Brush plated cobalt-molybdenum and cobalt-tungsten alloys for wear resistant applications

Brush plating solutions have been developed that enable sound cobalt alloy coatings containing up to 12% molybdenum or tungsten to be deposited at thicknesses up to 13 μm. The alloy deposits had a very fine grain size but their crystallographic structure could not be determined. The cobalt deposit alone had a mixed cph and fcc structure at room temperature. Evaluation of the wear resistant properties of the cobalt alloys was carried out in the laboratory using a pin and disc technique and a simulated hot forging test. Both tests showed the alloys to have relatively good wear characteristics. Extensive industrial trials have been undertaken to assess the value of these cobalt alloy coatings to enhance the performance of hot forging dies. The results have indicated that die life can be increased by up to 100%     

Comparison of the sliding wear process of various cast irons in the laser-surface-melted and as-cast forms

The sliding wear characteristics of cast irons having a range of compositions and initial graphite forms have been determined in both as-cast and laser-surface-melted conditions using a pin-on-ring test configuration. Observed differences in equilibrium wear behaviour between the as-cast alloys were principally in the mild-to-severe transition load and the nature of the severe wear process. Such effects are interpreted in terms of the mean interparticle spacing of graphite in the microstructure which determines the relative propensity for subsurface crack propagation during wear. The ledeburitic structures produced by laser surface melting of the cast iron substrates acted to stabilize a regime of mild equilibrium wear with substantially lower wear rates than for the mild oxidative wear of the as-cast microstructures. Metallographic observations of the laser-melted layer have identified a wear process consisting of fine polishing abrasion.     

A study of abrasive wear mechanisms using diamond and alumina scratch tests

Scratch tests using alumina (Al₂O₃) abrasive particles and Vickers diamond pyramids were employed to study material removal mechanisms in the abrasion of cobalt-base powder metallurgy alloys 6 and 19. The alloys were specially prepared to produce either fine or coarse carbides in order to study the effects of carbide size. Scanning electron microscopy was used to analyze the scratch grooves, the scratch tools and the wear debris particles.

Comparison of scratch tests with Al₂O₃ and diamond pyramids shows that many features produced by the extremely hard regularly shaped diamond tools are different from those produced by irregular Al₂O₃ particles. Except for differences produced by tool wear, multiple-pass Al₂O₃ scratch tests provide excellent reproduction of the material removal processes which occur in low stress Al₂O₃ abrasion. Al₂O₃ scratches produced both chip-like and fine irregular debris particles similar to those extracted from spent abrasive used in wear testing.

Material removal in the fine carbide alloys is facilitated by the direct removal of entire carbides within the volume of micromachining chips removed from the scratch groove. In coarse carbide alloys, machining chips from large carbides are observed, but the depth of cut in the carbide phase is less than that in the f.c.c. matrix and this leads to a decrease in the volume of material removed. Direct comparison of chips removed from fine and coarse carbide alloys by the same Al₂O₃ particle shows larger chips from the fine carbide material.

The effects of subsurface deformation and surface irregularities on material removal were studied by carrying out scratch tests on specimens subjected to prior abrasion and by investigating multiple-pass scratches in the same scratch groove.     

The influence of heat treatment on the sliding wear behavior of a ZA-27 alloy

The effects of heat treatment, involving solutionizing at temperature of 370 °C for a relatively short period of time (3 or 5 h), followed by quenching in water, on tribological behavior of ZA-27 alloys were examined.Dry sliding wear tests were conducted on as-cast and heat-treated ZA-27 samples using block-on-disk machine over a wide range of applied loads. To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning electron microscopy (SEM). The tribological results were related to the microstructure and mechanical properties.The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation. The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, both from the aspects of friction and wear. The improved tribological behavior of the heat-treated alloys, in spite of reduced hardness, could be the result of breaking the dendrite structure, when the fraction of interdendrite regions was considerably decreased and a very fine α and η mixture was formed at the same time. The wear response of the samples has been corroborated through characteristics of worn surfaces and dominant wear mechanisms.     

