压制方式对锆钛酸铅压电陶瓷密度及性能影响的研究

将低电压电磁成形引入陶瓷粉末成形,以锆钛酸铅(PZT)粉末为研究对象,采用间接加工方式对其进行低电压电磁压制.结果表明,相比于模压成形,通过选择放电参数,低电压电磁压制能提高PZT陶瓷压坯密度并改善陶瓷体的烧结性能.密度测试结果表明,经电磁压制后烧结的PZT制品密度较高.通过电性能参数测试,经电磁压制后烧结的PZT制品压电常数、相对介电常数、机电耦合系数均较高,介质损耗较低.     

工艺参数对高铟高锡银基钎料粉末电磁压制成形的影响

根据离散元相关理论, 利用EDEM软件对高铟高锡银基钎料粉末电磁压制过程进行仿真模拟, 探究工艺参数对Ag–Cu–Sn–In系钎料压制过程中的影响规律, 分析钎料粉末的致密化行为, 并研究Sn元素和In元素对钎料粉末相对密度的影响; 在不同电压和电容条件下, 对Ag–19.5Cu–15In–15Sn钎料粉末压制过程进行了仿真模拟, 分析不同放电参数对压坯相对密度的影响; 最后通过压制设备制备钎料压坯, 对仿真结果进行验证。结果表明, 在相同压制力下, In质量分数越高, 获得的压坯相对密度越大; 在电容相同的情况下, 电压越大压坯的相对密度越大, 但增幅逐渐减缓; 在电压相同的情况下, 电容越大压坯的相对密度越大, 但增幅大致不变。实验验证结果表明, 仿真误差小于8%, 钎料电磁压制离散元仿真模型具有一定的参考价值。     

烧结温度等参数对Fe2O3粉末烧结密度影响的试验研究

针对烧结温度等参数对Fe2O3粉末压制烧结密度的影响进行了试验.结果表明:在实验条件相同情况下,粉末粗细颗粒比在85%时压坯密度最高;随着压制压力的升高,在400MPa以下压坯密度上升速率较大,在400～650MPa之间压坯密度呈平台型和上升型交替趋势;烧结块在最终烧结温度为1240℃烧结获得的密度最高.     

粘结化铁基粉末的高速压制成形与烧结行为研究

研究了采用粉末改性处理和高速压制相结合的技术制备高密度铁基粉末冶金材料的工艺。所用的粘结化铁基粉末的名义成分(质量分数)为Fe-1.5Ni-0.5Cu-0.5C;重点研究了压制能量和粉末塑化改性对压坯密度的影响,以及高密度压坯的烧结致密化行为。结果表明:粘结化铁基粉末具有较高的流动性(25.1s/50g)和松装密度(3.2～3.4g/cm3)。未经塑化改性处理的粉末随着压制速度的增加,压坯密度提高缓慢,在8.7m/s高压制速度下,压坯密度为7.37g/cm3。塑化改性处理粉末具有优异的塑性变形能力,压坯密度随着冲击能量的增加而迅速增大,在6.2～8.7m/s的压制速度范围内,压坯密度为7.07～7.62g/cm3。经过8.7m/s高速压制和1 150℃烧结后,烧结体密度达到7.51g/cm3,相对密度为96.5%。     

钛合金粉末热复合磁脉冲压制试验研究

采用热复合磁脉冲成形方法对钛合金(牌号为TC4)粉末进行了成形试验研究.通过压坯平均致密度和光学金相分析,揭示了加热温度、放电电压和复压次数等成形条件对TC4粉末热复合磁脉冲成形压坯致密度的影响规律.结果表明,压坯致密度不随温度升高而线性增加,300 ℃时的致密度最高.在给定放电能量和300 ℃下,压坯致密度随电压和复压次数的增加而提高.     

超声振动对纯铁粉压坯密度的影响

为提高粉末冶金制品的密度,提出超声粉末压制的新方法,以纯铁粉为原料进行压制实验,研究超声振动对粉末冶金制品密度的影响。研究结果表明:超声振动能促进粉末颗粒内部的运动与重排,降低粉末颗粒与模壁之间的摩擦,同时也有利于降低粉末塑性变形阶段的冷焊与加工硬化程度;与常规压制相比,超声压制的压坯密度提高0.1～0.3 g/cm3,轴向最大密度差降低0.16 g/cm3,孔隙率降低4.3%;随着压制力提高与压制时间增加,超声振动对提高压坯密度的效果更明显,粉末压坯密度进一步提高。     

