PSI - Issue 20

Vinokurov G.G. et al. / Procedia Structural Integrity 20 (2019) 265–269 Vinokurov G.G., Popov O.N. / Structural Integrity Procedia 00 (2019) 000 – 000

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Introduction Nowadays high-energy technologies of powder metallurgy (gas-thermal deposition and welding, explosive pressing, arc metallization, and other methods with a characteristic energy flux of ~ 10 6 — 10 8 W/m 2 and above) are promising ways of improving physical and mechanical properties of machine parts and mechanisms and obtaining instrumental purpose materials. Depending on chosen powder material, processed products get specific performance properties: increased wear resistance, heat resistance, corrosion resistance, specified thermal and electrical characteristics, etc. However, obtained powder coatings and materials are characterized by high degrees of heterogeneity, layered structure, porosity, excessive release of dispersed and coagulated phases. This is due to specifics of high-energy technological processes that consist in fast (10 -3 — 10 -5 s) high temperature (up to melting point) heating of powder material particles and subsequent high-speed cooling during powder coating and material formation. The form of solidified particles and pore space between them define macrostructure of powder coating and material, as investigated by Kudinov et al. (1992). Formation of powder coatings and materials macrostructure is constantly influenced by random factors inherent in high-energy technological processes such as high temperature gas flow turbulence, granulometric composition of powder material, varying degrees of heat due to varying distribution of particles in the flow, etc. The impact of countless random factors on physical and chemical interaction of powder material particle and surrounding particles or the base surface practically brings to naught dynamic description of the formation of powder coatings and materials macrostructure. Therefore, to describe macrostructure of powder coatings and materials obtained by high-energy methods, most promising and efficient approach is a statistical one, as emphasized by Kudinov et al. (1990) or Bussmann et al. (1999) or Mostaghimi et al. (2002) or Fauchais et al. (2004) or Gnedovets et al. (2007) or Seok et al. (1998) or Kanouff et al. (1998) or Ghafouri-Azar et al. (2003) or Chen et al. (2001). Results and discussion Due to its physic-mechanical properties macrostructure of functional powder coatings and materials determines operational characteristics of the processed parts surface and quality of tools (wear resistance, heat resistance, corrosion resistance, etc.). As is known, correlations defined by Balshin-Huttig equations allow us to estimate basic physical and mechanical properties of powder materials as a function of macrostructure quantitative characteristics (porosity). The wear process of powder coatings and materials in sliding friction depends on actual contact area, its value being determined by friction surface microgeometry. Besides, the formation of friction surface microgeometry is influenced by powder coating and material macrostructure. Therefore, statistical laws that describe the macrostructure of wear-resistant coatings and materials obtained by high-energy methods are relevant to the wear process too, as pointed by Kordonsky et al. (1968) or Citrin et al. (1986) or Belousov et al. (1983) or Kholodilov et al. (1990) or Kudish (1990) or Tigetov et al. (2010) or Goritsky et al. (2014). To describe random microgeometry of the friction surface, most effective are probabilistic and geometric models of the powder coating and material, as shown by Bal'shin (1969) or Kaminsky et al. (1982) or Nikolenko et al. (1989) or Nikolenko (1998) or Сyternann (1986) or Kadushnikov et al. (1991) or Kadushnikov et al. (1991) or Dick et al. (2006). The point is that in describing wear processes in sliding friction the direction of friction is most signifi cant. Therefore, in the plane perpendicular to the given direction, microgeometry characteristics are statistically homogeneous values. If so, characteristics of probabilistic and geometric systems can be compared to random values of friction surface microgeometry, and their distribution and moments can be obtained by computing cross-section profilograms. This work generalizes results of the researches conducted by authors from 90th years of the last century at V.P. Larionov Institute of physical and engineering problems of the North of the Siberian Branch of the Russian Academy of Science, as reflected by Vinokurov et al. (2013). The developed statistical approaches for the description of formation and wear of a macrostructure of powder coatings and materials are given in tab. 1.