rus
Issue #2/2021
V. P. Biryukov
Enhancement the Wear Resistance of Parts and Tillage Tools in Agricultural Machinery by Laser Cladding
Enhancement the Wear Resistance of Parts and Tillage Tools in Agricultural Machinery by Laser Cladding
DOI: 10.22184/1993-7296.FRos.2021.15.2.132.142
The paper presents the results of metallographic and tribological studies of coatings with the addition of ultrafine titanium carbide powder to the multicomponent charge. With the help of a full factorial experiment, the geometric parameters of the cladded coating were determined depending on the power, processing speed and the diameter of the laser beam. Regularities of the change in the friction coefficients on pressure and sliding speed have been obtained. Scuff resistance and wear resistance of coatings is higher than hardened steels.
The paper presents the results of metallographic and tribological studies of coatings with the addition of ultrafine titanium carbide powder to the multicomponent charge. With the help of a full factorial experiment, the geometric parameters of the cladded coating were determined depending on the power, processing speed and the diameter of the laser beam. Regularities of the change in the friction coefficients on pressure and sliding speed have been obtained. Scuff resistance and wear resistance of coatings is higher than hardened steels.
Теги: abrasion resistance agricultural machinery cladded coating fiber lasers friction coefficient laser cladding scuff resistance wear resistance волоконные лазеры задиристость износостойкость коэффициент трения лазерная наплавка наплавочные покрытия сельскохозяйственная техника
Enhancement the Wear Resistance of Parts and Tillage Tools in Agricultural Machinery by Laser Cladding
V. P. Biryukov
Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN)
Moscow, Russia
The paper presents the results of metallographic and tribological studies of coatings with the addition of ultrafine titanium carbide powder to the multicomponent charge. With the help of a full factorial experiment, the geometric parameters of the cladded coating were determined depending on the power, processing speed and the diameter of the laser beam. Regularities of the change in the friction coefficients on pressure and sliding speed have been obtained. Scuff resistance and wear resistance of coatings is higher than hardened steels.
Keywords: Laser cladding, Fiber lasers, Cladded coating, Agricultural machinery, Friction coefficient, Scuff Resistance, Wear Resistance, Abrasion Resistance
Received: 06.03.2021
Accepted: 30.03.2021
Introduction
Increasing the service life of parts and friction units of agricultural machinery is an urgent task. In most cases, traditional structural materials and heat treatment technologies are inferior in wear resistance to new hardening technologies and coatings using concentrated energy sources, in particular, high-power lasers. As a cladding material [1], a spherical nickel-based alloy powder (Ni-Cr-B-Si-Fe-C) with a particle size of 50–150 μm was used. Laser cladding was performed on 316L stainless steel samples with an RFL–C3300 fiber laser (Raycus, Wuhan, China) using a DPSF‑2 powder feeder. The treatment was carried out at a radiation power of 1.8 kW, a spot diameter of 4 mm, and a travel speed of 5 mm / s. Friction and wear tests were carried out according to the ball (Al2O3 10 mm in diameter) – plane (deposited sample or base) scheme in accordance with ASTM G99–05 standard on a UMT‑2 friction machine. The friction path was 18 m at a sliding speed of 10 mm / s. The average microhardness of single-layer and three-layer coatings was 593 and 640 HV0.2, respectively, which is almost 2.5 times higher than that of the 316L substrate (about 250 HV0.2). The three-layer coating had the greatest wear resistance.
Ni-Cr-B-Si [2] coatings were deposited with a fiber laser source with a coaxial powder nozzle on an AISI 1020 mild steel substrate. Abrasion tests carried out according to ASTM G65. Better tribological characteristics were obtained for coatings with fewer cold cracks and a higher volume fraction of carbides.
The influence of the laser power 1500–1900 W, spot diameter 3–5 mm and beam scanning speed 2–4 mm / s on the geometric parameters, microhardness and wear resistance of the deposited Ni-Cr-B-Si coating on 42CrMo steel samples was determined [3]. The microhardness of the deposited layers varied within 520–690 HV. The width, height of the cladding tracks and the penetration depth were 1.47–1.8, 3.57–4.23 and 0.52–1.44 mm, respectively. The results obtained showed that the laser power was the main factor affecting the coating height. The spot diameter had the greatest effect on the width of a single ridge. The scan speed had a significant effect on the depth of the molten bath. The laser power showed the greatest influence on the microhardness and wear resistance of the coating. The wear mechanism of the coating is abrasive and adhesive.
