立方相对超细晶梯度硬质合金微观组织的影响

以超细WC粉末为原料,采用低压预烧结和梯度烧结两步法制备了超细晶梯度硬质合金。通过添加不同的立方相,研究了立方相对超细晶梯度硬质合金组织和性能的影响。结果表明,仅添加Ti(C,N)可以形成较厚的梯度层,但梯度烧结后WC晶粒尺寸有较大的增长。(W,Ti)C和(Nb,Ta)C的加入不利于较厚梯度层的形成,但在梯度烧结过程中可以抑制WC晶粒的生长。添加(Ti,W)C的合金在梯度烧结后出现了少量尺寸大于1 μm的WC晶粒,(Ta,Nb)C的加入可以很好的抑制合金中芯环结构立方相的形成。     

Ti(C,N)的碳氮比及粒度对脱β层梯度硬质合金的影响

研究了Ti(C,N)的粒度和组成对脱β层梯度硬质合金性能和组织结构的影响。结果表明,Ti(C,N)粒度范围位于1.5μm～3.0μm之间和碳氮质量比控制为1∶1最有利于梯度硬质合金脱β层的形成。     

WC碳量对高钴硬质合金性能与硬质相晶粒度的影响

本文通过选用碳含量不同的WC原料配制成4组WC-22%Co高钴硬质合金,采用物理性能检测、光学金相等分析方法,对比研究了不同碳含量WC对WC-22%Co高钴硬质合金烧结后的性能和硬质相粒度的影响。结果表明:在所有方案中,原料WC中碳质量分数为5.97%时,合金抗弯强度最高,达到2 590 MPa,但合金金相组织不均匀,粗大WC晶粒数量较多,WC粒度分布最宽;随着原料WC碳含量的增加,合金金相组织趋于均匀化,粗大晶粒数量逐渐减少且WC晶粒粒径离差系数同步减小,并在WC碳质量分数为6.14%时WC晶粒粒径离差系数出现最小值,为0.475 7。     

立方相对超细晶梯度硬质合金组织和性能的影响

以超细WC粉末为原料,采用低压预烧结和梯度烧结两步法制备了超细晶梯度硬质合金。通过添加不同的立方相,研究了立方相对超细晶梯度硬质合金组织和性能的影响。结果表明,仅添加Ti(C,N)可以形成较厚的梯度层,但梯度烧结后WC晶粒尺寸有较大的增长。(W,Ti)C和(Nb,Ta)C的加入不利于较厚梯度层的形成,但在梯度烧结过程中可以抑制WC晶粒的生长。添加(Ti,W)C的合金在梯度烧结后出现了少量尺寸大于1μm的WC晶粒,(Ta,Nb)C的加入可以很好地抑制合金中芯环结构立方相的形成。     

渗碳工艺对WC-Co梯度硬质合金的梯度结构和硬度的影响

对缺碳硬质合金采用渗碳处理制备梯度硬质合金,利用显微组织分析和维氏硬度测试等方法,研究渗碳工艺对梯度硬质合金的梯度结构和硬度的影响。结果表明：渗碳处理后随着渗碳时间延长,梯度层厚度增大,长时间渗碳还会出现梯度结构消失现象;渗碳时表面层WC晶粒长大,且渗碳时间越长晶粒长大越严重;渗碳后梯度硬质合金的表面硬度明显提高;渗碳后合金的表面硬度明显高于烧结态合金的表面硬度;随着渗碳时间的延长,合金表面硬度先增大后减小;合金的硬度在截面上沿梯度方向呈连续梯度变化,合金表面层因WC含量较高、钴含量较低而具有较高的硬度,中间层因钴含量较高、WC含量较低,其硬度较低。     

WC-TiC-TaC-Co硬质合金中TaC含量对其显微组织和力学性能的影响

利用SEM、EDS、三点弯曲装置及硬度计等手段研究了TaC含量对WC-TiC-TaC-Co硬质合金显微组织和力学性能的影响。结果表明,WC-TiC-TaC-Co硬质合金主要由3种相组成:WC相、(W, Ti, Ta)C相和γ相。随着TaC的质量分数从4.6%增加到7.3%,尺寸小于0.5μm的WC晶粒比例增加;尺寸大于1μm的复合碳化物(W, Ti, Ta)C晶粒比例增加,且均匀分散分布的(W, Ti, Ta)C开始聚集。合金的密度、硬度与断裂韧性均呈先下降后上升再下降的变化趋势;合金的抗弯强度呈先上升后下降的趋势。当TaC含量为6.3%时,合金的综合力学性能最佳:硬度、断裂韧性和抗弯强度分别为1749 HV_(30)、10.2 MPa·m~(1/2)和2247 MPa。     

