metals Article
Microstructure and Microhardness of Laser Metal Deposition Shaping K465/Stellite-6 Laminated Material Zhiguo Wang 1, * 1
2
*
ID
, Jibin Zhao 1 , Yuhui Zhao 1 , Hongyu Zhang 2 and Fan Shi 1
Equipment Manufacturing Technology Research Laboratory, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, China;
[email protected] (J.Z.);
[email protected] (Y.Z.);
[email protected] (F.S.) Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China;
[email protected] Correspondence:
[email protected]; Tel.: +86-24-8360-1225; Fax: +86-24-8360-1224
Received: 18 October 2017; Accepted: 16 November 2017; Published: 22 November 2017
Abstract: K465 superalloy with high titanium and aluminum contents was easy to crack during laser metal deposition. In this study, the crack-free sample of K465/Stellite-6 laminated material was formed by laser metal deposition shaping to control the cracking behaviour in laser metal deposition of K465 superalloy. The microstructure differences between the K465 superalloy with cracking and the laminated material were discussed. The microstructure and intermetallic phases were analyzed through scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the microstructure of K465/Stellite-6 laminated material samples consisted of continuous dendrites with a similar structure size in different alloy deposition layers, and the second dendrite arm spacing was finer compared with laser metal deposition shaping K465. The intermetallic phases in the different alloy deposition layers varied, and the volume fraction of carbides in K465 deposition layer of the laminated material was higher than only K465 deposition under the fluid flow effect. In addition, the composition and microhardness distribution of laminated materials variation occurred along the deposition direction. Keywords: laser metal deposition shaping; laminated material; microstructure; microhardness
1. Background K465 superalloy, known as a nickel-based alloy, is widely used for gas turbine blades and vanes [1]. K465 superalloy parts are mainly formed by conventional casting, leading to some disadvantages in forming efficiency and mechanical properties. Laser metal deposition shaping (LMDS) is an efficient way for producing components with near-net-shaped, directional solidification, and controlled porosity or chemical composition gradient [2,3], and it also knows direct laser fabrication (DLF), or laser solid form (LSF). Many LMDS nickel-based superalloys have been reported, such as Inconel 625 [4], Inconel 718 [5,6], Colmonoy 227-F [7], Rene 80 [8], IN 100 [9] et al.; nevertheless, some of them (e.g., Inconel 718 [6], Rene104 [10], IN100 [9], K465 [11], DZ4125 [12], and CM247LC [13] were prone to cracking. The crack sensitivity of nickel-based superalloy increases with the increasing of aluminum and titanium elements. As a result, the research focus of LMDS K465 superalloy concentrates on controlling the cracks. Based on previous studies, the crack category of laser deposition superalloy may contain solidification cracking, grain boundary liquation cracking and ductility dip cracking [10]. Among them, the liquation cracks are the most serious in nickel-based superalloy with a high content of (Al + Ti), and may originate from the liquation of low melting point eutectic in the previous build layers. Chen et al. [6] have found that liquation cracking in laser deposited 718 alloy was on account of
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the liquation of Laves/γ eutectic particles. Moreover, Yang et al. has proved that the cracking behavior of the DLFed Rene 104 was mainly because of high content of (Al + Ti) and heat history [10]. The crack sensitivity of nickel-based superalloy could be reduced by controlling the heat input during LMDS. Based on Hu’s studies [12], the liquation cracks occurred in LSFed DZ4125 superalloy sample with the lower heat input. However, when the contents of Al and Ti elements reach a certain level, the crack sensitivity cannot be completely eliminated [8]. Li et al. proposed that the crack-free K465 sample can be formed by LSF based on preheating of the substrate [11]; however, the preheating temperature was quite high, and was difficult to realize in the practical engineering application. In addition, Hu et al. [14] and Harrison et al. [15] have proved the cracking behaviour by changing the chemical composition; by mixing some alloys during LMDS, the mechanical properties and formability of the nickel-based superalloy could be changed significantly [16–18]. Accordingly, the cracking in LMDS K465 may disappear absolutely by changing the chemical composition. In addition, by adding another alloy, the crack sensitivity of K465 superalloy could be reduced without preheating. Metal–metal laminated composites have shown desirable structural properties with the combination of ductility and toughness of the soft layer with the high strength of the hard layer [19]. Soodi et al. [20] have proved that wafer type structures of specific constituent metal alloys have lower coefficient of thermal expansion (CTE) than those of original alloys, while Kolednik et al. [21] proved that the fracture resistance and fracture stress could be improved by spatial material property variations. In the present study, LMDS laminated material was formed to control the cracking during the LMDS process. The Stellite-6 was chosen to form laminated materials with K465, and cracking behaviors in LMDS K465 superalloy and K465/Stellite-6 laminated materials were discussed. In addition, the microstructure, chemical composition and hardness of K465/Stellite-6 laminated material were examined in detail. 2. Experiment For this study, three block samples with different chemical compositions were built by LMDS. The deposition system (Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang, China) consisted of a 6-axe multi-joint Staubli robot (Stäubli Corporation of South Carolina, Duncan, SC, USA), a “YLS-2000” 2000W fiber laser (IPG Laser, Barbuch, Germany) with the nozzle diameter of 3 mm, and a self-designed powder delivery system used for injecting powder to molten pool under the carrying of inert Argon gas, with a stainless steel plate was used as the building platform. Spherical gas-atomized K465 and Stellite-6 powders were supplied by the Institute of Metal Research, Chinese Academy of Sciences (IMR, Shenyang, China) and Shanghai Stellite Co., Ltd. (Shanghai, China), with particle size between 53 and 150 µm. Chemical composition of the two alloys are listed in Table 1. Table 1. Chemical composition of powders. Element
