Effects of Cooling Rate and Silicon Content on Microstructure and Mechanical Properties of Laser Deposited Ti-6Al-4V Alloy

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ScienceDirect Materials Today: Proceedings 5 (2018) 18368–18375

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Effects of Cooling Rate and Silicon Content on Microstructure and Mechanical Properties of Laser Deposited Ti-6Al-4V Alloy 1

O.S.Fatoba1*; E.T. Akinlabi1;M.E. Makahtha2 Department of Mechanical Engineering Science, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa. 2 Department of Metallurgy, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa.

Abstract The growth in the use of titanium alloy components in marine industries, aerospace, medical apparatus and power machinery has increased because of its good properties. Some detriments such as low hardness, poor thermal stability and poor tribological properties has however limits its wide range application to the industries. This has led to a search for techniques to improve the surface of Ti-6Al-4V alloy to enhance longevity in service. Laser deposition is one of the feasible techniques to modify the surface of titanium alloy which involves addition of reinforcements to improve properties without changing the bulk properties while optimizing the parameters.Hence, laser surface modification by incorporating chemical barrier coatings can be very beneficial and this lead to investigation aimed at enhancing the surface properties of Ti-6Al-4V alloy by incorporating Al-Si-Ti coatings. For this purpose, a 3-kW continuous wave ytterbium laser system attached to a KUKA robot which controls the movement during the alloying process was utilized to deposit coatings with stoichiometry Al-12Si-3Ti and Al-17Si-5Ti. The alloyed surfaces were investigated in terms of its mechanical properties as function of the laser processing conditions. Hardness measurements were done using a Vickers micro-hardness tester. The microstructures of the coated and uncoated samples were characterized by optical and scanning electron microscopy. The optimum performances were obtained for an alloy composition of Al-17Si-5Ti, at laser power of 900 W and coating speed of 1.2 m/min. Its performance enhancement compared to the unprotected substrate comprised a significant increase in hardness from 296 to 689 HV which translates to 57.04% in hardness values above that of the substrate.The enhanced increase in hardness of the coating can be traced to the presence of silicon and the various hard titanium aluminides intermetallic (TiAl, TiAl3, and Ti3Al) phases. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: Ti-6Al-4V alloy; Hardness; Microstructure; Al-Si-Ti coating;Yield strength; Tensile strength.

