石墨填料对浸渗热解-熔融浸渗方法制备的C/SiC复合材料结构和性能的影响

采用石墨树脂浆料浸渍三维针刺碳毡增强体,热解后得到C/C多孔体,并采用反应熔体浸渗法制备C/SiC复合材料.研究了石墨填料对C/C多孔体的结构以及C/SiC复合材料力学性能的影响.结果 表明,石墨树脂浆料浸渍时树脂填充束间小孔形成结构致密的亚结构单元,而石墨可以有效填充胎网层等大孔隙,一次浸渍热解后碳产率有效提高.所得...     

BCu93P丝状钎料的断裂分析

针对BCu39P钎料丝材在热挤压过程中易产生断裂，质量不稳定等缺陷，用金相法和扫描电镜（SEM），分析和研究了该钎料丝材的内部组织分布和断口形貌，找出了引起钎料断裂的原因，并提出了解决措施和钎料内部组织分布的理想模型。     

添加镍粉和二硼化锆防静电涂层的对比研究

对添加镍粉和二硼化锆涂层的导电性进行了对比试验，讨论了添加型防静电涂层的防静电机理。试验结果表明：添加型防静电涂层导电通路的形成是导电粒子的直接接触和隧道效应综合作用的结果。文中还推导了计算涂层中导电粒子间距的近似公式。     

用急冷Al基活性钎料钎焊Si3N4陶瓷的研究

研制了三种急冷Ａｌ基活性钎料。研究结果表明：急冷Ａｌ基活性钎料的组织明显细化，熔点明显下降，基体硬度升高。在较低的钎焊温度（７５０℃）下，下加Ｎｉ粉的接头的剪切强度较高（２０８．８ＭＰａ）。钎焊温度对接头强度影响较大。当超过一定钎焊温度后，接头强度明显下降；加Ｎｉ粉复合钎焊可明显提高接头的剪切强度，在钎焊温度为８００℃时接头的最高剪切强度为２２５ＭＰａ，加Ｎｉ粉的复合接头在界面两侧形成均匀分布富Ｎｉ带。这是接头强度提高的主要原因。     

填料的表面改性及其对涂层力学性能的影响

研究了填料经硅烷偶联剂和自制的处理剂进行表面改性后对涂层力学性能的影响.借助扫描电镜进一步分析了填料在树脂中的分散情况.结果表明填料经后一种方法处理后,与树脂基体相容性明显改善,涂层力学性能得到了显著提高.     

含硼镍基钎料钎焊IC-6合金接头显微组织分析

通过对Ni-B钎料在1220℃保温不同时间钎焊IC-6合金接头显微组织的分析,研究了钎缝中γ+γ′组织及近缝区硼化物的形成和变化.结果表明,仅依靠母材中Al元素的扩散钎缝中也能形成γ+γ′组织,但存在大量晶界,对接头高温性能不利.近缝区出现两种类型的硼化物,其Ni和Mo原子比分别近似为1∶1和1∶2,形貌和分布随保温时间不同而变化.     

保温时间对K452高温合金钎焊接头组织与性能的影响

采用钴基钎料及镍基合金粉料,分别在1170℃保温10min、60min和120min的钎焊工艺下,对K452镍基铸造高温合金进行真空钎焊实验,通过扫描电镜和能谱分析仪进行了接头显微组织观察与物相分析,并测试钎焊接头的高温力学性能。结果表明:在保温60min的工艺规范下,界面实现较好的结合,钎缝内部孔洞缺陷较少,钎缝组织均匀,有利于钎焊接头性能的提高;在更长的保温时间120min下,钎缝内部又有蚀孔缺陷形成,且较多的白色块状化合物在合金粉颗粒间聚集长大,但界面结合良好,钎焊接头性能较高,900℃抗拉强度达到400MPa,900℃/100MPa持久寿命为141h55min。     

大间隙钎焊用混合粉状高温镍基钎料的润湿性和显微组织

用一种含Al,Ti元素的镍基钎料粉末与γ’相沉淀强化型镍基高温合金FGH95的粉末混合,制备了大间隙钎焊用混合粉状高温镍基钎料。实验表明,采用合适的混合比例,混合粉状钎料对1Cr18Ni9Ti不锈钢具有较好的润湿铺展性。该混合钎料所获得的钎缝金属的合金化效应显著,Al+Ti合金元素的最大含量达到了5.49%。焊态钎缝中,除Nb,W等个别元素外,其他主要强化元素无明显偏析,且经1180℃/4h扩散处理可消除合金元素的偏析。钎缝金属的组织状态较为均匀,基体为等轴γ固溶体枝晶,枝晶间分布有颗粒状、短条状的化合物相以及少量的γ+γ’共晶组织。另外,在γ固溶体中分布着大量弥散细小γ’沉淀强化相。     

Wetting behavior of AgCu-4.5Ti filler reinforced by carbon nanotubes on C/C composite

The effect of Carbon Nanotubes (CNTs) content on the wettability of AgCu-4.5Ti + x CNTs (wt%) composite filler alloys on C/C composite was investigated. The results show that the added CNTs reacted with element Ti in the filler and produced the dispersed fine in situ synthesized TiC particles, which increased the consumption of element Ti and provided the nucleus for the growth of Ti-Cu compounds simultaneously. The above effects of introducing CNTs, inhibited the formation of Ti-Cu compounds, also changed the distribution of compounds, which dramatically influenced the interfacial microstructure and characteristics of wetting behavior. The increase of CNTs content refined and dispersed coarse Ti-Cu compounds, decreased the initial spreading temperature, and improved the wettability, but high content of CNTs (more than 0.3wt%) decreased the wettability of the filler alloy. The wetting interfacial microstructure of corresponding composite filler alloys were analyzed by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectrometer (EDS) and Transmission Electron Microscope (TEM), which consisted of TiC, TiCu, TiCu₂ and TiCu₄ compound. The typical wetting behavior of AgCu-4.5Ti + 0.3wt% CNTs composite filler on C/C composite was divided into four stages. The effect mechanism of CNTs content on the wetting behavior was proposed.     

Brazing diamond grits onto AA7075 aluminium alloy substrate with Ag–Cu–Ti filler alloy by laser heating

The brazing of diamond is a promising way to fabricate grinding wheels for efficient machining and precision grinding. This work investigated the feasibility of bonding diamond grits onto Aluminium Alloy 7075 (AA7075) substrate with a Ag–Cu–Ti filler alloy via laser fusion brazing. The interfacial microstructures and the strength of the brazed diamond joints were studied. The cross-section of the brazed diamond joint consists of a molten filler alloy layer, a molten pool, a heat effect zone, a columnar crystal zone and an equiaxed crystal zone. Within the interface of the filler alloy/substrate metal, microstructures observed possibly were Ag(s.s), Al(s.s), TixAl, Al2Cu and Mg intermetallic compounds. A layer of TiC with a thickness of about 30–50 nm was found at the bonding interface of the diamond/filler alloy. The averaged peak shear force of the brazed joints was found to be approximately 39.8 N. The abrasion grinding test indicated that the diamond/AA7075 brazed joint was adequate for grinding. However, the pulled-off of grit was found to be the primary failure of this type of brazed joint. This work broadened the brazing diamond technique and the range of applications of brazed diamond wheels for efficient grinding.