M. Ashfaq

Bio: M. Ashfaq is an academic researcher from King Saud University. The author has contributed to research in topics: Welding & Corrosion. The author has an hindex of 12, co-authored 19 publications receiving 608 citations. Previous affiliations of M. Ashfaq include National Institute of Technology, Tiruchirappalli & Indian Institute of Technology Madras.

Analysis and Characterization of the Role of Ni Interlayer in the Friction Welding of Titanium and 304 Austenitic Stainless Steel

Abstract: Joining of commercially pure Ti to 304 stainless steel by fusion welding processes possesses problems due to the formation of brittle intermetallic compounds in the weld metal, which degrade the mechanical properties of the joints. Solid-state welding processes are contemplated to overcome these problems. However, intermetallic compounds are likely to form even in Ti-SS joints produced with solid-state welding processes such as friction welding process. Therefore, interlayers are employed to prevent the direct contact between two base metals and thereby mainly to suppress the formation of brittle Ti-Fe intermetallic compounds. In the present study, friction-welded joints between commercially pure titanium and 304 stainless steel were obtained using a thin nickel interlayer. Then, the joints were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, and X-ray diffractometry. The mechanical properties of the joints were evaluated by microhardness survey and tensile tests. Although the results showed that the tensile strength of the joints is even lower than titanium base metal, it is higher than that of the joints which were produced without nickel interlayer. The highest hardness value was observed at the interface between titanium and nickel interlayers indicating the formation of Ni-Ti intermetallic compounds. Formation these compounds was validated by XRD patterns. Moreover, in tensile tests, fracture of the joints occurred along this interface which is related to its brittle nature.

A New Approach for Using Interlayer and Analysis of the Friction Welding of Titanium to Stainless Steel

Abstract: Dissimilar material joining is often more difficult than joining the similar material or alloys with minor differences in physical properties and composition. The formation of deleterious intermediate phases consisting of intermetallic compounds during welding of titanium and stainless steel is a challenge to the welding processes, for decades. Friction welding has been used in an attempt to reduce formation of intermetallic compounds through inserting an interlayer material. In recent years, a number of approaches have been developed to insert interlayer between the substrates to avoid the metallurgical incompatibility. In this research, dissimilar joint of titanium and stainless steel were welded effectively using a new technique of electrodeposited nickel coating on one of the substrate (stainless steel) as interlayer. The bonding interface of the joints was characterized using optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Tensile strength of the nickel interlayer joints was higher than the direct joints. The microstructural characterization in the interface of titanium and stainless steel showed the absence of brittle Fe–Ti intermetallic compounds, which was a condition attributed to the use of interlayer technique. Whereas, the characterization of interface were identified as the presence of Ti–Ni phases which were more plastic than Fe–Ti intermetallic compounds.

Investigations on the continuous drive friction welding of sintered powder metallurgical (P/M) steel and wrought copper parts

Abstract: The present investigation attempts to understand the friction welding characteristics of sintered P/M steel preforms–wrought copper dissimilar parts. In order to achieve sound weld between these two materials the process parameters were optimized and inferred that the preforms of lower densities with lower process parameters yields quality weldments, established through post-weld tests. This study also envisages the influence of process parameters which include resident preform densities, friction pressure, upset pressure, and burn-off length on microstructure and mechanical properties of the welds. This work consolidates information on the aspects of joining P/M component with wrought materials for practical execution.

Modeling machining of particle-reinforced aluminum-based metal matrix composites using cohesive zone elements

Abstract: Finite element modeling for the machining of heterogeneous materials like particle-reinforced metal matrix composites has not been much successful as compared to homogeneous metals due to several issues. The most challenging issue is to deal with severe mesh distortion due to nonuniform deformation inside the workpiece. Other problems are related to the modeling of the interface between reinforcement particles and matrix and tool-reinforcement particle interaction. In this study, different strategies are adopted for finite element models (FEM) to cope with the above issues and comparative analyses have been performed. These 2D FE models are based on plane strain formulations and utilize a coupled temperature displacement method. The workpiece is modeled using reinforcement particle size and volume fraction inside the base matrix. The interface between the reinforcement particles and the matrix is modeled by using two approaches, with and without cohesive zone elements, and the chip separation is modeled with and without using a parting line. This allows models to simulate the local effects such as tool-reinforcement particle interaction and reinforcement particle debonding. In addition, the models can predict cutting forces, chip morphology, stresses, and temperature distributions. The effects of different methodologies on the model development, simulation runs, and predicted results have been discussed. The results are compared with experimental data, and it has been found that the utilization of cohesive zone elements (CZE) with the parting line approach seems to be the best one for the modeling of metal matrix composite (MMC) machining.

Joining of dissimilar materials

Abstract: Emerging trends in manufacturing such as light weighting, increased performance and functionality increases the use of multi-material, hybrid structures and thus the need for joining of dissimilar materials. The properties of the different materials are jointly utilised to achieve product performance. The joining processes can, on the other hand be challenging due to the same different properties. This paper reviews and summarizes state of the art research in joining dissimilar materials. Current and emerging joining technologies are reviewed according to the mechanisms of joint formation, i.e.; mechanical, chemical, thermal, or hybrid processes. Methods for process selection are described and future challenges for research on joining dissimilar materials are summarized.

Additive manufacturing of functionally graded materials: A review

Abstract: Functionally graded materials (FGMs) represent a class of novel materials in which compositions/constituents and/or microstructures gradually change along single or multiple spatial directions, resulting in a gradual change in properties and functions which can be tailored for enhanced performance. FGMs can be fabricated using a variety of well-established processing methods; however, it is also known that there are inherent drawbacks to existing synthesis methods. As an emerging technology that provides a high degree of control over spatial resolution, additive manufacturing (AM) provides an intriguing pathway to circumvent the drawbacks of currently available methods. AM involves the selective deposition of individual layers of single or multiple materials, and as such it offers the potential of local control of composition and microstructure in multiple dimensions; such process conditions, in principle, can be tailored to construct complex FGMs with multi-dimensional and directional gradient structures. In this review paper, our current understanding of important issues, such as modeling, processing, microstructures and mechanical properties, as related to FGMs produced via AM, are described and discussed in an effort to assess the state of the art in this field as well as to provide insight into future research directions.

Linear and rotary friction welding review

Abstract: Friction welding (FW) is a high quality, nominally solid-state joining process, which produces welds of high structural integrity. Rotary friction welding (RFW) is the most commonly used form of FW, while linear friction welding (LFW) is a relatively new method being used mainly for the production of integrally bladed disc (blisk) assemblies in the aircraft engine industry. Numerous similar and dissimilar joints of structural metallic materials have been welded with RFW and LFW. In this review, the current state of understanding and development of RFW and LFW is presented. Particular emphasis is placed on the process parameters, joint microstructure, residual stresses, mechanical properties and their relationships. Finally, opportunities for further research and development of the RFW and LFW processes are identified.

Advances in friction welding process: a review

Abstract: Friction welding is now well established as one of the most economical and highly productive methods in joining similar and dissimilar metals. It is widely used in automotive and aerospace industrial applications. Friction welding is often the only viable alternative in this field to overcome the difficulties encountered in joining the materials with widely varying physical characteristics. This process employs a machine that is designed to convert mechanical energy into heat at the joint to weld using relative movement between workpieces, without the use of electrical energy or heat from other sources. This review deals with the fundamental understanding of the process. The focus is on the mechanism of friction welding, types of relative motions of the process, influence of parameters, heat generation in the process, understanding the deformation, microstructure and the properties of similar and dissimilar welded materials.