高速压制制备高密度纯铁软磁材料

以退火纯铁粉末为原料,采用粉末退火结合高速压制技术的方法制得高密度压坯(7.70 g·cm-3),经烧结后获得高密度高性能的纯铁软磁材料.研究退火粉末的高速压制行为,以及烧结时间和烧结温度对材料磁性能和晶粒大小的影响.结果显示:退火粉末的压坯密度随压制速度的增加而增加,压坯密度最高可达到7.70 g·cm-3,相对密度可达到98.10%.烧结温度为1450℃,烧结时间为4 h时,材料密度达到7.85 g·cm-3,相对密度为99.96%,最大磁导率达到13.60 m H·m-1,饱和磁感应强度为1.87 T,矫顽力为56.50 A·m-1.      

冲击电流对汽车零件用粉末压制过程的致密作用

采用氧化锆做绝缘阴模材料,设计研制能对压制中的粉末施加冲击电流的模具。研究电容组在不同的充电电压下,对处于不同压制压力下的汽车带轮用粉末瞬时放电,当电能以冲击电流的形式通过后,可引起压坯密度的变化。实验结果表明,施加冲击电流后,压坯密度增加,充电电压越高或粉末压坯初始密度越低,冲击电流对压坯密度增长的贡献越大。冲击电流作用后压坯温度升高,直径发生收缩,说明压坯密度增加是冲击电流的热效应与电磁效应共同作用的结果。     

装粉方式对钛粉压制成形影响的数值模拟

用MSC.Marc软件模拟了在3种不同装粉方式下钛粉压制成形过程中粉末的流动情况以及压坯的密度分布规律。研究结果表明:装粉方式对粉末压制过程及压坯密度具有较大的影响,与平式装粉方式相比,采用凸式装粉,试样的烧结坯密度提高6％,孔隙分布的均匀性得到相应的改善。     

高纯金属钒粉烧结性能研究

利用电子探针观察高纯金属钒粉粒度和形貌, 使用油压机将高纯金属钒粉压制成坯条, 并采用万能试验机测定钒坯条压溃变形力曲线, 分析钒坯条最优压制压力; 分别通过热压烧结和冷等静压+真空烧结的方法对高纯钒粉进行烧结, 研究烧结工艺对高纯钒粉烧结特性和力学性能的影响。结果表明: 采用冷等静压+真空烧结的方法, 在压制成形过程中, 钒粉压坯密度和相对密度随压力的增加而逐步提高, 压力提高到280 MPa时, 压坯密度和相对密度分别为3.99 g·cm-3和66.94%;经真空烧结后, 坯料密度和相对密度分别为5.28 g·cm-3和88.59%。压制压力由80 MPa提高到200 MPa时, 压溃强度从0.4 MPa增加到6.0 MPa, 增大趋势较为明显; 压制压力提高到280 MPa时, 压溃强度增加到7.4 MPa, 增大趋势变缓。经热压烧结坯料的相对密度比冷等静压+真空烧结坯料的相对密度高, 280MPa压力下热压烧结坯料密度和相对密度分别达到5.51g·cm-3和92.91%。     

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。     

Study of warm compaction of Alumix 123 L

Abstract

Although powder metallurgy (PM) material is dominated by ferrous alloys, there is a growing interest in Al PM. The usage of Al PM in automotive applications depends on the development of higher density and improved dynamic properties. Several approaches have been proposed to increase density of sintered parts. Warm compaction process of Al powder was used to achieve high density. In this study the authors focused on the effect of warm compaction on Alumix 123 L (ECKA Granules) powder blend. It has been found that warm compaction at 110°C led to a reduction in the ejection force by 27·9%, increased green density to 94% of theoretical density and increased sintered strength to 315 MPa as compared to those pressed at room temperature.     

New technological approach to fabrication of high density PM parts by cold pressing sintering

Abstract

A new technological approach to the fabrication of high density powder metallurgy (PM) parts via single pressing sintering, allowing cold compaction to be performed without admixed lubricants, has been studied. The influence of in pore gas on the compacts' green density and their sintered properties were evaluated. A mathematical expression relating in pore gas pressure in the compacts to the green density was developed. The expression showed that in order to reduce the negative influence of gases trapped in the pores it is necessary to ensure effective air drainage from the compaction zone. In order to ensure sufficient air evacuation during cold compaction, a new design of porous die was developed. The behaviour of powder mixes with different lubricants during cold compaction in porous die was investigated. All the test conditions were evaluated in terms of green and sintered properties, including the ejection force, green and sintered densities, tensile strength and surface hardness. In the context of the experimental work, compaction in porous die promoted the improved combination of green and sintered properties compared with compaction in conventional dies.     

