Numerical simulation and experimental validation of the cladding material distribution of hybrid semi-finished products produced by deposition welding and cross-wedge rolling

The service life of rolling contacts is dependent on many factors. The choice of materials in particular has a major influence on when, for example, a ball bearing may fail. Within an exemplary process chain for the production of hybrid high-performance components through tailored forming, hybrid solid components made of at least two different steel alloys are investigated. The aim is to create parts that have improved properties compared to monolithic parts of the same geometry. In order to achieve this, several materials are joined prior to a forming operation. In this work, hybrid shafts created by either plasma (PTA) or laser metal deposition (LMD-W) welding are formed via cross-wedge rolling (CWR) to investigate the resulting thickness of the material deposited in the area of the bearing seat. Additionally, finite element analysis (FEA) simulations of the CWR process are compared with experimental CWR results to validate the coating thickness estimation done via simulation. This allows for more accurate predictions of the cladding material geometry after CWR, and the desired welding seam geometry can be selected by calculating the cladding thickness via CWR simulation. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Simulation assisted process chain design for the manufacturing of bulk hybrid shafts with tailored properties

To manufacture semi-finished hybrid workpieces with tailored properties, a finite element simulation assisted process chain design was investigated. This includes the process steps of cross wedge rolling, hot geometry inspection, induction hardening, and fatigue testing. The process chain allows the utilisation of material combinations such as high-strength steels with low-cost and easy to process steels. Here, plasma transferred arc welding is applied to supply the process chain with hybrid specimen featuring different steel grades. An overview of the numerical approaches to consider the various physical phenomena in each of the process steps is presented. The properties of the component behaviour were investigated via the finite element method (FEM) and theoretical approaches. At first, the manufacturing of a hybrid workpiece featuring a near net shape geometry with improved mechanical properties due to recrystallising the weld was computed, using the example of a cross wedge rolling process. The rolling process was designed by means of FEM to determine suitable process parameters and to reduce experimental testing. An optical multi-scale geometry inspection of the hot workpiece is meant to be carried out after each manufacturing step to detect potential undesired forming or cooling-induced deformations. Due to the heat transfer from the hot component to the ambient medium, an optical measurement is affected by the developing inhomogeneous refractive index field in air. To gain a basic understanding of the refractive index field and induced light deflection effects, computations were conducted using heat transfer and ray tracing simulations. According to the proposed process route, a subsequent local heat treatment of the hybrid component is required to adapt the mechanical properties by a spray cooling assisted induction hardening. The heat treatment step was computed via a 2D FEM calculation. After finishing by machining, the hybrid material shafts are examined in fatigue tests under load conditions. To predict the component’s lifetime under rolling contact fatigue, a damage accumulation model was combined with an FE simulation. The resulting residual stress state after quenching and the geometry after the finishing process were used as input data for the fatigue life calculations

Investigation of the prediction accuracy of a finite element analysis model for the coating thickness in cross-wedge rolled coaxial hybrid parts

The Collaborative Research Centre 1153 (CRC 1153) "Process chain for the production of hybrid high-performance components through tailored forming" aims to develop new process chains for the production of hybrid bulk components using joined semi-finished workpieces. The subproject B1 investigates the formability of hybrid parts using cross-wedge rolling. This study investigates the reduction of the coating thickness of coaxially arranged semi-finished hybrid parts through cross-wedge rolling. The investigated parts are made of two steels (1.0460 and 1.4718) via laser cladding with hot-wire. The rolling process is designed by finite element (FE)-simulations and later experimentally investigated. Research priorities include investigations of the difference in the coating thickness of the laser cladded 1.4718 before and after cross-wedge rolling depending on the wedge angle β, cross-section reduction DA, and the forming speed v. Also, the simulations and the experimental trials are compared to verify the possibility of predicting the thickness via finite element analysis (FEA). The main finding was the ability to describe the forming behavior of coaxially arranged hybrid parts at a cross-section reduction of 20% using FEA. For a cross-section reduction of 70% the results showed a larger deviation between simulation and experimental trials. The deviations were between 0.8% and 26.2%. © 2019 by the authors

