Investigation on wear behaviour of cryogenically treated TiAlN coated tungsten carbide inserts in turning

Cryogenic treatment has been ascribed as a way of improving the cutting life of tungsten carbide turning inserts. Most of the research conducted till date has not reported any effort to excavate the effect of cryogenic treatment on the performance of coated tungsten carbide inserts in terms of adhesion strength of coatings deposited on tungsten carbide substrate. In order to understand the effect of cryogenic treatment on the adhesion strength of coatings, a comparative investigation of the wear behaviour and machining performance of cryogenically treated coated tungsten carbide inserts in orthogonal turning has been carried out in this study. The commercially available TiAlN coated square shaped tungsten carbide inserts (P25) were procured and subjected to cryogenic treatment at two levels −110 °C (shallow treatment) and −196 °C (deep treatment) of temperature independently. The criterion selected for determining the turning performance was based on the maximum flank wear (0.6 mm) as recommended in ISO 3685-1993. The results showed that shallow cryogenically treated coated tungsten carbide inserts performed significantly better as compared with deep cryogenically treated and untreated inserts. Major outcome of the present study includes a substantial decrease in tool life of deep cryogenically treated inserts as compared to untreated inserts indicating the destructive effect of deep cryogenic temperature (−196 °C) on TiAlN coated inserts which is further supported by VDI-3198 indentation test.     

Performance evaluation of cryogenically treated tungsten carbide tools in turning

This paper describes a study on the effects of cryogenic treatment of tungsten carbide. Cryogenic treatment has been acknowledged by some as a means of extending the tool life of many cutting tool materials, but little is known about the mechanism behind it. Thus far, detailed studies pertaining to cryogenic treatment have been conducted only on tool steels. However, tungsten carbide cutting tools are now in common use. The main aim of this study is to analyze the differences in tool performance between cryogenically treated and untreated tool inserts during orthogonal turning of steel. This will aid in the quest for optimal cutting conditions for the turning of steel using these inserts, and will also enhance the understanding of the mechanism behind the cryogenic treatment of tungsten carbide, and the changes in its properties after cryogenic treatment. In the process of ascertaining these findings, it was shown in this study that under certain conditions, cryogenic treatment can be detrimental to tool life and performance. It was also shown that cryogenically treated tools perform better while performing intermittent cutting operations.     

Ablation resistance of tungsten carbide cermets under extreme conditions

A cobalt-free tungsten carbide cermet (WC-FeNi) has been subjected to oxyacetylene flame tests to simulate extreme operating conditions such as a worst-case fusion reactor accident. In such an accident, air-ingress to the reactor may impinge on components operating at surface temperatures in excess of 1000 °C, leading to tungsten oxide formation and its subsequent hazardous volatilisation. Here, the most challenging accident stage has been simulated, where the initial air-ingress could lead to extremely rapid air-flow rates. These conditions were simulated using an oxidising oxyacetylene flame. The separation between flame nozzle and sample was varied to permit peak surface temperatures of ~950–1400 °C. When the peak temperature was below 1300 °C, the cermet gained mass due to the dominance of oxide scale formation. Above 1300 °C, the samples transitioned into a mass loss regime. The mass loss regime was dominated by liquid-phase ablation of the scale rather than its volatilisation, which was confirmed by performing a systematic thermogravimetric kinetic analysis. The result was unexpected as in other candidate shielding materials, e.g. metallic tungsten, volatilisation is considered the primary dispersion mechanism. The unusual behaviour of the cermet scale is explained by its relatively low melting point and by the lower volatility of its FeWO₄ scale compared to tungsten's WO₃ scale. The substantially lower volatility of the WC cermet scale compared to metallic W scales indicates it may have a superior accident tolerance.     

Evaluation of wear of turning carbide inserts using neural networks

Recent trends, being towards mostly unmanned automated machining systems and consistent system operations, need reliable on-line monitoring processes. A proper on-line cutting tool condition monitoring system is essential for deciding when to change the tool. Many methods have been attempted in this connection.Recently, artificial neural networks have been tried for this purpose because of its inherent simplicity and reasonably quick data-processing capability. The present work uses the back propagation algorithm for training the neural network of 5-3-1 structure. The technique shows close matching of estimation of average flank wear and directly measured wear value. Thus the system developed demonstrates the possibility of successful tool wear monitoring on-line.     

Oxidation of tungsten and tungsten carbide in dry and humid atmospheres

Oxidation experiments were performed on pure tungsten and hot-pressed tungsten carbide. The chemical state and thickness of the oxide products were determined by ESCA. The oxidation of W and WC in dry atmosphere was performed in oxygen at temperatures ranging from 20 to 500 °C. The oxide formed is WO₃. The thickness of the oxide layer increases slowly up to 200 °C, after which the oxide growth is rapid.

