rus
Issue #6/2025
E. V. Khriptovich, V. P. Biryukov, A. S. Zakharov, V. S. Bashlaev, D. V. Myasnikov, Ya. A. Goryunov
High-speed Laser Cladding of Hydraulic Cylinder Rods
High-speed Laser Cladding of Hydraulic Cylinder Rods
DOI: 10.22184/1993-7296.FRos.2025.19.6.454.464
During the study, the samples obtained by the high-speed laser cladding technology with the application of fiber lasers made by VPG Lazerone LLC were examined. This processing approach is a promising method for applying protective coatings to the metal surfaces. This article provides the coating results of 38Cr2MoAlA medium-carbon steel with the high-alloy iron-based powder materials. The resulting surface layer demonstrated the increased microhardness and wear resistance properties. The high process velocity minimized the sample heating that preserved the original geometric dimensions and minimized mixing of the deposited material with the base metal, while maintaining high adhesion between the coating and the base metal.
During the study, the samples obtained by the high-speed laser cladding technology with the application of fiber lasers made by VPG Lazerone LLC were examined. This processing approach is a promising method for applying protective coatings to the metal surfaces. This article provides the coating results of 38Cr2MoAlA medium-carbon steel with the high-alloy iron-based powder materials. The resulting surface layer demonstrated the increased microhardness and wear resistance properties. The high process velocity minimized the sample heating that preserved the original geometric dimensions and minimized mixing of the deposited material with the base metal, while maintaining high adhesion between the coating and the base metal.
Теги: волоконный лазер защитные покрытия износостойкость коэффициент трения лазерная наплавка микротвердость среднеуглеродистые стали
High-speed Laser Cladding of Hydraulic Cylinder Rods
E. V. Khriptovich1, V. P. Biryukov2, A.S. Zakharov1, V. S. Bashlaev1, D. V. Myasnikov1, Ya. A. Goryunov2
VPG Laserone LLC, Fryazino, Moscow region, Russia
Institute of Machine Science of the RAS, Moscow, Russia
During the study, the samples obtained by the high-speed laser cladding technology with the application of fiber lasers made by VPG Lazerone LLC were examined. This processing approach is a promising method for applying protective coatings to the metal surfaces. This article provides the coating results of 38Cr2MoAlA medium-carbon steel with the high-alloy iron-based powder materials. The resulting surface layer demonstrated the increased microhardness and wear resistance properties. The high process velocity minimized the sample heating that preserved the original geometric dimensions and minimized mixing of the deposited material with the base metal, while maintaining high adhesion between the coating and the base metal.
Keywords: laser cladding, protective coatings, wear resistance, medium-carbon steels, fiber laser, microhardness, friction coefficient
Article received: August 28, 2025
Article accepted: September 16, 2025.
Introduction
The solids of rotation being the key components of various machines and mechanisms, are widely used in various industries. During their operation, they are subject to high mechanical and chemical stress. For example, an element such as a piston rod, representing a solid of rotation, is an important component of such devices as the shock absorbers, pneumatic cylinders, hydraulic cylinders, etc. Moreover, such parts are applied in various aggressive environments and under the influence of significant mechanical and thermal loads.
To increase the service life and impart the required corrosion resistance to the solids of rotation, the thin-layer hard coatings are applied to their surfaces by the galvanic chromium plating method. The high-speed laser powder cladding technology replaces the environmentally destructive process of hard chromium plating. The process involves the high-frequency rotation of a cylindrical workpiece and introduction of the molten metal onto a laser-heated base material. Most part of the energy is spent for melting the powder material rather than developing a molten pool in the deposited alloy. This technology enables the application of functional coatings with the thicknesses above 50 µm, thereby reducing thermal stresses that cause any residual deformation. The high-speed cladding significantly increases the part processing velocity from 0.6–3 m/min to 6–100 m/min, while enabling the application of powders containing carbides without their dissociation.
The heat-proof nickel-based alloys [1] are widely used in the production of aircraft turbine blades and steam generators. In this article, a high-chromium alloy K648, cladded by laser during the high-speed machining was obtained for the first time. The influence of main process parameters on the geometric dimensions of the beads was investigated, and the microstructure and mechanical properties were determined. It was found that the maximum height and width of the deposited tracks were obtained at a radiation power of 1400 W, a scanning speed of 25 m/min, and a powder flow rate of 30 g/min. The average microhardness of the K648 alloy was 298.1 HV. The tensile strength during the K648 high-speed cladding was slightly lower than that of the forged heat-resistant alloy K648, but higher than that of K648 obtained by the conventional laser cladding.