Hybrid Bulk Metal Components

In recent years, the requirements for technical components have steadily been increasing. This development is intensified by the desire for products with a lower weight, smaller size, and extended functionality, but also with a higher resistance against specific stresses. Mono-material components, which are produced by established processes, feature limited properties according to their respective material characteristics. Thus, a significant increase in production quality and efficiency can only be reached by combining different materials in a hybrid metal component. In this way, components with tailored properties can be manufactured that meet the locally varying requirements. Through the local use of different materials within a component, for example, the weight or the use of expensive alloying elements can be reduced. The aim of this Special Issue is to cover the recent progress and new developments regarding all aspects of hybrid bulk metal components. This includes fundamental questions regarding the joining, forming, finishing, simulation, and testing of hybrid metal parts

Porosity, cracks, and mechanical properties of additively manufactured tooling alloys: A review

Additive manufacturing (AM) technologies are currently employed for the manufacturing of completely functional parts and have gained the attention of high-technology industries such as the aerospace, automotive, and biomedical fields. This is mainly due to their advantages in terms of low material waste and high productivity, particularly owing to the flexibility in the geometries that can be generated. In the tooling industry, specifically the manufacturing of dies and molds, AM technologies enable the generation of complex shapes, internal cooling channels, the repair of damaged dies and molds, and an improved performance of dies and molds employing multiple AM materials. In the present paper, a review of AM processes and materials applied in the tooling industry for the generation of dies and molds is addressed. AM technologies used for tooling applications and the characteristics of the materials employed in this industry are first presented. In addition, the most relevant state-of-the-art approaches are analyzed with respect to the process parameters and microstructural and mechanical properties in the processing of high-performance tooling materials used in AM processes. Concretely, studies on the additive manufacturing of ferrous (maraging steels and H13 steel alloy) and non-ferrous (Stellite alloys and WC alloys) tooling alloys are also analyzed

Compound Semiconductor-Based Thin-Film and Flexible Optoelectronics.

Compound semiconductors are the basis of modern optoelectronics due to their intrinsically superior optical and electronic properties compared with elemental semiconductors. However, their applications remain limited due to a prohibitive substrate cost. This limitation has driven the development of epitaxial lift-off (ELO) technology that separates the thin-film epitaxial layer from the substrate by selectively removing a sacrificial layer between them. However, ELO has its own limitations including a long process time, complicated transfer to a secondary, low cost host substrate, and wafer surface degradation which prevents wafer recycling. In this thesis, we address all of these limitations by developing a new, non-destructive ELO (ND-ELO) process. When combined with adhesive-free cold-weld bonding of the wafer directly to a plastic substrate, ND-ELO provides an approximately 100 times reduction in process time, and a considerably simplified transfer process compared with conventional ELO. Furthermore, it allows indefinite wafer reuse by employing the epitaxial protection layers, eliminating surface degradation of the parent wafer encountered in conventional ELO. We demonstrate the feasibility and generality of this process by applying it to optoelectronic devices including photovoltaic cells, LEDs, MESFETs and photodetectors on two compound semiconductor systems, InP and GaAs. Furthermore, we present an approach that can achieve an estimated cost of only 3% that of conventional GaAs solar cells using an accelerated ND-ELO wafer recycling process, and integrated with lightweight, thermoformed plastic, truncated mini-compound parabolic concentrators (CPC) that avoid the need for active solar tracking. Using solar cell/CPC assemblies, without daily solar tracking, the annual energy harvesting is increased by 2.8 times compared with planar solar cells. This represents a drastic cost reduction in both the module and balance of systems costs compared with heavy, rigid conventional modules and trackers that are subject to wind loading damage and high installation costs. The demonstration of cost-efficient and high performance compound semiconductor-based flexible thin-film optoelectronics is a critical step toward allowing their widespread deployment in mainstream state-of-the-art applications including wearable, flexible and conformal devices.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111479/1/kyusang_1.pd

Investigating the Durability of Stellitte Hardfacing Components Used in the Power Generation Industry