Laser cladding of Ni-Cr and Ni-Cr-TiC powders on AISI 420 steel was carried out with a pulsed Nd : YAG laser with simultaneous powder supply [4]. The influence of the powder feed rate, the radiation power and the beam scanning speed, the influence of each parameter on the laser cladding process was investigated, and the optimal parameters of the laser cladding were selected. It was found that the weight loss of the Ni-Cr-TiC composite coating is less than that of the Ni-Cr and steel substrate.
Fe-WC coatings on mild steel are obtained by laser cladding using a disk laser [5]. The processing was carried out at a laser beam power of 600, 700, and 800 W. The beam scanning speed was the same for all coatings and amounted to 600 mm / min. The spot diameter was 1.64 mm. Two modes of powder feeding were used, 6.25 g / min and 12.5 g / min. The highest microhardness and corrosion resistance were observed for coatings obtained at a powder flow rate of 12.5 g / min.
To obtain coatings from Stellite‑6 / WC powder, a Yb : YAG disk laser with a nominal power of 1 kW was used [6]. The coatings were applied to B27 boron steel. The treatment was carried out at a laser beam power of 550 W, a feed rate of 400 mm / min, and a powder flow rate of 10 g / min. It was found that Stellite‑6 / WC coatings contributed to an increase in the durability of agricultural implements used for soil cultivation.
Nickel (Ni) based alloy powders with different cobalt (Co) contents were applied to the surface of a 42CrMo steel substrate using a fiber laser [7]. With an increase in the Co content, the amount of carbides and borides M7 (C, B) 3, M23 (C, B) 6, and M2B gradually decreases. The microhardness decreases, but the wear resistance of the deposited layer gradually increases with an increase in the Co content. The wear resistance of the NiCo30 layer is 3.6 times higher than that of the NiCo00 layer. The wear resistance of the NiCo30 layer is 3.6 times higher than that of the NiCo00 layer. With an increase in Co content, the wear mechanism of the coating changes from abrasive to adhesive.
Laser cladding of iron-based powders Fe-Cr-Ni-Mo-Mn-C-Si was performed on AISI 4130 steel [8]. The coatings had high wear resistance and corrosion resistance. The microstructure mainly consisted of dendrites and eutectic phases such as (γ + α)-Fe and Fe-Cr(Ni) solid solution. Fe-based coatings had lower coefficients of friction than the substrate and the main wear mechanism was moderate abrasive wear.
A nickel-based coating was applied to the surface of 42CrMo steel using a 6 kW fiber laser [9]. The addition of Mo powder resulted in a crack-free composite coating. The main phases of the Ni45 + 10% Mo laser cladding layer are (Fe, Ni), Cr23C6, Cr3C2, Mo2FeB2 and Cr2B3. Composite coating Ni45 + 10% Mo had wear resistance 1.7 times higher than that of Ni45 coating and 2.4 times higher than that of 42CrMo steel.
The influence of processing parameters on the microhardness and wear resistance of an alloy based on Ni and titanium carbide (TiC) was investigated [10]. The results show that microhardness correlates with laser power and TiC powder additives. The amount of wear decreased with an increase in the proportion of TiC powder. The optimum machining parameter was a coating hardness of 62 HRC to obtain minimal volumetric wear.
The objectives of the work are to determine the parameters of the laser cladding zones and the tribological characteristics of multicomponent coatings when an ultradispersed titanium carbide powder is introduced into the charge.
