机械合金化Fe基预合金粉末对金刚石刀头性能的影响

探索了Fe-Cu-Ni-X(X=W、Mo、Ti、C、B4C)系粉末的机械合金化工艺,及其对热压烧结金刚石刀头强度和硬度的影响.发现干法球磨20小时可以得到15μm的预合金粉末,除W、B4C之外,其它元素均可固溶入Fe中;经930℃热压烧结后,Cu又从Fe中析出,同时形成WC等硬质相;B4C可能在球磨过程中产生了部分非晶化,经高温烧结后又恢复了结晶态,B4C并未与W、Mo、Ti等合金元素反应形成金属硼化物;将80vol％机械合金化预合金粉末与20vol％的45/50#镀Ti金刚石颗粒均匀混合后,进行930℃热压烧结,随着B4C含量增加,金刚石刀头的硬度逐渐增大,而抗弯强度在1％ B4C时达到最高值949MPa,硬度为HRB120.7.     

新型锯片刀头——金刚石涂层刀头问世

金刚石涂层刀头是利用化学气相沉积方法，以氢气、碳源气体等做原料，在低于1000摄氏度和小于一个大气压的条件下，在硬质合金刀头表面直接沉积和基体结合良好的纯金刚石薄膜涂层；此产品既有表面金刚石最好的硬度和耐磨性，又具有硬质合金基体良好的抗冲击韧性，性能价格比高，应用范围广，是锯片刀头产品的一次伟大革命。     

热压烧结工艺制备Si/SiC陶瓷的研究

α—SiC粉末为原料,Si为助烧剂,采用适当的热压烧结工艺,在1800℃,25MPa条件下获得了致密的SiC块体陶瓷,其抗弯强度为253MPa。     

影响金刚石烧结刀头尺寸偏差的原因分析及改进措施

通过分析影响烧结刀头尺寸偏差的原因后，认为烧结过程中模框等的热变形是造成烧结刀头齿厚尺寸偏差的主要原因，而齿厚偏差是引起齿高偏差的主要原因，并提出改进措施，很好地解决了烧结刀头尺寸偏差问题。     

烧成温度对多孔SiC陶瓷管性能的影响

以SiC为骨料,添加低共熔混合物烧结促进剂,煤粉作为造孔剂,在不同的温度下烧成制备多孔陶瓷管.考察了烧成温度对多孔SiC陶瓷管的孔隙率、气体渗透通量、孔径分布以及抗弯强度等性能的影响,并通过SEM对其结构形貌进行了表征.结果表明:随着烧成温度的提高,孔隙率、气体通量及抗弯强度下降,孔径分布变宽.     

稀土对铁基结合剂金刚石节块性能的影响

研究了不同含量CeO2及CeO2与Y2O3混合稀土的加入对铁基结合剂金刚石节块性能的影响。结果表明:稀土CeO2的加入对铁基结合剂金刚石节块的硬度和抗弯强度有一定的影响;混合稀土对铁基结合剂金刚石节块的硬度和抗弯强度影响显著,加混合稀土的金刚石节块的性能都优于没有加的;当CeO2和CeO2与Y2O3加入量为0.2%时,能得到最优的性能。此外,节块的应力-应变关系表现为陶瓷的特性。     

裂解碳包覆对SiC纳米纤维增强SiC陶瓷基复合材料性能的影响

以SiC纳米纤维(SiC_nf)为增强体,通过化学气相沉积在SiC纳米纤维表面沉积裂解碳(PyC)包覆层,并与SiC粉体、Al₂O₃-Y₂O₃烧结助剂共混制备陶瓷素坯,采用热压烧结工艺制备质量分数为10%的SiC纳米纤维增强SiC陶瓷基(SiC_nf/SiC)复合材料。研究了PyC包覆层沉积时间对SiC_nf/SiC陶瓷基复合材料的致密度、断裂面微观形貌和力学性能的影响。结果表明:在1 100 ℃下沉积60 min制备的PyC包覆层厚度为10 nm,且为结晶度较好的层状石墨结构;相比于纤维表面无包覆层的复合材料,复合材料的断裂韧性提高了35%,达到最大值(19.35±1.17) MPa·m^1/2,抗弯强度为(375.5±8.5) MPa,致密度为96.68%。复合材料的断裂截面可见部分纳米纤维拔出现象,但SiC_nf/SiC陶瓷基复合材料界面结合仍较强,纳米纤维拔出短,表现为脆性断裂。     

