机床用Al_2O_3/TiB_2复相陶瓷刀具材料的研究

以α-Al2O3和TiB2为主要原料,采用真空热压烧结工艺制备机床用Al2O3/TiB2复相陶瓷刀具材料。测试和分析了烧结样品的相对密度、弯曲强度、断裂韧性、硬度值、相组成以及显微结构。结果表明,当α-Al2O3添加量为75 wt%,微米TiB2添加量为20 wt%时,所制备的Al2O3/TiB2复相陶瓷刀具材料性能最佳,其相对密度值为98.8%,弯曲强度为606.25 MPa,断裂韧性为4.85 MPa·m1/2,硬度值为26.55 GPa。最佳样品的主晶相为刚玉(Al2O3)和硼化钛(TiB2),次要晶相为氧化钇(Y2O3)。     

TiB2材料氧化的热力学分析

采用物质吉布斯自由能函数法,对TiB2材料的氧化进行了热力学分析.热力学计算结果表明: TiB2材料从室温到高温均可以与氧发生反应生成TiO2;当温度T＜1450 K时,氧化产物为TiO2固相和B2O3液相,在氧化行为上表现为氧化增重;当温度T＞1450 K时,由于B2O3蒸气挥发,在材料中留下孔隙,增加了TiB2材料与氧气的接触面积,TiB2材料的氧化进程加速,此时,TiB2材料的抗氧化性逐渐下降;在PB2O3=101325 Pa的条件下,TiB2材料由"钝化氧化"向"活化氧化"的转变条件为T=1450 K;在氧化性气氛下,氧化反应的产物为TiO2,而随着氧分压降低,Ti4O7、Ti3O5、Ti2O3、TiO等氧化产物均有可能出现,尤其是在氧分压很低的情况下,TiO生成的可能性增大.     

全球切削刀具新材料和涂层技术现状

近代金属切削刀具材料从碳素工具钢、高速钢发展到今日的硬质合金、涂层硬质合金、陶瓷、立方氮化硼等超硬刀具材料,使切削速度从每分钟几米飚升到千米乃至万米。随着数控机床和难加工材料的不断发展,刀具实有难以招架之势。要实现高速切削、干切削、硬切削必须有好的刀具材料。在影响金属切削发展的诸多因素中,刀具材料起着决定性作用。     

普碳钢用陶瓷基高温防护涂层制备及其性能表征

采用机械混合法制备了一种针对碳钢的新型Al2O3-MgO-TiO2-CaO体系陶瓷基高温防护涂料,1300℃下可在Q235B钢表面形成致密保护层,提高钢抗氧化烧损性能.结果表明,在涂料粒度48～75μm、涂层厚度0.5mm的条件下,涂层防护性能优良.涂层的防护温度范围为900～1300℃,1300℃时比原样可降低氧化烧损59.36%,防护寿命长于8h.涂层的应用将氧化层由经典的Fe2O3/Fe3O4/FeO三层结构转变为一层尖晶石结构,同时减薄了氧化层厚度,显著降低了Fe元素的高温扩散速率.     

PcBN刀具硬态干切削条件对切屑形貌的影响

通过对PcBN刀具硬态干切削GCr15轴承钢的试验研究,观察分析研究了不同切削条件对切屑形貌的影响.结果表明,随着切削速度的增加,切屑锯齿化程度也越高,当切削速度大于200m/min时,切屑类似于挤裂状;随着进给量的增加,切屑的锯齿化程度越来越明显,且在进给量达到0.5mm/r时,切削产生严重变形;随着背吃刀量的增加,切屑的卷曲程度越大,但对锯齿化影响并不大,但当背吃刀量为0.05mm时,切削基本呈带状.     