Equipment and research methods
In experimental studies, the IMASH RAS laser system was used. Samples were made from steels 45 (490–525HV), 65G (570–625HV) with dimensions 15 × 20 × 70 mm. For the manufacture of the charge, powders based on iron (Fe-Cr-B-Si) and nickel (Ni-Cr-B-Si) in a ratio of 3: 1, respectively, with a particle size of 40–150 microns were selected. Powder of ultrafine titanium carbide TiC 5 and 10 wt.% Was added to the charge with a particle size of 0.5–5 microns. Slip coatings were applied with a thickness of 0.67–0.8 mm. An aqueous solution of hydroxyethyl cellulose was used as a binder. Metallographic studies of the cladded coating were carried out on a PMT‑3 microhardness tester at a load of 0.98 N, an Altami MET 1C metallographic microscope, and an AM417 digital microscope. The structure and chemical composition of the deposited layers were investigated using a TESCAN VEGA 3 SBH scanning electron microscope with an energy dispersive analysis system using reflected and secondary electron modes. To determine the tribological characteristics of the deposited samples, a test was carried out at normal temperature according to the plane (deposited sample) – ring (steel ШХ15, 60–62 steel) scheme. The sliding speed and pressure on the sample varied discretely in the range 0.25–3.5 m / s and 1–6 MPa, respectively. M10G2 oil was used as a lubricant. Abrasive wear tests were carried out according to the disk-plane scheme. A flat sample with a deposited coating with a load of 15 N was pressed against a rotating rubber disk. Quartz sand with a particle size of 200–600 microns was used as an abrasive. The test duration was 10 minutes.
The radiation power P=700–1000 W, the processing speed V=7–10 mm / s, and the beam diameter d=2.5–3.5 mm were chosen as the variable parameters. Scanning of the beam with a fixed frequency f=217 Hz was considered as an additional factor. To construct mathematical models when performing a full factorial experiment (FFE), the height H and width B of the deposited beads were considered as responses of the system. Table shows the levels of experimental factors.
Since PFE 23 was performed, the number of experiments was 8 for each series.
The regression equation is:
y = b0 + b1x1 + b2x2 + b3x3 +
+ b13x1x3 + b13x1x3 + b23x2x3 + b123x1x2x3, (1)
where: y – system response;
xi – levels of factors;
b – coefficients of the regression equation.
Experimental research results
Laser cladding of the samples was carried out in optimal modes with a defocused beam and with transverse oscillations of the beam along the normal to the laser processing speed vector. The microhardness of the cladded coating was (Fe-Cr-B-Si, Ni-Cr-B-Si), (Fe-Cr-B-Si, Ni-Cr-B-Si + 5 wt% TiC), (Fe-Cr- B-Si, Ni-Cr-B-Si + 10 wt% TiC) – 792–920, 870–998, 960–1270 HV. Fig. 1 (a, b) shows microsections of deposited tracks with an ultrafine titanium carbide content of 10 wt.% with dimensions 0.77 × 2.04 mm, and 0.79 × 4.26 mm, obtained by a defocused beam and a beam scanning at a frequency of 217 Hz, respectively.
The penetration zone of the base during processing with a defocused beam and a scanning beam was 174 and 56 μm, respectively, which indicates a high adhesion strength of the coating. The dimensions of the disordered blocks of the structure were 3–5 µm. The cross-sectional area of a single deposited layer when scanning the beam is 2.16 times larger than when cladding with a defocused beam.
The equation for determining the height of the roller without scanning, H, is:
H = 0,695 + 0,035x1 – 0,0725x2 + 0,0075x1 x2 +
+ 0,0125x1 x3 – 0,01x2 x3 + 0,01x1 x2 x3. (2)
Bead height when cladding with transverse beam vibrations, Hc:
Hс = 0,70125 + 0,03125x1 – 0,04625x2 + 0,00875x3 +
+ 0,01875x1 x3 + 0,01625x2 x3 + 0,00125x1 x2 x3. (3)
Width of the deposited bead without beam scanning, B:
В = 1,87375 + 0,11625x1 – 0,09375x2 + 0,06125x3 –
– 0,02125x1 x2 + 0,00375x2 x3 – 0,00875x1 x2 x3. (4)
Width of deposited beads with transverse oscillations of the beam Bc:
Bс = 4,34625 + 0,43375x1 – 0,26875x2 + 0,11625x3 –
– 0,26625x1 x2 – 0,03875x2 x3 + 0,02375x1 x2 x3. (5)
Calculations were carried out according to the regression equations (2–5), which were compared with the results of the experiment. The calculated values differ from the actual values of the depth and width of the hardening zones by no more than 2.98%.