C
Mo
Cr
Nb
Fe
Ti
Si
Al
W
Mn
Co
Ni
K465 Stellite-6
0.17 1.09
1.80 0.22
8.75 29.27
2.00 -
1.93
2.45 -
1.00
5.55 -
10.25 4.29
0.13
9.75 Bal.
Bal. 2.34
The three block samples deposition modes are illustrated in Figure 1. The K465 superalloy sample was built in a continuous way, as shown in Figure 1a. The K465/Stellite-6 laminated materials were built by LMDS alternately with deposition layer number ratios. One K465 deposited alternately with one and two Stellite-6 deposition layers, respectively, as shown in Figures 1b and 2c. Laser power of 1450 W, scanning speed of 4 mm/s and scanning interval of 4 mm were used as manufacturing process parameters. The deposition direction of LMDS was paraller to the z-axis direction. The laminated material with deposition layer numbers ratio 1:1 and 1:2 was also, respectively, called 1:1 and 1:2 K465/Stellite-6 laminated material.
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direction. Metals 2017, 7,The 512 laminated material with deposition layer numbers ratio 1:1 and 1:2 was 3also, of 10 respectively, called 1:1 and 1:2 K465/Stellite-6 laminated material. (b) (b)
(a) (a)
K465 K465 LMDS K465 K465 LMDS
Stellite-6 Stellite-6
(c) (c)
ZZ
K465 K465 LMDS K465/Stellite-6 K465/Stellite-6 laminated laminated material material LMDS
X X Y Y
Figure 1. 1. The The schematic schematic of of the the different different forming forming method method (a) (a)K465; K465;(b) (b)1:1 1:1K465/Stellite-6 K465/Stellite-6 laminated laminated Figure 1. different forming method (a) K465; (b) 1:1 K465/Stellite-6 material; (c) (c) 1:2 1:2 K465/Stellite-6 K465/Stellite-6 laminatedmaterial. material. K465/Stellite-6 laminated laminated material. material;
Specimens were were cut cut from from the the building building platform, platform, and and then then mounted mounted and and polished. polished. The The K465 K465 Specimens deposition sample was was electrochemical electrochemicaletched etchedwith withetchant etchant(H (H 33PO44 + HNO33 + H22SO44), using voltage deposition sample 3 PO4 + HNO3 + H2 SO4 ), using voltage of 6 V and etch time was 15 s. Two laminated materials were etched withwith chloroazotic acid. acid. The of 6 V and etch time was 15 s. Two laminated materials were etched chloroazotic microstructure of those specimens was observed by stereology microscopy (Stemi 2000, Carl Zeiss The microstructure of those specimens was observed by stereology microscopy (Stemi 2000, Carl Zeiss Shanghai Shanghai, China) and optical microscopy (Axiovert 200 MAT, Carl ZeissCarl Shanghai Shanghai Co., Co.,Ltd, Ltd., Shanghai, China) and optical microscopy (Axiovert 200 MAT, Zeiss Co., Ltd, Shanghai, China). Elemental analysis was done by the energy dispersive spectrometry Shanghai Co., Ltd., Shanghai, China). Elemental analysis was done by the energy dispersive during SEM (S.3400N, Hitachi Ltd, Tokyo, Japan) The phase constitutions of the specimens spectrometry during SEM (S.3400N, Hitachi Ltd.,analysis. Tokyo, Japan) analysis. The phase constitutions were an X-ray diffractometer Rigaku Corp., Tokyo, Japan) the of theidentified specimensby were identified by an X-ray(D/Max-2500PC, diffractometer (D/Max-2500PC, Rigaku Corp.,and Tokyo, hardness was measured by Vickers hardness tester (AMH43, LECO Corp., Saint Joseph, MI, USA) Japan) and the hardness was measured by Vickers hardness tester (AMH43, LECO Corp., Saint Joseph, with an indentation load of 200load g for s. g for 15 s. MI, USA) with an indentation of15 200 3. Results and and Discussion 3.1. Microstructure 3.1. Figure three samples in the X–Z section. As As shown in Figure 2a), Figure 22shows showsthe themacrostructure macrostructureofofthe the three samples in the X–Z section. shown in Figure many cracks in LMDS K465 extended to the deposition layers along the deposition direction. The cracks 2a), many cracks in LMDS K465 extended to the deposition layers along the deposition direction. The in laminated material with deposition layer numbers ratio 1:1 terminated in single deposition layer cracks in laminated material with deposition layer numbers ratio 1:1 terminated in single deposition (Figure 2b), and macrocracks disappeared in laminated material with layer (Figure 2b), and macrocracks disappeared in laminated material withdeposition depositionlayer layer numbers numbers ratio 1:2 small number of round-hole defects distributed irregularly on the three samples. ratio 1:2(Figure (Figure2c). 2c).A A small number of round-hole defects distributed irregularly on the three The deposition layer thickness of the bottom waszone smaller the top andzone, this could be samples. The deposition layer thickness of thezone bottom waswith smaller withzone, the top and this explained by different of the molten pool. It is pool. clear It that the temperature of the substrate could be explained by dimensions different dimensions of the molten is clear that the temperature of the and the previously layer increased as deposition which made the dimensions of the the substrate and the built previously built layer increased progressed, as deposition progressed, which made molten pool of become largerpool under the same condition of heat dimensions the molten become larger under the sameinput. condition of heat input. (a) (a)
