3D打印硬质合金研究进展
来源期刊:稀有金属2021年第4期
论文作者:刘云 郭子傲 王行 张锦芳 李晓峰
文章页码:484 - 492
关键词:3D打印;硬质合金;成型方式;力学性能;
摘 要:硬质合金由难熔金属碳化物(如WC,NbC,TiC等)与过渡族金属元素(Co,Fe,Ni等)组成,因其具有良好的硬度、强度、耐磨性以及耐腐蚀性被广泛用作钻探切削、冲压模具、磨损件等。然而目前在硬质合金的高质量制备存在一些难题,如:生产周期长,易出现晶粒长大;受制于模具的形状,难以制备复杂形状工件。而3D打印技术在的快速发展为复杂硬质合金的制造提供了可能。综述了3D打印硬质合金的研究进展,着重围绕当前硬质合金3D打印的成型方式进行了介绍与对比。3D打印技术通过减少材料的损失和制造步骤的数量,降低生产成本,可以有效实现硬质合金的快速、精确、便捷的生产,未来有望成为生产复杂结构硬质合金的方法之一。但目前3D打印制备的硬质合金零件存在致密度低、组织控制与力学性能不足等问题,需要在未来进行深入研究。
稀有金属 2021,45(04),484-492 DOI:10.13373/j.cnki.cjrm.XY19090015
刘云 郭子傲 王行 张锦芳 李晓峰
中北大学材料科学与工程学院
河南黄河旋风股份有限公司
中南大学粉末冶金国家重点实验室
硬质合金由难熔金属碳化物(如WC,NbC,TiC等)与过渡族金属元素(Co,Fe,Ni等)组成,因其具有良好的硬度、强度、耐磨性以及耐腐蚀性被广泛用作钻探切削、冲压模具、磨损件等。然而目前在硬质合金的高质量制备存在一些难题,如:生产周期长,易出现晶粒长大;受制于模具的形状,难以制备复杂形状工件。而3D打印技术在的快速发展为复杂硬质合金的制造提供了可能。综述了3D打印硬质合金的研究进展,着重围绕当前硬质合金3D打印的成型方式进行了介绍与对比。3D打印技术通过减少材料的损失和制造步骤的数量,降低生产成本,可以有效实现硬质合金的快速、精确、便捷的生产,未来有望成为生产复杂结构硬质合金的方法之一。但目前3D打印制备的硬质合金零件存在致密度低、组织控制与力学性能不足等问题,需要在未来进行深入研究。
中图分类号: TP391.73;TG135.5
作者简介:刘云(1967-),男,山西应县人,博士,教授,研究方向:铝合金液态成型及过程控制技术、增材制造,E-mail:997627968@qq.com;;*李晓峰,副教授,电话:13633518635,E-mail:lxf@nuc.edu.cn;
收稿日期:2019-09-18
基金:国家自然科学基金项目(51804280);山西省自然科学基金项目(201701D221086和201801D221146);山西省科技重大专项项目(20181101009);山西省教育厅科技创新项目(201802076);山西省回国留学人员科研资助项目(2017-095);山西省国际合作项目(201603D421024);山西省重点研发计划(国际科技合作)项目(201903D421075)资助;
Liu Yun Guo Ziao Wang Hang Zhang Jinfang Li Xiaofeng
School of Materials Science and Engineering,North University of China
Henan Huanghe Whirlwind Limited Company
State Key Laboratory For Powder Metallurgy,Central South University
Abstract:
Cemented carbide was composed of refractory metal carbides(such as WC,NbC,TiC,etc.) and transition metal elements(Co,Fe,Ni,etc.).Because of its good hardness,wear resistance and corrosion resistance,it was widely used for drilling and cutting,stamping dies and wear parts,etc.However,there were some difficulties in the high-quality preparation of cemented carbide at present,such as,long production cycle and easy grain growth;restricted by the shape of the mold,it was difficult to prepare workpieces with complex shapes.The rapid development of 3 D printing technology provided the possibility for the manufacture of complex cemented carbide.This paper reviewed the research progress of 3 D printing cemented carbide,focusing on the folding way of cemented carbide 3 D printing for introduction and comparison.3 D printing technology could effectively realize the fast,accurate and convenient production of cemented carbide by reducing the loss of materials,the number of manufacturing steps and reducing production costs.It was expected to become one of the methods for producing complex structure cemented carbide in the future.However,the current cemented carbide parts prepared by 3 D printing had problems such as low density,insufficient structure control and mechanical properties,which required in-depth research in the future.At present,the methods of additive manufacturing of cemented carbide were mainly pided into direct forming and indirect forming.The direct forming methods were mainly selective laser melting(SLM),laser engineered net shaping(LENS) and selective electron beam melting(SEBM);the indirect forming methods were mainly binder jetting 3 D printing(BJ3 DP),3 D gel-printing,and selective laser sintering(SLS).The direct forming method used high-energy laser beam or electron beam as the heating source to selectively melt the powder and deposit it layer by layer.The formed sample had better compactness,and the mechanical properties,such as hardness was better than that of those prepared by indirect forming.Although this method had high