热复合磁脉冲粉末压坯致密度的试验研究

对加热Cu粉末进行磁脉冲致密试验研究,探索提高压坯致密度且不使粉末颗粒产生明显长大的致密方法.通过压坯平均致密度和微观金相形貌分析,揭示了加热温度、放电参数和粉末体高径比等工艺参数对Cu粉末热复合磁脉冲致密压坯致密度的影响规律.研究表明:压坯致密度不随温度升高而线性增加,200℃时的致密度最高;在给定放电能量和200℃下,压坯的致密度随电压和电容量增加而提高,随粉末质量增加而降低;3次放电显著改善压坯致密效果,致密度达98.75%,再增加次数的影响甚微.     

爆炸压实中爆轰压力与粉末致密度的关系

在粉末材料爆炸压实试验中,爆轰压力是一个重要的工艺参数.本文结合质量不变条件、粉末材料泊松比与相对密度之间的关系、粉末材料的屈服准则以及粉末材料塑性变形时应力应变关系,研究爆炸压实工艺中爆轰压力与粉末致密度之间的关系,以便为实际的爆炸压实试验选择爆轰压力时提供理论依据.结果表明,随着爆轰压力增加,粉末爆炸压实坯的致密度也增加;当采用与其屈服强度相等的爆轰压力时,只能获得80.4%理论密度的棒坯;只有采用16倍屈服应力的爆轰压力时,爆炸压实才有可能获得99%理论密度的棒坯;无论爆轰压力多么大,爆炸压实法也不能得到完全致密的棒坯.     

不同放电能量下铜粉的电磁压实特性与烧结体性能研究

目的 研究放电能量对铜粉电磁压实特性与烧结体性能的影响,提升铜材料的制备效率与质量.方法 通过电磁粉末压实技术在不同放电能量下制备铜压坯,研究压坯的相对致密度与微观形貌随放电能量的变化趋势.随后对其进行真空烧结,对烧结体的拉伸性能与断口形貌进行测试,评估放电能量对烧结体性能的影响.结果 随着放电能量的增加,铜压坯的相对...     

气门座圈粉末锻造工艺的数值模拟与实验

目的研究气门座圈的粉末锻造工艺,提高产品的致密度。方法通过建立气门座圈粉末锻造数值模型,分析锻造过程中相对密度的变化过程,研究预制毛坯初始相对密度、锻造加热温度和成形速度对致密化的影响。在此基础上进行粉末锻造实验,并与模拟结果比较。结果随着预制毛坯初始致密度、加热温度的增加以及成形速度的降低,粉末锻造致密度化所需的成形力降低;预制坯初始密度对锻件密度均匀性影响最为显著。经过粉末锻造后的气门座圈,密度从6.6 g/cm~3提高到7.46 g/cm~3,致密度达到96.4%。结论相比传统压制-烧结工艺,粉末锻造可以大幅度提高气门座圈的致密度。     

冷压烧结Cu-Fe基金刚石超薄切锯胎体的组织和性能

为了研究冷压坯致密化机理及加载速率对烧结胎体组织和力学性能影响,采用单轴模压+热压烧结法,以Cu-Fe基元素混合粉末为原材料,在不同的冷压加载速率条件下制备Cu-Fe基金刚石复合材料超薄切锯胎体;用显微硬度仪、OM、SEM、XRD和万能力学试验机等表征冷压坯显微硬度、组织、烧结胎体组织和力学性能.结果表明:当加载速率较慢时,易变形的Cu、Ni粉在低压下发生加工硬化,抑制后续的塑性变形,阻碍压坯致密化;当加载速率过快时,压坯粉末的塑性变形不充分,造成脱模弹性后效,压坯密度下降;烧结Cu-Fe基胎体以Fe-Cr、(Fe,Ni)、Ni-Cr-Fe、Fe、Cr和(Cu,Sn)为主相;当加载速率为0.1 mm/min时烧结胎体的拉伸强度最大,拉伸断口形貌主要包括塑坑断口、解理断口和沿颗粒脆性断口.     

金属粉末压制成形机理及影响因素模拟分析

利用MSC.MARC有限元分析软件对金属粉末致密化成形过程进行了模拟分析。采用基于更新拉格朗日方法描述的大位移弹塑性分析,研究了不同工艺(压制方式、摩擦条件)对不同侧压系数(K=4、6、8)压坯中金属粉末致密化成形行为的影响规律。结果表明,双向压制工艺相比单向压制工艺可改善压坯应力和密度均匀性;摩擦条件的改善有利于增大金属粉末移动,减少应力集中,降低粉末压制力,提高压坯密度均匀性;而相同压制工艺下,压坯高径比小时,密度分布更均匀。     