微波烧结制备Ti3SiC2-金刚石复合材料的显微形貌及界面反应机理

采用Ti3SiC2粉体和金刚石粉体为原料,通过微波烧结制备Ti3SiC2结合剂金刚石复合材料,研究金刚石的含量和粒度对该复合材料的物相组成与显微形貌的影响.结果表明,通过高温微波烧结Ti3SiC2结合剂金刚石复合材料,金刚石表面会形成不同的涂层,从而与基体结合剂结合良好.金刚石的粒度和含量对复合材料中基体组成和金刚石的表面涂层状态有显著影响.烧结过程中,金刚石会不同程度的影响Ti3SiC2的分解.Ti3SiC2分解后生成Si与TiC.当金刚石含量相同(10％)、粒度较粗(30/40)时,金刚石表面会形成钛硅相与SiC涂层组织;基体的主相为Ti3SiC2、钛硅相与SiC.当金刚石粒度较细(W20)时,金刚石表面的C元素充分地与Si反应生成SiC涂层,基体主相变成TiC和Ti3SiC2.当金刚石粒度适中(120/140目与170/200目)时,基体的主相为Ti3SiC2.选取金刚石粒度为170/200目、金刚石含量较低时(5％与10％),基体的组成为Ti3SiC2与少量的SiC.金刚石含量较高时(20％与30％),基体的组成为Ti3SiC2与少量的TiC和SiC.各试样中金刚石表面都会形成钛硅相与SiC涂层组织.     

成型工艺对反应烧结SiC材料性能的影响

本文研究了不同成型工艺对反应烧结碳化硅陶瓷材料的素坯及烧结体的显微结构、力学性能的影响。研究发现：用原位凝固工艺获得的素坯比用干压和注浆成型的素坯孔径分布更加均匀、具有单峰性,孔洞形状规则。干压和注浆成型的烧结体中有大块残C与残余Si,原位凝固工艺的烧结体则无此缺陷,且具有更好的力学性能。     

碳源浓度对MPCVD金刚石涂层的影响研究

以CH₄和H₂为气源,采用微波等离子体化学气相沉积法(MPCVD),通过改变碳源浓度分别为5%、10%、15%,在硬质合金(YG6)上沉积了金刚石涂层样品。使用白光共聚焦显微镜、纳米压痕仪等研究了样品的微观形貌、表面粗糙度和弹性模量。结果表明：金刚石涂层表面光滑均匀,1 mm²区域表面粗糙度约为2μm,随着甲烷浓度升高,薄膜弹性模量呈先升高后下降的趋势,其中10%甲烷浓度制备的样品平均弹性模量约为457.9 GPa。     

电镀金刚石工具镀层脱落的原因分析

文章针对电镀金刚石工具在使用过程中镀层脱落常见的三种类型,讨论了镀层脱落的影响因素,提出了解决镀层脱落的基本对策。     

Effect of SiC coating and heat treatment on the thermal radiation properties of C/SiC composites

The effects of SiC coating and heat treatment on the emissivity were investigated for 2D C/SiC composites prepared by CVI in the 6–16 μm range. SiC coating had an obvious effect on the spectral emissivity of the composites but caused just 5% difference in the total emissivity. A radiation transport model was applied to explain those changes caused by SiC coating. Heat treatment affected the thermal radiation properties of the composites through the microstructure evolution. Base on the complementary analytical techniques, the changes in the emissivity were attributed to a good graphitization degree of carbon phases, large β-SiC grain sizes and high α-SiC content resulting in high emissivity.     

Preparing SiC/diamond coatings via chemical vapor deposition of SiC on diamond-coated graphite and their frictional properties

SiC/diamond coatings with excellent frictional properties were successfully prepared using graphite as substrate. Diamond particles with size of 25–38 μm were firstly bonded on graphite substrate through PVA glue, followed by chemical vapor deposition (CVD) of SiC with varied MTS flow on the diamond-coated graphite substrate to enhance the adhesion of diamond particles. The influence of the MTS flow on the SiC coatings was investigated. The results showed that polycrystalline SiC coating with good crystallinity has been obtained. With MTS flow increasing, the SiC grains feature increased surface roughness and greater sizes of the SiC crystallite resulting from the co-deposition of SiC and carbon with increased carbon containing species. Reciprocating sliding wear tests were conducted to investigate the coefficient of friction. With increasing applied load, while the low-flow specimens showed a remarkable increase in the friction coefficient resulting from degradation of the SiC coatings, the high-flow specimens maintained a relatively low friction coefficient during wear tests indicating strong holding force to diamond particles of the SiC coatings. The reason for low friction coefficient of the high-flow specimens was that GCr15 steel ball was wearing by the SiC/diamond coatings with good affinity to the substrate resulting in a flat–flat contact on the contact area.     

Research on maximizing the diamond content of diamond/SiC composite

Diamond content is a key factor affecting diamond/SiC composite performance, especially thermal and mechanical properties, but the composite with high diamond content manufacturing is still challenging issues. Hot mold pressing combined with liquid silicon infiltration to make diamond/SiC composites with high diamond content and relative density has been proposed in this paper. In addition, the effect of diamond particle size on the maximization of diamond content as well as properties of the composites were evaluated. The experiment shows that the content of diamond in the composites increases with the increase of the diamond particle size. When the particle size of diamond is 400 µm, the volume fraction of diamond reaches 59.08%. The highest thermal conductivity (d_dia= 300 µm) and highest bending strength (d_dia= 50 µm) are 616.77 W/m K (It is the maximum TC of diamond/SiC prepared by pressureless infiltration at present) and 380 MPa, respectively. This work provides a novel and efficient preparation method for further improving the thermal conductivity of diamond/SiC composites.     

