R. Mania

FeAl materials from intermetallic powders

FeAl materials with the aluminium concentration of 40 at.% were prepared from intermetallic powders, obtained by milling and screening of the products of self-propagating high-temperature synthesis (SHS), carried out in a loosely packed mixture of elemental powders. Pressureless sintering of the compacted intermetallic powders yielded porous materials that were densified by hot forming. The properties of dense bodies were strongly related to the grain size of the starting intermetallic powders. Two fractions with grain sizes of less than 25 mm and in the range from 25 to 40 mm were investigated. The amount of an oxide phase distributed along the grain boundaries of the intermetallic matrix was remarkably higher in the former case. The oxide dispersions adversely affected the room temperature strength and ductility of the material. # 2003 Elsevier Science Ltd. All rights reserved.

In-situ TEM heating of Ni/Al multilayers

Abstract Ni/Al multilayer coatings of period Λ = 110 nm and Λ = 16 nm were deposited using a double target magnetron system. Their microstructure was characterized by means of transmission electron microscopy using thin foils cut out with a focused ion beam. Next, thin foils were subjected to in-situ heating up to 550 °C or 600 °C at a rate of 100 K min–1. Phase changes were followed with the help of the electron diffraction method. The experiments helped to establish that for the large period (Λ∼110 nm) multilayer the reaction starts at 350 °C at Ni/Al internal interfaces through precipitation of the Al9Ni2 phase, which at 500 °C is substituted with NiAl phase. The small period multilayers (Λ∼16 nm) subject to heating react at an even lower temperature of 300 °C by direct precipitation of the NiAl phase. The latter reaction seems to start within the whole nickel layer simultaneously.

Effect of silicon additions in CrSi (10, 20, 30, 40 at. % Si) magnetron targets on microstructure of reactively deposited (Cr,Si)N coatings

The CrSi compacts containing 10, 20, 30 and 40 at. % Si sintered from mixed elemental powders were used as targets for reactively deposited magnetron (Cr,Si)N coatings. The silicon substrates were kept either at ambient temperature or heated up to 600 °C. The microstructure observations were performed using TECNAI FEG (200 kV) with EDAX X-ray Energy Dispersive Spectroscopy (EDS) system and JEOL 3010 (300 kV) with Gatan Energy Filtering (GIF) attachment microscopes. The thin foils were cut using QUANTA Focused Ion Beam (FIB) system. The performed investigations proved that increasing silicon content in coatings deposited at 600 °C using CrSi10, CrSi20 and CrSi30 targets caused a refining of their fully crystalline CrN-type columnar microstructure from ~ 40 to ~ 35 and ~ 25 nm. The deposition performed from the same targets, but at ambient temperatures, i.e. without resistive heating of the substrates, produced coatings of mixed crystalline-amorphous type. They were characterized by gradient microstructure, i.e. amorphous material was prevailing close to the substrate and decreasing close to coating surface. The rising of silicon content in the targets resulted in decreasing amount of crystalline phase. The coatings obtained from Cr40Si target were fully amorphous independently of substrate temperature during deposition. The measurements of local chemical compositions obtained using EDS technique indicated that the Cr:Si ratio in the coatings roughly reproduced that present in the targets used for their deposition. Additionally, these measurements indicated that all coatings are contaminated with oxygen. The mapping of chemical composition using GIF technique of mixed crystalline-amorphous coatings proved that they are enriched in Cr and Si, respectively. The present results showed, that relying on single CrSi target magnetron sputtering the crystalline-amorphous nano-composite could be obtain at silicon additions from 10 to 30 at %, i.e. well above were that type of microstructure is formed during deposition using double target magnetron systems. Additionally, for the first time, the measurements helped to prove that the crystallites and amorphous material are enriched in chromium and silicon respectively, i.e. confirmed presence of CrN/Si3N4 composite.