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Processing Parameters Influence on Microhardness in Laser Metal Deposited Titanium Alloy using Design if Experiment
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ScienceDirect Materials Today: Proceedings 5 (2018) 20437–20442
www.materialstoday.com/proceedings
ICMPC_2018
Processing Parameters Influence on Microhardness in Laser Metal Deposited Titanium Alloy using Design if Experiment Rasheedat M. Mahamood, Esther T. Akinlabi* Department of Mechanical Engineering Science, University of Johannesburg, Auckland Park, Kingsway Campus, Johannesburg, 2006, South Africa
Abstract Laser Metal Deposition (LMD) is an additive manufacturing process for producing complex parts directly from the Computer Aided Design (CAD) model of the part and for repair of an existing worn out part. The LMD process is governed by processing parameters: laser power, gas flow rate, powder flow rate and scanning speed that influence the microhardness produced during the LMD process. In this study, statistical design of experiment to was employed to investigate the influence of processing parameters on the microhardness of laser metal deposited of Ti6Al4V powder on Ti6Al4V substrate. Full factorial design was used in this study because of its ability to capture the main effects and possible interaction effects of these processing parameters. Each processing parameters was set at low and high values and a total of sixteen (16) experiments was performed and the microhardness of each sample was measured and analyzed. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: Laser Metal Deposition; Full factorial design; Microhardness; Processing parameters; Titanium alloy.
1. Introduction Laser Metal Deposition (LMD) process is an additive manufacturing technology that produced three dimensional (3D) object directly from the Computer Aided Design (CAD) model of the part in layer wise manner [1]. LMD is offer a lot of advantages to the manufacturing industries that includes its ability to repair worn out parts, capability to produce made with composite and functionally graded materials and the ability to reduce buy-to-fly ratio in the aerospace industry [2-4]. * Corresponding author. E-mail address: [email protected]
2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.
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Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
That main process parameters that significantly influence the deposited parts include the laser power, the scanning speed and powder flow rate [5, 6]. Research has shown that these processing parameters also interact with each other in the LMD process [7].This study, sought to understand the influence of these combination of process parameters on the developed microhardness in the deposited samples using full factorial design of experiment. Titanium alloy grade 5-Ti6Al4V is the most widely used Titanium alloy and often referred to as the power horse of the industries due to its excellent properties was used in this study. Four processing parameters namely: laser power, scanning speed, powder flow rate, and gas flow rate were investigated in this study. With each of the process parameters set at high and low settings. The results were statistically analyzed using Design Expert8 (statistical software) in order to be able to draw statistical inference on the results obtained. 2. Experimental Method The materials used in this study is are Ti6Al4V powder and sheet (substrate) both of 99. 6% purity. The Ti6Al4V powder is of particle size range between 150 and 250 µm. Nd-YAG laser was used to achieve the deposition process. Before the laser metal deposition process, the substrate was sandblasted and cleaned with acetone. so as to enhance the laser power absorption. Argon gas was used as powder carrying gas as well as a shielding gas for the laser deposited tracks. A glove box was improvised using plastic wrapping and box in order to protect the deposited track from atmospheric attack of Oxygen and Nitrogen gases in the air which could cloud the results. Titanium has high affinity for Oxygen at high temperature. The glove box was filled with argon gas in order to keep the oxygen level below 10 ppm. Full factorial design of experiment was used to design the experiment by setting each of the factors at two levels: high and low settings according to Table 1. A total of 16 experiments was conducted. After the deposition process, the samples were cut in transverse direction to the deposition direction in order to reveal the cross section of the sample. The cut samples were mounted in resin, grind and polished according to the standard metallographical sample preparation for titanium and its alloys. The microhardness was measured for each of the samples using Vickers microhardness indenter by Metkon under a load of 300 g and a dwelling time of 15 s according to the ASTM E92-16 standard [8] Table 1 Factors and their corresponding level settings High S/N Factor Level 1 Laser Power (kW) 3.0 2 Scanning Speed (m/s) 0.1 Powder Flow Rate 3 4 (g/min) 4 Gas Flow Rate (l/min) 4
Coded Value +1 +1
Low Level 1.5 0.05
Coded Value -1 -1
+1
2
-1
+1
2
-1
3. Results and Discursions The Table 2 presents the results of microhardness at each experimental treatment. Figure 1a shows the main effect plot of microhardness against laser power. Figures 1b, 1c and 1d show the main effect plots of the microhardness against the scanning speed, the powder flow rate and the gas flow rate respectively. The microhardness is seen to reduce with increase in laser power as shown in Figure 1a. The reason for this could be the slower solidification of the melt pool at high laser power due to larger volume of the melt pool. slower solidification rate favours the evolution of Widmanstätten grains in the microstructure which is softer and hence lower microhardness at high laser power. The scanning speed was found to be directly proportional to the microhardness as shown in Figure 1b. The microhardness increased with increase in scanning speed. The high microhardness produced at high scanning speed could be as a result of smaller volume of melt pool produced at high scanning speed.
