PSI - Issue 20

Fedorov M. V. et al. / Procedia Structural Integrity 20 (2019) 206–211 Fedorov M. V. et al. / StructuralIntegrity Procedia 00 (2019) 000–000

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1. Introduction High hardness and wear resistance of carbide materials allow them are widely used in industry in the processing of metals, minerals, drilling and other industries. Currently, Armstrong (2011); Panov et al. (2004); Kreimer (1966); Garcia et al. (2019); Wayne et al. (1990); Gordeev et al. (2014); Ho et al. (2000) studied improving quality and improve performance characteristics of hard alloys. At the same time, a main disadvantage of hard alloys is a predisposition to brittle fracture. One of the directions of these works is to obtain alloys with controlled grain size. Lebedev et al. (2010) obtained test specimens of carbide plates with ultrafine powder additives. According to Vasilyeva and Fedorov (2018) in the development of tungsten-cobalt carbide material the fundamental condition for the selection of ultrafine powder additives is the property of ultrafine powder as an inhibitor of tungsten carbide grain growth, whereas tungsten carbide forms carbide skeleton of hard alloy. According to Rechenko et al. (2015); Ovcharenko et al. (2010); Kosimov et al. (2015); Nikolenko et al. (2018) it is known that hard alloys are used as working elements of tools operated in extreme conditions: at high mechanical and impact loads, high temperatures of a cutting edge, in aggressive environments. As a result of operation, the carbide working element fracture and loses working capacity. In this case, the types of wear differ in a fracture character: abrasive, adhesive, chemical, diffusion, electroerosion, etc. Depending on the operating conditions of the tool, a type of wear is determined, which narrows the field of their use. There is a relationship between the structure and the character of the fracture of the material. Saito et al. (2006); Allen et al. (2001) note a significant increase in wear resistance of carbide materials with a decrease in the grain size of the carbide component. However, Shipway and Hogg (2005); Multanov (2002) showed an increase in the volumetric wear intensity with a decrease in the dispersion of material. On this basis, unequivocal assertions to improve the mechanical properties of carbide materials with fine-grained structure should be considered insufficiently substantiated. Numerous factors affect the performance and duration of hard-alloys materials: material composition and grain size, the presence of impurities and local stresses, the number and size of pores, manufacturing techniques, etc. Therefore, for each type of hard alloy, goal studies of the influence of various factors on changes in the physicomechanical properties are necessary. According to Smirnov et al. (2007); Cao et al. (2018); Su et al. (2014) an analysis of the fracture surface is carried out to predict the risk of premature destruction and failure of the material under study, and this allows us to establish many structural peculiarities of the materials and the causes of the type of fracture: brittle or ductile. This study aim to detect a character of fracture surfaces of prototypes made of hard-alloy materials with ultrafine powder additives in impact-abrasive wear. 2. Materials and Methods The object of the research is test specimens of tungsten-cobalt hard alloys with ultrafine additives of magnesium spinel powders MgAl 2 O 4 and specimens with the addition of silicon carbide SiC for comparative analyzes. A general view of the test specimens is shown in Fig. 1a. Test specimens without additives and with the additives of magnesium spinel MgAl 2 O 4 and silicon carbide SiC are the same size. The percentage of ultrafine additives in tungsten-cobalt hard alloy test specimens are given in Table 1. The test specimens are made by Lebedev et al. (2010); Vasilyeva and Fedorov (2018).

Fig. 1. Specimens of hard-alloy plates: (a) General view; (b) Research scheme of the cutting edge surface.