1.0.Introduction The aerospace industry applies titanium alloys widely due to its good corrosion resistance, low density and high specific strength. For these reasons, they are often used in the aeronautics industry in the manufacturing of the blade of the aviation engine. Their ability of being applied at high service temperatures and being exposed to severe wear conditions is limited by the poor wear resistance and inferior oxidation resistance[1, 2]. * 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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The automotive and aerospace industries have encouraged the improvement of advanced materials with low coefficient of thermal expansion, low density, high specific strength, and excellent resistance to wear and corrosion. Hypereutectic Al-Si alloys having transition metals are exceptional materials due to their specific properties. The addition of Cu, Fe, Cr, Mg and Ni to Al-Si alloys can improve the mechanical properties at both ambient and elevated temperatures [3]. Hypereutectic Al-Si alloys are being used in the manufacturing of automotive components and tools. It had been noticed that when the Si content increases, the wear resistance of these alloys increases as well [4]. However, the Si content should not exceed 20 wt.% in standard casting processes because large primary Si particles are formed, and they result in the reduction of the alloys’ mechanical properties [5]. The large proportions of coarse primary Si present in Al-Si alloys formed during conventional casting processes can decrease their anti-wear characteristic and ductility, in order to overcome this, the primary Si of the alloy should be refined [6].Aluminium-Silicon alloys have a wide application in the automotive, military and aerospace industries due to their excellent mechanical properties such as good weldability, sound castability, outstanding resistance to corrosion, low density, low thermal expansion coefficient, good casting ability and high wear resistance. Selective laser melting of the alloy can offer a wider range of application, such as structures that are complex involve cavities [6-8]. Although these properties are desirable, the alloys were stated to have a high corrosion rate in environments that contained salt [8].The development of uniform microstructures with improved performance has been necessitated by the growing importance of Al-Si based alloys as materials for engineering applications [9]. However, the processing of these alloys by conventional liquid metallurgy routes results in coarse grain microstructure with large degree of segregation of alloying elements [10]. Nevertheless, literature on hardness and wear resistance performance of Al-Si-Ti alloy coatings on Ti-6Al-4Valloy by laser surface alloying (LSA) technique are very scarce. LSA can rapidly provide a thick and crack-free layer in all instances with metallurgical bonds at the interface between the alloyed layer and the substrate. Powders surfaced on new or worn working surfaces of components by LSA provides specific properties such as high abrasive wear resistance, erosion resistance, corrosion resistance, heat resistance and combinations of these properties. Consequently, improvements in machinery performance and safety in aerospace, automotive, can be realized by the method [11]. The present study investigates the effect of laser processing parameters on the hardness performance and microstructural evolution of Al-Si-Ti coatings on Ti-6Al-4V alloy. 