Theresa C. Novak

Bio: Theresa C. Novak is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Tension (geology) & Plane stress. The author has an hindex of 1, co-authored 1 publications receiving 5 citations.

Plasticity and fracture behavior of Inconel 625 manufactured by laser powder bed fusion: Comparison between as-built and stress relieved conditions

Abstract: In this study, the influence of stress relief on the plasticity and fracture behavior of Inconel 625 fabricated through laser powder bed fusion additive manufacturing (AM) was investigated. The as-built versus stress relieved microstructures were compared, showing similar grain structures but the presence of ~10 vol % δ phase in the stress relieved condition, and no δ phase in the as-built condition. Mechanical tests under plane strain tension were performed on the stress relieved samples, and an anisotropic plasticity model was calibrated and validated using finite element simulations. Uniaxial and notched tension tests were performed on both as-built and stress relieved samples to probe the effect of stress relief on stress state- and direction-dependent fracture behavior. It was found that on average, the fracture strain of the stress relieved samples along the build direction was 30% higher than that along the perpendicular build direction in the stress state range studied, and the stress relief heat treatment resulted in a 45% decrease in fracture strain. The fracture strain in stress relieved samples was more strongly dependent on stress state than in as-built samples.

Review of Powder Bed Fusion Additive Manufacturing for Metals

Abstract: Additive manufacturing (AM) as a disruptive technology has received much attention in recent years. In practice, however, much effort is focused on the AM of polymers. It is comparatively more expensive and more challenging to additively manufacture metallic parts due to their high temperature, the cost of producing powders, and capital outlays for metal additive manufacturing equipment. The main technology currently used by numerous companies in the aerospace and biomedical sectors to fabricate metallic parts is powder bed technology, in which either electron or laser beams are used to melt and fuse the powder particles line by line to make a three-dimensional part. Since this technology is new and also sought by manufacturers, many scientific questions have arisen that need to be answered. This manuscript gives an introduction to the technology and common materials and applications. Furthermore, the microstructure and quality of parts made using powder bed technology for several materials that are commonly fabricated using this technology are reviewed and the effects of several process parameters investigated in the literature are examined. New advances in fabricating highly conductive metals such as copper and aluminum are discussed and potential for future improvements is explored.

Additive manufacturing of bimetallic structures

Abstract: ABSTRACT Current industrial applications demand materials with customised features and site-specific properties, and many such applications use bimetallic structures. Bimetallic structures offer unique properties from both materials. Bimetallic materials are made by joining two different materials via welding or brazing. Although welding techniques to join two metallic materials are economical, there are still many critical issues, such as managing the heat-affected zone, cracking, and premature failures due to brittle intermetallic phase formation, especially for joining two dissimilar metals, and reproducibility. In recent years, metal additive manufacturing (AM) has been explored towards processing bimetallic materials. Metal AM systems are designed with multiple feedstock materials, enabling various printing strategies to process bimetallic structures. This review aims to aid researchers in understanding AM processing of bimetallic structures. Various processing strategies, characterisation methods, challenges, and future directions are discussed. We envision that this review will help further the implementation of AM technologies in bimetallic structures.

A comprehensive literature review on laser powder bed fusion of Inconel superalloys

Abstract: Inconel superalloys are one of the main classes of materials with good potential for production using the additive manufacturing process of laser powder bed fusion (PBF-LB), which has a broad range of applications in the transportation and energy sectors. Thus, they have received considerable attention in the scientific literature, with researchers aiming to better understand their capabilities and limitations in recent decades. This review is based on around 340 publications spanning the past 14 years and highlights the most significant findings in the field along with the current challenges and research goals resulting from them. A contextualization is followed by a succinct microstructural review, which introduces the topics analyzed. The effects of the processing parameters, heat treatment and machining on the materials and their composites are evaluated and the performance of materials is compared in terms of their mechanical, corrosion and tribological behavior. Publications are mapped according to their research focus in order to reveal the current research trends in the literature. • Review of more than 330 experimental publications of the last 14 years. • Processing, post processing and performance aspects are covered. • Similarities and contrast between the behavior of alloys are displayed. • Research gaps and current challenges are identified. • Maps linking each reviewed publication and its research focus are provided.

Mechanical Behavior of Laser Powder Bed Fusion Processed Inconel 625 Alloy

Abstract: Inconel 625 (IN625) has an excellent suite of high temperature mechanical properties that encourages its use in fabricating jet engine and gas turbine components. Apart from conventional manufacturing methods, recent advances in laser powder bed fusion (LPBF), a laser-based additive manufacturing method, has enjoyed reasonable success in producing crack-free near net shaped components made of IN625. With the purpose of understanding its applications and limitations, the mechanical behavior of LPBF manufactured IN625 is reviewed in detail. First, the microstructural evolution in the as-built state is discussed. Furthermore, the changes in microstructure with respect to various heat treatments are well explained. Correlations between microstructural dependence and process-induced defects on uniaxial tensile characteristics at ambient and elevated temperatures are highlighted. Similarly, microstructural correlations are made with fracture, fatigue life and creep behaviors of LPBF IN625. Finally, the current research gaps and unfulfilled challenges are summarized to postulate future research directions.

Anisotropic cyclic plasticity modeling for additively manufactured nickel‐based superalloys

Abstract: The additively manufactured materials show anisotropic mechanical properties. In the present paper, a constitutive model for a nickel-based superalloy made by selective laser melting was established to characterize cyclic mechanical behaviors under multiaxial loading conditions. Detailed material tests revealed that the effects from the building orientation decrease with multiaxial cyclic loads. A cyclic constitutive model based on the Hill criterion was introduced for the superalloy and considered the orthotropic mechanical properties depending on loading cycles. The computation confirms the model can reasonably simulate the cyclic elastic-plastic behavior under non-proportional complex loading conditions and provides an applicable method for engineering applications.