温压工艺在粉末冶金中的研究与应用

介绍了温压工艺的特点及其致密化机理，并对粉末冶金研究中温压工艺参数的选择、温压材料的性能及聚合物的加入方式和选取原则进行了讨论。在此基础上，提出了今后温压工艺的研究发展方向和应用前景。     

粉末冶金温压工艺的技术特点及其新发展

本文概述了温压工艺的特点及其最新的发展,如流动温压、热模压制等,重点讨论了热模压制工艺的技术特点与应用,并指出以AncorMax D为代表的热模压制工艺由于工序比常规温压工艺更简单,压制温度更低,因此在将来很有可能取代常规温压工艺,成为高密度粉末冶金零件的一种非常有应用前景的方法.     

温压法制备铜铅轴承合金的研究

通过温压工艺制备了铜铅轴承合金材料 ,研究了温压成形温度和压力等因素对压坯致密化和烧结体性能的影响。结果表明 ,温压成形时可用经典的压制方程来描述粉末体的压形规律。温压温度的选择对压坯及烧结体的性能都有明显的影响 ,在合适的工艺条件下 ,温压法较冷压烧结法可制得更高密度和性能的铜铅轴承合金材料。     

温压法制备铜铅轴承合金的研究

通过温压工艺制备了铜铅轴承合金材料，研究了温压成型温度和压力等因素对压坯致密化和烧结体性能的影响，结果表明，温压成形时可经典的压制议程来描述粉末体的压形规律，温压温度的选择对压坯及烧结体的性能都有明显的影响，在合适的工艺条件下，温压法较冷压烧结法可制得更高密度的铜铅轴承合金材料。     

温压工艺在粘结NdFeB磁体中的应用

采用温压工艺与普通压制工艺制备粘结磁体，发现温压技术可以有效地提高粘结磁体的密度，改善磁体磁性能，且温压效果与温压温度的选择密切相关。通过对温压机理的分析，发现最佳温压温度由粘结剂的软化点、粘度和固化点三个因素共同决定。采用温压工艺，在70℃、97．4NPa的条件下，得到的粘结NdFeB磁体密度、最大磁能积分为5．28kg／m^3,6．23NGOe。     

铜基电触头材料温压成型工艺的研究

研究了铜基电触头材料的温压行为,通过温压试样性能分析得出了最佳的温压工艺参数,并与冷压压制试样的性能进行了比较.结果表明,在相同压力下,温压试样的电阻率、硬度和抗氧化性明显比冷压试样的好;压制温度的最佳值是130℃,润滑剂的最佳添加量为0.7%(质量分数).     

流动温压成型黏结钕铁硼/锶铁氧体复合磁体的研究EI北大核心CSCD

采用流动温压成型工艺制备黏结钕铁硼/锶铁氧体复合磁体,研究温压工艺参数对钕铁硼/锶铁氧体复合磁体磁性能的影响。结果表明:随着温压温度、压制时间以及保压压力的提高,黏结复合磁体的磁性能呈现先增大后减小的趋势。流动温压成型参数的选择与黏结剂有关,采用酚醛环氧树脂BPANE8200为黏结剂时,流动温压成型的最佳工艺参数:77℃加载900MPa并保压8min,复合磁体的剩磁B_r、内禀矫顽力H_(cj)以及最大磁能积(BH)max均获得最大值,即Br=522mT,Hcj=740.48kA/m,(BH)max=39.82kJ/m^3。     

木质粉末高密度滑动轴承无胶温压成形结合机理研究

按照木质粉末高密度滑动轴承制备工艺(160℃,70 MPa,保温、保压30 min),对小于350μm的杨木粉末的三级抽提物纤维素-木质素-半纤维素复合体、纤维素-木质素复合体和纤维素实施无胶温压成形,分析温压前后各样粉的微观结构、物相、官能团、纤维素结晶度等的变化情况。结果表明,木质粉末中的纤维素、半纤维素、木质素在无胶温压成形过程中均发生了化学反应,产生了化学链接。温压成形可改善各级抽提物的化学结构,提高其化学结合程度与纤维素结晶度,使其一体化、致密化、塑化程度与热稳定性明显提高。综合温压成形工艺成本与温压材料特性表征,以杨木粉末为基材制备生物质功能材料(如滑动轴承)宜采用一级抽提物或原粉。     