2.0 Experimental details 2.1. Materials specifications and sample preparation method The substrate material used in the present investigation was Ti-6Al-4V alloy as shown in Table 1. The substrate was cut, and machined into dimensions 70 x 70 x 4 mm3. Prior to laser treatment, the substrates (Ti-6Al-4V alloy) were sandblasted, washed, rinsed in water, cleaned with acetone and dried in hot air before exposure to laser beam to minimize reflection of radiation during laser processing and enhance the absorption of the laser beam radiation. Al (99.9 purity), Si (99.9% purity) and Ti (99.9%) reinforcement metallic powders were mixed in 85:12:3(A1), and 78:17:5(A2) ratio, respectively, in a shaker mixer (Turbular T2F; Glenn Mills, Inc.) for 18 hours at a speed of 49 rpm to obtain homogeneous mixture. The impressive efficiency of the tubular shaker-mixer originates from the use of rotation, translation and inversion as per the geometric theory according to Schatz. The particle shape of the powder used was spherical with 50-105 µm particle sizes. Laser surface alloying was performed using a 3-kW continuous wave (CW) Ytterbium Laser System (YLS) controlled by a KUKA robot which controls the movement of the nozzle head and emitting a Gaussian beam at 1064 nm. The nozzle was fixed at 4 mm from the titanium substrate. The admixed powders were fed coaxially by employing a commercial powder feeder instrument equipped with a flow balance to control the powder feed rate. The metallic powder was fed through the off-axes nozzle fitted onto the Ytterbium fibre laser and it was injected simultaneously into a melt pool formed during scanning of the titanium alloy substrate by the laser beam. Argon gas flowing at a rate of 3.0 L/min was used as a shielding gas to prevent oxidation of the sample during laser surface alloying. Overlapping tracks were obtained by overlapping of melt tracks at 70%. To determine the best processing parameters, optimization tests were performed with the laser power of 750 to 1000 W and scanning speed varied from 1.0 to 1.4 m/min. The final selection criteria during optimization tests was based on surface having homogeneous layer free of porosity and cracks determined from SEM analysis. The optimum laser parameters used were800 and 900 W power, a beam diameter of 3 mm, gas flow rate of 3.0 L/min, powder flow rate of 2.0 g/min and scanning speeds of 1.0 m/min and 1.2 m/min respectively. Prior to the characterization of the laser surface alloyed materials, samples were prepared by cutting to rectangles of 15 x 15 mm2, and cold mounted in clear thermosetting Bakelite resinfor black conductive thermosetting resin for

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SEM and energy dispersive spectroscopy (EDS) analysis. Specimens for SEM (JSM-7600F; JOEL, Ltd) were prepared by cutting samples in such a way to reveal the transverse section of the coatings. The specimens were automatically ground successively using 600, 800, 1000 and 1200 grits SiC papers. They were further polished using polishing cloths and diamond polishing suspensions of 9 to 1 μm to obtain a mirror-like surface. The polished surfaces were rinsed with distilled water and degreased with acetone and dried. Polished samples were etched with kroll’s reagent for microscopic observation and other characterization. Microhardness tests were conducted using Vickers microhardness Tester according to ASTME384 [12] standard to ensure consistent result. A load of 100 gf was applied at a dwell time of 15 s to create each indent. Indentations were made at a distance of 0.3 mm apart from the top of the clad cross section down into the substrate. The samples average hardness was recorded. 1. Table 1: Chemical composition of Titanium alloy Element H2 N2 O2 C Fe V Al Ti Wt. %

