Microstructure and properties of HVOF-sprayed chromium alloyed WC-Co and WC-Ni coatings

In this paper the influence of the type of binder metal (nickel or cobalt) and chromium as an additional alloying element on the microstructure, mechanical properties and wear resistance of high velocity oxy-fuel (HVOF)-sprayed WC-based hardmetal coatings was studied. Plain WC-Co and WC-Ni as well as five chromium alloyed compositions were sprayed with a liquid-fueled HVOF-spray process from commercial and experimental agglomerated and sintered feedstock powders. The coating characterization included optical microscopy and SEM of metallographically prepared cross-sections, hardness measurements, determination of the Young's modulus and phase composition by X-ray diffraction. Erosion and dry oscillating sliding wear were studied. The resistance to erosive wear was found to be improved when cobalt was used as binder metal. A dependence on the chromium content was not detected. For the oscillating sliding wear against a hardmetal counterbody there is no dependence of the wear rate on the type of binder metal or the amount of chromium.     

Effect of cobalt replacement by nickel on functionally graded cemented carbonitrides

Functionally graded cemented carbonitrides (FGCCs) are applied in cutting tools industry. Indexable inserts made from mentioned alloys have superior cutting performance and tool life thanks the formation of a surface modified layer with enhanced properties as well as crater wear resistance. Cemented carbonitrides are made of hard carbide/nitride/carbonitride particles that have been embedded in a metallic binder. Excellent wetting ability of tungsten carbide with cobalt has made this metal the first choice as binder. However, cobalt has high cost and environmental pollution impacts. Substitution of cobalt with other metals has always been figured out. Some other metals that have been used as binder are iron, nickel and manganese. In addition to lower cost, nickel has higher corrosion resistance than cobalt. In the present work, gradual substitution of cobalt with nickel in WC/2.5TiC_0.7N_0.3/2.5TiC/0.2VC/8Co (numbers indicate wt.%) cemented carbonitride has been studied. This is supposed to make some alterations in mechanical and magnetic properties as well as formation of Cubic Free Layer. As sintered samples with different binder characteristics were prepared by powder metallurgy techniques and use of Hot Isostatic Pressure (HIP) and vacuum furnaces. Magnetic saturation, coercive force, Vickers hardness, and transverse rupture strength tests were carried out together with optical and scanning electron microscopy. Computational thermodynamics was applied to explain changes in magnetic properties of investigated alloys as well as plotting phase diagrams. Complete displacement of cobalt by nickel made an increase in transverse rupture strength (TRS) of final alloy by 37% with less than 6% decrease in Vickers hardness and doubled the thickness of Cubic Free Layer.     

Chromium-doped Fe-Co-Ni binders for diamond cutting tools: The features of the structure,mechanical properties,and adhesion to diamond

This study is aimed at the development of novel chromium-doped Fe-Co-Ni binders for diamond cutting tools with enhanced mechanical properties, wear resistance and adhesion to diamond single crystals. Fe-Co-Ni-Cr powder mixtures were prepared by mechanical alloying to obtain uniform elemental distribution. The dependence of the mechanical properties of hot-pressed Fe-Co-Ni-Cr binders on Cr concentration has been studied. The Fe-Co-Ni-7%Cr binder fabricated by means of mechanical alloying and hot pressing is characterized by the maximal strength (3220 MPa) and hardness (114 HRB), which are due to the reduced stacking faults energy, caused by dissolution of chromium in α-Fe solid solution, and formation of Cr₂O₃ nanoparticles, which impede the dislocation gliding. The wear resistance of the Fe-Co-Ni-7%Cr binder with uniformly dissolved chromium is tenfold higher than that of the binder having the same composition but containing chromium as an individual phase. The presence of Cr in the binder leads to the improvement of its adhesion to diamond single crystals. Studies of the surface of diamond single crystals at fractures of diamond-containing segments showed that adhesion was improved due to the formation of chromium carbide (Cr₃C₂) sublayers.     

PCBN刀具切削性能和磨损机理研究综述

聚晶立方氮化硼(PCBN)刀具是继聚晶金刚石刀具之后的又一种超硬刀具,以其独特的“以车代磨”、“硬态加工”、“干式切削”等方式被誉为21世纪的绿色环保刀具。PCBN刀具在金属切削方面具有广泛的应用,主要用来加工各种淬硬钢、耐磨铸铁等铁基材料。本文介绍了PCBN刀具成分、几何形状、切削参数等对其切削性能的影响,在此基础上分析了不同材料加工时刀具的主要磨损机理,还简单对比了硬质合金和PCBN刀具切削性能上的差异。      

聚晶金刚石的研究进展与展望

聚晶金刚石(polycrystalline diamond,PCD)是以金刚石为骨架材料,以结合剂为黏结材料,在高压高温条件下烧结而成的复合材料.因其拥有优异的硬度与良好的耐磨性能,被广泛应用于刀具、拉丝模等领域.本文概述了PCD的结合剂种类、制备方法、影响性能的因素,分别介绍了金属型、陶瓷型和金属–陶瓷型等3种不同结...     

