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超细硬质合金晶粒长大抑制机理及热处理工艺研究
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摘要
在21世纪的今天,电子产品如手机、笔记本电脑等功能越来越强大,形状却越来越小巧,使得印制线路板(PCB:Printed Circuit Board)电路的集成化程度越来越高,电路的导通孔发展趋势为0.80mm→0.50mm→0.40mm→0.30mm→0.25mm→0.20mm→0.10mm→0.05mm。如此精细的孔对PCB微钻提出了相当苛刻的要求,不但要求极高的硬度以保证良好的耐磨性,更要求其具有良好的抗弯强度(TRS:Transverse Rupture Strength)以保证在加工过程中不出现折断等现象。超细晶硬质合金的出现,以其“双高”的优良性能,从材质的角度上使该需求得以实现。这一现象引起了世界范围内的广泛关注,国内外对于超细硬质合金的研究如火如荼,也越来越深入。而世界级的大公司,出于技术保密的原因,很少将其制备工艺公诸于世,因此研究开发出适合我国国情的高质量超细硬质合金具有现实而深远的意义。
     本文采用OMG公司生产的超细WC粉、南京寒锐公司生产的超细Co粉及长沙伟晖公司提供的VC、Cr_3C_2粉为原料,以真空干燥、低压烧结为制备手段,结合淬火并回火的热处理工艺,以高分辨透射电镜(HREM:Higll Resolution Electron Microscope)、扫描电镜(SEM:Scanning Electron Microscope)、X射线衍射(XRD:X-ray Diffractometer)、示差扫描量热计(DSC:Differential Scanning Calorimetry)、能量色散谱仪(EDS:Energy Dispersive Spectrometer)等分析手段,详细探讨了超细硬质合金制备过程中抑制剂的添加对性能的影响,深入的分析了WC晶粒长大过程及抑制剂的作用机理,并指出常用抑制剂VC、Cr_3C_2各自的利弊,系统的研究了热处理工艺对超细硬质合金性能的提高并解释其机理。
     试验结果表明,添加抑制剂VC、Cr_3C_2后,合金的WC晶粒明显细化,硬度和矫顽磁力提高,但是TRS值下降。其中,VC细化效果能力更强,提高合金的硬度也更加明显,但是对TRS的危害也更大。Cr_3C_2细化效果稍弱,少量添加对TRS有利。添加合适比例的复合抑制剂能取长补短,得到综合性能较高的超细硬质合金。本文利用HREM、EDS等分析手段,从微观机理上分析了WC在固相、液相烧结过程中的长大机制和VC、Cr_3C_2等抑制剂不同的作用机理。通过观察发现,VC、Cr_3C_2等抑制剂均固溶在粘结相里,阻碍WC通过溶解—析出的长大机制而抑制晶粒长大。其中VC阻碍WC溶解能力更强,且能降低合金的系统共晶温度,使烧结在更低温度下完成,具有多重细化WC晶粒的能力,因而比Cr_3C_2抑制WC晶粒长大的能力更强。添加VC的超细硬质合金中,WC颗粒较小且均匀,但有不光滑界面产生;粘结相分布不是很均匀,甚至出现了蜂窝状的疏松组织,这是VC容易被氧化,形成氧化物硬块,不易被液态的粘结相有效润湿的缘故。Cr_3C_2细化效果虽然不如VC,但是WC颗粒形状规则,界面平直光滑,使得粘结相易于流动,分布更加均匀,因而对合金的TRS有利。但有个别粗大晶粒现象,这是由于Cr_3C_2使W、C原子在粘结相中的溶解不一致,导致合金缺碳引起η相分解造成的。
     通过超细硬质合金的热处理工艺研究,找到了较为合理的淬火及回火工艺。实验表明,通过淬火可以使超细硬质合金WC—15Co—0.2VC—0.4Cr_3C_2合金的TRS提高13.6%,而硬度却基本保持不变,再通过合理的回火工艺,可以使TRS再进一步的提高10.5%以上。通过SEM对超细硬质合金进行微观形貌观察,发现经过淬火处理后,WC晶粒棱角溶解消失,从而变得圆润,这有利于合金的致密化;粘结相得到体积强化,分布也更加均匀;合金的断裂方式变为沿WC—Co界面的塑性断裂为主。利用XRD分析了粘结相中成份结构变化,从微观机制上解释了热处理提高了TRS的主要原因,最后利用DSC分析了热处理过程中粘结相相变温度点,从而为更科学的指导热处理工艺奠定了理论基础。
In the 21th century, electron products such as mobile and notebook PC have more and more strong function but smaller and smaller in the shape size. Which made circuit of PCB integrationlize more indensity than ever. the lead hole size of PCB is 0.80mm→0.50mm→0.40mm→0.30mm→0.25mm→0.20mm→0.10mm→0.05mm. Which demand machining tools not only have enough hardness to ensure superexcellence wearable, bu also have suffice TRS to assure it will not break in the work. Since the appear of Super fine cemented ceramic with It's higher hardness and higher TRS, the expectation to the machining tools will come into truth in the material aspect. These phenomena have arosed abroad attention all the world. More and more study on the super-fine ceramic at domestic and overseas become profundity. While, as the technology close off of world-class company, there are few report on the technics of super-fine cemented ceramic
     In This paper, we use imported Ultra-fine WC powders producted by American OMG company and Ultra-fine cobalt powders producted by NanJing HanRui Co. Ltd as crude materials, use vacuum-dryness and low-pressure sinter as process method, and use HREM、SEM、X—ray、EDS、DSC as analyse measure, discuss the effect on super-fine cemented ceramic capability of inhabitor particularly, discuss the advantage and disadvantage of VC Cr_3C_2, analyse the process of WC crystal grain growth and the working mechanism of inhabitor in-depth, study on the property-heighten of heat treatment to super-fine ceramic systemly.
     The results shows that both VC and Cr_3C_2 can inhabite WC crystal grow up, the hardness and Hc of alloy will increase while TRS decrease. VC can inhabite WC crystal particle grow up more effectively whlile Cr_3C_2 in favor of TRS, so the mix doped inhibitors of VC and Cr_3C_2 in light of appropriate proportion will obtain more excellent synthetical performance. no matter what kind of inhabitor, the append count must be appropriate, or else will do harm to property of ultra-fine cemented carbides.
     Study by HREM indicate that VC will make WC crystal particle become smaller and uniformity, while the shape will become abnormity, the felt phase will distributing not uniformity. Cr_3C_2 can make WC crysta grain'shape standardization and felt phase distributing abroadly, but there are some larger grains. Analysed by EDS, we found that VC and Cr_3C_2 both deposited in felt phase, which inhabite the WC crystal grain growth by slow the grain solvedeposit. between the two kind of inhabitor, VC has apparently restrain effect but bring about the strength decrease. The complex of Cr_3C_2 and VC have excellent synthesis effect.
     Heat treatment experiment shows that quench on super-cemented carbide will enhance 13.6 percent on TRS while the hardness remain. After temper treatment subsequently, the alloy will improve the TRS by 10.5percent, and then the hardness will ameliorate slightly. observed by SEM shows that, the edges and corners of WC grain will disappear, felt phase volume will strengthen, rupture method will change after heat treatment, We analyze ingredient transformation in the felt phase by XRD, data shows that content ofε—Co at will decrease whileα—Co increase, that is the main renson cause TRS strengthen. At lase, we use DSC find that the temperature of phase change variety with Co content, These results in our research have guidance meaning in industry production.
引文
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