INFLUENCE OF MICROSTRUCTURE ON WEAR RESISTANCE PARAMETER OF CERAMIC CUTTING TOOLS

This report examines the role of microstructure of a new type of cutting tool material on an existing relationship between its abrasion wear resistance, fracture toughness (K_IC), and hardness (H). Three alumina-silver composites with different amounts of metal particles have been prepared, and their hardness and fracture toughness properties have been determined together with the assessment of their microstructural features such as volume fraction of the second phase, porosity, etc. The mechanical wear on the flanks of cutting tool inserts, made from the developed composites, has also been estimated by machining experiments against 0.45% carbon steel. The results indicate that flank wear resistance of these silver toughened ceramic cutting tool inserts is not proportional to an existing wear resistance parameter K_IC^3/4H^1/2. A modified relation between flank wear resistance, hardness, and fracture toughness has been suggested here for these cutting tool materials. The modification incorporates consideration of the volume fraction of the second phase and the porosity in the developed metal toughened ceramics.     

Superior wear resistance of aggregated diamond nanorods

The hardness of single-crystal diamond is superior to all other known materials, but its performance as a superabrasive is limited because of its low wear resistance. This is the consequence of diamond's low thermal stability (it graphitizes at elevated temperature), low fracture toughness (it tends to cleave preferentially along the octahedral (111) crystal plains), and large directional effect in polishing (some directions appear to be "soft", i.e., easy to abrade, because diamond is anisotropic in many of its physical properties). Here we report the results of measurements of mechanical properties (hardness, fracture toughness, and Young's modulus) of aggregated diamond nanorods (ADNRs) synthesized as a bulk sample. Our investigation has shown that this nanocrystalline material has the fracture toughness 11.1 +/- 1.2 MPa.m(0.5), which exceeds that of natural and synthetic diamond (that varies from 3.4 to 5.0 MPa.m(0.5)) by 2-3 times. At the same time, having a hardness and Young's modulus comparable to that of natural diamond and suppressed because of the random orientation of nanorods "soft" directions, ADNR samples show the enhancement of wear resistance up to 300% in comparison with commercially available polycrystalline diamonds (PCDs). This makes ADNRs extremely prospective materials for applications as superabrasives.     

晶粒长大抑制剂VC对原位生成WCoB-TiC-Co复相金属陶瓷的影响

为细化WCoB-TiC-Co复相金属陶瓷晶粒,改善其组织,提高其力学性能,以WC、TiB_2和Co粉末为主要原材料,采用真空液相原位反应烧结工艺,在1 400℃真空烧结炉中制备了WCoB-TiC-Co复相金属陶瓷.利用FE-SEM、EDS和XRD等技术,研究了不同含量的晶粒长大抑制剂VC对WCoB-TiC-Co复相金属陶瓷组织、物相构成、硬度、密度、耐磨性及抗弯强度和断口形貌等性能的影响.结果表明:添加适量的VC能有效细化WCoB-TiC-Co复相金属陶瓷晶粒,使得材料获得更均匀细小的微观组织,增加材料韧性和断口不平整性,增强材料抗弯强度,并且提高硬度、密度和耐磨性;当VC的质量分数增加到0.9%时,金属陶瓷的晶粒平均尺寸可细化到约1.3μm,硬度随之升高到91.5 HRA,抗弯强度达到794 MPa;但VC的质量分数继续增加到1.2%、1.5%时,其硬度、密度、耐磨性及抗弯强度均会有所降低.     

The effects of functionally graded material structure on wear resistance and toughness of repaired weldments

To perform a long lasting, crack-free repair welding on ultrahigh strength steels, the filler metal must be chosen and applied properly. Avoiding several short-term repairs or replacements, the repaired weldment should reveal comparative characteristics such as wear resistance, toughness and hardness to base metal. In the present study, a novel functionally graded material have been introduced to obtain enhanced wear resistance and hardness at surface as well as improved fracture toughness at fusion line of repaired weldments. A comparative study of wear resistance of repaired weld metals has been carried out by pin-on-disk apparatus at 5 N normal load and 0.14 ms⁻¹ sliding speed. Fracture toughness of weld metal was also evaluated by charpy absorbed fracture energy tests and scanning electron microscopy fractograghs. The results show that by employing functionally graded layers, toughness was enhanced significantly while retaining the surface wear resistance.     