基于钴、碳迁移动力的梯度硬质合金制备与材料特性研究

功能梯度硬质合金(FG WC-Co)与WC-Co相比能够提供优异的硬度和断裂韧性组合。基于液相Co从高Co含量向低Co含量、从高C含量向低C含量迁移的钴、碳迁移动力,本文设计了富碳高钴的WC-15%Co和贫碳低钴的WC-6%Co双层样品。采用扫描电镜(SEM)、X射线衍射(XRD)等分析手段,研究了双层硬质合金的微观结构与力学性能。结果表明双层样品中Co相从富碳高钴层向贫碳低钴层迁移形成梯度结构,并且两层间C含量差别越小,Co浓度梯度越大;高钴层中WC晶粒尺寸比低钴层的大,并且两层间C含量差别越小,WC晶粒尺寸差别越大;随着两层间C含量差别减小,矫顽磁力(Hc)减小,钴磁(Com)增加;硬度从1 260 HV至1 408 HV逐渐升高,从WC-15%Co面加压测的抗弯强度2 612 MPa高于从WC-6%Co面加压测的抗弯强度2 388 MPa。     

真空-压力两步烧结制备的表层脱立方相梯度硬质合金的组织与性能

本文通过真空-压力两步烧结制备了脱立方相梯度硬质合金,并对材料的组织和性能做了研究。研究发现,相比于一步真空烧结制备的脱立方相梯度硬质合金,真空-压力两步烧结制备的梯度硬质合金脱立方相层更厚,合金内部的立方相晶粒尺寸更大。梯度硬质合金脱立方相层中的平均WC晶粒尺寸比内部的更大,这与脱立方相层中Co含量更高以及内部含Ti立方相的存在有关。梯度硬质合金中过渡层的微观硬度高于合金内部,而脱立方相层的硬度最低,微观硬度变化与Co、Ti等元素含量变化紧密相关。压力烧结对表面脱立方相层的致密化作用明显,使得脱立方相层的孔隙减少,梯度合金相对密度达到99.6%。脱立方相层厚度增加和孔隙缺陷减少促进了梯度硬质合金横向断裂强度的提高。     

WC-Co梯度硬质合金的制备及渗碳对其组织的影响

采用光学金相检测、扫描电镜分析、能谱分析等方法对WC-6Co硬质合金渗碳处理后的成分和梯度组织结构进行分析.结果表明:对硬质合金渗碳处理后可形成显微组织和钨、钴含量的梯度分布,其特征是合金表层和次表层的η相已经完全消失,属正常的WC γ两相组织,合金的芯部依然是含η相的三相组织,中间形成了一个富钴层;碳原子的扩散和液相钴的流动是形成梯度的原因;在各渗碳温度下,合金的梯度结构厚度均随渗碳时间的增加而增加;在渗碳时间和渗碳温度相同的情况下,合金的梯度层厚度均随合金初始总碳含量的增加而增厚.渗碳处理后外表面的WC晶粒可能会产生一定的粗化现象.     

烧结气氛对Ti(CN)基金属陶瓷组织和性能的影响

用X射线衍射、背散射扫描电镜及能谱仪等分析手段研究了烧结气氛(真空、N2、Ar)对不同成分TiC基和Ti(CN)基金属陶瓷合金显微组织和性能的影响.金属陶瓷在N2和Ar中烧结后,合金碳含量比在真空中烧结的碳含量低0.5%左右;在N2中烧结后,合金的氮含量提高了0.5%左右.环状结构心部可以是以钨等重金属元素为主要成分的碳化物,也可以是以钛为主要成分的碳化物和碳氮化物.环状结构为金属元素含量和分布不同的(Ti,W,Ta,Mo,Co,Ni)(C,N)固溶体,粘结相是与Ti,W,Ta,Mo,C,N等元素有不同溶解度的钴镍固溶体.真空烧结后组织结构比较均匀,合金的性能最好.在Ar、N2中烧结后,气氛中的氧和氮参加烧结反应,影响合金成分碳氮平衡,在合金表面形成壳层结构,产生表面缺陷,合金的密度、显微硬度、抗弯强度均有比较大的降低;N2气氛影响更大.     

