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Microstructural Evolution and Microhardness of Direct Laser Clad TiC Dispersed Titanium Aluminide (Ti45Al5Nb0.5Si) Alloy
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Procedia Manufacturing 35 (2019) 840–846
2nd International Conference on Sustainable Materials Processing and Manufacturing 2nd International Conference on Sustainable Materials Processing and Manufacturing (SMPM 2019) (SMPM 2019)
Microstructural Evolution and Microhardness of Direct Laser Microstructural Evolution and Microhardness of Direct Laser Clad TiC Dispersed Titanium Aluminide (Ti45Al5Nb0.5Si) Alloy Clad TiC Dispersed Titanium Aluminide (Ti45Al5Nb0.5Si) Alloy Jyotsna Dutta Majumdara* , Silja Katharina Rittinghausb, Konrad Wissenbach c, Daniel a b c c , Silja Katharina , Konrad Wissenbach , Daniel Jyotsna Dutta Majumdar Höched*, Carsten Blawert dRittinghaus , and Andreas Weisheit d d c Höche , Carsten Blawert , and Andreas Weisheit a Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, India, Lehrstuhl fürLasertechnik LLTand RWTH Aachen University,Indian Steinbachstraße D-52074 Kharagpur, Aachen, Germany, Department of Metallurgical Materials Engineering, Institute of 15, Technology India, c b fürLasertechnik ILT, Steinbachstraße 15, D-52074 Aachen, Germany, LehrstuhlFraunhofer-Institut fürLasertechnik LLT RWTH Aachen University, Steinbachstraße 15, D-52074 Aachen, Germany, d c Institut fürWerkstoffforschung, Helmholtz-ZentrumGeesthacht, Max-Planck-Straße D-21502 Geesthacht, Germany, Fraunhofer-Institut fürLasertechnik ILT, Steinbachstraße 15, D-520741,Aachen, Germany, d Institut fürWerkstoffforschung, Helmholtz-ZentrumGeesthacht, Max-Planck-Straße 1, D-21502 Geesthacht, Germany, ba
Abstract Abstract In the present study, the effect of TiC additions (10 wt.% and 20 wt.%) on the microstructure and microhardness of direct laser clad based titanium has been laser claddingand hasmicrohardness been conductedofusing high In theTi45Al5Nb0.5Si present study, the effect of TiCaluminide additionsalloy (10 wt.% and undertaken. 20 wt.%) onDirect the microstructure directa laser power (3 kW) fiber optic delivered laser (with beam diameter of 2 mm) using a 3-axis system in a layer by clad Ti45Al5Nb0.5Si based titaniumNd:YAG aluminide alloy has abeen undertaken. Direct laser cladding hashandling been conducted using a high layer on Ti-6Al-4V substrate to develop coupon withdiameter a dimension 10 mm mm xhandling 5 mm. Addition of aTiC leads powerfashion (3 kW)tofiber optic delivered Nd:YAG laser a(with a beam of 2 of mm) usingx a103-axis system in layer by to formation defect free microstructures under varied parameters, except aof few conditions. is formation of layer fashion of to on Ti-6Al-4V substrate to develop a coupon with a dimension 10 processing mm x 10 mm x 5 mm. There Addition of TiC leads complex carbides (Ti2AlC, addition to TiC phase in the microstructure of duplex There is phase. There of is to formation of defect free Ti microstructures underinvaried parameters, except a few processing conditions. formation 3AlC2 and Ti2AlC) improvement in microhardness due2 to TiC which increases with increased quantity of TiC. Laser power phase. and scan speed and Ti2addition, AlC) in addition to TiC phase in the microstructure of duplex There is complex carbides (Ti2AlC, Ti3AlC influences the in microhardness, powder feed which rate didincreases not influence it significantly. improvement microhardnesshowever, due to TiC addition, with increased quantity of TiC. Laser power and scan speed influences the microhardness, however, powder feed rate did not influence it significantly. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of Elsevier the organizing © 2019 The Authors. Published by B.V. committee of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019. Keywords: Titanium aluminide; titanium carbide; microstructure; XRD; microhardness Keywords: Titanium aluminide; titanium carbide; microstructure; XRD; microhardness
* Corresponding author. address:author. [email protected] * E-mail Corresponding E-mail address: [email protected] 2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review©under the organizing committee 2351-9789 2019responsibility The Authors. of Published by Elsevier B.V. of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019.