For dependences of the type H (P, V), B (P, V), comparative surfaces were constructed using the MsExcel program (Fig. 2) with a spot diameter of 2.5 mm.
The radiation power has the greatest influence on the geometrical parameters of the deposited beads. With increasing power, the width and height of the welded tracks grow. With increasing travel speed, the depth and width of the rollers decreases. With an increase in the diameter of the laser radiation, the height and width of the rollers increase.
The dependence of the friction coefficients of steel 45 in the hardened state and cladded coatingis shown in Fig. 3. One of the most important characteristics of friction units is a low coefficient of friction, which affects the indicators of fuel and lubricant consumption during the operation of agricultural machinery. As a rule, friction pairs with a low coefficient of friction have a higher seizure load. With an increase in the load from 1.2 to 4.0 MPa on hardened samples of steel 45, the friction coefficient decreases from 0.11 and 0.09. With a further increase in the load for the improved specimen, the coefficient of friction increases. The coefficient of friction for a multicomponent coating varies in the range of 0.04–0.05. The minimum friction coefficient of 0.018–0.025 was obtained on a coating with additives of 10 wt.% of TiC ultrafine powder. With an increase in the sliding speed (Fig. 3, b) from 0.25 to 1.3 m / s, with a load of 2.0 MPa, the friction coefficient for steel 45 decreases from 0.11 to 0.092. With a further increase in speed to 1.6 m / s, it increases slightly. For cladded coatingin the range of 0.6–1.6 m / s, the friction coefficient increases smoothly.
Fig. 4 shows the regularities of the change in the seizing load from the sliding speed. Hardened samples of steel 45 are inferior to deposited multicomponent coatings and with the addition of ultrafine titanium carbide powder. At a pressure of 5.5 MPa, jamming occurs at a rate 1.6–3 times lower for a hardened sample of steel 45, in comparison with cladding with a multicomponent coating and with 10 TiC mass additives.% respectively.
In fig. 5. Shown are the wear rates of hardened specimens of steel 45 and deposited coatings. Wear resistance, which is the reciprocal of the wear rate, increases for many component coatings by 1.4 times as compared to hardened steel 45 and by 2.4 and 3 times as compared to the addition of 5 and 10 wt% TiC ultrafine powder to the charge, respectively.
Tests for abrasive wear during friction with a loose abrasive grain of samples of hardened steel 65G and with coatings deposited on it (Fe-Cr-B-Si, Ni-Cr-B-Si), (Fe-Cr-B-Si, Ni-Cr- B-Si) + 5 TiC mass%, (Fe-Cr-B-Si, Ni-Cr-B-Si) + 10 TiC mass% showed that the weight loss of the samples was 0.064 ∙ 10–4, 0.046 ∙ 10–4, 0.033 ∙ 10–4 and 0.029 ∙ 10–4 kg, respectively.
Discussion of the results
The results obtained in the work show that an increase in the reliability of parts of the main units and working bodies of agricultural machinery is possible with the use of new modern technologies for applying coatings with high performance characteristics, which have a significant impact on the durability of agricultural machinery products.
Laser cladding of multicomponent coatings, and with the addition of ultradispersed titanium carbide powder, can be used for the restoration of worn camshafts and crankshafts, piston pins, shaft seats for rolling bearings and other parts of agricultural machinery. Furthermore, this technology can be used to increase the wear resistance of tillage implements, plowshares, disc harrows, cultivator paws, which are made of 45 and 65G steels. Losses on idle time of agricultural machines during the period of seasonal field work associated with harvesting and cultivation of agricultural crops lead to significant economic costs.
The effect of self-sharpening of the cutting edge is of great importance for the effective operation of the tines of cultivators and disc harrows. The use of laser cladding technology with multicomponent materials with the addition of ultradispersed titanium carbide powder with a layer thickness of 0.5–0.8 mm practically does not change the geometry of the cutting edges and at the same time ensures self-sharpening of tools. The introduction of a nickel-based powder into the composition of the charge will significantly increase the corrosion resistance of the coatings.
