rus
Issue #4/2025
V. G. Protsenko, D. Anufriev, M. V. Kuznetsov, A. A. Popovich
Laser Cladding of Nozzle Blades Made of Cobalt Alloy MAR-M 509 Using the Laser Gas-Powder Cladding Method
Laser Cladding of Nozzle Blades Made of Cobalt Alloy MAR-M 509 Using the Laser Gas-Powder Cladding Method
DOI: 10.22184/1993-7296.FRos.2025.19.4.282.290
The articles indicates the parameters of laser gas-powder cladding mode to restore the
MAN TURBO engine nozzle blades made of
cobalt alloy MAR-M 509 using the domestic
powder EP648. The process measures to prevent
crack formation during the laser cladding are
described. Restoration of a series of nozzle
blades was performed using a robotized station
for laser direct deposition.
The articles indicates the parameters of laser gas-powder cladding mode to restore the
MAN TURBO engine nozzle blades made of
cobalt alloy MAR-M 509 using the domestic
powder EP648. The process measures to prevent
crack formation during the laser cladding are
described. Restoration of a series of nozzle
blades was performed using a robotized station
for laser direct deposition.
Laser Cladding of Nozzle Blades Made of Cobalt Alloy MAR-M 509 Using the Laser Gas-Powder Cladding Method
V. G. Protsenko, D. Anufriev, M. V. Kuznetsov, A. A. Popovich Peter the Great Saint-Petersburg Polytechnic University, Saint-Petersburg, Russia
The articles indicates the parameters of laser gas-powder cladding mode to restore the MAN TURBO engine nozzle blades made of cobalt alloy MAR-M 509 using the domestic powder EP648. The process measures to prevent crack formation during the laser cladding are described. Restoration of a series of nozzle blades was performed using a robotized station for laser direct deposition.
Key words: laser gas-powder cladding, gas turbine engine blades, welding stresses, metallographic analysis, Inconel 625
Article received: June 01, 2025
Article accepted: June 20, 2025
Introduction
The manufacture of gas turbine engine (GTE) blades involves the use of expensive materials and comprehensive technologies that significantly affects their cost. The turbine blades are critical parts that are used under severe operating conditions specified by the prolonged mechanical and thermal stress, high temperatures and corrosion. If the defects are found during the scheduled inspection, the blades are replaced due to the limited applicability or lack of repair methods. Replacement of the damaged blades with new ones significantly increases the turbine operating costs, so interest in the repair technologies in this area is constantly deepening.
The laser direct deposition (LDD) technologies are very promising in relation to the repair of gas turbine engine blades [1]. The essence of LDD technology is as follows: a high-power laser beam is focused on the surface of the part while developing a molten pool. The metal powder is fed into this area, melts, and forms a bead of deposited material. A robotic manipulator moves the optical head [2] with a nozzle installed for feeding the metal powder along a pre-selected route and according to a 3D model of the product being grown. Thus, the product is deposited on a layer upon layer basis.
The main advantage of these technologies is the high power density and local heating in the impact area that allows cladding of thin-walled trailing edges without generation of a large heat-affected zone. An important specification of laser radiation as a heat source is its process flexibility that allows working in the pulsed modes with wide ranges of pulse time and pause time values. Control of these parameters makes it possible to monitor the molten pool volume, the duration of metal stay above the critical temperatures, cooling rates, and, if necessary, allows separating the heating process from the melting process [3].
This article examines an example of the development and application of laser gas-powder cladding for restoration of the MAN TURBO engine 2nd stage nozzle blades.
Laser gas powder cladding technology
During the laser cladding process (Fig. 1), the base and filler metal are melted using the laser radiation 1. The metal of the part 8 that has undergone phase and structural transformations during cladding, generates a heat-affected zone 7. In this process, the metal powder is used as a filler metal. It melts, mixes with the base metal, and forms a molten pool 6. The powder is fed into the molten pool through the injectors 3 located in the nozzle 2. In this paper, a C4-12 nozzle was applied, with four injectors focusing the gas-powder mixture 4 at a distance of 12 mm from the nozzle end. The argon shielding gas 5 is fed from the nozzle through the axial channel.
After the molten metal crystallization, a bead is formed. Some of its main parameters includes width, side penetration and reinforcement. The required dimensions of the bead are set based on the geometric dimensions of the part, requirements for machining allowance and surface cleanliness.
