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Vijay Narayanan ¹, R. Sellamuthu ¹, R. Saravanan ¹

Affiliations
1 Department of Mechanical Engineering, Amrita School of Engineering - Coimbatore, Amrita Vishwa Vidyapeetham University, Coimbatore - 641112, Tamil Nadu, IN

Abstract

Background: Stainless steels are mainly used where prevention of corrosion attack is the main criteria, but low surface hardness and high wear rate are key obstacles to extensive application. Methods: The surface alloying of AISI 304 stainless steel with titanium was carried out using the heat generated from the Gas Tungsten Arc (GTA). Experiments were conducted by varying the GTA parameters and the optimal parameter was determined. Composition of the surface alloyed layer was analysed using atomic emission spectrometer. The Ti alloyed surface layers were characterized using SEM imaging/EDAX analysis. Findings: Composition of the surface alloyed layer was analysed using atomic emission spectrometer and the results confirmed an increase in the Ti content on the surface layer when compared to the composition of the substrate. The EDAX analysis showed that intermetallic alloys are present in the Ti alloyed surface layers. The microhardness was measured using the Vickers microhardness testing machine and the hardness increased from 267.5 HV for the substrate to 2098 HV for the surface alloyed layer. The wear was measured using the pin-on-disk wear tester and the wear rate decreased from 14.78 x 10^-4 mm³/m for the substrate to 1.84 x 10^-4 mm³/m for the surface alloyed layer. The observation of the microstructure revealed that there is grain refinement in the Ti alloyed surface layer. Applications: The modified specimens can be used as medical implants, control rods in nuclear power plants, pump barrels petrochemical industry. This method can be used to improve the properties in specific area of a product.

Keywords

AISI304, GTA, Hardness, Microstructure, Surface Alloying, Ti, Wear Rate.

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R. Saravanan ¹, S. Srihari ¹, A. Arvind ¹, P. Sreeranj ¹, K. S. Dheeraj ¹, R. Sellamuthu ¹, Sanjivi Arul ¹

Affiliations
1 Department of Mechanical Engineering, Amrita School of Engineering - Coimbatore, Amrita Vishwa Vidyapeetham University, Coimbatore - 641112, Tamil Nadu, IN

Abstract

Background/Objectives: The study aims to improve surface properties of aluminium A356 alloy by surface alloying it with nitrided titanium, in a nitrogen environment, using Gas Tungsten Arc (GTA) as heat source. Methods/Statistical Analysis: Nitrided titanium sheets were surface alloyed with cast aluminium A356 blocks, in nitrogen environment, with GTA as heat source for melting. The cross-sectional microstructure of the specimens was studied using inverted metallurgical microscope. Further analysis was carried out using SEM/EDS to identify the formation of nitrides and intermetallic compounds. The hardness of the specimens was measured using Vickers hardness tester and the wear rate was determined using pin-on-disc wear tester. Findings: Microstructure analysis revealed a uniform and granular refined structure in the modified layer compared to the coarse and dendritic structure of the cast block. EDS analysis indicated the formation of hard-intermetallic compounds. The hardness was measured to be highest at the surface of the central fusion zone, with a maximum value of 656 HV while as-cast aluminium block exhibited only 76 HV. The measured wear rate was 10×10^-4 mm³/m for the modified layer, compared to 52×10^-4 mm³/m of the substrate. Alongside, the loss in weight after wear dropped by 4 mg. The coefficient of friction of the modified surface showed a constant trend during the wear-off period. The enhancement in these surface properties is attributed to the formation of nitrides and other intermetallic compounds that in the modified layer during surface alloying. Additionally, the use of GTA as heat source renders the surface alloying process to be economically feasible relative to other employable methods. Applications/Improvements: The devised surface alloying method used to enhance the surface properties of A356 is cheap, flexible and effective and finds intensive application in marine, automotive and manufacturing sectors.

Keywords

A356, Gas Tungsten Arc, Hardness, Nitriding, Surface Alloying, Titanium, Wear Rate.

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Aneesh Ravikumar ¹, R. Sellamuthu ¹, R. Saravanan ¹

Affiliations
1 Department of Mechanical Engineering, Amrita School of Engineering- Coimbatore, Amrita Vishwa Vidyapeetham University, Coimbatore – 641112, Tamil Nadu, IN

Abstract

Objectives: This paper investigates the effect of Cr addition on hardness, tensile properties and wear behaviour of Al-4.5Cu alloy A206. Methodology: The base alloy was melted and stirred well, fine Cr powder added in required amount, in oil fired pit furnace and poured into a permanent cast iron mold. The cast specimens were solution heat treated at 540⁰C for 4 hrs and were aged at 170⁰C for 17 hrs and 20 hrs. The as-cast and aged specimens were subjected to microstructure and EDAX evaluation followed by hardness, tensile and wear testing. Findings: The microstructure analysis and EDAX analysis reported an irregularly distributed polyhedral structures that appear blocky due to the phase formation of Al-Cr-Mn-Fe-Si. The hardness, ultimate tensile strength and yield strength were found to increase, reach a peak value and then decrease upon further chromium addition in aged condition. The wear rate decreased with increasing hardness and coefficient of friction remained constant with time. Application/Improvements: Evaluate the effect of Cr in Al alloys on the mechanical strength and wear properties.

Keywords

Al-Cu Alloy, Cr Addition, Heat Treatment, Tensile Properties, Wear Rate.

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R. Saravanan ¹, R. Sellamuthu ¹, Arjun Nair ¹, Sarat Dev Mangattu ¹, A. Susaritha ¹, S. Shruthilayaa ¹, Vineeth Vasudevan ¹

Affiliations
1 Department of Mechanical Engineering, Amrita School of Engineering – Coimbatore, Amrita Vishwa Vidyapeetham University, Coimbatore - 641112, Tamil Nadu, IN

Abstract

Objective: The main aim of this project is to modify the surface of LM 25 ingot in order to have a refined microstructure, improvement in hardness and in the wear rate of the modified region. Methods: Surface modification of LM 25 is carried out using GTA method. Argon flow was minimised and simultaneously pure nitrogen (99.999%) was introduced into the environment. Microstructural observation was carried out using Zeiss Axiovert 25CA metallurgical microscope and the hardness was measured using Mitutoyo Vicker’s hardness testing machine. Wear test was carried out for the substrate and the modified region using pin-on-disc wear tester. EDAX analysis was carried out to find the presence of intermetalic compounds. Findings: From the microstructure, it was observed that there is grain refinement in the modified region. The hardness for the substrate was found to be 80.6 HV and 764.4 HV for the modified region. The wear rate in the substrate was 49.34x10^-4 mm³/m and 7.9x10^-4 mm³/m for the modified region. As the hardness increases, wear rate decreases. EDAX report confirms the presence of intermetalic compound in the form of silicon nitride (Si₃N₄). The presence of the silicon nitride is not reported previously using GTA as heat source on surface modified LM25. The increase in the hardness and decrease in the wear rate is attributed to the presence of silicon nitride in the surface. Application/Improvements: Due to the presence of silicon nitride it can be used as an insulator and chemical barrier in electrical circuits etc. It can also have wider automobile and aeronautics applications as its hardness has increased.

Keywords

GTA, Hardness, Microstructure, Surface Modification, Wear Rate.

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