20 research outputs found
Enhancement of surface characteristics of additively manufactured γ-TiAl and IN939 alloys after laser shock processing
No full textThe enhancement in laser technology opened up new methods such as additive manufacturing (AM) of metals. While AM offers high design flexibility and reduced material usage, it can also produce problematic parts due to poor surface quality. A variety of post-processing techniques are available to address the drawbacks associated with the surface properties of AM. Laser Shock Processing (LSP) is one of the unique methods that induces compressive residual stress (CRS) on the surface and subsurface by creating severe plastic deformation. In this study, two critical aerospace alloys (gamma-TiAl and IN939) were manufactured through two different methods called Powder Bed Fusion with Electron Beam (PBF-EB) and Powder Bed Fusion with Laser Beam (PBF-LB). Subsequently, AM samples were investigated to observe single layer LSP effects on the surface. The results of the laser peening process were determined by residual stress, microhardness and surface roughness measurements. The residual stress profiles showed that LSP significantly induces CRS on the surfaces of AM alloys. For the gamma-TiAl and IN939 samples, the maximum values of CRS and depth of CRS were-460 MPa/1000 mu m and-516 MPa/700 mu m, respectively. Similarly, the microhardness of the materials was increased by 44.4 % for gamma-TiAl and 18.2 % for IN939 by laser post-processing. In addition, a comparison of the roughness of the unground and ground AM samples was carried out. Depending on the surface condition of the AM samples, LSP had different outcomes. For example, the extreme roughness of the AM samples was partially reduced by the thermal effects of the high-energy laser shots. When comparing the roughness values in terms of Ra and Rz, there were decreases in the range of 14.7-21.3 % and 3.34-39.3 % for unground IN939 samples. However, for unground gamma-TiAl samples, depending on the direction of measurement, roughness variations were observed as a 0.99 % decrease -5.3 % increase for Ra and a 2.2 % decrease -14.2 % increase for Rz. The roughness values for ground samples of both alloys were drastically increased, varying between 42.1 % and 7x increase. Sa values were recorded on unground AM samples. For IN939 and gamma-TiAl samples these values decreased by 8.41 % and 15.8 % respectively
The Effect of Thermohydrogen Process on the Mechanical Properties of the Ti-6Al-4V Alloy Produced by Selective Laser Melting
No full textSelective laser melting (SLM) is a powder bed fusion type additive manufacturing (AM) process that allows fabrication of complex and detailed components from computer aided design (CAD) model in one single step without the need of costly tools.Ti-6Al-4V alloy is widely used in the applications where high specific strength is required particularly in aero engine discs, frames and compressors.Production of the Ti-6Al-4V alloy with a conventional methodis inadequate in manufacturing complex shaped parts used especially in the aero engine industry; therefore, SLM processes arebeing developed in order to enable rapid manufacturing of the Ti-6Al-4V alloy forintricate components. However, in SLM technologydue to large thermal inputs during production ductility of Ti-6Al-4V parts are inferior to conventionally produced ones without post heat treatment.Therefore, post processing of SLM processed parts is highly required to obtain desired mechanical properties which meet the specifications of the aerospace industry. In this study, as an alternative to typical heat treatments, a thermohydrogen process (THP) based on hydrogenation and dehydrogenation steps were applied to SLM processed Ti-6Al-4V alloy to refine the microstructure and to improve its mechanical properties. The starting non-equilibrium Į′ martensitic phase of SLM processedTi-6Al-4V alloy was transformed to į (TiH2) and ȕ phases after the hydrogen treatment at 650°C for 1h. When the hydrogenated alloy was vacuum treated at 700°C for 18h, discontinuous and fine Į/ȕ duplex microstructure formed as a result of this dehydrogenation step. 2-step THP post-process heat treatmentwas found to increase the alloy’s ductility without degrading its strength. The effect of the novel 2-step THP was also compared with that of the 4-step THP which has been applied to cast and wrought Ti-6Al-4V parts conventionally. It was determined that the novel 2-stepTHP ismore beneficial for SLM fabricated Ti-6Al-4V parts in terms increasing their ductility while optimizing their strength in contrast to conventional 4-step THP
The Effect of Thermohydrogen Process on the Mechanical Properties of the Ti-6Al-4V Alloy Produced by Selective Laser Melting
No full textAssessment of potential predictive value of peripheral blood inflammatory indexes in 26 cases with soft tissue sarcoma treated by pazopanib: a retrospective study
