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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
07.02.2011. Faculty of Metallurgy and Materials Science
Candidate:
mr. sc. Raza Sunulahpašić
Mentor:
prof. dr. Mirsada Oruč

Thesis title:

Optimization Of Mechanical And Structural Characteristics Superalloys Nimonic 80a Designed To Work At Elevated Temperatures In The Automotive Industry

Summary:
Superalloy Nimonic 80A is a nickel-chromium alloy, with minor additions of carbon, cobalt and iron, as well as major alloying elements of aluminum (up to 1.8%) and titanium (up to 2.7%). This alloy has good mechanical properties, corrosion resistance at room and elevated temperatures. It is designed for operation at temperatures up to 815°C. The modern automotive industry has been expressing the need for engines with a turbocharger whose parts are made of materials that operate at high temperatures (around 720°C). Increasing engine performance is directly related to the increase in engine operating temperature. The exploration of possibilities of materials that have a stable structure during prolonged work at high temperatures is one of the most important objectives in developing the automotive industry. A special place in the research has superalloy Nimonic 80A, originally developed for the aviation industry, to over production of turbochargers for cars in auto racing has found application in a standard car.
This material has been long in use in modern industrial technologies, but their production is limited to a few of reputable manufacturers in the world, with patented technology. The basic technological parameters for production and processing of superalloy Nimonic 80A, were defined by preliminary studies, which preceded this paper.
Chemical composition of alloys Nimonic 80A has a dominant influence on its mechanical and technological properties. The effect of alloying elements Al, Ti and Co for superalloy Nimonic 80A is very important. They affect the matrix by precipitation hardening and solid solution hardening. Secondary hardening is achieved by fine precipitation of carbides mainly along grain boundaries.
Surveys which were carried out have included chemical testing and testing of mechanical properties of superalloy Nimonic 80A, on which was carried out regression analysis of the influence of chemical composition on mechanical properties.
Metallographic and X-ray tests have contributed to clarify the mechanisms of hardening, ie the influence of certain alloying elements that significantly affect the improvement of mechanical properties and ductile material Nimonic 80A.
As a result of research and insight into the qualitative and quantitative strength contributions of superalloy Nimonic 80A of all acting strengthen mechanisms was set acceptable theoretical model of the formation of optimum strength. The results of  regression are equations by which on the basis of known chemical composition, ie content of main alloying elements Al, Ti and Co can predict the mechanical properties of materials at room and elevated temperatures. On the basis of the square regression equations, was carried out an optimization of the chemical composition of materials for selected values of mechanical properties.

Key words:
superalloys, Nimonic 80A, mechanical properties, strengthening mechanisms, regression analysis, optimization


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