Effect of Hot Forging on Microstructure and Abrasion Resistance of Fe-B Alloy

The effect of hot forging on the microstructure and abrasion resistance of Fe-B alloy was studied. The results showed that boride networks are broken down by hot forging. After hot forging, the hardness of Fe-B alloy increased marginally, and the toughness increased considerably.

In the two-body abrasion test, unforged Fe-B alloy exhibited excellent wear resistance and soft abrasive tended to show higher wear resistance. When alloys were tested against very hard abrasives, the wear resistance of forged Fe-B alloy was similar to that of unforged Fe-B alloy, but in the case of soft abrasives the wear resistance of forged Fe-B alloy was lower than that of unforged Fe-B alloy.     

基于钴基合金覆层的多层金属热锻模原型制备与性能

基于功能梯度材料(FGM)的思想制备多层金属热锻模是提高模具寿命的有效方法。采用焊条电弧堆焊制备了多层金属热锻模的原型试样,试样经焊后热处理后,进行了金相组织分析、显微硬度测试、磨损实验和冲击韧性测试等实验。实验结果表明:钴基合金堆焊层与W6Mo5Cr4V2堆焊层界面冶金结合情况良好;截面显微硬度呈梯度分布,表面钴基合金硬度达到492HV;制备的多层金属试样耐磨性是H13钢耐磨性的2.5倍,冲击韧性处于合理范围。     

Wear characteristics of as-cast binary aluminium-silicon alloys

Binary as-cast aluminium alloys with silicon content varying up to 21% have been slid against hard steel. Wear rates have been measured at various loads and it is shown that, from the point of view of wear and load-carrying capability, a near-eutectic alloy is the optimum. The hypereutectic alloys wear more but not by more than about a factor of 2 compared with the hypoeutectic alloy. It is concluded that the beneficial effect of silicon is to decrease the propensity to seizure. High silicon alloys, however, wear even hard steel counterfaces. Results of particle size analysis are included to show that although silicon modifies the mode of wear of these aluminium alloys, the distribution of particle size appears to be independent of silicon content and load. Iso-wear lines are plotted for various combinations of silicon and load and it is suggested that this form of presentation will be of help to design engineers if carried out on actual components, e.g. plain bearings.     

Gradient DLC-Based Nanocomposite Coatings as a Solution to Improve Tribological Performance of Aluminum Alloy

The low hardness and poor tribological performance of aluminum alloy as moving component greatly restricts their wide applications in automotive fields. In this letter, an attempt to deposit gradient Ti/TiN/Si/(TiC/a-C:H) multi-layer on aluminum alloy is thus effectively performed by a combined arc ion plating and magnetron sputtering process based on the concept of involving coatings with a functionally graded interface. Multi-layered structure within DLC-based coatings has shown to significantly improve the load-bearing capacity, anti-wear and self-lubricating ability of Al alloys. The friction coefficient of gradient DLC-based coatings decreased to 0.18 under dry sliding condition while kept at 0.05 under the oil-lubricated conditions. The wear rate of gradient DLC multilayers was lower by two and even three orders of magnitude when compared with Al alloys both under dry wear and oil-lubricated conditions. Such gradient DLC-based coatings with good adhesion strength, high hardness, and excellent tribological performance are considered as potential protective surfaces of Al alloys for engine parts.     

Test procedure of cladded alloys for resistance against high temperature abrasive wear

This article discusses the development of procedure and assembly for testing metals and alloys for abrasive wear at ambient and higher temperatures of up to 600°C. The procedure can be applied both to evaluate the operating properties of alloys used to clad of machine parts and tools of metallurgical and refractory purposes, and to test various metal and composite materials. The wear of alloys as a function of temperature, the pressure on specimen, and its shape, as well as of the composition and dispersity of abrasive mass have been determined. Hardness and wear resistance of some experimental and commercial alloys have been presented, and the influence of alloy doping and modifying on their wear resistance at higher temperatures has been established.     

Über einige eigenschaften von aluminium-diffusionsschichten der ferritischen art

In the past few years research has been mainly directed towards the technology of application of Al coatings. Little attention has been paid to the properties of Al coatings and to methods of controlling these properties. The diffused aluminium coating consists of several layers. The number, thickness and structure of these layers may be varied by the choice of parameters of the treatment or by different heat treatments after aluminizing.Some mechanical properties of the diffused “ferritic” Al layers formed on carbon and alloy steels by annealing have been examined. Annealing of Al coatings changes the structure of the surface layer. Instead of layers of aluminium and intermetallic compounds, a single layer of a solid solution of Al in Fe having a characteristic structure similar to pure ferrite was formed. Microanalysis has confirmed that a diffusion process leads to the formation and growth of the “ferritic” type layer.Comparative studies of the wear resistance of carbon and alloy steels without Al coatings, with diffused coatings and with an annealed Al coating of the “ferritic” type have been carried out; aluminizing and annealing increased the resistance to wear of carbon and alloy steels. The most favourable performance was observed with low-carbon mild steels. Metallographie and hardness studies have shown that structural changes of diffused Al coatings occur at high temperature.     

