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Purpose: The work aims to establish the relationship between the chemical composition, mechanical properties and dimensional mismatch of crystal lattices of heat-resistant nickel alloys. Design/methodology/approach: The results of experimental and calculated data formed based on experimental and taken from open sources results are presented. The XRD method used Bragg-Brentano determined the phase composition, focusing on a RIGAKU MINIFLEX 600 diffractometer (CoKα-radiation). After heat treatment, strength characteristics were determined on cylindrical samples with a working part (diameter 5 mm, length 25 mm). Testing of the alloy for short-term strength was carried out on samples at a temperature of 20°C on UME-10TM and GCM-20 tensile machines. Alloy tests for long-term strength were carried out on similar samples at a temperature of 1000°C on AIMA-5-2 and ZTZ 3/3 machines by uniaxial stretching under a constant load based on 100 hours. Findings: It has been established that with an increase in the value of the mismatch of crystal lattices, the strength of the alloys decreases due to significant internal stresses. It was revealed that for alloys of equiaxed and directional crystallisation, an extremum is observed at a value of 1.5 ... 1.6 K; this is associated with a decrease in the number of elements in the ϒ-solid solution. Research limitations/implications: An essential problem is predicting the structure and properties of heat-resistant alloys without or with a minimum number of experiments. The results of comparative tests of the XDR method and calculated data are analysed. Practical implications: The obtained dependences can be used both for designing new heat-resistant alloys and for improving the compositions of industrial alloys. Originality/value: The value of this work lies in the fact that the dependences of the influence of alloying elements on the mechanical properties and the dimensional mismatch of crystal lattices were obtained, which made it possible to determine the properties without conducting experiments. It has been established that changes in the course of the relationship closely correlate with the processes taking place in the structure of alloys.
The Ni – base superalloys are used in aircraft industry for production of aero engine most stressed parts, as are turbine blades or turbine discs. The most stressing factor at Ni – base superalloys loading or working conditions are high temperature range of 700°C up to 850°C and, of course, centrifugal forces, and small vibrations, which produce bending of turbine blades inserted into turbine discs. All these factors cause various forms of microstructure degradation closely connected with decreasing of mechanical properties and shortening of working life as well. From this reason a dendrite arm spacing, carbides size and distribution, morphology, number and value of γ’ - phase are very important structural characteristics for blade lifetime prediction as well as aero engine its self. In this article are used methods of quantitative metallography for evaluation of structural characteristics mentioned above on experimental materials – Ni base superalloys ŽS6K and Inconel IN 738. The high temperature effect represented here by heat treatment at 800°C for 10 hours, and cooling rate, here represented by three various cooling mediums as water, air, and oil, on structural characteristics and application of quantitative methods evaluation with using of SEM are presented in this paper.
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