The paper [2] used the iron-based powder 1Cr17Ni2 with an average particle diameter of 30 µm and a tube-shaped blank made of carbon steel 45 with a diameter of 50 mm. The high-speed laser cladding (HSLC) process was performed at a radiation power of 4.0 kW, speed scanning 50 m/min and a powder consumption of 30 g/min. The covering thickness was approximately 533 µm. The martensitic transformation was performed at a temperature of 286 °C. The high-speed coating cooling process contributed to the preservation of a small amount of residual austenite (about 0.8%v/v) in the deposited layer. The thin transition layer with the thickness of 5 µm was obtained between the coating and the substrate.
To conduct the experiments in the paper [3], the samples were used for the substrates with the shape of discs made of medium-carbon steel 27SiMn with the thickness of 10 mm and a diameter of 100 mm. The laser cladding was carried out with the powder AISI 431 with the particle size of 15–45 µm, while using the 6 kW fiber laser produced by IPG YLR‑6000 and an optical head with a working spot diameter of 2 mm. For obtaining the dendrites with various dimensions in the structure of deposited tracks, the coatings were applied at the scanning speeds of 1.5, 15 and 100 m/min, a laser power of 1600 W, 3300 W and 3800 W, respectively, and a powder flow rate of 13 g/min. It was found that with increasing the scanning speed, the dimensions of dendrites were decreased. The average size of dendrites was about 1 µm at the processing speed of 100 m/min. In this case, the dense passive films were obtained due to which the coating corrosion resistance increased.
For the research [4] during the AISI 1045 steel laser cladding, the Ni45 nickel-based alloy powder with the particle size of 55–75 µm and 15–30 µm was used. The laser processing was performed at a radiation power of 2000 W, scanning speeds of 0.6 (1), 37.68 (2), 58 (3) and 76.9 (4) m/min. The surface roughness of the samples with a coarse-grained powder cladding was 24.9 microns and with a fine-grained powder cladding – 13.88 microns. The coating was subject to the friction and abrasion test with the reciprocating motion by using the UMT‑2 machine with the following scheme: “ball (Si3N4) – plane” under a load of 25 N, with a stroke of 10 mm, an average slip velocity of 10 mm/s and a cycle duration of 30 min. The microhardness of coatings for the samples (1), (2), (3) and (4) was 320–340, 420–560, 430–580 and 440–600 HV, respectively. The friction coefficients had average values for the samples (1), (2), (3) and (4) of 0.78; 0.65; 0.59 and 0.53, respectively. With increasing laser cladding velocity, the microstructure was improved, the large columnar crystals were transformed into the small dendrites, and the coating hardness and wear resistance were significantly increased. The coating corrosion resistance for the high-speed laser cladding was higher than that for the conventional laser cladding.
In the paper [5], the iron-based coatings with a particle size of 25–60 µm were deposited by the high-speed laser cladding method on a pipe made of Q235 steel. The treatment was performed at a radiation power of 2000 W, a scanning speed of 1.57 (1), 6.2 (2), 11.0 (3), 15.7 (4) and 20.4 (5) m/min and a powder consumption of 18.4 g/min. The deposited layer thickness and the average microhardness for the samples (1), (2), (3), (4) and (5) were 1258, 505, 469, 393 and 262 µm and 605, 585, 580, 570 and 550 HV, respectively. The coating corrosion resistance was first increased, and then it was decreased with increasing scanning speed. The sample (4) had the greatest resistance to the pitting corrosion.
The powder materials [6] for high-speed laser cladding included the following compositions: (1) 595.074 (Ni/CrC 44/56 vol%), (2) 380 (Ni21Cr9Mo4Nb) + 595.074 (Ni/CrC 56/44 vol%), (3) 380 + 70F-NS (Ni/CrC 50/50 vol%), (4) 380 + 70F-NS (Ni/CrC 80/20 vol%) with the particle size of 15–45 µm. The main materials applied for adjusting the process parameters were the steel rods made of S355 and 42CrMo4 with a diameter of 100 mm and a length of 500 mm. The high-speed laser cladding of the compositions (1) and (2) was carried out at a radiation power of 2000 W, and for (3) and (4) – at a radiation power of 1900 W with the scanning speed of 25 m/min. The samples for wear testing were welded on the S355 with the dimensions of 20 × 20 × 50 mm. The abrasion tests were performed at a room temperature according to the standard ASTM G65. The silica sand (SiO2) with the particle size from 0.1 to 0.6 mm was fed into the friction area between the generating surface of the rotating rubber wheels and a sample. The average microhardness of the coatings of samples (1), (2), (3) and (4) was 1100, 920, 830 and 580 HV, respectively. The hardest coating (1) had maximum abrasive resistance corresponding to the wear resistance of a coating obtained by the galvanic hard chromium plating method.
