Fe-Ni-Cu-Al-Ti-Cr ALLOY LAYERS OBTAINED BY LASER PROCESSING OF PREDEPOSITED POWDERS ON STEEL BASE Dan T.LEVCOVICI 1, Sanda M. LEVCOVICI 2, Adriana PREDA 3, Radu BOICIUC 4 Abstract In order to obtain surfaces with various tribological properties, two pastes having various concentrations of Ni, Cu, Al, Ti, Cr and Fe were predeposited on specimens of 1C35 steel grade. The specimens were processed with multiple passes on the numerically controlled x-y-z table at the rate v = 1 mm/s and the overlapping degree s = 35%. The simultaneous melting of added material and surface layer was performed by a CO 2 continuous wave laser with the 13 W power beam and the 1.2 mm diameter beam, under argon protection. The surface layers were analyzed by means of diffractometry, spectral analysis, metallographic analysis, microhardness and load carrying capacity measurements. KEYWORDS: laser alloyed layer, added materil, basic material, paste predeposited, X-ray diffractometry, metallographic analysis, microhardness measurement. 1. Introduction Laser change of chemical composition and microstructure of slight layer of steel pieces aims the slight hardening in order to increase efficiently the carrying capacity and wear resistance in frictional couples submitted to heavy running conditions. Laser slight alloying may be achieved by simultaneously melting of one added material precladded or injected in the melted bath of basic material, followed by convective mixing of those two materials and solidifying the alloyed layer. Ultra-rapidly heating speed by laser beam of small size melted bath causes a fast cooling speed (1 3-1 4 K/s), which leads to a fine hardening structure, beside the equilibrium. Structure and properties of the laser alloyed layer depend on both solidifying process and phase transformations in solid state after solidifying. A quenched alloyed layer from liquid phase on a hardened sub-layer by quenching in solid state of basic material is achieved. Changing the quantity of alloying material in laser beam running area, gives the possibility of getting a diversity of alloys in slight layers of steel pieces. Addition of alloying elements changes significantly the nature and the fraction of volume of phases from steel structure used as sub-layer. In this work, on analyses the influence of alloying material quantity from Ni-Cu-Al-Ti-Cr- Fe system over the chemical composition, kind of phases and hardness values in the slight layers of 1C35 steel, allied by laser from precladded powders mixture. 2. EXPERIMETAL METHOD Tests were realized on plates with dimensions 4 x 5 x 2 mm 3, made of 1C35 steel, SR EN 183-1:1994+2:1995. Samples were quenched in oil at 85 C, annealed at 55 C, and then rectified on 4 x 5 mm 2 faces. Added material (MA) was achieved as paste, by mixing one part hydroxyl-ethyl-pulp with three parts powder. Two recipes of added material with chemical composition given in table were tested. Added material quantity cladded on each sample was gravimetrically controlled. In table 2, paste quantities precladded on the steel samples from the two recipes of addition material. Samples were mounted on an x-y-z mass numerically controlled, coupled to a CO 2 continuous wave laser. Paste layer and steel sub-layer were melted at the same time by many steps sweeping with a beam with P = 12 W power, d = 1 mm diameter on the worked out surface and v = 6 mm/s speed. 44
