PSI - Issue 14

Sandeep Das et al. / Procedia Structural Integrity 14 (2019) 119–126 Sandeep Das et al. / Structural Integrity Procedia 00 (2018) 000–000

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the investigations on white surface layer, the use of an oil dielectric increases the carbon content in the white layer and appears as iron carbides (Fe 3 C) in columnar, dendritic structures. Samuel and Philip (1996) compared the performance of powder metallurgy (P/M) tool electrodes with conventional electrodes in normal electrical discharge machining conditions. P/M electrodes were found to be more sensitive to changes in pulse current and pulse duration and their impact on output parameters such as material removal rate and electrode wear was found to be different as compared to that of conventional electrodes. This study established that P/M electrodes were technically viable for EDM machining and their related properties could be controlled by varying compaction and sintering parameters. Kunieda et al. (2004) experimented dry EDM of steel with copper as tool electrode, and revealed that in dry EDM, the tool electrode wear ratio was much lower and MRR was much higher when tool electrode was negative. In case of EDM with liquid dielectric medium, there was more tool electrode wear and lower MRR when the polarity of the tool electrode is negative. Hence, the authors recommended negative polarity for material transfer from the tool electrode. Uan et al. (2012) studied microstructural and corrosion characteristics of alloying modified layer on 5083 Al alloy by electrical discharge alloying process with pure silicon electrode. They observed that the thickness of the layer increases as the discharge current and pulse duration increase, but the increase in the duty factor caused the thickness to decline. In the present work a systematic experimental study has been carried out to analyze the feasibility of alloying TiB 2 and SiC with aluminium 5052 alloy. Titanium boride (TiB 2 ) is a ceramic material and has sufficient electrical conductivity (10 5 S/Cm). It is a sintered ceramic material which has many industrial applications due to its excellent mechanical properties, such as impressive hardness, elastic modulus and abrasion resistance. Silicon (Si) shows good diffusion in aluminium (Al5083), therefore in this work it was thought interesting to alloy Si with Al5052. The details of experiments and relevant results are presented in the subsequent sections.

Table 1. Fixed parameters in EDA. Parameters

Value (unit)

Duty cycle

50%

Working time

5 min

Flushing pressure Forming pressure Dielectric Type

0.1 MPa 0.24 MPa

Hydrocarbon oil

Gap voltage Tool polarity

20 V

Negative

2. Experimental details Aluminium 5052 alloy is used as the work piece material. A circular tool electrode of 13 mm diameter made of copper is used. The alloying materials were titanium boride (TiB2) & silicon carbide (SiC) having grain size 10 µm. Aluminium was used the binding medium to prepare the powder metallurgy compact of TiB2 & SiC. The proportion used by mass was 40% TiB2, 30% SiC and 30% Al. The powders were thoroughly mixed in a ball mill. The mixture was used to prepare tool electrode compacts using a die. After that the compact was pasted to copper electrode using silver loaded epoxy. Figure 2 shows a typical tool electrode. Electrodes and work samples were weighed before starting the experiments and the data was recorded. The change in the sample weight before and after the experiment is the measure of the deposition occurred. The parameters which are kept fixed throughout the experiments are given in the table 1. According to these values, experiments were carried out. Figure 3 shows the image of the set-up. Precision profilometry was used to measure the surface finish in terms of Ra value. EDX analysis of the alloyed surface was done by using line scan images, electron images. The characteristics X-ray intensity profiles on cross sectional layers were obtained. EDX spectrum analysis using Cu- Kα X provides the weight percentage of different elements that transferred during the process.