Conclusion
The technology of laser cladding of multicomponent coatings with additions of ultrafine powder of titanium carbide 5 and 10 wt.% Has been developed. The wear resistance of the coatings is 1.4 times higher than that of hardened steel 45 and 2.4 and 3 times higher than the addition of 5 and 10 wt% TiC to the charge, respectively. At a sliding speed of 2.5 m / s, the seizing pressure of cladded coating with nano carbides was 1.8–2.5 times higher than that of hardened steel 45. Coatings with ultradispersed carbides had friction coefficients of 0.018–0.033. The abrasive wear resistance of the coating with 10 wt% TiC is 2.2 times higher than the hardened steel 65G.
ABOUT AUTHOR
Biryukov Vladimir, Candidate of Technical Sciences, laser‑52@yandex.ru, Senior Researcher, Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN), Moscow, Russia
V. P. Biryukov
Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN)
Moscow, Russia
The paper presents the results of metallographic and tribological studies of coatings with the addition of ultrafine titanium carbide powder to the multicomponent charge. With the help of a full factorial experiment, the geometric parameters of the cladded coating were determined depending on the power, processing speed and the diameter of the laser beam. Regularities of the change in the friction coefficients on pressure and sliding speed have been obtained. Scuff resistance and wear resistance of coatings is higher than hardened steels.
Keywords: Laser cladding, Fiber lasers, Cladded coating, Agricultural machinery, Friction coefficient, Scuff Resistance, Wear Resistance, Abrasion Resistance
Received: 06.03.2021
Accepted: 30.03.2021
Introduction
Increasing the service life of parts and friction units of agricultural machinery is an urgent task. In most cases, traditional structural materials and heat treatment technologies are inferior in wear resistance to new hardening technologies and coatings using concentrated energy sources, in particular, high-power lasers. As a cladding material [1], a spherical nickel-based alloy powder (Ni-Cr-B-Si-Fe-C) with a particle size of 50–150 μm was used. Laser cladding was performed on 316L stainless steel samples with an RFL–C3300 fiber laser (Raycus, Wuhan, China) using a DPSF‑2 powder feeder. The treatment was carried out at a radiation power of 1.8 kW, a spot diameter of 4 mm, and a travel speed of 5 mm / s. Friction and wear tests were carried out according to the ball (Al2O3 10 mm in diameter) – plane (deposited sample or base) scheme in accordance with ASTM G99–05 standard on a UMT‑2 friction machine. The friction path was 18 m at a sliding speed of 10 mm / s. The average microhardness of single-layer and three-layer coatings was 593 and 640 HV0.2, respectively, which is almost 2.5 times higher than that of the 316L substrate (about 250 HV0.2). The three-layer coating had the greatest wear resistance.
Ni-Cr-B-Si [2] coatings were deposited with a fiber laser source with a coaxial powder nozzle on an AISI 1020 mild steel substrate. Abrasion tests carried out according to ASTM G65. Better tribological characteristics were obtained for coatings with fewer cold cracks and a higher volume fraction of carbides.
The influence of the laser power 1500–1900 W, spot diameter 3–5 mm and beam scanning speed 2–4 mm / s on the geometric parameters, microhardness and wear resistance of the deposited Ni-Cr-B-Si coating on 42CrMo steel samples was determined [3]. The microhardness of the deposited layers varied within 520–690 HV. The width, height of the cladding tracks and the penetration depth were 1.47–1.8, 3.57–4.23 and 0.52–1.44 mm, respectively. The results obtained showed that the laser power was the main factor affecting the coating height. The spot diameter had the greatest effect on the width of a single ridge. The scan speed had a significant effect on the depth of the molten bath. The laser power showed the greatest influence on the microhardness and wear resistance of the coating. The wear mechanism of the coating is abrasive and adhesive.
Laser cladding of Ni-Cr and Ni-Cr-TiC powders on AISI 420 steel was carried out with a pulsed Nd : YAG laser with simultaneous powder supply [4]. The influence of the powder feed rate, the radiation power and the beam scanning speed, the influence of each parameter on the laser cladding process was investigated, and the optimal parameters of the laser cladding were selected. It was found that the weight loss of the Ni-Cr-TiC composite coating is less than that of the Ni-Cr and steel substrate.