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
Table 2. Microhardness results Run Standard Laser Order Order Power (kW) 14 5 11 6 1 7 3 2 4 15 16 9 13 12 10 8
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
3.0 3.0 1.5 3.0 1.5 1.5 3.0 3.0 3.0 3.0 1.5 1.5 3.0 1.5 1.5 1.5
Scanning Speed (m/s) 0.05 0.1 0.1 0.1 0.05 0.05 0.1 0.05 0.1 0.05 0.05 0.1 0.05 0.05 0.1 0.1
Powder Flow Rate (g/min) 2 2 4 4 2 4 2 2 4 4 4 2 4 2 4 2
Gas Flow Rate (l/min) 2 2 4 4 4 4 4 4 2 4 2 4 2 2 2 2
20439
Microhardn ess (HV) 325.83 378.12 410.15 380.21 381.78 395.02 376.87 323.87 386.23 360.31 396.92 396.02 346.87 383.97 401.81 395.02
The laser material interaction time at high scanning speed is short and hence the melt pool created is small. smaller melt pool solidifies rapidly causing the formation martensite in the microstructure that are very hard and hence the higher microhardness at low scanning speed. The powder flow rate is also found to be directly proportional to the microhardness as seen in Figure 1c. The microhardness increased as the powder flow rate increased. The lower microhardness at low powder flow rate could be as a result of less powder delivered into the melt pool that could be too low for the available laser power to melt. This will also cause the created melt pool to take a longer time to solidified and hence the lower microhardness. The gas flow rate is found to be the least significant process parameter out of all the four processing parameters considered in this study as shown in Figure 1d. The microhardness is found to slightly decrease with increasing gas flow rate. A very strong interaction is observed between the laser power and the scanning speed as shown in Figure 2. The microhardness increases with increasing scanning speed while it decreases with increasing laser power. At higher laser power and lower scanning speed, the microhardness is very low as a result of large melt pool created by the large laser power and high material integration time. The large melt pool created takes longer to solidify which results in larger heat affected zone as well as evolution of Widmanstätten microstructure that is softer and hence lower microhardness. For low laser power and high scanning speed, the microhardness is high. These combination of processing parameters results in the formation of smaller melt pool that solidifies rapidly. The rapid solidification promotes the formation of martensitic microstructure that promotes the higher hardness values observed. Processing parameters play an important role in laser metal deposition process [9, 10] and the right combinations of processing parameter is key in achieving the desire properties
20440
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
(a)
(b)
Figure1. The main effect plot of (a) Laser power (b) scanning speed (c) powder flow rate and (d) gas flow rate.
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
20441
Figure 2. Interaction plot of the laser power and the scanning speed
4. Conclusion The effect of processing parameters: laser power, scanning speed, powder flow rate and gas flow rate, on the microhardness property of laser metal deposited titanium alloy grade 5 was investigated using full factorial method of design of experiment. It can be concluded that the microhardness increased with increase in scanning speed and increase in powder flow rate while it decrease with increase in laser power. The gas flow rate has a minimum influence on the microhardness properties of the deposited samples. The microhardness reduced slightly with increasing gas flow rate. There is strong interaction between the laver power and scanning speed. The results of this study is very important especially in repair using laser metal deposition process. The right combination of processing parameters will yield the desired microhardness properties. Acknowledgment The support of University of Johannesburg research council and Rental Pool Programme of National Laser Centre, Council of Scientific and Industrial Research (CSIR-NLC ), Pretoria, South Africa are acknowledged.
