Surface Properties Changes Induced by Pulsed Plasma Flows

Abstract

The purpose of the research was the study of pulsed plasma flows influence on durability superficial properties of metal alloys used on different industrial technology. The technological applications of pulsed plasma flows for a semiconductors surface structure modification were submitted by the authors in [1]. This work is devoted to investigation of plasma flows influence on a various constructional materials.The detailed description of experimental device is given in work [2]. The plasma accelerator has two cylindrical electrodes with diameters of 90 mm (external) and 24 mm (internal). The energy of the capacitor bank is 32 kJ. The discharge current represents a decreasing harmonically signal with the period 14 pts. The maximum power density and, hence, efficient acceleration of the plasma flow was obtained at a work chamber pressure of about 0.1 Torr and it was equal to 45 Joule/cm2 at a discharge voltage of 25 kV.The formation of the modified layer on a surface after plasma processing is typical for metals. However, the high density of energy results in formation of roughness relief on a surface. This undesirable phenomenon can be avoided if one uses small density of energy. In all cases when the value of melted energy achieved 15-20 J/sM2, the recrystallization of the surface area and structure modification took place on the depth about 10-30 ptm depending on materials. The character of structural changes in metals depends on the energy density and the introduced doze (a doze is equivalent of plasma pulses quantity). Character of structure changes depends also on working gas used and on accelerators operation mode.For the carbon steel with the ferrite as a basic structure, the formation of austenitic and martensitic phases is observed after processing. At the same time for stainless steel the formation of nitride hardening phases is usual at processing by nitric and air plasmas. The microhardness of common steels, processed with pulsed plasma, increases by a factor 1,5-5. Consequently, the wear resistance of this steel increases. In the case of constructional steels CT3, treated with the nitrogen pulses, this increase amounts to factor 4. This parameter was determined by abrasive method for seven samples treated by different quantity of pulses. The stainless steel samples (12X18N) were treated by several pulses. The phase structure analysis of the processed samples show the presence of two basic phases: iron nitride and austenite in the processed layer of the surface.