67 Nonconventional Technologies Review ©2014 Romanian Association of Nonconventional Technologies Romania, September, 2014 COMPARATIVE EXPERIMENTAL RESEARCHES ON THE PROCESSING OF CAR PARTS MADE BY SINTERING OF AN AUSTENITIC STAINLESS STEEL - ALUMINA POWDER MIXTURE Toderita Nemes 1 , Marius Bibu 2 , Cristian Deac 3 , and Alina Gligor 4 1 "Lucian Blaga" University of Sibiu, toderita.nemes@ulbsibiu.ro 2 "Lucian Blaga" University of Sibiu, marius.bibu@ulbsibiu.ro 3 "Lucian Blaga" University of Sibiu, cristian.deac@ulbsibiu.ro 4 "Lucian Blaga" University of Sibiu, alina.gligor@ulbsibiu.ro ABSTRACT: The paper presents a part of the comparative experimental researches carried out by the authors on ring-type parts made of a powder mixture consisting of austenitic stainless steel AISI 316L and alumina (Al2O3) powder and on valve supports from the engines of Volkswagen and Audi cars. The purpose of the researches was to determine whether the mentioned valve supports could be manufactured also of the analysed powder mixture. The analysed powder mixture resulted from previous researches carried out by the authors and from studies in the speciality literature. The experiments first targeted the microstructures and microhardnesses of samples taken from the supports of admission and evacuation valves from Volkswagen (A1 and E1) and Audi (A2 and E2) cars, respectively. The same analyses were then applied to ring-shaped parts made by sintering from a mixture of austenitic stainless steel 316L + 30% alumina (Al2O3) powder. KEY WORDS: powder metallurgy, stainless steel, alumina, microstructure, microhardness 1. INTRODUCTION Given the current conditions of competition on the global market, industrial companies are more and more interested to find new technologies and new materials that would help to improve the performances of their products, but also to keep costs at a low level. In this regard, the automotive industry is one of the most active ones, so that many researches nowadays target materials and technologies to be applied in the manufacturing of cars and car parts. Iron-carbon alloys have for a long time dominated the list of materials for car parts, especially due to the outstanding strength properties and the possibility of applying well-known and relatively uncomplicated processing technologies. However, in the recent years, considerations such as the high specific mass and costs of specialised steels and cast irons have led to a search for other materials with similar structure and behaviour. Powder metallurgy can offer a very good alternative in this respect, as it deals with the elaboration of various metallic powders and with the manufacturing, from these powders, of either large- series parts or of specialised unique products with outstanding properties [1, 2]. The manufacturing of parts by sintering differs fundamentally from the classical manufacturing technologies, which require the parts to be processed through a large number of often complicated, costly and lengthy operations. Powder metallurgy implies essentially three main operations: first, the powders are obtained and mixed according to a given recipe, then they are compacted, most often by pressing in steel dies and afterwards the obtained blanks are subjected to the actual sintering, i.e. to a specific heat treatment that is usually carried out under a protective atmosphere and implies the heating of the materials below their actual melting point. The employment of a higher sintering temperature ensures a higher sintered density and the formation of less surface oxides [3]. This method allows obtaining parts directly with their final shape and dimensions, which also have an adequate surface quality [1]. Powder metallurgy allows the obtaining of compounds and parts with a precise and homogeneous composition, which often cannot be obtained by other means - pure highly refractory metals such as tungsten (W), pseudo-alloys such as W-Cu-Ag, copper-graphite combinations etc. Also, it is possible to obtain parts with controlled porosity, so that they can be employed, for example, as precise and fine filters. Another big advantage is that the tools involved in the obtaining of sintered parts are universal, a new part requiring only the replacement of the pressing die. The simplicity of operations makes it easy to