This paper investigates the impact of heat input and post-weld aging behavior at different temperatures on the laser paper welded maraging steel grade 250. Three different levels of heat inputs were chosen and CO2 laser welding was performed. Aging was done at six different temperatures: 360[Formula: see text]C, 400[Formula: see text]C, 440[Formula: see text]C, 480[Formula: see text]C, 520[Formula: see text]C and 560[Formula: see text]C. The macrostructure and microstructure of the fusion zone were obtained using optical microscope. The microhardness test was performed on the weld zone. Tensile tests and impact tests were carried out for the weld samples and different age-treated weld samples. Fracture surfaces were investigated by scanning electron microscopy (SEM). Microhardness values of the fusion zone increased with increasing aging temperature, while the base metal microhardness value decreased. Tensile properties increased with aging temperature up to 480[Formula: see text]C and reduced for 520[Formula: see text]C and 560[Formula: see text]C. This was mainly due to the formation of reverted austenite beyond 500[Formula: see text]C. XRD analysis confirmed the formation of reverted austenite.
Background 1 1.2 Motivation 5 1.3 Research Objectives 8 1.4 Thesis Organization CHAPTER 2: LITERATURE REVIEW 2.1 Rapid Prototyping and Applications 11 2.2 Laminated Tooling in Mold and Pattern Manufacturing 2.3 Friction Stir Welding
Due to the limitations of currently used materials like indirect band gap Si and Ge, binary and ternary compounds of high melting point, toxicity and scarcity of elements, there is a significant demand for alternate compound semiconductors towards energy harnessing applications. Tin selenide (SnSe), being a member of the IV-VI chalcogenide family, has gained wide attention due to its favorable physical properties such as direct band gap, high absorption coefficient and optimum melting temperature. Thin film deposition is intrinsically significant, because it offers a low temperature versatile process comprising low material consumption and provides large area module bearing tunable material properties compared to bulk counterparts. Therefore, special emphasis has been paid to prepare two dimensional SnSe thin film structures. In this regard, high pure (99.999%) Sn and Se elements were weighed in stoichiometric proportions and sealed in specially cleaned quartz ampoules. The ampoule containing the materials was heated in a muffle furnace and periodically rotated using a DC motor of 60 rpm, in order to forge the uniform SnSe precursor. Amorphous thin films have been deposited on glass substrates by thermal evaporation under high vacuum in room temperature using the stoichiometric SnSe charge. Optical microscopy (OM) and scanning electron microscopy (SEM) tools were employed to investigate the surface morphology of the prepared thin films. Systematic energy dispersive analysis by X-rays (EDAX) revealed the homogeneity and even distribution of Sn and Se in the samples. X-ray diffraction (XRD) studies were carried out to probe the atomic structure and quality. The grains were found distributed uniformly, without pinholes and the particle size has been enhanced upon controlled thermodynamic conditions.
A BSTRACT Aims and Objectives: This study aimed to evaluate the efficacy of Nd:YAG and Er:YAG lasers in removing the smear layer and to study the morphological and chemical alterations of the root surface using scanning electron microscopy (SEM) and infrared (IR) spectroscopy. Material and Methods: Fifty-five extracted upper incisor teeth were collected and 110 specimens of size 3 mm × 4 mm × 1 mm were prepared. For SEM evaluation, these samples were divided into six groups: A, B, and C. Group A comprised five samples that served as control. Groups B and C were further divided into five subgroups and each subgroup comprised five samples. All the specimens within the subgroups of B and C irradiated with 100, 200, 300, 400, and 500 mJ of Er:YAG laser and 211.66, 423.33, 635, 846.66, and 1058.33 J/cm 2 of Nd:YAG laser, respectively. The morphological changes of the laser-treated sites were observed qualitatively using an arbitrary scale under SEM. The data obtained were statistically analyzed by one-way analysis of variance (ANOVA) multiple range test by Turkey’s honestly significant difference and Mann–Whitney U test. In chemical structural changes, Group D comprised five samples that served as nonirradiated control and Groups E and F were irradiated with the same aforementioned parameter and evaluated using Fourier-transform infrared spectroscopy. Results: Er:YAG laser at 100 mJ effectively removed smear layer without any crater formation. The Nd:YAG laser removed the smear layer at the energy density of 211.66 J/cm 2 and 423.33J/cm 2 . The energy density of 1058.33 J/cm 2 showed visible charring and deep crater with increased area of melted and resolidified minerals in SEM. In the chemical changes, IR spectroscopy graph showed the reduction in peak intensity beyond 846.66 J/cm 2 of and new absorption band was noticed (2010cm –1 and 2017cm –1 ) at samples treated with 846.66 and 1058.33 J/cm 2 of Nd:YAG laser. Conclusion: Er:YAG laser at lower energy density effectively removed smear layer without production of toxic substance as compared with Nd:YAG laser. Thus, Er:YAG laser can be used as an effective root biomodification agent.
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