2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of SMPM 2019. 10.1016/j.promfg.2019.06.030
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Jyotsna Dutta Majumdar et al. / Procedia Manufacturing 35 (2019) 840–846 Author name / Procedia Manufacturing 00 (2019) 000–000
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1. Introduction A continued efforts on the development intermetallic alloys for gas turbine engines was driven by replacement of steels or Ni based alloys (density 8g/cm3to 8.5 g/cm3) by materials with lower density (4 g/cm3 to 7 g/cm3) [1].In this regard, dual phase gamma titanium aluminides (γ-TiAl) have attracted a significant attention in the last twenty years for application of high temperature components in high performance gas turbine engines due to its high specific strength [2]. Due to its high specific strength, γ-TiAl alloys have become leading candidates to replace Nibased superalloys in high performance gas turbine engines to reduce its structural weight by as much as 20-30% [3,4]. However, the major problems limiting the practical use of this compound are its low ductility and fracture toughness at ambient temperature [5, 6]. To improve these properties, recent trends lie on the development of TiAl based composites with the reinforcement of different particles [7-11]. Thus, intermetallic composites could provide the right combinations of high-temperature strength, creep resistance, and environmental stability with adequate ambient temperature ductility and low density. Due to its superior ductility as compared to -TiAl and high hardness, addition of Ti2AlC in small quantities have potential to improve ductility and hardness of -TiAl [12, 13].In the past, attempts have been made to develop ceramic particle dispersed composite by reactive processing [14], hot pressing [15] and spark plasma sintering [16,17]. In the present study, the effect of TiC additions (10 wt.% and 20 wt.%) on the microstructure and mechanical properties of direct laser clad Ti45Al5Nb0.5Si based titanium aluminide has been undertaken. Direct laser cladding has been conducted using a high power (3 kW) fiber optic delivered Nd:YAG laser (with a beam diameter of 2 mm) using a 3-axis handling system in a layer by layer fashion to on Ti-6Al-4V substrate to develop a coupon with a dimension of 10 mm x 10 mm x 5 mm. The effect of process parameters (applied power, scan speed and powder feed rate) on the on the thickness, integrity and microhardness of the clad zone has been studied. 2. Experimental In the present study, commercially available Ti45Al5Nb0.2Si alloy powder (particle size ranging from 20 – 90 µm) with the particle size in the range of 100-325 µm and TiC of particle size -325 µm in the ratio (weight) of 95:5 and 90: 10 have been mixed in a mechanical mixer for 2 hrs at 25 rpm and used as precursor powder for direct laser cladding (DLC). DLC was conducted by melting the precursor powder mixtures using a high power (3 kW) fiber optic delivered Nd:YAG laser (with a beam diameter of 2 mm) in a layer by layer fashion on to Ti-6Al-4V substrate to develop coupon with a dimension of 10 mm x 10 mm x 4 mm. During DLC, pre-heating was applied by using a hot plate capable of heating the samples up to 780 °C. The main process variables in the present study were applied power (400 W to 600 W), scan speed (200 mm/min to 400 mm/min) and powder flow rate (1.8 g/min to 2.6 g/min). The microstructures of the as-processed samples (both the top surface and cross section) were characterized by optical microscope (model no.: AXIO-Imager-Azm, Zeiss SMT AG, Germany) and a scanning electron microscopy (LEO 1455 EP, Zeiss SMT AG, Germany) coupled with energy dispersive X-ray (EDX) microanalyzer. Compositional analysis was carried out using energy dispersive spectroscopic analysis (EDX) (OXFORDX-mer). The phases present in the microstructure of the DLC coupon are analyzed by X-ray diffraction (XRD) (Philips X’Pert PRO Diffractometer, PANalytical, Almelo, The Netherlands) technique operated at an accelerating voltage of 40 kV and current equal to 30 mA using Co-Kα radiation. The microhardness of the top surface and cross section of DLC was carried out using Vicker’s microhardness tester at an applied load of 300 g with 15 s indentation duration. 3. Result and discussion Figures 1(a,b) show the scanning electron micrographs of the cross section of direct laser clad (a) Ti45Al5Nb0.5Si5TiC and (b) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and powder feed rate of 2.2 mg/s. From Figure 1 it may be noted that the direct laser clad zone consists of three regions and there is no sharp interface between the two successive layers. The different zones are labeled as 1, 2 and 3. Hence, it may be concluded that due to building of the successive layers, there are no defect formation or cracking at the interface. A comparison between Figure 1(a) with Figures 1(b) reveals that with the increase in TiC content,
Jyotsna Dutta Majumdar et al. / Procedia Manufacturing 35 (2019) 840–846 Author name / Procedia Manufacturing 00 (2019) 000–000
