A Further Study of the Beneficial Effects of Yttrium on Oxide Scale Properties and High-Temperature Wear of Stellite 21

Alloying yttrium to Co-based alloys has been proven to considerably improve their oxide scales that play an important role in resisting wear at elevated temperatures. In addition to the formation of Y₂O₃ phase in the oxide scale, the yttrium addition may also change the oxidation mechanism, which could be responsible for many benefits of yttrium to the wear resistance of this alloy at elevated temperatures. In this study, the effect of yttrium on the oxidation behavior of Stellite 21 alloy was investigated and correlated to the changes in microstructure and improvement in properties of the oxide scale formed at 600 °C which in turn improved high-temperature wear behavior.     

Tribological behavior of Stellite 21 modified with yttrium

Cobalt-base alloys have found a wide variety of tribological applications particularly at elevated temperatures or in corrosive environments in many industries, such as aerospace, automotive, power and gas turbines. One of the standard Co-base alloys, Stellite 21, is used predominantly to resist the synergistic effects of corrosion and mechanical attack, especially at elevated temperatures and continuing efforts have been made to improve its properties. One approach is to add reactive elements, such as yttrium, in order to beneficially affect its oxidation behavior.Research was conducted to investigate the effects of Y additions on Stellite 21 on its microstructure, mechanical behavior, and high-temperature wear performance. These studies employed various experimental tools, such as micro-mechanical probe, XRD, SEM, EDS, and high-temperature tribometer. The effects of Y addition on the properties of the oxide film formed on Stellite 21 were also investigated using grazing XRD and nano-mechanical probing techniques.It has been demonstrated that Y additions benefited the wear behavior of Stellite 21, especially at elevated temperatures. The oxide scale developed at 600 °C also showed markedly enhanced mechanical properties when Y was alloyed to the alloy.     

High-temperature abrasive wear testing of potential tool materials for thixoforming of steels

High temperature abrasive wear performance of Inconel 617, Stellite 6 alloys and X32CrMoV33 hot work tool steel was investigated. The wear resistance of the latter is degraded at 750 °C due to its inferior oxidation resistance. Extensive oxidation co-occuring with abrasive wear at 750 °C leads to substantial material loss due to the lack of a protective oxide scale, sufficiently ductile to sustain the abrasion without extensive spalling. The wear resistance of the Inconel 617 and Stellite 6 alloys, on the other hand, improves at 750 °C owing to protective oxides that sustain the abrasion without spalling.     

Corrosion and corrosion wear behaviour of plasma carburised Stellite 21 Co–Cr alloy

Abstract

Low temperature plasma surface alloying with carbon (i.e. plasma carburising) of Stellite 21 Co–Cr alloy was conducted at temperatures from 400 to 500°C for 15 h in a gas mixture of 98 vol.-%H₂ and 2 vol.-%CH₄. The surface treated layers were characterised by XRD, SEM and microhardness tests. The corrosion and corrosive wear behaviour of the plasma carburised Stellite 21 Co–Cr alloy were studied respectively using electrochemical tests and well designed reciprocating wear tests in 3·5% NaCl solution. The results show that low temperature (≤460°C) plasma carburising can improve the corrosion resistance of Stellite 21 alloy; the corrosive wear resistance of Stellite 21 can be enhanced by up to three times; and the best corrosive wear resistance is achieved at the highest treating temperature (500°C). The detailed studies on the wear tracks indicate that the corrosive wear process was dependent on the individual wear and corrosion, as well as the synergetic effect.     

