Makarov, A. V.

Malygina, I. Yu

Soboleva, N. N.

Journal of Physics Conference Series

Institutional repository of Ural Federal University named after the first President of Russia B.N.Yeltsin

1Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd1234567890 ‘’“”ELBRUS 2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 946 (2018) 012004  doi :10.1088/1742-6596/946/1/012004NiCrBSi coating obtained by laser cladding andsubsequent deformation processingN N Soboleva1,3, A V Makarov1,2,3 and I Yu Malygina11 Institute of Engineering Science of the Ural Branch of the Russian Academy of Sciences,Komsomolskaya Street 34, Ekaterinburg 620049, Russia2 Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, SofyaKovalevskaya Street 18, Ekaterinburg 620219, Russia3 Ural Federal University, Lenina Avenue 51, Ekaterinburg 620000, RussiaE-mail: natashasoboleva@list.ruAbstract. NiCrBSi coating (Ni: base; Cr: 18.2 wt%; B: 3.3 wt%; Si: 4.2 wt%; C: 0.92 wt%;Fe: 2.6 wt%) formed by gas powder laser cladding is subjected to subsequent deformationprocessing, namely, frictional treatment with a sliding indenter made of dense cubic boronnitride in air under loads of 300 to 700 N, with 2 to 5 scans of the surface. This treatmentstrengthens the surface and forms favorable residual compressive stress, whose level increaseswith the load on the indenter. Frictional treatment under loads of 500 N and higher causesintensive strain-induced dissolution of Ni3B borides and Cr7C3 carbides in a Ni-based γ-solidsolution.1. IntroductionIn modern engineering production the most important task is to increase the service life of partsand assemblies manufactured friction and introduced earlier in the operation of vehicles [1].Laser cladding is an advanced technology to restore the work dimensions of machine parts andextend the serviceability of machines. Self-fluxing NiCrBSi alloy powders characterized by highwear resistance [2–6] are finding a wide application as materials for this purpose.Significant surface undulation and roughness is a characteristic feature of clad layers [7]. Thisis inadmissible for precision friction units. Conventional grinding of clad surfaces by abrasivewheels may be accompanied by the appearance of “burns” and microcracks, as well as dangeroustensile stresses.The surface plastic deformation is an efficient way to increase the strength and wear resistanceof machine part surfaces. Prospects of the application of frictional treatment as finishing surfacedeformation processing of NiCrBSi coatings was demonstrated in [8] for the relatively plasticlaser clad coating PG-SR2, with average microhardness 570 HV 0.025 and the hardness ofthe strengthening phases not exceeding 1000–1050 HV (Ni: base; Cr: 14.8 wt%; B: 2.1 wt%;Si: 2.9 wt%; C: 0.48 wt%; Fe: 2.6 wt%).However, frictional treatment is also applicable to much more high-strength and hard-to-deform metal materials [9, 10]. The aim of this work is to study whether the use of frictionaltreatment can improve the characteristics of the surface layers of the NiCrBSi—PG-10N-01high-strength coating containing higher amounts of carbon, chromium, boron and silicon thanthe PG-SR2 clad coating.21234567890 ‘’“”ELBRUS 2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 946 (2018) 012004  doi :10.1088/1742-6596/946/1/0120042. ExperimentalA plate of low-carbon (0.20% C) steel was clad with a powder of grade PG-10N-01 (Ni: base;Cr: 18.2 wt%; B: 3.3 wt%; Si: 4.2 wt%; C: 0.92 wt%; Fe: 2.6 wt%) by continuous CO2laser. Cladding was performed in two passes with a radiation power of 1.4–1.6 kW, a speedof 160 mm/min, powder consumption of 2.9 to 3.8 g/min and a laser spot of 61.5 mm on thesurface. The clad surfaces were ground on a circular grinding machine with intensive cooling.Figure 1 shows a cross-section of a coated specimen after grinding.Frictional treatment of flat clad specimens, ground and mechanically polished, was performedby a reciprocal sliding of a hemispherical indenter made of dense cubic boron nitride (DBN) witha radius r = 3 mm (figure 2) under loads ranging from 300 to 700 N in air, with an averagespeed of 0.013 m/s, a stroke length of 18 mm, double stroke displacement of 0.1 mm, 2–5-foldscanning. The treatment offered the absence of any appreciable frictional heating of the frictionsurface.The coating surfaces were studied by using a VEGA II XMU scanning electron microscope.The surface roughness was examined on a Wyko NT-1100 optical profilometer. Microhardnesswas determined on a Shimadzu HMV-G21DT microhardness meter by the restored print method.Residual stresses in the surface layer of the coating were estimated by tilted photography alongthe (220) line of the Ni-based γ-solid solution on a Shimadzu XRD-7000 x-ray diffractometer.The phase composition of the coatings was studied with the use of a Shimadzu XRD-7000 x-raydiffractometer and a VEGA II XMU scanning electron microscope equipped with an INCAWave 700 wavelength dispersive microanalyzer and an INCA Energy 450 XT energy dispersivemicroanalyzer.3. Results and discussionThe process parameters of the frictional treatment of the