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Laser-based directed energy deposition (L-DED) offers significant advantages for repairing metal structures, particularly in the marine and offshore industry where corrosion-resistant materials like Monel K-500 (a Ni-Cu alloy) lack strength and wear resistance. This study addresses this issue by producing Monel K-500 with high-strength Stellite 6 (a Co-Cr alloy). Two types of multi-material samples were created using L-DED: interlayered and mixed powder samples. The interlayered samples experienced cracking at the material interface, while the mixed powder samples were crack-free and exhibited improved mechanical properties, with yield strength increasing from 208.3 MPa to 490.2 MPa and ultimate tensile strength from 429.7 MPa to 887.0 MPa compared to single Monel K-500 samples. This research demonstrated the potential of in-situ alloying during the L-DED process to enhance alloy properties and highlighted the challenges of abrupt compositional changes leading to cracking, suggesting mitigation strategies for successful production.

Majority of self-lubricating composites exhibit a high wear rate due to corrosion. In this study, Co-based self-lubricating composites with addition of Ag were prepared via spark plasma sintering to manage their tribocorrosion resistance. No interfacial reaction occurred after sintering. Their tribocorrosion behavior in 3.5 wt.% NaCl solution was characterized as a function of applied potentials. In corrosion-free conditions, i.e. applying a cathodic potential (−1 V), the addition of Ag enhances wear rate of the Co-based composites. While in a state of OCP or applying an anodic potential, galvanic corrosion occurs between Ag and Co-matrix. It promotes the formation of a loose oxide film and reserves most silver debris, which contributes synergistically to reduced friction coefficient and wear rate. With the addition of 12 wt.% Ag, Co-based self-lubricating composite exhibits the lowest friction coefficient of 0.09 and wear rate of 3.8 × 10−5 mm3/(Nm) at OCP.

The formation mechanisms for two carbides with co-existence and increasing stacking faults nearby the carbides during surfacing welding were investigated in this study. The results indicated that the surfacing layer had a two-phase structure of a matrix phase and a second phase, the density of the second phase was relatively small and the second phase was discontinuous, by contrast with the as-received welding wire. Relatively uniform microstructure of surfacing layer and the welding interface without melting of base metal were obtained, resulting in an inapparent change in the microhardness. A few carbides with blocky shape were identified in the surfacing layer. The mechanisms for (Cr,Co)23C6 of face-centered cubic crystal structure co-existing with (Cr,Co)7C3 of hexagonal close-packed crystal structure and (Cr,Co)23C6 subsequently forming close to the pre-formed (Cr,Co)7C3 during the cooling process were discussed in alloying element, calculated equilibrium phase diagram, Gibbs energy, etc. The relatively higher density of the stacking fault present around the carbides was understood from forming energy of stacking faults. [ABSTRACT FROM AUTHOR]

Elements tungsten and molybdenum are the key constituents of Stellite alloys as solutes to strengthen the solid solution matrix. Meanwhile, they also promote formation of W-rich and Mo-rich carbides when present in large quantities in high-carbon Stellite alloys. Extensive studies on tungsten Stellite alloys, in particular, Stellite® 6, have been reported in the literature; however, molybdenum Stellite alloys, especially, the influence of Mo content on the performance of the alloys, have been rarely investigated. In this research, the tribological performance of three molybdenum Stellite alloys with varying C and Mo contents is studied using pin-on-disk dry-sliding wear test at ambient temperature, focusing on the effect of test duration and interrupted test on the wear behavior of the alloys. The worn surfaces are examined using SEM/EDS, and the analyses of the surface morphologies help explore the wear mechanisms of these alloys in dry-sliding condition. A wear model is developed for molybdenum Stellite alloys, based on the Archard equation in check with the wear test data, using hardness as a controlling factor. [ABSTRACT FROM AUTHOR]

