Net shape formation of sub-micron alumina with reduced flaws by high-speed centrifugal compaction process

A new compacting method for powder materials is presented. High-Speed Centrifugal Compaction Process (HCP) utilizes centrifugal force of about 10,000 g for the compaction. HCP is suitable for net shape compaction of fine sub-micron and nano-powders. HCP possesses a unique compacting mechanism that is different from other colloidal processes including Pressure Casting (PC), and has a number of useful characteristics. HCP has a higher compacting speed than PC, wide applicability for net shape formation, as well as a defect removing function. Because of homogeneous and flawless green microstructure, HCP alumina shows superior sinterability and higher strength and hardness than most of other aluminas. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials“, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Solid phase compaction of polymeric powders: effects of compaction conditions on pressure and density variations

In a recent communication it was shown that the pressure losses during the solid phase compaction of a polymeric powder could be predicted from a simple relationship of the form:

$\text{P}{}_2\text{P}{}_1\text{=(K)}{}^{\mathrm{<mtext>h</mtext><mtext>d</mtext>}}$

where $\text{h}\text{D}$ is a function of the geometry of the compact. This has now been explored in more detail and it has been found that for PVdC and PVC the factor K is dependent on the rate of compaction and the die surface finish but is independent of compaction pressure and die diameter. To illustrate the effect of the pressure losses on the structural uniformity of the compacts, microhardness measurements were taken at a large number of points across a section of each sample. A computer plot of hardness contours provided a picture of the homogeneity of the sample which could be related to the compaction conditions and average density of the compact.     

静压挤密桩在湿险性黄土地基处理中的应用

为了解决水泥土挤密桩施工过程中噪音过大的问题,提出了地基处理的静压挤密桩施工法,并结合工程实际测试了静压挤密桩在湿险性黄土地基处理中应用的效果.测试结果表明,该方法在施工时噪音较小,施工速度高,满足设计要求,此为该地基处理方法的应用和推广提供了依据.     

Comparison of Skidding Performance of Small Track-type Experimental Prototype Skidder and J-50 Skidding Tractor

In this paper, field experimental comparison is made between a small track-type experimental prototype skidder and a J-50 skidding tractor. Experimental data, including skidding productivity, soil compaction on skidding trails, and damage rate of the residual trees, are analyzed. The results indicate that with the condition of scattered skidding area and low skidding volume per cycle, small track-type experimental prototype skidder has advantage on working and a higher skidding productivity. It makes lower soil compaction to the skidding trails in the depth of 0-5 cm, 5-10 cm, and 10-15 cm. Under the same work conditions, the damage rate of the residual trees made by small track-type experimental prototype skidder is only 1/5 of those made by J-50 type skidding tractor. The damage rate is reduced by 80%.     

温压用铁粉松装密度的优化粒级匹配试验研究

为提高温压用铁粉的流动性和松装密度，对典型粉末的粒度分布、流动性和松装密度进行了试验研究。结果表明，随温度的升高单一粒径粉体的流动性和松装密度均变差，而多粒级匹配粉末在120℃内基本保持不变，且粉体粒度分布对粉末的流动性和松装密度影响较大。通过正交试验优化了粉末的粒级匹配，获得了高松装密度的H1粉末，其流动性与国外粉W1相当，而松装密度比国外粉W1和国内粉N1分别提高了5．03％和8．99％。     

铁基粉末温模压制技术的研究

温压工艺是一种能以较低成本制备高密度铁基粉末冶金零部件的新技术，但该技术在工业化应用中，需要昂贵的设备投入及改造费用，限制了其大规模应用。论文作者利用具有优异室温润滑性能的润滑剂，以经过退火和未退火处理的雾化铁粉配制的、材质为Fe-2Ni-1.5Cu-0．5C的2种混合粉末为原料，研究制备高密度粉末冶金材料的常规压制和温模压制工艺。结果显示，粉末中较理想的润滑剂含量范围为0．1％～0．3％（质量分数），此时，润滑剂含量对压制效果影响不明显。在压制压力为763MPa、模具温度为100℃的条件下，含0．1％润滑剂的2种粉末压坯密度分别达到7．50g／cm^3和7．43g／cm^3，对应的脱模压力为34MPa和42MPa，与传统温压效果相接近，而采用传统的室温压制也可以获得7．36g／cm^3的压坯密度。     

粉末冶金高速压制技术的原理、特点及其研究进展

本文简述了粉末冶金高速压制技术(High Velocity Compaction,简称HVC)的基本原理、主要特点及其研究进展。HVC技术是一项低成本、高效率成形高密度(7.4~7.8 g/cm3)粉末冶金零件的新技术。粉末在0.02 s之内通过高能量冲击进行压制,通过附加间隔为0.3 s的多重冲击波将密度进一步提高。HVC技术拓展了PM成形技术的应用领域,具有广阔的应用前景。     

低温模压法制备的C/C-SiC复合材料的摩擦磨损性能

为深入了解低成本法制备的C/C-SiC复合材料的摩擦磨损规律,以短炭纤维、Si粉、炭粉和粘结剂为原料,通过均匀混合、模压成形、1 600℃反应烧结制备了C/C-SiC复合材料,研究了孔隙度、SiC含量及环境湿度对该复合材料摩擦磨损性能的影响,并用光学显微镜及X射线衍射仪对磨屑进行观测分析,对不同状况下的摩擦磨损机理进行研究。结果表明:C/C-SiC复合材料的致密度决定其磨损方式;SiC在摩擦过程中作为硬质支撑点,其含量对摩擦系数及其稳定性具有关键性影响;湿态时的摩擦系数与线磨损均略有下降,但仍能保持其良好的摩擦磨损性能。     

粘结剂处理的铁基混合粉的温压特性

研究的目标是结合粉末粘结技术和温压技术以制备高质量、高性能的粉末冶金材料。预粘结粉末的一大优点是能有效地降低成分偏析，因此在混粉过程中应尽量避免偏聚。本文采用两种混粉工艺制备预粘结铁基混合粉，通过不同的压制压力、不同的粘结剂含量以常温压制和温压压制制备出铁基粉末冶金材料，测量其压坯密度并进行比较分析。研究结果表明，不同预粘结工艺、压制温度和粘结剂含量对压坯密度影响很大。在一定的粘结剂含量范围内，生坯密度随粘结剂含量增加而呈线性减少。不同的预粘结工艺对生坯密度的影响随着粘结剂含量的增加而增大。     

机械合金化制备超细、纳米晶CuCr触头材料的探讨

分析探讨了机械合金化工艺制备超细、纳米晶CuCr材料中的晶粒尺寸、氧含量和材料密度控制等主要问题，提出了一种低成本制备高性能CuCr触头材料的新思路，即添加高性能晶粒长大抑制剂 普通真空烧结工艺。