Showing papers by "Srinivasa R. Bakshi published in 2023"
TL;DR: In this paper , a fine-grained microstructure with finer dispersoids in as-sintered and normalized condition was found to be retained even after subjecting the samples at 973 K for as long as 1000 h for long-term thermal aging trials, indicating at a possible superiority of this material over the conventional Oxide Dispersion-Strengthened steels.
Abstract: Abstract Technologically important Oxide Dispersion-Strengthened steels are synthesized using ZrO 2 as a dispersion strengthener instead of conventionally used Y 2 O 3 . Powder metallurgical route followed by spark plasma sintering is adopted for synthesizing the material. Detailed microstructural characterization revealed a fine-grained microstructure with finer dispersoids in as-sintered and normalized condition. The stable microstructure is found to be retained even after subjecting the samples at 973 K for as long as 1000 h for long-term thermal aging trials, indicating at a possible superiority of this material over the conventional Oxide Dispersion-Strengthened steels. The yield strength is calculated by making use of microstructural parameters and predictive models, both of which shown a good agreement. Mechanical property analysis through hardness measurements was correlated with microstructural observations and compared with the conventional Oxide Dispersion-Strengthened steels. The collective results indicate ZrO 2 as a potential alternate dispersoid for strengthening steel and future scope for vast exploration.
TL;DR: In this paper , the identification of phases, microstructure and morphology of phases in the coatings, elemental composition and distribution, interfacial behavior, and defects like porosities were investigated using advanced characterization techniques.
Abstract: Surface modification techniques are extensively utilized to improve the performance of the engineering components in their service life when exposed to elevated temperatures. Herein, the Tribaloy 400 (T 400) particles were deposited on the 17-4 PH stainless steel through the spark plasma sintering (SPS) technique to improve the high-temperature wear resistance of exhaust valve components which are typically manufactured using 17-4 PH stainless steel. The identification of phases, microstructure and the morphology of phases in the coatings, elemental composition and distribution, interfacial behavior, and defects like porosities were investigated using advanced characterization techniques. The obtained results revealed the presence of FCC and HCP – Co along with 52 vol% of laves phases (CoMoSi). The presence of laves phases in the Co matrix, fine grained structure and superior interfacial bond strength were promoted the hardness of the coating (~885 HV) than the substrate (~363 HV). The ball-on-disc wear studies were carried out using alumina balls as counter material at room temperature and high temperature (650 °C). The T 400 coating specimen provided better wear properties than the substrate at both temperature. The specific wear rate obtained for the T 400 coated specimen and 17-4PH substrate at room temperature was found to be 1.29 × 10−5 mm3/Nm and 120 × 10−5 mm3/Nm, whereas at 650 °C, it was found to be 0.037 × 10−5 mm3/Nm and 10.26 × 10−5 mm3/Nm, respectively. In T 400 coating, the developed transparent oxide film at 650 °C decreased the possibilities for metal-to-metal contact between the specimen and the counterpart.
TL;DR: In this paper , an annular co-flow nozzle with a circular central nozzle has been modelled for nitrogen gas and the reduction of nozzle divergent length from 189 mm to 99 mm showed an approximate 2.2% drop in particle velocity at high pressure operation while no variation at lower pressure operation.
Abstract:
The current work numerically evaluates the efficacy of a coflowing nozzle for cold spray applications with the aim to mitigate nozzle clogging by reducing the length of its divergent section. The high-pressure nitrogen flow through convergentdivergent axis-symmetric nozzles was simulated and the particle acceleration is modelled using a 2-way Lagrangian technique which is validated using experimental results. An annular co-flow nozzle with a circular central nozzle has been modelled for nitrogen gas. Reduction of nozzle divergent length from 189 mm to 99 mm showed an approximate 2.2% drop in particle velocity at high pressure operation while no variation at lower pressure operation was observed. Co-flow was introduced to the reduced nozzle length to compensate for particle velocity loss at higher operating conditions and it was found that co-flow facilitates momentum preservation for primary flow resulting in increased particle speed for a longer axial distance after the nozzle exit. The reduced divergent section nozzle, when combined with co-flow, is comparable to the original length nozzle.