forming accuracy and relatively good performance,the micropores and cracks produced by this method during the rapid solidification process had become problems that researchers need to solve urgently in the future.In comparison,after rebinding and high-temperature sintering,the blank formed by indirect forming had higher compactness and low porosity was close to that of traditional preparation methods to produce cemented carbide,but the post-processing process increased the cost.Shrinkage reduced accuracy.In addition,due to the larger layer thickness,the larger surface roughness of the green body and the larger shrinkage rate after sintering were also the current disadvantages of the indirect forming method.Regardless of the forming method,the control of structure and defects and their effects on performance had not yet found a specific corresponding relationship,so it was necessary to study a set of forming mechanisms to effectively control residual stress and pores.For the current mainstream SLM,fully dense cemented carbide produced with a density greater than 99% had not yet been produced,and it was necessary to perform heat treatment and infiltration after forming to increase its density.The green body prepared by BJ3 DP could reach fully dense cemented carbide samples after sintering,but the performance was not enough for industrial production.At present,the research on the preparation of cemented carbide by SEBM was still in its infancy,and there were few related studies.The high energy and fast-moving speed generated by the electron beam could inhibit the growth of grains to a certain extent,and the substrate preheating temperature could reduce high residual stress effectually,and it could be used as one of the feasible methods in the future.Defects were always the bottleneck of additive manufacturing applications.Most of the holes and cracks were caused by the residual stress with the rapid movement of the high-energy laser beam,which were mainly distributed in the initial deposition layer,because the substrates selected by the researchers were mostly 304 L or 316 L stainless steel.The large thermal expansion coefficient and undercooling of the two materials led to cracks,which could reduce the residual stress by increasing the preheating temperature of the substrate to inhibit the cracks.The powder morphology had a great influence on the structure morphology after forming.Compared with irregular powder,spherical powder had good fluidity,which could effectively inhibit the agglomeration of WC and segregation of Co,and the crystal grain dispersion was more uniform.In the method of preparing cemented carbide by additive manufacturing,the heat distribution was not uniform during the laser/electron beam melting process,the rapid solidification process and the rapid movement of the laser,so that the layered structure and uneven size could be observed in the microstructure,agglomeration of WC grains and Co.Not only that,according to the ternary phase diagram of WC-Co,the high residual stress generated during the high-temperature melting process of Co evaporation,carbon loss,and local powder melting by the laser beam promoted the formation of η phase and reduced the hardness the mechanical properties of the alloy.In contrast,during the preparation process of BJ3 DP and 3 DJP technology,the sample was heated evenly,the grain size of the sample was more uniform,and the brittle phase was greatly reduced.As a result,the samples prepared by BJ3 DP and 3 DJP technology were more similar to that prepared by traditional powder metallurgy processes.