Reinforcement of Hadfield steel matrix by oriented high‐chromium cast iron bars

To attain a wear‐resistant material compatible with high hardness and high toughness, Hadfield steel matrix was reinforced by oriented high chromium cast iron bars, through inserting high chromium alloys flux‐cored welding wires into Hadfield steel melt at 1500 ± 10 °C. The obtained composites were investigated by XRD, SEM, micro‐hardness, three‐body abrasion wear and impact toughness testers. The results show that the alloy powders inside the flux‐cored welding wires can be melted by the heat capacity of Hadfield steel melt and in situ solidified into high chromium cast iron bar reinforcements tightly embedded in the matrix. The micro‐hardness of reinforcements of the water‐quenched composite is about four times higher than that of the matrix. The impact toughness of the water‐quenched composite is higher than that of the as‐cast composite and lower than that of Hadfield steel, and its fracture mechanism is very complicated and refers to brittle and ductile mixture fracture mode. The excellent impact toughness and better wear resistance of the water‐quenched composite are attributed to combine fully the advantages and avoid the drawbacks of both Hadfield steel and high chromium cast iron. Additionally, in industrial application, the pulverizer plate produced by this composite, has also better wear resistance compared to the reference Hadfield steel pulverizer plate.     

Abrasive wear behaviour of bio-active glass ceramics containing apatite

In this study, abrasive wear behaviour of bio-active glass ceramic materials produced with two different processes is studied. Hot pressing process and conventional casting and controlled crystallization process were used to produce bio-active ceramics. Fracture toughness of studied material was calculated by fracture toughness equations using experimental hardness results of the bio-active glass ceramic material. Two fracture toughness equations in the literature were used to identify the wear behaviour of studied ceramics. Wear resistance results that identified with both of the equations were similar. The results showed that the abrasive wear resistance of the bio-active glass ceramics produced with hot pressing process was found to be higher than that of the ceramics produced by conventional casting and controlled crystallization process.     

Large sized cubic BN reinforced nanocomposite with improved abrasive wear resistance deposited by cold spray

In this work, large sized cubic BN (cBN) reinforced nanocomposites are prepared by cold spray deposition of blended powder mixtures of mechanically alloyed 40 vol.% cBN–NiCrAl nanocomposite particles and large sized cBN particles. Deposition behavior of the blended powders, microstructure and mechanical properties including hardness, fracture toughness and two-body dry abrasive wear behavior of the sprayed composites, are investigated. Results show that dense composites with large cBN particle content of 13–20 vol.%, depending on composition of the spray powders, can be obtained. Declining deposition efficiency is detected as increasing large cBN content due to the gradually enhanced sand blasting effect. Increasing content of large cBN in spray powder results in an increment in hardness and a decrement in fracture toughness. Abrasive wear resistance of the 40 vol.% cBN–NiCrAl nanocomposite is doubled by incorporating 20 vol.% of the large cBN particles. Worn surface morphology observation indicates that the improvement is due to the shielding effect of the large protruding cBN particles against SiC abrasive. Material removal mechanism of the sprayed composites during abrasive wear test is also studied.     

Characterization of structural alumina ceramics used in ballistic armour and wear applications

Structural alumina ceramics used in ballistic armour and wear applications with varying alumina contents and manufactured using both slip casting and dry pressing techniques, have been investigated and characterized in terms of their hardness, elastic modulus, fracture toughness, and microstructural characteristics. For a given alumina content, fracture toughness decreases with increasing hardness. Dry pressed samples show slightly higher hardness, and lower fracture toughness for the same alumina content. The hardness, elastic modulus and fracture toughness are higher for the 98% alumina samples while the differences between the lower alumina samples (95 and 91%) are negligible. The grain sizes are bimodal with the majority 3 m and the size range narrows with decreasing alumina content. The microstructures are composed of a matrix phase, corundum (-Al₂O₃), grain boundary phases consisting of a glassy phase with varying Al₂O₃, SiO₂, and CaO contents, a crystalline phase, triclinic anorthite (CaAl₂Si₂O₈), and an additional phase, spinel (MgAl₂O₄), in the lower alumina samples. The proportion of the boundary phase increases with decreasing alumina content and no effect of fabrication method is observed.     