Résumé Dans le secteur de la production d’énergie, les valves jouent un rôle essentiel dans la gestion du flux de vapeur à haute température et à haute pression. Elles sont utilisées pour démarrer et arrêter le flux, réguler le flux ou contrôler le sens du flux. Le fonctionnement des valves telles que l'ouverture et la fermeture peut provoquer l'usure des matériaux de la valve. Les progrès de la technologie des matériaux et des techniques de fabrication permettent aux valves de fonctionner à haute température. Par exemple, en appliquant l'alliage de surfaçage dur S6 sur les surfaces d'étanchéité des valves, un faible frottement est garanti et la résistance à l'oxydation et à la corrosion est également améliorée. Cependant, la délamination des alliages de surfaçage dur des valves représente un défi majeur pour le monde de la production d’électricité. Dans ce contexte, nous cherchons en premier lieu les causes de la délamination ; d'autre part, nous proposons des solutions pour améliorer la durabilité des composants de surfaçage dur Stellite. Afin d’accomplir ces objectifs, une étude de l’évolution de la microstructure et des propriétés méchaniques du surfaçage dur durant la fabrication et le service des composants. Un traitement thermique après soudage (PWHT) à 760 °C d’une durée de 2 h fût performé sur les composants de surfaçage dur durant le processus de fabrication. Les conditions de service du surfaçage dur furent étudiées par vieillissement à des températures variant entre 550 et 700 °C pour des durées variant entre 1008 et 8760 heures. La microstructure fût caractérisée par OM, SEM, EDS et EBSD. La caractérisation mécanique fût effectuée par micro et nano-indentation, tests d’impact Charpy et par test de tension. Les contraintes résiduelles ont été testées par diffraction de neutrons. Premièrement nous avons exploré l’effet du PWHT sur la microstructure, la dureté et les contraintes résiduelles des composants de surfaçage dur. Il a été observé que le PWHT diminue significativement la dureté du HAZ dans l’acier dû à la formation d’une microstructure en martensite revenue. De plus, il peut réduire substantiellement les contraintes résiduelles dans l’acier et homogénéiser les contraintes dans les composants de surfaçant dur. Après la fabrication, nous avons étudié l'évolution de la microstructure interfaciale F91/S21 des composants de surfaçage dur. Les résultats ont montré que l'interface F91/S21 est instable lors du vieillissement en raison de la formation d'une couche interfaciale dure. En étudiant sa cinétique de croissance, il a été constaté que cette couche interfaciale suit un taux de croissance parabolique. En appliquant des méthodes de caractérisation complémentaires, trois phases, à savoir une phase FexCoy de type BCC, un carbure de type M23C6 riche en Cr et une phase σ de type (Fe,Co) (Cr,Mo) ont été identifiées dans cette couche interfaciale. D'après les cartographies de nano-indentation obtenues sur l'interface F91/S21, les carbures M23C6 et la phase σ sont nettement plus durs que les autres phases. De plus, il a été constaté que les carbures M23C6 grandissaient avec la température et la durée de vieillissement, alors que la quantité de phase σ diminuait avec la température. Pour donner suite à l’exploration de l’évolution de la microstructure interfaciale F91/S21, nous avons étudié les effets de la microstructure interfaciale F91/21 sur les propriétés mécaniques des composants de surfaçage dur au moyen de tests d’impact Charpy. Une géométrie innovante de l’encoche en U Charpy a été conçue, c’est-à-dire que l’interface F91/S21 était centrée dans l’encoche. Une diminution considérable de l’énergie après le vieillissement est attribuée à la couche interfaciale formée, où les craques primaires se propagent. Les composants de surfaçage dur vieillis présentent des défaillances par fissures fragiles. Il a été trouvé que les carbures M23C6 jouent un rôle plus important que la phase σ dans la dégradation de la ténacité lors des tests d’impact. Il est proposé que les facteurs microstructuraux contribuant au délaminage des alliages de surfaçage dur des soupapes à haute température soient la formation de ces phases dures. Ensuite, nous avons réalisé une étude comparative sur l'évolution de la microstructure et les propriétés mécaniques des composants de surfaçage dur en utilisant l'IN82 comme alternative à la couche tampon S21. Comparativement aux composant de surfaçage dur S21, aucune couche interfaciale nuisible fût observée à l’interface F91/S21 après le vieillissement. La diminution de la ténacité des composants de surfaçage dur IN82 s’est avérée beaucoup moins importante que celle de S21, et, de plus, serait reliée à la formation grossière et à la précipitation des carbures intergranulaires/interdendritiques dans le IN82 plutôt qu’à l’interface F91/IN82. En plus du IN82, les composants de surfaçage dur IN625 furent étudiés en raison du bas prix. L’interface F91/IN625 et le matériel massif IN625 se sont démontrés comme moins stables que les composants de surfaçage dur IN82 dû aux précipités formés durant le vieillissement. Bien