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1、铁基粉末冶金材料内 容 提 要 概述 工艺过程 产品种类 混料、成型、烧结及后处理 发展趋势粉末冶金简介粉末冶金是：通过对所需基础粉末，合金粉末及添加剂混合， 然后将混粉填充在具有要求形状的模腔内进行压制成 形，再将成型坯体在保护气氛下进行烧结使各种颗粒 形成冶金结合， 经过后续处理后得到最终产品。由于精确的成型技术，粉末冶金产品具有以下特点：近净成型形状复杂优良的尺寸精度. 粉 末 冶 金 简 介粉末冶金技术发展迅速：其原料涵盖了近乎所有技术元素产品形状复杂程度日益提高粉末冶金产业主要分为两个领域：铁基粉末冶金非铁基粉末冶金铁基粉末冶金材料 自润滑制品 结构件 软磁材料自 润 滑 零 件结
2、构 件 零 件 软 磁 零 件粉 末 冶 金 产 品 优 势 近净成型 期望的力学性能 大规模的生产和重复性好 表面光洁度 高尺寸精度 允许不同材料组合 多孔及孔隙度可控（自润滑材料） 良好的磁性能（软磁材料）粉末冶金基本工艺过程后 续 处 理粉 末 原 料 基粉类型 合金体系 合金化方式基 粉 的 选 择混 料 混料要求 混合方式 均匀性与偏析 松装密度与流动性混粉及装粉过程中产生的细粉团聚压 制 压制方式 生坯密度与密度均匀性 生坯强度 生坯缺陷充模过程Care must be taken when filling thin sections as bridges may occur.Th
3、e min. cross section size is about 1mm.装粉高度与模冲进入量的计算DieCRUPLOPLIPt1t2H2LOPLIPUPDieH1FD= 3.2g/cm3 GD= 7.2g/cm3Example: t1=10mm t2=25mmH1=22.5mm H2=56 mm UPentry= 31mmH1=GD/FD*t1H2=GD/FD*t2UPentry=H2-t2粉末压制摩擦力 Between powder particles Between punches and the die-wall Between punches and powder particl
4、es Between powder particles and the die-wall摩擦力导致的后果 Losses of the applied force Variation of pressure and green density Higher ejection forces (Wear of the tool-set)密度分布双向压制示意图a)Stationary die, two moving punches.b)Stationary lower punch and floating die.c)Stationary lower punch, and the die being
5、withdrawn at half the speed of the top punch.如何减小摩擦力 加入润滑剂 模壁润滑 优化压制工艺 -压制速度 -压制温度 -滑动距离 -润滑剂含量对生坯理论密度的影响 ASC100.29 Amount of lubricant不同润滑剂对生坯理论密度的影响 ASC100.29 脱模力的变化过程 Due to residual radial stresses a significant force is required to eject compacts from the die. RRSs should be kept to a minimum t
6、o avoid high ejection forces, hence avoid tooling problems.模具润滑状况对脱模力的影响Good lubrication模具润滑状况对脱模力的影响 Excessive die wall wear or insufficient lubrication may result in cold welding of the compact to the die wall.Good lubricationBad lubrication Results in increased ejection force and stick-slip behav
7、iour (squeaky noise)压制缺陷SEM image of a crack no sintering necks过 压 分 层烧 结 烧结的作用脱除润滑剂 冶金粘结元素扩散 尺寸变化微观结构 防止氧化与还原氧化物 烧结温度、烧结时间、烧结气氛烧结过程Metal powder compact Porous metal Sintered state (bonding between particles)Green state (cold welding)生坯与烧结件After compactionAfter sintering烧结工艺示意图Temp.TimeRTDelubricati
8、on (300 - 700C)C - dissolution (800 - 950C)4321 Sintering (1100 - 1300C)Cooling (Cooling Rate)1234影响烧结的因素 Temperature Time Atmosphere Material composition Alloying method Lubricant content Sintering cycle烧结过程的实质 Particle bonding Microstructure Dimensional changeSintering necksPoresPhases/structuresS
9、izeShapeAlloyingHomogenization烧结驱动力V1 + V2 = V3 E1 + E2 E3123E1 + E2E3EHigh energy stateLow energy stateDriving Force: Surface energy固态烧结 By the Diffusion of the metal atomsCu spheres孔隙变化From sharp corners to flatter parts of the pore surfaceFrom small pores to near-by larger pores and grain boundar
10、ies均匀化过程 Ni in Fe-base影响均匀化的因素Ni particle size: 5 um, 10 umTemperature: 1000 - 1300CWeighing factor: Temperature Ni particle size TimeTime: 0.5 -500 h烧结的分类 Temperature (1150C) Furnace (batch, pusher, belt, walking beam) Atmosphere (“vacuum”, Endo, N2/H2) State (liquid, solid) Pressure (atmospheric,
11、pressure-assisted)高温烧结 Accelerates the atomic motion (better sintering necks) Improves the surface reduction of particles (activates sintering) Increases the sintered density Improves the homogenization Improves pore rounding Improves mechanical properties 瞬时液相烧结Secondary poreFe Cu系膨胀机理90%Fe 10%Cu11
12、50 CFe-Cu 系与Fe-Cu-C 系的尺寸变化 CuCu + 1%C烧结常见的问题 Achieve sufficiently tight tolerances Oxidation (alloying elements, sintering atmosphere) Carburisation (temperature, sintering atmosphere) Decarburisation (temperature, sintering atmosphere) Poor surface finish (delubrification)影响尺寸变化的因素 Particle size Al
13、loying element Uneven filling and compaction Uneven distribution of alloying elements in the component Liquid phase formation Sintering temperature and time Uneven temperature distribution of the sintering furnace Poor control of gas flow in the sintering furnace脱蜡缺陷 (Blistering) Fe + 2.5% Ni + 0.4%
14、 C烧结缺陷Poor sintering necks (sponge) Poor sintering necks (atomised) Oxidation during sintering弱烧结颈和游离石墨烧结脱碳NC100.24 + Cu + Ni + 1% C D. AB + 0.6% CAstaloy CrM + 0.3% C烧结渗碳PASC 30 + 0% C D. HP-1 + 0.5 % C 过低的烧结温度Free Cu in Distaloy material后 续 处 理TreatmentDefinitionExamplesCoatings- a deposition of a
15、 layer of a separate material onto the surface of the substrate without any chemical reactionElectroplating Painting metallizingChemical conversion treatmentsA chemical reaction between the surface layers of the original substrate and an external reactantSteam treatment Phosphatising, etcThermochemical treatmentsDiffusion of other species, such as C, N, into the surface layers of the original substrateCarburising Carbonitriding Nitrocarburising