Effect of carbide size on the abrasion of cobalt-base powder metallurgy alloys

A study of the effect of carbide size on the abrasion resistance of two cobalt-base powder metallurgy alloys, alloys 6 and 19, was conducted using low stress abrasion with a relatively hard abrasive, A1₂O₃. Specimens of each alloy were produced with different carbide sizes but with a constant carbide volume fraction. The wear test results show a monotonie decrease in wear rate with increasing carbide size.Scanning electron microscopy of the worn surfaces and of wear debris particles shows that the primary material removal mechanism is micromachining. Small carbides provide little resistance to micromachining because of the fact that many of them are contained entirely in the volume of micromachining chips. The large carbides must be directly cut by the abrasive particles. Other less frequently observed material removal mechanisms included direct carbide pull-out and the formation of large pits in fine carbide specimens. These processes are considered secondary in the present work, but they may have greater importance in wear by relatively soft abrasives which do not cut chips from the carbide phase of these alloys. Some indication of this is provided by limited studies using a relatively soft abrasive, rounded quartz.     

Real-time corrosion measurements to assess biotribocorrosion mechanisms with a hip simulator

Due to the reduced wear compared to the metal-on-polyethylene implant, second generation metal-on-metal hip prostheses have been widely used as the replacement in younger patients in recent years. Osteolysis induced by polyethylene wear debris was a major concern with metal-on-polyethylene hip replacements. In metal-on-metal total joint replacements, however, there has been concern about the incidents of pseudo tumours as a result of the production of very fine wear debris and the associated production of metallic ions of Co and Cr. The origins of the metallic ions may be from two potential sources: from the bearing surface and from the dissolution of wear debris produced by the tribological action or the production of ions by depassivation of the CoCr alloys.Although there has been extensive work on simulation of wear processes in hip joint replacements through hip simulators running over prolonged periods and mapping the wear rates, to date there have been several attempts to measure the interactions (biotribocorrosion) between corrosion and tribology in-situ in simulated body fluids using a hip simulator. This paper describes the instrumentation of an integrated hip joint simulator to provide electrochemical measurements in real-time. The open circuit potential and polarization experiment results are reported and the importance of these measurements to gain an understanding of the origins of metal ions and to complement the wealth of wear data available is discussed.     

Friction and wear of aluminium-silicon alloys

The friction and wear of aluminium-silicon alloys have been studied using a pin-on-disk machine together with metallographic investigations, microhardness testing and scanning electron microscopy. Silicon content does not appear to be a dominant factor in wear resistance. The eutectic alloy was the most wear resistant of the alloys studied. The predominant wear mode appears to be by separation of all or part of the work-hardened layers from random patches on the wear track. Nucleation sites for wear debris are probably created below the sliding surface as a result of Hertzian stressing.     

Microstructure and abrasive wear resistance of cast Ni-Cr-C alloys

The abrasive wear behaviour of directionally solidified Ni-Cr-C alloys was investigated using a pin-type test. M₇C₃ carbide volume fractions (CVF) were varied from 0 to 40%. Two sets of alloys with different carbide and dendrite spacings were abraded with bonded SiC and corundum particles, varying the grit size and applied load. M₇C₃ carbides greatly improved the abrasive wear resistance against fine-grained SiC particles within the whole range of compositions. By refining the primary carbide structure in hypereutectic alloys, the wear resistance against coarse-grained SiC particles was also improved with increasing CVF although SiC is known to be much harder than M₇C₃. Coarse SiC abrasive particles had a detrimental effect on the wear resistance of all hypoeutectic alloys and, even more, of hypereutectic alloys if the primary carbides were coarse. In testing with corundum, the wear resistance always improved with increasing carbide volume fraction.Wear damage was arranged in three classes. First, SiC and corundum abrasives were partially broken from the substrate at the entrance edge of the specimen. The edges of SiC grains stayed sharp during the wear process whereas the edges of corundum particles were rounded or the corundum was crushed by M₇C₃ carbides. Secondly, damage in the wear surface occurred by fracturing of the edges of carbides facing the wear surface. In addition, SiC abrasives were able to groove carbides. Thirdly, coarse SiC grains transmitted shear stresses causing severe subsurface damage leading to microstructure disintegration and spalling of primary carbides. SiC transmitted larger shear stresses than corundum because the latter was separated by a thin layer of wear debris from the unworn material.The microstructural parameters influencing wear were CVF, size, morphology and distribution of carbides. Optimum wear resistance depended on the abrasive mineral. Alloys with high CVF and coarse primary carbides were best suited for wear with corundum whereas fine primary carbides were required to resist wear by SiC.     