Estimation of die service life for a die cooling method in a hot forging process

Dies may have to be replaced for a number of reasons, such as changes in dimensions due to wear or plastic deformation, deterioration of the surface finish, breakdown of lubrication, and cracking or breakage. In this paper, die cooling methods are suggested to improve die service life with regards to wear and plastic deformation in a hot forging process. The yield strength of die decreases at higher temperatures and is dependent on hardness. Also, to evaluate die life due to wear, a modified Archard’s wear model has been proposed by considering the thermal softening of die expressed in terms of the main tempering curve. This paper describes the effects of die cooling methods such as cooling hole and direct spray cooling on the life of finisher die during the hot forging of an automobile part. It is shown that the cooling hole method during hot forging is necessary for an effective die service life to be obtained.     

Tribological characteristics of composite coatings formed by laser cladding of powders of nickel self-fluxing alloy and bronze

Microstructures, coefficients of friction, and relative wear of composite coatings based on the PG-12N-01 nickel self-fluxing alloy and PG-19M-01 bronze have been considered. It has been found that composite coatings have a complex structure. The bronze coating, which is deposited on the fillets of the nickel alloy, crystallizes in a form of dendrites with axes arranged under an angle of 45°. The nickel alloy has a globular-dendritic structure with the eutectic component crystallizing between its branches. Momentary coefficients of friction in conditions of the concentrated load are independent of the cladding rate, and their values are 0.08–0.12 depending on the load. In this case, the wear rate of coatings depends substantially on the laser cladding. Under conditions of the distributed contact, bilayer coatings have a considerable advantage, and the relative wear is reduced by several tens of times compared with single-layer ones.     

A comparative study of tribological behavior of microarc oxidation and hard-anodized coatings

Microarc oxidation (MAO), a novel coating technique capable of depositing dense, hard ceramic composite coatings on aluminium and its alloys, has the potential to replace conventional hazardous anodizing techniques. However, the emergence of such a scenario depends strongly on the properties and performance of MAO coatings in comparison to hard-anodized coatings. In order to facilitate such a comparative investigation, a 6061 T6 aluminium alloy was employed as the substrate and the coatings were deposited through microarc oxidation (MAO) and hard anodizing techniques. The tribological performance of the coatings was evaluated using dry-sand abrasive wheel tests at different normal loads and solid-particle erosion wear tests at different particle velocities and impact angles by employing silica as erodent. The hard-anodized coatings reduced the abrasive wear rate of 6061 Al alloy by a factor of 2, while the MAO coatings reduced the wear rate by a factor of 12-30. Under erosion conditions, the overall wear rate of MAO coatings is identical to that of bare alloy, whereas the hard-anodized coatings exhibit 10 times higher erosion rate.     

Effects of carbon content on the high temperature friction and wear of chromium carbonitride coatings

Chromium nitride-based coatings are often used in application at high temperature. They possess high wear and oxidation resistance; however, the friction coefficient is typically very high. Therefore, we doped CrN coatings by carbon with the aim to improve tribological properties at elevated temperature, particularly to lower the friction. CrCN coatings were prepared by cathode arc evaporation technology using constant N₂ flow and variable C₂H₂ flow. The coatings with a thickness of 3-4 μm were deposited on hardened steel substrates and high-temperature resistant alloy. The carbon content varied from 0 at.% (i.e. CrN) up to 31 at.%. The standard coating characterization included the nano-hardness, adhesion, chemical composition and structure (including hot X-ray diffraction). Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 700 °C. The coatings with carbon content 12-31 at.% showed almost identical tribological behaviour up to 700 °C.     

Guidelines for the selection of hardfacing alloys for sliding wear resistant applications

The work presented in this report summarizes an evaluation of the relative sliding wear characteristics of several commonly used commercial hardfacing alloys. The alloys studied include cobalt-base, nickel-base and Fe-Cr-Ni alloys which also contain small amounts of cobalt. Selecting the most effective alloy combination to withstand sliding wear is a challenge for materials engineers, equipment designers and fabricators. Accurate guidelines for selecting compatible alloys from a wear resistance point of view are not available. On the basis of the results of this work several hardfacing alloy combinations were identified which provide good sliding wear resistance. In addition, several hardfacing alloy combinations were found to exhibit poor wear resistance compatibility. The guidelines presented in this report will aid in the selection of suitable hardfacing alloy combinations with adequate sliding wear resistance. The wear guidelines are also supplemented with corrosion data in several environments of importance in the chemical process industries. These data should assist in the selection and optimization of hardfacing alloys in the presence of aggressive environments.     

