Study on the role of PVD TiN coating in improving the performance of electroplated monolayer superabrasive wheel

The monolayer grinding wheels, coated with a physical vapour deposited (PVD) coating (viz. TiN, HfN, TiN + ZrN etc.), have been reported to outperform their uncoated counterparts as claimed in some patented literatures. The present work aims at exploring the mechanism how PVD TiN augments the performance of nickel electroplated monolayer superabrasive wheels. This study also includes the effect of negative substrate bias voltage on performance of TiN coated electroplated cBN wheels during grinding of hardened bearing steel. TiN was deposited by pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS) technique in an in-house PVD coating system. The structure of the TiN coating and post-grinding condition of the wheels were observed using scanning electron microscopy (SEM). Energy dispersive X-ray (EDX) line scan, Electron probe micro analysis (EPMA) and secondary ion mass spectrometry (SIMS) depth profiling at the junction of TiN and nickel layer indicated the occurrence of inter-diffusion between them and grazing incidence X-ray diffraction (GIXRD) confirmed the formation of Ni-Ti intermetallic phases at their interface. The scratch test revealed a significant increase in cohesive and adhesive strengths of nickel layer when TiN was deposited at a bias voltage of −60 V or beyond that. The uncoated cBN wheel exhibited large number of grit fracture at the bond level and some grit pull-out. Such failures of grit were significantly arrested with TiN coating deposited at the bias voltages of −60 V and −90 V.     

Performance enhancement of single-layer miniature cBN wheels using CFUBMS-deposited TiN coating

This work investigated the effectiveness of TiN coating in enhancing the performance of two different types of single-layer cBN grinding wheels. One was galvanically bonded type where galvanic metal layer covered less than 50% of the grit height. In this paper, it is termed as underplated wheel. The other one was brazed cBN wheel which was developed in-house. In this case, the grits were bonded by a braze alloy layer. TiN coating, well known for its anti-wear and anti-friction characteristics, finds use in cutting tools and tribological applications. In this case study, such TiN was successfully deposited on the above-mentioned two types of grinding wheels with a dual cathode closed-field unbalanced magnetron sputtering (CFUBMS) system. Performance of those TiN-coated wheels was compared with that of uncoated counterparts in terms of grinding force and percentage of grit failure. Grinding tests were carried out in plunge mode and under dry condition. Experimental results clearly revealed the fact that the role of TiN coating was not that significant in reducing the friction at the wheel-workpiece contact zone. However, it was able to substantially reduce grit pullout of the underplated cBN wheel. On the other hand, uncoated brazed cBN wheel did not suffer from grit pullout, but severe premature breakage of cBN grits at the bond level was observed. This was remarkably arrested when TiN coating was applied on the active surface of the wheel.     

镀钛cBN磨料对超高速陶瓷砂轮强度的影响

采用扫描电子显微镜和X射线衍射仪等仪器对镀钛前后的cBN磨料和陶瓷结合剂烧结样条的显微结构进行了观察;分析了结合剂与cBN磨料的结合关系,并对陶瓷结合剂烧结样条进行了抗折强度试验。结果表明,cBN磨料镀钛前后其性能变化很小,未镀钛cBN磨料与结合剂烧结样条的抗折强度为61.97MPa,两者间是机械包镶式的结合;镀钛cBN磨料与结合剂烧结样条的抗折强度为67.65MPa,两者间还含有化学结合;cBN磨料镀钛后对砂轮强度的提高有益,但前者的抗折强度已满足超高速砂轮的需要,单就提高砂轮强度来说,无需镀钛。     

陶瓷磨削中新型多孔金属结合剂金刚石砂轮磨损特征研究

在磨削Al2O3工程陶瓷材料过程中,利用三维视频显微镜跟踪观察了新型多孔金属结合剂金刚石砂轮,金刚石的磨损过程以及砂轮表面形貌的变化。分析了新型砂轮中金刚石磨损的主要形式及原因,砂轮工作表面的状态变化特征。试验结果表明：新型多孔金属结合剂金刚石砂轮在加工过程中,金刚石的磨损形式包括磨耗磨损,破碎及脱落等磨损过程,其中以磨耗磨损为主;同时,随着结合剂的不断磨除,砂轮深层磨料能够不断出露,取代表面钝化失效、脱落的金刚石,且砂轮表面孔隙结构,随磨损过程呈交替更迭变化,砂轮具有较好的自锐性。     