que l’interface F91/IN625 ne soit pas le lien le plus faible durant les tests de tension, certains spécimens Charpy présentent des défaillances le long de l’interface F91/IN625, résultant possiblement des précipités parallèles à l’interface. La perte d’énergie d’impact est significative (88%) après un vieillissement de 650 °C pour 8760 h. Il n’est pas recommandé d’utiliser la couche tampon IN625. Finalement, l’étude d’un composant d’ex-service a validé notre étude en laboratoire sur les composants de surfaçage dur S21. La fissure de délamination s’est propagée dans les zones riches en phases σ de la couche de S21. Cela s’explique par le fait que la phase σ s’est formée loin de l’interface, profondément dans le S21 via le chemin de diffusion aux limites de grain après plusieurs années de service. Le temps de service réel et la température concorde avec le temps et la température équivalente attendue par extrapolation. Lors du service des valves, il existe également d'autres facteurs tels que le cyclage thermique et les contraintes induites par le fonctionnement (ouverture et fermeture des valves), en plus du vieillissement. Ils n'ont pas été pris en compte pour l'expérimentation. Cependant, nous pensons que les objectifs de ce travail ont été atteints. À savoir, les causes des défaillances prématurées ont été identifiées et les solutions alternatives pour améliorer la durabilité des composants de surfaçage dur ont été validées. Pour relever le défi du délaminage d'alliages de surfaçage dur provenant de valves haute température, la couche tampon IN82 constitue une bonne alternative pour remplacer la couche tampon problématique S21, qui peut améliorer la durabilité des composants de surfaçage dur. Néanmoins, en raison de la dilution plus élevée de Fe et de Ni, la dureté de la couche supérieure de S6 déposée sur la couche tampon IN82 est compromise par rapport au S6 déposé sur la couche tampon de S21. Par conséquent, il est proposé que davantage de couches de S6 puissent être déposées pour maintenir sa dureté en fonction des applications. De plus, les paramètres de soudure utilisés durant la fabrication peuvent être optimisés pour réduire la dilution et maintenir la dureté du S6. Pendant le service des valves, il y a aussi d’autres facteurs comme le cycle thermique et le stress induit par les opérations (ouverture et fermeture des valves) qui s’additionnent au vieillissement. Ces paramètres n’ont pas été pris en compte durant les expérimentations. D’autre part, nous croyons fortement que les objectifs établis dans le Chapitre 1 ont été atteints. Notamment, les causes d’échecs prématurés ont été identifiées et les solutions alternatives pour améliorer la durabilité des composants de surfaçage dur ont été validées. Afin de répondre au défi de la délamination des alliages de surfaçage dur dans les valves hautes-températures, la couche tampon de IN82 est une bonne alternative à celle problématique de S21, car elle peut améliorer la durabilité des composants de surfaçage dur. Néanmoins, due à une plus grande dilution de Fe et de Ni, la dureté de la couche supérieure de S6 déposée sur la couche tampon de IN82 est compromise quand elle est comparée avec le S6 déposé sur la couche tampon de S21. Donc, il est proposé que plus de couches de S6 peuvent être déposées afin de maintenir la dureté dans les applications où la résistance à l’usure est critique. ---------- Abstract In the power generation industry, valves play a vital role, which manage the flow of high-temperature and high-pressure steam. They are used to start and stop the flow, regulate the flow, or control the direction of the flow. Operation of valves such as opening and closing can cause wear of valve materials. Advances in material technology and manufacturing techniques enable valves to operate at high temperatures. For instance, by applying the hardfacing alloy S6 onto the sealing surfaces of valves, wear, oxidation and corrosion resistance are improved. However, delamination of hardfacing alloys from valves has presented a major challenge to the power generation world. In this context, we aim at investigating the causes of delamination failures. In addition, we target at proposing solutions to enhance the durability of Stellite hardfacing components. To fulfill the objectives, we carried out a comprehensive study on the microstructure evolution and mechanical properties of three types of hardfacing components during manufacturing and service. A PWHT at 760 °C for 2 h was performed on the hardfacing components during the manufacturing process. Valves are usually used at elevated temperatures for long duration. Aging experiments at four temperatures ranging from 550 to 700 °C for three exposure times within a one-year period were conducted on the hardfacing components. The microstructure was characterized using OM, SEM, EDS, and EBSD. The mechanical characterization was undertaken using nano- and micro-indentation, Charpy impact, and tensile testing. The residual strains/stresses were measured using neutron diffraction. First, we explored the effects of the PWHT on