Preparation a nickel-aluminide bonded diamond tool by self-propagating high-temperature synthesis and strengthening by nickel-chromium-phosphorus alloy and copper

Metal bonded diamond tools are normally manufactured by hot-press sintering, which is a high energy consuming process and using a large number of graphite moulds as well. Graphite dust is hazardous to operator's health and environment in machining of graphite mould. In present study, a metal bonded diamond tool is manufactured by self-propagating high-temperature synthesis (SHS) without hot press sintering and consuming of graphite moulds. In order to improve bonding of diamond grit and flexural strength of the tool for this method, nickel‑chromium‑phosphorus alloy and copper are introduced into nickel‑aluminum SHS in present study. The influence of nickel‑chromium‑phosphorus alloy and copper content on the combustion processes, the thermal behaviors, and the microstructures of the synthesized composite bonds are examined in detail. A diamond tool based on the optimized composite is prepared, and the grinding performance is examined. The results reveal that the addition of nickel‑chromium‑phosphorus alloy and copper inhibited the SHS reaction of nickel‑aluminum and reduced the combustion velocity, combustion temperature and reaction exothermic enthalpy. Copper can significantly improve flexural strength of the nickel aluminide bond. However, the maximum of nickel‑chromium‑phosphorus alloy or copper is about 60 wt% to sustain the SHS. A homogeneously dispersed and interconnected nickel-chromium-phosphorus phase in the matrix of nickel aluminides can be obtained with addition of over 40 wt% nickel‑chromium‑phosphorus alloy. A continuous chromium rich layer, composed of chromium carbide, has been formed at the interface between diamond grit and matrix, which renders a chemical bond of diamond grit. On the basis of the addition of 40 wt% nickel‑chromium‑phosphorus alloy and 10 wt% copper, an interconnected nickel‑chromium‑phosphorus phase for strong bonding of diamond grit and a flexural strength up to 700 MPa are achieved, which is considered as an excellent candidate material for diamond tools. The grinding test shows that the diamond tool owns a sound machining ability on the granite, and the diamond grit can be well retained and protruded.     

Effect of mechanical pretreatment on nucleation and growth of HFCVD diamond films on cemented carbide tools with a complex shape

To enhance the mechanical pretreatment efficiency for WC-Co complex-shaped cutting tools, a self-made vibrating grinding equipment and mixed abrasives made up of walnut shell and diamond particles are proposed. The technique can abrade the dozens of tools simultaneously, modify surface properties of tools, and maintain sharpness of the cutting edges. Several experiments are performed to explore effects of the different types and proportions of walnut shell and diamond powders on the properties of nucleation, growth, and adhesion of diamond films deposited via a chemical vapor deposition method. Subsequently, Field Emission Scanning Electron Microscopy (FE-SEM), Atomic Force Microscopy (AFM,), Laser scanning micro-gauge, Micro-Raman Spectroscopy, Stylus Profiler, and Rockwell hardness tester are adopted to characterize the as-pretreated substrates and as-deposited diamond films. According to the results, a low residual cobalt content around 0.2 wt% and a markedly increased surface defects are detected on the pretreated milling tools when the preferred types and proportions of mixed abrasives are applied, which can help to significantly enhance the nucleation density and growth rate of diamond films, and strengthen the adhesion between the films and substrates.     

Alternative binders for hard metals

Cobalt has been the metal of choice for bonding of carbide based hard metals since their inception. Lately there has been concern about continued availability and price instability. A number of workers have looked at alternates for full or partial substitution and some of these are now commercially important. Improvement of chemical erosion resistance can be noted for nickel and chromium substitution. Additions of nickel on the one hand can stabilize the face centered cubic structure to give an austentic ductile binder whereas ruthenium can raise the F.C.C.-HCP transition temperature resulting in hexagonal binder structures associated with reduced friction effect. High strength martensitic binders can be fabricated using iron, cobalt, nickel alloys. Thus, some innovative alternates to cobalt have emerged with some technical advantage for specific areas of application.     