Research equipment
The application of modes and works to restore a series of nozzle blades have been performed using a robotized station for laser direct deposition (RSLDD) (Fig. 2).
The modernized RSLDD includes the following equipment:
Robot Fanuc M‑20iA/20M;
Double-axis positioner Fanuc with a lifting capacity of 500 kg;
IPG ytterbium fiber laser with the power of 5 kW;
Powder feeder Oerlicon Twin 10 C;
Processing tool based on the FLW d30 laser head (IPG), including an adjustment unit (Saint-Petersburg Polytechnic University), a transition part (Saint-Petersburg Polytechnic University) and a C4–18 nozzle (Saint-Petersburg Polytechnic University);
An airtight chamber with a glove box, including the excess pressure generation and maintenance systems;
Process equipment with the ceramic heaters for preliminary and subsequent heating.
The RSLDD is designed for laser direct deposition and laser cladding in a controlled atmosphere. The cladding process automation ensures a minimum machining allowance.
Optimization of the cladding mode
Due to the need to restore thin-walled trailing edges with a thickness of 1 mm and parts with a compound section, a pulse mode was used for cladding. It has a larger number of parameters compared to the continuous mode that allows for a wide range of adjustments for the main parameters of the cladding process. In this case, the key function is the linear energy reduction that provides for a reduction in the residual longitudinal stresses in the weld. This is due to a change in the shape of temperature fields: the isotherms become more rounded, the ratio of the isotherm longitudinal axis to the transverse axis is decreased.
The metal heat-resistant nickel powder EP648 with a fraction of 40–200 μm was used as the adding material. The studies of mechanical properties of the samples obtained by the laser gas-powder cladding technology using a foreign analogue of EP648 have showed that the mechanical properties of deposited metal are close to the properties of cast alloys based on cobalt [4].
When optimizing the cladding mode, the results of papers [5, 6] were taken as a basis for varying the following parameters: laser radiation power P from 500 W to 1500 W, powder mass flow rate R from 3 to 7 g/min, pulse time Ti from 0.05 s to 1.5 s, pause time Tp from 0.1 s to 2 s, displacement along the x-axis from 0.8 to 1.2 mm, displacement along the z-axis from 0.2 to 0.5 mm; the distance to the head cut H has remained constant in all experiments. The cladding mode parameters that allow obtaining the high-quality formation are given in Table 1, the deposited layer section is shown in Fig. 3, the deposited layer appearance is shown in Fig. 4.
The deposited metal is generated by a columnar structure. During deposition, partial melting of the dendrite branches of the MAR-M 509 alloy occurs. It is well-known that the surface energy between the melt and two crystallites is greater than between two crystals, therefore, the solid phase nuclei are developed on the melted surfaces of the dendrites. The crystals are grown normally along the isothermal surface in the direction opposite to the heat removal. Continuous changes in the temperature gradient when the heat source is removed entails a continuous change in the crystallite growth direction. As a first approximation, it can be considered that the crystallite axes remain orthogonal to the surfaces of the crystallization front family. The change in the spatial orientation of the grains is visible on the deposited wall section (Fig. 5).
Due to the dissolution of carbides, the fusion line section has an increased hardness (Fig. 6). To reduce any residual stresses and decrease hardness in the fusion zone, stress-relief annealing was performed at a temperature of 650 °C for 2 hours [7].
To test the mechanical properties of the deposited metal, a series of cylindrical samples was prepared for static tensile testing according to GOST 1497-84, type IV, No. 8. The test was performed along and across the growth direction. The mechanical test results are given in Table 2. It is shown by the data given in Table 2 that the deposited material EP648 has high mechanical properties that allow it to be used for the restoration of blades.
Technological measures
to prevent crack formation during the laser cladding process
In an attempt to apply the optimized cladding method for the MAN TURBO engine 2nd stage nozzle blades, 2 types of cracks were formed (Fig. 7).
The main reason for their formation is welding deformations and stresses that occur as a result of casting shrinkage related to the decreased metal volume during crystallization and cooling [8] as well as due to the opening of microcracks occurred during operation (Fig. 8).
To reduce welding stresses and deformations, the following measures were taken:
Cleaning the surface layer of the blade metal in the area adjacent to the fusion line;
Pre-annealing at a temperature of 650 °C for 2 hours to relieve stresses that occur during operation;
Welding of an intermediate layer made of a material with the high plasticity Inconel 625;
Welding of stiffening ribs to reduce deformations;
Preheating and subsequent heating up to 300 °C to reduce the cooling rate in various areas of the welded joint;
Annealing to relieve stress after cladding at 650 °C for 2 hours.