Fe-WC coatings on mild steel are obtained by laser cladding using a disk laser [5]. The processing was carried out at a laser beam power of 600, 700, and 800 W. The beam scanning speed was the same for all coatings and amounted to 600 mm / min. The spot diameter was 1.64 mm. Two modes of powder feeding were used, 6.25 g / min and 12.5 g / min. The highest microhardness and corrosion resistance were observed for coatings obtained at a powder flow rate of 12.5 g / min.
To obtain coatings from Stellite‑6 / WC powder, a Yb : YAG disk laser with a nominal power of 1 kW was used [6]. The coatings were applied to B27 boron steel. The treatment was carried out at a laser beam power of 550 W, a feed rate of 400 mm / min, and a powder flow rate of 10 g / min. It was found that Stellite‑6 / WC coatings contributed to an increase in the durability of agricultural implements used for soil cultivation.
Nickel (Ni) based alloy powders with different cobalt (Co) contents were applied to the surface of a 42CrMo steel substrate using a fiber laser [7]. With an increase in the Co content, the amount of carbides and borides M7 (C, B) 3, M23 (C, B) 6, and M2B gradually decreases. The microhardness decreases, but the wear resistance of the deposited layer gradually increases with an increase in the Co content. The wear resistance of the NiCo30 layer is 3.6 times higher than that of the NiCo00 layer. The wear resistance of the NiCo30 layer is 3.6 times higher than that of the NiCo00 layer. With an increase in Co content, the wear mechanism of the coating changes from abrasive to adhesive.
Laser cladding of iron-based powders Fe-Cr-Ni-Mo-Mn-C-Si was performed on AISI 4130 steel [8]. The coatings had high wear resistance and corrosion resistance. The microstructure mainly consisted of dendrites and eutectic phases such as (γ + α)-Fe and Fe-Cr(Ni) solid solution. Fe-based coatings had lower coefficients of friction than the substrate and the main wear mechanism was moderate abrasive wear.
A nickel-based coating was applied to the surface of 42CrMo steel using a 6 kW fiber laser [9]. The addition of Mo powder resulted in a crack-free composite coating. The main phases of the Ni45 + 10% Mo laser cladding layer are (Fe, Ni), Cr23C6, Cr3C2, Mo2FeB2 and Cr2B3. Composite coating Ni45 + 10% Mo had wear resistance 1.7 times higher than that of Ni45 coating and 2.4 times higher than that of 42CrMo steel.
The influence of processing parameters on the microhardness and wear resistance of an alloy based on Ni and titanium carbide (TiC) was investigated [10]. The results show that microhardness correlates with laser power and TiC powder additives. The amount of wear decreased with an increase in the proportion of TiC powder. The optimum machining parameter was a coating hardness of 62 HRC to obtain minimal volumetric wear.
The objectives of the work are to determine the parameters of the laser cladding zones and the tribological characteristics of multicomponent coatings when an ultradispersed titanium carbide powder is introduced into the charge.
Equipment and research methods
In experimental studies, the IMASH RAS laser system was used. Samples were made from steels 45 (490–525HV), 65G (570–625HV) with dimensions 15 × 20 × 70 mm. For the manufacture of the charge, powders based on iron (Fe-Cr-B-Si) and nickel (Ni-Cr-B-Si) in a ratio of 3: 1, respectively, with a particle size of 40–150 microns were selected. Powder of ultrafine titanium carbide TiC 5 and 10 wt.% Was added to the charge with a particle size of 0.5–5 microns. Slip coatings were applied with a thickness of 0.67–0.8 mm. An aqueous solution of hydroxyethyl cellulose was used as a binder. Metallographic studies of the cladded coating were carried out on a PMT‑3 microhardness tester at a load of 0.98 N, an Altami MET 1C metallographic microscope, and an AM417 digital microscope. The structure and chemical composition of the deposited layers were investigated using a TESCAN VEGA 3 SBH scanning electron microscope with an energy dispersive analysis system using reflected and secondary electron modes. To determine the tribological characteristics of the deposited samples, a test was carried out at normal temperature according to the plane (deposited sample) – ring (steel ШХ15, 60–62 steel) scheme. The sliding speed and pressure on the sample varied discretely in the range 0.25–3.5 m / s and 1–6 MPa, respectively. M10G2 oil was used as a lubricant. Abrasive wear tests were carried out according to the disk-plane scheme. A flat sample with a deposited coating with a load of 15 N was pressed against a rotating rubber disk. Quartz sand with a particle size of 200–600 microns was used as an abrasive. The test duration was 10 minutes.
