- Email: [email protected]
Weld deposition of nickel on titanium for surface hardening with Ti-Ni-based intermetallic compounds
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Weld deposition of nickel on titanium for surface hardening with Ti-Ni-based intermetallic compounds Vivek Chaitanya Peddiraju a,⇑, Kranthi Kumar Pulapakura b, Desuru Sree Jagadeesh c, K.S. Athira a, Srinath Gudur d, S. Suryakumar d, Subhradeep Chatterjee a a
Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502285, India Presently with Rastriya Ispat Nigam Limited, Vizag Steel Plant, Visakhapatnam 53003, India Presently with Renault Nissan TBCI Pvt. Ltd., Mahindra World City, 603004, India d Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502285, India b c
a r t i c l e
i n f o
Article history: Received 29 July 2019 Accepted 17 September 2019 Available online xxxx Keywords: Surface alloying of titanium Weld deposition GMAW Ni-Ti Characterization Intermetallic compounds
a b s t r a c t Despite its excellent bulk mechanical properties, titanium performs poorly in tribological applications. Efforts to overcome this shortcoming have focused mainly surface modification using laser cladding with ceramic additives or intermetallic compounds (IMCs) formed during cladding. We present an alternative method using weld deposition for the production of IMC-based hard surface layer on titanium using gas metal arc welding (GMAW) with nickel as the filler wire. We observe formation of different Ti-Ni based IMCs (Ti2Ni, NiTi and Ni3Ti) in the fusion zone which results in considerable hardening of the surface. Microstructural characterization of the deposited samples give insight into the formation of IMCs. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Although titanium alloys possess high specific strength, excellent corrosion resistance and bio-compatibility which have led to their adoption in, for example, aerospace, chemical and biomedical applications, they have poor abrasion resistance, severe adhesion wear and susceptibility to fretting wear which limits their usability [1,2]. Efforts to improve their tribological properties by surface modification techniques have mainly focused on laser cladding technique [3,4]. While most studies focused on formation of in situ ceramic reinforcement phases along with IMC matrix in the microstructure of the coating [5–9], some were directed at creating pre-synthesized ceramic phase reinforcement with an in situ formed intermetallic compounds (IMCs) of titanium. For example, formation of Ti-Al IMCs by employing Ti/Al-X (X: TiC, AlN, AlB2) powder system has been reported [10–12]. Ti-Ni IMC based claddings have also been produced by using nickel-base powders on titanium [13,14]. Further, some researchers have employed nickel with ceramic reinforcements in the powder system [5,8,15].
⇑ Corresponding author. E-mail address: [email protected] (V.C. Peddiraju).
In the present work, we use an inexpensive alternative to laser cladding, viz. a gas metal arc welding (GMAW) based system to deposit nickel on commercially pure (CP) titanium substrate. Melting and mixing of substrate and filler wire result in an alloyed fusion zone whose constitution can be varied by changing the welding process parameters. We report the results of surface alloying in terms of composition, microstructure and hardness variation as a function of distance from the fusion interface in the substrate. Formation of different IMCs is further analysed and correlated with hardness of the alloyed layer.
