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.     

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.     

Friction and wear of Cu-Ni alloys

The friction and wear of Cu-Ni alloy blocks sliding against 440C and coated steel rings have been studied. Sliding speed was 50 mm s^?1 and test atmospheres were argon and dry air. A wide range of experimental techniques was used to characterize the worn specimen and the debris particles. X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis of X-rays have been particularly helpful. Transfer of ring material was observed in most cases, especially when the debris particles were ferromagnetic. The wear rates of the Cu-Ni blocks are largely determined by the amount of transferred ring material. The wear rates of the Cu-Ni alloys decrease with increasing transfer of ring material. However, the wear rate of the ring increases as transfer continues. This process often leads to a transition involving severe damage to the ring. Brushes which remove most of the loose debris significantly reduce transfer and postpone the transition.     

Investigation of abrasive wear resistance and wear mechanism of composite alloys

The abrasive wear resistance of composite alloys comprising hard tungsten carbide and soft CuNiMn matrix under different wear conditions has been investigated and compared with CrMo cast iron. It was found that Yz-composite alloy with hard cast angular tungsten carbide has greater wear resistance than CrMo cast iron under two-body wear conditions, but lower resistance than Cr-Mo cast iron under three-body wear conditions. It was found that under three-body wear conditions selective wear of the matrix and digging or fragmentation of tungsten carbide particles dominate in Yz-composite alloy, and microcutting and deformed ploughing is dominant under two-body wear conditions. The abrasive wear resistance of composite alloys under two-body wear condition is independent of bulk hardness, but is closely related to the microhardness of tungsten carbide.     

Abrasion and corrosion resistant cobalt base alloys for hardfacing

Previous investigations carried out at CRM have shown that adding Mo, singly or in combination with Ni and/or Cu, enhances greatly the corrosion and abrasion resistance of high-carbon Co-Cr-W-C cast alloys.On account of these improvements, coatings of several Mo-, Ni- and/or Cu-modified grades of a Co-2.2% C-13% W-32% Cr alloy were prepared either by oxyacetylene welding with cast electrodes or by plasma spraying with prealloyed powders. The abrasion/corrosion behavior of the experimental deposits was compared with that of commercial alloys. The test data reported in this paper reveal the particularly good behaviour of the 18.2% Ni-4% Cu-8.7% Mo modified grade.     

Medium carbon steel alloy design for wear applications

The fracture characteristics of steels are strongly influenced by martensite substructure, retained austenite stability, and morphology. Attractive strength-toughness properties have been attained with Fe-Cr-C-Mn alloys. These alloys, when tested under sliding wear conditions, also exhibit good wear resistance which compares favorably with that of commercial wear-resistant alloys. The most significant finding is an apparently strong correlation between sliding wear resistance and retained austenite, which in turn appears to correlate with Charpy impact properties. Little correlation was observed between hardness and wear resistance for the experimental steels.     

阻尼合金及应用

对几种典型阻尼合金的成分和特点作了透彻分析，并就阻尼合金的应用作了详细介绍。同时展望了阻尼合金今后的发展及应用前景。     

Multilayer composite ceramicmetal-DLC coatings for sliding wear applications

The design of anti-friction coatings able to perform well in different wear conditions without lubricants requires a combination of adequate hardness and toughness, good adhesion, a low friction coefficient and a low wear rate. Recently introduced metaldiamond like carbon (DLC) coatings produced by magnetron sputtering of metals from targets, which are to a controlled extent covered with carbon from the chamber atmosphere, can be a step towards the achievement of such a combination. These coatings consist of an amorphous a:CH matrix with the possible incorporation of metal (Ta, W, Nb, Ti), metal carbide and/or graphite grains. Previous studies of Ti_x%-DLC coatings showed their good protective properties against abrasive, impact and single scratch wear, as well as a requirement for supporting interlayers to successfully apply such coatings to low-cost steels. In the present work an example of the selection of metal-ceramic Ti-TiN-TiCN supporting interlayers is given based on studies of their morphology, structure and mechanical properties. This resulted in the development of Ti-TiN-TiCN-[TiC-(Ti_x%-DLC)] multilayer composite coatings. Several coatings were prepared with the same supporting interlayer and a variation in the preparation of the Ti_x%-DLC layer. Ball-on-disc experiments were carried out to investigate these coatings in conditions of sliding wear against steel and cemented tungsten carbide balls. CrN, TiN and TiCN coatings were also deposited and tested in the same conditions to provide a reference. Low friction coefficients (below 0.2 at an air humidity of 50% RH) in combination with low normalized wear rates were found for multilayer coatings with upper Ti_20%-DLC and Ti_35%-DLC layers.     

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.     

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.     

Strain hardening and wear resistance of nitrated steels and alloys

This study considers the results of an experimental evaluation of the ability of superficial layers of nitrated steels and alloys to resist damage in the conditions of frictional deformation and superficial plastic deformation. A new approach is offered to evaluate and choose modes of nitration of parts of friction assemblies.     