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there is decrease in thickness of cladding. A detailed study of the variation of the thickness of cladding with laser parameters was undertaken. Figure 2 shows the X-ray diffraction profiles of the top surface of direct laser clad (a) Ti45Al5Nb0.5Si, (b) Ti45Al5Nb0.5Si5TiC and (c) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and a powder feed rate of 2.2 g/min. From Figure 2(a) it may be noted that direct laser clad Ti45Al5Nb0.5Si mainly contains -TiAl and 2-Ti3Al. Addition of TiC leads to the formation of Ti3AlC phase (as evident from the presence of a few Ti3AlC peaks) in addition to the presence of a large numbers of TiC peaks. A comparison between Figure 2a and Figure 2b also confirms that the intensities of Ti3Al peaks reduce due to addition of TiC. Increase in TiC level (Ti45Al5Nb0.5Si10TiC) causes formation of few Ti3AlC2 and Ti2AlC peaks in addition to TiC and Ti3AlC peaks. From the above mentioned observation, it may be concluded that at lower TiC content, there is formation of Ti3AlC due to the reaction of Ti3Al and C from the dissociated TiC. With increase in TiC content, Ti2AlC and Ti3AlC2 formation occur by the following reactions: TiAl+TiC = Ti2AlC (1) Ti2AlC + TiC = Ti3AlC2
(2)
Figure 1 Scanning electron micrographs of the cross section of direct laser clad (a) Ti45Al5Nb0.5Si5TiC and (b) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and powder feed rate of 2.2 mg/s.
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Figure 2
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X-ray diffraction profiles of the top surface of direct laser clad (a) Ti45Al5Nb0.5Si, (b) Ti45Al5Nb0.5Si5TiC and (c) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and a powder feed rate of 2.2 g/min.
Figures 3(a-c) summarizes the bar chart showing the variation of average microhardness (plots 1a, 2a and 3a) and maximum microhardness (plots 1b, 2b and 3b) of direct laser clad Ti45Al5Nb0.5Si (plots 1a and plots 1b), Ti45Al5Nb0.5Si5TiC (plots 2a and 2b) and Ti45Al5Nb0.5Si10TiC (plots 3a and 3b) with (a) applied power (lased with a scan speed of 300 mm/min and powder feed rate of 2.2 g/s), (b) scan speed (lased with a power of 500 W and powder feed rate of 2.2 g/s), and (c) powder feed rate (lased with a power of 500 W and scan speed rate of 300 mm/min). From Figure 3(a) it may be noted that both the average and maximum microhardness of the direct laser clad zone increase with addition of TiC content and it increases with increase in TiC percentage in the clad mixture. Increase in applied power from 400 W to 600 W increases the microhardness of direct laser clad Ti45Al5Nb0.5Si marginally from 486 VHN to 500 VHN, though the maximum microhardness does not change with applied power (530 VHN). Hence, it may be noted that with increase in applied power, there is an increased microstructural uniformity, leading to a minimum difference in microhardness between the average and maximum one. Addition of TiC increases the microhardness (both the average and maximum) of the clad layer, with a maximum increase in maximum microhardness values. A systematic observation shows that the maximum microhardness of the clad zone of TiC added samples increase with increase in applied power from 400 W to 500 W following which it remains same. On the other hand, the average microhardness increases from with increase in applied power from 400 W to 500 W following which it decreases. The increase in average microhardness from 400 W to 500 W is possibly attributed to uniform distribution of TiC particles with increase in applied power. Further increase in power, might cause dissociation of TiC particles leading of a marginal decrease in microhardness value. However, as the average microhardness depends on microstructural refinement and a maximum quantity of TiC present in any location of microstructure, in increases with increase in applied power and remains same thereafter. A detailed study concerning the influence of individual component on the microhrdness improvement needs to be undertaken to conclude on that. The average and maximum microhardness were found to marginally increase with increase in scan speed. Due to increase in scan speed, there is an increase in cooling rate which might cause an increased microstructural refinement. On the other hand, due to increase in scan speed, possibly, there is a reduced degree of dissociation causing an increased numbers of TiC present on the microstructure and hence, an increase in maximum microhardness with increase in scan speed (cf. Figure 3b). A study of the variation of the average and maximum
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microhardness with power feed rate shows that there is no significant change in average and microhardness with powder feed rate. A systematic study also shows that effect of powder feed rate on the microhardness (both average and maximum values) does not follow any specific trend. In addition, it was further observed that increase in powder feed rate to 2.6 mg/min causes formation of cracks in the alloyed zone and hence, is not advised to be used (cf. Fig. 3c). From the above mentioned discussions it may be concluded that there is increase in average and maximum microhardness in the direct laser clad zone due to addition of TiC and increase in TiC content increases both the values as compared to base alloy. Applied power and scan speed have marginal influence in the microhardness of the clad layer. However, a systematic investigation needs to be undertaken through a detailed measurement of grain size and area fraction of carbides and subsequently, to correlate it with microhardness value to conclude the mechanism of micro-hardness enhancement and the role of laser parameters on it.