surface with sliding indenters areoptimized by the criteria of effective hardening and a high quality of the treated surface (lowroughness, the absence of seizure and microcracking).It follows from the data shown in table 1 that frictional treatment by a sliding DBN-indenterin air under all the used loads (P = 300–700 N) increases coating surface hardening (to 1165–1220 HV 0.025) as compared to the microhardness of the ground (1045 HV 0.025) and polished(990 HV 0.025) states. Besides, the ground coating is characterized by the presence of dangeroustensile stresses on the surface, whereas the frictional treatment of the coating causes favorablecompressive stresses (see table 1). As the load on the indenter increases, microhardness grows to1220 HV 0.025 and the level of residual compressive stresses grow to −1140 MPa under the loadsP = 700 N. A more effective hardening and a higher level of compressive residual stresses undermaximum loads (P = 700 N) are attained even with a smaller number (n = 2–4) of indenterpasses (scans) than under the loads P = 300–500 N (n = 5).According to figure 3, the frictional treatment of the PG-10N-01 coating forms higher qualitysurfaces than grinding does. It has been experimentally established that treatment under theloads P = 300–500 N ensures the absence of seizure on the coating surface with five scans(n = 5) of the surface by an indenter. The number of scans without seizure is n = 4 for the loadP = 700 N. Therewith, in all the studied cases, the value of the arithmetic mean deviation ofthe roughness profile does not exceed the value Ra = 0.2 µm. Figure 3(a) shows that, duringsurface preparation by machine grinding, the mechanism of abrasive wear with a large share ofmicromachining is implemented. After frictional treatment there are smoothed surfaces typicalof the fatigue mechanism of wear, see figure 3(b, c). Under the load P = 700 N, on the frictionsurface there appear separate microcracks perpendicular to the direction of the indenter motion,marked by arrows in figure 3(c). These cracks result from low-cycle friction fatigue [11].The phase composition of the PG-10N-01 coating in the initial clad state is as follows: aNi-based γ-solid solution, eutectics γ+Ni3B, the hardest strengthening phases Cr7C3 and CrB,31234567890 ‘’“”ELBRUS 2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 946 (2018) 012004  doi :10.1088/1742-6596/946/1/012004Figure 1. A cross-section photograph of acoated specimen after cladding and grinding.Figure 2. Scheme of frictional treatment witha hemispherical indenter.Table 1. Microhardness HV 0.025, residual stresses σ and the average values of the latticeparameters of the γ-solid solution d on the PG-10N-01 coating surface after grinding, polishingand frictional treatment with a DBN-indenter in air under a load P and the number of passesn.Treatment P (N) n HV 0.025 σ (MPa) d (A˚)Grinding — — 1045 ± 30 +90 —Polishing — — 990± 35 −85 3.5394Frictional treatment 300 5 1170 ± 70 −55 3.5374500 5 1210 ± 20 −135 3.5418700 2 1165 ± 30 −590 3.5422700 4 1220 ± 35 −1140 3.5424figure 4(a) [8]. The frictional treatment of the PG-10N-01 coating by a DBN-indenter under theminimum load (P = 300 N) does not lead to a qualitative change in the phase composition ofthe coating—only a decrease in the intensity of the lines of the strengthening phases is observedin the x-ray diffraction pattern, figure 4(b). This may testify to their partial strain-induceddissolution.In the process of frictional treatment under the loads P > 500 N, practically completestrain-induced dissolution of nickel borides Ni3B and chromium carbides Cr7C3 occurs in thethin surface layer. The phase composition on the coating surface after the treatment is asfollows: Ni-based γ-solid solution and the retained hardest strengthening phase CrB (up to2420 HV 0.025), see figure 4(c). The dissolution of the strengthening phases during frictionaltreatment with the loads P = 500–700 N and the number of indenter passes (scans) n = 2–441234567890 ‘’“”ELBRUS 2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 946 (2018) 012004  doi :10.1088/1742-6596/946/1/012004(a) (b)(c)Figure 3. The surfaces of the specimenswith PG-10N-01 coating after grinding (a) andfrictional treatment by a DBN-indenter in airat P = 300 N with n = 5 (b) and P = 700 Nwith n = 4 (c).increases the γ-lattice parameter (see table 1) due to the enrichment of the Ni-based γ-solidsolution with carbon, chromium and boron. The observed intensive strain-induced dissolutionof the phases is favored by the development of rotational plasticity in the surface layer duringfrictional treatment leading to the formation of the nanocrystalline state [12] and by a highdegree of accumulated plastic strain [13].The obtained results testify to a more efficient accumulation of plastic strain in the surfacelayer of the coating during frictional treatment when the load on the indenter grows from P = 300to 500–700 N. This manifests itself in the change of the phase composition of the coating, seefigure 4(c), and in the increased lattice parameter of the Ni-based γ-solid