Impact of a multi-step heat treatment on different manufacturing routes of 18CrNiMo7-6 steel

Effect of an optimized multi-step heat treatment routine on conventional (machining from wrought bar stock) and alternate manufacturing routes (hot forging and cold rotary forging) for producing flat cylindrical-shaped machine drive components from 18CrNiMo7-6 steel was investigated. The microstructure and mechanical properties of the final component manufactured using these three different routes were analyzed using optical microscopy, electron backscatter diffraction (EBSD), hardness testing, electro-thermal mechanical testing (ETMT), and rotary bending fatigue testing (RBFT) before and after implementing the multi-step heat treatment. It was found that the multi-step heat treatment transformed the as-received microstructure into the tempered martensitic microstructure, improving hardness, tensile, and fatigue properties. The heat treatment produced desired properties for the components manufactured by all three different routes. However the cold rotary forging, which is the most material utilizing route over the others, benefited the most from the optimized heat treatment

From Assistants to Partners: A Framework for Graduate Students as Partners in SoTL Research

Student-faculty partnerships are a growing practice in scholarship of teaching & learning (SoTL) projects. They can foster greater student engagement in higher education and help advance teaching & learning experiences. For graduate students, in particular those pursuing academic careers, such partnerships can offer opportunities for development of their professional identities as emerging SoTL scholars. In this article, we expand upon previous theorizations of partnerships to include the unique attributes of graduate student partnerships, such as in terms of longer timeframes, increased complexity, and long-term goals. Drawing on a two-year SoTL study, we present a three-layer framework characterizing key attributes for a successful graduate student-faculty partnership: 1) individual attributes in a partnership, 2) collective attributes for a partnership, and 3) outcomes of a partnership. The framework is grounded in literature and illustrative examples from our experiences as graduate students and faculty members working together in partnership with a SoTL project. This framework offers a structured mechanism to inform, create, and enhance the capacity of student-faculty partnerships in SoTL research

Impact of various heat treatments on the microstructure evolution and mechanical properties of hot forged 18CrNiMo7-6 steel

Carburizing is a method of enhancing the surface properties of components, primarily made from low to medium carbon steels, such as shafts, gears, bearings, etc. Carburized parts are generally quenched and tempered before being put into service; however, after quenching of carburized parts further annealing and hardening treatments can be employed before final tempering. This work analyses the impact of the two aforementioned heat treatment approaches on the development of subsequent microstructures and mechanical properties of hot forged 18CrNiMo7-6 steel. Moreover, this study aims to understand the impact of normalizing treatments prior to the two aforementioned heat treatment routes. Microstructural and mechanical tests were conducted on four as forged flat cylinder components that received a combination of the abovementioned heat treatments. In general, better microstructure refinement, in terms of prior austenite grain size (PAGS), was obtained for carburized parts that received the intermediate annealing and hardening treatments after quenching and prior to the final tempering. Additionally, further refinement of the martensitic pockets/blocks was observed for parts that did not receive a normalising treatment prior to carburisation. The studied heat treatments appear to have a negligible effect on the mechanical properties of the hot forged flat cylinder components

Finite element modelling of transient behaviours and microstructural evolution during dissimilar rotary friction welding of 316 austenitic stainless steel to A516 ferritic steel

Inertia friction welding (IFW) is a near-net-shape joining process that produces high-integrity welds. The transient nature of this joining process necessitates the availability of reliable computational models to predict the evolution of temperature and deformation throughout welding. In this study, a thermo-mechanical finite element (FE) model, based on an adaptive remeshing technique, is proposed to simulate dissimilar joining of A516 ferritic steel and 316L austenitic stainless steel (SS). The results of FE model were evaluated and verified via comparing the shape/size of the flash, upsetting load and angular velocity profile of a physical weld produced by IFW trials. A good agreement was achieved between the appearance of the weld/flash and those predicted by the FE model, thus verifying the predicted temperature and strain distributions. The microstructural features across different weld regimes were also examined to correlate the concomitant changes with the simulated temperature profile

Genetic compatibility exceeds possible ‘good genes’ effects of sexual selection in lake char

Mating is rarely random in nature, but the effects of mate choice on offspring performance are still poorly understood. We sampled in total 47 wild lake char (Salvelinus umbla) during two breeding seasons and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, 1,464 embryos that resulted from sperm competition trials were raised singly in either a stress- or non-stress environment. Offspring growth turned out to be strongly reduced with increased genetic relatedness between the parents while male coloration (that reveal aspects of male health) was no significant predictor of offspring performance. In a second experiment one year later, block-wise full-factorial in vitro breeding was used to produce 3,094 embryos that were raised singly after sublethal exposures to a pathogen or water only. Offspring growth was again strongly reduced with increased genetic relatedness between the parents while male coloration was no significant predictor of offspring performance. We conclude that the genetic benefits of mate choice would be strongest if females avoided genetic similarity, while male breeding colors seem more relevant in intra-sexual selection