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Figure 3 Variation of average microhardness (1a, 2a and 3a) and maximum microhardness (1b, 2b and 3b) of direct laser clad Ti45Al5Nb0.5Si (1a and 1b), Ti45Al5Nb0.5Si5TiC (2a, 2b) and Ti45Al5Nb0.5Si10TiC (3a, 3b) with (a) applied power, (b) scan speed, and (c) powder feed rate.
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4. Summary and Conclusions In the present study, the effect of TiC additions (10 wt.% and 20 wt.%) on the microstructure and microhardness of direct laser clad Ti45Al5Nb0.5Si based titanium aluminide has been undertaken. From the detailed investigations the following conclusions may be drawn: 1. Addition of TiC leads to formation of defect free microstructures under varied parameters, except a few processing conditions. 2.
The rate of cladding varied with applied power and scan speed, but independent of composition.
3.
There is formation of complex carbides (Ti2AlC, Ti3AlC2 and Ti2AlC) in addition to TiC phase in the microstructure of duplex phase. The microstructure was however, found to vary in different layers.
4.
There is a large difference in the average and maximum microhardness of the clad zone. Both the average and maximum microhardness increase with increase in TiC content.
Acknowledgement Partial financial supports from Alexander von Humboldt Foundation, Bonn (to J. Dutta Majumdar) for the said work is gratefully acknowledged. References [1] J. P. Immarigeon, R. T. Holt, A. K. Koul, L. Zhao, L. Wallace, J. C. Beddoes, Mater. Characterization 35(1) (1995), 41-67. [2] P. Krause, A. Bartolotta, L. David, Proceedings of International Symposium on Gamma Titanium Aluminides, 1999, CA, USA [3] W. Voice, M. Henderson, E. Shelton, X. Wu, TNB.Intermetallics 13(9) (2005) 959-964. [4] G. Das, H. Kestler, H. Clemens, P. A. Bartolotta, J. Mater. 56(11) (2004) 42-45. [5] C. Leyens, In: C. Leyens, M. Peters, editors. Titanium and titanium alloys.Weinheim, Germany: WILEY-VCH; 2003. p. 187 [6] M. P. Brady, W. J. Brindley, J. L. Smialek, I. E. Locci, JOM 48 (1996) 46-50. [7] K. T. VenkateswaraRao, G. R. Odette, O. R. Ritchie, Acta Metall. Mater, 40 (1992) 353-361. [8] K. T. VenkateswaraRao, O. R. Ritchie, Mater Sci Engg. A 153 (1992) 479-485. [9] D. E. Larsen, In: Anton DL, et al. editors. MRS SympProc, 194(1990) 285. [10] C. R. Feng, K. Sadananda, In: Baker I et al., editors. High-temperature ordered intermetallic alloys V, MRS Symp. Proc.,288 (1993) 1155.
[11] H. Mabuchi, K. KijiHarada, H. Tsuda, Y. Nakayama, ISIJ International, 31 (1991)1271-1278. [12] M. W. Barsoum, T. El-Raghy, J. Am. Ceram. Soc. 79 (1996) 1953-1956. [13] R. Ramaseshan, S. K. Senshadri, N. G. Nair et al., J. Jpn. Soc. Powder Metall. 45 (4) (1998) 330-335. [14] R. Ramaseshan, A. Kakitsuji, S. K. Seshadri, N. G. Nair, H. Mabuchi, T. Tsudaa, K. Matsui, K. Morii, Intermetallics, 7 (1999) 571577.