The oxidation behaviour of W and WC in humid atmospheres was studied at room temperature in air at relative humidities of 60 and 95%. It was found that the thickness of the oxide layer increases with increased humidity. No formation of hydroxide was observed. Exposing W to water for one week results in a thick layer of WO₂, WO₃ and hydroxide. In the case of WC no oxide at all was visible after exposure to water. Furthermore, WC is resistant to further oxidation after exposure.     

涂层硬质合金刀片车削典型CFRP的工程技术研究

用相同几何结构、不同材质的2种涂层硬质合金刀片车削碳纤维增强复合材料T800H棒料,通过多分量力学传感器、压力传感器和高速摄影机监测车削过程中的切削载荷和刀具工作状态,通过光学扫描系统和数码显微系统观测分析工件已加工表面和切屑的形貌特征。结果表明:车削T800H棒料时,每种刀具都存在一个临界切削速度v_cr,在相同进给量f和恒定切削深度a_p的情况下,切削速度v_c对工件已加工表面质量影响小。实验还表明:采用硬度更高的刀具车削碳纤维,能获得更好的表面质量。      

Atmospheric corrosion of copper under wet/dry cyclic conditions

The polarization resistance of copper subjected to NaCl and an ammonium sulfate solution under wet/dry cycling conditions was monitored using an EIS impedance technique. The copper samples were exposed to 1 h of immersion using different solutions of pH, temperature and surface orientation and 7 h of drying. The copper plates corroded more substantially on the skyward side than those for a ground ward side. The degree of protection copper oxide provides decrease in an acidic medium (pH 4) more than in a neutral medium (pH 7). The corrosion rate of copper increases rapidly during the initial stages of exposure then decreases slowly and eventually attains the steady state during the last stages of exposure. The corrosion products were analyzed using X-ray diffraction. The corrosion mechanism for copper studied under wet/dry cyclic conditions was found to proceed under the dissolution-precipitation mechanism.     

Laser-assisted high-speed finish turning of superalloy Inconel 718 under dry conditions

Inconel 718 (IN718) is used in aerospace applications due to its superior mechanical properties. This study investigates the high-speed machinability of this material under laser-assisted machining (LAM) and dry conditions. Finish turning tests were performed for cutting speeds up 500 m/min and feeds up to 0.5 mm/rev, using focused Nd:YAG laser beam and ceramic tool (SiAlON). At optimum machining conditions, nearly eight-fold increase in material removal rate and significant improvement in the tool life and surface finish were achieved, compared to conventional machining. The mechanisms of tool failure were identified. SEM analysis and microstructure examination of machined surfaces revealed the improvement in the surface integrity under LAM conditions.     

金刚石锯片干湿切对比试验研究

试验采用Ф105mm小尺寸金刚石锯片在干切和湿切两种工作条件下锯切瓷砖，结果表明，对于小尺寸锯片，加水切割的切割效率高于不加水切割，而寿命较不加水切割时低。本文从干湿切条件下单颗金刚石刻岩效率及单颗金刚石所受力矩两个方面分析产生这种差异的原因，通过分析：湿切时单颗金刚石单次刻取岩石的体积及其所承受的力矩是干切的数倍，金刚石的工作寿命较干切低。在排粉较畅通的条件下，冷却液不能够同时提高锯片的切割效率和工作寿命。     

Chemical mechanism of chemical mechanical polishing of tungsten cobalt cemented carbide inserts

To explore the chemical mechanism of tungsten‑cobalt cemented carbide inserts in H₂O₂-based polishing fluid. Before and after the YG8 cemented carbide inserts were corroded, surface phase, element and structure were characterized by XRD and SEM/EDS. The chemical mechanism of tungsten‑cobalt carbide inserts during chemical mechanical polishing (CMP) was analyzed. XPS was utilized to analyze the corrosion products formed on the surface of YG8 cemented carbide inserts during chemical reaction to determine the chemical reaction equation. In the H₂O₂ environment, the electrode potential of the Co layer at the boundary between the binder phase with larger crystal domains and the hard phase is greater than the electrode potential of the intermediate layer γ(Co-W-C solid solution) phase and WC, which creates a potential difference between the three, and occurs galvanic corrosion. The hard phase WC is protected as the cathode of the entire battery and has a tendency to stabilize. The Co layer at the phase boundary is the most anode feature to be corroded and dissolved first. The γ phase of the intermediate layer serves as the secondary anode feature and serves also as the cathode of the Co layer. When the Co layer at the phase boundary is corroded to a certain extent, a galvanic couple is formed between the γ phase and the testing phase WC to cause corrosion. In addition, the binder phase with smaller crystal domains directly forms galvanic corrosion with WC. The chemical products created on the surface of the blades are Co₃O₄ and WO₃. However, Co₃O₄ and WO₃ oxide films are small in size and have little effect on material removal during polishing. When the binder phase corrosion on the blades surface reaches a critical point, the stress exerted by the polishing abrasive is basically concentrated on the WC particle surface. The strength of the WC particles that have lost the supporting effect of the binder phase becomes low and the structure becomes brittle. Under the mechanical scratching and compressive stress of the abrasive particles of the polishing solution, the smaller WC particles are directly pulled out. The surface layer of the larger WC particles is broken into WC grains, and then the surface layer is mechanically removed.     

