提高三角形金刚石多晶烧结体耐磨性的研究

采用粉末冶金方法进行人造金刚石多晶体的烧结。研究了提高多晶烧结体耐磨性的方法。通过工艺配方的确定、合成条件的选择、调整真空净化处理工艺以及使用高品质人造金刚石等措施，提高了多晶烧结体的耐磨性。     

MORPHOLOGICAL STUDIES RELATING TO THE FRACTURE STRESS AND FRACTURE TOUGHNESS OF SILICON NITRIDE

Abstract— Microstructure and mechanical properties of HP (Hot Pressed), HP/GP (Gas Pressed), and HP/HIP (Hot Isostatic Pressed)—Si₃N₄ are studied using scanning electron microscopy, bending tests and the indentation fracture method. The grain diameter distribution is analyzed to clarify the relationship between microstructure and mechanical properties; and also the bending strength and fracture toughness. It is shown that bending strength increases with decreasing grain diameter. The results also show that a Hall—Petch type of relationship is obtained between grain diameter and fracture strength. The fracture toughness shows a linear relationship with , where σ_F= bending strength, β= a proportionality factor and d _a= average grain diameter, and is closely related to the aspect ratio of Si₃N₄ grains. It is concluded, from the morphological analysis, that a microstructure composed of Si₃N₄ grains, with both a small grain diameter and a large aspect ratio, is effective in improving both the fracture strength and fracture toughness.     

TiB_2基烧结材料的研究现状与进展

TiB_2基烧结材料再度受到材料研究者的关注,是因为它有一系列优异性能,并将成为新一代的陶瓷和硬质合金。本文报导了近几年国外对TiB_2基烧结材料研究现状和进展。     

Densification and anticorrosion performances of vacuum evaporated aluminium coatings on NdFeB magnets

Al coated NdFeB magnets obtained by vacuum evaporation technique were densified by high energy ball milling method.The surface morphology,metal composition and micro structure of the coatings were characterized by scanning electron microscopy,X-ray diffraction and X-ray photoelectron spectroscopy,respectively.The anticorrosive properties were investigated by potentiodynamic polarization curves and neutral salt spray test.The pores in the Al coatings of columnar crystals(Al) induced by the evaporation technique,were apparently filled in the following ball milling process,leading to the densification of Al coatings and the evident improvement of the anticorrosive performances.When treated with ball milling for 30 min,the sample achieves the best anticorrosive performances with the self-corrosion potential of-0.87 V,self-corrosion current density of 1.65 μA/cm~2 and the neutral salt spray(NSS) time of 144 h(red rust).The improvement of the anticorro sive performances of vacuum evaporated Al coating mainly lies in the densification effect of the coating,which depends on different loading conditions of ball milling process.     

The indentation size effect of sintered Fe/3.3 wt-%Cu + CnHm measured by Vickers scale

ABSTRACT

The aim of the submitted work is to study the influence of applied loads (test forces) between 0.09807 and 2.9421?N on the measured value of micro-hardness of sintered Fe/3.3?wt-%Cu?+?C_nH_m. The Indentation Size Effect (ISE), i.e. the influence of the load on the micro-hardness is expected. The results were evaluated by Meyer’s index n, t-test, and non-parametric tests. The applied load has a statistically significant influence on the type and size of the ISE. Tested sintered material shows ‘normal’ ISE with Meyer’s index n?=?1.7588.     

Comparative study on the densification process of different titanium powders

In the powder metallurgy of titanium and titanium alloys, titanium powders produced through hydrogenation/dehydrogenation (HDH) approach and titanium hydride powder are extensively used. The choice of initial powder greatly influences the properties and performance of as-sintered materials. In the present study, comparative experiments were performed on two powders of various sizes to elucidate the peculiarities of their densification process and the characteristics (as-sintered density, impurity content, and tensile properties) of the processed materials. As expected, the sintering performance of both powder-type compacts were greatly affected by the specific surface and contact areas, so finer powders and higher compaction pressures were used to achieve higher densities upon sintering. However, the systematic results clearly indicated the advantage of using titanium hydride powder as a starting material in titanium powder metallurgy. At equal size, compaction, and sintering parameters, materials processed from titanium hydride powder had higher density and lower impurity content, thereby providing better balance of tensile properties compared with materials processed from HDH titanium powder. This advantage is explained by the higher relative density of green compacts made of brittle titanium hydride powder and by the higher sintering ability of such compacts activated by powder-released hydrogen.     

湿式烧结金属摩擦片缩比模拟试验

湿式烧结金属摩擦片的摩擦性能测试,一般用实物在试验台架上进行,但国内大多厂家不具备建立试验台架的条件。本文介绍以一定比例缩小摩擦片实物尺寸,应用MM-15型多片式摩擦片离合器试验箱,模拟工况条件,进行摩擦片的摩擦系数、磨损率、滑磨功、滑磨功率及能量负荷许用值测试和计算,可以取得台架试验同样满意的试验结果。     

工艺条件对高性能石英砂烧结砖的显微结构影响研究

本文研究了利用低品位石英砂在不同工艺条件下制备的高性能石英砂烧结砖的显微结构,并通过显微结构与成型方法、成型压力、烧结温度及保温时间的关系分析,确立该烧结砖得到最高性价比时的最佳工艺条件.结果表明:该烧结砖采用100MPa冷等静压成型,在1150℃烧结2h的制备工艺所得的砖的显微结构最佳.     

烧结钕铁硼基底成分对晶界扩散效果的影响研究

晶界扩散作为一种能明显提升烧结钕铁硼磁体矫顽力同时实现对重稀土高质化利用的方法,日益成为目前稀土永磁学界和产业界的研究热点。本文利用自动化喷涂设备系统研究了晶界扩散烧结磁体批量制备过程中基底成分差异晶界扩散后磁体磁性能的影响,微观结构和EDS元素分析结果表明：晶界扩散后磁体矫顽力增长幅度的差异,同扩散后磁体内晶粒核壳结构形成充分与否、晶界相均匀分布与否和晶界相铁磁性元素含量高低有密切关联,同时利用晶界扩散工艺制备得到的磁体温度系数要优于传统工艺制备得到的相近似牌号的磁体。     

烧结式镍基板化学浸渍过程研究'

对烧结式镍基板的真空化学浸渍过程及机理进行了研究.提出了计算浸渍量的数学式,并讨论了影响浸渍量的因素,提出解决后期浸入率下降的新方法.