Search

TiB2-43vol.%Cu nanocomposite powders with titanium diboride particle size 50-100 nm were cold and detonation sprayed in order to fabricate coatings on a copper substrate. The powders were produced by self-propagating high-temperature synthesis (SHS) followed by mechanical milling. The temperatures during spraying were calculated and the change in the nanostructure of the powders during spraying was studied: in cold sprayed coatings the size of TiB2 particles was well retained, in detonation sprayed coatings the growth of the particles was observed, the mode of spraying greatly affecting the microstructure and the size of the particles. The hardness of cold sprayed coatings was higher compared to detonation sprayed coatings. This research shows the future potential for development of coatings with submicron and nanostructure by cold and detonation spraying of powders produced by mechanical milling.

TiB2-Cu composites in a nanostructured state are candidates for high-strength conductive and erosion-resistant materials. In this work, we studied formation of nanostructured TiB2-Cu composites under shock wave conditions. We investigated the influence of preliminary mechanical activation (MA) of Ti-B-Cu powder mixtures on the peculiarities of the reaction between Ti and B under shock wave. In the MA-ed mixture the reaction proceeded completely while in the nonactivated mixture the reagents remained along with the product – titanium diboride. The size of titanium diboride particles in the central part of the compact was 100-300 nm. This research shows that shock wave synthesis in mechanically activated powder mixtures with simultaneous compaction of the composite is a promising way to materials with submicron and nanostructures.

Dispersion-strengthened copper with TiB2 was produced by ball-milling and spark plasma sintering (SPS).Ball-milling was performed at a rotation speed of 300rpm for 30 and 60min in Ar atmosphere by using a planetary ball mill (AGO-2). Spark-plasma sintering was carried out at 650°C for 5min under vacuum after mechanical alloying. The hardness of the specimens sintered using powder ball milled for 60min at 300rpm increased from 16.0 to 61.8 HRB than that of specimen using powder mixed with a turbular mixer, while the electrical conductivity varied from 93.40% to 83.34%IACS. In the case of milled powder, hardness increased as milling time increased, while the electrical conductivity decreased. On the other hand, hardness decreased with increasing sintering temperature, but the electrical conductiviey increased slightly

Ti-Cu-Ni-Sn quaternary amorphous alloys of Ti50Cu32Ni15Sn3, Ti50Cu25Ni20Sn5, and Ti50Cu23Ni20Sn7 composition were prepared by mechanical alloying in a planetary high-energy ballmill (AGO-2). The amorphization of all three alloys was found to set in after milling at 300rpm speed for 2h. A complete amorphization was observed for Ti50Cu32Ni15Sn3 and Ti50Cu25Ni20Sn5 after 30h and 20h of milling, respectively. Differential scanning calorimetry analyses revealed that the thermal stability increased in the order of Ti50Cu32Ni15Sn3, Ti50Cu25Ni20Sn5, and Ti50Cu23Ni20Sn7.

The microstructure and properties of Cu-TiB2 composites produced by high-energy ball-milling of TiB2 powders and spark-plasma sintering (SPS) were investigated. TiB2 powders were mechanically milled at a rotation speed of 1000rpm for short time in Ar atmosphere, using a planetary ball mill. To produce Cu-xTiB2 composites( x = 2.5, 5, 7.5 and 10wt.% ), the raw and milled TiB2 powders were mixed with Cu powders by means of a turbular mixer, respectively. Sintering of mixed powders was carried out in a SPS facility under vacuum. High-energy ball-milling resulted in refinement of TiB2 particles. XRD patterns of milled TiB2 powders indicated broader TiB2 peaks with decreased intensities. After sintering at 950 for 5min using the raw and milled TiB2 mixture powders, the sintered density decreased with increasing TiB2 content regardless of milling of TiB2. In the case of raw TiB2, hardness rapidly increased from 4 to 44 HRB with increasing TiB2 content. The electrical conductivity changed from 95.5 to 80.7 %IACS. For mixtures of Cu powders with milled TiB2 powders, hardness increased from 38 to 67 HRB as TiB2 content increased, while the electrical conductivity varied from 88% to 51 % IACS. When compared to compacts sintered with raw and milled TiB2 powders, the electrical conductivity of specimens with raw TiB2 powder was higher than that of specimens with milled TiB2 powder, while hardness was slightly lower.

The particle size effect on the peritectic melting of FeSn2 particles in FeSn-FeSn2 nanocomposites was studied using differential scanning calorimetry and X-ray diffraction. FeSn-10 wt.% FeSn2 compounds, mechanically milled for 30 min and slowly heated in a differential scanning calorimeter, showed incongruent melting at 680 K. Although FeSn2 grains grew from 10 to 40 nm upon heating before peritectic melting set in, the melting temperature was more than 100 K lower than the equilibrium value. A small latent heat during peritectic melting and a large amount of interfacial energy of FeSn-FeSn2 nanocomposites are held responsible for this large particle size effect. Grain growth is hardly possible in the case of rapid local heating during mechanical milling. Therefore, a decrease in the peritectic melting temperature is even expected to be substantially larger.

