TEHNOLOGIJE NAŠTRCAVANJA

U uvodnom dijelu rada ukratko je opisano kako svojstva površinskih slojeva najviše utječu na trajnost i ekonomičnost strojnih dijelova, iz čega se zaključuje da je potrebno dobiti materijale koji su otporni na tribološka trošenja. Zatim su navedene znanstveno-stručne discipline koje se bave trenjem i trošenjem te koje se bave modificiranjem i prevlačenjem površinskih dijelova materijala s ciljem poboljšanja njihovih svojstava. Na kraju uvodnog dijela naveden je postupak toplinskog naštrcavanja koji se provodi radi dobivanja veće otpornosti na trošenje, otpornosti na koroziju te da bi se sveukupno produžio radni vijek strojnog dijela. U drugom poglavlju opisan je princip rada toplinskog naštrcavanja, zatim su navedene prednosti i nedostaci te njegova primjena. Također su opisani materijali prevlaka za toplinsko naštrcavanje, gdje su dati primjeri prevlaka iz kataloga. U daljnjem dijelu poglavlja navedene su i opisane tehnologije naštrcavanja, principi rada, parametri rada, koji se dodatni materijali koriste te karakteristike prevučenog sloja kod svake pojedine tehnologije toplinskog naštrcavanja. U eksperimentalnom dijelu prvo je naveden izbor osnovnog materijala na kojem će se provoditi postupak toplinskog naštrcavanja, zatim koje će se tehnologije naštrcavanja provoditi na ispitnim uzorcima te također koji će dodatni materijali biti naneseni na ispitne uzorke. Zatim je opisana priprema ispitnih uzoraka, gdje su navedene moguće metode ispitivanja naštrcanih prevlaka, kao što je ispitivanje tvrdoće prevlake, debljine prevlake, metalografska analiza, određivanje otpornosti na smično naprezanje, otpornosti na zakretanje te XRD analiza. U daljnjem eksperimentalnom dijelu provedeno je mjerenje debljine prevlake, mjerenje tvrdoće prevlake te je provedena metalografska analiza mikrostrukture datih ispitnih uzoraka. Nakon eksperimentalnog dijela provedena je analiza rezultata svih ispitnih uzoraka, gdje se međusobnom usporedbom dobivenih rezultata debljine prevlaka, tvrdoće prevlaka te metalografskim pretragama strukture s rezultatima iz literature dolazi do zaključka da se kod tehnologije plinskog (plamenog) naštrcavanja dobivaju deblje prevlake od tehnologije HVOF naštrcavanja. Također prevlake na osnovu karbida kao što su WC-Co, WC-Co-Cr i CrC-25%NiCr imaju značajno veću površinsku tvrdoću od ostalih prevlaka.
In the introductory part of this paper, it is briefly described how the properties of the surface layers have the greatest influence on the durability and economy of machine parts, from which it is concluded that it is necessary to obtain materials that are resistant to tribological wear. Next are listed the scientific and professional disciplines that deal with friction and wear, and that deal with modifying and coating the surface parts of materials with the aim of improving their properties. At the end of the introductory part, the thermal spraying procedure is mentioned, which is carried out in order to obtain greater wear resistance, corrosion resistance, and to extend the worktime of the machine part overall. In the second chapter, the working principle of thermal injection is described, then the advantages and disadvantages, as well as its application, are listed. Coating materials for thermal spraying are also described, where examples of coatings from the catalog are given. In the further part of the chapter, spraying technologies are listed and described, their working principles, their working parameters, which additional materials are used, and the characteristics of the coated layer for each individual thermal spraying technology. In the experimental part, the choice of the basic material on which the thermal injection process will be carried out is first specified, then which injection technologies will be applied to the test samples, and also which additional materials will be applied to the test samples. Next, the preparation of test samples is described, where possible methods of testing the sprayed layers are listed, such as testing the hardness of the coating, thickness of the coating, metallographic analysis, determination of resistance to shear stress, resistance to rotation, and XRD analysis. In the further experimental part, the thickness of the sprayed layer (coating) was measured, the hardness of the sprayed layer was measured, and a metallographic analysis of the microstructure of the given test samples was performed. After the experimental part, an analysis of the results of all test samples was carried out, where by mutual comparison of the obtained results of the thickness of the sprayed layer, hardness of the sprayed layer, and metallographic investigations of the structure with the results from the literature. The conclusion is reached that with gas (flame) spraying technology, thicker coating layers are obtained than of technology HVOF spraying, also coatings based on carbides such as WC-Co, WC-Co-Cr and CrC-25%NiCr have a significantly higher surface hardness than other coatings.