FeCrAl基高温抗氧化陶瓷涂层抗热震性能的研究

采用陶瓷粘结相与Cr2O3制成料浆,在空气中1300℃下熔烧制备FeCrAl基高温抗氧化陶瓷涂层。研究了分散相Cr2O3的添加量和涂层厚度对试样抗热震性能的影响。结果表明:当Cr2O3的添加量为50%(质量分数,下同)、涂层厚度100μm和熔烧制度为1300℃×60min的条件下,涂层试样的抗热震次数可达16次(室温←→1200℃)。采用SEM、高温热膨胀仪等测试手段对涂层试样的组织结构及性能进行表征,揭示了涂层组织结构与抗热震性能之间的关系。     

氧化对Al_2O_3－TiB_2陶瓷刀具材料磨损特性的影响

研究了Ａｌ_２Ｏ_３－ＴｉＢ_２陶瓷刀具材料的高温氧化特性以及氧化对刀具耐磨性能的影响。结果表明：随ＴｉＢ_２含量的增加，Ａｌ_２Ｏ_３－ＴｉＢ_２的氧化活化能降低，抗氧化能力下降．Ａｌ_２Ｏ_３－ＴｉＢ_２刀具材料在加工淬火钢时，因切削高温的氧化作用在刀具表面生成的ＴｉＯ_２既可减轻刀具的粘结磨损，又能起到固体润滑剂的作用，从而降低摩擦系数，因而提高刀具的耐磨性能。当切削速度大于１５０ｍ／ｍｉｎ时，随ＴｉＢ_２含量的增加，刀具抗磨损能力显著提高。     

涂层技术及刀具涂层知识

1,氮碳化钛（TiCN）涂层比氮化钛（TiN）涂层具有更高的硬度。由于增加了含碳量,使TiCN涂层的硬度提高了33%,其硬度变化范围约为Hv3000~4000（取决于制造商）。2,CVD金刚石涂层：表面硬度高达Hv9000的CVD金刚石涂层在刀具上的应用已较为成熟,与PVD涂层刀具相比,CVD金刚石涂层刀具的寿命提高了10~20倍。金刚石涂层刀具的高硬度,使得切削速度可比未涂层的刀具提高2~3倍,使CVD金刚石涂层刀具成为有色金属和非金属材料切削加工的不错选择。3,刀具表面的硬质薄膜对材料有如下要求：1硬度高、耐磨性能好;2化学性能稳定,不与工件材料发生化学反应;3耐热耐氧化,摩擦系数低,与基体附着牢固等。单一涂层材料很难全部达到上述技术要求。     

钛合金高温防护陶瓷涂层的制备与性能

以磷酸二氢铝作为粘接剂,氧化镁与氧化锌作为固化剂,氧化铝与氮化硼作为填料,正硅酸四乙酯作为助剂制备出水性涂料,通过空气喷涂将涂料喷涂到TC18钛合金表面固化后制备出高温防护陶瓷涂层,并对涂层防护的钛合金基体进行了900℃条件下的高温氧化试验与抗热震试验。结果表明:高温氧化试验结束后整个TC18钛合金基体完全氧化,涂层涂覆试样保持完好,在900℃高温氧化环境中达到弱抗氧化性级别。陶瓷涂层历经60次空冷与水冷的抗热震性试验后陶瓷涂层保持宏观完整,未发生大面积脱落现象。     

FeCrAl合金表面高温抗氧化陶瓷涂层的制备

用粘结料与Cr2O3制成料浆,用喷涂涂覆于FeCrAl合金表面,在空气中1 300℃熔烧制备了耐高温（1 200℃）抗氧化陶瓷涂层.用扫描电子显微镜,电子探针显微分析仪,X射线衍射仪,热膨胀仪等测试手段对涂层以及涂层与基体界面处进行表征.探讨了陶瓷涂层样品高温抗氧化性能的机理,获得了具有良好高温抗氧化性能的陶瓷涂层配方,其粘结料与Cr2O3的质量比为1;0.5.结果表明：在空气中1 200℃,360 h抗氧化实验后,这种涂层样品的氧化质量增加约为基体合金的1/22.揭示了涂层高温抗氧化性能与涂层的组成、显微结构之间的关系.     