20442
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
References 1) 2) 3) 4) 5) 6) 7)
8) 9) 10)
R. M. Mahamood, E. T. Akinlabi, M. Shukla and S. Pityana (2014). Revolutionary additive manufacturing: an overview. Lasers in Engineering, vol. 27, pp. 161- 178. Pinkerton AJ, Wang W, Li L (2008) Component repair using laser direct metal deposition. J Eng Manuf 222:827–836 Allen, J. (2006). An investigation into the comparative costs of additive manufacture vs. machine from solid for aero engine parts. In Cost Effective Manufacture via Net-Shape Processing, Meeting Proceedings RTO-MP-AVT-139, Paper 17, pp. 1–10 R.M. Mahamood, E.T. Akinlabi, (2015), Laser metal deposition of functionally graded Ti6Al4V/TiC, Materials & Design, Volume 84, pp. 402-410 Brandl E, Michailov V, Viehweger B, Leyens C (2011) Deposition of Ti–Al–4V using laser and wire, part I: microstructural properties of single beads. Surface & Coatings Technology 206:1120–1129 Mahamood RM, Akinlabi ET (2016) Process parameters optimization for material deposition efficiency in laser metal deposited titanium alloy. Lasers in Manufacturing and Materials Processing. doi:10.1007/s40516-015-0020-5 R. M. Mahamood, E. T. Akinlabi, M. Shukla and S. Pityana (2014). Effect of processing parameters on the properties of laser metal deposited Ti6Al4V using Design of Experiment. In: Chan Ao, Chan, Katagiri & Xu. Eds. Transactions on Engineering Sciences. London: Taylor & Francis Group, pp. 331 -339. DOI: 10.1201/b16763-37 ASTM E92 - 16. (2016). Standard test method for Vickers hardness and Knoop hardness of metallic materials, ASTM International Book of Standards, 03 (01), doi: 10.1520/E0092-16. Mahamood R.M, Akinlabi ET, Akinlabi SA (2015) Laser power and scanning speed influence on the mechanical property of laser metal deposited titanium-alloy. Lasers in Manufacturing and Materials Processing 2(1):43–55. R.M. Mahamood, E.T. Akinlabi , (2015), Effect of laser power and powder flow rate on the wear resistance behaviour of laser metal deposited TiC/Ti6Al4V composites, Materials Today: Proceedings, Volume 2, Issues 4–5, 2015, Pages 2679-2686 .
ScienceDirect Materials Today: Proceedings 5 (2018) 20437–20442
www.materialstoday.com/proceedings
ICMPC_2018
Processing Parameters Influence on Microhardness in Laser Metal Deposited Titanium Alloy using Design if Experiment Rasheedat M. Mahamood, Esther T. Akinlabi* Department of Mechanical Engineering Science, University of Johannesburg, Auckland Park, Kingsway Campus, Johannesburg, 2006, South Africa
Abstract Laser Metal Deposition (LMD) is an additive manufacturing process for producing complex parts directly from the Computer Aided Design (CAD) model of the part and for repair of an existing worn out part. The LMD process is governed by processing parameters: laser power, gas flow rate, powder flow rate and scanning speed that influence the microhardness produced during the LMD process. In this study, statistical design of experiment to was employed to investigate the influence of processing parameters on the microhardness of laser metal deposited of Ti6Al4V powder on Ti6Al4V substrate. Full factorial design was used in this study because of its ability to capture the main effects and possible interaction effects of these processing parameters. Each processing parameters was set at low and high values and a total of sixteen (16) experiments was performed and the microhardness of each sample was measured and analyzed. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: Laser Metal Deposition; Full factorial design; Microhardness; Processing parameters; Titanium alloy.
1. Introduction Laser Metal Deposition (LMD) process is an additive manufacturing technology that produced three dimensional (3D) object directly from the Computer Aided Design (CAD) model of the part in layer wise manner [1]. LMD is offer a lot of advantages to the manufacturing industries that includes its ability to repair worn out parts, capability to produce made with composite and functionally graded materials and the ability to reduce buy-to-fly ratio in the aerospace industry [2-4]. * Corresponding author. E-mail address: [email protected]
2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.