[15] Yan-Lin Chen, M. Yan, Y-M. Sun, Bing-Chu Mei, Jiao-Qun Zhu, Ceramics International, 35 (2009) 1807–1812. [16] B. Mei, Y. MiyaMoto, Mater. Chem. Phys, 75 (2002) 291–295. [17] Y. Yue, H. Wu, L. Zhang, Z. Wang, L. Zhang, J. Wuhan Univ. Technol.-Mater. Sci. Ed, 22 (2007) 7–11.
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2nd International Conference on Sustainable Materials Processing and Manufacturing 2nd International Conference on Sustainable Materials Processing and Manufacturing (SMPM 2019) (SMPM 2019)
Microstructural Evolution and Microhardness of Direct Laser Microstructural Evolution and Microhardness of Direct Laser Clad TiC Dispersed Titanium Aluminide (Ti45Al5Nb0.5Si) Alloy Clad TiC Dispersed Titanium Aluminide (Ti45Al5Nb0.5Si) Alloy Jyotsna Dutta Majumdara* , Silja Katharina Rittinghausb, Konrad Wissenbach c, Daniel a b c c , Silja Katharina , Konrad Wissenbach , Daniel Jyotsna Dutta Majumdar Höched*, Carsten Blawert dRittinghaus , and Andreas Weisheit d d c Höche , Carsten Blawert , and Andreas Weisheit a Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, India, Lehrstuhl fürLasertechnik LLTand RWTH Aachen University,Indian Steinbachstraße D-52074 Kharagpur, Aachen, Germany, Department of Metallurgical Materials Engineering, Institute of 15, Technology India, c b fürLasertechnik ILT, Steinbachstraße 15, D-52074 Aachen, Germany, LehrstuhlFraunhofer-Institut fürLasertechnik LLT RWTH Aachen University, Steinbachstraße 15, D-52074 Aachen, Germany, d c Institut fürWerkstoffforschung, Helmholtz-ZentrumGeesthacht, Max-Planck-Straße D-21502 Geesthacht, Germany, Fraunhofer-Institut fürLasertechnik ILT, Steinbachstraße 15, D-520741,Aachen, Germany, d Institut fürWerkstoffforschung, Helmholtz-ZentrumGeesthacht, Max-Planck-Straße 1, D-21502 Geesthacht, Germany, ba
Abstract Abstract In the present study, the effect of TiC additions (10 wt.% and 20 wt.%) on the microstructure and microhardness of direct laser clad based titanium has been laser claddingand hasmicrohardness been conductedofusing high In theTi45Al5Nb0.5Si present study, the effect of TiCaluminide additionsalloy (10 wt.% and undertaken. 20 wt.%) onDirect the microstructure directa laser power (3 kW) fiber optic delivered laser (with beam diameter of 2 mm) using a 3-axis system in a layer by clad Ti45Al5Nb0.5Si based titaniumNd:YAG aluminide alloy has abeen undertaken. Direct laser cladding hashandling been conducted using a high layer on Ti-6Al-4V substrate to develop coupon withdiameter a dimension 10 mm mm xhandling 5 mm. Addition of aTiC leads powerfashion (3 kW)tofiber optic delivered Nd:YAG laser a(with a beam of 2 of mm) usingx a103-axis system in layer by to formation defect free microstructures under varied parameters, except aof few conditions. is formation of layer fashion of to on Ti-6Al-4V substrate to develop a coupon with a dimension 10 processing mm x 10 mm x 5 mm. There Addition of TiC leads complex carbides (Ti2AlC, addition to TiC phase in the microstructure of duplex There is phase. There of is to formation of defect free Ti microstructures underinvaried parameters, except a few processing conditions. formation 3AlC2 and Ti2AlC) improvement in microhardness due2 to TiC which increases with increased quantity of TiC. Laser power phase. and scan speed and Ti2addition, AlC) in addition to TiC phase in the microstructure of duplex There is complex carbides (Ti2AlC, Ti3AlC influences the in microhardness, powder feed which rate didincreases not influence it significantly. improvement microhardnesshowever, due to TiC addition, with increased quantity of TiC. Laser power and scan speed influences the microhardness, however, powder feed rate did not influence it significantly. © 2019 The Authors. Published by Elsevier B.V. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of Elsevier the organizing © 2019 The Authors. Published by B.V. committee of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019. Keywords: Titanium aluminide; titanium carbide; microstructure; XRD; microhardness Keywords: Titanium aluminide; titanium carbide; microstructure; XRD; microhardness
* Corresponding author. address:author. [email protected] * E-mail Corresponding E-mail address: [email protected] 2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review©under the organizing committee 2351-9789 2019responsibility The Authors. of Published by Elsevier B.V. of SMPM 2019. Peer-review under responsibility of the organizing committee of SMPM 2019.
