负温度系数热敏电阻材料的等静压制研究

本文研究了负温度系数热敏电阻材料等静压制过程中物料水分含量、粘结剂的加入量、成形压力和保压时间对生坯强度、生坯密度及生坯内外密度均匀性的影响。研究表明:随着含水量的增加,粉料振实密度减小,压坯强度增加,水含量控制在0.2%~0.5%较为适宜;当粘结剂聚乙烯醇(PVA)的添加量从0.4%增加到1.5%时,生坯强度从0.78MPa增加到了3.17MPa。PVA添加量从1.5%增加到3.0%的过程中,试样的强度基本不变,合适的粘结剂含量为0.8%左右;生坯密度随着压制压力增加而增加,压力达到250MPa以后基本不再增加,压制达到了一个较稳定的状态。保压120s以上时,试样的内外密度差异比较小。     

含水量对喷雾干燥钼粉性能的影响

将钼粉末和聚乙烯醇（PVA）水溶液按一定比例配置悬浮浆料,经喷雾造粒后进行连续自动压制成型,研究了不同含水量对喷雾干燥钼粉松装密度、流动性和成型性的影响。结果表明：随着含水量的增加,喷雾干燥钼粉松装密度减小,流动性变差;在自动压制成型过程中,随着含水量的增加,填充密度、成型压力降低,压制回弹减小,水含量为0．08％～0．16％（质量分数）时压制效果较为理想。     

聚乙烯醇在镍铁氧体压坯中的脱脂行为

使用TGA、DSC等分析手段对聚乙烯醇(PVA)在NiFe2O4粉末压坯中的脱脂行为进行了实验研究,以期进一步揭露PVA热脱脂反应对NiFe2O4粉末压坯机械强度的影响。实验时,先用含1%PVA的NiFe2O4粉末及不含PVA的NiFe2O4粉末进行同轴压制,再将制得的压坯于空气中脱脂,并用径向受压实验测试压坯强度。试验表明在PVA脱脂过程中,其脱脂行为及粉末压坯强度随温度的升高呈明显的阶段性变化,粉末压坯的强度随粘结剂PVA的脱除逐渐降低。     

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%。     

铜基金属粉末温压工艺致密化的研究

研究了铜基金属粉末的温压压制行为,并与冷压压制进行了比较。结果表明:相同压力下,温压压制的压坯密度明显高于冷压压制,在压制压力为500-600 MPa时,密度增加达0.24 g/cm3;温压温度有一个最佳值,必须高于润滑剂的玻璃化温度,低于润滑剂的熔点温度;石墨含量增加,压坯密度下降,当石墨含量小于1%时,温压压制的优势较为明显。     

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。     

熔渗用多孔金刚石预制坯制备工艺的研究

采用压制工艺制备多孔金刚石预制坯,分别研究了PVA和酚醛树脂两种粘结剂对压制坯体性能的影响以及酚醛树脂不同的压制制度对坯体性能的影响。研究结果表明:采用酚醛树脂作为成形剂时,坯体具有比PVA更高的强度和开孔率;同时,采用多次升温、多次压制工艺,相比于单次升温、单次压制工艺,坯体具有更高的抗压强度,以及更理想的开孔率,适合于真空压力熔渗法制备金刚石增强的金属基复合材料。     

氢气流量和系统进出气流量比对钨粉性能及压坯强度的影响研究

以黄钨为原料，采用分步还原工艺制备钨粉，系统研究了氢气流量和系统进出气流量比对钨粉性能及压坯强度的影响。结果表明：随着氢气流量增加，钨粉粒度细化，但其压坯强度变化较小；当氢气流量为250 L/min时，钨粉粒度为3.3μm,压坯强度为4.1 MPa;当氢气流量增加到800 L/min时，钨粉粒度为2.72μm,压坯强度为4.2 MPa。同时，系统进出气流量比对钨粉压坯强度影响显著，当系统进出气流量比为1∶1时，钨粉粒度为2.76μm,压坯强度为1.6 MPa;提高系统进出气流量比至1∶0.9时，钨粉粒度上升到3.06μm,压坯强度提高到4.4 MPa。     

