R. K. P. Singh

Bio: R. K. P. Singh is an academic researcher. The author has contributed to research in topics: Friction stir processing & Dynamic recrystallization. The author has an hindex of 2, co-authored 4 publications receiving 63 citations.

A Review on Functionally Gradient Materials (FGMs) and Their Applications

Abstract: Functionally gradient materials (FGM) are innovative materials in which final properties varies gradually with dimensions. It is the recent development in traditional composite materials which retains their strengths and eliminates their weaknesses. It can be formed by varying chemical composition, microstructure or design attributes from one end to other as per requirement. This feature allows FGM to have best material properties in required quantities only where it is needed. Though there are several methods available for manufacturing FGMs, additive based metal deposition (by laser, electron beam, plasma etc.) technologies are reaping particular interest owing to their recent developments. This paper presents evolution, current status and challenges of functionally gradient materials (FGMs). Various manufacturing processes of different types of FGMs are also presented. In addition, applications of FGMs in various fields including aerospace, defence, mining, power and tools manufacturing sectors are discussed in detail.

Influence of Medium Used during Ferritic Nitro-Carburizing of AISI H-13 Hot Work Tool Steel

Abstract: Ferritic nitro-carburizing is one of the most popular surface hardening methods used to improve lifespan of hot work tool steels. Different types of mediums like gas, liquid, plasma and fluidized bed are generally used during ferritic nitro-carburizing process. In this paper, various ferritic nitro-carburizing methods were compared where gas, salt bath and fluidized are used as mediums. AISI H-13 hot work tool steel specimens were treated by using these different methods of nitro-carburizing and their performance was evaluated by using micro-structural and mechanical analysis. Optical microscopy, micro-hardness testing and X-ray stress analyzer were used for specimen characterization. Moreover, pin on disk dry sliding wear tests were performed to compare wear performance of specimens treated with different nitro-carburizing methods. It is perceived that, medium used during nitro-carburizing has significant influence on the final surface properties that can be achieved by ferritic nitro-carburizing.

Investigation of Process Parameters for Friction Stir Processing (FSP) of Ti-6Al-4V Alloy

Abstract: In the current work friction stir processing of the Ti-6Al-4V alloy was carried out. Various process parameters (tool traverse speed and tool rotation speed) were studied for successful FSP of Ti-6Al-4V. The process parameters were identified using macrostructure observation on the surface of processed plate and microstructure evolution in the stir zone (SZ) of the FSP specimen. The effect of tool traverse speed and tool rotation speed on microstructure evolution in the SZ, thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) were studied. The microstructure transformation from initial elongated α structure to prior β grains, with α layer grain boundary consisting of mixture of acicular α′ and very fine lamellar α/β colonies, was observed at SZ. This was the case for wide range of variations in parameters except for the tool rotation speed of 600 rpm and traverse speed of 60 and 100 mm/min. Under this combination of parameters, the bands of DRX α and transformed β structure were observed to evolve at SZ.

Multipass-friction Stir Processing (MFSP) of Ti-6Al-4V Alloy and Investigation of Flow Properties

Abstract: Multipass friction stir processing (MFSP) of the Ti-6Al-4V alloy was carried out at 600 tool rpm and 80 mm/min traverse speed. After first pass, the initial elongated α structure transformed to prior β grains, consisting of a mixture of acicular α'and very fine lamellar α colonies along with α layer grain boundary in stir zone (SZ). This subsequently transformed to equiaxed α grain via dynamic recrystallization (DRX) process. With the increase in the number of FSP passes the fraction of equiaxed α grains was found to increase, reaching almost fully equiaxed α structure in SZ upon completion of the fifth pass. Flow properties of MFSP Ti-6Al-4V alloy were investigated by differential strain rate test carried out at 927°C. There appears no significant variation in the strain rate sensitivity index (m ≥ 0.3) values between as received Ti-6Al-4V alloy and MFSP Ti-6Al-4V alloy specimens.

Additive manufacturing of functionally graded metallic materials using laser metal deposition

Abstract: Functionally graded materials (FGMs) have attracted much research interest in the industry due to their graded material properties, which result from gradually distributed compositions or structures. In recent years, metallic FGMs have been widely studied, and additive manufacturing (AM) has become an important approach to build metallic FGMs. This paper aims to provide an overview of the research progress in metallic FGMs fabricated by laser metal deposition (LMD), an AM process that is widely used in metallic materials. Firstly, the unique material properties and advantages of FGMs are introduced. Then, typical recent findings in transition path design, fabrication, and characterization for different types of metallic FGMs via LMD are summarized and discussed. Finally, challenges in fabricating metallic FGMs via LMD are discussed, and other related aspects in the area of FGMs such as model representation and numerical simulation are proposed for further investigation.

Functionally graded materials classifications and development trends from industrial point of view

Abstract: Over the last few years, many classifications have been proposed for functionally graded materials (FGMs). In this Paper, critical review of different available classifications for FGM based on their physical, structural and manufacturing characteristics are presented. Advantages and limitations of each fabrication method for use in a given application is correspondingly considered. In addition, new classifications based on gradation control and accuracy, residual stresses, specific energy consumption, environmental impact evaluated throughout the complete life cycle and manufacturing costs are proposed. These classifications mainly reflect the needs of both FGM designers and industrial manufacturers. Based upon the presented classifications and the recent advances in analysis and production techniques, new major directions for FGMs research are proposed.

PLA Composites Reinforced with Flax and Jute Fibers-A Review of Recent Trends, Processing Parameters and Mechanical Properties.

Abstract: Multiple environmental concerns such as garbage generation, accumulation in disposal systems and recyclability are powerful drivers for the use of many biodegradable materials. Due to the new uses and requests of plastic users, the consumption of biopolymers is increasing day by day. Polylactic Acid (PLA) being one of the most promising biopolymers and researched extensively, it is emerging as a substitute for petroleum-based polymers. Similarly, owing to both environmental and economic benefits, as well as to their technical features, natural fibers are arising as likely replacements to synthetic fibers to reinforce composites for numerous products. This work reviews the current state of the art of PLA compounds reinforced with two of the high strength natural fibers for this application: flax and jute. Flax fibers are the most valuable bast-type fibers and jute is a widely available plant at an economic price across the entire Asian continent. The physical and chemical treatments of the fibers and the production processing of the green composites are exposed before reporting the main achievements of these materials for structural applications. Detailed information is summarized to understand the advances throughout the last decade and to settle the basis of the next generation of flax/jute reinforced PLA composites (200 Maximum).

A review of impact resistant biological and bioinspired materials and structures

Abstract: Biological systems must have the capability to withstand impacts generated during collisions due to combat and defense. Thus, evolution has created complex materials’ architectures at various length scales that are capable of withstanding repeated, low-to-medium-velocity impacts (up to 50 m/s). In this paper, we review impact resistant biological systems with a focus on their recurrent structural design elements, material properties, and energy absorbing mechanisms. We classify these impact resistant structures at the micro- and meso-scales into layered, gradient, tubular, sandwich, and sutured and show how they construct global hierarchical, composite, porous, and interfacial architectures. Additionally, we review how these individual structures and their design parameters can provide a tailored response. We conclude with a future outlook and discussion of their potential for impact resistant bioinspired designs.