(b) (b)
Figure 2. Cont.
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Figure of Laser metalmetal deposition shaping (LMDS) samplessamples (a) K465; 1:1 Figure 2. 2. Macrostructure Macrostructure of Laser deposition shaping (LMDS) (a) (b) K465; K465/Stellite-6 laminated material; (c) 1:2 K465/Stellite-6 laminated material.material. (b) 1:1 K465/Stellite-6 laminated material; (c) 1:2 K465/Stellite-6 laminated
The deposition layer thickness of the laminated material was uneven in the single deposition The deposition layer thickness of the laminated material was uneven in the single deposition layer, whereas the K465 deposition layers had nearly homogeneous thickness, as shown in Figure 3. layer, whereas the K465 deposition layers had nearly homogeneous thickness, as shown in Figure 3. This difference is closely related to the laser scanning strategy. As stated before, the zig-zag laser This difference is closely related to the laser scanning strategy. As stated before, the zig-zag laser scanning strategy was used as shown in Figure 4. As illustrated in the left zone of Figure 4, the laser scanning strategy was used as shown in Figure 4. As illustrated in the left zone of Figure 4, the laser first moved along the solid line in red, and then moved along the dotted line in red to fill the gap left first moved along the solid line in red, and then moved along the dotted line in red to fill the gap left by previous scanning route. When LMDS was conducted on the previous layer, the top position of by previous scanning route. When LMDS was conducted on the previous layer, the top position of the previous deposition layer was remelted. Laser energy in distribution of Gaussian modes made the previous deposition layer was remelted. Laser energy in distribution of Gaussian modes made the remelted line appear in a wavy shape. The remelted line shape of different materials varied, and the remelted line appear in a wavy shape. The remelted line shape of different materials varied, this made the deposition layer thickness of laminated material non-uniform. The layer thickness of and this made the deposition layer thickness of laminated material non-uniform. The layer thickness deposition layer in laminated material was changed along the x-direction, as shown in Figure 3b,c. of deposition layer in laminated material was changed along the x-direction, as shown in Figure 3b,c. At the same time, the single layer thickness of K465 superalloy was uniform with nearly 0.47 mm. As At the same time,3b,c, the single layer thickness K465 superalloy uniform withzone, nearly 0.47 mm. shown in Figure the liquation crackingof first initiated from was the heat affected which was As shown in Figure 3b,c, the liquation cracking first initiated from the heat affected zone, which was near the fusion line in the pre-deposition layer. The liquidation of low melting point phase in K465 near the fusion in occurrence the pre-deposition The liquidation of low melting point phaseby inmany K465 superalloy leadsline to the of grain layer. boundaries liquation cracking, which was proved superalloy to the grainetboundaries cracking, which was superalloy proved by researchers leads like Yan et occurrence al. [22] andofChen al. [6,10,11].liquation The liquation crack in K465 many researchers like Yan et al. [22] and Chen et al. [6,10,11]. The liquation crack in K465 extended along several deposition layers, while extended only in the K465 single layer of superalloy laminated extended along several deposition layers, while extended only in the K465 single layer of laminated material. The crack behavior was related to hot ductility of the material, capability to absorb the stress material. behavior was related to hot ductility of the material, the of welding,The andcrack the grain boundary misorientation. The laminated materialscapability were freerto of absorb crack than stress of welding, and the grain boundary misorientation. The laminated materials were freer of crack K465 alone because of different material composition and welding dilution between different than K465 alone because of different material composition and welding dilution between different deposition layers. The crack difference between two laminated material was mainly because of deposition layers. The crack difference between two laminated material was mainly because different material composition. The 1:2 K465/Stellite-6 laminated material has more capability of to different material composition. The 1:2 K465/Stellite-6 laminated material has more capability to absorb the stress of deposition. absorb the7,stress deposition. Metals 2017, x FORof PEER REVIEW 5 of 11 (a)
(b)
(b)
(a)
crack crack
500um
500um
500 µ m
(c)
500 µ m
Figure 3. Cont.
