Taguchi Based Optimization for Micro Hardness of Cold Spray Coating Process

Taguchi Based Optimization for Micro Hardness of Cold Spray Coating Process

Tarun Goyal (Department of Mechanical Engineering, Shaheed Udham Singh College of Engineering and Technology, Mohali, India), T.S. Sidhu (Department of Mechanical Engineering, Shaheed Bhagat Singh State Technical Campus, Ferozepur Punjab, India) and R.S. Walia (Department of Production and Mechanical Engineering, Delhi Technological University, Delhi, India)
DOI: 10.4018/IJSEIMS.2014070102
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In this paper, low pressure cold spray process has been employed to produce coatings on three different substrates. The experiments have been designed using Taguchi L 18 array where the input parameters have been selected as the type of feed arrangement, substrate material, stagnation temperature, stagnation pressure of the compressed gas and stand-off distance. The effect of these key parameters on raw data and Signal to Noise (S/N) ratio for micro hardness of low pressure cold spray process has been studied. The coatings were successfully developed on the substrates and the micro hardness of the so produced coatings has been measured. The results show that a high value of micro hardness can be obtained by selecting the input parameters which increases the impact velocity of the striking particles. These high velocity impacting particles produces a peening effect to already attached powder particles thereby increasing the micro hardness of obtained coatings. It is seen that the significant process parameters are type of powder feeding arrangement, substrate material, stand-off distance stagnation pressure of carrier gas and stagnation temperature of the carrier gas.
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1. Introduction

There are many coating deposition techniques available, and choosing the best process depends on the functional requirements, adaptability of the coating material to the technique intended, level of adhesion required, size, shape, and metallurgy of the substrate, and availability and cost of the equipment. The commonly employed coating deposition techniques have been enlisted in Figure 1 (Goyal, 2010).

Figure 1.

Various coating deposition processes in commercial use

In the early nineteen hundreds, a young Swiss inventor named Dr. Max Schoop invented thermal spraying, after watching his son playing with his toy cannon. Dr. Schoop observed that the hot lead shots that were projected out of the cannon, stuck to almost any surface, the result of which gave him the idea that if metal could be melted and projected in a spray like manner, then a surface could be built up with that material.

The technology continued, but expanded in the 70s due to development of the thermal plasmas and the increasing demand of high-temperature and wear resistant materials and coating systems (Knotek, 2001). Thermal spraying is one of the most versatile hard facing techniques available for the application of coating materials used to protect components from abrasive wear, adhesive wear, erosive wear or surface fatigue and corrosion (such as that caused by oxidation or seawater) (Marceau, 1995; Groshart, 1995; Ishikawa, 1993).

Cold spray as a coating technology was initially developed in the mid-1980s at the Institute for Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Science in Novosibirsk (Bishop, 1993; Alkhimov, 1994; Tokarev, 1996). The cold-gas dynamic-spray process, often referred to as simply “cold spray,” is a high-rate material deposition process in which fine, solid powder particles (generally 1–50 µm in diameter) are accelerated in a supersonic jet of compressed (carrier) gas to velocities in a range between 500 and 1000 m/s. As the solid particles impact the target surface, they undergo plastic deformation and bond to the surface, rapidly building up a layer of deposited material. A simple schematic of a typical low- pressure cold-spray set up is shown in Figure 2 (Maev, 2008).

Figure 2.

A typical scheme of LPCS device

In this paper, surface coatings have been produced by low-pressure cold spray process (Figure 2) by varying input parameters using Taguchi L18 array. The design parameters selected for producing the coatings were selected to be type of substrate material, stagnation pressure, stagnation temperature of the carrier gas, type of powder feeding arrangement, and stand-off distance. The paper talks about the development of coatings produced by the process for electro-technical applications and measuring raw data and calculating S/N ratio for the micro hardness of the developed coatings. Similar technique had been used for optimization of coating thickness, coating density and surface roughness of the developed coatings (Goyal, 2012; Goyal, 2012b; Goyal 2011). Many researchers have used Taguchi optimization for optimization of their coating processes(Jones, 2008; Sahu, 2010; Mishra, 2009; Kucuk, 2012).

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