solution after frictionaltreatment under the loads P = 500–700 N with the number of scans n = 2–5. However, in thecase of frictional treatment with a minimum load on the indenter (P = 300 N) the deformation51234567890 ‘’“”ELBRUS 2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 946 (2018) 012004  doi :10.1088/1742-6596/946/1/012004(a) (b)60 80 100 120 140 160010203040501- 2 - CrBIntensity2 21 1212 o(c)Figure 4. X-ray diffraction patterns of thePG-10N-01 coating surface without frictionaltreatment (a) and after frictional treatmentby a DBN-indenter in air at P = 300 N withn = 5 (b) and P = 700 N with n = 4 (c).processes are less developed even with five scans. This results in a less intensive strain-induceddissolution of nitrides and carbides, see figure 4(b), and in the absence of any increase in theγ-lattice parameter (see table 1).The high level of microhardness (1165–1220 HV 0.025) on the coating surface after frictionaltreatment shown in table 1 is attributed to the effect of the following strengthening mechanisms:(1) solid solution strengthening—due to the saturation of the Ni-based γ-solid solution withcarbon, chromium and boron, with partial or complete strain-induced dissolution of nitridesand carbides;(2) dislocation and grain-boundary hardening—due to the formation of a fine-grained structurein the surface layer, with a high dislocation density and developed grain and subgrainboundaries, this being typical of the frictional treatment of high-strength alloys [10,12];(3) dispersion hardening—due to the presence of dispersed and incompletely dissolved particlesof the strengthening phases.61234567890 ‘’“”ELBRUS 2017 IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 946 (2018) 012004  doi :10.1088/1742-6596/946/1/0120044. ConclusionThe frictional treatment of the PG-10N-01 high-strength (990 HV 0.025) NiCrBSi laser coatingwith a sliding hemispherical indenter made of dense cubic boron nitride additionally strengthensthe surface to 1165–1220 HV 0.025 and forms favorable residual compressive stresses. As theload on the indenter grows from 300 to 1000 N, the level of residual compressive stresses increasesfrom −55 to −1140 MPa.Frictional treatment under a minimum load of 300 N does not change the initial phasecomposition of the surface layer, where, along with the Ni-based γ-solid solution and the γ+Ni3Beutectics, there are the strengthening Cr7C3 and CrB phases. Only a partial strain-induceddissolution of borides and carbides seems to occur. The increase of the load on the indenterduring frictional treatment to 500–700 N results in the intensive strain-induced dissolution ofborides Ni3B and carbides Cr7C3. This increases the lattice parameter of the Ni-based γ-solidsolution and activates the solid-solution strengthening mechanism due to the enrichment of thesolid solution with carbon, chromium and boron.AcknowledgmentsThe work was done with a financial support from the Russian Foundation for Basic Research,grant No. 16-38-00452; with a financial support from the Foundation for Assistance to SmallInnovative Enterprises, project UMNIK No. 108692015; within the complex program UB RAS,project No. 15-9-12-45; within the state order for IES UB RAS, No. 01201375904 and withinthe state order of the Federal Agency for Scientific Organizations on the subject “Structure”No. 01201463331. The experimental research was done using the equipment installed at theCollective Use Center “Plastometriya” IES UB RAS.References[1] Biryukov V 2014 Photonics 45 24–31[2] Makarov A V, Gorkunov E S, Malygina I Yu, Kogan L K, Savrai R A and Osintseva A L 2009 Rus. J.Nondestr. Test. 45 797–805[3] Xuan H F, Wang Q Y, Bai S L, Liu Z D, Sun H G and Yan P Ch 2014 Surf. Coat. Technol. 244 203–9[4] Xu J S, Zhang X C, Xuan F Z, Wang Z D and Tu S T 2014 Surf. Coat. Technol. 239 7–15[5] Savrai R A, Makarov A V, Soboleva N N, Malygina I Yu and Osintseva A L 2016 J. Mater. Eng. Perform.25 1068–75[6] Makarov A V, Soboleva N N, Malygina I Yu and Osintseva A L 2015 Diagnostics, Resource and Mechanicsof Materials and Structures 3 83–97[7] Singh R, Kumar D, Mishra S K and Tiwari S K 2014 Surf. Coat. Technol. 351 87–97[8] Soboleva N N, Makarov A V, Malygina I Yu and Savrai R A 2016 AIP Conf. Proc. 1785 030028[9] Makarov A V, Savrai R A, Gorkunov E S, Yurovskikh A S, Malygina I Yu and Davydova N A 2015 Phys.Mesomech. 18 43–57[10] Makarov A V, Korshunov L G, Savrai R A, Davydova N A, Malygina I Yu and Chernenko N L 2014 Phys.Met. Metallogr. 115 303–14[11] Kragelsky I V and Alisin V V 2001 Tribology: Lubrication, Friction, and Wear (London: ProfessionalEngineering Pub.)[12] Makarov A V, Pozdejeva N A, Savrai R A, Yurovskikh A S and Malygina I Yu 2012 J. Frict. Wear 33 433–42[13] Vychuzhanin D A, Makarov A V, Smirnov S V, Pozdeeva N A and Malygina I Yu 2011 J. Mach. Manufact.Reliab. 40 554–60

NiCrBSi coating obtained by laser cladding and subsequent deformation processing

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NiCrBSi coating obtained by laser cladding and subsequent deformation processing

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