0.0003

0.005

0.12

0.07

0.15

3.9

6.2

Balance

3.0. Results and discussion 3.1. Microstructural Analysis Figure 1 shows the optical micrograph of Ti-6Al-4V alloy which showed a well-defined surface texture. The substrate consists of (α+β) phases with lamellar structure. The darker (α+β) mainly situated at grain boundaries. Region analyzed was depicted by SEM image on the well-polished Ti-6Al-4V alloy surface as presented in Figure 1(a). The surface is observed in the grey phase. Figure 1(a) illustrates the grain structure of titanium alloy. The average grain size is approximately 76ߤ݉. The microstructure of substrate is represented by light and dark regions indicating two phases namely the alpha (α) and beta (β) phase that are equally distributed through the area of the substrate as shown in Figure 1(b). This is the basic structure of titanium substrate that is used in this investigation.

2. Figure 1: Micrograph image of the substrate (Ti-6Al-4V alloy) Region analyzed was depicted by SEM image on the well-polished Ti-6Al-4V alloy surface as presented in Figure 2. The surface is observed in the grey phase. The surface is shown by elemental peak intensities in Figure 2 and EDS maps showing elemental distribution of titanium, aluminium and vanadium.

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Figure 2: SEM and EDS spectra of Ti-6Al-4V alloy Figures 3 and 4 show the SEM images of Al-17Si-5Ti and Al-12Si-3Ti coatings at scanning speed of 1.2 m/min. While Figure 5 shows the EDS of Al-17Si-5Ti at the same 1.2 m/min.

3. Figure 3: SEM Images of Al-17Si-5Ti Ternary Coating at 1.2 m/min scanning speedand at magnification of x 100 and x 500

4. Figure 4: SEM Image of Al-12Si-3Ti Ternary Coating at 1.2 m/min scanning speed.

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Figure 5: EDS of Al-17Si-5Ti Ternary Coating at 1.2 m/min scanning speed It was observed that all the samples had good metallurgical bonding. The phase of the Al-Si-Ti coatings mainly consisted of Ti-Al reinforced by Ti5Si3, the amount of the latter phase increased with the increase in silicon content. The increased amount of silicon improved the oxidation resistance at elevated temperatures.The results showed that the thickness of the layer varied depending on the powder feed rate, laser power and scanning speed. A thin coating thickness was produced by a faster speed and lower laser power. EDS in Figure 5 revealed that the layer consisted of Al-rich intermetallic compounds. For a higher laser power, TiAl and Al3Ti phases were present and for a lower energy and fast process, TiAl, Al3Ti and α-Al intermetallic phases were identified. The coating was found to be a stable Ti-Al compound enriched with Al which would provide improved corrosion resistance for the Titanium alloy substrate. The reaction between elemental powders of Ti and Al led to the formation of TiAl3, Ti3Al, and TiAl according to the binary phase diagram of Ti-Al. The formation of titanium-aluminides intermetallics took place through an exothermic reaction between solid titanium and liquid aluminium [13]. On the other hand, TiAl2 and Ti2Al5 would require TiAl as an intermediate product for their formation [13]. During high temperature processing of Ti-6Al-4V, the precipitation of Ti-Al intermetallics (TiAls) such as TiAl, TiAl3, and TiAl5 had been reported. In addendum, the presence of Al and Ti in the reinforcement powders is expected to favour the formation of TiAls [14, 15]. Besides, the precipitation of TiAls happens at elevated temperature [14]. The change in the Gibbs free energy of formation, ΔG determines the formation of intermetallics. Taking the melting point of the titanium alloy as 1660 0C, the ΔGf of the various titanium aluminides (TiAl3, Ti3Al, TiAl and TiAl2) were reported to have values of 33.7, -17.98, -9.28 and -25.64 KJ/mol respectively as reported by Chen [16].The enhanced increase in hardness of the coating can also be traced to the presence of silicon and the various hard titanium aluminides intermetallic (TiAl, TiAl3, and Ti3Al) phases. The hardness of the titanium aluminides intermetallics (TiAl, TiAl3, and Ti3Al) phases ranges between 2.4 and 2.9 GPa [17]. According to Dey et al. [18], titanium aluminides are ordered intermetallics with strong bonding of the compounds and high critical ordering temperature (Tc) of the material which gives rise to good thermophysical properties; such as high melting point, low density, high elastic modulus and good structural stability. Intermetallics phases with high melting points are good candidate for structural application at moderate or high temperature which requires homogeneous, fine and stable distribution of crystal [19]. Al3Ti, because of its relatively low density (3.3 g/cm3) and high melting point (1350oC) is very attractive among all intermetallics [20] and it is intrinsically stable [21]. Grain refinement effect of titanium which plays a vital function in influencing the critical properties of aluminium products have been studied by previous researchers. It enhances plasticity and tensile intensities, and reduces the tendency of porosity and hot tearing [22]. This is due to the peritectic reaction occurrence at the end of aluminium rich in aluminium-titanium phase diagram [23]. 3.2. Mechanical Properties of Al-Si-Ti Ternary Coatings Research had been made to estimate the mechanical properties of materials from bulk hardness measurement ever since indentation testing has come into existence, especially yield and tensile strengths [24-26]. Tensile and yield strengthsof the coatings can be determined from equations (1) and (2) as reported by Cahoon et al. [27] and [28]. The calculated values form these equations are included in Table2.