Applicability of DLC and WC/C low friction coatings on Al2O3/TiCN mixed ceramic cutting tools for dry machining of hardened 52100 steel

The present work examines the applicability of DLC and WC/C low friction coatings on Al₂O₃/TiCN based mixed ceramic cutting tools for the dry and hard turning of AISI 52100 steel (62 HRC). The characterization of coated tools reveals that the coatings retain very low values of surface roughness, whereas the DLC coating exhibits much higher microhardness when compared to the WC/C coating. On the other hand, the WC/C coating exhibit a coarse surface morphology virtually due to the tungsten doping. Later, continuous turning tests were executed with the help of coated and uncoated cutting tools under dry cutting conditions, and their performance was investigated in terms of machining forces, cutting temperature and tool wear. Coating delamination by flaking and peeling is quite prominent in the case of both the coatings; however, it is less severe for the WC/C coated tool. The coatings help to reduce machining forces, cutting temperatures and tool wear, but the performance of coated tools converge towards uncoated tool as the cutting speed, and feed rate is increased. Both the coatings prevent the development of cracks near the cutting edge with WC/C coating exhibiting superior wear behavior basically due to its multilayered structure and better thermal stability. Moreover, the tested low friction coatings don't serve as thermal barriers and only the lubrication generated due to graphitization at the chip-tool interface is mostly responsible for the improved machining performance.     

Diamond coatings for micro end mills: Enabling the dry machining of aluminum at the micro-scale

We show that thin diamond coatings can dramatically enhance the performance of micrometer-scale cutting tools. We present a new approach for coating 300 μm diameter tungsten carbide (WC) micro end mills using a tailored seeding method and hot filament chemical vapor deposition (HFCVD) to obtain uniform, conformal, and continuous diamond coatings less than 2 μm in both thickness and grain size. The performance of the uncoated and coated tools has been evaluated by dry machining channels in 6061-T6 aluminum. The test results demonstrate far lower tool wear and breakage, much lower adhesion of aluminum to the tool, and significantly lower cutting forces for the coated tools. The coatings achieve a more predictable surface finish and enable dry machining at high speeds (40,000 rpm) with little or no burr formation. The improved performance of the coated tools is a result of the superior tribological properties of fine-grained diamond against aluminum, specifically low friction, low adhesion, and low wear of the film. Since the coating allows machining without lubricants and essentially eliminates metal burrs, this approach can reduce the environmental impact of micro-machining processes and offers greatly improved performance for micro and meso-scale manufacturing applications.     

Improvement of structural/tribological properties and milling performances of tungsten carbide cutting tools by bilayer TiAlN/TiSiN and monolayer AlCrSiN ceramic films

In this study, bilayer TiAlN/TiSiN and monolayer AlCrSiN ceramic films were grown on carbide cutting tool material by cathodic arc physical vapor coating (CAPVD) method to improve the structural/tribological properties and milling performances. The ceramic films were applied on cylindrical test samples and carbide end mills. The coated materials' structural, mechanical, and tribological properties were determined via scanning electron microscope (SEM), X-ray diffraction meter (XRD), tribometer, microhardness tester, and optical profilometer. DIN 40CrMnNiMo8-6-4 steel workpieces were machined by using a CNC vertical machining center to determine the actual working performance of the coated and uncoated cutting tools. The wear performance of the cutting tools after machining was determined by measuring the flank wear widths and mass losses. The hardness and adhesion results of the coated sample with bilayer TiAlN/TiSiN were higher than the coated sample with monolayer AlCrSiN. According to the scratch test results, the best adhesion results were obtained for TiAlN/TiSiN coating. The critical load value was determined as about 105 N. As a result, the wear rate value of the TiAlN/TiSiN thin film coated sample was lower. After machining, the mass loss of TiAlN/TiSiN coated tools was lower than AlCrSiN coated tools. In addition, the surface roughness value of the workpiece machined by the cutting tool coated with AlCrSiN was higher than the cutting tool coated with TiAlN/TiSiN.     

Hard machining performance of PVD AlCrN coated Al2O3/TiCN ceramic inserts as a function of thin film thickness

In the present work, AlCrN coating was deposited on Al₂O₃/TiCN ceramic inserts with varying thin film thickness using physical vapor deposition (PVD) technique. The thickness, surface morphology, chemical composition, hardness and adhesion strength of the coating to the substrate were characterized by field-emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro-indentations and scratch tests respectively. The machining performance of uncoated and coated tools was investigated in hard turning of AISI 52100 steel (62 HRC) under dry environment. The cutting behavior was analyzed in terms of machining forces, tool temperature, wear, friction and chip morphology. Further, a 3D finite element model with hybrid friction criterion has been adopted to support the experimental findings. The results revealed that coating/substrate adhesion and edge radius were the deciding criteria for the machining performance of coated tools with 3 µm coating thickness tool exhibiting best turning performance on Al₂O₃/TiCN mixed ceramic insert.     