碳化硼耐火材料生坯成型工艺的探究

为了得到将碳化硼除尘废料加工成耐火材料的最优成型条件,考察了黏结剂的种类、黏结剂的添加量、压制压力及保压时间等因素对生坯性能的影响。研究表明,当黏结剂选择羟丙基甲基纤维素且含量为1.0%,制坯压力为100 MPa,保压时间为120 s时,所得生坯密度达到1.406 g/cm~3,抗压强度达到27.9 MPa,为论文试验最优效果。因此黏结剂羟丙基甲基纤维素含量为1.0%,制坯压力为100 MPa,保压时间为120 s为试验最优生坯成型工艺条件。     

不同成型工艺下钕铁硼模压成型过程的力学行为分析

为了优化钕铁硼粉末模压成型工艺, 通过离散元软件EDEM建立模压成型过程的离散元模型, 分析不同成型工艺条件(压制速度和摩擦系数)对压坯力学特征(压制力和压坯内应力)的影响, 为优化钕铁硼成型工艺提供理论参考。结果表明: 在成型过程中, 钕铁硼粉末位置状态基本保持与布粉时一致, 只有靠近模冲区域的粉末发生较大位移; 压坯成型时会出现应力松弛现象, 不同速度压制成型对压制力峰值影响不同, 但压制力最终均会收敛至相近的平衡值; 添加润滑剂能改善压坯内部受力状态, 减小压制力, 但是也会减小压坯相对密度; 对于大尺寸压坯成型宜采用双向压制方式。     

Sintering Characteristics of Al–Pb/Fly-Ash Metal Matrix Composites

Aluminum–lead/10 wt% fly-ash powder mixtures containing 0–20 wt% lead (Pb) were prepared. These powder mixes were compacted in the pressure range of 200–400 MPa by single action die compaction process. The prepared compacts were sintered in the temperature range of 500, 530, 560 and 590 °C in an argon gas atmosphere for duration of 45 min. For the sintered compacts, the sintered density, hardness and compressive strength were reported. Sintered density, hardness and compressive strength increased with the increase in compaction pressure. Sintered density increased whereas the hardness and the compressive strength decreased with the addition of Pb.     

Effect of atomisation medium on sintering properties of austenitic stainless steel by eliminating influence of particle shape and particle size

Abstract

Gas and water atomised 316L stainless steel powders with similar powder morphology and particle size were injection moulded and sintered. The results show that compacts prepared from the gas atomised powder exhibit higher density and tensile strength, whereas those prepared from the water atomised powder exhibit higher elongation, finer grain size and superior corrosion resistance. Chemical analysis shows that the water atomised powder has a higher Si and O content, and microstructural analysis of the sintered compacts reveals that SiO₂ particles disperse as a second phase in the compacts prepared from the atomised powder, which accounts for the property behaviour. Due to the presence of SiO₂, the porosity increases, whereas the pore coarsening and grain growth are inhibited. Besides, SiO₂ particles can also improve the passivation effect of stainless steel, and hence increase the corrosion resistance.     

Cu粉特性对热导管烧结毛细结构性能的影响

研究热导管铜粉的松装密度、粉末粒度、粉末粒径分布对铜粉烧结的毛细结构体断裂强度、孔隙率、毛细力吸水通量的影响。结果表明:在烧结温度为980℃,烧结时间60 min的条件下松装烧结所得铜热导管毛细结构体综合性能良好,当铜粉松装密度2.1 g/cm~3,粒径范围100~250μm,其中粒径150~250μm的质量分数为40%~70%时,铜粉烧结毛细结构体的断裂强度为9.11~9.67 MPa,孔隙率52.6%~53.8%,毛细力吸水通量1.30×10~(-3)~1.42×10~(-3) g/(s·mm~2)。     