Keyword:
3D printing; cemented carbide; folding way; machnical property;
Received: 2019-09-18
硬质合金是以难熔金属碳化物(如WC,Nb C,Ti C等)为基体,Fe,Co,Ni等过渡族金属为粘结相,通常采用粉末冶金工艺制备而成
传统硬质合金成型方法主要以粉末冶金为主,将粉末混合均匀后进行压制(或注塑、挤压),最后用高温烧结等热处理方法保证其致密度和力学性能。同时该制备手段也存在一些问题,如生产周期长,易出现晶粒长大;受制于模具的形状,难以制备复杂形状的硬质合金工件;机械加工复杂零件时,容易发生开裂等现象;使用模具制备硬质合金零件时,需组合多套模具实现,增加了成本。
增材制造(3D打印)技术是以三维模型为基础,利用“离散-堆积”原理,通过逐层堆积的方式成型实体零件的制造方法。因其具有快速成型复杂零件的优点,一定程度上为实现制备硬质合金零件提供了解决方案。经过近几年的发展,3D打印技术在制备精密零件发挥了越来越重要的作用。目前3D打印硬质合金成型包含了喷胶粘粉技术(binder jetting 3D printing,BJ3DP),选择性激光烧结技术(selective laser sintering,SLS),选区激光熔化(selective laser melting,SLM)等。本文将针对不同快速成型方式制备硬质合金的进展和存在的问题进行综述。
1 喷胶粘粉成型3D打印(BJ3DP)硬质合金
BJ3DP通过计算机执行STL文件以粘合剂粘合连接粉末层并逐层沉积的方法构成生坯
Enneti等
Cramer等
目前BJ3DP制备硬质合金大多数采用渗碳或熔渗的后处理方式增加致密度,进而提高性能。然而,烧结后尺寸变形大,表面质量差,对成型复杂结构零件依然是考验。
2 选择性激光烧结(SLS)成型硬质合金
选择性激光烧结(SLS)是快速成型(RP)技术之一,分别为间接激光烧结(EMLS)和直接激光烧结(DMLS)
Wang等
图1 1485℃压力下烧结30 min的样品腐蚀后的SEM照片
Fig.1 SEM images of etched microstructures of samples pres-sure sintered at 1485°C for 30 min
图2 熔渗Co后金属陶瓷材料烧结1,60 min和WC粉末的X射线衍射(XRD)图谱
Fig.2 XRD patterns of cermet processed for 1,60 min and WC powder
Subrata等
顾冬冬教授
图3 模拟和测量数据在烧结区与扫描速度的对比
Fig.3 Sintering zone dimension versus scan speed:compari-son between simulations and measurements with differ-ent Nd:YAG laser power
(a)8.18 W;(b)17.9 W;(c)28.1 W
表1 激光烧结后样品熔渗前和熔渗后的密度 下载原图
Table 1 Density of laser sintered samples with and with-out infiltration
3 选区激光熔化(SLM)打印硬质合金
选区激光熔化技术(SLM)使用高能激光束选择性地熔化和凝固粉末层,逐层打印零件。因其具有灵活性和高性能、复杂结构复合材料零件近净成型的潜力,镍合金
Khmyrov等
Eckart等
图4 沿Z方向不同高度的维氏硬度和压痕断裂韧性
Fig.4 Profile of Vickers hardness and indentation fracture toughness at different height level along Z direction
图5 激光扫描速度为1.2,1.0和0.8 m·s-1SLM加工试样的低倍微观组织(SEM)
Fig.5 Low-magnification SEM images of SLM-processed samples at laser scan speeds of 1.2 m·s-1(a),1.0 m·s-1(b)and 0.8 m·s-1(c)
Alexey等
图6 WC-Co颗粒的形态及SLM制成的硬质合金的SEM照片
Fig.6 SEM images of WC-Co granules and cemented car-bides
