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Abstract:Purpose of this paper: The main objective of this research paper is to investigate and evaluate the optimal values of laser process parameters: laser power, scanning speed, and focused position for the simultaneous minimization and maximization of heat input and tensile strength respectively by Taguchi method and utility concept approach in laser transformation hardening of commercially pure titanium sheet of 1.6mm thickness using continuous wave (CW) Nd:YAG laser beam. Design/methodology/approach: The effect of laser process parameters on the heat input and tensile strength properties of commercially pure titanium and subsequent optimal settings of the parameters have been obtained using Taguchi's parametric design approach and utility concept. The response performance is analyzed based on signal-to-noise ratio and analysis of variance (ANOVA). The optimal levels of the laser process parameters were determined through the Analysis of Means (ANOM). Findings: The optimization results revealed that a combination of higher levels of scanning speed and focused position i.e., increase in defocus along with laser power in the lower level play important role in order to simultaneously minimize the heat input and to maximize the tensile strength (σ). The predicted optimal values of tensile strength and heat input of commercially pure titanium sheet produced by laser transformation hardening process are 464 N/mm 2 and 141.667 Watts, respectively, for the optimized laser process parameters with minimum LP=750 Watts, maximum SS=3000mm/min, and lower value of FP=-30mm (increase in defocus). Research limitations/implications: Research range is limited to investigation of optimization laser hardening process parameters for the simultaneous minimization and maximization of heat input and tensile strength respones.of commercially pure titanium. Hardness test responses are also be optimized in future research work. Practical implications: Laser transformation hardening is an innovative and advanced laser surface modification technique has been employed in aerospace, marine, chemical applications, heat exchangers, cryogenic vessels, components for chemical processing and desalination equipment, condenser tubing, airframe skin, and nonstructural components which introduces the advantageous residual stresses into the surface, improving the mechanical properties like wear, resistance to corrosion, tensile strength, and fatigue strength. Originality/value: Authors made an effort to optimize the laser process parameters in order to minmize the heat input and maximize tensile strength of laser transformation hardening of commercially pure titanium using Taguchi methodology and utility concept.

This research paper presents the laser transformation hardening (LTH) to improve the surface hardness of commercially pure titanium, nearer to ASTM Grade3 chemical composition of 1.6[Formula: see text]mm thickness sheet using a CW (continuous wave) 2[Formula: see text]kW, with radiation wavelength [Formula: see text][Formula: see text][Formula: see text]m Nd:YAG laser. Full factorial and response surface design approach in Design Expert 9 software have been discussed and evaluated by statistical regression analysis and analysis of variance. The experiment was carried out as the full factorial design (FFD) array of 27 with 3 factors, 3 levels, i.e. 3[Formula: see text] experiments. The selected input parameters are: laser power, scanning speed and focused position, and responses are: Vickers Microhardness on top surface, in fusion zone, and in heat affected zone. FFD and response surface methodology (RSM) were applied to evaluate and optimize the effects of laser process parameters on Vickers microhardness of laser hardened surface. The results show that, the hardness of as-received commercially pure titanium is approximately 153[Formula: see text]VHN and the hardness after laser transformation hardened bead geometrical surface is in the range of 200–240[Formula: see text]VHN. The hardness can be increased with the increase in the scanning speed and decrease in the optimum value of laser power i.e. heat input applied. It has been found that the quadratic model is best fitted for prediction of the Vickers microhardness of laser hardened surface. These findings are significant in modern development of hard surface coatings for corrosion and wear resistant applications. Application of experimental results will be considered in the aerospace, marine, chemical, medicine, automobile and the engineering industries.

In this research paper, overlapped multipass Laser Transformation Hardening (LTH) of Ti-6Al-4V titanium alloy sheet of 2 mm thickness was analyzed experimentally for uniformly intense, CW spherical beam moving with constant speed using 2 kW Nd: YAG laser. Experiments were conducted for optimized two sets of laser process parameters: 1. High Laser Process Parameter (HLPP), Lp = 800 Watts, Ss = 3000 mm/min, Fp = -10 mm, with heat input 180 J/cm and 2. Low Laser Process Parameter (LLPP), Lp = 600 Watts, Ss = 2000 mm/min, Fp = -10 mm, with heat input 160 J/cm respectively having same Fp = -10 mm. The maximum, minimum and average hardened depths of 0.27, 0.19 and 0.23 mm respectively, achieved for HLPP were found to be minimum, as compared to the maximum, minimum and average hardened depths of 0.38, 0.29 and 0.33 mm, respectively, for LLPP. Measurements of Vickers micro-hardness survey of the hardened zone of the laser processed Ti-6Al-4V alloy are presented. Vickers micro-hardness of an as-received two-phase (α+β) Ti-6Al-4V titanium alloy is 328 HV. The results showed that Vickers micro-hardness on top of the surface (TS), in hardened or fusion zone (Fz), at the interface of Fz -Haz, in the heat affected zone (Haz) is higher than the bulk material. The high hardness values of 450 HV and 445 HV were investigated on the top surface for high and low laser process parameters respectively. This can be the quality characteristics of the dissolution of small amounts of oxygen, nitrogen, and carbon with hard martensite α' (transformed β) formation, thereby ensuring an increase in wear resistance of laser treated hardened surface of Ti-6Al-4V considerably in relation to the untreated or base alloy.

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