2. Materials and methods The weld deposition system consists of a static GMAW torch rigidly fixed by a support on the work table. The substrate is mounted on a microprocessor controlled stage movable in two in-plane directions. A trailing shield with an argon gas inlet is attached to the welding torch for deposition under inert atmosphere. CP titanium (grade 2) is used as the substrate material and pure nickel electrode (ERNi-1) is used as the filler wire. Weld depositions are made using Fronius pulsed GMAW (GMAW-P) set up (CMT advanced 4000 R power source equipped with RCU 5000-i remote control unit) in synergic mode. In this mode, wire
https://doi.org/10.1016/j.matpr.2019.09.075 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
2
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 1 Process parameters for single track weld deposition experiments. S. No
Wire feed rate (m/min)
Current (Ampere)
Voltage (Volt)
Travel Speed (mm/min)
1 2 3
2.0 2.2 2.5
68 76 87
23 23.4 24
400 400 400
(SEM), coupled with an EDAX Octane Elite energy dispersive spectroscope (EDS) are used study the phase formation. Hardness variation in the samples is studied using a Vicker’s micro indentation instrument (EMCO TEST, Durascan 20) under a load of 0.3 kgf for 10 s. 3. Results and discussions
feed rate is given as input and appropriate current-voltage values are chosen dynamically according to the program selected. To investigate alloying and phase formation in the fusion zone of the substrates, we carried out three single track deposition experiments with varying process parameters (see Table 1). For microstructural observation and microhardness studies, samples are cut from these tracks using electro discharge machining (EDM). Standard mounting, grinding, polishing and etching techniques were followed to prepare samples for metallographic observation. A mixture of 8–10% v/v HF, 14–16%v/v HNO3 and balance deionized H2O is used as an etchant. A Leica DM 2700 M optical microscope is used to collect weld pool microstructures at low magnification. A JEOL JSM-7800F scanning electron microscope
Fig. 1(a)–(c) shows the macroscopic views of the surface alloyed layer for the three chosen wire feed rates. It is clear that the 2.0 m/min feed rate conditions results in a coating having poor bonding with the substrate and significant porosity. However, the conditions 2.2 m/min and 2.5 m/min resulted in a good bonding of the alloyed layer with unalloyed substrate without any macroscopic cracks or porosity. Good metallurgical continuity from base metal to the coated metal without any cracks at interface was observed under these latter conditions. To reveal variation of microstructure in the alloyed fusion zone, a large number of low magnification optical microscope images were taken and superimposed to form a composite image. Fig. 2 shows a collage made from the longitudinal section sample #3
Fig.1. Surface alloyed layers deposited at wire feed rates (a) 2.0 m/min, (b) 2.2 m/min, (c) 2.5 m/min.
Fig. 2. Collage of the longitudinal section of track deposited with 2.5 m/min feed rate.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
(2.5 m/min feed rate). It clearly shows the heat effected zone, the interface zone and fusion zone. The interface zone is dark due to slight over etching. Different contrast exhibited in this image as a function of depth from surface is because of the variation in phases and the resulting microstructures in different locations. Identifica-
3
tion of the various phases and microstructures is based on SEM and EDS results presented later. A composition line scan across the fusion zone obtained using EDS is shown in Fig. 3(a). The approximate location of the line indicated in the inset. Near the fusion interface (within a distance of
Fig. 3. (a) Composition line scan across the fusion zone (b) Ti-Ni binary phase diagram [16].
Fig 4. Fusion zone microstructures: (a) Ti2Ni dendrites with E1 in the interface zone, (b) NiTi with pockets of Ti2Ni (c) Ni3Ti with eutectic E2, (d) NiTi dendrites with E2.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
4
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 5. (a) Hardness variation from base metal toward the top surface (wire feed rate indicated in the legend), (b) A schematic representation of microstructural variation in the fusion zone.
