铁基粉末冶金材料

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
• Microstructure
Phases/structures
Shape Alloying Homogenization
• Dimensional change
烧结驱动力
V1 + V2 = V3 E1 + E2 > E3 Driving Force: Surface energy
2
1 3
High energy state
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. The min. cross section size is about 1mm.
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 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）
D. AB + 0.6% C
Astaloy 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
Treatment Coatings Definition - a deposition of a layer of a separate material onto the surface of the substrate without any chemical reaction A chemical reaction between the surface layers of the original substrate and an external reactant Diffusion of other species, such as C, N, into the surface layers of the original substrate Examples Electroplating Painting metallizing Steam treatment Phosphatising, etc Carburising Carbonitriding Nitrocarburising Nitriding Plasma treatments, etc
Good lubrication
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 元素扩散 微观结构 冶金粘结 尺寸变化 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
Green state (cold welding)
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.
Chemical conversion treatments
Thermochemical treatments
后续处理
Treatment Definition Change in microstructure of the surface layers of the original substrate by thermally cycling through a phase transformation Mechanical deformation in the surface layers of the original substrate, mainly to induce compressive stresses, but also to provide densification of the surface layer Examples Induction hardening Laser hardening
装粉高度与模冲进入量的计算
UP UP H1 t1 t2 Die LIP LOP H2 Die FD= 3.2g/cm3 GD= 7.2g/cm3 H1=GD/FD*t1 H2=GD/FD*t2 UPentry=H2-t2 Example: t1=10mm t2=25mm H1=22.5mm H2=56 mm UPentry= 31mm
E1 + E2 ∆E E3
Low energy state
固态烧结
• By the Diffusion of the metal atoms
Cu spheres
孔隙变化
From sharp corners to flatter parts of the pore surface
From small pores to near-by larger pores and grain boundaries
脱蜡缺陷 (Blistering) Fe + 2.5% Ni + 0.4% C
烧结缺陷
பைடு நூலகம்
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
b)
Stationary lower punch and floating die.
c)
Stationary lower punch, and the die being 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
瞬时液相烧结
Secondary pore
Fe – Cu系膨胀机理 系膨胀机理
90%Fe 10%Cu 1150 C
Fe-Cu 系与 系与Fe-Cu-C 系的尺寸变化
Cu
Cu + 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)
均匀化过程 Ni in Fe-base
影响均匀化的因素
Ni particle size: 5 um, 10 um Temperature: 1000 - 1300C Time: 0.5 -500 h Weighing factor: • Temperature • Ni particle size • Time
烧结的分类
• Temperature (< 1150C, >1150C) • Furnace (batch, pusher, belt, walking beam) • Atmosphere (“vacuum”, Endo, N2/H2) • State (liquid, solid) • Pressure (atmospheric, pressure-assisted)
LOP LIP
CR
粉末压制
摩擦力
• • • • Between powder particles Between punches and the die-wall Between punches and powder particles 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.
Sintered state (bonding between particles)
Metal powder compact
Porous metal
生坯与烧结件
After compaction
After sintering
烧结工艺示意图
Temp.
1 RT
2
3
4
Time 1 Delubrication (300 - 700C) 2 C - dissolution (800 - 950C) 3 Sintering (1100 - 1300C) 4 Cooling (Cooling Rate)
影响尺寸变化的因素
• • • • • • • • Particle size Alloying 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
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
Bad lubrication • Excessive die wall wear or insufficient lubrication may result in cold welding of the compact to the die wall. • Results in increased ejection force and stick-slip behaviour (squeaky noise)
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
Sintering necks Size Pores
-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. • RRS’s should be kept to a minimum to avoid high ejection forces, hence avoid tooling problems.