表面无立方相层功能梯度硬质合金的研究进展

综述了目前应用于涂层基体的无立方相层含氮功能梯度硬质合金的研究进展;详细介绍无立方相层的形成热力学基础、梯度结构特征、机理和动力学研究进展以及力学性能和切削性能;重点评述C、N含量以及组分对无立方相层的影响规律;提出获取合金系统真实的热力学相图和动力学数据是今后研究工作的重点。     

Fabrication of WC-Co/(Ti,W)C graded cemented carbide by spark plasma sintering

The WC-Co/(Ti, W)C graded cemented carbide was prepared by spark plasma sintering. The substrate is WC-8Co, and the hard layer is (Ti, W)C solid-solution. The effects of sintering temperature and holding time on the microstructure and properties of graded cemented carbide were analyzed. The hard layer is mainly formed by dissolving WC in the Co-phase and then by solid-solution reaction with TiC. As the sintering temperature increases, the migration rate of WC increases. When the holding time is 5 min, the thickness and the W content of the (Ti, W)C solid-solution hard layer increases with the increasing of sintering temperature. The thickness of the (Ti, W)C solid-solution can reach 51 ± 2 μm at the sintering temperature of 1700 °C for the holding time of 5 min. The hardness of hard layer surface increases first and then decreases with the increasing of sintering temperature. The Vickers hardness is the highest at 1600 °C, which can reach HV_0.221.53GPa. As the holding time increases, the thickness of the solid-solution hard layer increases, but the rate of growth decreases. As the thickness increases, the difference in the W element concentration between the solid-solutions of the same pitch decreases along the layer depth direction, and W element concentration in the entire hard layer increases. The oxidation behavior of graded cemented carbide at 400 °C and 600 °C was investigated. The (Ti, W)C hard layer has superior oxidation resistance relative to the WC-Co substrate.     

Microstructure and mechanical properties of functionally gradient cemented carbides fabricated by microwave heating nitriding sintering

A new method is presented for the fast preparation of functionally graded cemented carbide materials by microwave heating nitriding sintering. The influence of composition and sintering temperature on the mechanical properties, microstructure, and phase composition of the materials was studied. Results showed that functionally graded cemented carbides with the desired mechanical properties can be obtained rapidly by microwave heating nitriding sintering. A gradient layer with a Ti(C, N)-enriched surface layer, and underneath a Co-enriched layer formed on the top of the hard alloy substrate. The nitriding process had little effect on the microstructure of the matrix. A lower surface roughness, and the similar layer thickness as seen in conventional heating nitriding was obtained by microwave heating nitriding sintering in a short period of time. The thickness of the gradient layer increased with increasing temperature. The high Ti content in the raw material was beneficial to the formation of the gradient layer; however, the Co content had little effect on the gradient layer thickness when it increased from 6% to 10%.     

Effect of secondary carbides addition on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-based cermets

(Ti, W, Mo, V)(C, N)-based cermets were prepared by mixing Mo₂C, WC and TaC with ultrafine (Ti, W, Mo, V)(C, N) powders, and then processed via a conventional P/M technique. The effect of Mo₂C, WC and TaC on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co systems was investigated. The Mo₂C content was varied from 0 to 10 wt.% and additive WC or TaC was added at a level of 5 wt.% with Mo₂C addition. The results show that the densification of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co cermets was improved significantly by the addition of Mo₂C. With the increase of Mo₂C content, there is a coarsening tendency in the microstructure of (Ti, 20W, 15Mo, 0.2V)(C, N)-8Ni-7Co system, but the refinement for (Ti, 15W, 5Mo, 0.2V)(C, N)-8Ni-7Co. TaC addition decreases the density of (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-8Ni-7Co cermet and thus weakens its bending strength. (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-5WC-8Ni-7Co cermet has optimal mechanical properties: bending strength of 1999 MPa, hardness (H_v) of 1677 MPa and toughness of 9.95 MPa m^1/2 respectively by adding WC, which is due to its ultrafine and weak core/rim structure.     

接触材料含碳量对高钴硬质合金烧结后底部形貌及成分的影响

本文通过对硬质合金烧结中使用的5种接触材料表面进行了元素能谱分析(EDX),并使用这些接触材料对高钴(WC-22%Co)硬质合金进行烧结,利用SEM及EDX对硬质合金底部与接触材料的接触面进行了表面形貌观察和元素能谱分析,并对合金底部表面形貌和成分组成进行了分析讨论。结果表明:含碳量在79%(文中含量均为质量分数)左右的接触材料适宜高钴硬质合金的烧结,合金底部表面没有出现钴富集和WC异常长大现象;而接触材料含碳量过低(17.38%)时,合金底部出现了钴的富集,易造成合金粘附接触材料并发生化学反应;接触材料含碳量过高(≥89.99%)时,合金底部表面出现WC晶粒的异常长大,WC晶粒异常长大的形貌为典型的三角形棱柱体。     