No full textCem Mirili,1 Semra Paydaş,1 Isa B Guney,2 Ali Ogul,1 Serkan Gokcay,1 Mahmut Buyuksimsek,1 Abdullah E Yetisir,1 Bilgin Karaalioglu,1 Mert Tohumcuoglu,1 Gulsah Seydaoglu3 1Department of Medical Oncology, Çukurova University Faculty of Medicine, Adana, Turkey; 2Department of Nuclear Medicine, Çukurova University Faculty of Medicine, Adana, Turkey; 3Department of Bioistatistics, Çukurova University Faculty of Medicine, Adana, Turkey Purpose: The aim of this study was to evaluate the prognostic and predictive value of neutrophil-to-lymphocyte ratio (NLR), derived neutrophil-to-lymphocyte ratio (DNLR), lymphocyte-to- monocyte ratio (LMR), and platelet-to-lymphocyte ratio (PLR) in soft tissue sarcoma (STS) cases treated with pazopanib. Materials and methods: The study population included 26 STS cases treated with pazopanib for at least 3 months. NLR, DNLR, LMR, and PLR were evaluated at baseline, and at third month of therapy and also compared with response to pazopanib. Median measurements were taken as cutoff for NLR (4.8), DNLR (3.1), LMR (3.6), and PLR (195). The associations between these cutoff values and survival times (progression-free survival [PFS] and overall survival [OS]) were assessed by Kaplan–Meier curves and Cox proportional models. Results: Patients with low pretreatment NLR and DNLR had longer OS (P=0.022, P=0.018), but low PLR was found to be associated only with longer OS. Additionally, decrease in NLR and DNLR after 3 months of therapy as compared with pretreatment measurements was found to be associated with an advantage for OS (P=0.021, P=0.010, respectively) and PFS (P=0.005, P=0.001, respectively). Response to pazopanib; changes in NLR, DNLR, LMR, and PLR; and >3 metastatic sites were found to be independent risk factors in univariate analysis, but NLR was the only independent risk factor in multivariate analysis. Conclusion: Low pretreatment and decrease in NLR and DNLR values, and regression/stable disease after 3 months of pazopanib are predictive factors for longer OS and PFS. Keywords: soft tissue sarcoma, STS, pazopanib, angiogenesis, inflammation, neutrophil-to-lymphocyte ratio, NLR, derived neutrophil-to-lymphocyte ratio, DNL
Optimization of the Mechanical Properties of the Ti 6Al 4V Alloy Fabricated By Additive Manufacturing Using Thermochemical Processes
No full textTailoring the Mechanical Properties of Additively Manufactured Ti-6Al-4V Alloys by Post Processing
No full textMicrostructural Refinement of Ti 6Al 4V Alloy Fabricated by Additive Manufacturing Using Th ermochemical Processes
No full textInvestigations on the effect of secondary treatments on Ti48Al2Cr2Nb alloy manufactured by electron beam powder bed fusion method
No full textAs-built Ti48Al2Cr2Nb alloy samples produced by electron beam powder bed fusion (PBF-EB) exhibited notable brittleness. The low ductility was attributed to coarse γ bands aligned perpendicular to the building and tensile direction. Additionally, variations in aluminum content and hardness between the coarse colonies and fine γ/α2 lamellae contribute to this phenomenon. Electron backscattered diffraction (EBSD) studies revealed a higher amount of dislocation density and inherent strain after PBF-EB manufacturing. Hence, usage of Ti48Al2Cr2Nb alloy in the as-built condition in aviation applications with high loads and demanding environments is not found to be viable. To eliminate these negative aspects and make PBF-EB produced Ti48Al2Cr2Nb alloy available for demanding applications, two distinct post-processing heat treatments; namely, hot isostatic pressing (HIP) and annealing heat treatment (HT) were employed at 1200 °C. A comprehensive characterization covering microstructure analysis, EBSD, fracture surface examination, as well as room and high-temperature tensile tests allowed determination of the effect of post-processes. HIPing altered the banded structure observed in the as-built samples by increasing the amount of α2 phase and grain size. On the other hand, HT made the banded structure more pronounced without significantly increasing the amount of α2 phase. HT also strengthened the texture, while HIPing introduced randomization of grains. On the other hand, complete recrystallization is achieved as a result of HT at 1200 °C for 2 h, whereas HIPing at the same temperature for 2 h induced only 80.5 % recrystallization. In both post-processes, dislocation density and inherent strain were reduced. Room temperature and high-temperature tensile tests demonstrated that both HIPing and HT eliminated the extreme brittleness of the as-built samples
Tailoring the Mechanical Properties of Additively Manufactured Ti-6Al-4V Alloys by Post Processing
No full textOptimization Of The Mechanical Properties Of The Ti 6Al 4V Alloy Fabricated By Additive Manufacturing Using Thermochemical Processes
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