The radiation power P=700–1000 W, the processing speed V=7–10 mm / s, and the beam diameter d=2.5–3.5 mm were chosen as the variable parameters. Scanning of the beam with a fixed frequency f=217 Hz was considered as an additional factor. To construct mathematical models when performing a full factorial experiment (FFE), the height H and width B of the deposited beads were considered as responses of the system. Table shows the levels of experimental factors.
Since PFE 23 was performed, the number of experiments was 8 for each series.
The regression equation is:
y = b0 + b1x1 + b2x2 + b3x3 +
+ b13x1x3 + b13x1x3 + b23x2x3 + b123x1x2x3, (1)
where: y – system response;
xi – levels of factors;
b – coefficients of the regression equation.
Experimental research results
Laser cladding of the samples was carried out in optimal modes with a defocused beam and with transverse oscillations of the beam along the normal to the laser processing speed vector. The microhardness of the cladded coating was (Fe-Cr-B-Si, Ni-Cr-B-Si), (Fe-Cr-B-Si, Ni-Cr-B-Si + 5 wt% TiC), (Fe-Cr- B-Si, Ni-Cr-B-Si + 10 wt% TiC) – 792–920, 870–998, 960–1270 HV. Fig. 1 (a, b) shows microsections of deposited tracks with an ultrafine titanium carbide content of 10 wt.% with dimensions 0.77 × 2.04 mm, and 0.79 × 4.26 mm, obtained by a defocused beam and a beam scanning at a frequency of 217 Hz, respectively.
The penetration zone of the base during processing with a defocused beam and a scanning beam was 174 and 56 μm, respectively, which indicates a high adhesion strength of the coating. The dimensions of the disordered blocks of the structure were 3–5 µm. The cross-sectional area of a single deposited layer when scanning the beam is 2.16 times larger than when cladding with a defocused beam.
The equation for determining the height of the roller without scanning, H, is:
H = 0,695 + 0,035x1 – 0,0725x2 + 0,0075x1 x2 +
+ 0,0125x1 x3 – 0,01x2 x3 + 0,01x1 x2 x3. (2)
Bead height when cladding with transverse beam vibrations, Hc:
Hс = 0,70125 + 0,03125x1 – 0,04625x2 + 0,00875x3 +
+ 0,01875x1 x3 + 0,01625x2 x3 + 0,00125x1 x2 x3. (3)
Width of the deposited bead without beam scanning, B:
В = 1,87375 + 0,11625x1 – 0,09375x2 + 0,06125x3 –
– 0,02125x1 x2 + 0,00375x2 x3 – 0,00875x1 x2 x3. (4)
Width of deposited beads with transverse oscillations of the beam Bc:
Bс = 4,34625 + 0,43375x1 – 0,26875x2 + 0,11625x3 –
– 0,26625x1 x2 – 0,03875x2 x3 + 0,02375x1 x2 x3. (5)
Calculations were carried out according to the regression equations (2–5), which were compared with the results of the experiment. The calculated values differ from the actual values of the depth and width of the hardening zones by no more than 2.98%.
For dependences of the type H (P, V), B (P, V), comparative surfaces were constructed using the MsExcel program (Fig. 2) with a spot diameter of 2.5 mm.
The radiation power has the greatest influence on the geometrical parameters of the deposited beads. With increasing power, the width and height of the welded tracks grow. With increasing travel speed, the depth and width of the rollers decreases. With an increase in the diameter of the laser radiation, the height and width of the rollers increase.