粉末冶金工艺对纯铁软磁材料性能的影响

利用粉末冶金技术制备纯铁软磁材料,在不同温度和压力下将不同粒径铁粉压制成生坯,并在保护气氛下进行烧结。结果表明:不同粒径铁粉混合有助于压坯密度的增加,适宜的压制温度可以有效地促进粉末流动,避免大尺寸孔洞的形成,优化组织。140℃、800 MPa温压条件下雾化铁粉压坯密度最高可达7.35 g·cm-3。对比常温压制,温压压坯烧结后孔洞分布均匀。烧结体密度随温度的升高而上升,雾化铁粉压坯在1250℃烧结后密度最高可达7.47 g·cm-3。在一定范围内,软磁材料磁性能与密度成正比,混粉压制试样的密度接近理论值,但在混合铁粉中,较细的铁粉夹杂于粗粉中,阻碍磁畴壁移动,造成饱和磁化强度（M_s）偏小、矫顽力（H_c）偏大的现象,M_s为205.51 emu·g-1,Hc为7.9780 Oe。     

Comparison of sintering of titanium and titanium hydride powders

Abstract

The cold compaction and vacuum sintering behaviour of a Ti powder and a Ti hydride powder were compared. Master sintering curve models were developed for both powders. Die ejection force, green strength and green porosity were lower for hydride powder than for Ti powder, all probably resulting from reduced cold welding and friction during compaction. For sintering temperatures above ～1000°C, most of the difference in the sintered density of Ti and hydride is explained by assuming equal densification, while taking into account the lower green porosity of compacts made from hydride powder. However, there is evidence that particle fracture during compaction also contributes to increased sintered density for hydride powder. The Ti powder conformed to a master sintering curve model with apparent activation energy of 160 kJ mol^?. The activation energy for Ti hydride also appeared to be about 160 kJ mol^?, but the model did not fit the experimental data well.     

用温压制造高密度材料的关键参数

温压技术是由在加热的阴模中压制预热的粉末组成[1],已知温压有助于零件密实,从而改进烧结件的性能[2,3]。温压需要在适合温压的温度范围内进行。特别是,粉末混合粉应具有好的流动性,同时对阴模模壁有良好润滑性,以减小脱模力。在试验室和工业生产中都研究了用粘结剂处理的和未经粘剂处理的用温压技术制造的材料的性状与性能。为了确定和定量各种关键生产参数,诸如压制压力,粉末温度与阴模温度,生产速率及零件大小对生坯和烧结件特性和零件脱模力的影响,进行了专门的试验研究。依照粉末流动性与松装密度的稳定性,压制压力与温度以及压制零件的重量与密度讨论了温压的工艺性。     

Effect of Molybdenum Additions on Compaction during Sintering of Fine-Grained Iron-Copper Pseudoalloys

The effect of added molybdenum powder on compaction and the properties of sintered fine-grained iron-copper pseudoalloys is studied. The original powder mixtures are prepared by mechanical alloying, and the original powder particle size in mixtures does not exceed 0.5 μm. Specimens are sintered in the range 600-1130°C. It is shown that addition of molybdenum powder to the original charge accelerates compaction of fine pseudoalloys in both the solid phase and liquid-phase sintering compared with compaction of the same pseudoalloys without adding molybdenum. After solid-phase sintering the maximum relative density of specimens is 98.8%, and after liquid-phase sintering it is 99.3%. The main reasons for acceleration of compaction are prolonged retention of a fine-grained structure of sintered specimens up to the melting temperature for the phase based on copper and mutual diffusion between iron and molybdenum; to a significant extent the latter occurs during specimen heating in the solid phase.     

Ti-29Nb-13Ta-4.6Zr高速压制行为及其烧结性能的研究

利用自主研发的机械蓄能式高速压机成形Ti-29Nb-13Ta-4.6Zr粉末并进行真空烧结,研究冲击能量对试样的密度及力学性能的影响。结果表明:随着冲击能量的提高,试样生坯密度提高,在冲击能量为1 805 J时,获得的最大生坯密度达到5.63 g/cm~3(相对密度94.1%);径向弹性后效随着冲击能量增加而增加;经真空1 250℃烧结后,烧结坯的密度随着冲击能量的增加而增加,但烧结坯的体积发生了膨胀,最大烧结密度为5.53 g/cm~3(相对密度为92.5%);真空烧结2.0 h后,钛合金的抗拉强度和硬度达到最大值,分别为629.8 MPa和324.5 HV。