T .S  (

H n n )( ) 2.9 0.217

(1)

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Y .S  (

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H )(0.1) n 3

(2) H is the Vicker's hardness number, and n is the strain hardening coefficient, taken to be 0.15 [27]. The results show that both the yield and tensile strengths for the coatings have improved as compared to the substrate as shown in Table 2. Pavlina and Van Tyne [29] also reported simple linear relationships to estimate the ultimate tensile strength and yield strength using the Vickers hardness number for as follows:

T .S  99.8  3.734HV Y .S  90.7  2.876HV

(3)

(4) These relationships do not require the knowledge of any other parameter than hardness for estimation of strength.The results showed that the laser alloying process enhances the hardness value of the substrate as shown in Table2. Hardness values range between 296 to 689 HV. The hardness values of 296, 616, 668, 677, and 689 HV were obtained for substrate, Al-12Si-3Ti-1.0, Al-12Si-3Ti-1.2, Al-17Si-5Ti-1.0 and Al-17Si-5Ti-1.2 respectively. A raise of 56.28 and 57.04% in hardness values above that of the substrate at Al-17Si-5Ti-1.0 and Al-17Si-5Ti-1.2 respectively. The enhanced increase in hardness of the coating can be traced to the presence of silicon and the various hard titanium aluminides intermetallic (TiAl, TiAl3, and Ti3Al) phases. The hardness of the titanium aluminides intermetallics (TiAl, TiAl3, and Ti3Al) phases ranges between 2.4 and 2.9 GPa [17]. According to Dey et al. [18], titanium aluminides are ordered intermetallics with strong bonding of the compounds and high critical ordering temperature (Tc) of the material which gives rise to good thermophysical properties; such as high melting point, low density, high elastic modulus and good structural stability.Silicon is the most frequent impurity and common alloying element in commercial pure aluminium [30]. In addendum, silicon also has a low density (2.34 g cm-3), which may be an advantage in reducing the overall weight of the fabricated coatings. Silicon has a very low solubility in aluminium; it therefore precipitates as virtually pure silicon, which is hard and hence improves the abrasion resistance.Primary dendrite Al-phase formation (α–matrix), and the eutectic transformation (eutectic Si particles in α-matrix) are the two stages of microstructural evolution of hypoeutectic Al-Si alloys during solidification. The distribution and the shape of the silicon particles has great influence on the mechanical properties of Al-Si alloys. [31].Increase in silicon content leads to increase in hardness of the coatings. Laser alloying of the multiple tracks serves as heat treatment which produced a finer microstructure and resulted in a uniform distribution of the intermetallic compounds and it also modifies the eutectic Si phase and hence improves the mechanical properties of the alloy. This also corroborates the work of Mathai et al. [32]. According to Shuai et al. [33], average grain size increases on decreasing laser scanning speed. The grain size becomes larger when the scanning speed is further decreased. Moreover, according to Akinlabi and Akinlabi [34] and Fatoba et al. [35], increase in number of scan changes to type of heat treatment and produces strain hardening in material causing the grain sizes to be reduced as laser scans increases. In addendum, increase of the scanning speed results in finer microstructure due to the larger cooling rate during solidification as reported by Gong et al. [36] and Makhatha [37] and Fatoba et al. [38] It was reported by Kalhapure and Dighe [39] that increase in silicon content would lead to increase in ultimate tensile strength of Al–Si alloys to maximum value 175 MPa at 14 wt. % of silicon. In the present research, increase in the silicon content lead to increase in the yield and tensile strengths of the coatings to maximum of 2.21 and 1.60 GPa respectively at 17 wt. % of silicon. The results show that both the yield and tensile strengths for the coatings have improved as compared to the substrate. Table 2: Coating Properties Samples Laser Power (W) Average Hardness Yield strength (GPa) Tensile strength (HV0.1) (GPa) Ti-6Al-4V alloy 296 ± 8.12 0.95 0.69 Al-12Si-3Ti-1.0 800 616 ± 8.12 1.97 1.43 Al-12Si-3Ti-1.2 800 668 ± 8.12 2.14 1.55 Al-17Si-5Ti-1.0 900 677 ± 8.12 2.20 1.57 Al-17Si-5Ti-1.2 900 689 ± 8.12 2.21 1.60

