Strukturne i termijske karakteristike mehanohemijski tretiranih metalnih prahova

Abstract

U ovom radu je ispitivano dobijanje neravnotežnin struktura u metalima mehanohemijskim tretmanom. Strukturne i termijske karakteristike prahova mehanohemijski tretiranih različito vreme mlevenja su ispitivane rendgenskom strukturnom analizom, diferencijalnom skanirajućom kalorimetrijom, diferencijalnom termijskom analizom, kao i skanirajućom i transmisionom elektronskom mikroskopijom. Eksperimentalni rezultati su diskutovani sa kinetičkog i termodinamičkog stanovišta. Mehanohemijski tretmani, tj. mehaničko legiranje smeša čistih prahova aluminijuma i molibdena različitih početnih sastava (Al-0, 3, 10, 17, 20, 27, 50, 75 i 100 at.%Mo) su rađeni u horizontalnom kugličnom mlinu. U svim sličajevima mlevenje proizvodi nanokristalnu i/ili amorfnu strukturu. Tokom naknadnog termijskog tretmana, ovakvi metastabilni proizvodi lako reaguju obrazujući intermetalna jedinjenja: Al12Mo, Al5Mo, Al4Mo, AlgMo3 i AlMo3. Smesa prahova nikla i molibdena (Ni-50 at.%Mo) je mlevena u različitim tipovima mlinova. Mehaničkim legiranjem u horizontalnom kuglicnom mlinu dobija se amorfna faza. U planetarnom i vibracionom mlinu, zbog veće energije mlevenja, dobija se neuređeno intermetalno jedinjenje. Mehanohemijska reakcija amortizacije u oba ispitivana sistema je slična i odvija se u četiri stupnja: (i) obrazovanje veoma finog kompozitnog praha, (ii) obrazovanje čvrstog rastvora Al(Mo) ili Ni(Mo), (iii) transformacija presićenog čvrstog rastvora u amorfnu fazu i (iv) postepeno rastvaranje zaostalih kristalita molibdena u amorfnoj matrici.

In this study the formation of non-equilibrium structures in metals by mechanochemical treatment has been investigated. The structural and thermal properties of powders mechanochemically treated for various milling times have been studied by X-ray diffraction, differential scanning calorimetry, differential thermal analysis, as well as scanning and transmission electron microscopy. The experimental results were discussed from kinetic and thermodynamic point of view. Mechanochemical treatment, i.e. mechanical alloying of mixture of aluminium and molybdenum powders of various starting compositions (Al-O, 3, 10, 17, 20, 27, 50, 75 and 100 at.%Mo) was performed in a horizontal ball mill. In all cases milling produced nanocrystalline or/and amorphous structures. During subsequent heat treatment such metastable products easily react leading to the formation of intermetallic phases: Al12Mo, Al5Mo, Al4Mo, Al8Mo3 and AlMo3. Mixture of nickel and molybdenum powders (Ni-50 at.%Mo) was treated in various types of mills. Mechanical alloying in the horizontal ball mill yields an amorphous phase while in planetary and vibrating ball mill a disordered intermetallic compound was produced as a result of greater milling energies. The formation of amorphous phase in both systems is similar and occurs in four stages: (i) formation of very fine composite powders, (ii) formation of solid solution either Al(Mo) or Ni(Mo), (iii) collapse of supersaturated solid solution into the amorphous phase and (iv) gradual dissolution of residual molybdenum crystallites into the amorphous matrix.