Influence of the carbon content on the corrosion and tribocorrosion performance of Ti-DLC coatings for biomedical alloys

Biomedical alloys are prone to suffer corrosion and wear phenomena coming from the hostile environment of the body and friction processes, respectively. Diamond-like carbon (DLC) coatings are known to be excellent candidates for using as protective coatings on biomedical alloys, not only due to their excellent tribological properties but also due to their chemical composition and stability. In this work, three Ti-DLC PVD coatings with different compositions were deposited on Ti6Al4V alloy and their corrosion and tribocorrosion responses were evaluated in simulated body fluid. Excellent tribocorrosion response has been found especially in case of coatings with high carbon content. Additionally significative reduction of friction and wear has been obtained in comparison to the substrate response.     

Wear resistance of a coated hard-alloy tool in the machining of high-temperature chromium alloys

The influence of the hard-alloy substrate and the composite coatings of a tool on its wear resistance in the machining of high-temperature chromium alloys is investigated. The effectiveness of the coated hardalloy tool is determined by the properties of the hard alloy and the coatings. For hard alloys characterized by relatively low strength and crack resistance, the coatings prove ineffective, on account of the brittle failure of the substrate and the consequent destruction of the coating. On alloys with low thermal stability, the coatings are ineffective on account of weakening of the binder at the high temperatures associated with machining. It makes sense to use a hard alloy with mechanical properties such that the coating may operate effectively. Better properties are not needed.     

Wear analysis of hot forging dies

In hot forging, die wear is the main cause of failure. In this paper, the wear analysis of a closed hot forging die used at the final stage of a component has been realized. The simulation of forging process was carried out by commercially available software based on finite volume method and the depth of wear was evaluated with a constant wear coefficient. By comparing the numerical results with the measurement taken from the worn die, the wear coefficient has been evaluated for different points of the die surface and finally a value of wear coefficient is suggested.     

The effect of substrate properties on tribological behaviour of composite DLC coatings

The unique features of DLC coatings in providing low friction and low wear and, at the same time, causing low wear to the counterface make them very attractive in industrial applications, in improving tribological performance of mechanical components on various substrates. In this study, composite DLC coatings have been deposited on sintered ferrous alloy, M42 tool steel, 2618 aluminium alloy, and 6063 aluminium extrusion substrates using the combined CFUBMS–PACVD technique. The effect of mechanical properties of substrate materials on tribological behaviour of the composite DLC coatings has been investigated at various loads on a ball-on-disk wear machine in dry air. A transition load was usually observed for coatings on the various substrates except for the aluminium extrusion; above the transition load the coating was completely destroyed via some spallation/fragmentation process after 2 h sliding, and the wear rate increased dramatically with further increase in load. The coating system on sintered ferrous alloy substrate exhibited the highest transition load among the four types of substrates studied. This is considered to have resulted from the combined effects of the lower elastic modulus of the porous sintered ferrous alloy substrate, which decreases the stress concentrations in the contact region, and the surface roughness and porosity, which enhance the bonding strength between the coating and the substrate under multi-contact conditions. The high elastic modulus of the tool steel substrate leads to tensile stress conditions in the sliding contact region and therefore makes coatings deposited on such a substrate more prone to breakdown/fragmentation, resulting in a transition load close to that for coatings on the soft 2618 aluminium alloy substrate. For coatings on the 6063 aluminium extrusion substrate, significant plastic deformation occurred in the substrate at loads above 1.5 N. However, despite the heavy deformation in the substrate, coatings on this substrate were not scraped off, as were coatings on the 2618 aluminium alloy substrate, even at a load as high as 20 N. The specific wear rate increased continuously with load, no apparent transition load being explicitly identifiable. This study shows that hard DLC coatings can be applied on both hard and soft substrates for improvement of the tribological behaviour of mechanical components.     