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4.0.Conclusion. 5. Well optimized process parameters and carefully chosen reinforcement materials fractions produced coatings with enhanced mechanical properties. Crack formation was eliminated through optimization of laser processing parameters, leading to enhanced quality of the coatings, surface adhesion between substrate and reinforcement materials, and microstructural evolution.Laser alloying of the multiple tracks serves as heat treatment which produced a finer microstructure and resulted in a uniform distribution of the intermetallic compounds and it also modifies the eutectic Si phase.The composition proportion of mixed powders has a great influence on the phase structure of the laser deposited coatings. In addendum, titanium-aluminides such as Al3Ti, and AlTi3 formed exhibit significant potential to be a good alternative to existing conventional iron-aluminides. The enhanced increase in hardness of the coating can be traced to the presence of silicon and the various hard titanium aluminides intermetallic (TiAl, TiAl3, and Ti3Al) phases. Different titanium aluminide compounds such as TiAl3, Ti3Al and TiAl also influence the mechanical properties. Laser power and scanning speed are the two most significant parameters which influence the quality of the coatings. Increase of the scanning speed results in finer microstructure due to the larger cooling rate during solidification 5.0.References. [1] HUANG, C., ZHANG, Y., VILAR, R., & SHEN, J. 2012. Dry sliding wear behavior of laser clad TiVCrAlSi high entropy alloy coatings on Ti–6Al–4V substrate. Materials and Design. 41:338-343. [2] DAI, J., ZHANG, F., WANG, A., YU, H. & CHEN, C. 2017. Microstructure and properties of Ti-Al coating and Ti-Al-Si system coatings on TI-6Al-4V fabricated by laser surface alloying. Surface & Coatings Technology. 309:805-813. [3] Ma, P., Jia, Y., Prashanth, K.G., Scudino, S., Yu, Z. & Eckert, J. 2016. Microstructure and phase formation in Al-20Si-5Fe-3Cu-1Mg synthesized by selective laser melting. Journal of Alloys and Compounds.657:430-435. [4] Kang, N., Coddet, P., Liao, H., Baur, T. & Coddet, C. 2016. Wear behavior and microstructure of hypereutectic Al-Si alloys prepared by selective laser melting. Applied Surface Science. 378:142-149. [5] Grigoriev, S.N., Tarasova, T.V., Gvozdeva, G.O. & Nowotny S. 2014. Structure Formation of Hypereutectic AlSi-Alloys Produced by Laser Surface Treatment. Journal of Mechanical Engineering. 60:389-394. [6] Zhao, L.Z., Zhao, M.J., Song, L.J. & Mazumder, J. 2014. Ultra-fine Al–Si hypereutectic alloy fabricated by direct metal deposition. Materials and Design. 56:542-548. [7] Kempen, K., Thijs, L., Van Humbeeck, J. & Kruth, J.-P. 2012. Mechanical properties of AlSi10Mg produced by Selective Laser Melting. Physics Procedia. 39:439-446. [8] Liang, Z.X., Ye, B., Zhang, L., Wang, Q.G., Yang, W.Y., & Wang, Q.D. 2013. A new high-strength and corrosion-resistant Al–Si based casting alloy. Materials Letters. 97: 104-107. [9] V. Bhattacharya, K. Chattopadhyay, Microstructure and wear behaviour of aluminium alloys containing embedded nanoscaled lead dispersoids. Acta Materialia. 52 (2004) 2293-2304. [10] X.J. Ning, J.H. Kim, H.J. Kim, C.J. Li, C. Lee, Characteristics and heat treatment of cold-sprayed Al-Sn binary alloy coatings. Surf. Coat. Technol. 202 (2008) 1681. [11] O.S Fatoba, E.T. Akinlabi and M.E. Makhatha ME. Effect of process parameters on the microstructure and tribological property of Zn-Sn-Ti coatings on AISI 1015 steel: laser alloying technique.International Journal of Surface Science and Engineering. 11 (6), 2017, 489-511. [12] A.S.T.M. Standard, E384(2010e2): Standard test method for Knoop and Vickers hardness of materials, ASTM Standards, ASTM International, West Con-shohocken, PA, 2010. [13] M. Sujata, S. Bhargava, S. Suwas and S. Sangal. On Kinetics of TiAl3 Formation during Reaction Synthesis from Solid Ti and Liquid Al, Journal of Materials Science Letters, 20, 2001, 2207-2209. [14] C. Xue, J.K. Yu, Z.Q .Zhang, Insitu joining of titanium to SiC/Al composites by low pressure infiltration, Mater.Des.47(2013)267–273. [15] R. Jiangwei, L.Yajiang, F.Tao, Microstructure characteristics in the interface zone of Ti/Al diffusion bonding, Mater.Lett. 56(2002) 647–652. [16] C. C. Chen, “Phase equilibria at Ti–Al interface under low oxygen pressure,” Atlas J. Mater. Sci. 1(1), 1–11 (2014). [17] J. A. Hawk and D. E. Alman, “Abrasive wear of intermetallic-based alloys and composites,” J. Mater. Sci. Eng. A 239–240, 899–906 (1997).