The above measures have made it possible to prevent crack formation during the cladding process and subsequent heat treatment.
The preliminary and subsequent heating up to 300 °C was performed using the specialized equipment including the ceramic infrared emitters with a spherical radiating surface and a scattering angle of 75°. The total power of the emitters was 2 000 W. The heating temperature was controlled using an infrared non-contact thermometer. The blade was installed on a support located between two emitters (Fig. 9).
While using the above-described technological process, two series of nozzle blades in a total of 20 pieces were restored by the laser cladding. The first series successfully passed the controlled tests for 12 thousand hours as a part of a MAN TURBO engine and is still currently in use.
Conclusions
As a result of the works performed, the laser gas-powder cladding mode was optimized. Based on the metallographic analysis, it was found that the causes of cracks are microcracks in the surface layers that occurred in the metal during operation. During the thermal deformation cycle of cladding, the microcracks are opened up, while forming macrocracks. With due regard to the nature of their occurrence, a technology was developed that allows reducing the risk of cracks. 20 blades made of cobalt alloy MAR-M 509 were restored using the domestic powder EP648. The controlled tests were carried out, confirming the functional reliability of the blades restored by the laser gas-powder cladding process.
AUTHORS
Protsenko Vladimir G., engineer of the research laboratory “Laser and Additive Technologies”, Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: arc augmented laser hybrid welding, laser welding, additive technologies, laser cladding, direct laser deposition.
Anufriev Dmitry, Engineer of the Research Laboratory “Laser and Additive Technologies”, Research Laboratory “Laser and Additive Technologies”, Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: Laser additive technologies, direct laser deposition, laser and laser-arc welding, laser heat treatment; e-mail: dmitriyanufriyev23@yandex.ru.
ORCID: 0009-0005-5698-9625
Kuznetsov Mikhail V., Cand.of Technical Sciences, Head of the Research Laboratory “Laser and Additive Technologies”, Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: arc augmented laser hybrid welding, laser welding, additive technologies, laser cladding, direct laser deposition. E-mail: kuznetsov_mich@mail.ru.
ORCID: 0000-0002-9981-1078
Popovich Anatoly A., Doctor of Technical Sciences, professor, director of the Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: development of theoretical fundamentals and efficient technologies for obtaining powders of refractory compounds and related alloys in the conditions of high-temperature mechanochemical synthesis, development of new anode and cathode materials for lithium-ion polymer batteries, additive technologies.
ORCID: 0000-0002-5974-6654
CONFLICT OF INTEREST
The authors declare no conflict of interest. All authors contributed to the paper in accordance with the task distribution. The authors agree with the text.
V. G. Protsenko, D. Anufriev, M. V. Kuznetsov, A. A. Popovich Peter the Great Saint-Petersburg Polytechnic University, Saint-Petersburg, Russia
The articles indicates the parameters of laser gas-powder cladding mode to restore the MAN TURBO engine nozzle blades made of cobalt alloy MAR-M 509 using the domestic powder EP648. The process measures to prevent crack formation during the laser cladding are described. Restoration of a series of nozzle blades was performed using a robotized station for laser direct deposition.
Key words: laser gas-powder cladding, gas turbine engine blades, welding stresses, metallographic analysis, Inconel 625
Article received: June 01, 2025
Article accepted: June 20, 2025
Introduction
The manufacture of gas turbine engine (GTE) blades involves the use of expensive materials and comprehensive technologies that significantly affects their cost. The turbine blades are critical parts that are used under severe operating conditions specified by the prolonged mechanical and thermal stress, high temperatures and corrosion. If the defects are found during the scheduled inspection, the blades are replaced due to the limited applicability or lack of repair methods. Replacement of the damaged blades with new ones significantly increases the turbine operating costs, so interest in the repair technologies in this area is constantly deepening.
The laser direct deposition (LDD) technologies are very promising in relation to the repair of gas turbine engine blades [1]. The essence of LDD technology is as follows: a high-power laser beam is focused on the surface of the part while developing a molten pool. The metal powder is fed into this area, melts, and forms a bead of deposited material. A robotic manipulator moves the optical head [2] with a nozzle installed for feeding the metal powder along a pre-selected route and according to a 3D model of the product being grown. Thus, the product is deposited on a layer upon layer basis.