500 µ m
crack
500 µ m
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500um
500 µ m
Figure 3. Optical microscopy (OM) images of LMDS samples: (a) K465; (b) 1:1 K465/Stellite-6 laminated material; (c) 1:2 K465/Stellite-6 laminated material. Figure Figure 3.3. Optical Optical microscopy microscopy (OM) (OM) images images of of LMDS LMDS samples: samples: (a) (a) K465; K465; (b) (b)1:1 1:1K465/Stellite-6 K465/Stellite-6 laminated material; (c) 1:2 K465/Stellite-6 laminated material.
laminated material; (c) 1:2 K465/Stellite-6 laminated material.
Figure of laminated laminatedmaterials. materials. Figure4.4.The Theschematic schematic of of LMDS LMDS of
Figure 5 shows dendriticmicrostructures microstructures of of different different forming Figure 5 shows dendritic formingmethods, methods,and andthe themicrostructure microstructure Figure 4. The schematic of LMDS of laminated materials. grew with orientation of three samples mostly consist of dendrite structures. Mostly, the dendrites of three samples mostly consist of dendrite structures. Mostly, the dendrites grew with orientation nearly parallel thebuilding buildingdirection, direction, apart apart from from the bonding. nearly parallel toto the the microstructure microstructurenear nearthe theinterlayer interlayer bonding. Figure 5 shows dendritic microstructures oftodifferent forming methods, and the microstructure The dendrite arm spacing (DAS) was often used evaluate solidification microstructures [23]. After The dendrite arm spacing (DAS) was often used to evaluate solidification microstructures [23]. of calculating three samples mostly consist of dendrite Mostly, the dendrites grew with orientation the average second dendrite armstructures. spacing (SADS) of different forming methods by SEM After calculating the average second dendrite arm spacing (SADS) of different forming methods nearly parallel to the buildingofdirection, from were the microstructure nearwith the single interlayer images, the microstructures laminatedapart materials refined compared K465bonding. alloy. by SEM images, the microstructures of laminated materials were refined compared with single The dendrite arm spacing (DAS) evaluate solidification microstructures [23]. After The SADS of LMDS K465 alloy was wasoften near used 10.18 to μm, while the laminated material with deposition K465 alloy. The SADS of LMDS K465 alloy was near 10.18 µm, while the laminated material with calculating the average dendrite armInspacing (SADS) of different forming methods bythe SEM layer numbers ratio 1:1second had 3.44 μm SADS. addition, the primary dendritic developd more in deposition layer numbers ratio 1:1 had 3.44 µm SADS. In addition, the primary dendritic developd single the alloymicrostructures than the laminated materials. The deposition microstructure difference partly caused images, of laminated materials were refined compared withwas single K465 alloy. more in the single alloy than the laminated materials. The deposition microstructure difference bySADS the variation of deposition mode. sample formed by LMDS contentiously, the The of LMDS K465 alloy was The nearK465 10.18 μm, was while the laminated material with while deposition was partly caused bybuilt the variation of deposition mode.different The K465 sample was formed by LMDS laminated materials by LMDS had a pause between material deposition layer-to-layer. layer numbers ratio 1:1 had 3.44 μm SADS. In addition, the primary dendritic developd more in the contentiously, while the laminated materials built by LMDSsamples had a pause between different material The alloy deposition temperature of laminated materials wasdifference greater than K465 samples single than the laminatedgradient materials. The deposition microstructure was partly caused deposition layer-to-layer. The deposition temperature gradient of laminated materials samples was the same parameters, made the refined. Mohammad H. bywith the variation of process deposition mode. Thewhich K465 sample wasmicrostructure formed by LMDS contentiously, while the greater than K465 samples with the same process parameters, which made the microstructure refined. Farshidianfar has proven that the solidification structure and the geometrical dilution were closely laminated materials built by LMDS had a pause between different material deposition layer-to-layer. Mohammad has proven thatComparing the solidification structure and the geometrical related to H. theFarshidianfar real-time cooling rateof[24]. the dendritic microstructures the dilution three The deposition temperature gradient laminated materials samples was greater thanof K465 samples were closelyforming related to the real-time cooling Comparingofthe microstructures different methods, it is clear thatrate the [24]. microstructure thedendritic laminated material with of with the same process parameters, which made the microstructure refined. Mohammad H. thedeposition three different it isthe clear that the microstructure of the laminated material with layer forming numbersmethods, ratio 1:1 was smallest. Farshidianfar has proven that the solidification structure and the geometrical dilution were closely deposition layer FOR numbers ratio 1:1 was the smallest. Metals 2017, PEER REVIEW of 11 related to the7, xreal-time cooling rate [24]. Comparing the dendritic microstructures of6 the three (a) (b different forming methods, it is clear that the microstructure of the laminated material with ) (b) (a) deposition layer numbers ratio 1:1 was the smallest.