工艺条件对WC-12%Co超细硬质合金性能的影响

采用不同粒度的WC粉,加入VC、Cr3C2做抑制剂,制备WC-12%Co超细硬质合金。采用D60-25型钴磁仪测量合金磁饱和,利用排水法测定合金密度,采用三点弯曲法在CMT4504拉伸机上检测合金的抗弯强度,试样抛光后在JEOL-6701F扫描电镜下观察合金的显微组织。研究了不同的WC粉末粒度、球磨时间、烧结工艺对WC-12%Co的超细硬质合金性能的影响。结果表明:过压烧结可明显提高合金抗弯强度、硬度和密度;随着球磨时间的增加,合金硬度不断上升,抗弯强度先增后减;采用0.55μm粒度WC粉制备的合金的硬度明显高于0.70μm粒度WC粉制备的合金。在本次实验中,选用0.55μm的WC粉末原料,混合料球磨85 h,通过过压烧结,可制备出性能优良的WC-12%Co超细硬质合金,硬度HV≥1 800,抗弯强度≥3 400 N/mm2。     

Effect of pre-alloyed raw materials on the microstructure of a (Ti,W)(C,N)–Co cermet

Four alloys manufactured from different combinations of powders (TiC + TiN + WC; Ti(C,N) + WC; (Ti,W)C + TiN and (Ti,W)(C,N)) were studied using X-ray diffractometry, optical microscopy (OM), scanning electron microscopy (SEM) and analytical electron microscopy (AEM). The alloy manufactured from binary powders had a smaller grain size and a more inhomogeneous microstructure than the other alloys. The alloys manufactured with WC contained an inner rim around Ti(C,N) cores, as well as W-rich cores. Thermodynamic calculations suggest that these are formed during solid-state sintering at 900°C in a low nitrogen activity. The outer rim had a composition that is in good agreement with calculations of the equilibrium during liquid phase sintering at 1450°C.     

细WC配比对非均匀YG20C合金性能的影响

研究了碳化钨粗颗细粒搭配对YG20C合金的力学性能与组织结构的影响,即在WC颗粒平均粒径为25μm的合金中,加入不同比例的平均粒径为2.0μm的WC颗粒,构成非均匀晶粒硬质合金。结果表明,非均匀YG20C合金的硬度和抗弯强度随着细晶粒碳化钨含量的增加都是先升高再降低。当细颗粒碳化钨比例为20%(文中含量均为质量分数)时,YG20C合金的综合力学性能最好,硬度和抗弯强度都达到"双高",其值分别为HRA83.5和2 800 MPa,比均匀YG20C合金的硬度和抗弯强度分别提高HRA1.2和400 MPa。并且非均匀YG20C合金的冲压使用效果最佳。     

微量铁对YG8硬质合金硬度、磁性能及孔隙度的影响

以钨粉筛上物制备的碳化钨为研究对象,采用湿磨、压制、真空烧结制备了YG8硬质合金,研究了WC中铁含量分别为0.33%和1.08%时,其加入量对YG8硬质合金矫顽磁力、钴磁、硬度及微观组织的影响规律。研究结果表明:含微量Fe的WC粉末结晶不完整、团聚严重;随着铁含量的增加,硬质合金的密度逐渐下降,而钴磁逐渐增加;随着铁含量的增加,硬质合金的矫顽磁力和硬度先下降再增加;当铁含量增加到一定值时硬质合金的孔隙度开始明显增加。当硬质合金中铁含量控制在0.3%以下时,可烧结出致密化程度高的YG8硬质合金,其孔隙度达到A02B00。     

Influence of preparation process on sintering behavior and mechanical properties of ultrafine grained Ti（C, N）-based cermets

The influences of forming and sintering processes on distortion, cracking as well as mechanical properties of sintered bodies of ultrafine grained Ti（C, N）-based cermets were investigated. The results show that lubricant is indispensable to fabrication of ultrafine Ti（C, N）-based cermets, however, with low binder content in powder mixture, the lubrication action of paraffin is attenuated. A appropriate level of 2% （mass fraction） paraffin is determined for a cermet with binder content of 36% （mass fraction）. It is also found that the influence of compaction pressure on distortion and cracking of sintered bodies presents a complex relationship. A relatively lower or higher compaction pressure, less than 100 MPa and more than 400 MPa respectively, favors uniform density distribution in green compact. The heating rate of sintering should be strictly controlled. Too fast heating rate results in enclosed pores to burst and forms large size pores in sintering body. A heating rate of 3 ℃/min is recommended.