(a)Granule A,made by spray drying;(b)Granule B,madeby cold pressing followed by crushing;(c)Cemented carbidesmade from(a)Granule A;(d)Cemented carbides made from(b)Granule B after SLM processing
4 其他3D打印硬质合金成型方法
4.1 3D冷打印技术制备硬质合金
3D冷打印技术(3D gel printing)是基于增材制造理念,以金属/陶瓷和凝胶体系制备出的稳定悬浮浆料为原料,通过选择逐层堆积和固化悬浮浆料,制造三维实体的技术
Zhang等
图7 不同装载量喷胶粘粉成型的WC-20Co浆料打印烧结后样品的SEM图像
Fig.7 SEM images of sintered samples printed by 3DGP using WC-20Co slurries with different solid loading
4.2 选择性电子束熔化(selective electron beammelting,SEBM)
SEBM可用于制备硬质合金零件,可一步成形,现在主要应用于金属合金,其高温的特性适用于难熔金属和对氧气、氮气亲和力高的金属,在制备硬质合金领域有广阔前景,扫描速率过高易导致高孔隙率,需要后期处理提高致密性。SEBM原理虽然类似于SLM,铺粉后将粉末床熔化,逐层堆叠,但是其热源是高能光束,且SEBM所需的环境是真空状态,需要基板预热温度比SLM高许多,扫描速率对成形效果具有重要影响。
为探究不同扫描速率对试样孔隙率的影响,Konyashina等
4.3 定向能量沉积技术制备硬质合金
激光在基板快速移动的同时在沉积区域产生熔池,材料以粉末或丝状直接送入熔池中,融化后快速凝固,逐层沉积完成零件打印,这种成型方法被称为定向能量沉积技术(directed energy deposition,DED)。DED主要是以激光近净成型制造(laser engineered net shaping,LENS)和金属直接沉积(direct metal deposition,DMD)技术为主。Xiong等
5 力学性能分析
目前3D打印硬质合金尚在起步阶段,大多研究者成型小试样,硬度被作为衡量成型效果的主要力学性能之一,如表2所示。从表中的数据可以看出,相同Co含量的硬质合金激光成型方式硬度高于粘结喷射成型方式。对于BJ3DP技术探究合适的粘结剂饱和度以及成型参数为以后更好的成型效果提供有效手段。
图8 不同扫描速率下热处理前、后试样表面的光学显微镜(OM)照片及扫描速率在800 mm·s-1时试样的XRD图谱
Fig.8 OM images showing surface of sample before and after heat treatment with different scanning velocity
(a,b)4500 mm·s-1;(c,d)2250 mm·s-1;(e)800 mm·s-1;(f)XRD pattern of sample(without heat treatment)with scanning veloci-ty of 800 mm·s-1
表2 不同3D打印方法制备的硬质合金硬度对比 下载原图
Table 2 Hardness of cemented carbide built with different 3D printing method
6 总结与展望
硬质合金因具有优异的综合力学性能,被广泛应用于工业各个领域。但目前对复杂零件及个性化的需求,3D打印成型硬质合金,未来一段时间仍然可能是科技及产业界关注的重点。
激光粉末床技术在成型硬质合金过程中由于熔池的高凝固速率,WC和Co的高熔点差,导致成型后的试样易产生裂纹。成型后熔渗、烧结等易引起收缩变形。
目前采用间接3D打印方法和粉末床成型方法制备硬质合金,其将粉末冶金和3D打印的特点相结合,成本较低,能大幅度提高硬质合金成型效率,具有成型复杂结构的可能,部分力学性能指标逐步提高。
浆料成型方法在打印时压力较小,仅靠逐层沉积和交联剂的粘结成型作用,制备出的硬质合金致密度与硬度较低。未来的研究方向除了进行热处理及烧结方式以外,还可采用液态粘结剂和粉末交替层层堆叠成形的溶剂法喷印3D打印技术,能有效的避免喷头堵塞和烧结后的高收缩率等问题,值得进一步探索与研究。
为了扩展硬质合金3D打印的适用性并实现高质量硬质合金的工业生产,未来研究中需要结合传统硬质合金生产液相烧结工艺,解决复杂硬质合金的3D成型难题,达到低成本、高性能硬质合金零件的研发。
参考文献