The resistance of nickel and iron aluminides to cavitation erosion and abrasive wear

The abrasive wear and cavitation erosion resistance of several alloys based on the Intermetallic compounds Ni₃Al and Fe₃Al have been investigated. The erosion resistance of the nickel aluminides is relatively insensitive to alloying with iron or chromium and is comparable with or superior to that of many commercial erosion-resistant alloys; the abrasive wear resistance is found to be decreased by alloying, despite increased room temperature strength and refined grain size. Preliminary results for the iron aluminides indicate increased resistance to abrasive wear with increasing alloy content. It is suggested that the abrasive wear process causes temperature increases in the damage zone that are sufficient to cause the elevated temperature properties of the alloys to become dominant. Under these conditions, the wear resistance can be related to the tendency to disorder, either thermally or through plastic deformation.     

铣削TC4钛合金的刀具磨损对比试验

TC4钛合金是典型难加工材料之一,极易造成工具磨损。本文通过铣削TC4钛合金试验,跟踪铣削过程中铣刀每个齿的磨损量及磨损形态,比较了不同细晶粒硬质合金铣刀的磨损过程。结果表明,铣刀切削刃发生崩刃会直接缩短铣刀的使用寿命。     

Effect of grain refinement and modification on the dry sliding wear behaviour of eutectic Al-Si alloys

The present study deals with an investigation of dry sliding wear behaviour of grain refined and or modified eutectic (Al-12Si) Al-Si alloy by using a Pin-On-Disc machine. The indigenously developed Al-1Ti-3B and Al-10Sr master alloys were used as grain refiner and modifier for the grain refinement of α-Al dendrites and modification of eutectic Si, respectively. Various parameters have been studied such as alloy composition, sliding speed, sliding distance and normal pressure. The cast alloys, master alloys and worn surfaces were characterized by SEM/EDX microanalysis. Results suggest that, the wear resistance of eutectic Al-Si alloys increases with the addition of grain refiner (Al-1Ti-3B) and or modifier (Al-10Sr). Further, the worn surface studies show that adhesive wear was observed in Al-12Si alloy in the absence of grain refiner and modifier. However, an abrasive and oxidative wear was observed when the grain refiner and modifier are added to the same alloy. Commercially available LM-6 (12.5%Si) alloy was used for comparison.     

The influence of oxides on the friction and wear of alloys

Development of compacted oxides, particular y so-called ‘glazes’, on sliding metal and alloy surfaces can result in significant decreases in friction coefficients and wear rates. This paper describes how such ‘glazes’ can form on many alloys under a wide range of sliding conditions. ‘Glazes’ consist of very fine, compacted, crystalline particles of almost any oxide or oxides. Formation of the oxide, the subsequent development of the ‘glaze’, and the mechanisms by which the ‘glaze’ reduces friction and wear are discussed     

New materials resistant to wear and corrosion to 1000°C

An unusual combination of wear and corrosion resistance has been developed in cobalt and nickel base alloys known as Tribaloy⁷ intermetallic materials. These two-phase alloys depend on the unique properties of a Laves intermetallic phase to resist wear under poor or unlubricated conditions from cryogenic temperatures to about 1000°C. The constituent elements are partitioned so that both the Laves intermetallic and the solid solution phases have generally good resistance to corrosion also. At higher chromium content the corrosion resistance is excellent in most environments.Parts can be fabricated by powder metallurgy, plasma spray coating, casting or hardfacing. Several wear tests are used to demonstrate the qualities of Tribaloy. Wear resistance was excellent at 25°, 315°, 650° and 980°C in air. Another wear test compares several Tribaloy compositions with other commercial, corrosion resistant alloys in 5% hydrochloric acid. Some examples of applications are described.     