microstructure, hardness and residual stresses of the hardfacing components to reduce the risk of failures introduced in process. The PWHT was found to soften the high-hardness HAZ in the steel significantly due to the formation of the tempered-martensitic microstructure. Moreover, it can reduce the residual stresses in steel substantially and homogenize the strains across the hardfacing component. After manufacturing, we studied the F91/S21 interfacial microstructure evolution of the problematic S21 hardfacing components. A layer was found to grow along the F91/S21 interface during aging, which follows a parabolic rate of growth. Three phases including an (Fe,Co)(Cr,Mo)-type σ phase and a Cr-rich M23C6-type carbide were identified in this interfacial layer through the complementary characterization methods. This interfacial layer is harder than the S21 and the F91 materials due to the presence of the hard σ phase and M23C6 carbides. The M23C6 carbides were found to grow with aging temperature and time. However, lesser amount of the σ phase was observed at higher temperatures studied. Following the exploration of the F91/S21 interfacial microstructure evolution, we investigated the effects of F91/S21 interfacial microstructure on the mechanical properties of S21 hardfacing components by means of Charpy impact testing. An innovative Charpy U-notch geometry was designed. That is, the F91/S21 interface was centered in the notch. The significant decrease in impact energy after aging is resulted from the interfacial layer formed, where the primary cracks propagate. The aged S21 hardfacing components were found to fail in a brittle fashion. Both the the σ phase and M23C6 carbides were found to contribute to the toughness degradation during the impact testing, though the M23C6 carbides play a more important role than the σ phase. It is proposed that these two hard phases are the microstructural causes for the delamination of Stellite hardfacing from valves. Then, we performed a comparative study on the microstructure evolution and mechanical properties of hardfacing components using the IN82 alloy as an alternative to the problematic S21 buffer layer. Compared with the S21 hardfacing components, no deleterious interfacial layer was observed along the F91/IN82 interface after aging. The impact toughness degradation in the IN82 hardfacing components was found to be much less significant than that of the S21, and in addition, to be related to coarsening and precipitation of the intergranular/interdendritic carbides in the IN82 bulk material rather than the F91/IN82 interface. In addition to the IN82 alloy, the IN625 hardfacing components were investigated due to low cost. Both the F91/IN625 interface and the IN625 bulk material were found to be not as stable as the IN82 hardfacing components because of the presence of precipitates during aging. Though the F91/IN625 interface is not the weakest link during the tensile testing, some Charpy specimens were found to fail along the F91/IN625 interface possibly resulted from the precipitates parallel to the interface. The impact energy loss is significant (88%) after aging at 650 °C for 8760 h. It is not recommended to use the IN625 buffer layer. Finally, the examination of an ex-service wedge gate valve validates our laboratory study on the S21 hardfacing components. The delamination crack was observed in the zones enriched with the σ phase of the S21 bulk material. It is because large amounts of the σ phase precipitate deeply into the S21 bulk material via the grain boundary diffusion path after years of service. The service time and temperature of this ex-service component fulfill the expected equivalent time and temperature by extrapolation. During service of valves, in addition to aging, there are other factors such as thermal cycling and operation induced stresses (opening and closing of valves). They were not taken into account by our experimentation. However, we do believe that the objectives of this work have been fulfilled. Namely, the causes of the premature failures have been identified and the alternative solutions to enhance the durability of the hardfacing components have been validated. To meet the challenge of delamination of hardfacing alloys from high-temperature valves, the IN82 buffer layer is a good alternative to replace the problematic S21 buffer layer, which can enhance the durability of the hardfacing components. However, due to higher dilution of Fe and Ni, the hardness of S6 top layer deposited on the IN82 buffer layer is compromised compared with the S6 deposited over the S21 buffer layer. To mitigate this downside, it is proposed that more S6 layers can be deposited to maintain its hardness according to the applications. Moreover, the welding parameters used during manufacturing can be optimized to reduce the dilution, and thus to maintain the S6 hardness

Cumulative Index to NASA Tech Briefs, 1963 - 1966

Cumulative index of NASA Tech Briefs dealing with electrical and electronic, physical science and energy sources, materials and chemistry, life science, and mechanical innovation