During the high-speed laser cladding [7], the pipes made of carbon steel C45 and 304SS with a diameter of 50 mm and a wall thickness of 10 mm were used. The coating was applied using the high-entropy alloy (HEA) powder FeCoNiCrAl. The treatment was carried out at a power 6.0 kW, a scanning speed of 50 m/min and a powder flow rate of 30 g/min. The longitudinal travelling velocity of the nozzles was 159 mm/min that led to the displacement of deposited tracks by 0.5 mm. The surface of the deposited coating on 304SS steel was free of any defects, while the longitudinal and transverse cracks were found in the coating on 45 steel. The total thickness of each coating was about 450 µm, such coatings consisted of three layers with a thickness of 150 µm. The average hardness of coatings was 600 HV.
The stainless steel (grade 304) was applied as a substrate material in [8]. The coatings were deposited using an RC–LCD‑4000-IPG HSLC system at a radiation power of 2.5 kW, a scanning speed of 100 mm/s, a powder flow rate of 7.2 g/min, with an overlapping factor of 80%. The wear tests were conducted using a multifunctional system (BRUKER UMT‑5) with a reciprocating motion, a load of 5 N, an average slip velocity of 0.1 m/s, a stroke of 5 mm, and a cycle duration of 60 minutes. The Al2O3 ball with a diameter of 6 mm was used as a counter sample.
The microstructures of both coatings included the same metallic phases, Fe-Cr-Ni, (Fe, Cr) and Cr. The ceramic phase in the coating (A) was zirconium diboride (ZrB2). Titanium diboride (TiB2) was added in the coating (B). The average hardness of the coatings A and B was 719 and 1130 HV0.5, respectively. The average friction coefficients of the coatings A and B were 0.73 and 0.68. The specific volume wear was reduced from 8.89 · 10–6 mm3/N · m for the coating A to 5.0 · 10–6 mm3/N · m for the coating B. Thewear mechanism of the coating A was abrasive wear, while for the coating B there was slight abrasive and oxidative wear.
During the laser cladding [9] of Stellite 6 powder, the steel 45 with the sample sizes of 100 × 50 × 10 mm was used as the substrates. The processing was performed on a fiber laser with a radiation power of 1600, 2000 and 2400 W, scanning speeds of 4.0, 5.0 and 6.0 m/min, and a powder flow rate of 0.45 g/s. The corrosion and erosion wear tests were performed in the suspension containing a mixture of 3.5% NaCl solution and silica sand with the ratio of volumes 4 : 1. The thickness of the deposited coatings at a radiation power of 1600, 2000 and 2400 W and a speed of 6.0 and 4.0 m/min was 430–620, 480–670 and 500–870 µm, respectively. The sample weight loss during the erosive wear of Stellite 6 coating was 2–5 times lower than that for steel 45, and it was lower in the samples with higher microhardness.
Equipment and research methods
The samples were processed using a YLR‑6000-U-R fiber laser with a power of 6 kW produced by VPG Lazerone LLC. This series of lasers is equipped with a back reflection shield and a self-diagnostic system. The main specifications of the source are given in Table 1. The laser spot diameter ranged from 1 to 3 mm. The linear speed of cylindrical samples was 6–60 m/min. The laser power varied from 3 to 5.5 kW. The longitudinal movement of the optical head was 0.4–4 mm/s. The flow rates of the shielding and crimping gases were 16 and 4 l/min, respectively. The flow rate of the powder transporting gas did not exceed 10 l/min.
During the research works, the cylindrical specimens made of 38Cr2MoAlA medium-carbon steel with the diameters of 24 and 38 mm and the lengths of 25 and 100 mm, respectively, were applied. This material is widely used for the manufacture of various components, such as shafts, axles, and bushings, operating under the elevated temperatures and loads. The metal powder with a particle size of 20–100 μm was used for cladding (Table 2). The microhardness measurements were performed using a DuraScan‑70 microhardness tester in two directions (horizontal and vertical) at a load HV0.1 with a measurement increment of 100 μm (along the depth of the cladding area) and 200 μm (along the width of the cladding area).
A special coaxial nozzle was designed and manufactured to deliver powder to the molten region. It enabled the uniform powder feed at a throughput of up to 3.5 kg/hour for both conventional and high-speed laser cladding processes. The appearance of the coaxial nozzle and the powder feed path are shown in Fig. 1. The designed nozzle is equipped with the removable cones with various powder focus distances from 10 to 20 mm. This feature enables coating applications on various surfaces with a high powder utilization rate of up to 93%. During the work, two batches of samples were deposited: the first one to determine the adhesion strength of the coatings to the base metal, and the second one to determine the tribological properties of the coatings. The method for determining the adhesion strength of the deposited layer to the base metal was as follows: a cylindrical specimen of the test material, with an annular band deposited on it, was turned on both sides, installed in a matrix and forced through it on a tensile testing machine. In this case, under the action of tangential stresses, the deposited layer sheared, and the shear stress determined the adhesion strength of the deposited layer to the base metal. The shear testing machine provided loading at a specified constant movement speed of the active grip, measuring the load with an error of no more than 1%. To compare the shear adhesion strength of the coating and the base metal, the standard samples were prepared in the form of a cylinder with a diameter of 24 mm and a length of 25 mm with a cylindrical band of 25 mm in diameter (Fig. 2). The ultimate adhesion strength of the coating to the base metal under the shear of deposited coating was determined by the following formula:
τ =, (1)
where P – maximum load prior to shear of the coating band; h – a band width, mm; D – a sample diameter, mm.
