μm时,复合材料的强度和塑性最佳,抗拉强度(R_m)、屈服强度(R_(p0.2))分别为582, 382 MPa,延伸率(A)为10%,断裂韧性(K_(IC))为33.7 MPa·m~(1/2)。SiC颗粒尺寸为3.5μm时,复合材料的断裂以SiC颗粒周围的铝基体韧性撕裂为主, SiC颗粒尺寸超过5.0μm时,复合材料断裂方式为SiC颗粒周围的铝基体韧性撕裂和SiC颗粒脆性断裂的共同作用,由于SiC-Al界面结合较好,未发现SiC-Al界面脱粘的失效形式。     

混料时间和挤压对SiC增强纯Al基复合材料显微组织和力学性能的影响

采用粉末冶金法制备SiC颗粒增强工业纯Al基复合材料,研究混料时间和挤压对复合材料显微组织和力学性能的影响。研究表明:机械混粉过程存在最佳的混料时间,混料时间为16 h时SiC颗粒分布均匀,复合材料的密度高、力学性能好。挤压可以改善复合材料的界面结合强度、减少孔洞的数量,从而提高材料的致密度和力学性能。烧结态复合材料的断裂机制以基体的脆性断裂以及增强相与基体的界面脱粘为主。挤压态复合材料的断裂以基体的韧性断裂以及SiC颗粒的脆性断裂为主,伴随着少量的基体与SiC颗粒的界面脱粘。     

高硅铝合金及颗粒增强铝基复合材料组织性能的探究

采用真空热压烧结工艺制备Al-30Si合金、30%Sip/Al、30%SiCp/2024Al、30%SiCp/6061Al(均为体积分数)复合材料,测定其热膨胀系数及力学性能。利用扫描电镜(SEM)、能谱仪(EDS)对其微观组织结构及断口形貌进行表征,探究了高硅铝合金及颗粒增强铝基复合材料的组织与性能,分析了材料的断裂机制。结果表明:SiCp/2024Al复合材料中SiC颗粒分布均匀,组织致密,综合性能好,热膨胀系数(CTE)为13.69×10-6/K,硬度达到134 HB,极限抗拉强度达353 MPa。SiCp/6061Al复合材料中SiC颗粒分布较均匀,界面结合较好,组织不够致密,有少许孔隙,性能较好。SiCp/6061Al和SiCp/2024Al复合材料的断裂方式都是界面基体的撕裂结合SiC颗粒的断裂。Sip/Al复合材料中Si颗粒分布较均匀,断裂方式为界面脱开,性能较差。Al-30Si合金在烧结过程中形成大量板条状的Si相,性能最差,断裂方式以合金撕裂为主。     

单一纳米及纳/微米SiC混合颗粒增强铝基复合材料研究

通过真空热压工艺制备了单一纳米及纳/微米SiC混合颗粒增强的Al-Si复合材料,研究了SiC颗粒的加入对复合材料的组织、致密度及硬度的影响。结果表明:纳米SiCp/Al-Si复合材料与基体合金相比晶粒细化,随着纳米SiC含量的增加,纳米SiCp/Al-Si复合材料的硬度、致密度都是先增大后减小,当纳米SiC含量为3%时硬度取得最大值64.4HV,较基体材料提高了28.8%;用扫描电镜对纳/微米SiCp/Al-Si复合材料的组织、形貌进行观察,发现微米SiC颗粒与基体合金结合紧密,界面无明显反应物生成。纳米SiC含量为3%时,随着微米SiC含量的增加,纳/微米SiCp/Al-Si复合材料的硬度、致密度都是先增大后减小,当增强颗粒含量为3%SiCnm+15%SiCμm时硬度取得最大值76.7HV,较基体材料提高了53.4%。     

颗粒尺寸及分布均匀性对SiC/Al-30Si复合材料组织性能的影响

采用真空热压法制备SiCp/Al-30Si复合材料.利用扫描电镜对材料的微观组织进行表征,检测力学性能.结果表明:随着SiC颗粒平均粒径的增大,材料的组织中SiC颗粒的团聚现象逐渐消失,其在基体中的分布更加均匀.抗拉强度与增强体颗粒尺寸有关,SiC颗粒平均粒径为13 μm时,材料的抗拉强度最大.材料的断裂方式为脆性断裂,SiC颗粒粒径为4μm时,断口表面有团聚、裸露的SiC颗粒;SiC颗粒粒径为13μm时,断口SiC颗粒表面包覆着一层铝硅合金;SiC颗粒粒径为30μm时,断口处有断裂的SiC颗粒,部分SiC颗粒从基体中被拔出.     

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.