金属结合剂金刚石工具研究进展

金刚石工具广泛用于天然石材、陶瓷、玻璃、混凝土、硬质合金等的磨削和切割,金属结合剂金刚石工具因具有良好的机械和热学性能而成为金刚石工具的主力军。随着新型陶瓷混凝土等加工对象的不断出现和变化,要求金刚石工具要持续改进,以提高其切削效率、减少自身磨损、同时降低其制造和使用成本。本文综述了人造金刚石颗粒的性能、不同类型金属结合剂的成分组成和基本性能、金刚石与金属结合剂的界面结合状态以及提高其结合强度的措施,并对金属结合剂金刚石工具的发展作了进一步展望。      

采用含不同粘结剂的碳化钨粉末进行HVOF沉积处理的效果

通过零件的表面硬化来提高其耐磨性是表面工程领域的一个持久性研究课题,采用HVOF（高速氧燃料）热喷涂处理可获得具有良好耐磨性和（或）耐蚀性的涂层,常用含某种金属粘结剂的碳化钨来获得这种涂层。本文采用钴粘结剂或镍粘结剂,通过HVOF处理来获得碳化钨涂层,并用光学和电子显微分析、硬度和密度测试,以及X射线衍射分析来表证涂层的特性。用HVOF处理获得的涂层结构致密,孔隙率低,平均硬度高达1100HV左右。HVOF沉积处理不会使所用粉末很快变质。     

Using PCD for machining CGI with a CO2 coolant system

Polycrystalline diamond is widely used as a economic cutting material for machining non-ferrous materials such as aluminum. It is perceived that diamond cannot be used for cutting ferrous materials due to the high affinity of carbon to iron. Nevertheless, under certain conditions it is possible to use diamond materials for cutting ferrous metals. In order to avoid graphitization of the diamond matrix, it is necessary to keep the cutting temperature below the critical level of diamond graphitization. This paper presents the influence of a cryogenic CO₂ coolant strategy on the cutting process using PCD tools for cutting high strength compacted graphite iron (CGI). Investigations show, that tool wear behavior strongly correlates with the cutting speed, the cutting forces, cutting temperatures, and surface roughness of the workpiece. The test results show, that the tool life of PCD for cutting cast iron is dependent on the diamond grain size, the binder material, and the cutting parameters.     

Ni-Cr合金真空单层钎焊金刚石砂轮

单层高温钎焊超硬磨料砂轮具有传统电镀砂轮无法比拟的优异磨削性能 ,国内应及早研制开发应用此种砂轮。本文利用真空炉中钎焊的方法 ,用Ni Cr合金钎料 ,适当控制钎焊温度、保温时间和冷却速度 ,实现了金刚石与钢基体间的高强度连接。扫描电镜X射线能谱 ,结合金相及试样逐层的X射线结构分析 ,剖析了Ni Cr合金与金刚石和钢基体钎焊界面的微区组织结构 ;揭示了Ni Cr合金对金刚石和钢基体表面的浸润和钎焊机理。即在钎焊过程中会在金刚石界面形成富Cr层并与金刚石表面的C元素反应生成Cr7C3,在钢基体结合界面上Ni Cr合金和钢基体中的元素相互扩散形成冶金结合 ,这是实现合金层与金刚石和钢基体都有高结合强度的主要因素。最后重负荷磨削试验表明金刚石为正常磨损 ,没有整颗金刚石脱落 ,说明金刚石确有高的把持强度     

超硬磨具用金属结合剂国内外研究进展

金属结合剂超硬磨具广泛应用于石材、陶瓷和硬质合金的加工领域。介绍了目前常用的钴、铜、铁基等纯金属结合剂的特点、类型和力学性能。分析了不同添加物对金属–陶瓷复合结合剂性能的影响。重点阐述了近些年发展起来的金属–树脂复合结合剂的发展状况及趋势。最后提出了金属基复合结合剂发展中存在的问题。     

Co含量对金刚石–WC–Co复合材料耐磨性的影响

随着采矿和城市基建等行业的发展,对矿用WC–Co采掘工具的耐磨性提出了更高的要求。通过添加金刚石增强WC–Co矿用工具的耐磨性是一种可行的新思路。在烧结制备金刚石–WC–Co复合材料的过程中钴相作为催化剂会加速金刚石向石墨转变。为研究Co对复合材料中金刚石石墨化程度的影响,采用放电等离子体烧结技术(SPS)制备金刚石–WC–Co复合材料,分析了复合材料中金刚石石墨化程度并采用砂轮法研究了复合材料的磨损性能和磨损机理。结果表明：金刚石–WC–Co复合材料中金刚石可以起到增韧效果;Co含量增加会促进复合材料致密化进程,同时也会降低复合材料的硬度;随着Co含量增加,复合材料材料耐磨性变差。磨损过程中 WC–Co基体率先被磨损去除,金刚石后被磨损,金刚石会增强材料的耐磨性能。     

Comparative investigation of smooth polycrystalline diamond films on dental burs by chemical vapor deposition