• The cracking of Stellite 6 + 20 %WC laser cladding layers can be eliminated using ultrasonic impact treatment. • Residual stress could be decreased obviously using ultrasonic impact treatment. • After ultrasonic impact, the residual stress could decrease by nearly 100 MPa. Enhancing the wear resistance of coatings is a widely used technique that involves adding WC ceramic particles to Stellite alloy. Practical applications may be challenging due to the significant coating breaking that might result from the inclusion of WC ceramic particles. In this paper, the ultrasonic impact treatment (UIT) method was used to decrease the residual stress during the cladding process of WC reinforced Stellite 6 alloy coating, consequently reducing the coating's tendency to crack. The results showed that the cracking can be eliminated in the coating reinforced by 20 % WC ceramic particles utilizing UIT. [ABSTRACT FROM AUTHOR]

The corrosion performance of 700 series Stellite alloys including Stellite 706, Stellite 712 and Stellite 720, which are high-carbon high-molybdenum Stellite alloys, in various media such as Green Death solution, 3.5 wt.% NaCl solution and morpholine solution with pH 9.5, is studied using electrochemical and immersion methods. The obtained polarization curves are analyzed along with the corroded surfaces examined using SEM/EDS to investigate the corrosion mechanisms of these alloys. The experimental results reveal that the 700 series Stellite alloys possess excellent corrosion resistance in the tested media, even in the severe corrosive condition—Green Death solution at 60 °C where no noticeable pitting is found on the surfaces of the alloys. It is shown that the corrosion resistance of these Stellite alloys depends strongly on the behavior of the passivation film formed on the alloy surfaces. Additional Mo content in these alloys benefits the stabilization of the passivation film thus enhances the corrosion resistance of the alloys. Both carbon and molybdenum contents affect the passivation film formation and stabilization. [ABSTRACT FROM AUTHOR]

Low-carbon Stellite alloys such as Stellite 21 exhibit good high-temperature and corrosion properties but need improved wear resistance in some applications. In this research, two low-carbon Stellite alloys with highly increased molybdenum content are produced via laser cladding. The microstructures of the laser cladding hardfacings are studied using scanning electron microscopy (SEM) with an energy dispersive X-ray (EDS) spectroscopy, and X-ray diffraction. The wear resistance of the hardfacings is evaluated using a pin-on-disc tribometer. The corrosion performance of the hardfacings is investigated under electrochemical tests in 3.5 wt.% sodium chloride (NaCl) solution and in Green Death solution. The experimental results show that the presence of Mo-rich intermetallic compounds enhances the wear resistance of the alloy hardfacings significantly. Since Stellite alloys are all able to form protective oxide films due to high chromium content against corrosion of the substrates, the bonding strength and repair ability of the oxide films dominate the corrosion resistance of the hardfacings in the corrosive environments. Stellite 21 hardfacing is also studied under the same testing conditions for comparison. [ABSTRACT FROM AUTHOR]

In this paper, the water droplet erosion (WDE) performance of typical martensitic precipitation substrate 0Cr17Ni4Cu4Nb in steam turbine final stage, laser solid solution strengthened sample, laser cladding sample and brazed stellite alloy samples have been studied based on a high-speed rotating waterjet test system. The WDE resistance of several materials from strong to weak is in sequence: Brazed stellite alloy > laser cladding sample > laser solid solution sample > martensitic substrate. Furthermore, the WDE resistance mechanism and the failure mode of brazed stellite alloy have been revealed. It is found that the hard carbide in the stellite alloy is the starting point of crack formation and propagation. Under the continuous droplet impact, cracks grow and connect into networks, resulting in the removal of carbide precipitates and WDE damage. It is proved that the properties of the Co-based material itself is the reason for its excellent WDE resistance. And the carbides have almost no positive contribution to its anti-erodibility. These new findings are of great significance to process methods and parameter selection of steam turbine blade materials and surface strengthened layers.

