P. Maj

Microstructure and strain-stress analysis of the dynamic strain aging in inconel 625 at high temperature

Serrated flow is a result of unstable plastic flow, which occurs during tensile and compression tests on some dilute alloys. This phenomenon is referred as the Portevin Le-Chatelier effect (PLC effect). The aim of this research was to investigate and analyze this phenomenon in Inconel 625 solution strengthened superalloy. The tested material was subjected to tensile tests carried out within the temperature range 200-700 °C, with three different strain rates: 0.002 1/s, 0.01/s, and 0.05 1/s and additional compression tests with high deformation speeds of 0.1, 1, and 10 1/s. The tensile strain curves were analyzed in terms of intensity and the observed patterns of serrations Using a modified stress drop method proposed by the authors, the activation energy was calculated with the assumption that the stress drops’ distribution is a direct representation of an average solute atom’s interaction with dislocations. Subsequently, two models, the standard vacancy diffusion Bilby-Cottrell model and the realistic cross-core diffusion mechanism proposed by Zhang and Curtin, were compared. The results obtained show that the second one agrees with the experimental data. Additional microstructure analysis was performed to identify microstructure elements that may be responsible for the PLC effect. Based on the results, the relationship between the intensity of the phenomenon and the conditions of the tests were determined.

The Influence of Laser Treatment and the Application of Reduced Pressure Force Piston Rings on the Engine Exhaust Emissions under the Conditions of Engine Lubrication with Different Engine Oils

The paper discusses the investigations on combustion engines that aim at the evaluation of the influence of engine design modifications on the exhaust emissions under application of lubricants of different physicochemical parameters. In the engines the authors applied laser treated cylinder liners, piston rings of reduced pressure force on the cylinder liner and optimized the assembling clearances in the slide bearings. The research was carried out in accordance with the ESC and ELR compliant procedures using different engine lubricants. The measurement series were performed for diesel engines of the capacity of 1.3 dm3 of the power outputs of 51 kW and 66 kW. The tested objects were fitted with aftertreatment systems (oxycat and DPF filter).