鐵基粉末冶金材料.ppt

1、鐵基粉末冶金材料,內(nèi) 容 提 要,概述 工藝過程 產(chǎn)品種類 混料、成型、燒結(jié)及后處理 發(fā)展趨勢,粉末冶金簡介,粉末冶金是： 通過對所需基礎(chǔ)粉末，合金粉末及添加劑混合，然后將混粉填充在具有要求形狀的模腔內(nèi)進(jìn)行壓制成形，再將成型坯體在保護(hù)氣氛下進(jìn)行燒結(jié)使各種顆粒形成冶金結(jié)合， 經(jīng)過后續(xù)處理后得到最終產(chǎn)品。 由于精確的成型技術(shù)，粉末冶金產(chǎn)品具有以下特點： 近凈成型 形狀復(fù)雜 優(yōu)良的尺寸精度.,粉 末 冶 金 簡 介,粉末冶金技術(shù)發(fā)展迅速： 其原料涵蓋了近乎所有技術(shù)元素 產(chǎn)品形狀復(fù)雜程度日益提高 粉末冶金產(chǎn)業(yè)主要分為兩個領(lǐng)域： 鐵基粉末冶金 非鐵基粉末冶金,鐵基粉末冶金材料,自潤滑制品 結(jié)構(gòu)件 軟磁材

2、料,自 潤 滑 零 件,結(jié) 構(gòu) 件 零 件,軟 磁 零 件,粉 末 冶 金 產(chǎn) 品 優(yōu) 勢,近凈成型 期望的力學(xué)性能 大規(guī)模的生產(chǎn)和重復(fù)性好 表面光潔度 高尺寸精度 允許不同材料組合 多孔及孔隙度可控（自潤滑材料） 良好的磁性能（軟磁材料）,粉末冶金基本工藝過程,后 續(xù) 處 理,粉 末 原 料,基粉類型 合金體系 合金化方式,基 粉 的 選 擇,混 料,混料要求 混合方式 均勻性與偏析 松裝密度與流動性,混粉及裝粉過程中產(chǎn)生的細(xì)粉團(tuán)聚,壓 制,壓制方式 生坯密度與密度均勻性 生坯強(qiáng)度 生坯缺陷,充模過程,Care must be taken when filling thin sections

3、 as bridges may occur. The min. cross section size is about 1mm.,裝粉高度與模沖進(jìn)入量的計算,t1,t2,FD= 3.2g/cm3 GD= 7.2g/cm3,粉末壓制,摩擦力,Between powder particles Between punches and the die-wall Between punches and powder particles Between powder particles and the die-wall,摩擦力導(dǎo)致的后果,Losses of the applied force Variat

4、ion of pressure and green density Higher ejection forces (Wear of the tool-set),密度分布,雙向壓制示意圖,Stationary die, two moving punches. Stationary lower punch and floating die. c)Stationary lower punch, and the die being withdrawn at half the speed of the top punch.,如何減小摩擦力,加入潤滑劑 模壁潤滑 優(yōu)化壓制工藝 -壓制速度 -壓制溫度 -滑

5、動距離 -,潤滑劑含量對生坯理論密度的影響 ASC100.29,Amount of lubricant,不同潤滑劑對生坯理論密度的影響 ASC100.29,脫模力的變化過程,Due to residual radial stresses a significant force is required to eject compacts from the die.,RRSs should be kept to a minimum to avoid high ejection forces, hence avoid tooling problems.,模具潤滑狀況對脫模力的影響,Good lubr

6、ication,模具潤滑狀況對脫模力的影響,Excessive die wall wear or insufficient lubrication may result in cold welding of the compact to the die wall.,Good lubrication,Bad lubrication,Results in increased ejection force and stick-slip behaviour (squeaky noise),壓制缺陷,SEM image of a crack no sintering necks,過 壓 分 層,燒 結(jié),

7、燒結(jié)的作用 脫除潤滑劑 冶金粘結(jié) 元素擴(kuò)散 尺寸變化 微觀結(jié)構(gòu) 防止氧化與還原氧化物 燒結(jié)溫度、燒結(jié)時間、燒結(jié)氣氛,燒結(jié)過程,Metal powder compact Porous metal,Sintered state (bonding between particles),Green state (cold welding),生坯與燒結(jié)件,After compaction,After sintering,燒結(jié)工藝示意圖,Temp.,Time,RT,Delubrication (300 - 700C) C - dissolution (800 - 950C),4,3,2,1,Sinteri

8、ng (1100 - 1300C) Cooling (Cooling Rate),1,2,3,4,影響燒結(jié)的因素,Temperature Time Atmosphere Material composition Alloying method Lubricant content Sintering cycle,燒結(jié)過程的實質(zhì),Particle bonding Microstructure Dimensional change,Sintering necks,Pores,Phases/structures,Size,Shape,Alloying,Homogenization,燒結(jié)驅(qū)動力,V1 +

9、 V2 = V3 E1 + E2 E3,1,2,3,E1 + E2,E3,E,High energy state Low energy state,Driving Force: Surface energy,固態(tài)燒結(jié),By the Diffusion of the metal atoms,Cu spheres,孔隙變化,From sharp corners to flatter parts of the pore surface,From small pores to near-by larger pores and grain boundaries,均勻化過程 Ni in Fe-base,影

10、響均勻化的因素,Ni particle size: 5 um, 10 um,Temperature: 1000 - 1300C,Weighing factor: Temperature Ni particle size Time,Time: 0.5 -500 h,燒結(jié)的分類,Temperature (1150C) Furnace (batch, pusher, belt, walking beam) Atmosphere (“vacuum”, Endo, N2/H2) State (liquid, solid) Pressure (atmospheric, pressure-assisted)

11、,高溫?zé)Y(jié),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,瞬時液相燒結(jié),Secondary pore,Fe Cu系膨脹機(jī)理,90%Fe 10%Cu 1150 C,Fe-Cu 系與

12、Fe-Cu-C 系的尺寸變化,Cu,Cu + 1%C,燒結(jié)常見的問題,Achieve sufficiently tight tolerances Oxidation (alloying elements, sintering atmosphere) Carburisation (temperature, sintering atmosphere) Decarburisation (temperature, sintering atmosphere) Poor surface finish (delubrification),影響尺寸變化的因素,Particle size Alloying el

13、ement 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,脫蠟缺陷 (Blistering)Fe + 2.5% Ni + 0.4% C,燒結(jié)缺陷,P

14、oor sintering necks (sponge) Poor sintering necks (atomised),Oxidation during sintering,弱燒結(jié)頸和游離石墨,燒結(jié)脫碳,NC100.24 + Cu + Ni + 1% C D. AB + 0.6% C,Astaloy CrM + 0.3% C,燒結(jié)滲碳,PASC 30 + 0% C D. HP-1 + 0.5 % C,過低的燒結(jié)溫度,Free Cu in Distaloy material,后 續(xù) 處 理,后 續(xù) 處 理,發(fā) 展 趨 勢,高密度 高性能 高尺寸精度 低單位成本 新工藝 新材料,發(fā) 展 趨 勢,粉 末