On the wear characteristics of cobalt-based hardfacing layer after thermal fatigue and oxidation

High temperature wear characteristics of Stellite 6 alloy containing Cr₃C₂ after thermal fatigue and oxidation treatment at 700°C were investigated. The hardfacing layer was deposited by plasma transferred arc (PTA) process. After thermal fatigue treatment, cracks propagated along boundaries of incoherent chromium carbide particles. Significant oxidation occurred mainly on the clad layer containing Cr₃C₂. The wear test results revealed a slightly higher wear volume on Stellite 6 with Cr₃C₂ due to the existence of cracks. The formation of oxide on the surface could effectively reduce the wear volume by reducing the real contact area between mating surfaces. Lower sliding speed resulted in higher wear volume. The mechanism was interpreted by the friction coefficient change during sliding wear. Wear test results were further interpreted by investigating the wear trace via SEM. Possible wear mechanisms were postulated. Analysis of wear debris showed severe oxidation on the Stellite 6 with Cr₃C₂. It could be concluded that oxidation on the clad layer was beneficial to the wear resistance at elevated temperature. Thermal fatigue cracking on the surface might be detrimental to the wear resistance, however, this could be partly compensated by the existence of oxide.     

Friction and Wear Characteristics of Single Crystal Ni-Based Superalloys at Elevated Temperatures

The purpose of this study was to investigate the friction and wear behavior of single crystal superalloys at elevated temperatures. Pin-on-plate experiments were conducted using a custom-built high-temperature fretting/wear apparatus. Measurements were performed on two single crystal Ni-based alloys and Waspaloy^® (used as a baseline material). The coefficient of friction for the single crystal materials (i.e., during running-in and steady state) was lower compared to the Waspaloy^®. In addition, the experiments showed that the friction coefficient of the single crystal is dependent on the crystallographic plane; the friction coefficient was lower for the tests on the {100} plane compared to the {111} plane. The wear behavior was aligned with the friction behavior, where the single crystal Ni-based alloys showed slightly higher wear resistance compared to the Waspaloy^®. Ex situ analysis by means of FIB/SEM and XPS analysis revealed the formation of Co-base metal oxide layer on the surface of the single crystal alloy. Similarly, a Co-base oxide layer is observed on the counterface providing a self-mated oxide-on-oxide contact and thus lower friction and wear compared to the Waspaloy^®.     

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.     

Friction behavior of laser cladding magnesium alloy against AISI 52100 steel

The use of magnesium alloys in engineering applications is becoming increasingly important as a relatively low density allows savings in energy consumption and therefore reduction in air pollution. An associated reduction in inertia makes these alloys potential candidates for friction components, but they suffer from poor wear resistance. Laser surface alloying with appropriate powder mixture is an innovative technique to improve surface properties of metallic alloys. In this study, the effect of laser surface alloying using Al12%Si powder on wear resistance of a magnesium alloy ZE41 is investigated. Hardness and wear resistance of the alloy are significantly enhanced after treatment.     

Cr5系堆焊合金碳、铬过渡形式对高温磨损性能影响的研究

在轧辊堆焊复合制造中,为节约贵重碳化物及提高堆焊材料的性价比,在堆焊熔敷金属成分基本保持不变的条件下,利用埋弧堆焊研究药芯焊丝碳、铬不同加入方式对堆焊合金微观组织与性能的影响。通过磨损试样前后硬度、高温拉伸、常温韧性与高温磨损量的量化,结合磨损前后金相组织、扫描电镜等辅助手段分析微观组织、加入方式与耐磨性之间的关系;结果表明:堆焊金属600℃的高温耐磨性能与合金高温强度及硬度呈正比,并随合金韧性的增加耐磨性能提高;直接加石墨和铬粉的药芯焊丝堆焊熔敷金属的耐磨性能优于在焊丝中直接加碳化铬的堆焊熔敷金属。高温磨损是合金氧化、切削、疲劳开裂与剥离等多种因素作用的结果,理想的高温耐磨堆焊材料不仅与采用的堆焊合金系有关,还与堆焊金属的显微组织、抗氧化性能及高温强韧性等因素有关。同时得出改变合金的加入方式是不添加变质剂及外加激振法外,能够促使组织均匀及强化熔敷金属的另一种方式。     

Microstructure and hardness of Stellite 21 deposited on hot forging die using direct metal deposition technology

Journal of Mechanical Science and Technology - The Stellite 21 superalloy has excellent creep resistance and mechanical strength at elevated temperatures, is resistant to wear and thermal fatigue,...     