The wear rate and friction coefficients were determined by testing the materials on a friction machine using the “pad-roller” configuration (Fig. 3), when the roller, sample 2 (38Cr2MoAlA steel, Fe-Cr-Ni-Mo coating), was rotated in relation to a stationary pad 1 of the counter-sample, made of grade 45 steel with a babbit layer with the thickness of 1.5 mm. A test load N was applied to the sample. The TP22S steam turbine oil was supplied to the friction area by the drip lubrication method.
The friction coefficient in a pair was determined using the following formula (2):
f = , (2)
where N is the normal load for the pair, r is the nominal joint radius, T is the force of the spring dynamometer, l is a forces’ arm relative to the axis of rotation of the roller sample.
The wear intensity was determined using the following formula [9]:
J = , (3)
where h is the value of linear wear, L is the friction length.
Results of the experimental studies
The appearance of the sample and microsections after laser cladding are shown in Fig. 4.
The metallographic studies (Fig. 4b) revealed that the layer height during the high-speed cladding was 670–718 µm. The visual inspection, analysis of the obtained microsections, and dye penetrant inspection revealed no cracks or pores in the deposited layer. The mixing area between the base and deposited layers is minimal during the high-speed laser cladding process that is another advantage of the process under study. To determine the effect of the coating application method on the deposited layer microhardness, a study was conducted on the samples obtained by two types of technologies: a high-speed process (Fig. 5a) and a typical process (Fig. 5b). An analysis of the obtained dependencies determined that the deposited layer microhardness during the high-speed cladding was 630–680 HV0.3, while during the typical process it was 540–650 HV0.3. The obtained results allow us to conclude that, by changing the thermal cycle, this processing method has a significant effect not only on the microhardness distribution, but also on its minimum and maximum values.
An analysis of the adhesion strength test results for coatings obtained using the high-speed cladding and the base material, 38Cr2MoAlA steel, showed that the shear stresses were 600–690 and 432–440 MPa, respectively. The 1.5‑fold increase in the shear adhesion strength for the coatings obtained by high-speed cladding compared to the base material is due to both the superior mechanical properties of the coating and the altered properties of the steel’s surface layer as a result of laser beam heating above the critical austenite transition point and high-rate cooling during the transition to a martensitic structure with a small amount of retained austenite.
Table 3 shows the results of tribological tests of samples obtained using the high-speed laser cladding process, as well as the reference samples made from the base material without a deposited layer.
An analysis of the test results has demonstrated that the wear rates of coatings deposited according to the mode 1 (with a higher beam scanning speed) and to the mode 2 were 3.2 and 2.25 times lower, respectively, compared to the base material. The friction coefficients for the coatings deposited according to the modes 1 and 2 were significantly lower compared to the friction pair of 38Cr2MoAlA steel and Babbitt B83.
Conclusion
This paper presents the experimental results of high-speed laser machining in order to apply a surface layer and increase the wear resistance of contact areas of metal parts. Machining with a beam with a diameter of 1 mm to 3 mm made it possible to melt the metal powder and a thin surface layer to a depth of 40–60 μm in a single pass. When using a laser with a power of up to 6 kW, it was possible to achieve the high-speed cladding of metal parts with a layer thickness of 50–700 μm. The obtained results demonstrate the technological feasibility of applying coatings to the solids of rotation without any defects in the form of pores and cracks. The advantages of this coating application method, compared with the high-speed spraying and galvanic deposition, include the high adhesion strength of the deposited layer to the substrate (up to 690 MPa) and the wear resistance of the coatings that is 3, 2, and 2.25 times higher compared to the base material. The friction coefficients of the coatings were significantly lower than those obtained for the “steel-Babbitt” friction pair.
The high-speed laser cladding technology can be used for the standard lathes provided with the VPG Laserone LLC equipment. This enables not only mechanical processing but also the coating application in order to restore the original geometric shape of worn parts and improve the surface quality of new parts.