High bandwidth temperature measurement in interrupted cutting of difficult to machine materials

High-speed milling is used across industries from aerospace to electronics. Tool wear can be affected by cutting interruptions in milling that lower tool-chip interface temperatures but also cause thermal and stress cycling. Micro-thermal imaging was used to determine the temperature during interrupted cutting of titanium alloy Ti6Al4V and AISI 4140 steel for percentage of time-in-cut from 100% to 10%. TiAlN/TiN coated carbide milling inserts were used with cutting speeds up to 180 and 640 m min⁻¹. This technique is the first to allow spatial mapping of thermal fluctuations on the tool which may be critical to determining causes for tool failure.     

Experimental investigation on performance of touch-dressed single-layer brazed cBN wheels

Electroplated single-layer grinding wheels, in spite of offering unique useful features like geometrical flexibility, large chip accommodation volume in the inter-grit space, etc., produce high transverse surface roughness on the ground surface of the workpiece. Non-participation of all the superabrasive particles (grits) attributes to this limiting factor. Moreover, in plunge grinding the situation is the worst to deal with. This work is an attempt to reduce the same to an acceptable magnitude so that post-grinding finishing operations can be executed effectively. However, this procedure has been implemented on indigenously developed brazed-type single-layer cBN wheels. This class of grinding wheel has been found superior to its galvanically bonded counterpart in the view of larger grit protrusion and flexibility to print any pattern of grit distribution. In this investigation, brazed cBN wheels with different grit distribution patterns have been conditioned by touch-dressing method so that grit tips get micro-conditioned and allow the underlying grits to participate and consequently increase the quality of finish. The outcome of this attempt appeared highly encouraging. A substantial improvement of transverse surface roughness could be achieved with all three categories of brazed wheels and the role of grit distribution pattern in obtaining good finish was thoroughly investigated.     

A sol-gel route to nanocrystalline TiN coated cubic boron nitride particles

For the purpose of increasing microstructural homogeneity and enhancing the reinforcement-matrix interfacial area, cubic Boron Nitride, cBN particles were coated by nanocrystalline TiN by a sol-gel route that required neither the need for pH adjustment nor the use of surfactants or additives. Uniform shells of amorphous titania having thicknesses in the nanometers scale were formed on the surface of the cBN particles by hydrolysis and condensation reactions of titanium (IV) isopropoxide. The amorphous coated cBN powder was nitrided to crystalline TiN coated cBN by treating in NH₃ gas at 900 °C. After nitridation the amorphous layer was completely converted to nanocrystalline TiN particles that uniformly covered the surface of cBN. Changes in the TiO_x coated layer thickness and the size of the TiN particles were investigated as a function of alkoxide content. TiO₂ nanoparticles were synthesized using the same reaction conditions, but without the presence of cBN. These nanoparticles were calcined in air at different temperatures (250-700 °C) and then nitrided at 900 °C. The nitridation behavior of TiO₂ nanoparticles was studied as a function of calcination temperature.     

不锈钢根管锉镀覆TiN、ZrN膜的沉积工艺与性能研究

目的通过在不锈钢根管锉表面镀覆Ti N、Zr N薄膜,以提高其切削性能。方法采用磁控溅射技术,调整沉积时间、基片偏压、占空比等工艺参数在不锈钢根管锉上分别沉积Ti N、Zr N薄膜。对Ti N、Zr N膜层进行SEM断面分析、XRD相组成分析、表面硬度测试、膜层附着力测试,考查了Ti N、Zr N薄膜的厚度、相组成、硬度以及附着力。通过对镀膜后的根管锉进行电化学腐蚀试验、模拟临床切削试验,分析了镀膜后根管锉的耐蚀性和切削性能。结果随着工艺参数的变化,Ti N、ZrN薄膜的厚度、相结构以及硬度均显示了规律性的变化。镀覆Ti N、Zr N薄膜的不锈钢根管锉的自腐蚀电流密度相对于未镀膜的根管锉均明显降低。确定了Ti N膜层和Zr N膜层的优化沉积工艺分别为沉积时间1 h、负偏压100 V、占空比60%和沉积时间1h、负偏压150V、占空比60%。优化工艺下镀膜的不锈钢根管锉的切削数量和切削效率显著提高。结论和未镀膜不锈钢根管锉相比,镀覆Ti N、ZrN薄膜的不锈钢根管锉的表面硬度、耐蚀性能均有显著提高。最优工艺下制备的镀覆Ti N、Zr N薄膜的不锈钢根管锉兼具切削数量、切削效率以及切削稳定性等方面的综合优势,和未镀膜不锈钢根管锉相比,切削效率提高60%～75%,切削树脂模拟根管数量达到1.7～2倍,实现了切削性能的显著提升。     