Sliding wear behavior of hardfacing alloys in a pressurized water environment

In this study, sliding wear behavior of newly developed Fe-base Co-free hardfacing alloy (Fe–Cr–C–Si) was investigated and compared to that of Stellite 6 and Fe-base NOREM 02 in the temperatures ranging from 300 to 575 K under a contact stress of 103 MPa (15 ksi) in pressurized water. The weight loss of Fe–Cr–C–Si was equivalent to that of Stellite 6 over all temperatures range in 100-cycle wear test. The weight loss of Fe–Cr–C–Si 1000-cycle wear test increased almost linearly with increasing temperature up to 575 K. The weight loss of NOREM 02 was nearly equivalent to that of Stellite 6 below 475 K, however, galling occurred above 475 K in 100-cycle wear test. It was also found that the lubrication effect of pressurized water on the sliding wear behavior of the alloys was negligible under the present test conditions.     

Study of particle erosion damage in Haynes Stellite 6B I: Scanning electron microscopy of eroded surfaces

The erosion behavior of metals and alloys by solid particles entrained in relatively slow moving gases is of current interest as a result of ongoing efforts in coal conversion and the consequent production of dust-laden gases. Haynes Stellite 6B represents a typical alloy used for erosive wear resistance in such situations and also provides an appropriate alloy for the study of the mechanisms of erosion because it comprises essentially large brittle carbide phases in a ductile matrix. A scanning electron microscope study of the surface of Stellite 6B after erosion by alumina particles is described, and the types of erosion damage incurred by the ductile metal matrix and the brittle carbides are characterized. The only mechanism of material loss of the ductile metal for which positive evidence was found was cutting, with the possibility that fracture on a very fine scale may also be involved. The mechanism of material removal from the carbides appeared to be by surface crack interlinkage. Under the conditions studied, corners of the eroding alumina particles were found to break off and to adhere to the alloy or carbide surface; at the highest impact velocity studied an extensive layer of embedded alumina fragments was built up on the alloy surface and probably modified its erosion behavior.     

Studies on high temperature wear and its mechanism of Al-Si/graphite composite under dry sliding conditions

Wear behaviours of aluminum silicon alloy and Al-Si/graphite composite were investigated at ambient and elevated temperatures. The trend showed a decrease in wear rate with increase in temperature. The reduction in wear rate was mainly attributed to the formation of glazing layer and oxide layer at higher temperature. This was invariably observed in alloy and composites. In addition, the presence of graphite in composite offered better wear resistance for all temperatures under consideration. The wear due to oxidation was predominant during high temperature sliding.     

Tribocorrosion of Stellite 706 and Tribaloy 400 superalloys

Abstract

Co based superalloys such as Stellites and Tribaloys have been extensively used in many engineering applications owing to their inherent superior corrosion and wear resistance and hot hardness property at elevated temperatures. The combined interaction among wear and corrosion which is known as tribocorrosion often results in a significant increase in material loss especially in aqueous environments. In this study tribocorrosion performance of Stellite 706 and Tribaloy T400 was investigated by electrochemical techniques such as potentiodynamic (anodic polarisation) and open circuit potential (OCP) measurement with three electrode electrochemical cell set-up under sliding contact in 3·5% NaCl solution. The effect of friction on anodic polarisation behaviour of superalloys was studied at different loads of 20 and 80 N. During OCP measurements the frequency was increased from 0·5 to 1·5 Hz by an increment of 0·5 Hz. Thus the effect of frequency on tribocorrosion behaviour of superalloys was determined. Tribaloy 400 exhibited greater performance in potentiodynamic polarisation test. On the other hand, Tribaloy 400 was more affected by corrosive wear in OCP measurements as compared to Stellite 706.     