60 mm), composition changes in a step-like discontinuous manner. Away from the fusion interface, it fluctuates around a mean composition in bulk of the fusion zone. The composition profile is correlated with phases and microstructure in the alloyed layer. The Ti-Ni binary phase diagram presented in Fig. 3(b) shows that the composition goes through the regions of existence of the different IMCs in this system, viz. Ti2Ni, NiTi and Ni3Ti. Microstructural details in the fusion zone, as revealed in SEM images, are presented in Fig. 4. Fig. 4(a) shows that the fusion interface in the titanium substrate is marked by dendrites which grow from the fusion zone toward the base metal. EDS analysis confirmed these dendrites to be Ti2Ni. A eutectic structure is observed in between these dendrites with a composition of 25– 27 at.% Ni, which according to the Ti-Ni equilibrium phase diagram [15], corresponds to the Ti + Ti2Ni eutectic (denoted here as E1). Fig. 4(b) shows a location above this Ti2Ni-rich layer. The weld composition here is approximately 55 at.% Ni and NiTi is the primary phase with pockets of Ti2Ni. Further into the weld pool, in Fig. 4(c), the microstructure consists mainly of faceted Ni3Ti phase and another eutectic mixture. The average composition of this mixture (65 at.% Ni) points to the NiTi + Ni3Ti eutectic in the Ti-Ni phase diagram and is denoted here by E2. Further towards the top, in Fig. 4(d), the microstructure changes over to NiTi dendrites and an interdendritic E2 eutectic. Fig. 5(a) shows microhardness variation in the fusion zone for different choice of process parameters (viz. wire feed rate). In all cases, hardness increases from a relatively low value in the substrate to considerably higher values into the fusion zone. The peak hardness is in the range of 650–700 HV. The hardness variation in the coating is a direct result of the heterogeneous IMC based microstructures formed during the surface alloying process. A threefold increase in hardness of the base metal is achieved with this process without employing any ceramic reinforcements. The peak hardness corresponded to regions having NiTi dendrites with small fraction of interdendritic eutectic E2. A lower feed rate of 2.0 mm/min resulted in the highest hardness among the three samples studies. The diverse microstructures observed in the fusion zone is summarized schematically in Fig. 5(b). We note that formation of a combination of these IMCs has also been reported previously during laser cladding of titanium with Ni powders [6,7,14,17,18]. It can be understood by referring to the binary Ti-Ni phase diagram
in Fig. 3(b). As the composition of the mixed zone changes progressively from Ti-rich in the bottom to relatively Ni-rich in the top, formation of different intermetallic phases, viz., Ti2Ni, NiTi and Ni3Ti respectively, becomes feasible. Formation Ni3Ti in the intermediate depth (Figs. 2 and 4(c)), however, does not follow this monotonic pattern; it most likely formed due to local Ni-enrichment in certain regions produced by incomplete mixing of the nickel droplets in the alloy melt. Formation of Ni3Ti phase, as well as the Ni3Ti + NiTi eutectic (E2), have in general not been reported in the cladding studies, where the required stoichiometry for their formation might not have been reached. However, both Ni3Ti and eutectic have been observed to form during dissimilar welding of Ti and Ni [19]. The highest hardness observed in the present study without any ceramic reinforcements can be attributed to the composite structure of NiTi dendrites with E2 eutectic in its interdendritic space. The only E2-dominated regions in the fusion zone lead to a lower hardness compared to the former. By varying the process parameters judiciously, it may be possible to increase the extent of the harder region further and enhance the wear resistance of titanium entire through the in situ formation of IMCs. 4. Conclusions