2351-9789 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of SMPM 2019. 10.1016/j.promfg.2019.06.030
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Jyotsna Dutta Majumdar et al. / Procedia Manufacturing 35 (2019) 840–846 Author name / Procedia Manufacturing 00 (2019) 000–000
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1. Introduction A continued efforts on the development intermetallic alloys for gas turbine engines was driven by replacement of steels or Ni based alloys (density 8g/cm3to 8.5 g/cm3) by materials with lower density (4 g/cm3 to 7 g/cm3) [1].In this regard, dual phase gamma titanium aluminides (γ-TiAl) have attracted a significant attention in the last twenty years for application of high temperature components in high performance gas turbine engines due to its high specific strength [2]. Due to its high specific strength, γ-TiAl alloys have become leading candidates to replace Nibased superalloys in high performance gas turbine engines to reduce its structural weight by as much as 20-30% [3,4]. However, the major problems limiting the practical use of this compound are its low ductility and fracture toughness at ambient temperature [5, 6]. To improve these properties, recent trends lie on the development of TiAl based composites with the reinforcement of different particles [7-11]. Thus, intermetallic composites could provide the right combinations of high-temperature strength, creep resistance, and environmental stability with adequate ambient temperature ductility and low density. Due to its superior ductility as compared to -TiAl and high hardness, addition of Ti2AlC in small quantities have potential to improve ductility and hardness of -TiAl [12, 13].In the past, attempts have been made to develop ceramic particle dispersed composite by reactive processing [14], hot pressing [15] and spark plasma sintering [16,17]. In the present study, the effect of TiC additions (10 wt.% and 20 wt.%) on the microstructure and mechanical properties of direct laser clad Ti45Al5Nb0.5Si based titanium aluminide has been undertaken. Direct laser cladding has been conducted using a high power (3 kW) fiber optic delivered Nd:YAG laser (with a beam diameter of 2 mm) using a 3-axis handling system in a layer by layer fashion to on Ti-6Al-4V substrate to develop a coupon with a dimension of 10 mm x 10 mm x 5 mm. The effect of process parameters (applied power, scan speed and powder feed rate) on the on the thickness, integrity and microhardness of the clad zone has been studied. 2. Experimental In the present study, commercially available Ti45Al5Nb0.2Si alloy powder (particle size ranging from 20 – 90 µm) with the particle size in the range of 100-325 µm and TiC of particle size -325 µm in the ratio (weight) of 95:5 and 90: 10 have been mixed in a mechanical mixer for 2 hrs at 25 rpm and used as precursor powder for direct laser cladding (DLC). DLC was conducted by melting the precursor powder mixtures using a high power (3 kW) fiber optic delivered Nd:YAG laser (with a beam diameter of 2 mm) in a layer by layer fashion on to Ti-6Al-4V substrate to develop coupon with a dimension of 10 mm x 10 mm x 4 mm. During DLC, pre-heating was applied by using a hot plate capable of heating the samples up to 780 °C. The main process variables in the present study were applied power (400 W to 600 W), scan speed (200 mm/min to 400 mm/min) and powder flow rate (1.8 g/min to 2.6 g/min). The microstructures of the as-processed samples (both the top surface and cross section) were characterized by optical microscope (model no.: AXIO-Imager-Azm, Zeiss SMT AG, Germany) and a scanning electron microscopy (LEO 1455 EP, Zeiss SMT AG, Germany) coupled with energy dispersive X-ray (EDX) microanalyzer. Compositional analysis was carried out using energy dispersive spectroscopic analysis (EDX) (OXFORDX-mer). The phases present in the microstructure of the DLC coupon are analyzed by X-ray diffraction (XRD) (Philips X’Pert PRO Diffractometer, PANalytical, Almelo, The Netherlands) technique operated at an accelerating voltage of 40 kV and current equal to 30 mA using Co-Kα radiation. The microhardness of the top surface and cross section of DLC was carried out using Vicker’s microhardness tester at an applied load of 300 g with 15 s indentation duration. 3. Result and discussion Figures 1(a,b) show the scanning electron micrographs of the cross section of direct laser clad (a) Ti45Al5Nb0.5Si5TiC and (b) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and powder feed rate of 2.2 mg/s. From Figure 1 it may be noted that the direct laser clad zone consists of three regions and there is no sharp interface between the two successive layers. The different zones are labeled as 1, 2 and 3. Hence, it may be concluded that due to building of the successive layers, there are no defect formation or cracking at the interface. A comparison between Figure 1(a) with Figures 1(b) reveals that with the increase in TiC content,