Table 1. Chemical composition of added material MA Chemical composition [%] Ni Cu Al Ti Cr Fe 1 56. 25.5 1.6 7.5 6.2 3.2 2 24. 41.5 18. 12.4 2.6 1.3 Table 2. Addition material quantities distribution Sample code 1 2 3 4 5 6 7 8 MA1 cladded (mg/cm 2 ) MA2 cladded (mg/cm 2 ) 27.5 35.2 41.7 66.9 49.4 86.2 114.2 166.7 On used a Zn-Se focusing glass with 127 mm focuses distance. Under argon continuous protection 35% overlapping of melted strips was made. The alloyed layers achieved were characterized by spectral chemical analysis, phase qualitative analysis by X ray difractometry, hardness measurements HV 49 (49N load). In layers cross section the optical microstructure analysis and micro hardness measurements HV.98 (1 g load) were performed. 3. EXPERIMENTAL RESULTS AND DISCUTIONS 3.1. Spectral analysis of chemical composition of added layers DV 6 optical transmission spectrometer manufactured by BAIRD COMPANY performed the findings. In table 3 the precladded added material quantities and average chemical composition achieved in layer as a result of laser alloying were given. Table 3. Chemical composition of alloyed layers Sample MA, Chemical composition, % code mg/cm 2 C Mn Si P S Cr Ni Cu Ti Al Basic material 1. -.36.73.25.29.19.34.28.31 -.49 Added material 1 1.1 27.5.37.34.14.28.18.61 3.89 1.96.1.13 1.2 35.2.38.29.31.26.17 1.25 1.74 3.4.2.12 1.3 41.7.4.27.36.25.17 1.48 11.63 4.36.4.11 1.4 66.9.41.23.69.23.11 2.3 17.67 6.13.9.13 Added material 2 1.5 49.4.4.25.39.24.15 1.16 7.36 6.57 2.3 4.34 1.6 86.2.41.22.6.23.11 1.23 7.76 7.38 2.49 6.24 1.7 114.2.44.2.75.19.1 1.44 9.29 8.78 3.59 1.3 1.8 166.7.46.18.81.18.8 1.56 9.82 9.33 3.74 13.48 For basic material composition influence study over assimilation degree of alloying elements in samples slight layers, as a result of laser melting process, in figures 1 and 2 the elements contents variation by added material quantities managed to each sample was given. On observes that when added material quantity increases the carbon content from the alloyed layer easily increases, due to presence of carbide making elements chrome and titan. Contents of Mn, S, P, decrease due to redistribution of those elements in the alloyed layer, which come from the basic material. Contents of Ni, Cr, Cu, Ti, which come from the added material grow. Aluminum content (element which comes from the basic material) drops off in slight layers worked out by recipe MA1 strongly increases in slight layers processed by recipe MA2. Nickel submitted the best assimilating degree among the elements managed by the two recipes of the added material. 45
2.5 2. 1.5 1..5.. 2. 4. 6. 8. 2. 18. 16. 14. 12. 1. 8. 6. 4. 2... 2. 4. 6. 8. C Mn Si Cr Ni Cu.1.9.8.7.6.5.4.3.2.1.. 2. 4. 6. 8. Ti Al Fig. 1. Variation of C, Mn, Si şi Cr, Ni, Cu, Ti, Al contents depending on addition material quantities precladded in recipe MA1 1.8 1.6 1.4 1.2 1..8.6.4.2.. 5. 1. 15. 2. 16. 14. 12. 1. 8. 6. 4. 2... 5. 1. 15. 2. C Mn Si Cr Ni Cu Ti Al Fig. 2. Variation of C, Mn, Si şi Cr, Ni, Cu, Ti, Al contents depending on addition material quantities precladded in recipe MA1 46
On observes as Al assimilating degree increasing in the slight layers performed by recipe MA2 was favored by increasing the titan content from the addition material. Difference of affinity for oxygen between Ti and Al explains the differences recorded at their assimilation degree in the slight layer processed by laser. 