(c)
Figure 5. Cont.
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(c)
Figure 5. The dendritic microstructures of different forming methods: (a) K465; (b) 1:1 K465/Stellite-6 laminated (c) 1:2 microstructures K465/Stellite-6oflaminated material. Figurematerial; 5. The dendritic different forming methods: (a) K465; (b) 1:1 K465/Stellitelaminated material; (c) 1:2 K465/Stellite-6 laminated material. 3.2. Phase6Compositions
3.2 Compositions ThePhase phases of laser additive manufacturing K465 and Stellite-6 have been studied by
many researchers. to Li’smanufacturing research, theK465 microstructure laserbeen additive The phasesAccording of laser additive and Stellite-6ofhave studiedmanufacturing by many consisted of γ’, MC and γ [25]. According to the research of microstructure of Stellite-6 [26–28], researchers. According to Li’s research, the microstructure of laser additive manufacturing consisted of γ’, MCdeposition and γ [25]. microstructure According to themight research of microstructure of carbide Stellite-6formations [26–28], the (M Stellite-6 the Stellite-6 consist of γ (Co) and 23 C6 , M6 C, microstructure might consist of γ (Co) and carbide formations (M 23 C 6, M6C, M 7C3). Figure M7 Cdeposition ). Figure 6a illustrates the microstructures of K465 by LMDS, and white precipitates appear 3 6a illustrates the microstructures of K465 by LMDS, white precipitates appear discontinuously discontinuously in the interdendritic, which was anand MC phase. The microstructure and phase of in the interdendritic, which was an MC phase. The microstructure and phase of laminated material laminated material with deposition layer numbers ratio 1:1 varied on account of different dissimilar with deposition layer numbers ratio 1:1 varied on account of different dissimilar alloys deposition alloys deposition layers. As shown in Figure 6b, carbide distributed on the upper part of the picture layers. As shown in Figure 6b, carbide distributed on the upper part of the picture by block and by block and continuous network morphology, while these disappear on the remaining part of continuous network morphology, while these disappear on the remaining part of the image. The the image. interface material of laminated material wasinfine, as shown in Figure No near defects interfaceThe of laminated was fine, as shown Figure 6b. No defects were6b. found the were found near the interface between different deposition layers, and the border of different material interface between different deposition layers, and the border of different material deposition layer deposition layer was clear. The dendritic microstructures of different materials near similar. the border was clear. The dendritic microstructures of different materials near the border were The were microstructures and phasesand of laminated withmaterial deposition layer numbers ratio and 1:1 ratio similar. The microstructures phases ofmaterial laminated with deposition layer1:2 numbers had1:1 similar as illustrated in Figure 6c,d. Figure 6c,d K465 andwere Stellite-6 deposition 1:2 and had distribution, similar distribution, as illustrated in Figure 6c,d.were Figure 6c,d K465 and Stellite-6 layers, respectively. The white carbide phases in piece and branch developed were thein the deposition layers, respectively. The white carbide phases in piece and branch developed in were interdendritic zone of K465 deposition layer, while the carbide phase in branch developed distributed interdendritic zone of K465 deposition layer, while the carbide phase in branch developed distributed in the interdendritic zone of Stellite-6 deposition layer. in the interdendritic zone Stellite-6 deposition layer. Metals 2017, 7, x FOR PEER of REVIEW 7 of 11 (a)
(b)
K465 Interface
20 µm
(c)
Stellite-6
100 µ m
(d)
20 µm
20 µm