Continuous drive friction welding of AISI 8630 low-alloy steel : experimental investigations on microstructure evolution and mechanical properties

Continuous drive friction welding (CDW) is a state-of-the-art solid-state welding technology for joining metallic components used in aerospace, oil and gas, and power generation industries. This study summarizes the results of mechanical and microstructural investigations on a modified AISI-8630 steel subjected to CDW. The effects of welding process parameters, including rotational speed, friction, and forge forces, during CDW were explored to determine an optimum welding condition. The mechanical properties of the weld, and microstructural characteristics across different regions of the weld were measured and examined. The microstructure characterization results suggest that the weld zone (WZ) experiences temperatures above the Ac3 and the thermo-mechanically affected zone (TMAZ) experiences temperatures between Ac1 and Ac3 of the material. Investigations with electron backscatter diffraction (EBSD) demonstrated the occurrence of strain-induced dynamic recrystallization in the weld. The weld demonstrated higher yield and ultimate tensile strengths at the expense of ductility and hardening capacity compared to the base metal (BM). The strain-hardening profiles of the welds exhibited a dual-slope characteristic, an indication of different levels of plastic deformation experienced by the constituent phases (i.e., martensite, bainite and ferrite) present in the microstructure. The maximum strength-to-ductility combination and static toughness values were obtained for the weld produced under the highest rotational speed, maximum friction force and an intermediate forge force of 1200-1400 rpm, 375-425 kN, and 600-650 kN, respectively

Inter-relationship between microstructure evolution and mechanical properties in inertia friction welded 8630 low-alloy steel

The evolution of microstructure and mechanical properties in AISI 8630 low-alloy steel subjected to inertia friction welding (IFW) have been investigated. The effects of three critical process parameters, viz. rotational speed, friction and forge forces, during welding of tubular specimens were explored. The mechanical properties of these weld joints, including tensile and Charpy V-notch impact were studied for determining the optimum welding parameters. The weld joints exhibited higher yield strength, lower hardening capacity and ultimate tensile strength compared to base metal (BM). The maximum strength and ductility combination was achieved for the welds produced under a nominal weld speed of ~ 2900–3100 rpm, the highest friction force of ~ 680–720 kN, and the lowest axial forging load of ~ 560–600 kN. The measured hardness distribution depicted higher values for the weld zone (WZ) compared to the thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ) and BM, irrespective of the applied welding parameters. The substantial increase in the hardness of the WZ is due to the formation of microstructures that were dominated by martensite. The observed microstructural features, i.e. the fractions of martensite, bainite and ferrite, show that the temperature in the WZ and TMAZ was above Ac 3, whereas that of the HAZ was below Ac 1 during the IFW. The fracture surface of the tensile and impact-tested specimens exhibited the presence of dimples nucleating from the voids, thus indicating a ductile failure. EBSD maps of the WZ revealed the formation of subgrains inside the prior austenite grains, indicating the occurrence of continuous dynamic recrystallisation during the weld. Analysis of crystallographic texture indicated that the austenite microstructure (i.e. FCC) in both the WZ and TMAZ undergoes simple shear deformation during IFW

A cross-sectional study of depressive symptoms and diabetes self-care in African Americans and Hispanics/Latinos with diabetes: the role of self-efficacy

Purpose The purpose of this study is to examine the relationship between depressive symptoms and diabetes self-care in African American and Hispanic/Latino patients with type 2 diabetes and whether the association, if any, is mediated by diabetes-related self-efficacy. Methods The sample included self-report baseline data of African American and Hispanic/Latino patients with type 2 diabetes who were aged ≥18 years and enrolled in a diabetes self-management intervention study. Depressive symptoms were assessed with the 9-item Patient Health Questionnaire. The Summary of Diabetes Self-care Activities measured engagement in healthy eating, physical activity, blood glucose checking, foot care, and smoking. The Diabetes Empowerment Scale–Short Form assessed diabetes-related psychosocial self-efficacy. Indirect effects were examined with the Baron and Kenny regression technique and Sobel testing. Results Sample characteristics (n = 250) were as follows: mean age of 53 years, 68% women, 54% African American, and 74% with income <$20 000. Depressive symptoms showed a significant inverse association with the self-care domains of general diet, specific diet, physical activity, and glucose monitoring in the African American group. In Hispanics/Latinos, depression was inversely associated with specific diet. Self-efficacy served a significant mediational role in the relation between depression and foot care among African Americans. Conclusions Self-efficacy mediated the relationship between depression and foot care in the African American group but was not found to be a mediator of any self-care areas within the Hispanic/Latino group. In clinical practice, alleviation of depressive symptoms may improve self-care behavior adherence. Diabetes education may consider inclusion of components to build self-efficacy related to diabetes self-care, especially among African American patients