Structure/property relationships in sintered and thermally sprayed WC-Co

Thermally sprayed WC-Co is widely used as a wear-resistant coating for a variety of applications. Although it is well established that thermal spray processes significantly affect chemistry, microstructure, and the phase distribution of WC-Co coatings, little is known about how these changes influence wear resistance. In this study, the microstructure and wear behavior of sintered and thermally sprayed WC-Co materials are examined. Powders of WC-12 wt% Co and WC-17 wt% Co were pressed and sintered, as well as thermally sprayed by high-velocity oxy-fuel (HVOF), air plasma spray (APS), and vacuum plasma spray (VPS) techniques. Results indicated considerable differences in the resulting microstructures, mechanical properties, and wear resistance. The thermally sprayed coatings showed anisotropic fracture toughness, whereas the sintered materials did not. It was also shown that a combined mechanical property/microstructure parameter, based on considerations of indentation fracture mechanisms, can be used in most cases to describe abrasive and erosive wear resistance of thermally sprayed WC-Co materials as follows: Wear resistance a whereK _ic is the indentation fracture toughness,H is hardness, andV ^Co _f is the volume fraction of cobalt. This relationship provides a means for assessing wear resistance of WC-Co coatings intended for industrial applications requiring abrasion and/or erosion resistance.     

Recent progress of CERN RD50 Collaboration

The objective of the CERN RD50 Collaboration is to develop radiation hard semiconductor detectors for very high luminosity colliders, in particular, for the upgrade of the large hadron collider （LHC） which itself is scheduled to be operational in 2007. The approach of the RD50 has two major research lines, material engineering and device engineering. These are further subdivided into projects covering defect characterization and engineering, new detector materials, detector characterization, new detector structures and full detector systems. Presently, 264 members from 53 institutes are actively participating in the RD50 Collaboration. Detectors made of defect engineered substrates, e.g. high resistivity magnetic Czochralski （MCz-Si）, epitaxial silicon （Epi-Si） on Czochralski silicon （Cz-Si） substrate, intentionally thermal donor （TD） compensated p-type MCz-Si and oxygen enriched （DOFZ） silicon, have been demonstrated by the RD50 Collaboration. An overview and highlights of the results of these defect engineering techniques were given in this report.     

内氧化法制备Al2O3/Cu复合材料的再结晶

利用内氧化法制备了Al2O3/Cu复合材料,研究了该材料在不同冷拔变形量和Al2O3含量下,其硬度值随退火温度变化的规律,并进行了显微组织结构分析。结果表明:采用内氧化法制备的Al2O3/Cu复合材料,在铜基体中弥散分布着纳米级的Al2O3颗粒;经900℃×1h退火后,其硬度可保持室温的87%以上;其再结晶温度高达1000℃;变形量和Al2O3含量增加均使硬度提高,但对软化和再结晶温度影响不大。     

压缩机阀片的失效分析与离子渗氮工艺

从断口形貌、渗氮层组织相结构、性能和残余应力的角度出发，对离子渗氮表面强化的30CrMnSiA压编机阀片进行了失效分析。结果表明，阀片的损坏主要以疲劳断裂为主；渗氮层太薄或过渗氮时都将导致阀片过早的疲劳失效；阀片的渗氮层最佳深度为30—80μm。     

激光熔覆用高硬度铁基合金的研究与应用

研究了激光熔覆Fe-Ni-Cr—B—Si合金粉末时粉末中的碳含量对于熔覆层组织、开裂敏感性、硬度和硬度均匀性的影响。结果表明，粉末含碳量的微小变化能显著改变熔覆层的组织和性能；在相同工艺条件下，粉末含碳量在一定范围内可显著提高熔覆层的硬度、降低熔覆层开裂敏感性，从而获得高硬度无裂纹的熔覆层；碳含量的增加可提高熔覆层的硬度均匀性。本文还报道了用自制Fe基合金粉末成功修复大型轧辊的实例。     

高强度高导电性铜合金强化理论的研究与应用发展

高强度高导电性铜合金在现代工业中有广泛的用途,近几年来其国内外市场需求量快速增长,目前我国已成为世界上铜合金及其产品的消耗大国.本文结合作者多年从事高强度高导电性铜合金研究与开发的实际,全面地综述了国内外对高强度高导电性铜合金强化理论的研究与应用发展,重点介绍了铜合金强化理论在实际应用中的最新研究成果.     

耐磨焊条中铁、石墨和碳化硼的优化设计

堆焊焊条设计试验采用L9（34）式正交表设计,以石墨、碳化硼和铁粉3个因素为变量,通过工艺性能定性分析,硬度值正交回归,最优化计算,得到优化试验配方和建立堆焊层金属硬度的回归方程,从而找到药皮主要成分石墨、碳化硼、铁粉对堆焊金属硬度、耐磨性等性能的影响规律.其中,碳化硼影响最大,铁粉次之,最小是石墨.随着碳化硼、铁粉、石墨增加硬度与耐磨性提高.铁粉量增加焊缝成型好,飞溅小.而石墨增加焊缝成型不好.碳化硼增加,飞溅加大.得到的最佳堆焊焊条配方,其焊接工艺性能优良,硬度值达68～71 HRC.     

硼对AZ91镁合金组织及性能的影响

研究了硼对AZ91镁合金显微组织和硬度的影响。结果表明：当B的加入量小于0．01％（质量分数）时，随硼加入量的增加，合金铸态组织和平均晶粒尺寸显著减小，布氏硬度明显提高；B加入量为0．01％时，合金平均晶粒尺寸由未加B的120μm细化到30μm左右；当加入量超过0．01％时，晶粒有粗化的趋势；分析认为具有密排六方结构的高熔点化合物AlB2（Tm=980℃）可作为α-Mg的异质核心，大量异质结晶核心的存在是使α-Mg晶粒细化的主要原因。     

钛合金表面双层辉光离子渗铝的研究

利用双层辉光渗金属技术，以铝为源极、TC4(Ti-6Al-4V)为阴极、氩气为工作气体，依靠辉光放电和不等电位空心阴极效应在TC4表面形成合金层。采用X射线衍射和辉光放电光谱分析了合金层的相组成及渗层内Al元素的分布．并对其进行硬度测试。结果表明：渗层由Ti3Al和α-Ti组成；铝的含量可达18％；渗层厚度可达13μm；其硬度比经渗铝处理后的有了较大程度的提高。     

Cu/Ti3SiC2新型受电弓滑板材料的研究

选用具有高导电、高导热性的新型陶瓷Ti3SiC2作为弥散强化相，通过与Cu的混合，采用热压和无压烧结后制备成Cu／Ti3SiC2复合材料。该材料是一种具有优良性能的新型受电弓滑板材料。实验中分析了掺杂含量、保温时间及烧结制度等因素对复合材料基本性能的影响。