Date of Award

19-9-2024

Document Type

Thesis

School

School of Mechanical Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.T.K.Kandavel

Second Advisor

Name of Co-Guide Dr.V.M.Sreehari

Keywords

Powder Metallurgy, ATOMET 4601, Hybrid Alloys, Corrosion, Sliding Wear

Abstract

Powder metallurgy enables the development of new materials to manufacture products for applications requiring unique properties. The present research initially investigates the mechanical and tribological behaviour of powder metallurgy alloys made from ATOMET 4601 prealloyed powder and varying amounts of elemental carbon (0, 0.5, and 1.0 wt%) as reinforcement. ATOMET 4601 is a high-strength, water-atomized prealloyed powder capable of being compressed to higher densities, with applications in producing near-net or net-shaped parts for the industrial field.

Mechanical behaviour studies on sinter-forged ATOMET 4601, ATOMET 4601+0.5C, and ATOMET 4601+1.0C alloy steels revealed increased hardness, tensile strength, and impact strength, with ATOMET 4601+1.0C having the highest strength. Fracture analysis of ATOMET 4601, ATOMET 4601+0.5C, and ATOMET 4601+1.0C tensile test specimens revealed ductile, quasi-static, and brittle fractures, respectively.

Subsequently, dry sliding wear studies were conducted on the above alloys which address the effect of load (15 to 50 N) and speed (300 to 1200 rpm) on wear behaviour using a pin-on-disc tribometer. ATOMET 4601+0.5C and ATOMET 4601+1.0C have exhibited a lesser wear rate due to their higher hardness and strength. A soft ferritic–pearlite phase matrix and lesser hardness could have caused a higher wear rate in the base alloy. Carbide and oxide formation caused a lower wear rate in both carbon-reinforced alloys. Both load and speed significantly affected the coefficient of friction in all three alloys.

Based on the mechanical and tribological test results, the research focus was narrowed down to develop and study the performance of ATOMET 4601+0.35C (Hybrid alloy 1) and ATOMET 4601+0.35C+0.25Mn+0.1Si+0.9Cr (Hybrid alloy 2) which can replace products made from conventional medium carbon steel (AISI 1035) and EN24 wrought steel respectively. The sintered preforms are considered to study the formability parameters like true lateral strain, true height strain, relative density, and hardness. The research on workability revealed that the hybrid alloy 2 test specimens have undergone lesser densification and deformation due to the work hardening mechanism caused by the addition of alloying elements.

Microstructures of the cold upset test specimens are correlated with the densification behaviour. Further, the study investigated the corrosion behaviour of sintered hybrid preforms with different densities in an 18% HCl corrosive solution for 25, 50, 75 and 100 hours. Results showed that hybrid alloy 2 had a lesser corrosion rate than hybrid alloy 1 due to the presence of different alloying elements. The XRD, optical, and SEM images of corroded surfaces of the test specimens were correlated with corrosion mechanisms.

After understanding the better strength and corrosion resistance of hybrid alloy 2, the wear test was conducted for hybrid alloy 2. Dry sliding wear studies on sintered hybrid alloy 2 revealed its lowest wear rate among all the alloys. Coefficient of friction is higher than the base alloy and lesser than ATOMET 4601+1.0C at the lowest load conditions. Finally, empirical relations were developed, and model adequacy was checked using ANOVA. Thus, the research provides insights to assist the powder metallurgy designer in developing the high performance materials for functional parts in engineering industries.

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