Anti-corrosion characteristics of nitride-coated AISI 316L stainless steel coronary stents

The corrosion resistance of TiN and TaN coatings deposited on AISI 316L stainless steel thread-coiled coronary stents by pulsed bias arc ion plating is evaluated by electrochemical methods in deaerated Tyrode's simulated body fluids (37 ± 1 °C). The free corrosion potential of the TaN-coated stents is found to be nobler than that of the TiN-coated and uncoated stents throughout most of the immersion time. The potentiodynamic polarization test results indicate that the TaN coatings offer better passivation stability and anti-breakdown performance. The longer-term 6-month immersion tests disclose slight localized corrosion on the surface of both coatings, but no film delamination or large area pitting can be observed indicating reasonably good corrosion resistance after the long period.     

High temperature corrosion of nanoceria coated 9Cr-1Mo ferritic steel in air and steam

In this article, air and steam oxidation resistance of bare and nanoceria coated 9Cr-1Mo ferritic steel at 650 °C for 500 h is reported. The kinetics of the oxidation process and the changes in the morphology and the chemistry for both the specimens were analyzed by backscattered electron and EPMA mapping. The nanoceria coated 9Cr-1Mo ferritic steel showed better oxidation resistance than uncoated steel under similar conditions. The thickness of the oxide scales formed on the coated samples was significantly reduced as compared to the uncoated substrates. The effectiveness of such a thin and simple nanocoating to improve the oxidation resistance of 9Cr-1Mo ferritic steel compared to the pristine is attributed to the change in the migration of cations from outward to inward diffusion of oxygen as the major mechanism.     

Investigations on the effects of multi-layered coated inserts in machining Ti-6Al-4V alloy with experiments and finite element simulations

This paper presents investigations on turning Ti-6Al-4V alloy with multi-layer coated inserts. Turning of Ti-6Al-4V using uncoated, TiAlN coated, and TiAlN + cBN coated single and multi-layer coated tungsten carbide inserts is conducted, forces and tool wear are measured. 3D finite element modelling is utilized to predict chip formation, forces, temperatures and tool wear on these inserts. Modified material models with strain softening effect are developed to simulate chip formation with finite element analysis and investigate temperature fields for coated inserts. Predicted forces and tool wear contours are compared with experiments. The temperature distributions and tool wear contours demonstrate some advantages of coated insert designs.     

On the corrosion mechanism of AISI 204Cu stainless steel in chlorinated alkaline media

Electrochemical techniques (CV, SECM, CPT) and surface analysis techniques (EDX, SEM) have been employed to assess the corrosion behaviour of the AISI 204Cu stainless steel. The behaviour of this steel has been compared with that of AISI 304 and AISI 434 stainless steels in chlorinated alkaline media. All samples performed well at room temperature under potentiodynamic polarisation up to a chloride to hydroxyl ratio of 10. At this ratio the AISI 204Cu and the AISI 434 steels presented pitting potential at +0.47 V vs. SCE and +0.31 V vs. SCE, respectively. Moreover, the critical pitting temperature was higher for the AISI 204Cu steel than for the AISI 434 steel, respectively 58 °C and 28 °C.In terms of corrosion performance of the AISI 204Cu stainless steel can be classified better than the AISI 434 steel and worse than the AISI 304 steel.Local electrochemical and chemical examinations allowed evidencing the local activity of some pits over long period, and to conclude that the improved corrosion performance of the low nickel alloy AISI 204Cu stainless steel should be ascribed to copper cementation at active corrosion sites.     