Assessment of machining performance using the wear map approach in micro-drilling

It is well established that nickel-based super alloys exhibit poor machinability. One of the challenges in micro-drilling of these alloys is to increase productivity while maintaining acceptable tool wear rates. In this regard, the wear map approach is a useful way to identify an operating window of cutting conditions. The progression of tool wear has been studied in relation to tool edge radius and undeformed chip thickness. A characteristic wear map of cutting conditions is constructed for the micro-drilling process. This helps identify the zones of lowest wear rate, commonly referred to as safe zones, as well as a scale effect in the micro-domain. The new wear rate map provides a quick and useful reference for selecting suitable cutting conditions with the aim of reducing manufacturing costs and/or increasing production rate for micro-drilling. A preliminary tool wear mechanism study suggests that abrasion, adhesion and micro-chipping are the active tool wear modes associated with wet micro-drilling of nickel-based super alloys.     

Inter-relation of Microstructural Features and Dry Sliding Wear Behavior of Monotectic Al–Bi and Al–Pb Alloys

Immiscible Al-based alloys of monotectic composition have a particular feature of minority phases embedded into the Al-rich matrix. The disseminated particles may act as in situ self-lubricating agents due to their lower hardnesses compared with that of the Al-rich matrix, favoring good tribological behavior. There is a lack of systematic fundamental studies on the microstructural evolution of monotectic alloys connected to application properties. In the present investigation, the monotectic Al-1.2wt%Pb and Al-3.2wt%Bi alloys have been chosen to permit the effect of microstructural parameters on the wear behavior to be analyzed. Directional solidification experiments were carried out under transient heat flow conditions allowing a large range of cooling rates to be experienced, permitting a representative variation on the scale of the microstructure to be examined. Samples of the monotectic alloys having different interphase spacing, λ, have been subjected to microadhesive wear tests, and experimental laws correlating the wear volume with the microstructural interphase spacing and test time are proposed. It was found that microstructural features such as the interphase spacing and the morphology of the minority phase play a significant role on the wear process and that for the alloys examined λ exhibits opposite effects on the corresponding wear volume.     

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.     

Effect of sodium octanoate on the tribocorrosion behaviour of 5052 aluminium alloy

ABSTRACT

The 5000 series aluminium alloys are commonly used in a marine application where it is exposed to environments containing the chloride ions, which cause corrosion of aluminium alloy. The situation becomes even worse when aluminium alloys, in some situations, may suffer from combined corrosion and wear actions. The present study has been carried out to investigate the effect of sodium octanoate as a corrosion inhibitor on the corrosive wear behaviour of aluminium alloy 5052 in 0.5?M NaCl solution as simulated seawater. The effects of electrochemical potentials on the corrosive wear performance are also discussed.     

Studies on the Tribological Properties and Structure of Antifrictional Iron-Containing Aluminum Alloys

Experimental aluminum alloys with the addition of iron (about 1%) have been considered in order to simulate alloys obtained from secondary raw materials (wastes of domestic manufacture, scrap, etc.). In particular, the alloys have been studied using sclerometric tests according to a criterion of relative shear strength (τ/σ_mc). The tribological testing of the alloys has been also carried out according to the block-pad and ball–plane schemes of loading. A mathematical model of the wear process has been used to process the results of wear testing for the ball-plane scheme of friction contact. As a result, the wear law parameter K_w has been determined for all of the experimental alloys. The results of testing have confirmed that, in general, it is possible to use aluminum alloys that contain iron for manufacturing monometallic plain bearings. The structure and chemical composition of the surface have been studied for both the initial samples and the samples after testing.     

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.     

Analysis of tool wear patterns in finishing turning of Inconel 718

This paper focuses on the analysis of tool wear mechanisms in finishing turning of Inconel 718, one of the most used Ni alloys, both in wet and dry cutting. Cemented carbides, ceramics and CBN tools are suitable for machining Ni alloys; coated carbide tools are competitive for machining operations of Ni alloys and widely used in industry. Commercial coated carbide tools (multilayer coating TiAl/TiAlN recommended for machining Ni alloys) were studied in this work. The feasibility of two inserts tested for dry cutting of Inconel 718 has been shown in the work. Experimental test were performed in order to analyze wear patterns evolution. It was found great influence of side cutting edge angle in tool wear mode.