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.     

Investigation of FEM Simulation of Machining of Titanium Alloy Using Microgroove Cutting Insert

In this paper, FEM simulation of machining of titanium alloy using microgroove cutting insert has been carried out using DEFORM-3D software. The cutting insert with microgroove has been made with Solidworks software. The 3D machining simulations of all the different types of microgroove patterns in cutting inserts were done at constant cutting variable, i.e. cutting speed of 125.6 m/min, feed of 0.23 mm/rev and depth of cut of 2 mm respectively. The simulation results were partially validated with experiments. There was good agreement between experiment and simulation. The cutting temperature, effective stress, tool wear rate and temperature at the chip/tool interface has been determined. There was an improvement in the machinability criteria using cutting tool with microgroove pattern.     

Cutting performance of microwave-sintered sub-crystal Al2O3/SiC ceramic tool in dry cutting of hardened steel

Tool life and failure mechanisms of a microwave-sintered sub-crystal Al₂O₃/SiC ceramic tool (AS) in dry turning hardened steel were studied. The AS tool with plane face shows better cutting performance and wear resistance than the commercial ceramic tool SW500 and cemented carbide tool YG8 at both low and high cutting speeds. It's suitable for dry cutting at high speed (210–270 m/min), the cutting distance is 5–8 times longer than that of other two tools. The results indicate that the ceramic tool fabricated by this pressureless sintering technology can satisfy the requirements of high-speed machining. Wear forms of AS tool at low cutting speed are slight crater wear and groove wear, which were mainly caused by abrasion. At high cutting speed, tool failure forms are cater wear, groove wear and slight chipping caused by severe abrasion and adhesion.     

Characterization of TiCN and TiCN/ZrN coatings for cutting tool application

Coating a cutting tool improves wear resistance and prolongs tool life. Coating performance strongly depends on the mechanical and chemical properties of the coating material. In a machining process, the type of selected coating depends on the cutting condition because of the properties of the applied coating material. In addition, many factors, such as coating thickness, composition ratio, sequences of layers in multilayer coatings, and the deposition method influence the performance of a coating. In this study, the mechanical properties of TiCN and TiCN/ZrN were investigated using a ball on disk test. The substrate material made from a carbide-based cutting tool was also developed in-house. The analysis performed shows that the performances of TiCN and TiCN/ZrN coatings were found to be comparable to that of the commercial TiN-coated carbide-based cutting tool. Both the in-house and commercial coated inserts had significantly lower coefficient of friction than uncoated inserts, and the friction coefficient of TiCN coatings was constantly slightly lower than that of TiN coatings. Moreover, the coefficient of friction of the in-house developed TiCN was slightly lower than that of commercial TiN coating. However, the coefficient of friction of the in-house developed uncoated carbide inserts was slightly higher than that of commercial uncoated carbide inserts.     

Effect of nano-scale texture pretreatment on wear resistance of WC/Co tools with/without TiAlN coated flank-face in dry turning of green Al2O3 ceramics

Advanced ceramics after sintering are almost processed by grinding or non-traditional machining. Nevertheless, these methods are limited by complexity of processing efficiency, tool wear and economic effectiveness. So machining green ceramics before sintering is introduced, it is environmentally friendly, efficient and cheap with high removal rate of materials. During dry turning green ceramics, flank-wear of tools and processing quality of compacts are two main elements to evaluate cutting performance of tools. The processing efficiency and economic effectiveness are mainly effected by the cutting performance of tools. In this paper, polished tool, tool with nano-scale textured flank-face, tool with TiAlN coating deposited on polished flank-face, and tool with TiAlN coating deposited on nano-scale textured flank-face were prepared. Effect of nano-scale texture pretreatment on wear-resistance of WC/Co tools with/without TiAlN coated flank-face was studied in turning of green Al₂O₃ ceramics. Results displayed that nano-scale textures on the flank-face had prominent effects on the enhancement of flank-wear resistance of tools. Relevant mechanisms were explored that nano-scale textures exhibited “derivative cutting” to protect unworn face from abrasion, and nano-scale textures pretreated on the flank-face could enhance the adhesion strength between coating and matrix. These developed tools could also significantly improve the processing quality of machined surfaces.