Nanosize nickel powders were successfully produced by electrical explosion of wire (EEW). In EEW, the nickel wire was discharged in a chamber filled with nitrogen or argon gas, and the produced powders were subsequently stabilized by air-passivation at room temperature for 2 h. X-ray diffraction only showed the nickel phase of FCC crystal structure, whereas TEM and XPS analyses showed the formation of a very thin oxide layer of NiO on the surface of particles. Particles were spherical in shape, and the mean particle size calculated by specific surface area was about 100 nm. The particle size decreased with increasing charging voltage and with increasing ambient gas pressure. Argon gas was more effective in producing finer particles than nitrogen gas.

Al-La-Ni-Fe alloys of three different compositions (Al82La10Ni4Fe4, Al85La9Ni3Fe3 and Al88La6Ni3Fe3) were prepared high-energy milling in a planetary ball-mill (AGO-2). Complete amorphization was observed for the Al82La10Ni4Fe4 alloy after milling for 350 h at a rotational speed of 300 rpm. In contrast, the Al85La9Ni3Fe3 and Al88La6Ni3Fe3 powders contained the FCC Al phase even for prolonged milling. The amorphization tendency was found to increase in the order of Al88La6Ni3Fe3 < Al85La9Ni3Fe3 < Al82La10Ni4Fe4, which may well be ascribed to the increasing atomic size mismatch of the constituent elements on La addition. DSC analyses of amorphous samples revealed two-stage crystallization processes for all three alloys, however, with strong variations in the thermal stability upon compositional changes. As observed by SEM, amorphous powders consisted of particles with nearly spherical shape and diameters ranging from 5 to 20 µm.

Ultrafine tantalum carbide (TaC)–5 wt.% Co composite powders were synthesized by a spray-carbothermal process, which includes (i) preparation of precursor powder by spray drying of a liquid solution of tantalum oxalate and cobalt nitrate hexahydrate, (ii) calcination to evaporate volatile components in the precursor powder and synthesis of nanostructured tantalum–cobalt composite oxides and (iii) ball milling with carbon, and subsequent carbothermal reaction in hydrogen. The formation temperature of TaC in this process (1050 °C) is significantly lower than that in the conventional method (1500 °C). The observed particle size of TaC–Co composite powders was smaller than 200 nm.

Ultrafine TaC powders were synthesized by mechano-chemical process (MCP). The synthesis procedures include (1) preparation of precursor powder by spray drying of liquid solution of tantalum oxalate, (2) calcinations to evaporate volatile components in the precursor powder and synthesis of nanostructured tantalum oxides, (3) ball milling with carbon homogeneously, and then carbothermal reaction in hydrogn. The formation temperature (1050 °C) of TaC in this process is significantly lower than that (1500 °C) in the conventional method. The observed size of TaC composite powders by TEM was smaller than 200 nm.

The TaC/VC inhibitor was added in nanophase WC/Co powders by either a mechanicalor chemicaldoping method. The microstructure and mechanical properties have been investigated for the WC/Co hard alloys which were sintered with these powders. After sintering, most of the WCs maintained their original round morphology and fine microstructure. In the mechanically doped alloy, exaggerated and abnormal local grain growth was observed which was supposed to be caused by the non-uniform distribution of the TaC/VC dopant. However, such an abnormal grain growth problem does not appear in the alloy when the inhibitors were chemically doped into the powders. Due to relatively fine and homogeneous microstructure, the nanophase WC/Co doped by the chemicalmethod showed a higher hardness and better transverse rupture strength than that doped by the mechanicalmethod.

Nanocomposite Cu-TiB/sub 2/ powder was in situ synthesized by means of self-propagating high-temperature synthesis (SHS) using high-energy ball milled Ti-B-Cu elemental mixtures as powder precursors. The effect of the preliminary mechanical treatment on the SHS reaction was studied. The size of TiB/sub 2/ particles produced by SHS was shown to decrease with increasing duration of the preliminary mechanical treatment. Subsequent mechanical treatment of the SHS products led to a reduction of TiB/sub 2/ particle sizes down to 30-50 nm. The microstructural evolution of the synthesized powder compacts during sintering was investigated. During spark plasma sintering a fine-grained skeleton of TiB/sub 2/ with well connected particles is formed. This interpenetrating phase composite of Cu-TiB/sub 2/ is produced by the simultaneous action of pressure, temperature and electrical current. TiB/sub 2/ nanoparticles distributed in the copper matrix agglomerate and form a fine-grained skeleton.

Ultrafine TaC powders were synthesised by spray drying using tantalum oxalate solution. The spray dried powders were spherical shape and less than 30 in size. The powders calcined at 500 and X showed amorphous structures and phase was obtained by calcining at . The particle size and shape remains constant after calcination. The calcined spherical powders were composed of an agglomerate of primary particles under 50 nm in size. The complete formation of TaC could be achieved by heat treatment at for 6 hrs. The observed size of TaC powders by TEM was less than 200 nm.