An alternative to ceramic particle induced hardening of titanium using laser cladding process is introduced in the present study. We used a GMAW based set up to produce Ti-Ni IMCs in situ through surface alloying of CP titanium with pure nickel. This resulted in a significant hardness enhancement of the surface layer of the substrate. Microstructure of the alloyed layer varied across the fusion zone and it was rationalized by referring to the phase diagram of the Ti-Ni system. Microstructural characterization highlighted the scope of further property optimization through variation in deposition parameters. Acknowledgements SC acknowledges financial grant from DST-SERB, Govt. of India under ECR/2016/001185 for this work. All authors acknowledge DST-FIST (SR/FST/ETI-421/2016) grant for the microscopy facility at Department of MSME, IITH which was used in this work. Authors
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
acknowledge Mr. Ramu, Mr. Ramesh, and Mr. Kiran of IITH Manufacturing Lab for their help in setting up the weld deposition system. References [1] K.G. Budinski, Tribological properties of titanium alloys, Wear 151 (21) (1991) 203–217. [2] H. Dong, Tribological properties of titanium-based alloys, in: Surface Engineering of Light Alloys, Woodhead Publishing, 2010, pp. 58–80. [3] Y.S. Tian, C.Z. Chen, S.T. Li, Q.H. Huo, Research progress on laser surface modification of titanium alloys, Appl. Surf. Sci. 242 (1-2) (2005) 177–184. [4] F. Weng, C. Chen, H. Yu, Research status of laser cladding on titanium and its alloys: a review, Mater. Des. 58 (2014) 412–425. [5] L.L. Bai, J. Li, J.L. Chen, R. Song, J.Z. Shao, C.C. Qu, Effect of the content of B4C on microstructural evolution and wear behaviors of the laser-clad coatings fabricated on Ti6Al4V, Opt. Laser Technol. 76 (2016) 33–45. [6] S. Feng, H. Tang, S. Zhang, H. Wang, Microstructure and wear resistance of laser clad TiB–TiC/TiNi–Ti2Ni intermetallic coating on titanium alloy, Trans. Nonferrous Met. Soc. China 22 (7) (2012) 1667–1673. [7] R. Song, J. Li, J.Z. Shao, L.L. Bai, J.L. Chen, C.C. Qu, Microstructural evolution and wear behaviors of laser cladding Ti2Ni/a (Ti) dual-phase coating reinforced by TiB and TiC, Appl. Surf. Sci. 355 (2015) 298–309. [8] P.A. Molian, L. Hualun, Laser cladding of Ti-6Al-4V with BN for improved wear performance, Wear 130 (2) (1989) 337–352. [9] M. Li, J. Huang, Y.Y. Zhu, Z.G. Li, Effect of heat input on the microstructure of insitu synthesized TiN–TiB/Ti based composite coating by laser cladding, Surf. Coat. Technol. 206 (19–20) (2012) 4021–4026.
5
[10] L. Jianing, C. Chuanzhong, Z. Lei, Microstructure characteristics of Ti3Al/TiC ceramic layer deposited by laser cladding, Int. J. Refract. Metal Hard Mater. 29 (1) (2011) 49–53. [11] H. Liu, X. Zhang, Y. Jiang, R. Zhou, Microstructure and high temperature oxidation resistance of in-situ synthesized TiN/Ti3Al intermetallic composite coatings on Ti6Al4V alloy by laser cladding process, J. Alloys Compd. 670 (2016) 268–274. [12] Y. Feng, K. Feng, C. Yao, Z. Li, J. Sun, Microstructure and properties of in-situ synthesized (Ti3Al + TiB)/Ti composites by laser cladding, Mater. Des. 157 (2018) 258–272. [13] Q. Meng, L. Geng, D. Ni, Laser cladding NiCoCrAlY coating on Ti-6Al-4V, Mater. Lett. 59 (22) (2005) 2774–2777. [14] F. Liu, Y. Mao, X. Lin, B. Zhou, T. Qian, Microstructure and high temperature oxidation resistance of Ti-Ni gradient coating on TA2 titanium alloy fabricated by laser cladding, Opt. Laser Technol. 83 (2016) 140–147. [15] R.L. Sun, Y.W. Lei, W. Niu, Laser clad TiC reinforced NiCrBSi composite coatings on Ti–6Al–4V alloy using a CW CO2 laser, Surf. Coat. Technol. 