快速凝固AlFeX耐热铝合金喷射沉积坯锻造成型工艺试验研究

喷射沉积AlFeVSi合金锭坯需要采用高温（450℃）锻压来实现致密化．通过沿不同取向锻压试验了解了喷射沉积坯及其压实坯的变形能力和锻造损伤情况，采用钢包套锻造工艺制备了完全致密化的喷射沉积Al-9．20Fe-1．37V-2．30Si合金锻件．通过金相、透射电镜、扫描电镜、力学性能检测等研究手段研究了锻造变形对喷射沉积A1FeVSi合金锻坯组织性能的影响．结果表明，喷射沉积AlFeVSi合金坯可以通过锻压变形实现致密化，达到冶金结合状态．喷射沉积AlFeVSi合金压实坯锻造道次压下率可以确定为20—40％，锻造加载方向最好是垂直于喷射沉积原坯沉积面，且需增加可塑性包套来限制侧表面的自由变形．采用钢包套自由锻造工艺可以在累积78％的压缩变形率条件下制备具有良好组织性能的锻造制品．     

烧结TiH_2粉末制备钛合金的工艺及组织EI北大核心CSCD

以TiH2粉末为原料,通过组元球磨混合、压制成形和烧结工艺制备钛合金。用扫描电镜对球磨过程TiH2粉末的粒度、形貌变化以及烧结CP-Ti,Ti-6Al-4V合金的组织形貌进行了观察;采用热重分析方法研究了TiH2粉末脱氢的特性;用热膨胀技术研究了TiH2,TiH2-Al-V两种粉末压坯的烧结致密化特性。结果表明:TiH2粉末经过球磨后迅速变细,其粒度随球磨时间的延长而减小,粉末形貌由原来的不规则形状逐渐变为等轴状;TiH2粉末在烧结过程的脱氢将使α-Ti产生强烈收缩、同时因脱氢后获得的新鲜钛表面所发生的快速粘接而使烧结体迅速致密、得到相对密度大于99%的烧结坯体;TiH2-Al-V粉末压坯在烧结时因为伴随着合金元素的溶解而使其烧结致密特性不如纯TiH2粉末压坯的好;TiH2粉末经过成型、烧结脱氢工艺可获得典型的等轴状纯钛组织,TiH2-Al-V粉末经过相同工艺可获得典型的层片状α+β钛合金组织、且合金元素分布均匀。     

SDC电解质致密化研究

以共沉淀-喷雾干燥法制备的Ce0.8 Sm0.2 O1.9(SDC)粉体为原料,模压成型后高温烧结获得SDC电解质陶瓷片.研究模压成型过程中加压时间、压力大小以及烧结温度对烧结体致密度的影响,利用XRD和SEM分别对不同烧结温度获得的烧结体结构和表面形貌进行分析.研究表明,压力30MPa、加压时间30min后获得的坯体,随着烧结温度的升高,烧结体致密度呈上升趋势,烧结温度达到1450℃时进入烧结后期,烧结体具有较高的致密度.此外,通过测定烧结过程中坯体收缩率,对SDC电解质陶瓷片的烧结动力学进行了研究,从而确定SDC电解质致密化的烧结温度为1300～1500℃.     

成型工艺对氮氧化铝微观结构和性能的影响

氮氧化铝(AlON)透明陶瓷具有优异的光学、热学和机械性能,可广泛应用于光电窗口、整流罩、透明装甲等领域。成型高致密度、结构均匀的素坯是制备氮氧化铝透明陶瓷的关键技术环节。但是纳米粉体比表面积大,易产生非均匀团聚,导致成型坯体致密度差。为了提高素坯密度和均匀性,本文首先通过优化喷雾造粒工艺实现纳米粉体微球化,获得直径大于10μm、具有良好流动性的致密球形颗粒。然后分析成型压力对素坯的密度、微观结构、平均孔径及陶瓷性能的影响,得到相对密度58.8%的素坯,烧结陶瓷片在200 nm处直线透过率达到83%(厚度2 mm)。最后采用冷等静压成型/常压烧结技术制备出Φ170 mm平板和Φ110 mm球罩样件。     

超声压制粉体成形技术研究进展

超声粉体压制技术适合众多种类的粉体材料以及较难加工的高分子材料等,不但制得的压坯密度和均匀度能有效提高,而且压制过程环保、安全。国内外开展了金属粉末、无机物中的陶瓷粉末、高分子材料中的塑料粉末,以及高分子含能材料的复合粉末等的超声压制成形研究,取得了许多成果,大大促进了超声压制粉体成形技术在国民经济和国防建设中的广泛应用。该文介绍了超声压制粉体成形技术的研究进展。     

Density Gradients in Multilayer Compacted Iron Powder Parts

The use of multilayer compaction to form powder metal (P/M)components, is encouraging. With this process, a part is formed by successively compacting layers of powder. The formation of parts with larger than conventional height to diameter ratios is possible. Multilayer compaction also reduces the density gradients normally observed in large parts from conventional double action compaction. Optimization of the layer thickness based on the powder characteristics can lead to greatly reduced density gradients.