3.2. Metallographic analysis OLYMPUS microscope used, endowed by image analysis system using the IMAGE PRO Plus program, with which measured alloyed layer depths (h melted) as well of those quenched from solid state (h quenched) under laser beam action and metallographic analysis of material in those areas was made. In table 4 enters the outcomes of those measurements and remarks with regard to the presence of several defaults in alloyed layer: p pores; f cracks. When the addition material 1 was used the laser alloyed layers thickness increased by the addition material quantity. At addition material 2, on observes larger thickness of alloyed layers and laser quenched sublayers. Changing the alloying recipe, by modifying the compound elements weight, resulted in a growth by cca.2% of specific heat and important increasing of heating conductivity of addition material, which explains increasing of laser alloyed layers thickness in relation with the first recipe.. 1.1 1.2 1.3 1.4 Fig. 3. Surface layers microstructure of samples alloyed by recipe MA1. Attack with nital 1%.(X2) 47
1.5 1.6 1.7 1.8 Fig. 4 Surface layers microstructure of samples alloyed by recipe MA2. Attack with nital 1%.(X2) Table 4 Layer depths worked out by laser on MB 1. Sampl MA h melted (mm) h quenched Default e code (mg/cm 2 ) Max. Min. Average (mm) Added material 1 1.1 27.5.3.21.23.66 f 1.2 35.2.33.2.23.68 f 1.3 41.7.4.24.36.7 f 1.4 66.9.44.25.37.7 - Added material 2 1.5 49.4.6.46.56.97-1.6 86.2.57.44.5.83-1.7 114.2.54.43.5.88 p 1.8 166.7.52.43.48.85 p Based on the performance limits of laser generator power, to quantities of addition material larger than 8 mg/cm 2 on find a decrease of those depths. Metallographically speaking, the alloyed layer shows a microstructure with columnar dendritic aspect, inter-metallic compounds and primary carbides, while the quenched sub-layer contents martensite and a decreased quantity of residual austenite. 48
I/Imax., [%] Cod 1.3 1 9 8 7 6 5 4 3 2 1 Fe γ (111) Fe α (11) Fe γ (2) Fe α (2) 3 4 5 6 7 8 9 1 11 Unghiul de difractie 2 θ [ o ] Fig. 5. Relative intensity variation by angle of diffraction at sample 1.3. Fe α (211) Fe γ (311) Fe α (22) I/Imax., [%] Cod 1.4 1 9 8 7 6 5 4 3 2 1 AlTi 3 (4) CuAl 2 (121) AlTi 3 (2) AlTi 3 (13) CuAl 2 (22) Fe γ (111) Fe α (11) Fe 2 Ti (21) Fe γ (2) Fe 2 Ti (14) Fe 2 Ti (23) CuAl 2 (4) Fe 2 Ti (3) CuAl 2 (24) Fe γ (22) Fe 2 Ti (24) CuAl 2 (24) 3 4 5 6 7 8 9 1 11 Unghiul de difractie 2 θ [ ] o Fe γ (311) CuAl 2 (152) Fe γ (222) CuAl 2 (134) Fig. 6. Relative intensity variation by angle of diffraction at sample 1.4. I/Imax., [%] Cod 1.5 1 9 8 7 6 5 4 3 2 1 Fe 3 AlC (11) FeAl 3 (21) Fe 2 Ti (11) AlTi (121) FeAl 3 (13) Fe 2 Ti (112) Fe α (11) Fe γ (111) Fe 2 Ti (21) AlTi (13) Fe 3 AlC (21) FeAl 3 (2) AlTi (141) Fe α (2) Fe 2 Ti (32) Fe 2 Ti (213) Fe 3 AlC (22) Fe γ (22) FeAl 3 (24) Fe α (211) Fe 3 AlC (311) 3 4 5 6 7 8 9 1 Unghiul de difractie 2 θ [ o ] Fig. 7. Relative intensity variation by angle of diffraction at sample 1.5. 49 Fe γ (311) Fe γ (222)
In figures 3 and 4 microstructural aspects from cross section of alloyed layers are given. At samples 1.1, 1.2, 1.3, in slight alloying conditions, this is made of residual martensite and residual austenite. Increasing the alloying degree the inter-metallic compounds show up. Enlarging the addition material quantity favors the austenite heterogeneous germination and finishing the dendritic structure. 