203 (10-11) (2009) 1395–1399. [16] T.B. Massalski, H. Okamoto, P. Subramanian, L. Kacprzak, Binary Alloy Phase Diagrams, ASM International, Materials Park, 1990, pp. 2874–2876. [17] H.M. Wang, Y.F. Liu, Microstructure and wear resistance of laser clad Ti5Si3/ NiTi2 intermetallic composite coating on titanium alloy, Mater. Sci. Eng.: A 338 (1-2) (2002) 126–132. [18] G.J. Li, J. Li, X. Luo, Effects of post-heat treatment on microstructure and properties of laser cladded composite coatings on titanium alloy substrate, Opt. Laser Technol. 65 (2015) 66–75. [19] S. Chatterjee, T.A. Abinandanan, G. Madhusudhan Reddy, K. Chattopadhyay, Microstructure formation in dissimilar metal welds: electron beam welding of Ti/Ni, Metall. Mater. Trans. A 47 (2) (2016) 769–776.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Weld deposition of nickel on titanium for surface hardening with Ti-Ni-based intermetallic compounds Vivek Chaitanya Peddiraju a,⇑, Kranthi Kumar Pulapakura b, Desuru Sree Jagadeesh c, K.S. Athira a, Srinath Gudur d, S. Suryakumar d, Subhradeep Chatterjee a a
Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502285, India Presently with Rastriya Ispat Nigam Limited, Vizag Steel Plant, Visakhapatnam 53003, India Presently with Renault Nissan TBCI Pvt. Ltd., Mahindra World City, 603004, India d Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad, Sangareddy 502285, India b c
a r t i c l e
i n f o
Article history: Received 29 July 2019 Accepted 17 September 2019 Available online xxxx Keywords: Surface alloying of titanium Weld deposition GMAW Ni-Ti Characterization Intermetallic compounds
a b s t r a c t Despite its excellent bulk mechanical properties, titanium performs poorly in tribological applications. Efforts to overcome this shortcoming have focused mainly surface modification using laser cladding with ceramic additives or intermetallic compounds (IMCs) formed during cladding. We present an alternative method using weld deposition for the production of IMC-based hard surface layer on titanium using gas metal arc welding (GMAW) with nickel as the filler wire. We observe formation of different Ti-Ni based IMCs (Ti2Ni, NiTi and Ni3Ti) in the fusion zone which results in considerable hardening of the surface. Microstructural characterization of the deposited samples give insight into the formation of IMCs. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Although titanium alloys possess high specific strength, excellent corrosion resistance and bio-compatibility which have led to their adoption in, for example, aerospace, chemical and biomedical applications, they have poor abrasion resistance, severe adhesion wear and susceptibility to fretting wear which limits their usability [1,2]. Efforts to improve their tribological properties by surface modification techniques have mainly focused on laser cladding technique [3,4]. While most studies focused on formation of in situ ceramic reinforcement phases along with IMC matrix in the microstructure of the coating [5–9], some were directed at creating pre-synthesized ceramic phase reinforcement with an in situ formed intermetallic compounds (IMCs) of titanium. For example, formation of Ti-Al IMCs by employing Ti/Al-X (X: TiC, AlN, AlB2) powder system has been reported [10–12]. Ti-Ni IMC based claddings have also been produced by using nickel-base powders on titanium [13,14]. Further, some researchers have employed nickel with ceramic reinforcements in the powder system [5,8,15].
⇑ Corresponding author. E-mail address: [email protected] (V.C. Peddiraju).
In the present work, we use an inexpensive alternative to laser cladding, viz. a gas metal arc welding (GMAW) based system to deposit nickel on commercially pure (CP) titanium substrate. Melting and mixing of substrate and filler wire result in an alloyed fusion zone whose constitution can be varied by changing the welding process parameters. We report the results of surface alloying in terms of composition, microstructure and hardness variation as a function of distance from the fusion interface in the substrate. Formation of different IMCs is further analysed and correlated with hardness of the alloyed layer.