Jyotsna Dutta Majumdar et al. / Procedia Manufacturing 35 (2019) 840–846 Author name / Procedia Manufacturing 00 (2019) 000–000
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there is decrease in thickness of cladding. A detailed study of the variation of the thickness of cladding with laser parameters was undertaken. Figure 2 shows the X-ray diffraction profiles of the top surface of direct laser clad (a) Ti45Al5Nb0.5Si, (b) Ti45Al5Nb0.5Si5TiC and (c) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and a powder feed rate of 2.2 g/min. From Figure 2(a) it may be noted that direct laser clad Ti45Al5Nb0.5Si mainly contains -TiAl and 2-Ti3Al. Addition of TiC leads to the formation of Ti3AlC phase (as evident from the presence of a few Ti3AlC peaks) in addition to the presence of a large numbers of TiC peaks. A comparison between Figure 2a and Figure 2b also confirms that the intensities of Ti3Al peaks reduce due to addition of TiC. Increase in TiC level (Ti45Al5Nb0.5Si10TiC) causes formation of few Ti3AlC2 and Ti2AlC peaks in addition to TiC and Ti3AlC peaks. From the above mentioned observation, it may be concluded that at lower TiC content, there is formation of Ti3AlC due to the reaction of Ti3Al and C from the dissociated TiC. With increase in TiC content, Ti2AlC and Ti3AlC2 formation occur by the following reactions: TiAl+TiC = Ti2AlC (1) Ti2AlC + TiC = Ti3AlC2
(2)
Figure 1 Scanning electron micrographs of the cross section of direct laser clad (a) Ti45Al5Nb0.5Si5TiC and (b) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and powder feed rate of 2.2 mg/s.
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Figure 2
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X-ray diffraction profiles of the top surface of direct laser clad (a) Ti45Al5Nb0.5Si, (b) Ti45Al5Nb0.5Si5TiC and (c) Ti45Al5Nb0.5Si10TiC lased with a power of 400 W, scan speed of 300 mm/min and a powder feed rate of 2.2 g/min.
Figures 3(a-c) summarizes the bar chart showing the variation of average microhardness (plots 1a, 2a and 3a) and maximum microhardness (plots 1b, 2b and 3b) of direct laser clad Ti45Al5Nb0.5Si (plots 1a and plots 1b), Ti45Al5Nb0.5Si5TiC (plots 2a and 2b) and Ti45Al5Nb0.5Si10TiC (plots 3a and 3b) with (a) applied power (lased with a scan speed of 300 mm/min and powder feed rate of 2.2 g/s), (b) scan speed (lased with a power of 500 W and powder feed rate of 2.2 g/s), and (c) powder feed rate (lased with a power of 500 W and scan speed rate of 300 mm/min). From Figure 3(a) it may be noted that both the average and maximum microhardness of the direct laser clad zone increase with addition of TiC content and it increases with increase in TiC percentage in the clad mixture. Increase in applied power from 400 W to 600 W increases the microhardness of direct laser clad Ti45Al5Nb0.5Si marginally from 486 VHN to 500 VHN, though the maximum microhardness does not change with applied power (530 VHN). Hence, it may be noted that with increase in applied power, there is an increased microstructural uniformity, leading to a minimum difference in microhardness between the average and maximum one. Addition of TiC increases the microhardness (both the average and maximum) of the clad layer, with a maximum increase in maximum microhardness values. A systematic observation shows that the maximum microhardness of the clad zone of TiC added samples increase with increase in applied power from 400 W to 500 W following which it remains same. On the other hand, the average microhardness increases from with increase in applied power from 400 W to 500 W following which it decreases. The increase in average microhardness from 400 W to 500 W is possibly attributed to uniform distribution of TiC particles with increase in applied power. Further increase in power, might cause dissociation of TiC particles leading of a marginal decrease in microhardness value. However, as the average microhardness depends on microstructural refinement and a maximum