The main advantage of these technologies is the high power density and local heating in the impact area that allows cladding of thin-walled trailing edges without generation of a large heat-affected zone. An important specification of laser radiation as a heat source is its process flexibility that allows working in the pulsed modes with wide ranges of pulse time and pause time values. Control of these parameters makes it possible to monitor the molten pool volume, the duration of metal stay above the critical temperatures, cooling rates, and, if necessary, allows separating the heating process from the melting process [3].
This article examines an example of the development and application of laser gas-powder cladding for restoration of the MAN TURBO engine 2nd stage nozzle blades.
Laser gas powder cladding technology
During the laser cladding process (Fig. 1), the base and filler metal are melted using the laser radiation 1. The metal of the part 8 that has undergone phase and structural transformations during cladding, generates a heat-affected zone 7. In this process, the metal powder is used as a filler metal. It melts, mixes with the base metal, and forms a molten pool 6. The powder is fed into the molten pool through the injectors 3 located in the nozzle 2. In this paper, a C4-12 nozzle was applied, with four injectors focusing the gas-powder mixture 4 at a distance of 12 mm from the nozzle end. The argon shielding gas 5 is fed from the nozzle through the axial channel.
After the molten metal crystallization, a bead is formed. Some of its main parameters includes width, side penetration and reinforcement. The required dimensions of the bead are set based on the geometric dimensions of the part, requirements for machining allowance and surface cleanliness.
Research equipment
The application of modes and works to restore a series of nozzle blades have been performed using a robotized station for laser direct deposition (RSLDD) (Fig. 2).
The modernized RSLDD includes the following equipment:
Robot Fanuc M‑20iA/20M;
Double-axis positioner Fanuc with a lifting capacity of 500 kg;
IPG ytterbium fiber laser with the power of 5 kW;
Powder feeder Oerlicon Twin 10 C;
Processing tool based on the FLW d30 laser head (IPG), including an adjustment unit (Saint-Petersburg Polytechnic University), a transition part (Saint-Petersburg Polytechnic University) and a C4–18 nozzle (Saint-Petersburg Polytechnic University);
An airtight chamber with a glove box, including the excess pressure generation and maintenance systems;
Process equipment with the ceramic heaters for preliminary and subsequent heating.
The RSLDD is designed for laser direct deposition and laser cladding in a controlled atmosphere. The cladding process automation ensures a minimum machining allowance.
Optimization of the cladding mode
Due to the need to restore thin-walled trailing edges with a thickness of 1 mm and parts with a compound section, a pulse mode was used for cladding. It has a larger number of parameters compared to the continuous mode that allows for a wide range of adjustments for the main parameters of the cladding process. In this case, the key function is the linear energy reduction that provides for a reduction in the residual longitudinal stresses in the weld. This is due to a change in the shape of temperature fields: the isotherms become more rounded, the ratio of the isotherm longitudinal axis to the transverse axis is decreased.
The metal heat-resistant nickel powder EP648 with a fraction of 40–200 μm was used as the adding material. The studies of mechanical properties of the samples obtained by the laser gas-powder cladding technology using a foreign analogue of EP648 have showed that the mechanical properties of deposited metal are close to the properties of cast alloys based on cobalt [4].
When optimizing the cladding mode, the results of papers [5, 6] were taken as a basis for varying the following parameters: laser radiation power P from 500 W to 1500 W, powder mass flow rate R from 3 to 7 g/min, pulse time Ti from 0.05 s to 1.5 s, pause time Tp from 0.1 s to 2 s, displacement along the x-axis from 0.8 to 1.2 mm, displacement along the z-axis from 0.2 to 0.5 mm; the distance to the head cut H has remained constant in all experiments. The cladding mode parameters that allow obtaining the high-quality formation are given in Table 1, the deposited layer section is shown in Fig. 3, the deposited layer appearance is shown in Fig. 4.
The deposited metal is generated by a columnar structure. During deposition, partial melting of the dendrite branches of the MAR-M 509 alloy occurs. It is well-known that the surface energy between the melt and two crystallites is greater than between two crystals, therefore, the solid phase nuclei are developed on the melted surfaces of the dendrites. The crystals are grown normally along the isothermal surface in the direction opposite to the heat removal. Continuous changes in the temperature gradient when the heat source is removed entails a continuous change in the crystallite growth direction. As a first approximation, it can be considered that the crystallite axes remain orthogonal to the surfaces of the crystallization front family. The change in the spatial orientation of the grains is visible on the deposited wall section (Fig. 5).