钼粉物理性能对其压坯挠曲强度的影响

钼压坯的挠曲强度是衡量钼粉质量的重要指标之一。通过对钼粉的粒度分布、费氏粒度、松装密度、振实密度以及颗粒形貌等对钼压坯挠曲强度的影响研究,探讨其相互关系,有利于产品质量管理前置。研究结果表明,钼压坯的挠曲强度值的大小取决于钼粉的颗粒团聚状况和粒度分布;钼粉的松装密度和振实密度越大,钼粉中小颗粒聚集和颗粒熔融形成的"硬"团聚越少,粒度分布越接近标准正态分布,所得压坯的挠曲强度值则高。     

粉末注射成形奥氏体不锈钢的疲劳和冲击强度

本文的目的是研究粉末性能对粉末注射成形奥氏体不锈钢的力学性能(特别是疲劳和冲击强度)的影响。试样用混有聚酰氨粘结剂系的水雾化(WA)和气雾化(GA)粉末制成。注射坯在空气中脱粘，而后在不同温度、不同保温时间下真空烧结。粉末性能对烧结体的密度、显微组织和力学性能有显著影响。孔和析出物显示出Ostward时效，而孔和析出物的长大满足Lifshitz-Wagner方程。WA和GA粉末试样的疲劳极限分别约为300MPa和310MPa。它们的疲劳强度略低于常规锻材。烧结体的冲击值随密度增加线性增大。     

Influence of Lubricants on Dimensional Changes and Mechanical Properties of Sintered Ferrous Compacts

Abstract

The influence of admixed zinc stéarate on the shrinkage of uniaxially pressed iron powder compacts has been studied. For pressing conditions which caused inhibition of compaction the removal of the stéarate during sintering produced an increase in shrinkage parallel to the pressing axis and in direct proportion to lubricant content. Additions of stearic acid (varying particle size), zinc stearate, lithium stearate, stearamide, and Cosmic 64 wax were used to investigate the influence of lubricant on mechanical properties of green and sintered iron powder compacts. Green strength was reduced relative to unlubricated material only by lubricants whose physical and chemical properties enabled them to produce and maintain extensive interparticle films during pressing. Vapour from the rapid initial decomposition of lubricants which reduced green strength could have a deleterious physical influence on the tensile strength of dewaxed or sintered Fe compacts. Decomposing lubricants also produced undesirable chemical effects. These arose from reactions between lubricant decomposition products and the matrix or by these products interfering with reactions between matrix and sintering atmosphere.     

The Effect of Cooling Rate on the Strength of Sintered Fe—Cu Compacts

Abstract

The effect of cooling rate from the sintering temperature upon the tensile strength of compacts from a mixture of iron and copper powder was investigated. The compacts were pressed at 450 and 390 MPa and sintered in hydrogen at 1120°C for 40 min. The copper content of the compacts varied from 0 to 12%. For alloys with Cu content >4% the tensile strength was found to be strongly dependent upon the cooling rate in the temperature range between 850 and 600°C, with rapidly cooled specimens being considerably stronger. In specimens with 8%Cu the tensile strength increased from 206 to 343 MPa when the cooling rate was increased from 10 to 200 degC min^?1. In specimens with 2%Cu cooling rates above and below 600 degC min^?1 appear to influence the tensile strength. Possible explanations for the observed effects of cooling rate upon tensile strength in sintered Fe–Cu alloys are discussed.     

润滑剂含量对钛粉高速压制性能的影响

采用高速冲击压机压制钛粉,研究润滑剂含量对压坯性能的影响.结果表明:加入适量的润滑剂可以提高钛粉成形时的质量能量密度,从而获得更高密度的压坯.当润滑剂加入量为0.3%(质量分数)时,钛粉成形的最大质量能量密度为0.192 KJ/g,压坯密度为4.38 g/cm3,相对密度为97.4%.此外,适量的润滑剂能提高钛粉压制过...