Figure 6. Scanning electron microscope (SEM) images of LMDS K465 superalloy: (a) K465; Figure 6. Scanning electron microscope (SEM) images of LMDS K465 superalloy: (a) K465; (b) 1:1 (b) 1:1 K465/Stellite-6 laminated material; (c) K465 deposition layer in 1:2 K465/Stellite-6 laminated K465/Stellite-6 laminated material; (c) K465 deposition layer in 1:2 K465/Stellite-6 laminated material; material; Stellite-6 deposition in 1:2 K465/Stellite-6 laminated material. (d)(d) Stellite-6 deposition layer inlayer 1:2 K465/Stellite-6 laminated material. Figure 7 illustrates the X-ray diffraction (XRD) result of laminated materials’ X–Z section. According to the results, MC and γ were found in the laminated material with deposition layer numbers ratio 1:1, while laminated material with deposition layer numbers ratio 1:2 had γ, γ’, MC, M23C6, and M7C3. Figure 8 shows the EDS of different layers of laminated material with deposition layer numbers ratio 1:2, and the carbide phase distributions in the interdendritic of both K465 and
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Figure 7 illustrates the X-ray diffraction (XRD) result of laminated materials’ X–Z section. Figure to 7 illustrates diffraction (XRD) result of laminated X–Z section. According the results,the MCX-ray and γ were found in the laminated materialmaterials’ with deposition layer According to the MC and γmaterial were found in the laminated materialratio with1:2 deposition numbers ratio 1:1,results, while laminated with deposition layer numbers had γ, γ’,layer MC, numbers ratio 1:1, while laminated material deposition numbersmaterial ratio 1:2with had deposition γ, γ’, MC, M23C6, and M7C 3. Figure 8 shows the EDS ofwith different layers layer of laminated M C , and M C . Figure 8 shows the EDS of different layers of laminated material with deposition layer numbers ratio 1:2, and the carbide phase distributions in the interdendritic of both K465 and 23 6 7 3 layer numbers ratio 1:2, and the carbide phase distributions in the interdendritic of both K465 and Stellite-6 deposition layers had higher content of Cr and C elements than other areas. Apart from Stellite-6 deposition layerswhich had higher Cr and other areas. Apart from matrix phase elements, were content Ni andofCo, otherC elements than distribute without dendritic matrix phase elements, which andresults Co, other elements distributecomposition without dendritic segregation. segregation. On account of were the Ni XRD and the elements test, the carbide On account ofinthe results andstructure the elements the carbide distributions in the distributions theXRD interdendritic werecomposition M7C3. The Mtest, 7C3 phase also existed in laminated interdendritic were M7 Cnumbers C3 phase also existed laminated withto deposition material withstructure deposition layer 1:1 based on theinSEM image.material According the SEM 3 . The M7ratio layer ratio magnitude, 1:1 based on as theshown SEM image. According to the6c, SEM in distributed a higher magnitude, imagenumbers in a higher in A zone in Figure γ’/γimage phase near the as shown in A zone in Figure 6c,K465 γ’/γ deposition phase distributed near thelaminated interdendritic structure of the K465 interdendritic structure of the layer in both materials. Therefore, the deposition in both laminated materials. layer Therefore, the laminated material of sample laminated layer material sample with deposition numbers ratio 1:2 consisted γ’, γ, with MC, deposition M23C6, and layer M7C3.numbers ratio 1:2 consisted of γ’, γ, MC, M23 C6 , and M7 C3 .
Figure 7. X-ray diffraction (XRD) spectra of different laminated materials.
7. X-ray diffraction (XRD) spectra of different laminated materials. Metals 2017, 7, xFigure FOR PEER REVIEW (a)
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Figure 8. Energy dispersive dispersiveX-ray X-rayspectroscopy spectroscopy(EDS) (EDS)ofof different layers laminated material Figure 8. Energy different layers of of laminated material 1:2.1:2. (a) Figure 8 Energy dispersive X-ray spectroscopy (EDS) of different layers of laminated material 1:2. (a) (a) K465 deposition laye; Stellite-6 deposition layer. K465 deposition laye; (b)(b) Stellite-6 deposition layer. K465 deposition laye; (b) Stellite-6 deposition layer.