模壁润滑温压工艺的研究

对模壁润滑温压工艺进行了较为系统的研究,分析了温度、粉末中润滑剂添加量、模壁润滑剂种类及其浓度等对温压效果的影响.结果表明,粉末温度在100℃时温压效果最好;Fe-1.5Cu-0.5C粉末中添入0.2%内润滑剂时效果最好,而Fe-1.5Ni-0.5Mo-0.5Cu-0.5C粉末中最佳润滑剂含量为0.3%;模壁润滑剂A、B分别适合于较低和较高压制压力条件,2种模壁润滑剂均在浓度低时温压效果较好;在686MPa时,Fe-1.5Cu-0.5C和Fe-1.5Ni-0.5Mo0.5Cu 0.5C粉末分别获得了7.48、7.39g/cm3的压坯密度;模壁润滑温压工艺较适用于压缩性良好的粉末,对压缩性较差的粉末没有优势;模壁润滑工艺的脱模压力比内润滑工艺小35%～45%,可以减少模具损耗.     

压扭工艺改善钼粉末温压成形的模拟分析

运用MSC.Marc有限元仿真软件,采用基于更新拉格朗日方法的热-机耦合分析方法,模拟了钼粉温压和温压扭成形过程,获得了2种工艺条件下的粉坯相对密度分布规律,验证了有限元模型的可靠性。结果表明:压扭工艺可以减小粉坯端面边缘处相对密度分布梯度,增大侧壁附近粉末变形量,并显著提高平均相对密度及相对密度分布的均匀性。     

粉末高速压制成形密度分布的数值模拟及影响因素分析

将研究不连续体力学行为的离散单元法应用于粉末高速压制致密化过程的研究,将粉末视为黏弹性的离散颗粒,建立粉末高速压制过程颗粒接触模型及每个颗粒的基本运动方程,推导了力与位移表达的粉末高速压制黏弹性本构关系。基于PFC软件实现了铁粉高速压制过程中粉末颗粒二维流动情况及压坯密度分布的数值模拟,模拟结果的密度分布规律与实际压制的密度分布规律较为一致;利用数值模拟结果对影响压坯密度分布的摩擦因数、高径比、双向压制因素进行了具体分析。     

粉末冶金高致密化的新途径

针对粉末冶金行业近年来出现的提高制品致密化的新途径，重点综述了温压技术、模壁润滑技术、动态磁力压制技术、爆炸压制技术、高速压制技术、等离子放电烧结技术的原理、特点和应用情况。     

高心墙堆石坝坝面碾压施工仿真理论与应用

在对高心墙堆石坝坝面碾压系统进行全面分析的基础上,提出了以填筑单元为仿真单位的碾压施工仿真理论,建立了能够反映碾压过程中不确定因素的精细化仿真模型,保证仿真贴近实际施工。研究成果在糯扎渡心墙堆石坝工程的填筑单元中得到了应用,验证了方法的可靠性,对于大坝现场碾压施工具有指导意义,为工程进度控制和管理提供了技术支持。     

Creep compaction behavior of 3D carbon interlock fabrics with lubrication and temperature

This study aims at understanding and improving the compaction of 3D carbon interlock fabrics with water lubrication, high temperature and a combination of them. The creep compaction behavior was characterized in a mechanical testing machine under different lubrication and temperature conditions. Three different interlock fabrics were studied at high temperature in order to assess the influence of the weaving pattern on the creep compaction behavior. Finally, an experimental study was carried out to point the impact of fiber sizing on the creep compaction behavior and its evolution with temperature. The results of this work demonstrate the strong impact of temperature and lubrication on the compaction ability of 3D interlock fabrics and its link to the fiber sizing.     

芦苇秆粉末高密度材料无胶温压成形与表征

为寻求高质清洁利用农林木质剩余物的新途径,运用响应面实验设计与分析方法对芦苇秆粉末实施无胶温压成形,制备高密度木质材料,用三维立体数码显微镜、扫描电子显微镜、傅里叶红外光谱、核磁共振光谱、热重分析和热解析-气相色谱/质谱联用分析技术对试件的微观结构、物相、纤维素结晶度、热脱附挥发物进行研究。结果表明,芦苇秆粉末粒度对试件性能的影响不明显;芦苇秆粉末在压力、温度、时间的复合作用下,木质素发生软化与流展,纤维素的结晶度得以提高,粉末颗粒间发生化学反应并产生化学链接;芦苇秆粉末的最优无胶温压工艺条件:成形压力为70 MPa,成形温度为160℃,保温保压时间为30 min;在最优工艺条件下制备的木质材料塑化明显,质硬而耐磨,具有韧性断裂特征,且在40、60、90、160℃环境温度下的挥发物中,有益、有害成分的种类和芦苇杆原粉相当,但有益成分的总含量远高于原粉,表明温压成形工艺具有环境友好性,无胶温压成形可以获得高品质人工木质材料。     