Resistance to wear and cavitation erosion of bearing alloys

Sliding wear and vibratory cavitation erosion tests in paraffin oil were carried out on bearing alloys, i.e. tin-based and lead-based white metals, Cu-Pb alloy and leaded bronze. In lubricated wear under mild conditions the surface is worn smooth and a slight difference exists between the wear resistances of the four alloys. In cavitation erosion an eroded surface which is much rougher than the worn surface is formed. Cavitation erosion is affected strongly by the composition and crystal structure of the alloy and thus the erosion resistances of the four alloys differ greatly, the ranking of resistance being lead-based white metal < Cu-Pb alloy < tin-based white metal < leaded bronze. The surface damage, which is caused by the joint action of cavitation erosion and wear, was also investigated by rubbing the eroded surfaces which had been exposed to cavitation erosion for various times. This damage becomes larger with increasing cavitation damage. The resistance to this damage differs much more in the four alloys tested and tends to correlate with the results of the erosion tests rather than those of the wear tests. Therefore, it is clear that the cavitation erosion resistance should be considered in the selection of bearing materials.     

The unlubricated adhesive wear resistance of metastable austenitic stainless steels containing silicon

The unlubricated adhesive wear resistance of metastable austenitic stainless steels can be improved by silicon additions. At low surface temperatures (under the M_d temperature) metastability appears helpful in maintaining the alloy in a state of mild wear. Silicon was not found to promote alloy metastability but did tend to strengthen the alloy by solid solution hardening. At lower temperatures the silicon had little effect on the mild wear rates of metastable alloys but did act to lower the severe wear rates of stable alloys. At high surface temperatures (above the M_d temperature) the silicon additions (2–4%) were found very beneficial in promoting mild wear rates while metastability had little or no effect. Silicon additions were also found to be beneficial to the oxidation resistance and did not increase the running-in period for the alloys. Improving the oxidation resistance of these alloys is more effective in promoting mild wear than is increasing the hardness through metastability.     

碳纤维增强铜基轴承合金的制造工艺和性能研究

在碳纤维增强铜基轴承合金前期研究的基础上，对短碳纤维增强铅青铜基和锡青铜基复合轴承合金的机械性能和摩擦磨损性能作进一步研究，探讨了制造工艺对其性能的影响。结果表明，碳纤维的加入明显提高了两种轴承合金的减摩耐磨性能和机械性能；除热压法外，二次压制烧结法也是制造碳纤维／铜基轴承合金的可行方法；碳纤维加入铜基轴承合金中对其摩擦对偶件没有特殊的要求。     

Cr3C2/镍基合金等离子堆焊层的组织及耐磨性能

采用光学显微镜、扫描电镜、X射线衍射仪以及磨损试验机等,研究了加入不同量的Cr3C2对等离子堆焊镍基合金堆焊层组织和耐磨性能的影响.结果表明:纯镍基合金堆焊层组织主要是由γ(Ni,Fe)、CrB和M7(C,B)3等物相构成,且存在着明显的成分偏析;加入Cr3C2以后,合金层中出现了Cr3C2相,且使堆焊层枝晶破碎,组织变细,成分偏析减弱直至消失;Cr3C2颗粒的加入,提高了堆焊层的磨粒磨损性能,且随其加入量的增加,耐磨性逐渐提高;当加入量达到30%时,耐磨性最好,随后耐磨性开始降低.     

The tribological behaviour of nickel and nickel-chromium alloys at temperatures from 20° to 800 °C

Measurements are presented of friction and wear during sliding of specimens of Ni-Cr alloys containing 0% to 40% Cr on like specimens in air at 20°, 400° and 800 °C. The worn specimens have been examined by optical and scanning electron microscopy, electron probe microanalysis and electron diffraction and microhardness measurements have been made.Under the sliding conditions used, all the alloys show a transition temperature above which a low coefficient of friction and usually relatively low wear are observed after a time and below which these parameters remain relatively high throughout. Above the transition temperatures, the frictiontime loci show sharp reproducible changes from relatively high to low coefficients of friction. Such changes can be associated with the formation of a thermally softened oxide layer (termed a glaze) on the bearing areas during sliding. Once the glaze is formed, very little further wear occurs for the high chromium-content alloys, although further damage does take place with the weaker low chromium-content alloys, especially at temperatures just above the transition temperature. These tribological properties of the glaze are associated with its low shear strength and the strength of the underlying alloy substrate.During sliding at temperatures below the transition temperatures, metal-to-metal contact takes place, although oxide is formed on the bearing area of the low chromium-content alloys even at 20 °C. The friction and wear behaviour is largely determined by the strength and work-hardenability of the alloy.Correlations between the tribological behaviour of these binary Ni-Cr alloys and commercial Nimonic alloys indicate that the trace elements in the latter play only a relatively minor role in determining this behaviour. It is concluded that high strengths and relatively rapid transient oxidation rates of the alloys, and appropriate physical properties of the resulting oxide films, are important qualities of the alloys under the conditions used.