Wear of CrC-coated carbide tools in dry machining

This paper discusses the tribological characteristics and cutting performance of chromium carbide (Cr_x%C)-coated carbide tool inserts and micron-drills in dry machining. Cr_x%C coatings have been deposited with different optical emission monitoring (OEM) set values, x%, of chromium target “poisoning” by unbalanced magnetron sputtering and OEM control. The microstructures and mechanical properties of Cr_x%C coatings have been measured by the experiments of scanning electron microscope (SEM), nanoindentation and adhesion. Experimental results indicate that the coating microstructure, mechanical properties and wear resistance vary according to OEM set values. Cr_10%C-coated inserts showed the best wear resistance in AISI 1045 steel turning test. Cr_50%C-coated tools have performed exceptionally well in both copper turning and printed circuit board (PCB) through-hole drilling tests. The service life of Cr_50%C-coated tool is four times higher than that of an uncoated tool in the PCB through-hole drilling test.     

聚酰亚胺树脂和酚醛树脂在干湿条件下的磨削试验

本文研究了聚酰亚胺树脂和酚醛树脂作为砂轮结合剂的耐磨情况,通过力学性能测试、综合热分析和磨削实验对树脂进行性能表征。研究结果表明:(1)两种树脂的抗拉强度、抗折强度和冲击强度相差不大,但酚醛树脂的洛氏硬度偏低;(2)聚酰亚胺的耐高温性优良,最高分解温度达到623℃;(3)用聚酰亚胺作为结合剂制得的砂轮无论在干磨或者湿磨条件下都比酚醛树脂具有更优良的耐磨性,干磨时更明显。     

Tribological characteristics of C/C-SiC braking composites under dry and wet conditions

C/C-SiC braking composites, based on reinforcement of carbon fibers and matrices of carbon and silicon carbide, were fabricated by warm compaction and in situ reaction process. The tribological characteristics of C/C-SiC braking composites under dry and wet conditions were investigated by means of MM-1000 type of friction testing machine. The influence of dry and wet conditions on the tribological characteristics of the C/C-SiC composites was ascertained. Under dry condition, C/C-SiC braking composites show superior tribological characteristics, including high coefficient of friction （0.38）, good abrasive resistance （thickness loss is 1.10 μm per cycle） and steady breaking. The main wear mechanism is plastic deformation and abrasion caused by plough. Under wet condition, frictional films form on the worn surface. The coefficient of friction （0.35） could maintain mostly, and the thickness loss （0.70 μm per cycle） reduces to a certain extent. Furthermore, braking curves are steady and adhesion and oxidation are the main wear mechanisms.     

Wear and cutting performance of diamond composite material-a comparison with tungsten carbide

A series of wear and rock cutting tests were undertaken to assess the wear and cutting performance of a thermally stable diamond composite (TSDC). The wear tests were conducted on a newly designed wear testing rig in which a rotating aluminium oxide grinding wheel is turned (also known as machined) by the testing tool element.The rock cutting tests were performed on a linear rock-cutting planer. The thrust and cutting forces acting on the tool were measured during these tests. A tungsten carbide element was also studied for comparative purposes. The wear coefficients of both materials were used to evaluate wear performance while cutting performance was assessed by tool wear and the rates of increase in forces with cutting distance.     

Wear,cutting forces and chip characteristics when dry turning ASTM Grade 2 austempered ductile iron with PcBN cutting tools under finishing conditions

Experimental studies of wear, cutting forces and chip characteristics when dry turning ASTM Grade 2 austempered ductile iron (ADI) with polycrystalline cubic boron nitride (PcBN) cutting tools under finishing conditions were carried out. A depth of cut of 0.2 mm, a feed of 0.05 mm/rev and cutting speeds ranging from 50 to 800 m/min were used. Flank wear and crater wear were the main wear modes within this range of cutting speeds. Abrasion wear and thermally activated wear were the main wear mechanisms. At cutting speeds greater than 150 m/min, shear localization within the primary and secondary shear zones of chips appeared to be the key-phenomenon that controlled the wear rate, the static cutting forces as well as the dynamic cutting forces. Cutting speeds between 150 and 500 m/min were found to be optimum for the production of workpieces with acceptable cutting tool life, flank wear rate and lower dynamic cutting forces.     

