Characterization of vacuum plasma spray VPS - W coating deposited on stainless steel substrates

Abstract

In this paper, studied was the melting of W powder particles in plasma, their behavior at oxidation as well as the mechanism of hardening on the surface of the substrate. Tungsten coating layers were deposited with vacuum plasma spray technology (VPS) on the test specimens of steel Č.4171 (X15Cr13 EN10027). VPS technology has advantages over the APS technology due to decreased oxidation of melted powder particles, by producing a coating with a controlled proportion of micro pores and greater uniformity of the deposited layers. Evaluation of mechanical characteristics of the layers was done by examining the microhardness using the HV0.3 method and tensile bond strength by tensile testing. The microstructures of the deposited layers were analyzed by means of optical microscopy (OM) and scanning electron microscopy (SEM). The results obtained showed that the tungsten coating consisted of well melted particles that interconnected and were overlapping, which shows a typical lamellar microstructure. Present in the microstructure are micro pores in very small proportion at the inter-lamellar boundaries. Tests have shown that layers of W coating deposited by plasma spray in inert gas shielding at low pressure have good mechanical properties and microstructure, which in the fully enables its use in exploitation.

U ovom radu proučavano je topljenje čestica praha W u plazmi, njihovo ponašanje na oksidaciju kao i mehanizam očvršćavanja na površini substrata. Slojevi volfram prevlake su deponovani sa vakuum plazma sprej tehnologijom (VPS) na ispitnim uzorcima od čelika Č.4171 (X15Cr13 EN10027). VPS tehnologija ima prednosti u odnosu na APS tehnologiju zbog smanjene oksidacije istopljenih čestica praha, proizvodeći prevlaku sa kontrolisanim udelom mikro pora i većom uniformnosti deponovanih slojeva. Procena mehaničkih karakteristika slojeva je urađena ispitivanjem mikrotvrdoće metodom HV0.3 i zatezne čvrstoće spoja ispitivanjem na zatezanje. Analizirane su mikrostrukture deponovanih slojeva pomoću optičke mikroskopije (OM) i skening elektronske mikroskopije (SEM). Dobijeni rezultati su pokazali da se volfram prevlaka sastojala od dobro istopljenih čestica međusobno povezanih i preklopljenih, koja pokazuje tipičnu lamelarnu mikrostrukturu. U mikrostrukturi su prisutne mikro pore u veoma malom udelu koje se nalaze na među-lamelarnim granicama. Ispitivanja su pokazala da slojevi W prevlake deponovani plazma sprejom u zaštritnoj atmosferi inertnog gasa na niskom pritisku imaju dobre mehaničke osobine i mikrostrukturu, koje u potpunosti omogućavaju njenu primenu u eksploataciji.