AUTHORS
Khriptovich Evgeny Vladimirovich, head of the laser cladding and heat treatment group, VPG Lazerone LLC; e-mail: eHriptovich@VPGlaserone.ru; Fryazino, Moscow region, Russia
ORCID 0000-0001-9935-1414
Biryukov Vladimir Pavlovich, leading researcher, Ph.D. in technical sciences, Institute of Machine Science of the Russian Academy of Sciences; e-mail: laser‑52@yandex.ru; Moscow, Russia
ORCID 0000-0001-9278-6925
Zakharov Aleksander Sergeevich, process engineer at VPG Lazerone LLC, Fryazino, Moscow region, Russia
ORCID 0009-0004-1581-8830
Bashlaev Vladimir Sergeevich, process engineer at VPG Lazerone LLC
ORCID 0009-0001-2517-6753
Myasnikov Daniil Vladimirovich, deputy director general for advanced research and development, VPG Lazerone LLC, e-mail: dMyasnikov@vpglaserone.ru; Fryazino, Moscow region, Russia
ORCID 0009-0008-2669-5484
Goryunov Yaroslav Alekseevich, junior researcher, Institute of Machine Science of the Russian Academy of Sciences, Moscow, Russia
ORCID 0009-0002-1614-0174
E. V. Khriptovich1, V. P. Biryukov2, A.S. Zakharov1, V. S. Bashlaev1, D. V. Myasnikov1, Ya. A. Goryunov2
VPG Laserone LLC, Fryazino, Moscow region, Russia
Institute of Machine Science of the RAS, Moscow, Russia
During the study, the samples obtained by the high-speed laser cladding technology with the application of fiber lasers made by VPG Lazerone LLC were examined. This processing approach is a promising method for applying protective coatings to the metal surfaces. This article provides the coating results of 38Cr2MoAlA medium-carbon steel with the high-alloy iron-based powder materials. The resulting surface layer demonstrated the increased microhardness and wear resistance properties. The high process velocity minimized the sample heating that preserved the original geometric dimensions and minimized mixing of the deposited material with the base metal, while maintaining high adhesion between the coating and the base metal.
Keywords: laser cladding, protective coatings, wear resistance, medium-carbon steels, fiber laser, microhardness, friction coefficient
Article received: August 28, 2025
Article accepted: September 16, 2025.
Introduction
The solids of rotation being the key components of various machines and mechanisms, are widely used in various industries. During their operation, they are subject to high mechanical and chemical stress. For example, an element such as a piston rod, representing a solid of rotation, is an important component of such devices as the shock absorbers, pneumatic cylinders, hydraulic cylinders, etc. Moreover, such parts are applied in various aggressive environments and under the influence of significant mechanical and thermal loads.
To increase the service life and impart the required corrosion resistance to the solids of rotation, the thin-layer hard coatings are applied to their surfaces by the galvanic chromium plating method. The high-speed laser powder cladding technology replaces the environmentally destructive process of hard chromium plating. The process involves the high-frequency rotation of a cylindrical workpiece and introduction of the molten metal onto a laser-heated base material. Most part of the energy is spent for melting the powder material rather than developing a molten pool in the deposited alloy. This technology enables the application of functional coatings with the thicknesses above 50 µm, thereby reducing thermal stresses that cause any residual deformation. The high-speed cladding significantly increases the part processing velocity from 0.6–3 m/min to 6–100 m/min, while enabling the application of powders containing carbides without their dissociation.
The heat-proof nickel-based alloys [1] are widely used in the production of aircraft turbine blades and steam generators. In this article, a high-chromium alloy K648, cladded by laser during the high-speed machining was obtained for the first time. The influence of main process parameters on the geometric dimensions of the beads was investigated, and the microstructure and mechanical properties were determined. It was found that the maximum height and width of the deposited tracks were obtained at a radiation power of 1400 W, a scanning speed of 25 m/min, and a powder flow rate of 30 g/min. The average microhardness of the K648 alloy was 298.1 HV. The tensile strength during the K648 high-speed cladding was slightly lower than that of the forged heat-resistant alloy K648, but higher than that of K648 obtained by the conventional laser cladding.
The paper [2] used the iron-based powder 1Cr17Ni2 with an average particle diameter of 30 µm and a tube-shaped blank made of carbon steel 45 with a diameter of 50 mm. The high-speed laser cladding (HSLC) process was performed at a radiation power of 4.0 kW, speed scanning 50 m/min and a powder consumption of 30 g/min. The covering thickness was approximately 533 µm. The martensitic transformation was performed at a temperature of 286 °C. The high-speed coating cooling process contributed to the preservation of a small amount of residual austenite (about 0.8%v/v) in the deposited layer. The thin transition layer with the thickness of 5 µm was obtained between the coating and the substrate.
To conduct the experiments in the paper [3], the samples were used for the substrates with the shape of discs made of medium-carbon steel 27SiMn with the thickness of 10 mm and a diameter of 100 mm. The laser cladding was carried out with the powder AISI 431 with the particle size of 15–45 µm, while using the 6 kW fiber laser produced by IPG YLR‑6000 and an optical head with a working spot diameter of 2 mm. For obtaining the dendrites with various dimensions in the structure of deposited tracks, the coatings were applied at the scanning speeds of 1.5, 15 and 100 m/min, a laser power of 1600 W, 3300 W and 3800 W, respectively, and a powder flow rate of 13 g/min. It was found that with increasing the scanning speed, the dimensions of dendrites were decreased. The average size of dendrites was about 1 µm at the processing speed of 100 m/min. In this case, the dense passive films were obtained due to which the coating corrosion resistance increased.