Assessment of the machinability of Ti-6Al-4V alloy using the wear map approach

The high strength to density ratio of titanium alloys coupled with excellent corrosion resistance even at elevated temperatures make them ideal for aerospace applications. Moreover, the biocompatibility of titanium also enables its widespread use in the biomedical and food processing industries. However, the difficulty in machining titanium and its alloys along with the high cost of its extraction from ore form presents a major economic constraint. In the context of machining economics, the wear map approach is very useful in identifying the most suitable machining parameters over a feedrate–cutting velocity plane. To date, wear maps have only been prepared for the machining of ferrous alloys. In this article, a review of the machinability of Ti-6Al-4V alloy is presented with emphasis on comparing the wear performance of various tool materials. In addition, a new wear map for Ti-6Al-4V alloy is presented based on unified turning tests using H13A grade carbide inserts. This wear map can be used as a guide in the selection of cutting variables that ensure the least tool wear rates. This article contrasts the occurrence of a safety zone in the case of machining steels to that of an avoidance zone for Ti-6Al-4V alloy.     

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.     

Influence of Combined Addition of Boron and Strontium on High-Temperature Wear Behavior of A356 Alloy

In the present study, the effect of the combined addition of boron (B) and strontium (Sr) on the high-temperature dry sliding wear behavior of A356 alloy has been investigated using a pin-on-disc wear testing machine attached with a furnace. During wear studies, the effect of alloy composition, normal pressure, sliding speed, and sliding distance on A356 alloy at four temperatures, namely, room temperature and 100, 200, and 300°C, have been investigated. Further, the cast alloys and worn surfaces of A356 alloy with and without B and Sr were characterized by scanning electron microscopy (SEM)/energy-dispersive spectroscopy (EDS) microanalysis. Results indicate that the combined addition of B and Sr to A356 alloy has led to improvements in wear properties. This is due to a change in microstructure, improvement in mechanical properties, and the formation of an oxide layer between the mating surfaces during the sliding wear process.     

Wear behavior of Al-Mg-Cu-based composites containing SiC particles

The friction and wear behavior of Al-Mg-Cu alloys and Al-Mg-Cu-based composites containing SiC particles were investigated at room conditions at a pressure of 3.18 MPa and a sliding speed of 0.393 m/s using a pin-on-disk wear testing machine. This study is an attempt to investigate the effects of adding copper as alloying element and silicon carbide as reinforcement particles to Al-4 wt% Mg metal matrix. The wear loss of the copper containing alloys was less than that for the copper free alloys. It was observed that the volume losses in wear test of Al-Mg-Cu alloy decrease continuously up to 5%. Also it was found that the silicon carbide particles play a significant role in improving wear resistance of the Al-Mg-Cu alloying system. The formation of mechanically mixed layer (MML) due to the transfer of Fe from counterface disk to the pin was observed in both Al-Mg-Cu alloys and Al-Mg-Cu/SiC composites.     

Chemical factors in carbon brush wear

Chemical factors involved in the wear of carbon brushes on metal slip rings are discussed. Under conditions of elevated temperature operation in an oxidizing atmosphere, a correlation is found between the oxidation characteristics and the wear rates of carbon brushes. It is demonstrated that temperatures in the oxidation range can readily be generated by current converging through high resistance constrictions in the contact zone. Copper and other metals present in the slip ring can act as catalysts for the oxidation, the metal oxide particles migrating into the interior of the brush and causing enhanced gasification rates and increased porosity. Treatment of the brush with oxidation inhibitors, such as phosphorus oxychloride, and surface alloying of the ring with non-catalytic materials, such as zinc, can reduce the wear rate at elevated temperatures under favorable conditions. Graphite surfaces are also attacked by reactive gaseous species such as atomic nitrogen and oxygen, ozone and nitrogen oxides which may form near the brush surface during arcing.     

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.