Size Ratio Effects on Particle Contact Evolution at Uniaxial Powder Compaction

Cold compaction of composite powders has been analyzed using a discrete element method (DEM). Powder aggregates consisting of up to approximately 10,000 particles and formed by two powder populations with known material strength and size ratios have been compacted both isostatically and uniaxially (die compaction). The particles were assumed constitutively to be perfectly plastic or rigid and as a result, local contacts between the particles were described by a linear force-displacement relation given by previous in-depth analyses of spherical indentation problems. Particular emphasis has been placed on investigating the particle contact evolution at die compaction and to compare the results with previous ones pertinent to the isostatic case. Consequently, the predictive capability of the fundamental assumptions frequently used in theoretical analyses of compaction problems is determined for a uniaxial situation. The main conclusion is that size ratio effects are substantial at die compaction and when such features are present, theoretical predictions overestimates the (average) number of contacts per particle. It was also found that the mechanical behaviors at isostatic and die compaction are very similar even though die compaction values are slightly higher at high values on the relative density of powder materials.     

深厚砂土地基共振致密机理

利用颗粒离散元对深厚砂性土地基进行共振致密模拟与机理分析,详细地研究了高频共振致密过程中,土体内部孔隙率、位移、孔隙水压力的变化情况,以及振动杆杆端及杆周土体的力学特性;对振动频率、振幅及颗粒级配对共振致密效果的影响进行了分析。结果表明:高频共振致密能很好地用于处理深厚粉砂土地基,振动结束后,土体的孔隙率明显减小,表层位移明显,振动杆杆端及杆周的土体力学特性也发生较大变化;共振致密的效果受振动杆振幅、频率及土体级配状况等因素的影响,振幅和频率过大或过小都无法获得最佳致密效果。在实际工程中,应根据土体的特性确定最佳的振幅和频率。     

Sintering of ultra high molecular weight polyethylene

Ultra high molecular weight polyethylene (UHMWPE) is a high performance polymer having low coefficient of friction, good abrasion resistance, good chemical resistance etc. It is used in shipbuilding, textile industries and also in biomedical applications. UHMWPE is processed by powder processing technique because of its high melt viscosity at the processing temperature. Powder processing technique involves compaction of polymeric powder under pressure and sintering of the preforms at temperature above its melting point. In this study, we report our results on compaction and sintering behaviour of two grades of UHMWPE with reference to the powder morphology, sintering temperatures and strength development.     

The hot compaction of polyethylene terephthalate

A process is described for the successful compaction of polyethylene terephthalate fibres. The measurement of mechanical properties shows that a very high proportion of the original fibre properties are retained and that the compacted samples have a good degree of coherence. Electron microscopy studies of suitably etched samples reveals the effect of the compaction temperature on the structure of the compacted samples.     

Effect of aspect ratio on the compaction characteristics and micromorphology of copper powders by magnetic pulse compaction

Magnetic pulse compaction (MPC) technology has the advantages of near net shape, high efficiency and density. In this paper, the effect of aspect ratio on the deformation characteristics of copper powders compacted by MPC technology was studied. Specifically, the compaction velocity, volume strain, micromorphology and micro hardness of compacts at various aspect ratios were obtained. Results showed that the compaction velocity and volume strain increased and then decreased with the increase of aspect ratio. The maximum compaction velocity reached 10.28 m/s at aspect ratio of 1.2. At the same compaction moment, the volume strain was decreased as the aspect ratio increased. Then the relationship between compaction pressure and volume strain was revealed. The aspect ratio range of the optimal compaction effect was 0.6–1.0, and the fluctuation degree of relative density was only 1.03%. The aspect ratio had less effect on the micromorphology distribution in the axial direction of the compacts. The micro hardness value of the upper surface was higher than that of the lower surface, and the edge position was greater than the center position.