Effects of fabrication processes on the properties of SiC/SiC composites

Precursor infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI) were used to fabricate SiC/SiC composites on a four-step 3D SiC fibre preform deposited with a pyrolytic carbon interface. The effects of fabrication processes on the microstructure and mechanical properties of the SiC/SiC composites were studied. Results showed the presence of irregular cracks in the matrix of the SiC/SiC composites prepared through PIP, and the crystal structure was amorphous. The room temperature flexural strength and modulus were 873.62 MPa and 98.16 GPa, respectively. The matrix of the SiC/SiC composites prepared through CVI was tightly bonded without cracks, the crystal structure had high crystallinity, and the room temperature bending strength and modulus were 790.79 MPa and 150.32 GPa, respectively. After heat treatment at 1300 °C for 50 h, the flexural strength and modulus retention rate of the SiC/SiC composites prepared through PIP were 50.01% and 61.87%, and those of the composites prepared through CVI were 99.24% and 96.18%, respectively. The mechanism of the evolution of the mechanical properties after heat treatment was examined, and the analysis revealed that it was caused by the different fabrication processes of the SiC matrix. After heat treatment, the SiC crystallites prepared through PIP greatly increased, and the SiOxCy in the matrix decomposed to produce volatile gases SiO and/or CO, ultimately leading to an increase in the number of cracks and porosity in the material and a decrease in the material load-bearing capacity. However, the size of the SiC crystallites prepared through CVI hardly changed, the SiC matrix was tightly bonded without cracks, and the load-bearing capacity only slightly changed.     

The effects of adding nano-alumina filler on the properties of polymer-derived SiC coating

In this paper, SiC coating was prepared using the polymer-derived ceramic method; then the effect of nano-alumina as a filler material was studied. First of all, polycarbosilane(PCS) was dissolved in xylene; after that, different amounts of nano-alumina particles were added to the solution. The coating was deposited on the alumina substrate using the dip-coating method; this was followed by sintering at 1200℃. The phase content and microstructure of the samples were studied by X-ray diffraction and scanning electron microscope methods, respectively. Nanohardness, Young's modulus, and coating adhesion were investigated by a nanoindentation method. The sheet resistance was evaluated using the four-point probe technique; also, the wear resistance of the coating was studied by applying the pin-on-disk method. It was found that the addition of the nano-alumina filler up to 20 wt% drastically improved the adhesion and wear resistance of the SiC coating.     

Effects of hydrogen on electronic properties of doped diamond

We have investigated the effects of hydrogen on the electronic structure of diamond doped boron and sulfur using cluster model method within the frame of ab initio density functional theory (DFT). The results show that the presence of hydrogen results in a deep donor level with no change of conductivity type in sulfur-doped diamond samples and the formation of the multiple hydrogen-boron complexes may cause a conductivity type transition in the hydrogen-rich boron-doped diamond samples.     

形核密度对CVD金刚石涂层附着性能的影响

采用热丝化学气相沉积法(HFCVD)在硬质合金基体上进行金刚石的形核生长,使用扫描电镜(SEM)对金刚石涂层形核情况进行分析,研究了不同形核密度对CVD金刚石涂层附着力的影响。结果表明:当碳源浓度达到3%时,表面形核密度最高,约为107/cm2;浓度增大为4%时,形核密度降低。通过压痕实验对比分析得出形核工艺中碳源浓度为3%时沉积的金刚石涂层压痕最浅,压痕直径最小,金刚石涂层具有良好的附着性能。     

Effects of tool coating materials and coating thickness on cutting temperature distribution with coated tools

Coated tools are currently widely used tool technology in machining. The influence of tool coating on heat transfer has become an active field of research enjoying constantly increasing attention in the field of machining. This paper is devoted to the cutting temperature in machining H13 hardened steel with monolayer coated tools (TiN, TiAlN, and Al₂O₃) and multilayer coated tools (TiN/TiC/TiN and TiAlN/TiN). Equivalent composite thermal conductivity and thermal diffusivity of multilayer coated tools were calculated using the equivalent approach. The established heat transfer analytical models estimated coating temperature in turning. The effect of tool coating in steady and transient heat transfer was studied, as well as the cutting temperature distribution. It reveals that the tool coating material and coating thickness can influence the cutting temperature distribution of coated tool. Thermal conductivity of coating material affects the steady cutting temperature distribution, and thermal diffusivity of coating material affects the transient cutting temperature distribution of coating tools.