适用于车削高温合金的刀片

车削高温合金的加工方法有多种,＂加工方法＂往往成为关键字。高温合金材料对机床的要求可能是最高的。切削刀具和应用知识的发展有助于改善高温合金工件的车削性能和加工结果。新研发的独特的刀具材料与切削槽形的组合在这一方面有了新的发展。     

Thin layer activation for measuring fretting wear and material transfer in iron alloys

An important difference between fretting wear and macroscopic wear processes lies in the amounts of wear volume. Because of the small relative displacements in fretting wear the wear volumes are much smaller than in (classical) macroscopic wear processes. Classical wear measuring techniques such as weighing and 2D-profilometry often fail to determine the fretting wear volumes. Their sensitivity as well as their accuracy are inadequate. 3D-profilometry partially solves this problem but the obtained wear results do not take eventual material transfer between the test specimens into account. In this work thin layer activation (TLA) is presented as a potentially powerful tool for quantitative fretting studies, especially in relation to material transfer. In contrast with the other mentioned wear measuring technique TLA allows measurements of very small amounts of wear as well as material transfer between the test specimens. Preliminary results are reported for steel specimens. A surface zone of 7 mm² of one test specimen, in which the wearing zone during the fretting experiment is situated, is irradiated with protons from a cyclotron. As a result of a nuclear reaction the iron in the irradiated test specimen forms radionuclides, mainly cobalt-56, in a surface layer of 260 μm depth. The amount of cobalt-56 as compared to iron is negligible so that the physical and chemical properties of the irradiated zone remain unaffected. Measuring the gamma rays of cobalt-56 in the wear debris gives quantitative information about the wear volume and measuring the mating surface gives information on the transfer volume.     

Friction and wear of aluminium alloys containing copper and zinc

The friction and wear characteristics of 99.7% aluminium and alloys containing 1 to 8% copper and zinc respectively, were determined over a load range of 0.5 to 8 kgf and over a sliding speed range of 2.4 to 16.0 m/sec on a pin-on-disc wear machine. Protective surface films formed during running-in were maintained during mild wear but were broken up by the plastic flow of a thermally weak substrate at the start of severe wear. Increasing copper content increased the load and sliding distance to seizure with an optimum improvement at 4%. Zinc on the other hand reduced the load and sliding distance to seizure. Seizure resistance is related to high temperature strength and in this respect the copper alloys are best. Seizure resistance has been examined by continuously recording the friction force and this, rather than wear, gives the most useful indication of the imminence of a seizure condition arising.     

Binder extrusion in sliding wear of WC-Co alloys

It has previously been proposed that preferential removal of the cobalt binder is an important mechanism in the abrasive wear of cemented carbides in the WC-Co family. It is here demonstrated that binder extrusion occurs also in metal-to-metal sliding wear contacts. The wear scar generated by sliding a hardened steel ball repeatedly over a polished WC-Co surface was studied by scanning electron microscopy. The extruded cobalt fragments accumulate at surface defects, such as cracks caused by the sliding loaded ball, and gradual microfragmentation of the carbide grains follows. The energy required to extrude the cobalt and to cause the gradual change in surface layer microstructure is provided by the frictional forces.     

Abrasive wear of ferricarbonic alloys during frictional heating

Frictional heating is analyzed to check the wear resistance of major structural components of undoped ferricarbonic alloys during abrasive wear. It is established that the wear resistance of austenite drops twofold once the temperature leaps to 130°C. The wear resistance of other structural components (ferrite, perlite, and martensite) diminishes in heating less intensively, but the wear resistance of unstable austenite is at the maximum level at any temperature within the studied range (up to 290°C).     

Three-body impact wear study on conventional and new P/M + HIPed wear resistant materials

A new hammer-mill type impact wear testing facility was built for impact wear testing and characterization. Tests with the hammer-mill impact wear device were carried out on conventional wear resistant materials such as Mn-steels of different compositions, white cast iron, and on new P/M+HIPed wear resistant materials. To verify the validity in using this laboratory wear testing apparatus, wear behavior and worn surfaces obtained on conventional and new Mn-steels generated from this device were compared with wear phenomena and worn surfaces developed in industrial applications, i.e. from certain types of rock crushers. The strain hardening effect in different Mn-steel grades was studied first. Second, the wear resistance of materials with different properties was studied using two different grades of abrasive. With silica sand (high hardness, low compressive strength), conventional Mn-steel and white cast iron perform in a manner comparable with the P/M+HIPed materials. With volcanite sand (low hardness, very high compressive strength), the P/M+HIPed wear resistant materials appear to have the best wear resistance.     

Mechanical properties and lubricated wear of Zn-25Al-based alloys

Seven alloys based on Zn-25Al were produced as binary alloys or with silicon or copper ternary additions. Tensile properties, hardness and dimensional stability were studied in the as-cast state and as a function of aging.The lubricated wear behaviour was studied using a special pin-on-disc method and compared with that of SAE 660 bronze and SAE 73 brass.The addition of copper was found to be more effective than silicon in improving the mechanical properties of Zn-A1 alloys but silicon gave greatly improved wear resistance and dimensional stability. The wear resistance of Zn-Al-Si alloys was found to be superior to that of all the other materials tested.A heat treatment performed to simulate long term aging reduced the hardness and tensile strength of all the zinc-based alloys by about the same amount but improved ductility. The wear resistance was reduced by an increase in the break-in wear but was only significant for the alloy containing copper.It is concluded that Zn-Al-Si alloys have good bearing properties but may not have adequate strength after prolonged aging. An alloy with a composition close to that of ZA27, but with reduced copper and added silicon, may produce an improved combination of mechanical strength and wear resistance with a slight reduction in density.     

Comparison of the machinability and wear properties of magnesium alloys

AZ and AS series magnesium alloys were used in this study and had different contents (i.e., 0 to 9 wt.% Al). The effect of zinc (Zn) and silicon (Si) on wear resistance and machinability was analyzed in AZ and AS series magnesium alloys. Zn amount in AZ series (1 %) and Si amount in AS series (1 %) were kept at a fixed rate. The effect of the changes in Al amount on hardness, wear resistance, and machinability in AZ and AS series magnesium alloys was comparatively analyzed. A higher increase was observed in the wear resistance of alloys in AS series magnesium alloys due to the rise in Al amount compared with AZ series. Intermetallic phases found in the microstructure of alloys (β-Mg₁₇Al₁₂ and Mg₂Si) were established to have an impact on the wear resistance and machinability of alloys.