For the research [4] during the AISI 1045 steel laser cladding, the Ni45 nickel-based alloy powder with the particle size of 55–75 µm and 15–30 µm was used. The laser processing was performed at a radiation power of 2000 W, scanning speeds of 0.6 (1), 37.68 (2), 58 (3) and 76.9 (4) m/min. The surface roughness of the samples with a coarse-grained powder cladding was 24.9 microns and with a fine-grained powder cladding – 13.88 microns. The coating was subject to the friction and abrasion test with the reciprocating motion by using the UMT‑2 machine with the following scheme: “ball (Si3N4) – plane” under a load of 25 N, with a stroke of 10 mm, an average slip velocity of 10 mm/s and a cycle duration of 30 min. The microhardness of coatings for the samples (1), (2), (3) and (4) was 320–340, 420–560, 430–580 and 440–600 HV, respectively. The friction coefficients had average values for the samples (1), (2), (3) and (4) of 0.78; 0.65; 0.59 and 0.53, respectively. With increasing laser cladding velocity, the microstructure was improved, the large columnar crystals were transformed into the small dendrites, and the coating hardness and wear resistance were significantly increased. The coating corrosion resistance for the high-speed laser cladding was higher than that for the conventional laser cladding.
In the paper [5], the iron-based coatings with a particle size of 25–60 µm were deposited by the high-speed laser cladding method on a pipe made of Q235 steel. The treatment was performed at a radiation power of 2000 W, a scanning speed of 1.57 (1), 6.2 (2), 11.0 (3), 15.7 (4) and 20.4 (5) m/min and a powder consumption of 18.4 g/min. The deposited layer thickness and the average microhardness for the samples (1), (2), (3), (4) and (5) were 1258, 505, 469, 393 and 262 µm and 605, 585, 580, 570 and 550 HV, respectively. The coating corrosion resistance was first increased, and then it was decreased with increasing scanning speed. The sample (4) had the greatest resistance to the pitting corrosion.
The powder materials [6] for high-speed laser cladding included the following compositions: (1) 595.074 (Ni/CrC 44/56 vol%), (2) 380 (Ni21Cr9Mo4Nb) + 595.074 (Ni/CrC 56/44 vol%), (3) 380 + 70F-NS (Ni/CrC 50/50 vol%), (4) 380 + 70F-NS (Ni/CrC 80/20 vol%) with the particle size of 15–45 µm. The main materials applied for adjusting the process parameters were the steel rods made of S355 and 42CrMo4 with a diameter of 100 mm and a length of 500 mm. The high-speed laser cladding of the compositions (1) and (2) was carried out at a radiation power of 2000 W, and for (3) and (4) – at a radiation power of 1900 W with the scanning speed of 25 m/min. The samples for wear testing were welded on the S355 with the dimensions of 20 × 20 × 50 mm. The abrasion tests were performed at a room temperature according to the standard ASTM G65. The silica sand (SiO2) with the particle size from 0.1 to 0.6 mm was fed into the friction area between the generating surface of the rotating rubber wheels and a sample. The average microhardness of the coatings of samples (1), (2), (3) and (4) was 1100, 920, 830 and 580 HV, respectively. The hardest coating (1) had maximum abrasive resistance corresponding to the wear resistance of a coating obtained by the galvanic hard chromium plating method.
During the high-speed laser cladding [7], the pipes made of carbon steel C45 and 304SS with a diameter of 50 mm and a wall thickness of 10 mm were used. The coating was applied using the high-entropy alloy (HEA) powder FeCoNiCrAl. The treatment was carried out at a power 6.0 kW, a scanning speed of 50 m/min and a powder flow rate of 30 g/min. The longitudinal travelling velocity of the nozzles was 159 mm/min that led to the displacement of deposited tracks by 0.5 mm. The surface of the deposited coating on 304SS steel was free of any defects, while the longitudinal and transverse cracks were found in the coating on 45 steel. The total thickness of each coating was about 450 µm, such coatings consisted of three layers with a thickness of 150 µm. The average hardness of coatings was 600 HV.
The stainless steel (grade 304) was applied as a substrate material in [8]. The coatings were deposited using an RC–LCD‑4000-IPG HSLC system at a radiation power of 2.5 kW, a scanning speed of 100 mm/s, a powder flow rate of 7.2 g/min, with an overlapping factor of 80%. The wear tests were conducted using a multifunctional system (BRUKER UMT‑5) with a reciprocating motion, a load of 5 N, an average slip velocity of 0.1 m/s, a stroke of 5 mm, and a cycle duration of 60 minutes. The Al2O3 ball with a diameter of 6 mm was used as a counter sample.