A novel Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN composite was designed and prepared for the first time by hot pressing. The addition of cBN was found to be very effective in simultaneously enhancing the hardness and toughness of the Al 2 O 3 -Ti(C 0.7 N 0.3 ) ceramics. The optimum cBN content of the Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN composite was determined to be 5 vol%. The optimal properties were achieved by sintering at 1400 °C for 20 min under 40 MPa，and the Vickers hardness, bending strength, and fracture toughness were 20 GPa, 548 MPa, and 5.3 MPa m 1/2 , respectively. When turning stellite 3 using the Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN insert, the longest cutting length achieved at a cutting speed of 117 m/min was 5122 m, 73% and 45% longer than those of the Al 2 O 3 -Ti(C 0.7 N 0.3 ) and commercial A66N inserts, respectively. This indicates that the Al 2 O 3 -Ti(C 0.7 N 0.3 )-cBN composite is a promising tool material for the turning of stellite alloys. [ABSTRACT FROM AUTHOR]

The wear performance of Stellite 6B versus AISI M2 steel in dry sliding at various sliding velocities (from 0.95 to 4.71 m/s) were systematically studied by pin-on-disc wear test and analysis of debris, tribo-layers and worn surfaces of both pin and disc. The mechanical performance of pin and disc were also studied by hot hardness test. The results showed that Stellite 6B underwent a severe-to-mild wear transition with the increase of sliding velocity in the Stellite 6B alloy/steel tribo-system. The temperature at worn surface increased with the increase of velocity and load, leading to the oxidation of the worn surface and the variation of mechanical strength of pin and disc. It was the surface state rather than the variation of the mechanical strength that impacted the wear transition. The critical transition sliding velocity for the Stellite 6B alloys was 2.51 m/s, which divided the sliding velocities into two regions. When the velocity was among 0.95–2.51 m/s, the wear mechanism turn from abrasive and delamination wear to adhesive wear gradually, resulting in the decrease of wear rate. While in the region that the sliding velocity was above 2.51 m/s, oxidative wear prevailed and the wear rate decreased due to the formation of mechanically mixed layer (MML). [ABSTRACT FROM AUTHOR]

A Stellite alloy mixture hardfacing consisting of 70% Stellite 3 and 30% Stellite 21, is created via laser cladding for control valve seat sealing surfaces, aiming at enhancing hardness and wear resistance compared with Stellite 6, and improving cracking in laser cladding compared with Stellite 3. The Stellite alloy mixture hardfacing is made on 316 stainless steel substrate and does not show any cracking in liquid penetrant testing. The microstructure of the hardfacing is analyzed using SEM, EDS and XRD. The hardness, dry sliding wear resistance, cavitation-erosion resistance in NaOH solution and corrosion resistance in morpholine solution at pH 9.5 to simulate the amine environment of boiler feedwater service in power generation plants, are evaluated. The Stellite 6 hardfacing prepared with the same laser process parameters is also analyzed and tested under the same conditions for comparison. The experimental results and real industrial test demonstrate superior performance of the Stellite alloy mixture hardfacing to the Stellite 6 hardfacing for control valve seat sealing application. [ABSTRACT FROM AUTHOR]

The strengthening agents of Stellite alloys are commonly various carbides, but intermetallic compounds may play a similar role to the carbides. In this research two low-carbon Stellite alloys with high molybdenum content are developed and studied, which are modified version of Stellite 21. This particular elemental content combination results in large amounts of Co 3 Mo intermetallic compound precipitated in these alloys. The microstructures of the alloys are analyzed using SEM/EDX/XRD and DSC. The dry sliding wear resistance and solid-particle erosion resistance of the alloys are evaluated experimentally. The corrosion performance of the alloys in 3.5 wt.% sodium chloride (NaCl) aqueous solution is investigated under electrochemical tests. It is shown that the intermetallic compounds enhance hardness and wear resistance as the carbides do in Stellite alloys, but do not favor solid-particle erosion resistance due to their brittleness. The presence of the intermetallic compounds does not worsen corrosion resistance, compared to Stellite 21. [ABSTRACT FROM AUTHOR]