3.3. Phase qualitative analysis of alloyed layers Phases appeared in the slight laser alloyed layer were recognized by X ray diffraction. A DRON 3. difractometer was used in a first stage in CoK α radiation in order to find a network parameter of Fe. In the second stage CoK α radiation was used that allowed the deceleration of inter-metallic compounds existing in strained matrix and which shows a strong fluoresce in CoK α radiation. Processing parameters used for analysis were: U = 36KV,I = 26 ma, gaps 2;.5;.5; moving speed of detector ω = 2/min; moving speed of paper v = 72 mm/h. On observed as at small alloying degrees by recipe MA1 (samples 1.1 1.3) the structure contends martensite and residual austenite alloyed. At higher alloyed sample 1.4 the AlTi 3, CuAl 2 and Fe 2 Ti inter-metallic compounds showed up. In case of recipe MA2, in martensitical structure with residual austenite, Fe 3 AlC, Fe 3 Al, Fe 2 Ti, AlTi 3 compounds emphasized. Residual austenite quantity grows by its alloying degree, respectively by addition material quantity. In figures 7-9 it is shown the difractograms aspect at samples 1.3,1.4, alloyed by recipe MA 1 and at sample 1.5 alloyed by recipe MA 2respectively. The network parameter evolution of Feα and Feγ by addition material cladded emphasizes its growing by additional alloying of martensite and residual austenite. To a quantity of 66,9 mg/cm 2 (sample1.4) the network parameter grows by 1%, the martensite quantity (Fe) substantially decreases, the slight layer being practically made by a matrix of alloyed austenite unchanged, in which inter-metallic compounds precipitate. Presence of inter-metallic compounds like precipitates in unchanged austenite as well as alloying elements dissolved in this matrix, strain strongly the crystalline network and lead to additional hardening of slight layer treated by laser, fact confirmed by results of micro-hardening measurements. 8 7 6 HV.98 [MPa] 5 4 3 1.1 1.2 1.3 1.4 2 1.2.4.6.8 1 1.2 1.4 distanta de la suprafata [mm] Fig. 8. Variation of micro-hardness HV.98 on depth of layer in samples: 1.1=27,5mg/cm 2 ; 1.2=35,2mg/cm 2 ; 1.3=41,7mg/cm 2 ; 1.4=66,9mg/cm 2. 5
9 8 7 HV.98 [MPa] 6 5 4 3 1.5 1.6 1.7 1.8 2 1.2.4.6.8 1 1.2 1.4 distanta de la suprafata [mm] Fig. 9. Variation of micro-hardness HV.98 on depth of layer in samples: 1.5=49,4mg/cm 2 ; 1.6=86,2mg/cm 2 ; 1.7=114,2mg/cm 2 ; 1.8=166,7mg/cm 2. 3.4. Hardening analysis Structural changes resulted by laser alloying of samples slight layer have determined changing of material micro-hardness and hardness correlated to new formed microstructural compounds. In figures 8 and 9 the variations of micro-hardness HV.98 in laser alloyed layers depending on quantities of additional material given were represented. When alloying by recipe MA1, on observed that alloyed layer micro-hardness decreases by degree of alloying, respectively by residual austenite quantity. At sample 1.4, the alloyed layer has the micro-hardness below the value of laser quenched sub-layer from solid phase. When alloying by recipe MA2, microhardness increases by degree of alloying as a result of inter-metallic compounds quantity growing, which have the governing role in hardening process. Also, HV 49 hardness measurements were performed on laser worked out samples surface in order to estimate effects of slight alloying over the carrying capacity of slight layers (table 5). On find out that the slight hardness is made agree with structural and micro-hardness changes. When alloying by recipe MA1 the hardness decreases by addition material quantity and growing of residual austenite quantity. When alloying by recipe MA2 the hardness grows by addition material quantity, 51 by structure inter-metallic compounds respectively. 2 Table 5 Hardness measurements HV 49. Sample MA Hardness HV 49 code mg/cm (MPa) Support Alloyed layer Addition material 1 1.1 27,5 262 581 1.2 35,2 274 317 1.3 41,7 284 519 1.4 66,9 272 235 Addition material 2 1.5 49,4 276 545 1.6 86,2 264 544 1.7 114,2 27 66 1.8 166,7 263 636 4. CONCLUSIONS 1. Laser alloying of steel piece surfaces allows the controlled getting of a diversity of alloys from Ni-Fe-Ti-Al-Cu system by change of precladded addition material quantity. 2. Spectral analyses of chemical composition showed that in the slight layer Ni had the best assimilation degree among the elements managed by the two recipes of addition material. Increasing Al assimilation degree in slight layers performed by recipe