2. Materials and methods The weld deposition system consists of a static GMAW torch rigidly fixed by a support on the work table. The substrate is mounted on a microprocessor controlled stage movable in two in-plane directions. A trailing shield with an argon gas inlet is attached to the welding torch for deposition under inert atmosphere. CP titanium (grade 2) is used as the substrate material and pure nickel electrode (ERNi-1) is used as the filler wire. Weld depositions are made using Fronius pulsed GMAW (GMAW-P) set up (CMT advanced 4000 R power source equipped with RCU 5000-i remote control unit) in synergic mode. In this mode, wire
https://doi.org/10.1016/j.matpr.2019.09.075 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
2
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
Table 1 Process parameters for single track weld deposition experiments. S. No
Wire feed rate (m/min)
Current (Ampere)
Voltage (Volt)
Travel Speed (mm/min)
1 2 3
2.0 2.2 2.5
68 76 87
23 23.4 24
400 400 400
(SEM), coupled with an EDAX Octane Elite energy dispersive spectroscope (EDS) are used study the phase formation. Hardness variation in the samples is studied using a Vicker’s micro indentation instrument (EMCO TEST, Durascan 20) under a load of 0.3 kgf for 10 s. 3. Results and discussions
feed rate is given as input and appropriate current-voltage values are chosen dynamically according to the program selected. To investigate alloying and phase formation in the fusion zone of the substrates, we carried out three single track deposition experiments with varying process parameters (see Table 1). For microstructural observation and microhardness studies, samples are cut from these tracks using electro discharge machining (EDM). Standard mounting, grinding, polishing and etching techniques were followed to prepare samples for metallographic observation. A mixture of 8–10% v/v HF, 14–16%v/v HNO3 and balance deionized H2O is used as an etchant. A Leica DM 2700 M optical microscope is used to collect weld pool microstructures at low magnification. A JEOL JSM-7800F scanning electron microscope
Fig. 1(a)–(c) shows the macroscopic views of the surface alloyed layer for the three chosen wire feed rates. It is clear that the 2.0 m/min feed rate conditions results in a coating having poor bonding with the substrate and significant porosity. However, the conditions 2.2 m/min and 2.5 m/min resulted in a good bonding of the alloyed layer with unalloyed substrate without any macroscopic cracks or porosity. Good metallurgical continuity from base metal to the coated metal without any cracks at interface was observed under these latter conditions. To reveal variation of microstructure in the alloyed fusion zone, a large number of low magnification optical microscope images were taken and superimposed to form a composite image. Fig. 2 shows a collage made from the longitudinal section sample #3
Fig.1. Surface alloyed layers deposited at wire feed rates (a) 2.0 m/min, (b) 2.2 m/min, (c) 2.5 m/min.
Fig. 2. Collage of the longitudinal section of track deposited with 2.5 m/min feed rate.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
(2.5 m/min feed rate). It clearly shows the heat effected zone, the interface zone and fusion zone. The interface zone is dark due to slight over etching. Different contrast exhibited in this image as a function of depth from surface is because of the variation in phases and the resulting microstructures in different locations. Identifica-
3
tion of the various phases and microstructures is based on SEM and EDS results presented later. A composition line scan across the fusion zone obtained using EDS is shown in Fig. 3(a). The approximate location of the line indicated in the inset. Near the fusion interface (within a distance of
Fig. 3. (a) Composition line scan across the fusion zone (b) Ti-Ni binary phase diagram [16].
Fig 4. Fusion zone microstructures: (a) Ti2Ni dendrites with E1 in the interface zone, (b) NiTi with pockets of Ti2Ni (c) Ni3Ti with eutectic E2, (d) NiTi dendrites with E2.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
4
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 5. (a) Hardness variation from base metal toward the top surface (wire feed rate indicated in the legend), (b) A schematic representation of microstructural variation in the fusion zone.