Depositions of hot filament chemical vapor-deposited diamond on cobalt-cemented tungsten carbide (WC-Co) rotary cutting dental burs are presented. Conventional dental tools made of sintered polycrystalline diamond have a number of problems associated with the heterogeneity of the crystallite, decreased cutting efficiency, and short life. A preferential (111) faceted diamond was obtained after 15 h of deposition at a growth rate of 1.1 μm/h. Diamond-coated WC-Co dental burs and conventional sintered burs are mainly used in turning, milling, and drilling operations for machining metal ceramic hard alloys such as CoCr, composite teeth, and aluminum alloy in the dental laboratory. The influence of structure, the mechanical characteristics of both diamond grains and hard alloys on the wear behavior, as well as the regimen of grinding on diamond wear are considered. Erosion wear properties are also investigated under air-sand erosion testing. After machining with excessive cutting performance, calculations can be made on flank and crater wear areas. Diamond-coated WC-Co dental burs offered significantly better erosion and wear resistance compared with uncoated WC-Co tools and sintered burs. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

超细Fe粉和Cu粉在金刚石薄壁工程钻中的应用研究

在Fe-Cu和Fe-Cu-Ni基胎体中探究超细Fe粉和Cu粉对胎体烧结硬度、应力-应变曲线、烧结界面形貌的影响机理,进而总结出使用超细金属粉对工程薄壁钻头使用性能的影响。实验表明:将超细金属粉应用于Fe-Cu、Fe-Cu-Ni基胎体,可使2种烧结体的硬度分别提高6.25%和12.20%;将2种配方钻头的使用寿命分别提高21.6%和82.5%,钻切速度分别下降4.5%和16.2%;2种钻头刀头顶刃的磨损表面较细腻、光滑,与钻切材料的摩擦系数低。但采用超细粉制备的Fe-Cu-Ni基胎体耐磨性过强,金刚石的出刃高度明显降低。      

Fe－B－C合金冲击磨料磨损性能及磨损机制的研究

以高铬铸铁为对比材料,采用MLD-10型冲击磨料磨损试验机,研究了Fe—B—C合金冲击磨料磨损性能：借助子扫描电镜,探讨了Fe—B—C合金的磨损机制。结果表明：Fe—B—C合金的硬度和冲击韧度与高铬铸铁相当,耐磨性能达到高铬铸铁水平,具有良好的性价比;Fe—B—C合金的磨损机制是以微观切削为主,同时存在微观断裂和微观犁沟的混合磨损。     

Surface structuring of polycrystalline diamond (PCD) using ultrashort pulse laser and the study of force conditions

In the metal working industry, cutting tools for high precision application are usually made from non-conventional super hard materials, for example, diamond (D) and cubic boron nitride (CBN). These materials are composites of geometrically undefined grains embedded in metallic binder. For some special applications, these tools are constructed from one or several cutting edges and guide rails. Typical examples are honing and guided reaming tools for the fine machining of bores. These tools improve the form, dimension and surface quality, as well as the geometrical tolerances of the machined workpieces. The guide rails of the tool play an important role as they usually support the tool shaft in the rotating movement, for example the guiding stones of the honing tool. In the case of dynamic contact, higher demands on material properties such as hardness and wear resistance are necessary. In this study, a polycrystalline diamond (PCD) grade is employed as a new material for guide rails. Contacting surfaces of the PCD guide rails are textured with three defined patterns by a femtosecond laser setup. It is aimed to improve the force conditions by means of changing the contacting conditions. Within this regard, the tribological properties of the three patterns on PCD rails are characterized using a nanotribometer and compared to the conventional guide rails made of cemented tungsten carbides. A force simulation based on the honing processes is built up and conducted to predict the force conditions of each different pattern. At the same time, morphological modification, assessment of surface and microstructural integrity of the structured PCD guide rails are also studied in this work.     

我国高速高效精密超硬材料磨具制造技术的新进展

本文介绍了"十一五"期间我国高速高效精密超硬材料磨具制造领域研究开发的汽车发动机曲轴高速高效磨削用cBN砂轮、集成电路(IC)晶圆背面减薄磨削用金刚石系列砂轮、晶圆划片与分割用电镀结合剂高精度超薄金刚石切割砂轮、精密研磨用陶瓷结合剂超硬材料磨盘、高硬度刀片磨边用新型复合结合剂金刚石砂轮等5种新产品。重点描述了在新型结合剂、成型技术、加工技术等方面取得的技术突破以及产品应用效果,并对该领域未来发展趋势做了简要分析。     

A brief review of brazing diamond in cutting tools

Diamond has high hardness and good wear resistance. It is widely used in cutting tools and workpieces. Brazing is an effective method to realize high quality cemented carbide joints in various materials connection technologies. This paper analyzes the research status of diamond brazing in detail. The materials used as brazing filler in diamond brazing are reviewed. Copper base filler and nickel base filler are the most commonly used brazing filler in diamond brazing. The advantages and disadvantages of diamond grinding tools under different production methods are analyzed. In addition, a series of new brazing alloys such as amorphous Ni based brazing filler metals are analyzed. Finally, the development trend of diamond brazing is pointed out.