The carbide carbide content in K465 K465 andand laminated materials was different, which influenced the The content in and laminated materials the The carbide content in K465 laminated materialswas wasdifferent, different, which which influenced influenced the performance of the the deposition alloy. TheThe volume fraction ofof carbides was calculated by Image ImagePlus Plus performance ofdeposition the deposition alloy. volume fraction carbideswas wascalculated calculated by Image performance of alloy. The volume fraction of carbides Plus Pro software (5.0, Media Cybernetics Inc., Rockville, MD, USA), and the volume fraction of carbides Pro software (5.0, Media Cybernetics Inc., Rockville, MD, USA), and the volume fraction of carbides Pro software (5.0, Media Cybernetics Inc., Rockville, MD, USA), and the volume fraction of carbides in LMDS single superalloy 3.17%. two kindsof laminatedmaterials, materials, the the volume in LMDS LMDS single K465K465 superalloy waswas 3.17%. In In thethe two kinds ofoflaminated laminated materials, the volume volume in single K465 superalloy was 3.17%. In the two kinds fraction of carbides in K465 superalloy deposition layers increased 5.01%.The Thecontent content of of C fraction of carbides carbides in K465 K465 superalloy deposition layers increased toto5.01%. 5.01%. The content of C Celement element fraction of in superalloy deposition layers increased to element in Stellite-6 was higher K465. content C element increasedininthe thedeposition deposition layer in Stellite-6 was higher thanthan K465. TheThe content of of C element increased layer of ofK465 K465 in laminated materials because of the remelting of Stellite-6 deposition layer. According to Tang’s research, fluid flow in the moving molten pool occurred under the effect of recoil pressure and thermal-capillary force [29]. The top of the Stellite-6 previous deposition layer was melted, mixed, resulting in the content of C element in the K465 layer increasing. As a result, the deposition layer of K465 superalloy had a higher content of carbide.
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in Stellite-6 was higher than K465. The content of C element increased in the deposition layer of in laminated materials because of the remelting of Stellite-6 deposition layer. According to Tang’s K465 in laminated materials because of the remelting of Stellite-6 deposition layer. According to research, fluid flow in the moving molten pool occurred under the effect of recoil pressure and Tang’s research, fluid flow in the moving molten pool occurred under the effect of recoil pressure and thermal-capillary force [29]. The top of the Stellite-6 previous deposition layer was melted, mixed, thermal-capillary force [29]. The top of the Stellite-6 previous deposition layer was melted, mixed, resulting in the content of C element in the K465 layer increasing. As a result, the deposition layer of resulting in the content of C element in the K465 layer increasing. As a result, the deposition layer of K465 superalloy had a higher content of carbide. K465 superalloy had a higher content of carbide.
3.3. 3.3. Composition Composition Distribution Distribution The The contents contents of of Co, Co, Ni Ni and and Cr Cr elements, elements, which which were were the the fundamental fundamental formation formation of of phases, phases, cyclically fluctuate as shown in Figure 9. At the same time, the Al element, which was the formation cyclically fluctuate as shown in Figure 9. At the same time, the Al element, which was the formation of of γ’ γ’ in in K465 K465 superalloy, superalloy, also also cyclically cyclically fluctuated. fluctuated. This This phenomenon phenomenon of of composition composition changing changing along along the deposition direction was consistent with the formation of laminated materials. Steep composition the deposition direction was consistent with the formation of laminated materials. Steep composition content content changes changes occurred occurred near near the the interface interface of of laminated laminated material. material. As As shown shown in in Figure Figure 9a, 9a, the the Ni Ni content drastic variation from K465 to Stellite-6 deposition layer was a little weakened with Stellitecontent drastic variation from K465 to Stellite-6 deposition layer was a little weakened with Stellite-6 6deposition depositionlayer layertotoK465 K465deposition depositionlayer. layer.This Thiscan can be be explained explained by by the the fluid fluid flow flow phenomenon phenomenon as as mentioned before, where, during the deposition of Stellite-6 layer, the alloy of K465 mentioned before, where, during the deposition of Stellite-6 layer, the alloy of K465 was was remelted remelted and and mixed. mixed. The The Ni Ni content content in in the the bottom bottom of of the the Stellite-6 Stellite-6 deposition deposition layer layer was was weakly weakly increased increased compared with Stellite-6 powders. The Co content variation in laminated materials compared with Stellite-6 powders. The Co content variation in laminated materials with with deposition deposition layer numbers ratio ratio1:2 1:2(Figure (Figure9b) 9b) was nearly same. thickness of compositional variation layer numbers was nearly thethe same. TheThe thickness of compositional variation zone zone was nearly 50–60 μm. was nearly 50–60 µm. (a)
Building direction
(b)
Figure 9. 9. EDS EDSline linescan scanprofiles profilesalong along the build directions of different laminated materials: (a) 1:1; Figure the build directions of different laminated materials: (a) 1:1; (b) (b) 1:2. 1:2.