Wear Behavior of Deep-Cryogenic Treated High-Speed Steels at Different Loads

Tools for the cold-working applications are typically made from the high-speed steels. However, due to wear and plastic deformation their performance in several applications is not adequate and should be further improved. By using appropriate combination of vacuum heat-treatment in conjunction with a deep-cryogenic treatment (duplex treatment) the microstructure of high-speed steel matrix can be substantially changed and the hardness and fracture toughness can be modified and optimised. In the present work we have investigated the effect of four different tempering temperatures of vacuum and cryogenically treated ESR AISI M2 high-speed steel on the resulting combinations of microstructure, hardness and toughness and their effect on the wear mechanisms at different loads. The results showed that at relatively high loads the different treatments resulted in an order-of-magnitude difference of wear resistance, while at low loads the selected treatments were efficient enough to keep the wear within the mild wear regime and small variations between the samples. However, the overall wear transition did not occur at any load used or any sample treatment, although some small differences in wear mechanisms can be seen, primarily depending on the fracture toughness of the samples.     

轧机机架衬板工作层材料热处理工艺研究

研究了热处理工艺对钢管连轧机架耐磨复合衬板工作层材料力学性能的影响。结果显示,硬度随淬火温度升高而升高,但高于900℃时,硬度反而下降;低于920℃时,冲击韧性变化不明显,高于920℃时,冲击韧性略有下降。随着回火温度升高,冲击韧性和断裂韧性提高,高于400℃时,伸长率和断面收缩率大幅度提高。但高于450℃时,硬度明显降低。耐磨性在350℃回火后达到最大值。耐磨复合衬板工作层材料的最优热处理工艺为900～920℃淬火+350～370℃回火。     

Characterization of the microstructure of high-chromium cast irons using Mössbauer spectroscopy

The finish grinding process for cement materials uses ball mills with differently sized grinding balls. Because the grinding takes place through the impact and friction of the balls, balls with a high wear resistance are desirable and the materials of choice are the high-chromium white cast irons. This article examines the behavior of these cast irons when subjected to various heat treatments. The emphasis is on the dependence of the microstructure properties on the chemical composition of the alloys and the heat treatment parameters. The content of retained austenite and that of carbon in the martensite phase were determined by the use of Mössbauer spectroscopy. The results verify that a higher proportion of retained austenite with low carbon content and a martensite with higher hardness produce a material with good fracture toughness and resistance to abrasive wear.     

Metallurgical aspects of steels designed to resist abrasion,and impact-abrasion wear

Many abrasion resistant steels rely on a martensitic microstructure to ensure hardness, which in general correlates with better wear performance. However, in practice the steel may be subjected to a complex combination of conditions where hardness alone may not be sufficient to ensure tribological performance. This review is a critical assessment of the mechanical and metallurgical parameters that control wear resistance of steel in impact-abrasion conditions, although relevant work dealing with abrasion has also been included. It is found, for example, that fracture toughness and work-hardening behaviour have a role in enhancing the wear resistance of hard steels.     

深冷处理对GCr15组织和力学性能的影响

对经不同深冷处理后的GCr15钢进行了组织观察、力学性能检测和摩擦磨损试验。试验结果表明:深冷处理可提高GCr15钢的硬度;淬火后进行深冷处理+180℃×8h回火处理后,GCr15钢的冲击韧性有所降低;深冷处理可明显提高GCr15钢耐磨性并降低钢中残留奥氏体含量,其中深冷处理6h后效果最为显著,其相对磨损率下降了30%、残留奥氏体含量降幅高达81%。     

Processing and characterization of glass-filled polyamide composite coatings

Glass-polyamide composite coatings have been successfully plasma sprayed on to steel by simultaneous injection of glass and polyamide particles into the plasma jet. The deposition conditions were selected such that the polyamide melts in the jet in order to provide the matrix, whereas the glass remains solid to avoid overheating the polymer. The deposition efficiency of glass is significantly less than that of polyamide, particularly in the initial stages of spraying, because the solid glass particles deform elastically on impact with the substrate and rebound, whereas the kinetic energy of the molten polyamide particles is absorbed by viscous flow. The presence of the glass filler reduces the wear rate of polyamide by an order of magnitude because of its load-supporting action and reduction of adhesive and abrasive wear. However, there is a minimum in wear rate at a glass filler content of 50 wt%, because higher glass contents adversely affect wear performance by reducing the fracture toughness. The results also show that refining the glass particle size provides a considerable reduction in wear rate of the composite. The first-order theory of adhesive and abrasive wear, in which the wear rate is inversely related to hardness, is shown not to hold for this class of materials.     

