Requirements to Limiting Relative Concentration of Oxygen and Nitrogen Impurity in Subsurface Layers of Filler Powder ZhS32 for Microplasma Surfacing

O. V. Yarovytsyn$^{1}$, A. V. Mykytchyk$^{2}$

$^{1}$E. O. Paton Electric Welding Institute, NAS of Ukraine, 11 Kazymyr Malevych Str., UA-03150 Kyiv, Ukraine
$^{2}$SE ‘International Center of Electron-Beam Technologies of E. O. Paton Electric Welding Institute’, NAS of Ukraine, 68 Antonovych Str., UA-03150 Kyiv, Ukraine

Received: 05.05.2019; final version - 11.02.2021. Download: PDF

A complex procedure for evaluation of quality of filler powder of nickel–nickel-based superalloys for microplasma powder surfacing is developed. It assumes investigation of its sample by means of evaluation of weight-average gases contents [O] and [N] using reduction melting of powder sample in a jet of inert gas-carrier and determination of relative concentration of these additives applying X-ray structural (EDX) microanalysis on a surface of disperse particles of powder in comparison with their cross section. As proved experimentally and in calculation way, the internal volumes of disperse particles of filler powder ZhS32 independent on quality have approximately similar gas content (approximately [O] = 0.005–0.010% wt., [N] = 0.0005–0.0015% wt.). As shown, the weight-average gas content of the sample of filler powder is considerably effected (from 0.1 to 6–8 times) by relationship between local concentration of content of oxygen and nitrogen impurity in the subsurface layer of up to 4 $\mu$m thickness of separate disperse particle of powder and in its cross section. It is determined that except for corresponding requirements to weight average gases content [O] $\leq$ 0.025% wt. and [N] $\leq$ 0.004% wt. in the subsurface layer of particles of quality filler powder ZhS32 in comparison with their cross section the next relative limiting increase of their content $K_{\textrm{[O]}}$ < 9.0, $K_{\textrm{[N]}}$ < 6.0 is allowed. Further increase of relative concentration of oxygen and nitrogen indicate improper filler powder. First its type (after 4–5 cycles of repeated heating) is characterized with presence of some amount of particles, examination of surface of which using EDX-analysis method shows next relative rise of contents [O] and [N]: $K_{\textrm{[O]}}$ = 16.56–21.21, $K_{\textrm{[N]}}$ = 2.88–7.41. Discovery of such type of improper filler powder by means of determination of weight-average gas content is complicated through insignificant increment of general gas content (< 20–30%) in comparison with quality one. Second type of improper filler powder ZhS32 is provoked by deviation or irrational selection of gas atomization technology. It is characterized with presence of preferred amount of particles, examination of surface of which using XRSM method indicated the next relative increase of contents [O] and [N]: $K_{\textrm{[O]}}$ = 38.17 and $K_{\textrm{[N]}}$ = 15.34. Such increased concentration of these additives in the subsurface layers has already very significant effect on weight-average gas content and takes it outside the limits of the recommended weight-average values for quality powder ZhS32. Increase of contents [O] and [N] over the experimentally determined limiting values (as weight-average for separate particle of filler powder ZhS32 as well as relatively to its subsurface layer) in microplasma surfacing provokes the need of increase of heat input into the product by 25–50% in bead formation at a blade edge. This, first of all, has negative effect on efficiency of its build-up and laboriousness of its further machining. It is also registered that at increased terms of service of blades of aircraft GTE D18-T the additional heat input into the product in 300–500 J/mm amount caused by exceed of content of these additives in filler powder can be the reason of rapid rise of tendency to crack formation in ‘base-deposited metal’ welded joint of ZhS32 type.

Key words: difficult to weld nickel-based superalloys, filler powder for microplasma surfacing, subsurface layer, reduction melting of powder sample in a jet of inert gas-carrier, X-ray structural microanalysis, content of oxygen and nitrogen impurities, quality criteria.



PACS: 61.72.S-, 61.82.Bg, 68.37.Yz, 81.20.Ev, 81.70.Jb

Citation: O. V. Yarovytsyn and A. V. Mykytchyk, Requirements to Limiting Relative Concentration of Oxygen and Nitrogen Impurity in Subsurface Layers of Filler Powder ZhS32 for Microplasma Surfacing, Metallofiz. Noveishie Tekhnol., 43, No. 4: 519—540 (2021) (in Ukrainian)

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