A high-tungsten Stellite alloy is developed for wear and erosion resistance application in this research, taking the advantage of tungsten in Stellite alloys. The microstructure of this alloy is analyzed using SEM/EDX and XRD. The sliding wear resistance of the alloy is evaluated on a pin-on-disc tribometer and the solid-particle erosion behavior is investigated using a micro-blasting jet machine at two particle impact velocities (84 and 98 m s −1 ) and two impingement angles (30° and 90°). The experimental results of the alloy are compared with those of well-known wear-resistant Stellite 3 and Stellite 6. The worn and eroded surfaces of the specimens are studied using SEM/EDX to explore the wear and erosion mechanisms of this new alloy. The experimental results show that this novel high-tungsten Stellite alloy has superior sliding wear and solid-particle erosion resistance to Stellite 3 and Stellite 6, owing to the formation of large amounts of large-size W-rich carbides in the alloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Develop advanced Stellite alloys with improved metal-on-metal bearing. [•] Increase chromium content to improve the wear resistance of Stellite 21. [•] Increase chromium content to improve the corrosion resistance of Stellite 21. [•] Develop advanced Stellite alloys as potential hip implant materials. [ABSTRACT FROM AUTHOR]

This article presents a study of the corrosion behavior of two wrought Stellite alloys, Stellite 6B, and Stellite 6K, in Green Death solution, utilizing the extreme value analysis (EVA) model, which is a statistics tool developed based on the Gumbel distribution. Green Death solution a typical oxidized testing solution used in industry for assessing the corrosion resistance of materials. The data of maximum pit depths are obtained from the immersion tests on these alloys for various exposure periods. The top ten maximum pit depths in each specimen surface after the immersion test are measured using a surface texture and contour measuring instrument. These data are the input parameters of the EVA model and the outcomes of the model are the extreme values (minimum thickness) required for the alloys under a given service condition. It is shown that Stellite 6K, which contains higher carbon content but smaller-size carbides, exhibits better corrosion resistance in regard to the extreme value. The results and mechanisms of Stellite 6B and Stellite 6K in Green Death solution corrosion are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to investigate the nanoscale sliding wear behaviour of re-HIPed (Hot Isostatically Pressed) and cast cobalt-based Stellite 6 alloys. A nanoindentation system equipped with a wear testing module was used to simulate single asperity deformation behaviour using a sphero-conical indenter. The test load was either increased linearly over the sliding distance or ramped upto full load at the initial stage of the test. Post-test evaluations included X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and atomic force microscopy (AFM) measurements. An elastic–plastic finite element model (FEM) was used to compare the displaced volume with the experimental data. Results are discussed in terms of the structure–property relationships and indicated that the nanoscale wear was dominated by the composition and nanomechanical properties of the metal matrix, and also the shape and size of carbides. Wear predominantly occurred due to plastic deformation of the metal matrix phase. Relatively higher scratch resistance and hardness of the metal matrix phase, coupled with the microstructural homogeneity of re-HIPed alloy led to its lower wear volume loss, in comparison to the cast counterpart. The FEM predictions were in agreement with the experimental results, and the error between the two ranged from 0% to 25% under the loading conditions considered in this investigation. [Copyright &y& Elsevier]

Highlights: [•] Eliminate the disadvantages of carbides in Stellite alloys. [•] Improve tribological properties of Stellite alloys due to incorporation of carbon fibres. [•] Induce graphite films as solid lubricant because of the presence of carbon fibres. [•] Help dissipation of friction heat because of good thermal conductivity of carbon fibre. [Copyright &y& Elsevier]