quantity of TiC present in any location of microstructure, in increases with increase in applied power and remains same thereafter. A detailed study concerning the influence of individual component on the microhrdness improvement needs to be undertaken to conclude on that. The average and maximum microhardness were found to marginally increase with increase in scan speed. Due to increase in scan speed, there is an increase in cooling rate which might cause an increased microstructural refinement. On the other hand, due to increase in scan speed, possibly, there is a reduced degree of dissociation causing an increased numbers of TiC present on the microstructure and hence, an increase in maximum microhardness with increase in scan speed (cf. Figure 3b). A study of the variation of the average and maximum
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microhardness with power feed rate shows that there is no significant change in average and microhardness with powder feed rate. A systematic study also shows that effect of powder feed rate on the microhardness (both average and maximum values) does not follow any specific trend. In addition, it was further observed that increase in powder feed rate to 2.6 mg/min causes formation of cracks in the alloyed zone and hence, is not advised to be used (cf. Fig. 3c). From the above mentioned discussions it may be concluded that there is increase in average and maximum microhardness in the direct laser clad zone due to addition of TiC and increase in TiC content increases both the values as compared to base alloy. Applied power and scan speed have marginal influence in the microhardness of the clad layer. However, a systematic investigation needs to be undertaken through a detailed measurement of grain size and area fraction of carbides and subsequently, to correlate it with microhardness value to conclude the mechanism of micro-hardness enhancement and the role of laser parameters on it.
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Figure 3 Variation of average microhardness (1a, 2a and 3a) and maximum microhardness (1b, 2b and 3b) of direct laser clad Ti45Al5Nb0.5Si (1a and 1b), Ti45Al5Nb0.5Si5TiC (2a, 2b) and Ti45Al5Nb0.5Si10TiC (3a, 3b) with (a) applied power, (b) scan speed, and (c) powder feed rate.
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4. Summary and Conclusions In the present study, the effect of TiC additions (10 wt.% and 20 wt.%) on the microstructure and microhardness of direct laser clad Ti45Al5Nb0.5Si based titanium aluminide has been undertaken. From the detailed investigations the following conclusions may be drawn: 1. Addition of TiC leads to formation of defect free microstructures under varied parameters, except a few processing conditions. 2.
The rate of cladding varied with applied power and scan speed, but independent of composition.
3.
There is formation of complex carbides (Ti2AlC, Ti3AlC2 and Ti2AlC) in addition to TiC phase in the microstructure of duplex phase. The microstructure was however, found to vary in different layers.
4.
There is a large difference in the average and maximum microhardness of the clad zone. Both the average and maximum microhardness increase with increase in TiC content.
Acknowledgement Partial financial supports from Alexander von Humboldt Foundation, Bonn (to J. Dutta Majumdar) for the said work is gratefully acknowledged. References [1] J. P. Immarigeon, R. T. Holt, A. K. Koul, L. Zhao, L. Wallace, J. C. Beddoes, Mater. Characterization 35(1) (1995), 41-67. [2] P. Krause, A. Bartolotta, L. David, Proceedings of International Symposium on Gamma Titanium Aluminides, 1999, CA, USA [3] W. Voice, M. Henderson, E. Shelton, X. Wu, TNB.Intermetallics 13(9) (2005) 959-964. [4] G. Das, H. Kestler, H. Clemens, P. A. Bartolotta, J. Mater. 56(11) (2004) 42-45. [5] C. Leyens, In: C. Leyens, M. Peters, editors. Titanium and titanium alloys.Weinheim, Germany: WILEY-VCH; 2003. p. 187 [6] M. P. Brady, W. J. Brindley, J. L. Smialek, I. E. Locci, JOM 48 (1996) 46-50. [7] K. T. VenkateswaraRao, G. R. Odette, O. R. Ritchie, Acta Metall. Mater, 40 (1992) 353-361. [8] K. T. VenkateswaraRao, O. R. Ritchie, Mater Sci Engg. A 153 (1992) 479-485. [9] D. E. Larsen, In: Anton DL, et al. editors. MRS SympProc, 194(1990) 285. [10] C. R. Feng, K. Sadananda, In: Baker I et al., editors. High-temperature ordered intermetallic alloys V, MRS Symp. Proc.,288 (1993) 1155.
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