60 mm), composition changes in a step-like discontinuous manner. Away from the fusion interface, it fluctuates around a mean composition in bulk of the fusion zone. The composition profile is correlated with phases and microstructure in the alloyed layer. The Ti-Ni binary phase diagram presented in Fig. 3(b) shows that the composition goes through the regions of existence of the different IMCs in this system, viz. Ti2Ni, NiTi and Ni3Ti. Microstructural details in the fusion zone, as revealed in SEM images, are presented in Fig. 4. Fig. 4(a) shows that the fusion interface in the titanium substrate is marked by dendrites which grow from the fusion zone toward the base metal. EDS analysis confirmed these dendrites to be Ti2Ni. A eutectic structure is observed in between these dendrites with a composition of 25– 27 at.% Ni, which according to the Ti-Ni equilibrium phase diagram [15], corresponds to the Ti + Ti2Ni eutectic (denoted here as E1). Fig. 4(b) shows a location above this Ti2Ni-rich layer. The weld composition here is approximately 55 at.% Ni and NiTi is the primary phase with pockets of Ti2Ni. Further into the weld pool, in Fig. 4(c), the microstructure consists mainly of faceted Ni3Ti phase and another eutectic mixture. The average composition of this mixture (65 at.% Ni) points to the NiTi + Ni3Ti eutectic in the Ti-Ni phase diagram and is denoted here by E2. Further towards the top, in Fig. 4(d), the microstructure changes over to NiTi dendrites and an interdendritic E2 eutectic. Fig. 5(a) shows microhardness variation in the fusion zone for different choice of process parameters (viz. wire feed rate). In all cases, hardness increases from a relatively low value in the substrate to considerably higher values into the fusion zone. The peak hardness is in the range of 650–700 HV. The hardness variation in the coating is a direct result of the heterogeneous IMC based microstructures formed during the surface alloying process. A threefold increase in hardness of the base metal is achieved with this process without employing any ceramic reinforcements. The peak hardness corresponded to regions having NiTi dendrites with small fraction of interdendritic eutectic E2. A lower feed rate of 2.0 mm/min resulted in the highest hardness among the three samples studies. The diverse microstructures observed in the fusion zone is summarized schematically in Fig. 5(b). We note that formation of a combination of these IMCs has also been reported previously during laser cladding of titanium with Ni powders [6,7,14,17,18]. It can be understood by referring to the binary Ti-Ni phase diagram
in Fig. 3(b). As the composition of the mixed zone changes progressively from Ti-rich in the bottom to relatively Ni-rich in the top, formation of different intermetallic phases, viz., Ti2Ni, NiTi and Ni3Ti respectively, becomes feasible. Formation Ni3Ti in the intermediate depth (Figs. 2 and 4(c)), however, does not follow this monotonic pattern; it most likely formed due to local Ni-enrichment in certain regions produced by incomplete mixing of the nickel droplets in the alloy melt. Formation of Ni3Ti phase, as well as the Ni3Ti + NiTi eutectic (E2), have in general not been reported in the cladding studies, where the required stoichiometry for their formation might not have been reached. However, both Ni3Ti and eutectic have been observed to form during dissimilar welding of Ti and Ni [19]. The highest hardness observed in the present study without any ceramic reinforcements can be attributed to the composite structure of NiTi dendrites with E2 eutectic in its interdendritic space. The only E2-dominated regions in the fusion zone lead to a lower hardness compared to the former. By varying the process parameters judiciously, it may be possible to increase the extent of the harder region further and enhance the wear resistance of titanium entire through the in situ formation of IMCs. 4. Conclusions An alternative to ceramic particle induced hardening of titanium using laser cladding process is introduced in the present study. We used a GMAW based set up to produce Ti-Ni IMCs in situ through surface alloying of CP titanium with pure nickel. This resulted in a significant hardness enhancement of the surface layer of the substrate. Microstructure of the alloyed layer varied across the fusion zone and it was rationalized by referring to the phase diagram of the Ti-Ni system. Microstructural characterization highlighted the scope of further property optimization through variation in deposition parameters. Acknowledgements SC acknowledges financial grant from DST-SERB, Govt. of India under ECR/2016/001185 for this work. All authors acknowledge DST-FIST (SR/FST/ETI-421/2016) grant for the microscopy facility at Department of MSME, IITH which was used in this work. Authors