Wear and tool life of tungsten carbide, PCBN and PCD cutting tools

The wear mechanisms of cutting tools made of tungsten-carbide (WC), PCBN and PCD were investigated using the tool life and temperature results available in the literature. For tool/work combinations WC/steel and PCBN/hardened-steel, under practical conditions, tool wear was found to be greatly influenced by the temperature. It was concluded that the most likely dominant tool wear mechanism for WC is diffusion and that for PCBN is chemical wear. For PCD, more experimental results and hence further research is required to determine the dominant wear mechanism.     

Tool wear and machining performance of cBN–TiN coated carbide inserts and PCBN compact inserts in turning AISI 4340 hardened steel

PCBN is the dominant tool material for hard turning applications due to its high hardness, high wear resistance, and high thermal stability. However, the inflexibility of fabricating PCBN inserts with complex tool geometries and the prohibitive cost of PCBN inserts are some of the concerns in furthering the implementation of CBN based materials for hard turning. In this paper, we present the results of a thorough investigation of cBN plus TiN (cBN–TiN) composite-coated, commercial grade, carbide inserts (CNMA 432, WC–Co (6% Co)) for hard turning applications in an effort to address these concerns. The effect of cutting speed and feed rate on tool wear (tool life), surface roughness, and cutting forces of the cBN–TiN coated carbide inserts was experimented and analyzed using analysis of variance (ANOVA) technique, and the cutting conditions for their maximum tool life were evaluated. The tool wear, surface roughness, and cutting forces of the cBN–TiN coated and commercially available PCBN tipped inserts were compared under similar cutting conditions. Both flank wear and crater wear were observed. The flank wear is mainly due to abrasive actions of the martensite present in the hardened AISI 4340 alloy. The crater wear of the cBN–TiN coated inserts is less than that of the PCBN inserts because of the lubricity of TiN capping layer on the cBN–TiN coating. The coated CNMA 432 inserts produce a good surface finish (<1.6 μm) and yield a tool life of about 18 min per cutting edge. In addition, cost analysis based on total machining cost per part was performed for the comparison of the economic viability between the cBN–TiN coated and PCBN inserts.     

Wear characterisation and tool performance of sintered carbide inserts during automatic machining of AISI 1045 steel

This paper presents tool condition monitoring (TCM) of dry turning processes on automatic lathes, and describes the information generated by different measuring systems applied to the single point turning situation. The outputs measured were correlated with the state and wear rate of the cutting tools.     

A cBN-TiN composite coating for carbide inserts: Coating characterization and its applications for finish hard turning

Cubic boron nitride (cBN)-titanium nitride (TiN) composite coating combines the thermal stability and super abrasiveness of cubic boron nitride (cBN) and the good lubricity of TiN, offering the opportunity for designing cutting tools with application specific new geometries (flat, chip breaker, and round shape) and cost effectiveness. In particular, the cBN based coating on carbide inserts is complementary to widely used polycrystalline cubic boron nitride (PCBN) compact tools for finish hard turning applications. This paper reports the results of a study addressing the surface morphology, surface roughness, coating cross section, chemical composition, crystal structure, microhardness, adhesion, and the wear life of this cBN-based coating deposited on carbide inserts (SNMG432) for finish turning of hardened AISI 4340 steel bars. The surface quality of machined workpieces in terms of their surface roughness and white layer formation are also analyzed and the results are presented.     

Heat treated twin wire arc spray AISI 420 coatings under dry and wet abrasive wear

The influence of applying two different heat treatments such as: deep cryogenic and tempering on dry/wet abrasive wear resistance of twin wire arc spray martensitic AISI 420 coatings was evaluated by using a modified rubber wheel type test apparatus. A load dependency was observed on the abrasive wear rate behavior of both; dry and wet tests. Three body (rolling) and two body (sliding) wear mechanisms were identified in dry conditions, prevailing rolling at lower and higher loads. However, at higher loads, more presence of grooving and pits formation was observed. Coatings tempered at 205 °C/1 h displayed better wear resistance than cryogenic treated ones. A change in wear mechanism between dry and wet conditions was observed; two body wear mechanism predominated respect to three body. In both; dry and wet conditions the microstructure (several inter-splat oxides) as well as strain and residual stress promotes brittle material removal which was more evident in cryogenic and as-sprayed samples during dry test and at higher loads in wet conditions.