Low-carbon Stellite 21 has been used as hip implant material for a number of decades; however, its limited metal-on-metal bearing has resulted in loosening between the femoral head and the acetabular cup of hip implants. In order to improve the metal-on-metal bearing, it is proposed that a high-carbon alloy, Stellite 720, surface coating be applied on Stellite 21 hip implants to improve mechanical and tribological performance. For this coating to be practical, it must also meet the requirements of corrosion resistance for orthopedic implant materials. In this research, Stellite 720 is investigated with pin-on-disk wear tests, and electrochemical and immersion corrosion tests in simulated human body fluid (Hank's solution; pH 7.4 at temperature of 37°C). The experimental results demonstrate that Stellite 720 exhibits much better wear resistance than Stellite 21, and has the potential for better corrosion resistance as well. The applicability of coating Stellite 21 hip implants with Stellite 720 is discussed. [ABSTRACT FROM AUTHOR]

This article presents the analytical modeling of erosion behavior of Stellite alloys under solid-particle impact. The erosion rates of five selected Stellite alloys, which are currently or potentially applied in an environment condition involving erosion, are investigated experimentally at two particle impact velocities of 84 and 98ms−1, and at two impingement angles of 30° and 90°. The Sheldon–Kanhere (S–K) model that utilizes the indentation hardness theory to derive a particle penetration equation is modified to fit the experimental data of Stellite alloys. The most significant improvement of this modified model is to include the effect of particle impingement angle. This introduces two parameters in the model, which are determined by fitting the experimental data of the five Stellite alloys. With this modified model, for Stellite alloys that have similar chemical compositions to the alloys studied in this research, the erosion rates at the particle impact velocity of 84ms−1 or 98ms−1 can be predicted for any particle impingement angles less than 30°. The limitations of this model are discussed. [ABSTRACT FROM AUTHOR]

The chemical composition of Stellite® 21 alloy was modified by doubling the molybdenum (Mo) content for enhanced corrosion and wear resistance. The specimens were fabricated using a casting technique. Half of the specimens experienced a heat treatment at 1050°C for an hour. The microstructure and phase analyses of the specimens were conducted using electron scanning microscopy and X-ray diffraction. The mechanical properties of the specimens were determined in terms of the ASTM Standard Test Method for Tension Testing of Metallic Materials (E8-96). The mechanical behaviors of individual phases in the specimen materials were investigated using a nano-indentation technique. The wear resistance of the specimens was evaluated on a ball-on-disk tribometer. The experimental results revealed that the increased Mo content had significant effects on the mechanical and tribological properties of the low-carbon Stellite® alloy and the heat treatment also influenced these properties. [ABSTRACT FROM AUTHOR]

Abstract: Co-base alloys Tribaloy T-800 and Stellite 6 are widely used bearing materials in the galvanizing industry. Tribaloy alloys are strengthened by Laves intermetallic phase while Stellite alloys depend on carbide dispersed strengthening. The chemical composition influences the amount and mechanical properties of the strengthening phases in these alloys, which consequently influence the overall performance of the materials. Currently preferred compositions of alloys Tribaloy T-800 and T-400 are hypereutectic with primary Laves phase dendrites and interdendritic eutectics. A new hypoeutectic alloy Tribaloy T-401 with primary Co-rich dendrites and interdendritic eutectics is obtained by adjusting Cr, Mo, Si and C contents. The new alloy Tribaloy T-401 has better ductility than alloys Tribaloy T-800 and T-400. Tribaloy alloys T-800, T-400 and T-401 as well as Stellite 6 have been dipped in an Fe-saturated Zn bath containing about 0.22wt.% Al at 470°C for various lengths of time up to 604,800s (168h) to study their corrosion resistance. It is found that all four alloys have reacted with the Zn–Al baths. Tribaloy alloys outperform Stellite 6 in corrosion resistance in molten Zn–Al bath and Tribaloy T-401 performs best in terms of the thickness of reaction layer. [Copyright &y& Elsevier]