The dependence of the friction coefficients of steel 45 in the hardened state and cladded coatingis shown in Fig. 3. One of the most important characteristics of friction units is a low coefficient of friction, which affects the indicators of fuel and lubricant consumption during the operation of agricultural machinery. As a rule, friction pairs with a low coefficient of friction have a higher seizure load. With an increase in the load from 1.2 to 4.0 MPa on hardened samples of steel 45, the friction coefficient decreases from 0.11 and 0.09. With a further increase in the load for the improved specimen, the coefficient of friction increases. The coefficient of friction for a multicomponent coating varies in the range of 0.04–0.05. The minimum friction coefficient of 0.018–0.025 was obtained on a coating with additives of 10 wt.% of TiC ultrafine powder. With an increase in the sliding speed (Fig. 3, b) from 0.25 to 1.3 m / s, with a load of 2.0 MPa, the friction coefficient for steel 45 decreases from 0.11 to 0.092. With a further increase in speed to 1.6 m / s, it increases slightly. For cladded coatingin the range of 0.6–1.6 m / s, the friction coefficient increases smoothly.
Fig. 4 shows the regularities of the change in the seizing load from the sliding speed. Hardened samples of steel 45 are inferior to deposited multicomponent coatings and with the addition of ultrafine titanium carbide powder. At a pressure of 5.5 MPa, jamming occurs at a rate 1.6–3 times lower for a hardened sample of steel 45, in comparison with cladding with a multicomponent coating and with 10 TiC mass additives.% respectively.
In fig. 5. Shown are the wear rates of hardened specimens of steel 45 and deposited coatings. Wear resistance, which is the reciprocal of the wear rate, increases for many component coatings by 1.4 times as compared to hardened steel 45 and by 2.4 and 3 times as compared to the addition of 5 and 10 wt% TiC ultrafine powder to the charge, respectively.
Tests for abrasive wear during friction with a loose abrasive grain of samples of hardened steel 65G and with coatings deposited on it (Fe-Cr-B-Si, Ni-Cr-B-Si), (Fe-Cr-B-Si, Ni-Cr- B-Si) + 5 TiC mass%, (Fe-Cr-B-Si, Ni-Cr-B-Si) + 10 TiC mass% showed that the weight loss of the samples was 0.064 ∙ 10–4, 0.046 ∙ 10–4, 0.033 ∙ 10–4 and 0.029 ∙ 10–4 kg, respectively.
Discussion of the results
The results obtained in the work show that an increase in the reliability of parts of the main units and working bodies of agricultural machinery is possible with the use of new modern technologies for applying coatings with high performance characteristics, which have a significant impact on the durability of agricultural machinery products.
Laser cladding of multicomponent coatings, and with the addition of ultradispersed titanium carbide powder, can be used for the restoration of worn camshafts and crankshafts, piston pins, shaft seats for rolling bearings and other parts of agricultural machinery. Furthermore, this technology can be used to increase the wear resistance of tillage implements, plowshares, disc harrows, cultivator paws, which are made of 45 and 65G steels. Losses on idle time of agricultural machines during the period of seasonal field work associated with harvesting and cultivation of agricultural crops lead to significant economic costs.
The effect of self-sharpening of the cutting edge is of great importance for the effective operation of the tines of cultivators and disc harrows. The use of laser cladding technology with multicomponent materials with the addition of ultradispersed titanium carbide powder with a layer thickness of 0.5–0.8 mm practically does not change the geometry of the cutting edges and at the same time ensures self-sharpening of tools. The introduction of a nickel-based powder into the composition of the charge will significantly increase the corrosion resistance of the coatings.
Conclusion
The technology of laser cladding of multicomponent coatings with additions of ultrafine powder of titanium carbide 5 and 10 wt.% Has been developed. The wear resistance of the coatings is 1.4 times higher than that of hardened steel 45 and 2.4 and 3 times higher than the addition of 5 and 10 wt% TiC to the charge, respectively. At a sliding speed of 2.5 m / s, the seizing pressure of cladded coating with nano carbides was 1.8–2.5 times higher than that of hardened steel 45. Coatings with ultradispersed carbides had friction coefficients of 0.018–0.033. The abrasive wear resistance of the coating with 10 wt% TiC is 2.2 times higher than the hardened steel 65G.
ABOUT AUTHOR
Biryukov Vladimir, Candidate of Technical Sciences, laser‑52@yandex.ru, Senior Researcher, Mechanical Engineering Research Institute of the Russian Academy of Sciences (IMASH RAN), Moscow, Russia
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