The physical properties of multilayer compacted components are investigated as a function of layer thickness. The research has been performed with two iron powders of varying characteristics. The compressibility of the powder versus the layer thickness is discussed and related to the density distribution in the component.     

Evolution of fractal features of pores in compacting and sintering process

As an index of molding, the fractal dimension of pores can reflect system varying details as the density. Pores in the powder aggregates with a composition of Fe–2%Cu–0.5%C were researched. The change tendency of dimension of pores as a function of compaction pressure or sintering temperature was investigated. Result indicates that the dimensions of pores in this ternary system decrease both in the process of compacting and sintering. It is convenient to build up some theories by combining compacting and sintering based on the variation of pore dimensions.     

Mechanical properties and thermal stability of bulk Cu cold consolidated from atomized powders by high-pressure torsion

It is difficult to densify and consolidate round-shaped metallic powders by conventional compaction techniques because powder interlocking forces are small and the powders easily slip and rotate instead of being plastically deformed and densified. In this paper, atomized Cu (99.5 % purity) powders of round shapes were cold consolidated to bulk specimens by high-pressure torsion (HPT) under 10 GPa to avoid powder slippage by the shape effect. A relative density over 98 %, high tensile strengths of 642 and 570 MPa, and moderate ductility of 7.5 % with thermally stable ultrafine grained structures are achieved after the HPT consolidation process. The specimens HPT processed at RT show higher tensile strength due to more dislocations and finer grain sizes than the specimen processed at 373 K. Higher ductility in the elevated temperature (373 K)-processed specimen than in the RT-processed specimen is attributed to good bonding between particles, decreased dislocation density, and increased grain size.     

Cracking cone fracture after cold compaction of argillaceous particles

Cold uniaxial pressing of powder into a green body is a common forming process used in ceramic and pharmaceutical industries. Argillaceous particles are used as a model system to investigate granule failure during compaction. Indeed, the volume enclosed between the die and punches is reduced and the powder consolidates until a final height is obtained or a prescribed compacting pressure is reached. Desired properties of the green body are high strength, uniform density, no defects and fracture. In this work an experimental investigation has been focused on the ‘cracking cone’ fracture in powder compacts. This includes studies of crack propagation and determination of operating conditions to avoid the green body fracture. The numerical modelling is implemented using a finite element method based on the Von Mises criterion. A case of simulation is presented to demonstrate the ability of the model to compute the distribution of the relative stresses.     

Effects of lubrication procedure on the consolidation, sintering and microstructural features of powder compacts

The role of lubrication procedure on the consolidation behavior of metallic powders and subsequent microstructural development during sintering was investigated. Iron powder and iron–0.8 w/o graphite powder mixture were used as model materials. The effects of die wall lubrication procedure were compared to the traditional admixed powder lubrication method. The influences of manufacturing parameters such as the compacting pressure in the range of 150–800 MPa and the sintering temperature from 400 to 1300 °C were studied. It was found that the lubrication procedure has a great influence on the consolidation and microstructural features of the materials investigated. Admixed lubricant aids the densification in the low-pressure region but limits the maximum density at high pressure. On the other hand, die wall lubrication offers the possibility of achieving the required density in single pressing for parts made by conventional double pressing and double sintering route or by warm compaction technique. The method also results in the formation of more metal/metal contacts during compacting, which leads to better green strength. Moreover, during sintering at moderate temperatures the area of metallic contacts is more and stronger compared to the powder lubricated specimens. Consequently, better mechanical properties are obtained. However, after sintering at a high temperature (>1000 °C) only less total porosity of the unlubricated compacts attributes to higher performance.     

含成形剂的纳米微晶ZrO2粉末压形规律的研究

本文对管道反应制备的纳米微晶ＺｒＯ２粉末的模压数据进行处理。结果表明,该ＺｒＯ２粉末压形规律黄培云压形方程。     

铁粉的高速压制成形

采用高速压制技术制备铁基制品,探讨了冲击能量及冲击速度与冲击行程之间的关系,并研究了冲击能量、压制方式对生坯密度、最大冲击力、脱模力和径向弹性后效的影响.结果表明:在高速压制过程中,冲击能量与冲击行程呈线性关系,而冲击速度与冲击行程呈抛物线关系.生坯密度随着冲击能量的增加而逐渐增大.单次压制时,当冲击能量增加到6510 J时,生坯密度达到7.336 g/cm~3,其相对密度约为97%.在总冲击能量相同的情况下,两次压制制备出的试样生坯密度最大,三次压制的最小.在高速压制过程中,试样的脱模力及其径向弹性后效均远低于传统压制.