MA2 was favored by the advanced deoxidation of melt to titan content increase. 3. Metallographic analysis by optical microscope emphasized that in case of addition material MA1 (56%Ni + 25,5%Cu + 1,6%Al + 7,5%Ti + 6,2%Cr + 3,2%Fe), the laser alloyed layers thickness grew by addition material quantity. At alloying recipe MA2 (24%Ni + 41,5%Cu + 18,%Al + 12,4%Ti + 2,6%Cr + 1,3%Fe), the laser alloyed layers thickness increases by action of component elements of growing the specific heat and thermal conductivity of addition material. 4. Laser alloyed layer microstructure has a columnar dendritic aspect. Increasing the addition material favors the austenite heterogeneous germination and dendritic structure finishing. At recipe MA1, in low alloying conditions, the microstructure is made of martensite and residual austenite. When increasing the alloying degree the inter-metallic compounds AlTi3, CuAl 2, Fe 2 Ti, Fe 3 AlC, Fe 3 Al appear. 5. On observes a good correlation of microhardness values measured in cross section of alloyed layers with phases nature emphasized by difractometry and metallographic analysis, as well as with hardness values measured on the samples surface. In low alloying conditions the layer hardening is determined mainly by the relative ratio between the quantity of martensite and residual austenite alloyed. Increasing the alloying degree, the intermetallic compounds appear, which become the governing factor of hardening at recipe MA2. 6. The alloying run, which provides an optimal hardened layer, without tightness defaults (pores, cracks), corresponds to sample 1.5, alloyed by recipe MA2. The average thickness of alloyed layer is.56 mm, and the slight hardness HV 49 = 545 MPa, with 97,4% larger than that of the basic material. REFERENCES [1] Cordier-Robert C., Foct J., Crampon J. Surface Alloying of Iron by Laser Melting: Microstructure and Mechanical Properties, Proc. XI International Conference on Surface Modification Technologies SMT XI (1997), p. 581. [2] Grünenwald B., Shen J., Dausinger F., Nowotny St. - Laser Cladding with a Heterogeneous Powder Mixture of WC/Co and NiCrBSi, Proc. ECLAT '92, (1992), p. 411. [3] Levcovici D., T., Sumurduc M., M., Stavăr D., G. Paste for Hardening by Laser surface Alloying of Steel and Iron, R Patent 4,113,122, March 31, 1998. [4] Levcovici D.,T., Stavăr S., Levcovici M.,S., Măcrescu V., Sumurduc M., M. Procedure for Laser Thermochemical Treatment, R Patent R 4,114,156, December 31, 1998. [5] D.T. Levcovici, V. Munteanu, S.M.Levcovici, L. Benea, O. Mitoşeriu, M.M. Paraschiv, Laser Processing of MMC Layers on a Metal Base, Materials and Manufacturing Processes (USA), July 1999, vol. 14, no. 4, p. 475. AUTHORS 1. Dr. ing. Dan Teodor LEVCOVICI, S.C. UZINSIDER Engineering S.A. Galaţi, Romania, dan.levcovici@uzineng.ro. 2. Dr.ing.Sanda Maria LEVCOVICI, University DUNAREA DE JOS of Galaţi, sandalevcovici@hotmail.com. 3. Dr.ing. Adriana PREDA, S.C. UZINSIDER Engineering S.A. Galaţi, Romania, research@uzineng.ro. 4. Ing. Radu BOICIUC, S.C. UZINSIDER Engineering S.A. Galaţi, Romania, radu.boiciuc@uzineng.ro. 52