3.4. Microhardness Microhardness Analysis Analysis 3.4. The microhardness microhardness variation occurred along the building direction of laminated materials as the the The composition variation, variation, as as demonstrated demonstrated in in Figure Figure 10. 10. According According to to the the analysis analysis of of Vickers Vickers hardness composition (HV)) test and microstructure, microstructure, the Stellite-6 deposition layer had had the the higher higher value value of of Vickers Vickers hardness hardness (HV compared to to the the K465 deposition deposition layer. The The microhardness microhardness difference difference was was mainly mainly affected affected by by the the compared grain size size of of structure structure and and phase phase compositions. compositions. The The Stellite-6 Stellite-6 layer layer in in laminated laminated materials materials had had higher higher grain contents of ofcarbide carbidethan thanthe theK465 K465 layer, and both of the microstructure grain similar. contents layer, and both of the microstructure grain sizessizes werewere similar. The The microhardness difference between the different deposition decreased the deposition microhardness difference between the different deposition layer layer decreased as theasdeposition layer layer height increased awaythe from the substrate. The microhardness had a dissimilarity height increased away from substrate. The microhardness variationvariation had a dissimilarity between between the building previous layer building othersthe because therate dilution of thedeposition previous deposition the previous and layer othersand because dilution of therate previous layer was layer was lower former process. deposition As thelayer deposition layer grew, the substrate lower during the during former the deposition As process. the deposition grew, the substrate temperature temperature of the next deposition layer was increased and stabilized. This made the dilution rate of the next deposition layer was increased and stabilized. This made the dilution rate of the former of the former deposition layer increase, to the different composition reduced. deposition layer increase, leading to leading the different composition phases phases being being reduced. The The microhardness of laminated materials with different deposition layernumbers numbersratio ratiohad had similar similar microhardness of laminated materials with different deposition layer evolution rules, rules, where where the the microhardness microhardness of of layer layer numbers numbers ratio ratio 1:1 1:1 and and 1:2 1:2 were, were, respectively, respectively, evolution around 400 and 380 HV0.2 Theweak weakdifference differencewas wascaused causedby bydeposition depositiondirection direction and and grain grain size. size. around 0.2. .The
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Figure laminated materials. materials. Figure 10. 10. Hardness Hardness curve curve of of K465/Stellite-6 K465/Stellite-6 laminated
4. Conclusions Conclusions 4. (1) The laminated materials materials was was significantly significantly reduced reduced (1) The crack crack tendency tendency in in LMDS LMDS K465/Stellite-6 K465/Stellite-6 laminated compared with LMDS single K465 superalloy. compared with LMDS single K465 superalloy. (2) The The microstructure in laminated materials was was refined refined compared compared with with LMDS single K465 (2) microstructure in laminated materials LMDS single K465 superalloy. Compared K465 deposition layer in laminated material samples had superalloy. Comparedwith withLMDS LMDSK465, K465,the the K465 deposition layer in laminated material samples a higher content of carbide. The K465/Stellite-6 1:2 laminated material sample consisted of γ, γ’, MC, had a higher content of carbide. The K465/Stellite-6 1:2 laminated material sample consisted of γ, γ’, M23 CM 6 ,23M 3 7phases. MC, C76,CM C3 phases. (3) The The composition composition and and microhardness microhardness distribution distribution of of laminated laminated materials materials showed showed aa variation variation (3) occurring along the building direction. A weak composition gradual variation happened on the the occurring along the building direction. A weak composition gradual variation happened on interface of layer. The microhardness of interface of different different layers layersbecause becauseof ofthe theremelting remeltingofofthe theprevious previousbuild build layer. The microhardness layer numbers ratio 1:1 and 1:2 were, respectively, around 400 and 380 HV . 0.2 0.2. of layer numbers ratio 1:1 and 1:2 were, respectively, around 400 and 380 HV Acknowledgments: Acknowledgments: The The authors authors would like to acknowledge the National Science-technology Support Plan 2015BAF08B01-01) and and the the National National Key Research and Development Programme of China Projects (Grant No. 2015BAF08B01-01) (Grant No. (Grant No. 2016YFB1100502) 2016YFB1100502) Jibin Zhao Zhao and and Zhiguo Zhiguo Wang Wang conceived Fan Shi Shi and and Author Contributions: Author Contributions: Jibin conceived and and designed designed the the experiments; experiments; Fan Hongyu Zhang performed the experiments; Zhiguo Wang and Yuhui Zhao analyzed the data; Zhiguo Wang wrote Hongyu the paper.Zhang performed the experiments; Zhiguo Wang and Yuhui Zhao analyzed the data; Zhiguo Wang wrote the paper. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest.
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