The microstructures of both coatings included the same metallic phases, Fe-Cr-Ni, (Fe, Cr) and Cr. The ceramic phase in the coating (A) was zirconium diboride (ZrB2). Titanium diboride (TiB2) was added in the coating (B). The average hardness of the coatings A and B was 719 and 1130 HV0.5, respectively. The average friction coefficients of the coatings A and B were 0.73 and 0.68. The specific volume wear was reduced from 8.89 · 10–6 mm3/N · m for the coating A to 5.0 · 10–6 mm3/N · m for the coating B. Thewear mechanism of the coating A was abrasive wear, while for the coating B there was slight abrasive and oxidative wear.
During the laser cladding [9] of Stellite 6 powder, the steel 45 with the sample sizes of 100 × 50 × 10 mm was used as the substrates. The processing was performed on a fiber laser with a radiation power of 1600, 2000 and 2400 W, scanning speeds of 4.0, 5.0 and 6.0 m/min, and a powder flow rate of 0.45 g/s. The corrosion and erosion wear tests were performed in the suspension containing a mixture of 3.5% NaCl solution and silica sand with the ratio of volumes 4 : 1. The thickness of the deposited coatings at a radiation power of 1600, 2000 and 2400 W and a speed of 6.0 and 4.0 m/min was 430–620, 480–670 and 500–870 µm, respectively. The sample weight loss during the erosive wear of Stellite 6 coating was 2–5 times lower than that for steel 45, and it was lower in the samples with higher microhardness.
Equipment and research methods
The samples were processed using a YLR‑6000-U-R fiber laser with a power of 6 kW produced by VPG Lazerone LLC. This series of lasers is equipped with a back reflection shield and a self-diagnostic system. The main specifications of the source are given in Table 1. The laser spot diameter ranged from 1 to 3 mm. The linear speed of cylindrical samples was 6–60 m/min. The laser power varied from 3 to 5.5 kW. The longitudinal movement of the optical head was 0.4–4 mm/s. The flow rates of the shielding and crimping gases were 16 and 4 l/min, respectively. The flow rate of the powder transporting gas did not exceed 10 l/min.
During the research works, the cylindrical specimens made of 38Cr2MoAlA medium-carbon steel with the diameters of 24 and 38 mm and the lengths of 25 and 100 mm, respectively, were applied. This material is widely used for the manufacture of various components, such as shafts, axles, and bushings, operating under the elevated temperatures and loads. The metal powder with a particle size of 20–100 μm was used for cladding (Table 2). The microhardness measurements were performed using a DuraScan‑70 microhardness tester in two directions (horizontal and vertical) at a load HV0.1 with a measurement increment of 100 μm (along the depth of the cladding area) and 200 μm (along the width of the cladding area).
A special coaxial nozzle was designed and manufactured to deliver powder to the molten region. It enabled the uniform powder feed at a throughput of up to 3.5 kg/hour for both conventional and high-speed laser cladding processes. The appearance of the coaxial nozzle and the powder feed path are shown in Fig. 1. The designed nozzle is equipped with the removable cones with various powder focus distances from 10 to 20 mm. This feature enables coating applications on various surfaces with a high powder utilization rate of up to 93%. During the work, two batches of samples were deposited: the first one to determine the adhesion strength of the coatings to the base metal, and the second one to determine the tribological properties of the coatings. The method for determining the adhesion strength of the deposited layer to the base metal was as follows: a cylindrical specimen of the test material, with an annular band deposited on it, was turned on both sides, installed in a matrix and forced through it on a tensile testing machine. In this case, under the action of tangential stresses, the deposited layer sheared, and the shear stress determined the adhesion strength of the deposited layer to the base metal. The shear testing machine provided loading at a specified constant movement speed of the active grip, measuring the load with an error of no more than 1%. To compare the shear adhesion strength of the coating and the base metal, the standard samples were prepared in the form of a cylinder with a diameter of 24 mm and a length of 25 mm with a cylindrical band of 25 mm in diameter (Fig. 2). The ultimate adhesion strength of the coating to the base metal under the shear of deposited coating was determined by the following formula:
τ =, (1)
where P – maximum load prior to shear of the coating band; h – a band width, mm; D – a sample diameter, mm.
The wear rate and friction coefficients were determined by testing the materials on a friction machine using the “pad-roller” configuration (Fig. 3), when the roller, sample 2 (38Cr2MoAlA steel, Fe-Cr-Ni-Mo coating), was rotated in relation to a stationary pad 1 of the counter-sample, made of grade 45 steel with a babbit layer with the thickness of 1.5 mm. A test load N was applied to the sample. The TP22S steam turbine oil was supplied to the friction area by the drip lubrication method.