Abstract: The new Coph name="sbnd" />Moought alloy Stellite 706K is an improved alloy over the Coph name="sbnd" />Wought alloy Stellite 6K in wear and corrosion resistance. The microstructure of Stellite 706K is characterized by Coph name="sbnd" />Mo solid solution matrix with banding and occasional twinning and various carbide phases. Pin-on-disc wear resistance of Stellite 706K at room temperature is evaluated. Solution treatment at temperatures from 1235 to 1250°C on the mill annealed Stellite 706K decreases the bulk hardness and the hardness of Coph name="sbnd" />Mo matrix while increases the wear resistance. The excellent properties of Stellite 706K come from the combination of the high volume fraction of carbide particles and the tough Coph name="sbnd" />Mo matrix due to the alloying addition of Mo. [Copyright &y& Elsevier]

This investigation reports on the tribomechanical evaluations of a Co-based alloy obtained by the hot isostatic pressing (HIPing) of a blend of two standard gas atomized cobalt alloy powders. A HIPed blend of Stellite 6 and Stellite 20 was used to investigate the effect of varying the C, Cr, and W content simultaneously on the structure-property relationships. Microstructural evaluations involved scanning electron microscopy and x-ray diffraction. Experimental evaluations were conducted using hardness, impact, tensile, abrasive wear and sliding wear tests to develop an understanding of the mechanical and tribological performance of the alloys. Results are discussed in terms of the failure modes for the mechanical tests, and wear mechanisms for the tribological tests. This study indicates that powder blends can be used to design for a desired combination of mechanical strength and wear properties in these HIPed alloys. Specific relationships were observed between the alloy composition and carbide content, hardness, impact energy and wear resistance. There was a linear relationship between the weighted W- and C-content and the carbide fraction. The abrasive wear performance also showed a linear relationship with the weighted alloy composition. The pin-on-disc and ball-on-flat experiments revealed a more complex relationship between the alloy composition and the wear rate. • An approach of blending standard alloy powders to design new alloys for specific tribo-mechanical properties. • Structure-property relationships (hardness, modulus, yield strength, ductility, impact energy and wear) of HIPed alloys. • Mathematical models to predict material strength and wear. • Failure modes and wear mechanisms in the blended HIP alloy. [ABSTRACT FROM AUTHOR]

In this paper, the water droplet erosion (WDE) performance of a typical martensitic blade material 17-4 PH (0Cr17Ni4Cu4Nb), surface strengthened laser cladding stellite and brazed stellite alloy is studied based on high-speed water jet test system. The WDE resistances from high to low are the brazed stellite alloy, laser cladding stellite alloy and 17-4 PH. For the same material, the greater the initial roughness of the target surface, the more severe is the WDE damage. Improving the surface finish of the target is conducive to the diversion and expansion of the liquid flow, prolonging the incubation period, and thus enhancing the WDE resistance. Image 1 • The WDE resistance from high to low: brazed stellite, laser cladding and 17-4 PH. • The greater the initial surface roughness, the more serious is the WDE damage. • The incubation period decreases with the increase of the impact angle and roughness. • The material with higher surface finish has better anti-erodibility. [ABSTRACT FROM AUTHOR]

In this paper, the water droplet erosion (WDE) performance of typical martensitic precipitation substrate 0Cr17Ni4Cu4Nb in steam turbine final stage, laser solid solution strengthened sample, laser cladding sample and brazed stellite alloy samples have been studied based on a high-speed rotating waterjet test system. The WDE resistance of several materials from strong to weak is in sequence: Brazed stellite alloy > laser cladding sample > laser solid solution sample > martensitic substrate. Furthermore, the WDE resistance mechanism and the failure mode of brazed stellite alloy have been revealed. It is found that the hard carbide in the stellite alloy is the starting point of crack formation and propagation. Under the continuous droplet impact, cracks grow and connect into networks, resulting in the removal of carbide precipitates and WDE damage. It is proved that the properties of the Co-based material itself is the reason for its excellent WDE resistance. And the carbides have almost no positive contribution to its anti-erodibility. These new findings are of great significance to process methods and parameter selection of steam turbine blade materials and surface strengthened layers. [ABSTRACT FROM AUTHOR]