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Univerzitet u Zenici
  Doctoral theses defended at the University in Zenica

Date and place of thesis defense:
05.07.2013, Faculty of Metallurgy and Materials Science
Milenko Rimac
Prof. dr. sc. Mirsada Oruč

Thesis title:

Investigations of Structure of NiCrAlY Metallic Coating Applied by Diamond Jet Process on Iron-Based Superalloy A286

Current trends in the development of car-industry, are continually setting new requirements to improve the operation and performance of the engine. Research is mainly focused on increasing the mechanical properties and the exploitation of materials for work at elevated temperatures, which is directly related to the increase of engine performance. One way of improving the exploitation properties of materials for work at elevated temperatures, is the new process of surface modification by metal coating, which have the function to increase the durability and functionality of the individual parts of a structural element. The basic concept of the research, is the application of metallic coating NiCrAlY, using HVOF method (High Velosity Oxyfuel) by Diamond Jet procedure, to achieve satisfactory exploitation properties at elevated temperatures of structural elements made of Iron-based super-alloy A286.
In this task, are carried out extensive experimental researches, which included the production and processing of experimental melts, coating by Diamond Jet procedure on samples and specimens of A286 super-alloys, which are used for complex laboratory tests.
In laboratory studies were made tests of tensile properties at room and elevated temperatures, testing of hardness and micro-hardness, creep resistance and fire resistance, and examination of microstructure on the optical and scanning electron microscopy. The results showed that the coating of metal powder NiCrAlY, can improve the exploitation properties of super-alloy A286, especially when working at elevated temperatures. It was found that in this alloy with coating, when it has the average chemical composition, can be significantly increased its resistance to high-temperature oxidation, and achieved high surface hardness and a satisfactory level of creep resistance, with a slight decrease of tensile properties. It was also found that the A286 super- alloys with coatings, can be made with reduced content of nickel and chrome, if you provide content above 2.0% titanium, and aluminum above 1.2%.

By statistical - mathematical analysis, is established a correlation between the content of the main alloying elements and the thickness of coatings, with values of tensile properties at room and elevated temperatures. Derived relations are in agreement with the obtained test results, with high correlation coefficients.

Key words :
super-alloys, metal coatings, mechanical properties, creep, fire resistance, microstructure, intermetallic phases, regression analysis

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