cBN砂轮在低速磨削中的应用

cBN砂轮在高速设备上使用非常广泛,但在老式低速磨床上采用cBN砂轮的非常少。我们在这方面做了大胆的尝试,就是在老式磨床上不做任何改进,直接更换相同直径的陶瓷cBN砂轮,通过更换皮带轮改变传动比,把砂轮速度从51.4 m/s提升到64.8 m/s,增大冷却液流量、压力,确定冷却液冲刷位置,改变切削的进给量,使cBN砂轮的一个修整频次内寿命大幅提升。最后证明陶瓷cBN砂轮在低速磨床中一样可以替代刚玉砂轮,并且不需要大的改造投资,可以获得非常好的综合经济效益。     

Interfacial reaction and wetting behavior of active Ag-Cu filler alloys on surface of cBN grits and its influence on failure patterns of brazed joint

Cubic boron nitride (cBN) abrasive grits are often brazed on steel to produce monolayer grinding wheels. Establishing a strong cBN brazement is a challenge. In the current work, performance of three different active Ag-Cu alloys have been investigated in-depth considering microstructure of alloys, interfacial reaction phase formation and wetting capability of the reaction product towards the alloy. In the current study, all three alloys contain Ti as active element but with different wt%. One of alloys was so chosen that Indium (In) was present as an additional alloying element, which is responsible for its low liquidus temperature, high Young's modulus and good ductility. Segregation of Ti towards the interface was critically examined. To evaluate joint strength, a miniature twin-ring grinding wheel was produced with these alloys. Interestingly, the alloy containing higher Ti, which required higher brazing temp, resulted in intense reaction but with inferior joint strength. On the other hand, the very presence of indium in Ag-Cu alloy, containing low wt% of Ti not only lowered the brazing temperature but also led to effective wetting and higher joint strength. Failure pattern indicates the prevalence of high residual stress at the bond level for the alloy containing the highest percentage of titanium.     

Experiments and finite element simulations on micro-milling of Ti–6Al–4V alloy with uncoated and cBN coated micro-tools

This paper presents experimental investigations and finite element simulations on micro-milling of Ti–6Al–4V alloy with fine grain uncoated and cBN coated micro-end mills. Micro-milling of Ti–6Al–4V using uncoated and cBN coated tungsten carbide micro-end mills are conducted; surface roughness, burr formation and tool wear are measured. Effects of machining parameters on surface roughness, burr formation, and tool wear for uncoated and cBN coated micro-tools are investigated. Finite element modelling is utilized to predict forces, temperatures, and wear rate for uncoated and cBN coated micro-tools. Predicted temperature and tool wear contours for uncoated and cBN coated micro-tool edges reveal advantages of cBN coatings. Optimization studies on the experimental results are also conducted to identify the optimum process parameters which minimize both surface roughness and burr formation concurrently.     

AgCuTi合金钎焊单层立方氮化硼砂轮

为研制我国新一代单层钎焊CBN(立方氮化硼 )磨料砂轮 ,尝试Ni-Cr和Ag -Cu-Ti两种活性钎料 ,在真空炉中钎焊。试验结果表明 ,Ni-Cr合金钎料对CBN磨料不浸润 ,钎焊后CBN磨料全部脱落 ;而Ag -Cu -Ti合金钎料对CBN则表现出良好的浸润性并将CBN牢牢钎焊住。借助扫描电镜、X射线能谱和X射线衍射对界面微区组织的分析研究表明 ,钎焊过程中Ag -Cu -Ti合金钎料中的Ti向CBN磨料界面富集 ,并与CBN磨料表面的N和B元素反应生成TiN和TiB ,这是实现Ag -Cu -Ti合金钎料与CBN磨料高结合强度的关键因素。断口形貌的分析研究表明 ,CBN与Ag -Cu -Ti合金钎料间的断口发生在Ag -Cu -Ti合金钎料层 ,说明CBN磨料与Ag -Cu -Ti合金钎料的结合强度已超过了Ag-Cu -Ti合金钎料本身强度。最后将研制出的单层钎焊CBN磨料砂轮与传统电镀CBN砂轮进行了重负荷磨削对比试验 ,钎焊砂轮表现出明显的优势     

Machining performance and decomposition of TiAlN/TiN multilayer coated metal cutting inserts