20438
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
That main process parameters that significantly influence the deposited parts include the laser power, the scanning speed and powder flow rate [5, 6]. Research has shown that these processing parameters also interact with each other in the LMD process [7].This study, sought to understand the influence of these combination of process parameters on the developed microhardness in the deposited samples using full factorial design of experiment. Titanium alloy grade 5-Ti6Al4V is the most widely used Titanium alloy and often referred to as the power horse of the industries due to its excellent properties was used in this study. Four processing parameters namely: laser power, scanning speed, powder flow rate, and gas flow rate were investigated in this study. With each of the process parameters set at high and low settings. The results were statistically analyzed using Design Expert8 (statistical software) in order to be able to draw statistical inference on the results obtained. 2. Experimental Method The materials used in this study is are Ti6Al4V powder and sheet (substrate) both of 99. 6% purity. The Ti6Al4V powder is of particle size range between 150 and 250 µm. Nd-YAG laser was used to achieve the deposition process. Before the laser metal deposition process, the substrate was sandblasted and cleaned with acetone. so as to enhance the laser power absorption. Argon gas was used as powder carrying gas as well as a shielding gas for the laser deposited tracks. A glove box was improvised using plastic wrapping and box in order to protect the deposited track from atmospheric attack of Oxygen and Nitrogen gases in the air which could cloud the results. Titanium has high affinity for Oxygen at high temperature. The glove box was filled with argon gas in order to keep the oxygen level below 10 ppm. Full factorial design of experiment was used to design the experiment by setting each of the factors at two levels: high and low settings according to Table 1. A total of 16 experiments was conducted. After the deposition process, the samples were cut in transverse direction to the deposition direction in order to reveal the cross section of the sample. The cut samples were mounted in resin, grind and polished according to the standard metallographical sample preparation for titanium and its alloys. The microhardness was measured for each of the samples using Vickers microhardness indenter by Metkon under a load of 300 g and a dwelling time of 15 s according to the ASTM E92-16 standard [8] Table 1 Factors and their corresponding level settings High S/N Factor Level 1 Laser Power (kW) 3.0 2 Scanning Speed (m/s) 0.1 Powder Flow Rate 3 4 (g/min) 4 Gas Flow Rate (l/min) 4
Coded Value +1 +1
Low Level 1.5 0.05
Coded Value -1 -1
+1
2
-1
+1
2
-1
3. Results and Discursions The Table 2 presents the results of microhardness at each experimental treatment. Figure 1a shows the main effect plot of microhardness against laser power. Figures 1b, 1c and 1d show the main effect plots of the microhardness against the scanning speed, the powder flow rate and the gas flow rate respectively. The microhardness is seen to reduce with increase in laser power as shown in Figure 1a. The reason for this could be the slower solidification of the melt pool at high laser power due to larger volume of the melt pool. slower solidification rate favours the evolution of Widmanstätten grains in the microstructure which is softer and hence lower microhardness at high laser power. The scanning speed was found to be directly proportional to the microhardness as shown in Figure 1b. The microhardness increased with increase in scanning speed. The high microhardness produced at high scanning speed could be as a result of smaller volume of melt pool produced at high scanning speed.
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
Table 2. Microhardness results Run Standard Laser Order Order Power (kW) 14 5 11 6 1 7 3 2 4 15 16 9 13 12 10 8
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
3.0 3.0 1.5 3.0 1.5 1.5 3.0 3.0 3.0 3.0 1.5 1.5 3.0 1.5 1.5 1.5
Scanning Speed (m/s) 0.05 0.1 0.1 0.1 0.05 0.05 0.1 0.05 0.1 0.05 0.05 0.1 0.05 0.05 0.1 0.1
Powder Flow Rate (g/min) 2 2 4 4 2 4 2 2 4 4 4 2 4 2 4 2
Gas Flow Rate (l/min) 2 2 4 4 4 4 4 4 2 4 2 4 2 2 2 2
20439
Microhardn ess (HV) 325.83 378.12 410.15 380.21 381.78 395.02 376.87 323.87 386.23 360.31 396.92 396.02 346.87 383.97 401.81 395.02
The laser material interaction time at high scanning speed is short and hence the melt pool created is small. smaller melt pool solidifies rapidly causing the formation martensite in the microstructure that are very hard and hence the higher microhardness at low scanning speed. The powder flow rate is also found to be directly proportional to the microhardness as seen in Figure 1c. The microhardness increased as the powder flow rate increased. The lower microhardness at low powder flow rate could be as a result of less powder delivered into the melt pool that could be too low for the available laser power to melt. This will also cause the created melt pool to take a longer time to solidified and hence the lower microhardness. The gas flow rate is found to be the least significant process parameter out of all the four processing parameters considered in this study as shown in Figure 1d. The microhardness is found to slightly decrease with increasing gas flow rate. A very strong interaction is observed between the laser power and the scanning speed as shown in Figure 2. The microhardness increases with increasing scanning speed while it decreases with increasing laser power. At higher laser power and lower scanning speed, the microhardness is very low as a result of large melt pool created by the large laser power and high material integration time. The large melt pool created takes longer to solidify which results in larger heat affected zone as well as evolution of Widmanstätten microstructure that is softer and hence lower microhardness. For low laser power and high scanning speed, the microhardness is high. These combination of processing parameters results in the formation of smaller melt pool that solidifies rapidly. The rapid solidification promotes the formation of martensitic microstructure that promotes the higher hardness values observed. Processing parameters play an important role in laser metal deposition process [9, 10] and the right combinations of processing parameter is key in achieving the desire properties
20440
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
(a)
(b)
Figure1. The main effect plot of (a) Laser power (b) scanning speed (c) powder flow rate and (d) gas flow rate.
