Characterization of tantalum coatings deposited using vacuum plasma spray process

Abstract

Tantalum is a very popular material for the industry as a whole because of very important characteristics such as: high melting point, significant thermal and electrical conductivity, high toughness and resistance to corrosion and good biocompatibility. Since the tantalum metal is sensitive to O, N and H gases, tantalum coating layers are deposited only using the vacuum plasma spray process (VPS), which has, in the past few years been used successfully for preparing coatings which are widely used in the preparation of metal implants. The aim of this paper was to, at a low pressure inert gas eliminate the influence of the surrounding atmosphere on the melted Ta powder particles and produce coatings with mechanical and structural characteristics which will find application in biomedicine. For depositing the coating a commercial tantalum powder AMPERIT® 151065 grain size of 10 - 30 μm was used. The powder was deposited with a plasma F4 gun at a distance of substrates at 300 mm. The Ta coating layers were deposited with a thickness of 60 to 70 μm on steel substrates. As the plasma gas used was a mixture of Ar and He inert gases. The microhardness of the coating was tested using the HV0.3 method and the tensile strength of the coatings bond was tested by the tensile method in accordance with the ASTM C633-1 standard. The microstructure of the coating in deposited state and after etching was studied on an optical microscope (OM) and scanning electron microscope (SEM). Etching the coating was carried out in the reagent which consisted of two parts of nitric acid, two parts hydrofluoric acid, and five parts water (2HNO3: 2HF: 5H2O). The structure of the coating consists solely of a tough αTa phase with a body centered cubic lattice. Tests have shown that layers of VPS - Ta coatings have the microstructure and mechanical properties which completely support the use of the coating in the process of making implants.

Tantal je veoma atraktivan materijal za industriju u celini zbog veoma bitnih osobina kao što su: visoka temperatura topljenja, značajna toplotna i električna provodljivost, visoka žilavost i otpornost na koroziju i dobra biokompatibilnost. Pošto je tantal metal osetljiv na gasove O, N i H, slojevi prevlake tantala se isključivo deponuju vakuum plazma sprej procesom (VPS), koji se u poslednjih nekoliko godina uspešno koristi za izradu prevlaka koje imaju široku primenu u izradi metalnih implanata. Cilj rada bio je da se na niskom pritisku inertnog gasa eliminiše uticaj okolne atmosfere na istopljene čestice praha Ta i proizvedu prevlake mehaničkih i strukturnih karakteristika koje će naći primenu u biomedicini. Za deponovanje prevlake koristio se komercijalni prah tantala AMPERIT® 151.065 granulacije od 10 - 30µm. Prah je deponovan sa plazma pištoljem F4 na odstojanju podloge od 300 mm. Slojevi Ta prevlaka su deponovani sa debljinom od 60 do 70µm na čeličnim podlogama. Kao plazma gas koristila se mešavina inertnih gasova Ar i He. Mikrotvrdoća prevlake ispitana je metodom HV0.3 a zatezna čvrstoća spoja prevlake ispitana je metodom na zatezanje u skladu sa standardom ASTM C633-1. Mikrostruktura prevlake u deponovnom stanju i u stanju posle nagrizanja ispitana je na optičkom mikroskopu (OM) i na skening elektronskom mikroskopu (SEM). Nagrizanje prevlake sprovedeno je u reagensu koji se sastojao od dva dela azotne kiseline, dva dela fluorovodonične kiseline i pet delova vode (2HNO3 : 2HF : 5H2O). Struktura prevlake se isključivo sastoji od žilave α-Ta faze sa zapreminski centriranom kubnom rešetkom. Ispitivanja su pokazala da slojevi VPS - Ta prevlake imaju mikrostrukturu i mehaničke karakteristike koje u potpunosti omogućavaju primenu prevlake u procesu izrade implanata.