The wear resistance of metal cutting inserts coated with metastable Ti_0.34Al_0.66N/TiN multilayers was tested in continuous turning of an AISI 316L stainless steel. The multilayers had periods of 25 + 50, 12 + 25 and 6 + 12 nm (Ti_0.34Al_0.66N + TiN) with a total multilayer stack thickness of 2 μm. Inserts coated with monolithic TiN and Ti_0.34Al_0.66N deposited under similar conditions were used as references. The multilayer coated inserts show a decrease of wear with decreased multilayer period, both on the rake and flank face. The wear on the rake face was lower on all the multilayer coated tools compared to the references. Scanning transmission electron imaging and energy dispersive spectroscopy elemental mapping of a worn multilayer coating show decomposition of the Ti_0.34Al_0.66N to domains rich of Al and Ti. High resolution transmission electron micrography shows preserved epitaxy between the TiN and Ti_0.34Al_0.66N layers. The improved wear resistance of the multilayer coated inserts is discussed in terms of an improved thermal stability of the multilayer stacks.     

Analysis of the influence of tool type, coatings, and machinability on the thermal fields in orthogonal machining of AISI 4140 steels

Micro-thermal imaging was used to determine the amount of heat flowing into the tool, chip and workpiece during orthogonal cutting at speeds up to 400 m min⁻¹. Two AISI 4140 steels with different machinability ratings and three types of tools were compared: (i) uncoated with 0° rake angle, (ii) coated with −6° rake angle and (iii) coated with chip breaker. A control volume approach was used to estimate the energy partition from thermal images and energy outflow was compared to direct measurement of the cutting power. This provides a new physical tool for examining machinability, tool wear and subsurface damage.     

Influence of vitrified bond structure on radial wear of cBN grinding wheels

This paper presents the results of research concerning the radial wear of super hard grinding wheels in the process of internal grinding of bearing rings. The new-developed grinding wheel is designed for bonding the abrasive grains of submicrocrystalline boron nitride using a glass–ceramic bond. This grinding wheel is compared to cBN grinding wheels composed from ceramic bonding systems, currently having application in industry. A crystalline phase from a group of single-diagonal pyroxenes of an XYSi₂O₆ type was generated at the glass–ceramic bond from a CaO–MgO–Al₂O₃–B₂O₃–SiO₂ system. An influence of the presence of this phase on the bond fracture toughness coefficient K_Ic and the elastic modulus E of cBN grinding wheels was examined. Compared to grinding wheels comprising the commercial bond from a Na₂O–K₂O–Al₂O₃–B₂O₃–SiO₂ system, the microcrystalline structure of the new-developed bond limits the range of its fragmentation in the process of grinding. It exerts a marked influence on the formation of different roughness profiles on the wheel working surface and the wear resistance, compared to a grinding wheel composed from a commercial bond.     

Magnetron reactively sputtered Ti-DLC coatings on HNBR rubber: The influence of substrate bias

In this study, Ti-containing diamond-like carbon (Ti-DLC) coatings have been deposited on HNBR (hydrogenated nitrile butadiene) rubber and also on Si wafer as reference via unbalanced magnetron reactive sputtering from a Ti target in C₂H₂/Ar plasma. The deposition rates of coatings on rubber and Si wafer were about the same. Columnar structures resulting from a rough interface were often observed in the coatings deposited on rubbers. Only at a high bias voltage of − 300 V the coating on HNBR rubber became column-free whereas a bias voltage of − 100 V could already restrain the columnar structure and thus produced dense and smooth coatings on Si wafer. A segmented morphology of the coatings on HNBR rubber is formed as a result of the large difference in thermal expansion between the coating and HNBR rubber. The crack network that separates the patches plays an important role in maintaining the coating flexibility. The size of the patches reduces with increasing bias voltage and thus the variation of deposition temperature. A high bias voltage enhances the hardness of Ti-coating and the rubber-coating adhesion, and guarantees a good tribological performance. When sliding against ø6 mm 100Cr6 steel ball counterpart, very low coefficients of friction were achieved (< 0.25 for the coated rubber versus > 1.3 for the uncoated). The Ti-DLC coating can be considered as a promising material for the enhancement of tribological performance of rubbers.