Due to the dissolution of carbides, the fusion line section has an increased hardness (Fig. 6). To reduce any residual stresses and decrease hardness in the fusion zone, stress-relief annealing was performed at a temperature of 650 °C for 2 hours [7].
To test the mechanical properties of the deposited metal, a series of cylindrical samples was prepared for static tensile testing according to GOST 1497-84, type IV, No. 8. The test was performed along and across the growth direction. The mechanical test results are given in Table 2. It is shown by the data given in Table 2 that the deposited material EP648 has high mechanical properties that allow it to be used for the restoration of blades.
Technological measures
to prevent crack formation during the laser cladding process
In an attempt to apply the optimized cladding method for the MAN TURBO engine 2nd stage nozzle blades, 2 types of cracks were formed (Fig. 7).
The main reason for their formation is welding deformations and stresses that occur as a result of casting shrinkage related to the decreased metal volume during crystallization and cooling [8] as well as due to the opening of microcracks occurred during operation (Fig. 8).
To reduce welding stresses and deformations, the following measures were taken:
Cleaning the surface layer of the blade metal in the area adjacent to the fusion line;
Pre-annealing at a temperature of 650 °C for 2 hours to relieve stresses that occur during operation;
Welding of an intermediate layer made of a material with the high plasticity Inconel 625;
Welding of stiffening ribs to reduce deformations;
Preheating and subsequent heating up to 300 °C to reduce the cooling rate in various areas of the welded joint;
Annealing to relieve stress after cladding at 650 °C for 2 hours.
The above measures have made it possible to prevent crack formation during the cladding process and subsequent heat treatment.
The preliminary and subsequent heating up to 300 °C was performed using the specialized equipment including the ceramic infrared emitters with a spherical radiating surface and a scattering angle of 75°. The total power of the emitters was 2 000 W. The heating temperature was controlled using an infrared non-contact thermometer. The blade was installed on a support located between two emitters (Fig. 9).
While using the above-described technological process, two series of nozzle blades in a total of 20 pieces were restored by the laser cladding. The first series successfully passed the controlled tests for 12 thousand hours as a part of a MAN TURBO engine and is still currently in use.
Conclusions
As a result of the works performed, the laser gas-powder cladding mode was optimized. Based on the metallographic analysis, it was found that the causes of cracks are microcracks in the surface layers that occurred in the metal during operation. During the thermal deformation cycle of cladding, the microcracks are opened up, while forming macrocracks. With due regard to the nature of their occurrence, a technology was developed that allows reducing the risk of cracks. 20 blades made of cobalt alloy MAR-M 509 were restored using the domestic powder EP648. The controlled tests were carried out, confirming the functional reliability of the blades restored by the laser gas-powder cladding process.
AUTHORS
Protsenko Vladimir G., engineer of the research laboratory “Laser and Additive Technologies”, Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: arc augmented laser hybrid welding, laser welding, additive technologies, laser cladding, direct laser deposition.
Anufriev Dmitry, Engineer of the Research Laboratory “Laser and Additive Technologies”, Research Laboratory “Laser and Additive Technologies”, Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: Laser additive technologies, direct laser deposition, laser and laser-arc welding, laser heat treatment; e-mail: dmitriyanufriyev23@yandex.ru.
ORCID: 0009-0005-5698-9625
Kuznetsov Mikhail V., Cand.of Technical Sciences, Head of the Research Laboratory “Laser and Additive Technologies”, Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: arc augmented laser hybrid welding, laser welding, additive technologies, laser cladding, direct laser deposition. E-mail: kuznetsov_mich@mail.ru.
ORCID: 0000-0002-9981-1078
Popovich Anatoly A., Doctor of Technical Sciences, professor, director of the Institute of Mechanical Engineering, Materials and Transport, Federal Autonomous Educational Institution of Higher Education “Peter the Great St. Petersburg Polytechnic University”, Saint-Petersburg, Russia. Area of expertise: development of theoretical fundamentals and efficient technologies for obtaining powders of refractory compounds and related alloys in the conditions of high-temperature mechanochemical synthesis, development of new anode and cathode materials for lithium-ion polymer batteries, additive technologies.
ORCID: 0000-0002-5974-6654
CONFLICT OF INTEREST
The authors declare no conflict of interest. All authors contributed to the paper in accordance with the task distribution. The authors agree with the text.
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