The friction coefficient in a pair was determined using the following formula (2):
f = , (2)
where N is the normal load for the pair, r is the nominal joint radius, T is the force of the spring dynamometer, l is a forces’ arm relative to the axis of rotation of the roller sample.
The wear intensity was determined using the following formula [9]:
J = , (3)
where h is the value of linear wear, L is the friction length.
Results of the experimental studies
The appearance of the sample and microsections after laser cladding are shown in Fig. 4.
The metallographic studies (Fig. 4b) revealed that the layer height during the high-speed cladding was 670–718 µm. The visual inspection, analysis of the obtained microsections, and dye penetrant inspection revealed no cracks or pores in the deposited layer. The mixing area between the base and deposited layers is minimal during the high-speed laser cladding process that is another advantage of the process under study. To determine the effect of the coating application method on the deposited layer microhardness, a study was conducted on the samples obtained by two types of technologies: a high-speed process (Fig. 5a) and a typical process (Fig. 5b). An analysis of the obtained dependencies determined that the deposited layer microhardness during the high-speed cladding was 630–680 HV0.3, while during the typical process it was 540–650 HV0.3. The obtained results allow us to conclude that, by changing the thermal cycle, this processing method has a significant effect not only on the microhardness distribution, but also on its minimum and maximum values.
An analysis of the adhesion strength test results for coatings obtained using the high-speed cladding and the base material, 38Cr2MoAlA steel, showed that the shear stresses were 600–690 and 432–440 MPa, respectively. The 1.5‑fold increase in the shear adhesion strength for the coatings obtained by high-speed cladding compared to the base material is due to both the superior mechanical properties of the coating and the altered properties of the steel’s surface layer as a result of laser beam heating above the critical austenite transition point and high-rate cooling during the transition to a martensitic structure with a small amount of retained austenite.
Table 3 shows the results of tribological tests of samples obtained using the high-speed laser cladding process, as well as the reference samples made from the base material without a deposited layer.
An analysis of the test results has demonstrated that the wear rates of coatings deposited according to the mode 1 (with a higher beam scanning speed) and to the mode 2 were 3.2 and 2.25 times lower, respectively, compared to the base material. The friction coefficients for the coatings deposited according to the modes 1 and 2 were significantly lower compared to the friction pair of 38Cr2MoAlA steel and Babbitt B83.
Conclusion
This paper presents the experimental results of high-speed laser machining in order to apply a surface layer and increase the wear resistance of contact areas of metal parts. Machining with a beam with a diameter of 1 mm to 3 mm made it possible to melt the metal powder and a thin surface layer to a depth of 40–60 μm in a single pass. When using a laser with a power of up to 6 kW, it was possible to achieve the high-speed cladding of metal parts with a layer thickness of 50–700 μm. The obtained results demonstrate the technological feasibility of applying coatings to the solids of rotation without any defects in the form of pores and cracks. The advantages of this coating application method, compared with the high-speed spraying and galvanic deposition, include the high adhesion strength of the deposited layer to the substrate (up to 690 MPa) and the wear resistance of the coatings that is 3, 2, and 2.25 times higher compared to the base material. The friction coefficients of the coatings were significantly lower than those obtained for the “steel-Babbitt” friction pair.
The high-speed laser cladding technology can be used for the standard lathes provided with the VPG Laserone LLC equipment. This enables not only mechanical processing but also the coating application in order to restore the original geometric shape of worn parts and improve the surface quality of new parts.
AUTHORS
Khriptovich Evgeny Vladimirovich, head of the laser cladding and heat treatment group, VPG Lazerone LLC; e-mail: eHriptovich@VPGlaserone.ru; Fryazino, Moscow region, Russia
ORCID 0000-0001-9935-1414
Biryukov Vladimir Pavlovich, leading researcher, Ph.D. in technical sciences, Institute of Machine Science of the Russian Academy of Sciences; e-mail: laser‑52@yandex.ru; Moscow, Russia
ORCID 0000-0001-9278-6925
Zakharov Aleksander Sergeevich, process engineer at VPG Lazerone LLC, Fryazino, Moscow region, Russia
ORCID 0009-0004-1581-8830
Bashlaev Vladimir Sergeevich, process engineer at VPG Lazerone LLC
ORCID 0009-0001-2517-6753
Myasnikov Daniil Vladimirovich, deputy director general for advanced research and development, VPG Lazerone LLC, e-mail: dMyasnikov@vpglaserone.ru; Fryazino, Moscow region, Russia
ORCID 0009-0008-2669-5484
Goryunov Yaroslav Alekseevich, junior researcher, Institute of Machine Science of the Russian Academy of Sciences, Moscow, Russia
ORCID 0009-0002-1614-0174
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