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[18] S. R. Dey, A. Hazotte, and E. Bouzy, “Crystallography and phase transformation mechanisms in TiAl-based alloys – A synthesis,” Intermetallics 17, 1052–1064 (2009). [19] S.I. Talabi, S.O. Adeosun, A.F. Alabi, I.N. Aremu and S. Abdulkareem. Effect of Heat Treatment on the Mechanical Properties of Al-4% Ti Alloy, International Journal of Metals, 2013, 1-4. [20] K.R. Cardoso, D.N. Travessa, A.G. Escorial and M. Lieblich. Effect of Mechanical Alloying and Ti Addition on Solution and Ageing Treatment of an AA7050 Aluminium Alloy, Materials Research, 10,2007, 199-203. [21] L.A. Dobrzański, K. Labisz and A. Olsen, A. Microstructure and Mechanical Properties of the Al-Ti Alloy with Calcium Addition, Journal of Achievements in Materials and Manufacturing Engineering, 26, 2008, 183-186. [22] X.F. Liu, Z.Q. Wang, Z.G. Zhang and X.F. Bian. The Relationship between Microstructures and Refining Performances of Al-Ti-C Master Alloys, Materials Science and Engineering:A, 332, 2002, 70-74. [23] R.O. Kaibyshev, I.A. Mazurina and D.A. Gromov. Mechanisms of Grain Refinement in Aluminum Alloys in the Process of Severe Plastic Deformation. Metal Science and Heat Treatment, 48, 2006, 57-62. [24] D. Tabor, “The hardness and strength of metals,” Journal Institute of Metals, vol. 79, pp. 1–18, 1951. [25] J. R. Cahoon, “An improved equation relating hardness to ultimate strength,” Metallurgical Transactions, vol. 3, no. 11, p. 3040, 1972. [26] J. R. Cahoon, W. H. Broughton, and A. R. Kutzak, “The determination of yield strength from hardness measurements,” Metallurgical Transactions, vol. 2, no. 7, pp. 1979–1983, 1971. [27] J.R. Cahoon, W.H. Broughton, A.R. Kutzak, The determination of yield strength from hardness measurements, Met.Trans. 2(1971)1979–1983. [28] K.S. Chenna, G.N. Kumar, K. JhaAbhay, P. Bhanu, On the prediction of strength from hardness for copper alloys, J.Mater.(2013). [29] E. J. Pavlina and C. J. Van Tyne, “Correlation of Yield strength and Tensile strength with hardness for steels,” Journal of Materials Engineering and Performance, vol. 17, no. 6, pp. 888–893, 2008 [30] M. Johnsson: Z. Metallkd.”Influence of Zr on grain refinement of aluminium”, 85 (1994) 781-785. [31] William F Smit, Javad Hashemi, Ravi Prakash, Materials Science and Engg. Tata McGraw Hill (2004) 4th edition. [32] Mathai, B., Mathew, C., Pratheesh, K., & Varghese, C. K. Effect of Silicon on Microstructure and Mechanical Properties of Al-Si Piston Alloys.International Journal of Engineering Trends and Technology (IJETT) – Volume 29 Number 6 - November 2015 [33] C. Shuai, P. Feng, L. Zhang, C. Gao, H. Hu, S. Peng, A. Min. Correlation between Properties and Microstructure of Laser Sintered Porous β-TriCalcium Phosphate Bone Scaffolds, Sci. Technol. Adv. Mater. 14, 2013, 1-10. [34] E.T. Akinlabi, S.A. Akinlabi. Effect of Heat Input on the Properties of Dissimilar Friction Stir Welds of Aluminium and Copper. Amer. J. Mater. Sci. 2, 2012, 147-152. [35] O.S. Fatoba, E.T. Akinlabi and M.E. Makhatha. Influence of rapid solidification on the thermophysical and fatigue properties of laser additive manufactured Ti-6Al-4V alloy, Fiber Laser, Dr. Subbarayan Sivasankaran (Ed.), InTech, 2017. http://dx.doi.org/10.5772/intechopen.71697 [36] X. Gong, J. Lydon, K. Cooper, K. Chou. Beam Speed Effects on Ti-6Al-4V Microstructures in Electron Beam Additive Manufacturing, J. Mater. Res. 29, 2014b, 1951-1959. [37] M.E. Makhatha, O.S. Fatoba and E.T. Akinlabi E.T. Effects of rapid solidification on the microstructure and surface analyses of laser-deposited Al-Sn coatings on AISI 1015 steel. Int J Adv Manuf Technol. 2017, 1-15. https://doi.org/10.1007/s00170-017-0876-y [38] O.S. Fatoba, M.E. Makhatha and E.T. Akinlabi. The effects of rapid cooling on the improved surface properties of aluminium based coatings by direct laser deposition, Fiber Laser, Dr. Subbarayan Sivasankaran (Ed.), InTech, 2017. http://dx.doi.org/10.5772/intechopen.71698. [39] Kalhapure, M. G., & Dighe, P. M. (2015). Impact of silicon content on mechanical properties of aluminum alloys. Int. J. Sci. Res, 4, 38-40.