Mechanical and electrical properties of hot-pressed borosilicate glass matrix composites containing multi-wall carbon nanotubes

Borosilicate glass matrix composites reinforced with 10 wt% multiwall carbon nanotubes (CNTs) were fabricated using a conventional powder processing route and uniaxial hot pressing. The microstructure of the composites contained aggregates of CNTs which had not been infiltrated by the viscous glass during hot-pressing leaving a ∼9% residual porosity. As a result, the mechanical properties (hardness, elastic modulus, fracture toughness and fracture strength) were not improved in comparison to those of the monolithic glass matrix. However the brittleness index (B), which is the ratio of hardness to fracture toughness, decreased with addition of CNTs, which indicates that the composites should exhibit improved contact damage and wear resistance. Electrical resistivity measurements revealed that the addition of 10 wt% CNTs to the normally insulating borosilicate glass decreased its resistivity to 13 Ω cm in comparison to the high value (10¹⁵ Ω cm) of the monolithic glass.     

系列奥氏体锰钢耐磨性研究

测定了系列锰钢的冲击磨粒磨损性能，发现在低冲击功下锰钢的耐磨性与磨面硬度近似线性关系，而在高冲击功下耐磨性几乎与磨面硬度无关。对冲击功、冲击韧性及耐磨性三者之间关系研究得出：当冲击韧性与冲击功比值在３０—７０范围内时锰钢具有较高耐磨性     

中锰奥氏体基耐磨钢的热处理工艺及性能研究

合理设计了中锰奥氏体基耐磨钢的成分,并选择合适的水韧处理３工艺来获得一种介稳的单相奥氏体组织,在此组织基础上进行了不同的等温热处理工艺,获得一定量的马氏体,以提高基体的初始硬度,又不恶化其冲击韧性,再通过与高锰钢（Ｍｎ１３）在同等式况条件下进行耐磨性模拟对比实验,来选择适合中锰钢在中、低冲击磨料磨损条件下使用的热处理工艺和组织。同时对试样进行了金相组织观察及力学性能测试。     

Tribological properties of Cr-Si-N nanocomposite film adherent silicon under various environments

Chromium nitride thin films have good corrosion resistance and mechanical properties. However, their hardness is slightly lower than that of other hard coatings. The concept of nanocomposite thin films is employed by adding silicon to form Cr-Si-N thin films with enhanced hardness and wear resistance. In this study, Cr-Si-N films with various Si contents were coated on silicon wafer to enhance the tribological properties and anticorrosion by a bipolar symmetry pulsed DC reactive magnetron sputtering process. The tribological properties were studied by a pin-on-disk tester. The tests were conducted with the same operating condition under three different environments. They were performed in the ambient atmosphere (in 55% humid air), DI water, and 0.01 M NaCl aqueous solution, respectively. The wear tests revealed that, as the silicon content was increased, even though the Cr-Si-N films had a better anticorrosion property they had an inferior performance on wear resistance. The results were concluded to be mainly due to Cr-Si-N films’ microstructures and adhesion to the Si substrate rather than their hardness and toughness.     

等离子喷涂CoCrW涂层微动磨损特性的研究

对等离子喷涂CoCrW涂的微动磨损特性进行了研究,结果表明,等离子喷涂CoCrW涂层的微动磨损可分为开始,过渡和稳定三个阶段,开始阶段以粘着磨损为主,过渡阶段以氧化磨损为主,稳定阶段以疲劳磨损为主,等离子涂CoCrW涂层具有合适的硬度和良好的韧性,从而具有比较好的耐策动磨损性能。     

水溶性胶态成型工艺制备氮化硅耐磨结构陶瓷

以氮化硅粉末为原料, 采用水溶性胶态成型工艺制备高耐磨氮化硅陶瓷. 采用正交设计的方法来优化制备高品质注浆料, 并研究了掺杂分散剂后Zeta电位的变化. 同时, 还对氮化硅陶瓷烧结体的显微结构、力学性能和耐磨性能进行了研究. 结果表明: 当氮化硅浆料中固相体积分数为45%时, 可制得体积密度较高的精细氮化硅陶瓷材料, 断裂韧性可达7.21MPa·m^1/2, 硬度为9.30GPa. 通过抗耐磨损实验研究表明: 干摩擦条件下, 氮化硅陶瓷发生了晶粒脆性断裂和脱落; 水润滑条件下, 摩擦表面产生了氢氧化硅 反应膜, 降低了磨损, 主要是化学腐蚀磨损.