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
20441
Figure 2. Interaction plot of the laser power and the scanning speed
4. Conclusion The effect of processing parameters: laser power, scanning speed, powder flow rate and gas flow rate, on the microhardness property of laser metal deposited titanium alloy grade 5 was investigated using full factorial method of design of experiment. It can be concluded that the microhardness increased with increase in scanning speed and increase in powder flow rate while it decrease with increase in laser power. The gas flow rate has a minimum influence on the microhardness properties of the deposited samples. The microhardness reduced slightly with increasing gas flow rate. There is strong interaction between the laver power and scanning speed. The results of this study is very important especially in repair using laser metal deposition process. The right combination of processing parameters will yield the desired microhardness properties. Acknowledgment The support of University of Johannesburg research council and Rental Pool Programme of National Laser Centre, Council of Scientific and Industrial Research (CSIR-NLC ), Pretoria, South Africa are acknowledged.
20442
Rasheedat M. Mahamood et al./ Materials Today: Proceedings 5 (2018) 20437–20442
References 1) 2) 3) 4) 5) 6) 7)
8) 9) 10)
R. M. Mahamood, E. T. Akinlabi, M. Shukla and S. Pityana (2014). Revolutionary additive manufacturing: an overview. Lasers in Engineering, vol. 27, pp. 161- 178. Pinkerton AJ, Wang W, Li L (2008) Component repair using laser direct metal deposition. J Eng Manuf 222:827–836 Allen, J. (2006). An investigation into the comparative costs of additive manufacture vs. machine from solid for aero engine parts. In Cost Effective Manufacture via Net-Shape Processing, Meeting Proceedings RTO-MP-AVT-139, Paper 17, pp. 1–10 R.M. Mahamood, E.T. Akinlabi, (2015), Laser metal deposition of functionally graded Ti6Al4V/TiC, Materials & Design, Volume 84, pp. 402-410 Brandl E, Michailov V, Viehweger B, Leyens C (2011) Deposition of Ti–Al–4V using laser and wire, part I: microstructural properties of single beads. Surface & Coatings Technology 206:1120–1129 Mahamood RM, Akinlabi ET (2016) Process parameters optimization for material deposition efficiency in laser metal deposited titanium alloy. Lasers in Manufacturing and Materials Processing. doi:10.1007/s40516-015-0020-5 R. M. Mahamood, E. T. Akinlabi, M. Shukla and S. Pityana (2014). Effect of processing parameters on the properties of laser metal deposited Ti6Al4V using Design of Experiment. In: Chan Ao, Chan, Katagiri & Xu. Eds. Transactions on Engineering Sciences. London: Taylor & Francis Group, pp. 331 -339. DOI: 10.1201/b16763-37 ASTM E92 - 16. (2016). Standard test method for Vickers hardness and Knoop hardness of metallic materials, ASTM International Book of Standards, 03 (01), doi: 10.1520/E0092-16. Mahamood R.M, Akinlabi ET, Akinlabi SA (2015) Laser power and scanning speed influence on the mechanical property of laser metal deposited titanium-alloy. Lasers in Manufacturing and Materials Processing 2(1):43–55. R.M. Mahamood, E.T. Akinlabi , (2015), Effect of laser power and powder flow rate on the wear resistance behaviour of laser metal deposited TiC/Ti6Al4V composites, Materials Today: Proceedings, Volume 2, Issues 4–5, 2015, Pages 2679-2686 .