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075
V.C. Peddiraju et al. / Materials Today: Proceedings xxx (xxxx) xxx
acknowledge Mr. Ramu, Mr. Ramesh, and Mr. Kiran of IITH Manufacturing Lab for their help in setting up the weld deposition system. References [1] K.G. Budinski, Tribological properties of titanium alloys, Wear 151 (21) (1991) 203–217. [2] H. Dong, Tribological properties of titanium-based alloys, in: Surface Engineering of Light Alloys, Woodhead Publishing, 2010, pp. 58–80. [3] Y.S. Tian, C.Z. Chen, S.T. Li, Q.H. Huo, Research progress on laser surface modification of titanium alloys, Appl. Surf. Sci. 242 (1-2) (2005) 177–184. [4] F. Weng, C. Chen, H. Yu, Research status of laser cladding on titanium and its alloys: a review, Mater. Des. 58 (2014) 412–425. [5] L.L. Bai, J. Li, J.L. Chen, R. Song, J.Z. Shao, C.C. Qu, Effect of the content of B4C on microstructural evolution and wear behaviors of the laser-clad coatings fabricated on Ti6Al4V, Opt. Laser Technol. 76 (2016) 33–45. [6] S. Feng, H. Tang, S. Zhang, H. Wang, Microstructure and wear resistance of laser clad TiB–TiC/TiNi–Ti2Ni intermetallic coating on titanium alloy, Trans. Nonferrous Met. Soc. China 22 (7) (2012) 1667–1673. [7] R. Song, J. Li, J.Z. Shao, L.L. Bai, J.L. Chen, C.C. Qu, Microstructural evolution and wear behaviors of laser cladding Ti2Ni/a (Ti) dual-phase coating reinforced by TiB and TiC, Appl. Surf. Sci. 355 (2015) 298–309. [8] P.A. Molian, L. Hualun, Laser cladding of Ti-6Al-4V with BN for improved wear performance, Wear 130 (2) (1989) 337–352. [9] M. Li, J. Huang, Y.Y. Zhu, Z.G. Li, Effect of heat input on the microstructure of insitu synthesized TiN–TiB/Ti based composite coating by laser cladding, Surf. Coat. Technol. 206 (19–20) (2012) 4021–4026.
5
[10] L. Jianing, C. Chuanzhong, Z. Lei, Microstructure characteristics of Ti3Al/TiC ceramic layer deposited by laser cladding, Int. J. Refract. Metal Hard Mater. 29 (1) (2011) 49–53. [11] H. Liu, X. Zhang, Y. Jiang, R. Zhou, Microstructure and high temperature oxidation resistance of in-situ synthesized TiN/Ti3Al intermetallic composite coatings on Ti6Al4V alloy by laser cladding process, J. Alloys Compd. 670 (2016) 268–274. [12] Y. Feng, K. Feng, C. Yao, Z. Li, J. Sun, Microstructure and properties of in-situ synthesized (Ti3Al + TiB)/Ti composites by laser cladding, Mater. Des. 157 (2018) 258–272. [13] Q. Meng, L. Geng, D. Ni, Laser cladding NiCoCrAlY coating on Ti-6Al-4V, Mater. Lett. 59 (22) (2005) 2774–2777. [14] F. Liu, Y. Mao, X. Lin, B. Zhou, T. Qian, Microstructure and high temperature oxidation resistance of Ti-Ni gradient coating on TA2 titanium alloy fabricated by laser cladding, Opt. Laser Technol. 83 (2016) 140–147. [15] R.L. Sun, Y.W. Lei, W. Niu, Laser clad TiC reinforced NiCrBSi composite coatings on Ti–6Al–4V alloy using a CW CO2 laser, Surf. Coat. Technol. 203 (10-11) (2009) 1395–1399. [16] T.B. Massalski, H. Okamoto, P. Subramanian, L. Kacprzak, Binary Alloy Phase Diagrams, ASM International, Materials Park, 1990, pp. 2874–2876. [17] H.M. Wang, Y.F. Liu, Microstructure and wear resistance of laser clad Ti5Si3/ NiTi2 intermetallic composite coating on titanium alloy, Mater. Sci. Eng.: A 338 (1-2) (2002) 126–132. [18] G.J. Li, J. Li, X. Luo, Effects of post-heat treatment on microstructure and properties of laser cladded composite coatings on titanium alloy substrate, Opt. Laser Technol. 65 (2015) 66–75. [19] S. Chatterjee, T.A. Abinandanan, G. Madhusudhan Reddy, K. Chattopadhyay, Microstructure formation in dissimilar metal welds: electron beam welding of Ti/Ni, Metall. Mater. Trans. A 47 (2) (2016) 769–776.
Please cite this article as: V. C. Peddiraju, K. K. Pulapakura, D. S. Jagadeesh et al., Weld deposition of nickel on titanium for surface hardening with Ti-Nibased intermetallic compounds, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.075